# Human Physiology/Development: birth through death

## Overview

We are born, we grow up, we age, and then we die. Unless disease or
trauma occurs, most humans go through the various stages of the life
described above. Human Development is the process of growing to maturity
and mental ability. Traditionally, theories that explain senescence have
generally been divided between the programmed and stochastic theories of
aging. Programmed theories imply that aging is regulated by biological
clocks operating throughout the life span. This regulation would depend
on changes in gene expression that affect the systems responsible for
maintenance, repair and defense responses. Stochastic theories blame
environmental impacts on living organisms that induce cumulative damage
at various levels as the cause of aging. Examples of environmental
impacts range from damage to DNA, damage to tissues and cells by oxygen
radicals (widely known as free radicals countered by the even more well
known antioxidants), and cross-linking. However, aging is now seen as a
combination of genetic and environmental processes; a progressive
failure of homeostatic mechanisms involving maintenance and repair
genes, stochastic events leading to molecular damage and molecular
heterogeneity, and chance events determining the probability of death.
Homeostasis, as we have seen throughout this book, is maintained through
complex and interacting systems, and aging is considered to be a
progressive shrinkage of homeostatic capabilities, mainly due to
increased molecular heterogeneity. In this chapter we explore the
physiology of all stages of human development, with a particular
emphasis on the aging process.

## Apoptosis

!A cell undergoing apoptosis. In just one of many scenarios of
apoptosis, the process is triggered by another neighboring cell; the
dying cell eventually transmits signals that tell the phagocytes, which
are a part of the immune system, to engulf
it.{width="200"}

Apoptosis is the process of regulated cell death and removal. In some
cases cell damage can trigger apoptosis, but it is usually a normal
function of the cell. Apoptosis results in controlled auto digestion of
the cells content. The cell membrane stays in place and the cells
contents are not dispersed. When this process is near completion, \"eat
me\" signals, like phosphatidylserine, appear on the surface of the cell
membrane. This in turn attracts phagocytic scavengers that complete the
process of removing the dead cell without eliciting an inflammatory
response. Unlike necrosis, which is a form of cell death that results
from acute cellular injury, apoptosis is carried out in an ordered
process that generally confers advantages during an organism\'s life
cycle.

Apoptosis Rates:The rate at which cells of the body die varies widely between different cell types. Some cells, such as white blood cells, live for only a matter of hours while other cells can live throughout the duration of the lifespan of the individual.

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Homeostasis:Apoptosis is a regulated function that results in a relatively consistent number of cells in the body. This balancing act is part of homeostasis (see chapter 1) that is required by living organisms. An example for this is that blood cells are constantly being produced and apoptosis takes place to eliminate a similar number of older cells. Homeostasis was discovered by Claude Bernard around the year 1851.

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Development:Apoptosis also plays a key role in growth and development. An example of how apoptosis enables development is the differentiation of human fingers in a developing embryo. Apoptosis is the function that enables the embryos fingers to separate.

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Disorders:Too much apoptosis causes cell loss disorders such as osteoporosis, whereas too little apoptosis results in uncontrolled cell proliferation, namely cancer.

## Growth and development

Growth and development is an ongoing process that begins at conception
and continues through the remainder of our lives. There is a broad
spectrum of physical and psychological changes that are part of the
maturation and life of the individual.

Growth is a physical change that can be weighed and measured.
Development is psychological and social changes to the individual such
as behaviors and thinking patterns. Growth and development are two
complimentary processes that together make up the individual.

Examples of this difference are all around us. One notable example
involves infants. Infants understand speech much earlier than their
bodies have matured enough to physically perform it. Thus it is evident
that their speech patterns develop before the physical growth of their
vocal chords is adequate to facilitate speech.

The rate of development and growth varies dependent on many factors such
as age and genetic disposition. Babies grow at roughly the same pace and
benchmarks for their physical and social development are roughly
standard. However, as any parent can tell you, no two children develop
exactly within the same time frame. Thus an appropriate time span should
be used. For example: one brother may gain weight faster than another.
Growth spurts can vary. Some children can speak entire sentences before
their first year while others may not speak at all until two or three.
This creates a greater diversity among human beings.

The following chart focuses on reflexes of the developing infant.

  Reflex              Stimulation                                                                                                                                                  Response                                                                                                                                                  Age of disappearance                                                                                               Function
  ------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------ --------------------------------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------ ---------------------------------------------------------------------------------------
  Eye blink           Bright light shinning in eyes or clap hands by eyes                                                                                                          closes eyelids quickly                                                                                                                                    Permanent                                                                                                          This reflex protects the infant from a lot of stimulation
  Withdrawal          Stick sole of foot with stimulus like a pin                                                                                                                  This cause the foot to withdraw, this occurs with the use of flexing of the knee to hip                                                                   Decreases after the 10th day of birth                                                                              This is a protection for the infant in the instance of unpleasant tactile stimulation
  Rooting             Touch cheek near the corner of the mouth                                                                                                                     The infants head will turn towards the site of stimulation                                                                                                3 weeks (due to the voluntary response that is now capable for infant to do at this time)                          This reflex helps baby to find the mothers nipple
  Sucking             Place fingers in infant\'s mouth                                                                                                                             The infant will suck finger rhythmically                                                                                                                  4 months (voluntary sucking will come about)                                                                       This helps with feeding
  Swimming            Place the baby in pool of water face down                                                                                                                    The baby paddles and kicks in swimming movements                                                                                                          4 to 6 month                                                                                                       This helps baby to survive if dropped into the water
  Moro                Hold infant in a cradling horizontal position and slightly lower the baby in a fast motion toward the ground while making a loud sound supporting the baby   The baby will make a embracing motion and arch its back extending its legs throwing its arms outward, and finally it will bring arms in toward its body   6 months                                                                                                           In the evolutionary past this may have helped the baby cling to the mother
  Palmar grasp        Place the finger in baby\'s palm and press against the palm                                                                                                  The baby will immediately grasp the finger                                                                                                                3 to 4 months                                                                                                      This prepares infant for when voluntary grasping comes about
  Tonic neck          Turn the baby\'s head to one side while the baby is awake                                                                                                    This will cause the baby to extend one arm in front of its eye on one arm to the side to which the head has been turned                                   4 months                                                                                                           This may prepare for voluntary reaching
  Stepping/marching   When you hold the baby under the arm and permit the bare feet of the baby to touch a flat surface                                                            The baby will lift one foot after the other in a stepping fashion                                                                                         2 months (this applies to a baby who has gained weight a baby who is not as heavy this reflex may be submissive)   This prepares the baby for voluntary walking
  Babinski            Touch the foot in a stroking manner form the toe toward the heel                                                                                             The baby\'s toes will fan out and curl as the foot twists in                                                                                              8 to 12 months                                                                                                     Unknown
                                                                                                                                                                                                                                                                                                                                                                                                                                                                

## Neonatal

The neonatal period extends from birth to somewhere between 2 weeks and
1 month.

Immediately after the baby is born, uterine contractions force blood,
fluid, and the placenta from the mother\'s body. The umbilical
cord---the baby\'s lifeline to it\'s mother---is now severed. Without
the placenta to remove waste, carbon dioxide builds up in the baby\'s
blood. This fact, along with the actions of medical personnel,
stimulates the control center in the brain, which in turn responds by
triggering inhalation. Thus the newborn takes its first breath. As the
newborn\'s lungs begin to function, the bypass vessels of fetal
circulation begin to close. The bypass connecting the atria of the
heart, known as the foramen ovale, normally closes slowly during the
first year.

During this period the body goes through drastic physiological changes.
The most critical need is for the body to get enough oxygen as well as
an adequate supply of blood. (The respiratory and heart rate of a
newborn is much faster than that of an adult.)

!Newborn infant, just seconds after vaginal
delivery.{width="260"}

### The newborn\'s appearance

A newborn\'s skin is oftentimes grayish to dusky blue in color. As soon
as the newborn begins to breathe, usually within a minute or two of
birth, the skin\'s color returns to normal tones. Newborns are wet,
covered in streaks of blood, and coated with a white substance known as
vernix caseosa, which is believed to act as an antibacterial barrier.
The newborn may also have Mongolian spots, various other birthmarks, or
peeling skin, particularly at the wrists, hands, ankles, and feet.

A newborn\'s shoulders and hips are narrow, the abdomen protrudes
slightly, and the arms and legs are relatively short. The average weight
of a full-term newborn is approximately 7 ½ pounds (3.2kg), but can be
anywhere from 5.5--10 pounds (2.7--4.6kg). The average total body length
is 14--20 inches (35.6--50.8cm), although premature newborns may be much
smaller. The Apgar score is a measure of a newborn\'s transition from
the womb during the first ten minutes of life.

A newborn\'s head is very large in proportion to the rest of the body,
and the cranium is enormous relative to his or her face. While the adult
human skull is about 1/8 of the total body length, the newborn\'s is
twice that. At birth, many regions of the newborn\'s skull have not yet
been converted to bone. These \"soft spots\" are known as fontanels; the
two largest are the diamond-shaped anterior fontanel, located at the top
front portion of the head, and the smaller triangular-shaped posterior
fontanel, which lies at the back of the head.

During labor and birth, the infant\'s skull changes shape to fit through
the birth canal, sometimes causing the child to be born with a misshapen
or elongated head. This will usually return to normal on its own within
a few days or weeks. Special exercises sometimes advised by physicians
may assist the process.

Some newborns have a fine, downy body hair called lanugo. It may be
particularly noticeable on the back, shoulders, forehead, ears and face
of premature infants. Lanugo disappears within a few weeks. Likewise,
not all infants are born with lush heads of hair. Some may be nearly
bald while others may have very fine, almost invisible hair. Some babies
are even born with a full head of hair. Amongst fair-skinned parents,
this fine hair may be blond, even if the parents are not. The scalp may
also be temporarily bruised or swollen, especially in hairless newborns,
and the area around the eyes may be puffy.

!Traces of vernix caseosa on a full term
newborn{width="260"}

A newborn\'s genitals are enlarged and reddened, with male infants
having an unusually large scrotum. The breasts may also be enlarged,
even in male infants. This is caused by naturally-occurring maternal
hormones and is a temporary condition. Females (and even males) may
actually discharge milk from their nipples, and/or a bloody or
milky-like substance from the vagina. In either case, this is considered
normal and will disappear in time.

The umbilical cord of a newborn is bluish-white in color. After birth,
the umbilical cord is normally cut, leaving a 1--2 inch stub. The
umbilical stub will dry out, shrivel, darken, and spontaneously fall off
within about 3 weeks. Occasionally, hospitals may apply triple dye to
the umbilical stub to prevent infection, which may temporarily color the
stub and surrounding skin purple.

Newborns lose many of the above physical characteristics quickly. Thus
prototypical older babies look very different. While older babies are
considered \"cute\", newborns can be \"unattractive\" by the same
criteria and first time parents may need to be educated in this regard.

Neonatal jaundice:Neonatal jaundice is usually harmless: this condition is often seen in infants around the second day after birth, lasting until day 8 in normal births, or to around day 14 in premature births. Serum Bilirubin initially increase because a newborn does not need as many red blood cells as it did as a fetus (since there is a higher concentration of oxygen in the air than what was available through the umbilical vein). The newborn\'s liver processes the breakdown of the extra red blood cells, but some bilirubin does build up in the blood. Normally bilirubin levels drop to a low level without any intervention required. In babies where the bilirubin levels are a concern (particularly in pre-term infants), a common treatment is to use UV lights (\"bili lights\") on the newborn baby.

## Changes in body Size and Muscle fat makeup

By the end of the first year an infant\'s height is increased by 50% and
by the age of 2 the baby will have grown 75% greater.

By 5 months a baby will have doubled its weight, and tripled its weight
by the first year. By the age of 2, a baby\'s weight will have
quadrupled.

Infants and toddlers grow in little spurts over the first 21 months of
life. A baby can go through periods of 7 to 63 days with no growth but
they can add as much as an inch in one 24 hour period. During the day
before a growth spurt, parents describe their babies as irritable and
very hungry.

The best way to estimate a child\'s physical maturity is to use
*skeletal age*, a measure of bone development. This is done by having a
x-ray of the long bones of the body to see the extent to which soft,
pliable cartilage has hardened into bone.

-   Changes in body Proportions

**Cephalocaudal trend** means that growth occurs from head to tail. The
head develops more rapidly than the lower part of the body. At birth the
head takes up to one fourth of the total body length and legs only one
third. The lower body catches up by age 2 and the head accounts for only
one fifth and legs for nearly one half of the body length.

**Proximodistal trend** means that head growth proceeds literally from
near to far or from center of the body outward.

At birth the brain is nearer its adult shape and size than any other
physical structure. The brain continues to develop at an astounding pace
throughout infancy and toddlerhood.

-   The Brain Development

The neurons of infants and adults differ in 2 significant ways: Growth
of neural fibers and synapses increases connective structures. When
synapses are formed, many surrounding neurons die. This occurs in 20 to
80 percent of the brain region.

**Dendrites synapses**: Synapses are tiny gaps between neurons where
fiber from different neurons come close together but do not touch.
Neurons release chemicals that cross the synapses sending messages to
one another. During the prenatal period the neural tube produces far
more neurons than the brain will ever need. **Myelinization**: The
coating of neural fibers with a fatty sheath called myelin that improves
the efficiency of message transfer. Multi-layered lipid cholesterol and
protein covering produced by neuralgia cause a rapid gain in overall
size of brain due to neural fibers and myelination.

**Synaptic pruning**: Neurons seldom stimulated soon loose their
synapses. Neurons not needed at the moment return to an uncommitted
state so they can support future development. However, if synaptic
pruning occurs in old age neurons will lose their synapses. If neurons
are stimulated at a young age, even though neurons were pruned, they
will be stimulated again.

**Cerebral Cortex**: Surrounding the brain, it is the largest most
complex brain structure. The cortex is divided into four major lobes:
occipital lobe, parietal lobe, temporal lobe, and frontal lobe which is
the last to develop.

**Brain plasticity**: The brain is highly plastic. Many areas are not
yet committed to specific functions. If a part of the brain is damaged,
other parts can take over tasks that they would not normally have
handled.

-   Changing states of Arousal

How children develop more regular "sleep patterns" around 4 to 6 months
of age: Sleep patterns are more developed as the brain develops. It is
not until the first year of life that the secretion of *melatonin*, a
hormone produced in the brain, affects more drowsiness in the night than
in the day. In addition, REM is decreased.

## Infancy

!Infant Infancy is the period that
follows the neonatal period and includes the first two years of life.
During this time tremendous growth, coordination and mental development
occur. Most infants learn to walk, manipulate objects and can form basic
words by the end of infancy. Another characteristic of infancy is the
development of deciduous teeth.

**Deciduous Teeth**

*Deciduous teeth*, otherwise known as milk teeth, baby teeth, or primary
teeth, are the first set of teeth in the growth development of humans
and many other animals. They develop during the embryonic stage of
development and erupt - become visible in the mouth - during infancy.
They are usually lost and replaced by permanent teeth, but in the
absence of permanent replacements, they can remain functional for many
years. (Concise)

Deciduous teeth start to form during the embryo phase of pregnancy. The
development of deciduous teeth starts at the sixth week of development
as the dental lamina. This process starts at the midline and then
spreads back into the posterior region. By the time the embryo is eight
weeks old, there are ten areas on the upper and lower arches that will
eventually become the deciduous dentition. These teeth will continue to
form until they erupt in the mouth. In the deciduous dentition there are
a total of twenty teeth: five per quadrant and ten per arch. In most
babies the eruption of these teeth begins at the age of six months and
continues until twenty-five to thirty-three months of age. The first
teeth seen in the mouth are the mandibular centrals and the last are the
maxillary second molars. However it is not unheard of for a baby to be
born with teeth. right\|framed\|Deciduous
teeth.

The deciduous dentition is made up of centrals, laterals, canines, first
molars, and second molars; there is one in each quadrant, making a total
of four of each tooth. All of these are replaced with a permanent
counterpart except for the first and second molars; they are replaced by
premolars. These teeth will remain until the age of six. At that time,
the permanent teeth start to appear in the mouth resulting in mixed
dentition. The erupting permanent teeth causes root resorption, where
the permanent teeth push down on the roots of the deciduous teeth
causing the roots to be dissolved and become absorbed by the forming
permanent teeth. The process of shedding deciduous teeth and the
replacement by permanent teeth is called exfoliation. This will last
from age six until age twelve. By age twelve there are only permanent
teeth remaining.

Deciduous teeth are considered essential in the development of the oral
cavity by dental researchers and dentists. The permanent teeth
replacements develop from the same tooth bud as the deciduous teeth;
this provides a guide for permanent teeth eruption. Also the muscles of
the jaw and the formation of the jaw bones depend on the primary teeth
in order to maintain the proper space for permanent teeth. The roots of
deciduous teeth provide an opening for the permanent teeth to erupt
through. These teeth are also needed in the development of a child's
ability to speak and chew their food correctly.

## Adolescence

!United States\|American high school
students{width="250"}

Adolescence is the period of psychological and social transition between
childhood and adulthood. Adolescence is the transitional stage of human
development in which a juvenile matures into an adult. This transition
involves biological, social, and psychological changes, though the
biological ones are the easiest to measure objectively. The time is
identified with dramatic changes in the body, along with developments in
a person\'s psychology and academic career. In the onset of adolescence,
children usually complete elementary school and enter secondary
education, such as middle school or high school. A person between early
childhood and the teenage years is sometimes referred to as a pre-teen
or \'tween.

Physical maturation resulting from puberty leads to an interest in
sexual activities, sometimes leading to teenage pregnancy. Since teens
may not be emotionally or mentally mature enough or financially able to
support children, sexual activity among adolescents is considered
problematic.

At this age there is also a greater probability of drug and alcohol use,
mental health disorders such as schizophrenia, eating disorders such as
anorexia, and clinical depression. The unstable emotions or lack of
emotional intelligence among some adolescents may also lead to youth
crime.

Searching for a unique identity is one of the problems that adolescents
often face. Some, but not all, teenagers often challenge the authority
or the rules as a way to establish their individuality. They may crave
adulthood and be eager to find their place in society. While adolescents
are eager to grow up and be treated like adults, they also idolize
athletes, movie stars and celebrities. They want to be like these role
models - whether or not these role models actually have qualities that
should be aspired to.

### Female

In females, puberty is caused by alterations in brain functions that
result in increased secretion by the hypothalamus of
gonadotropin-releasing hormone (GnRH). Increased levels of GnRH
stimulate secretion of pituitary gonadatrophins FSH and LH which cause
follicle development and estrogen secretion. Estrogen is responsible for
accessory sex organs and secondary sex characteristics. Menarche, the
first menstrual cycle, occurs at about 12.5 years of age as a result of
the release of FSH.

**Breast development**

The first physical sign of puberty in girls is usually a firm, tender
lump under the center of the areola(e) of one or both breasts, occurring
on average at about 10.5 years. This is referred to as thelarche. By the
widely used Tanner staging of puberty, this is stage 2 of breast
development (stage 1 is a flat, prepubertal breast). Within 6-12 months,
the swelling has clearly begun in both sides, softened, and can be felt
and seen extending beyond the edges of the areolae. This is stage 3 of
breast development. By another 12 months (stage 4), the breasts are
approaching mature size and shape, with areolae and papillae forming a
secondary mound. In most young women, this mound disappears into the
contour of the mature breast (stage 5), although there is so much
variation in sizes and shapes of adult breasts that distinguishing
advanced stages is of little clinical value.

**Pubic hair in girls**

Pubic hair is often the second unequivocal change of puberty. It is
referred to as pubarche and the pubic hairs are usually visible first
along the labia. The first few hairs are described as Tanner stage 2.
Stage 3 is usually reached within another 6--12 months, when the hairs
are too numerous to count and appear on the mons as well. By stage 4,
the pubic hairs densely fill the \"pubic triangle.\" Stage 5 refers to
spread of pubic hair to the thighs and sometimes as abdominal hair
upward towards the umbilicus. In about 15% of girls, the earliest pubic
hair appears before breast development begins.

**Vagina, uterus, ovaries**

The mucosal surface of the vagina also changes in response to increasing
levels of estrogen, becoming thicker and a duller pink in color (in
contrast to the brighter red of the prepubertal vaginal mucosa). Whitish
secretions (physiologic leukorrhea) are a normal effect of estrogen as
well. In the next 2 years following thelarche, the uterus and ovaries
increase in size. The ovaries usually contain small cysts visible by
ultrasound.

**Menstruation and fertility**

The first menstrual bleeding is referred to as **menarche**. The average
age of menarche in American girls is about 12.7 years, usually about 2
years after thelarche. Menses (menstrual periods) are not always regular
and monthly in the first 2 years after menarche. Ovulation is necessary
for fertility, and may or may not accompany the earliest menses. By 2
years after menarche, most girls are ovulating at least several times a
year. Over 90% of girls who experience menarche before age 13 years are
experiencing very regular, predictable menses accompanied by ovulation
within 2 years, and a higher proportion of those with later menarche may
not establish regular ovulation for 4 years or more. However, initiation
of ovulation after menarche is not inevitable, and a high proportion of
girls with continued irregularity several years from menarche will
continue to have prolonged irregularity and anovulation, and are at
higher risk for reduced fertility.

**Pelvic shape, fat distribution, and body composition**

During this period, also in response to rising levels of estrogen, the
lower half of the pelvis widens. This prepares the body for the time
when she will give birth by enlarging the birth canal. Fat tissue
increases to a greater percentage of the body composition than in males,
especially in the typical female distribution of breasts, hips, and
thighs. This produces the typical female body shape. Also, the fat goes
to the buttocks of a girl, giving their buttocks more shape and curve.

**Body and facial hair in girls**

In the months and years following the appearance of pubic hair, other
areas of skin which respond to androgens develop heavier hair
(androgenic hair) in roughly the following sequence: underarm (axillary)
hair, perianal hair, upper lip hair, sideburn (preauricular) hair, and
periareolar hair. Arm and leg hair becomes heavier gradually over a
period of 10 years or more. While the appearance of hair in some of
these areas is not always wanted, particularly in Western culture, it
rarely indicates a hormone imbalance unless it occurs elsewhere as well,
such as under the chin and in the midline of the chest.

**Height growth in girls**

The estrogen-induced pubertal growth spurt in girls begins at the same
time the earliest breast changes begin, or even a few months before,
making it one of the earliest manifestations of puberty in girls. Growth
of the legs and feet accelerates first, so that many girls have longer
legs in proportion to their torso in the first year of puberty. The rate
of growth tends to reach a peak velocity (as much as 7.5-10 cm or 3-4
inches per year) midway between thelarche and menarche and is already
declining by the time menarche occurs. In the 2 years following menarche
most girls grow about 5 cm (2 inches) before growth ceases at maximal
adult height. This last growth primarily involves the spine rather than
the limbs.

**Body odor, skin changes, and acne** right\|framed\|**Acne** on the
face and body.

Rising levels of androgens can change the fatty acid composition of
perspiration, resulting in a more \"adult\" body odor. This often
precedes thelarche and pubarche by 1 or more years. Another androgen
effect is increased secretion of oil (sebum) from the skin. This change
increases the susceptibility to acne vulgaris, a characteristic
affliction of puberty greatly variable in its severity.

### Male

The onset of puberty for males is similar to that of females. GnRH
secretion from the hypothalamus results in an increase in pituitary
gonadatropins secretion of LH / ICSH and FSH. The pituitary
gonadatropins stimulate the seminiferous tubules and testosterone
secretion. Testosterone causes changes in the accessory reproductive
organs, secondary sex characteristics and male sex drive.

**Testicular size, function, and fertility**

In boys, testicular enlargement is the first physical manifestation of
puberty. It is termed gonadarche. The testes in prepubertal boys change
little in size from about 1 year of age to the onset of puberty,
averaging about 2--3 cc in volume and about 1.5-2 cm in length.
Testicular size continues to increase throughout puberty, reaching
maximal adult size about 6 years later. While 18-20 cc is reportedly an
average adult size, there is wide variation in the normal population.

The testes have two primary functions: to produce hormones and to
produce sperm. The Leydig cells produce testosterone (as described
below), which in turn produces most of the changes of male puberty.
However, most of the increasing bulk of testicular tissue is
spermatogenic tissue (primarily Sertoli and interstitial cells). The
development of sperm production and fertility in males is not as well
documented. Sperm can be detected in the morning urine of most boys
after the first year of pubertal changes (and occasionally earlier).

**Genitalia**

A boy\'s penis grows little from the fourth year of life until puberty.
Average prepubertal penile length is 4 cm. The prepubertal genitalia are
described as stage 1. Within months after growth of the testes begins,
rising levels of testosterone promote growth of the penis and scrotum.
This earliest discernible beginning of pubertal growth of the genitalia
is referred to as stage 2. The penis continues to grow until about 21
years of age, reaching an average adult size of about 7-15.5 cm.

Although erections and orgasms occur in prepubertal boys, they become
much more common during puberty, accompanied by a markedly increased
libido. Ejaculation becomes possible early in puberty; prior to this
boys may experience dry orgasms. Emission of seminal fluid may occur due
to masturbation or spontaneously during sleep (commonly termed a wet
dream, and more clinically called a nocturnal emission). The ability to
ejaculate is a fairly early event in puberty compared to the other
characteristics. However, in parallel to the irregularity of the first
few periods of a girl, for the first one or two years after a boy\'s
first ejaculation, his seminal fluid may contain few active sperm.

**Pubic hair in boys**

Pubic hair often appears on a boy shortly after the genitalia begin to
grow. As in girls, the first appearance of pubic hair is termed pubarche
and the pubic hairs are usually first visible at the dorsal (abdominal)
base of the penis. The first few hairs are described as stage 2. Stage 3
is usually reached within another 6--12 months, when the hairs are too
numerous to count. By stage 4, the pubic hairs densely fill the \"pubic
triangle.\" Stage 5 refers to spread of pubic hair to the thighs and
upward towards the umbilicus as part of the developing abdominal hair.

**Body and facial hair in boys**

In the months and years following the appearance of pubic hair, other
areas of skin which respond to androgens develop heavier hair
(androgenic hair) in roughly the following sequence: underarm (axillary)
hair, perianal hair, upper lip hair, sideburn (preauricular) hair,
periareolar hair, and the rest of the beard area. Arm, leg, chest,
abdominal, and back hair become heavier more gradually. There is a large
range in amount of body hair among adult men, and significant
differences in timing and quantity of hair growth among different ethnic
groups.

**Voice change**

Under the influence of androgens, the voice box, or larynx, grows in
both genders. This growth is far more prominent in boys, causing the
male voice to drop, rather abruptly, about one octave, because the
larger vocal folds have a lower fundamental frequency. Occasionally,
this is accompanied by cracking and breaking sounds in the early stages.
Most of the voice change happens during stage 4 of male puberty around
the time of peak growth. However, it usually precedes the development of
significant facial hair by several months to years.

**Height growth in boys**

Compared to girls\' early growth spurt, growth accelerates more slowly
in boys and lasts longer, resulting in a taller adult stature among
males than females (on average about 10 cm or 4 inches). The difference
is attributed to the much greater potency of estradiol compared to
testosterone in promoting bone growth, maturation, and epiphyseal
closure. In boys, growth begins to accelerate about 9 months after the
first signs of testicular enlargement and the peak year of the growth
spurt occurs about 2 years after the onset of puberty, reaching a peak
velocity of about 8.5--12 cm or 3.5--5 inches per year. The feet and
hands experience their growth spurt first, followed by the limbs, and
finally ending in the trunk. Epiphyseal closure and adult height are
reached more slowly, at an average age of about 17.5 years. As in girls,
this last growth primarily involves the spine rather than the limbs.

**Male musculature and body shape**

By the end of puberty, adult men have heavier bones and nearly twice as
much skeletal muscle. Some of the bone growth (e.g., shoulder width and
jaw) is disproportionately greater, resulting in noticeably different
male and female skeletal shapes. The average adult male has about 150%
of the lean body mass of an average female, and about 50% of the body
fat.

This muscle develops mainly during the later stages of puberty, and
muscle growth can continue even after a male is biologically adult. The
peak of the so-called \"strength spurt,\" the rate of muscle growth, is
attained about one year after a male experiences his peak growth rate.

**Breast development in boys: pubertal gynecomastia**

Estradiol is produced from testosterone in male puberty as well as
female, and male breasts often respond to the rising estradiol levels.
This is termed gynecomastia. In most boys, the breast development is
minimal, similar to what would be termed a \"breast bud\" in a girl, but
in many boys, breast growth is substantial. It usually occurs after
puberty is underway, may increase for a year or two, and usually
diminishes by the end of puberty. It is increased by extra adipose
tissue if the boy is overweight.

Although this is a normal part of male puberty, breast development for
some boys is as unwelcome as upper lip hair in girls. If the boy\'s
distress becomes too substantial during development, breast tissue can
be removed and corrected surgically.

## Adulthood

The term \"adult\" generally refers to a fully developed person from
maturity (the end of puberty) onward. The age at which a person is
physiologically an adult is age 17 for females and age 18 for males.
Adulthood can also refer to a person\'s ability to care for them self
independently, and raise a family of their own; or it can simply mean
reaching a specified age. Graduating high school, residing in one\'s own
residence and attaining financial independence are all synonymous with
adulthood in the United States.

### Adult characteristics

There are some qualities that symbolize adultness in most cultures. Not
always is there a concordance between the qualities and the physical age
of the person.

The adult character is comprised of:

-   **Self-control** - restraint, emotional control.
-   **Stability** - stable personality, strength.
-   **Independence** - ability to self-regulate.
-   **Seriousness** - ability to deal with life in a serious manner.
-   **Responsibility** - accountability, commitment and reliability.
-   **Method/Tact** - ability to think ahead and plan for the future,
    patience.
-   **Endurance** - ability and willingness to cope with difficulties
    that present themselves.
-   **Experience** - breadth of mind, understanding.
-   **Objectivity** - perspective and realism.

!This diagram shows Maslow\'s hierarchy of needs, represented as a
pyramid with the more primitive needs at the
bottom.{width="400"}

Abraham Maslow, a psychologist, developed Maslow\'s Hierarchy of Needs.
It is a chart outlining basic needs that a person must meet to function
and survive in life. It also attempts to explain what motivates people
in life. The needs on the lower level must be met before moving up the
ladder, as the higher needs only come into focus once all the needs that
are lower down in the pyramid are satisfied. People can get stuck on
levels and some people may never reach certain levels because of
circumstances in their life. When one stage is fulfilled you naturally
move to the next.

**Physical or Physiological:** These include shelter, oxygen, food,
water, rest and elimination, all of which are vital to a person\'s life
and essential to survival.

**Security or Safety:** This involves not only actually being secure and
safe, but also the feeling of safety and security. This is something
that people typically learn from their childhood and something that
helps lay the groundwork for developing other skills and moving up to
the next step in the ladder.

**Social (Love/Belonging):** This involves developing friendships and
eventually relationships. This involves emotionally-based relationships
in general, such as friendship, sexual intimacy, and having a supportive
and communicative family.

**Esteem:** This is where people learn to develop self-esteem and
confidence. According to Maslow, all humans have a need to be respected,
to have self-respect, and to respect others. People need to engage
themselves in order to gain recognition and have an activity or
activities that give the person a sense of contribution, be it in a
profession or hobby,

**Self-Actualization:** The highest level you can reach according to
Maslow. Maslow writes the following of self-actualizing people:

-   They embrace the facts and realities of the world (including
    themselves) rather than denying or avoiding them.
-   They are spontaneous in their ideas and actions.
-   They are creative.
-   They are interested in solving problems; this often includes the
    problems of others. Solving these problems is often a key focus in
    their lives.
-   They feel a closeness to other people, and generally appreciate
    life.
-   They have a system of morality that is fully internalized and
    independent of external authority.
-   They have discernment and are able to view all things in an
    objective manner. Prejudices are absent.

In short, self-actualization is reaching one\'s fullest potential.

Most people accomplish the two lower levels in their lifetime, but may
get stuck on upper levels. While self-actualization is a useful concept
to many, others insist there is no proof that every individual has this
capacity or even the goal to achieve it.

## Menopause

Menopause occurs as the ovaries stop producing estrogen, causing the
reproductive system to gradually shut down. As the body adapts to the
changing levels of natural hormones, vasomotor symptoms such as hot
flashes and palpitations, psychological symptoms such as increased
depression, anxiety, irritability, mood swings and lack of
concentration, and atrophic symptoms such as vaginal dryness and urgency
of urination appear. Together with these symptoms, the woman may also
have increasingly scanty and erratic menstrual periods.

Technically, menopause refers to the cessation of menses; whereas the
gradual process through which this occurs, which typically takes a year
but may last as little as six months or more than five years, is known
as climacteric. Popular use, however, replaces climacteric with
menopause. A natural or physiological menopause is that which occurs as
a part of a woman\'s normal aging process. However, menopause can be
surgically induced by such procedures as hysterectomy (when this
procedure includes oophorectomy, removal of the ovaries).

The average onset of menopause is 50.5 years, but some women enter
menopause at a younger age, especially if they have suffered from cancer
or another serious illness and undergone chemotherapy. Premature
menopause (or premature ovarian failure) is defined as menopause
occurring before the age of 40, and occurs in one percent of women.
Other causes of premature menopause include autoimmune disorders,
thyroid disease, and diabetes mellitus. Premature menopause is diagnosed
by measuring the levels of follicle stimulating hormone (FSH) and
luteinizing hormone (LH); the levels of these hormones will be higher if
menopause has occurred. Rates of premature menopause have been found to
be significantly higher in both fraternal and identical twins;
approximately five percent of twins reach menopause before the age of
40. The reasons for this are not completely understood. Transplants of
ovarian tissue between identical twins have been successful in restoring
fertility.

Post-menopausal women, especially Caucasian women of European descent,
are at increased risk of osteoporosis.

Animals other than human beings rarely experience menopause, possibly
because they simply do not live long enough to reach it. However, recent
studies have shown menopause in gorillas, with an average age of 44 at
onset.

Perimenopause refers to the time preceding menopause, during which the
production of hormones such as estrogen and progesterone diminishes and
becomes more irregular. During this period fertility diminishes.
Menopause is arbitrarily defined as a minimum of twelve months without
menstruation. Perimenopause can begin as early as age 35, although it
usually begins much later. It can last for a few months or for several
years. The duration of perimenopause cannot be predicted in advance.

### Grandmother Hypothesis

Human females have the unique distinction of being one of the only
species to stop reproduction well before the end of their life span.
This evolutionary distinction is odd because most other species continue
to reproduce until death, thus maximizing the number of offspring they
produce. The grandmother hypothesis essentially states that the presence
of a grandmother has beneficial effect on the survival of an infant.
Humans are one of the slowest developing species in the animal kingdom,
and unlike many species, infants, toddlers and children must be
continuously cared for to ensure their survival. (Compare that to the
salmon that swims up stream, spawns and dies.)

### Etiology

The cessation of menses is the result of the eventual atresia
(degeneration and reabsorption) of almost all oocytes in the ovaries.
This causes an increase in circulating FSH and LH levels as there are a
decreased number of oocytes responding to these hormones and producing
estrogen. This decrease in the production of estrogen leads to the
post-menopausal symptoms of hot flashes, insomnia, osteoporosis,
atherosclerosis, vaginal atrophy and depression.

Cigarette smoking has been found to decrease the age of menopause by as
much as one year however, premature menopause (before the age of 40) is
generally idiopathic.

### Symptoms

The clinical features of menopause are caused by the estrogen
deficiency.

-   vasomotor instability
-   hot flashes, hot flushes
-   sleep disturbances
-   Urogenital atrophy
-   dyspareunia
-   itching
-   dryness
-   bleeding
-   urinary frequency
-   urinary urgency
-   urinary incontinence
-   skeletal

**Breast Atrophy**

-   skin thinning
-   decreased elasticity
-   Psychological

**Mood Disturbance**

-   irritability
-   fatigue
-   decreased libido
-   memory loss
-   depression

**Treatments:** Medical treatments for menopausal symptoms have been
developed. Most notably, Hormone Replacement Therapy (HRT), has been
used to reduce the weakening of bones (known as osteoporosis). However,
some women have resisted the implication that menopause is a disorder,
seeing it as a natural stage of life. There has also been scientific
controversy over whether the benefits of HRT outweigh the risks. For
many years, women were advised to take hormone therapy after menopause
to reduce their risk of heart disease and various aspects of aging.
However, a large, randomized, controlled trial (the Women\'s Health
Initiative) found that women undergoing HRT had an increased risk of
Alzheimer\'s disease, breast cancer, heart disease and stroke.

### Osteoporosis

Osteoporosis is a skeletal disease resulting in bone loss and changes in
the bone quality that leads to diminished bone strength and an increased
risk to sustain fractures. The main cause of osteoporosis is a loss
estrogen following menopause. Osteoporosis can be prevented and treated
using a number of different drugs and lifestyle modifications including
proper diet, exercise and hormone replacement therapy. The link to
Wikipedia Osteoporosis is a great source of additional information.

**Preventing Osteoporosis** The old saying that an ounce of prevention
is worth a pound of cure holds true for osteoporosis. In researching
osteoporosis I found that while there are some treatments for
osteoporosis, a healthy lifestyle throughout your life is a much more
effective way of combating the effects of this disease. It is generally
acknowledged that a regular weight bearing exercise plan is helpful in
maintaining bone mass. Additionally, adequate dietary calcium and
vitamin D intake throughout ones life are important factors in building
up and maintaining bone mass.

Estrogen and progesterone treatments in postmenopausal women have proven
to be effective in treating bone loss. There are also two groups of
drugs that interfere with the re-absorption of bone by osteoclasts
called bisphosphonates and
lective
estrogen receptor modulators (SERMS).

An estimated 52 million men and woman will be afflicted with crumbling,
weakened bones by the year 2010. Osteoporosis is three to four times
more common in woman than men. While some men do get osteoporosis, they
are less likely to do so because men have frames that are 25 percent
larger and heavier than women. Women are also more susceptible to the
disease because they are more likely than a man to go on crash diets.
This kind of diet may interfere with the three main factors associated
with osteoporosis and having healthy bones: having enough vitamin D,
having enough calcium, and having enough estrogen. There are
approximately 1 million to 1.3 million hip fractures every year that are
related to osteoporosis. Men on steroids, people with arthritis, people
undergoing chemotherapy, along with those suffering from anorexia all
have an increased chance of having osteoporosis.

#### Osteoporosis related links

Wikipedia Osteoporosis Page This is
a wikipedia link with a complete discussion of osteoporosis.

National Osteoporosis Foundation
This page links to the National Osteoporosis Foundation

## Old Age

!Hmong
women{width="220"}

### Why do people age?

Some researchers believe we are programmed by an internal biological
clock to age. The idea is that each type of cell, tissue and organ is
like a clock that ticks at its own pace. In the body our cells divide 80
to 90 times at the most. At the end of each chromosome there are
repeated stretches of DNA called telomeres. These Telomeres prevent
Uncontrollable division which might lead to genetic deficits , producing
Cancer cells. A bit of each telomere is lost during every cell division.
When only a nub remains the cells stop dividing and die.

A different hypothesis is that aging is a result of accumulated damage
to DNA from environmental attacks and a decline in DNA\'s mechanism of
self repair. Things such as free radicals attack DNA and other molecules
causing structural changes. These changes in DNA endanger the synthesis
of enzymes and other proteins that are required for life. This damage
interferes with cell division. Organ wear out (over time) can cause
excessive damage to DNA ; unable to repair itself , DNA slowly starts
degrading in function thus increasing the chance of mistakes in
replication .

Most researchers believe that aging is a combination of an internal
clock that ticks out the life span of cells and the accumulation damage
to DNA.

## Old Age Diseases

### Diabetes

Diabetes mellitus is a disease characterized by persistent hyperglycemia
(high blood sugar levels), resulting either from inadequate secretion of
the hormone insulin, an inadequate response of target cells to insulin,
or a combination of these factors. Diabetes is a metabolic disease
requiring medical diagnosis, treatment and lifestyle changes

Type 1 diabetes mellitus is characterized by loss of the
insulin-producing beta cells of the islets of Langerhans of the
pancreas. Sensitivity and responsiveness to insulin are usually normal,
especially in the early stages. This type comprises up to 10% of total
cases in North America and Europe, though this varies by geographical
location. This type of diabetes can affect children or adults, but has
traditionally been termed \"juvenile diabetes\" because it represents a
majority of cases of diabetes affecting children. The most common cause
of beta cell loss leading to type 1 diabetes is autoimmune destruction,
accompanied by antibodies directed against insulin and islet cell
proteins. The principal treatment of type 1 diabetes, even from the
earliest stages, is replacement of insulin. Without insulin, ketosis and
diabetic ketoacidosis can develop.

Type 2 diabetes mellitus is due to a combination of defective insulin
secretion and defective responsiveness to insulin (often termed reduced
insulin sensitivity). In early stages the predominant abnormality is
reduced insulin sensitivity, characterized by elevated levels of insulin
in the blood. The initial defect of insulin secretion is subtle and
initially involves only the earliest phase of insulin secretion. In the
early stages, hyperglycemia can be reversed by a variety of measures and
medications that improve insulin sensitivity or reduce glucose
production by the liver, but as the disease progresses the impairment of
insulin secretion worsens, and therapeutic replacement of insulin often
becomes necessary. Type 2 diabetes is quite common, comprising 90% or
more of cases of diabetes in many populations. There is a strong
association with obesity and with aging, although in the last decade it
has increasingly begun to affect older children and adolescents. In the
past, this type of diabetes was often termed adult-onset diabetes or
maturity-onset diabetes.

Gestational diabetes, Type III, also involve a combination of inadequate
insulin secretion and responsiveness, resembling type 2 diabetes in
several respects. It develops during pregnancy and may improve or
disappear after delivery. Even though it may be transient, gestational
diabetes may damage the health of the fetus or mother, and about 40% of
women with gestational diabetes develop type 2 diabetes later in life.

### Congestive Heart Failure

Congestive heart failure (CHF), also called congestive cardiac failure
(CCF) or just heart failure, is a condition that can result from any
structural or functional cardiac disorder that impairs the ability of
the heart to fill with or pump a sufficient amount of blood throughout
the body. It is not to be confused with \"cessation of heartbeat\",
which is known as asystole, or with cardiac arrest, which is the
cessation of normal cardiac function in the face of heart disease.
Because not all patients have volume overload at the time of initial or
subsequent evaluation, the term \"heart failure\" is preferred over the
older term \"congestive heart failure\". Congestive heart failure is
often undiagnosed due to a lack of a universally agreed definition and
difficulties in diagnosis, particularly when the condition is considered
\"mild\".

### Stroke

!Stroke{width="150"} A stroke,
also known as cerebrovascular accident (CVA), is an acute neurologic
injury whereby the blood supply to a part of the brain is interrupted.
Stroke can also be said to be a syndrome of sudden loss of neuronal
function due to disturbance in cerebral perfusion. This disturbance in
perfusion is commonly on the arterial side of the circulation, but can
be on the venous side.

The part of the brain with disturbed perfusion can no longer receive
adequate oxygen carried by the blood; brain cells are therefore damaged
or die, impairing function from that part of the brain. Stroke is a
medical emergency and can cause permanent neurologic damage or even
death if not promptly diagnosed and treated. It is the third leading
cause of death and adult disability in the US and industrialized
European nations. On average, a stroke occurs every 45 seconds and
someone dies every 3 minutes. Of every 5 deaths from stroke, 2 occur in
men and 3 in women.

### Progeria

The term Progeria narrowly refers to Hutchinson-Gilford Progeria
syndrome, but the term is also used more generally to describe any of
the so-called \"accelerated aging diseases\". The word progeria is
derived from the Greek for \"prematurely old\". Because the
\"accelerated aging\" diseases display different aspects of aging, but
never every aspect, they are often called \"segmental progerias\" by
biogerontologists. Hutchinson-Gilford Progeria syndrome is an extremely
rare genetic condition which causes physical changes that resemble
greatly accelerated aging in sufferers. The disease affects between 1 in
4 million (estimated actual) and 1 in 8 million (reported) newborns.
Currently, there are approximately 40-45 known cases in the world. There
is no known cure. Most people with progeria die around 13 years of age.
Progeria is of interest to scientists because the disease may reveal
clues about the process of aging. Unlike most other \"accelerated aging
diseases\" (such as Werner\'s syndrome, Cockayne\'s syndrome or
xeroderma pigmentosum), progeria is not caused by defective DNA repair.
It is caused by mutations in a LMNA (Lamin A protein) gene on
chromosome 1. Nuclear lamina is a protein scaffold around the edge of
the nucleus that helps organize nuclear processes such as RNA and DNA
synthesis.

## The effects of Aging on the Body

### **Cardiovascular System**

The heart loses about 1% of its reserve pumping capacity every year
after we turn 30. Change in blood vessels that serve brain tissue reduce
nourishment to the brain, resulting in the malfunction and death of
brain cells. By the time we turn 80, cerebral blood flow is 20% less,
and renal blood flow is 50% less than when we were age 30. As we age our
heart goes through certain structural changes: the walls of the heart
thicken and the heart becomes heavier, heart valves stiffen and are more
likely to calcify, and the aorta, the major vessel carrying blood out of
the heart, becomes larger. 

Heart Attack / Myocardial infarction:Acute myocardial infarction (AMI or MI), commonly known as a heart attack, is a disease that occurs when the blood supply to a part of the heart is interrupted, causing death of heart tissue. It is the leading cause of death for both men and women all over the world. The term myocardial infarction is derived from myocardium (the heart muscle) and infarction (tissue death). The phrase \"heart attack\" sometimes refers to heart problems other than MI, such as unstable angina pectoris and sudden cardiac death.

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Congestive Heart Failure: In the elderly, ventricular diastolic stiffness can lead to pulmonary circulatory congestion. Aortic stenosis and aortic insufficiency, elevate left ventricular preload to the point where the left ventricle becomes stiff and noncompliant, and is common in people 75 years of age or older. Elevated pressures are transmitted to the pulmonary vasculature and lead to pulmonary edema.

### **Musculoskeletal System**

Bones: Aging is accompanied by the loss of bone tissue. The haversian systems in compact bone undergo slow erosion, lacunae are enlarged, canals become widened, and the endosteal cortex converts to spongy bone. The endosteal surface gradually erodes until the rate of loss exceeds the rate of deposition. Bone remodeling cycle takes longer to complete because bone cells slow in the rate of resorption and deposition of bone tissue. The rate of mineralization also slows down. The number of bone cells also decreases because the bone marrow becomes fatty and unable to provide an adequate supply of precursor cells. Because bones become less dense, they become more prone to fractures. Although bone degeneration is inevitable, it is variable if steps are taken before the mid-twenties -around this time our bones break down faster than they rebuild. Bone density increases when our bones are stressed, so physical activity is important. Vitamins and good diet also help build up bone mass.

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Joints: Cartilage becomes more rigid, fragile, and susceptible to fibrillation. Loss of elasticity and resiliency is attributed to more cross-linking of collagen to elastin, decrease in water content, and decreasing concentrations of glycosaminoglycans. Joints are also more prone to fracture due to the loss of bone mass.

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Muscles: Decrease in the range of motion of the joint is related to the change of ligaments and muscles. As the body ages, muscle bulk and strength declines especially after the age of 70. As much as 30% of skeletal muscle are lost by age 80. Muscle fibers, RNA synthesis and mitochondrial volume loss may all be contributors to muscle decline. Other factors that could contribute to muscle loss of the aged are: change in activity level, reduced nerve supply to muscle, cardiovascular disease, and nutritional deficiencies. In women, menopause will cause muscle mass to decrease significantly, especially in the first three post-menopausal years.

### **Nervous System**

One of the effects of aging on the nervous system is the loss of
neurons. By the age of 30, the brain begins to lose thousands of neurons
each day. The cerebral cortex can lose as much as 45% of its cells and
the brain can weigh 7% less than in the prime of our lives. Associated
with the loss of neurons comes a decreased capacity to send nerve
impulses to and from the brain. Because of this the processing of
information slows down. In addition the voluntary motor movement\'s slow
down, reflex time increases, and conduction velocity decreases.
Parkinson\'s disease is the most common movement disorder of the nervous
system. As we age there are some degenerative changes along with some
disease\'s involving the sense organ\'s that can alter vision, touch,
smell, and taste. Loss of hearing is also associated with aging. It is
usually the result of changes in important structures of the inner ear.

#### Dementia

Dementia (from Latin de- \"apart, away\" + mens (genitive mentis)
\"mind\") is the progressive decline in cognitive function due to damage
or disease in the brain beyond what might be expected from normal aging.
Particularly affected areas may be memory, attention, language and
problem solving, although particularly in the later stages of the
condition, affected persons may be disoriented in time (not knowing what
day, week, month or year it is), place (not knowing where they are) and
person (not knowing who they are). Symptoms of dementia can be
classified as either reversible or irreversible depending upon the
etiology of the disease. Less than 10% of all dementias are reversible.
Dementia is a non-specific term that encompasses many disease processes,
just as fever is attributable to many etiologies.

#### Alzheimers disease

Alzheimer\'s disease (AD) is a neurodegenerative disease characterized
by progressive cognitive deterioration together with declining
activities of daily living and neuropsychiatric symptoms or behavioral
changes. It is the most common cause of dementia. The most striking
early symptom is short term memory loss (amnesia), which usually
manifests as minor forgetfulness that becomes steadily more pronounced
with illness progression, with relative preservation of older memories.
As the disorder progresses, cognitive (intellectual) impairment extends
to the domains of language (aphasia), skilled movements (apraxia),
recognition (agnosia), and those functions (such as decision-making and
planning) closely related to the frontal and temporal lobes of the brain
as they become disconnected from the limbic system, reflecting extension
of the underlying pathological process. This consists principally of
neuronal loss or atrophy, together with an inflammatory response to the
deposition of amyloid plaques and neurofibrillary tangles. Genetic
factors are known to be important, and autosomal dominant mutations in
three different genes (presenilin 1, presenilin 2, and amyloid precursor
protein) have been identified that account for a small number of cases
of familial, early-onset AD. For late onset AD (LOAD), only one
susceptibility gene has so far been identified: the epsilon 4 allele of
the apolipoprotein E gene. Age of onset itself has a heritability of
around 50%.

### **Digestive System**

The changes associated with aging of the digestive system include loss
of strength and tone of muscular tissue and supporting muscular tissue,
decreased secretory mechanisms, decreased motility of the digestive
organs, along with changes in neurosensory feedback regarding enzyme and
hormone release, and diminished response to internal sensations and
pain. In the upper GI tract common changes include periodontal disease,
difficulty in swallowing, reduced sensitivity to mouth irritations and
sores, loss of taste, gastritis, and peptic ulcer disease. Changes that
may appear in the small intestine include, appendicitis, duodenal
ulcers, malabsorption, and maldigestion. Other pathologies that increase
in occurrence with age are acute pancreatitis, jaundice, and gallbladder
problems. Large intestinal changes such as hemorrhoids and constipation
may also occur. Cancer of the rectum are quite common.

### **Urinary System**

As we get older kidney function diminishes. By the age of 70, the
filtering mechanism is only about half as effective as it was at age 40.
Because water balance is altered and the sensation of thirst diminishes
with age, older people are more susceptible to dehydration. This causes
more urinary tract infections in the elderly. other problems may include
nocturia (excessive urination at night), increased frequency of
urination, polyuria (excessive urine production), dysuria (painful
urination), incontinence, and hematuria (blood in the urine). Some
kidney diseases that are common as we age include acute and chronic
kidney inflammations and renal calculi (kidney stones). The prostate
gland is often implicated in various disorders of the urinary tract.
Prostate cancer is the most common cancer in elderly males. Because the
prostate gland encircles part of the urethra, an enlarged prostate gland
may cause difficulty in urination

### **Respiratory Systems**

With the advancing of age, the airways and tissue of the respiratory
tract become less elastic and more rigid. The walls of the alveoli break
down, so there is less total respiratory surface available for gas
exchange. This decreases the lung capacity by as much as 30% by the age
of 70. Therefore, elderly people are more susceptible to pneumonia,
bronchitis, emphysema, and other pulmonary disorders. For a more
complete discussion of the respiratory system please visit Chapter 12
The Respiratory
System.

#### Lung cancer

right\|framed\|Correlation between lung cancer and smoking
tobacco.

Lung cancer is a cancer of the lungs characterized by the presence of
malignant tumors. Most commonly it is bronchogenic carcinoma (about
90%). Lung cancer is one of the most lethal forms of cancer worldwide,
causing up to 3 million deaths annually. Only one in ten patients
diagnosed with this disease will survive the next five years. Although
lung cancer was previously an illness that affected predominately men,
lung cancer rate for women has been increasing in the last few decades.
This has been attributed to the rising ratio of female to male smokers.
More women die of lung cancer than any other cancer, including breast
cancer, ovarian cancer and uterine cancers combined. Current research
indicates that the factor with the greatest impact on risk of lung
cancer is long-term exposure to inhaled carcinogens. The most common
means of such exposure is tobacco smoke.

#### Vision

Changes in vision begin at an early age. The cornea becomes thicker and
less curved. The anterior chamber decreases in size and volume. The lens
becomes thicker and more opaque, and also increases rigidity and loses
elasticity. The ciliary muscles atrophy and the pupil constricts. There
is also a reduction of rods and nerve cells of the retina.

#### Hearing

Approximately one third of people over the age of 65 have hearing loss.
The ability to distinguish between high and low frequency diminishes
with age. Loss of hearing for sounds of high-frequency (presbycusis) is
the most common, although the ability to distinguish sound localization
also decreases. It is believed that the hearing loss isn\'t so much an
age change as it is due to the accumulation of noise damage.

#### Taste and Smell

Sensitivity to odors and taste decline with age. The sense of smell
begins to degenerate with the loss of olfactory sensory neurons and loss
of cells from the olfactory bulb. The decline in taste sensation is more
gradual than that of smell. The elderly have trouble differentiating
between flavors. The number of fungiform papillae of the tongue decline
by 50% by the age of 50. Taste could also be affected by the loss of
salivary gland secretions, notably amylase. This loss of taste and smell
can have a significant effect on an elder\'s health. With the reduced
ability to taste and smell, it is difficult to adjust food intake as
they can no longer rely on their taste receptors to tell them if
something is too salty, or too sweet. This can also cause the problem in
that they might not be able to detect if something is spoiled, making
them at a higher risk for food poisoning.

### **Cellular Aging**

As people age, oxygen intake decreases as well as the basal metabolic
rate. The decrease in the metabolic rate, delayed shivering response,
sedentary lifestyle, decreased vasoconstrictor response, diminished
sweating, and poor nutrition are reasons why the elderly cannot maintain
body temperature. There is also a decrease in total body water (TBW). In
newborns, TBW is 75% to 80%. TBW continues to decline in childhood to
60% to 65%, to less than 60% in adults.

### **Organism Aging**

Aging is generally characterized by the declining ability to respond to
stress, increasing homeostatic imbalance and increased risk of disease.
Because of this, death is the ultimate consequence of aging. Differences
in maximum life span between species correspond to different \"rates of
aging\". For example, inherited differences in the rate of aging make a
mouse elderly at 3 years and a human elderly at 90 years. These genetic
differences affect a variety of physiological processes, probably
including the efficiency of DNA repair, antioxidant enzymes, and rates
of free radical production.

## Life Expectancy

<http://www.senescence.info/definitions.html>

## Stages of Grief- Death and Dying

We go through several stages of grief as we near death, receive
catastrophic news, or go through some type of life-altering experience.
There are five defined stages according to Elisabeth Kübler-Ross. She
states, however, that these steps don\'t always come in order, and are
not always experienced all together by everyone. She does claim that a
person will always experience at least two of the stages.

The stages are:

**Denial**- This isn\'t happening, there must have been some mistake.

**Anger**- Why me? It\'s not fair, how could you do this to me?!? (aimed
toward some other \"responsible\" party)

**Bargaining**- Just give me 2 more years\...let me live to
see\_\_\_\_\_\_\_\_.

**Depression**- extreme sadness, lack of motivation or desire to fight
anymore

**Acceptance**- I\'m ok with this.

## Sidenotes: Aubrey de Grey

Aubrey David Nicholas Jasper de Grey, Ph.D., (born 20 April 1963 in
London, England) is a controversial biomedical gerontologist who lives
in the city of Cambridge, UK. He is working to expedite the development
of a cure for human aging, a medical goal he refers to as engineered
negligible senescence. To this end, he has identified what he concludes
are the seven areas of the aging process that need to be addressed
medically before this can be done. He has been interviewed in recent
years in many news sources, including CBS 60 Minutes, BBC, the New York
Times, Fortune Magazine, and Popular Science. His main activities at
present are as chairman and chief science officer of the Methuselah
Foundation and editor-in-chief of the academic journal Rejuvenation
Research. Here are the seven biological causes of senescence and
possible solutions:

1.  Cell loss or atrophy. Cell depletion can be partly corrected by
    therapies involving exercise and growth factors. But stem cell
    therapy is almost certainly required for any more than just partial
    replacement of lost cells. This research would involve a large
    number of details, but is occurring on many fronts.
2.  Nuclear mutations and epimutations. A mutation in a functional gene
    of a cell can cause that cell to malfunction or to produce a
    malfunctioning product. Because of the sheer number of cells Dr. de
    Grey believes that redundancy takes care of this problem, although
    cells that have mutated to produce toxic products might have to be
    disabled. In Dr. de Grey\'s opinion, the effect of mutations and
    epimutations that really matters is cancer, since if even one cell
    turns into a cancer cell it might spread and become deadly. This is
    to be corrected by whole-body interdiction of lengthening telomeres,
    or any other cure for cancer, if any is ever found.
3.  Mutant mitochondria. Because of the highly oxidative environment in
    mitochondria and their lack of the sophisticated repair systems
    found in the cell nucleus, mitochondrial mutations are believed to a
    be a major cause of progressive cellular degeneration. This is to be
    corrected by moving the DNA for mitochondria completely within the
    cellular nucleus, where it is better protected. In humans all but 13
    proteins are already protected in this way. It has been
    experimentally shown the operation is feasible.
4.  Cellular senescence. Cellular senescence might be corrected by
    forcing senescent cells to destroy themselves, a process called
    apoptosis. Cell killing with suicide genes or vaccines was suggested
    for making the cells do apoptosis. Healthy cells would multiply to
    replace them.
5.  Extracellular cross-links. These are chemical bonds between
    structures that are part of the body, but not within a cell. In
    senescent people many of these become brittle and weak. The proposal
    is to further develop small-molecular drugs and enzymes to break
    links caused by sugar-bonding (glycation), and other common forms of
    chemical linking.
6.  Junk outside cells. Junk outside cells might be removed by enhanced
    phagocytosis (the normal process used by the immune system), and
    small drugs able to break chemical beta-bonds. The large junk in
    this class can be removed surgically. Junk here means useless things
    accumulated by a body, but which cannot be digested or removed by
    its processes, such as the amyloid plaques characteristic of
    Alzheimer\'s disease. The oft-mentioned \'toxins\' that people claim
    cause many diseases would probably also fit under this class.
7.  Junk inside cells. Junk inside cells might be removed by adding new
    enzymes to the cell\'s natural digestion organ, the lysosome. These
    enzymes would be taken from bacteria, molds and other organisms that
    are known to completely digest animal bodies.

Dr. de Grey\'s research proposals are highly controversial, with many
critics arguing the highly complicated biomedical phenomena involved
contain too many unknowns for intervention to be considered remotely
foreseeable.

## Discoveries In Growth And Development

-   **Medieval times**

In this time the thought was once children emerged form infancy, they
were regarded as miniature already formed adults.

-   **Religious influence of parenting 16th Century**

Puritan belief harsh restrictive parenting practices were recommended as
the most efficient means of taming the depraved child.

-   **John Locke\'s 17th Century**

Tabula Rosa = Blank slate in this the thought was that children are to
begin with nothing at all and all kinds of experiences can shape their
characters. This is seen as a negative vision of the development of
children because children do contribute to his or her own development.

-   **Jean Jacques Rousseau 18th Century**

Noble savages = endowed with a sense of right or wrong. Children have
built in moral sense 1st concept of stage, 2nd maturation of growth
refers to genetically determined naturally unfolding course. He saw
development as a discontinuous stagewise process mapped cut by nature.

-   **Charles Darwin the forefather of Scientific Child Study 1859-1936,
    19th century**

The famous theory of evolution, *the survival of the fittest*, and
*natural selection*.

-   **G. Stanley Hall regarded as the founder of the child study
    movement 1846-1924**

One of the most influential American psychologists of the early
twentieth century. The Normative Approach = normative period measures of
large numbers of individuals and age related averages are computed to
represent typical development.

-   **The mental testing movement early 20th Century**

French psychologist Alfred Binet and Colleague Theodore Simon were the
first to come up with a successful intelligence test IQ at Stanford
University.

-   **Sigmund Freud 1856-1939**

Theory *\'psychosexual theory*, ID, Ego, and Superego.

-   **Erik Erikson 1902-1994**

Theory *psychosocial theory*

-   **John Watson 1978-1958**

Behaviorism and Social Learning Theory

-   **Ivan Pavlov**

Classical conditioning

-   **B.F. Skinner**

Operant Conditioning

-   **Albert Bandura**

Social learning theory

-   **Jean Piaget\'s**

Cognitive-developmental theory

## Review Questions

Answers for these questions can be found here

1\. Growth is the most rapid in

:   A\) puberty
:   B\) childhood
:   C\) infancy
:   D\) adulthood
:   E\) Growth is always the same

2\. This hormone stimulates puberty

:   A\) GnRH
:   B\) LH
:   C\) FSH
:   D\) TSH

3\. Compared to girls\' early growth spurt, growth
\_\_\_\_\_\_\_\_\_\_in boys and \_\_\_\_\_\_\_\_\_\_

:   A\) is quicker, lasts longer
:   B\) accelerates more slowly, lasts longer
:   C\) is slower, shorter
:   D\) None of the above

4\. This quality symbolizes adulthood in most cultures

:   A\) stability
:   B\) method/tact
:   C\) endurance
:   D\) objectivity
:   E\) all of the above

5\. Susie has a very hard time keeping friends, according to Maslow,
this could be because

:   A\) as a child she had a supportive family
:   B\) she likes to help solve the problems of others
:   C\) as a teenager her self-esteem was low
:   D\) as a baby she wasn't breastfed
:   E\) as a child she lived in an environment that never made her feel
    safe

6\. According to Maslow, in order for me to reach my full potential of
self-actualization I must first

:   A\) feel safe
:   B\) gain self-esteem
:   C\) have friendship
:   D\) have food
:   E\) all of the above

7\. Humans are one of the \_\_\_\_\_\_\_\_\_ developing species in the
animal kingdom

:   A\) slowest
:   B\) quickest
:   C\) average
:   D\) none of the above

8\. Jenny thinks that she might be going through menopause, a symptom of
this is

:   A\) bleeding
:   B\) frequent urination
:   C\) itchiness
:   D\) none of the above
:   E\) all of the above

9\. It is estimated that 52 million people will be afflicted with this
by 2010

:   A\) Progeria
:   B\) osteoporosis
:   C\) Alzheimer's
:   D\) dementia

10\. This is the leading cause of death for both men and women

:   A\) progeria
:   B\) cancer
:   C\) congestive heart failure
:   D\) osteoporosis
:   E\) heart attack

## Glossary

Alzheimer\'s disease: The most common form of dementia. It is a progressive condition that destroys brain cells, resulting in the loss of intellectual abilities

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Apoptosis: The process of regulated cell death

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Appositional bone growth: The growth in diameter of bones around the diaphysis occurs by deposition of bone beneath the periosteum.

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Bilirubin: A chemical breakdown product of hemoglobin.

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canaliculi: small channels or canals in bone.

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Deciduous teeth: The first set of teeth in the growth development of humans and many other animals. (milk teeth, baby teeth, or primary teeth)

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Dementia: The progressive decline in cognitive function due to damage or disease in the brain beyond what might be expected from normal aging.

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Epiphyseal Plate: The cartilage in growing long bones that allows lengthwise growth. The plate ossifies at the end of puberty.

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Haversian system: The basic structural unit of compact bone which includes a central canal, lamellae, lacunae, osteocytes, and canaliculi.

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Intramembranous ossification: The type of bone formation responsible for the development of flat bones, especially those found in the skull. In intramembranous ossification mesenchymal cells develop into bone without first going through a cartilage stage.

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lacunae: spaces between bone lamellae.

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lamellae: concentric layers of bone matrix.

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Menopause: The permanent cessation of menstrual cycles.

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Menarche:The first menstrual bleeding, usually occurs at about 12.7 years of age.

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Mongolian spots: are common among darker-skinned races, such as Asian, East Indian, and African. They are flat, pigmented lesions with unclear borders and irregular shape. They appear commonly at the base of the spine, on the buttocks and back. They may also can appear as high as the shoulders and elsewhere. Mongolian spots are benign skin markings and are not associated with any conditions or illnesses.

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Necrosis:A form of cell death that results from acute cellular injury.

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Osteoporosis: A condition that is characterized by a decrease in bone mass and density, causing bones to become fragile.

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Puberty: The process of physical changes by which a child\'s body becomes an adult body capable of reproduction

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Pyloric Stenosis: Narrowing of the pyloric sphincter that reduces or eliminates the passage of food from the stomach to the small intestine, often causing projectile vomiting in infants.

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Trabeculae: spongy bones that make plates or bars instead of concentric layers.

## References

-   Methuselahmouse.org
-   Van De Graaff (2002) *Human Anatomy 6th ed.* McGraw-Hill Higher
    Education
-   Windmaier, P.W. Raff, H. Strang, T.S. (2004) *Vander, Sherman, &
    Luciano\'s Human Physiology, the Mechanisms of Body Function 9th
    ed.* Mcgraw-Hill
-   Starr & McMillan (2001) *Human Biology 6th ed.* Thomson-Brooks/cole.
-   McCance, Kathryn L., Heuther, Sue E. (1994) *Pathophysiology: the
    biological basis for diseases in adults and children.* Mosby-Year
    Book, Inc.
