# Human Physiology/Integumentary System

## Introduction

The **integumentary system** consists of the skin, hair, nails, the
subcutaneous tissue below the skin,and assorted glands.The most obvious
function of the integumentary system is the protection that the skin
gives to underlying tissues. The skin not only keeps most harmful
substances out, but also prevents the loss of fluids.

A major function of the subcutaneous tissue is to connect the skin to
underlying tissues such as muscles. Hair on the scalp provides
insulation from cold for the head. The hair of eyelashes and eyebrows
helps keep dust and perspiration out of the eyes, and the hair in our
nostrils helps keep dust out of the nasal cavities. Any other hair on
our bodies no longer serves a function, but is an evolutionary remnant.
Nails protect the tips of fingers and toes from mechanical injury.
Fingernails give the fingers greater ability to pick up small objects.

There are four types of glands in the integumentary system: Sudoriferous
glands, Sebaceous glands, Ceruminous glands, and Mammary glands.
Sudoriferous glands are sweat producing glands. These are important to
help maintain body temperature. Sebaceous glands are oil producing
glands which help inhibit bacteria, keep us waterproof and prevent our
hair and skin from drying out. Ceruminous glands produce earwax which
keeps the outer surface of the eardrum pliable and prevents drying.
Mammary glands produce milk.

## Skin

In zoology and dermatology, skin is an organ of the integumentary system
made up of a layer of tissues that guard underlying muscles and organs.
As the interface with the surroundings, it plays the most important role
in protecting against pathogens. Its other main functions are insulation
and temperature regulation, sensation and vitamin D and B synthesis.
Skin is considered one of the most important parts of the body.

Skin has pigmentation, melanin, provided by melanocytes, which absorbs
some of the potentially dangerous radiation in sunlight. It also
contains DNA repair enzymes which reverse UV damage, and people who lack
the genes for these enzymes suffer high rates of skin cancer. One form
predominantly produced by UV light, malignant melanoma, is particularly
invasive, causing it to spread quickly, and can often be deadly. Human
skin pigmentation varies among populations in a striking manner. This
has sometimes led to the classification of people(s) on the basis of
skin color.

Damaged skin will try to heal by forming scar tissue, often giving rise
to discoloration and depigmentation of the skin.

The skin is often known as \"the largest organ in the human body\". This
applies to exterior surface, as it covers the body, appearing to have
the largest surface area of all the organs. Moreover, it applies to
weight, as it weighs more than any single internal organ, accounting for
about 15 percent of body weight. For the average adult human, the skin
has a surface area of between 1.5-2.0 square meters, most of it is
between 2-3 mm thick. The average square inch of skin holds 650 sweat
glands, 20 blood vessels, 60,000 melanocytes, and more than a thousand
nerve endings.

The use of natural or synthetic cosmetics to treat the appearance of the
face and condition of the skin (such as pore control and black head
cleansing) is common among many cultures.

### Layers

The skin has two major layers which are made of different tissues and
have very different functions. !Diagram of the layers of human
skin{width="400"} Skin
is composed of the *epidermis* and the *dermis*. Below these layers lies
the *hypodermis or subcutaneous adipose layer*, which is not usually
classified as a layer of skin.

The outermost epidermis consists of stratified squamous keratinizing
epithelium with an underlying basement membrane. It contains no blood
vessels, and is nourished by diffusion from the dermis. The main type of
cells which make up the epidermis are keratinocytes, with melanocytes
and Langerhans cells also present. The epidermis can be further
subdivided into the following *strata* (beginning with the outermost
layer): corneum, lucidum, granulosum, spinosum, basale. Cells are formed
through mitosis at the innermost layers. They move up the strata
changing shape and composition as they differentiate, inducing
expression of new types of keratin genes. They eventually reach the
corneum and become sloughed off (desquamation). This process is called
*keratinization* and takes place within about 30 days. This layer of
skin is responsible for keeping water in the body and keeping other
harmful chemicals and pathogens out.

Blood capillaries are found beneath the dermis, and are linked to an
arteriole and a venule. Arterial shunt vessels may bypass the network in
ears, the nose and fingertips.

The dermis lies below the epidermis and contains a number of structures
including blood vessels, nerves, hair follicles, smooth muscle, glands
and lymphatic tissue. It consists of loose connective tissue otherwise
called areolar connective tissue---collagen, elastin and reticular
fibers are present. Erector muscles, attached between the hair papilla
and epidermis, can contract, resulting in the hair fiber pulled upright
and consequentially goose bumps. The main cell types are fibroblasts,
adipocytes (fat storage) and macrophages. Sebaceous glands are exocrine
glands which produce a mixture of lipids and waxy substances known as
sebum. Sebum serves many functions, including lubrication,
water-proofing, softening, and also provides antimicrobial properties.
Sweat glands open up via a duct onto the skin by a pore.

The dermis is made of an irregular type of fibrous connective tissue
consisting of collagen and elastin fibers. It can be split into the
*papillary* and *reticular* layers. The papillary layer is outermost and
extends into the epidermis to supply it with vessels. It is composed of
loosely arranged fibers. Papillary ridges make up the lines of the hands
giving us fingerprints. The reticular layer is more dense and is
continuous with the hypodermis. It contains the bulk of the structures
(such as sweat glands). The reticular layer is composed of irregularly
arranged fibers and resists stretching.

The hypodermis is not part of the skin, and lies below the dermis. Its
purpose is to attach the skin to underlying bone and muscle as well as
supplying it with blood vessels and nerves. It consists of loose
connective tissue and elastin. The main cell types are fibroblasts,
macrophages and adipocytes (the hypodermis contains 95% of body fat).
Fat serves as padding and insulation for the body.

### Functions

![](Pili.JPG "Pili.JPG")

1.  Protection: Skin gives an anatomical barrier between the internal
    and external environment in bodily defense; Langerhans cells in the
    skin are part of the immune system
2.  Sensation: Skin contains a variety of nerve endings that react to
    heat, cold, touch, pressure, vibration, and tissue injury; see
    somatosensory system
    and touch.
3.  Heat regulation: The skin contains a blood supply far greater than
    its requirements which allows precise control of energy loss by
    radiation, convection and conduction. Dilated blood vessels increase
    perfusion and heat loss while constricted vessels greatly reduce
    cutaneous blood flow and conserve heat. Erector pili muscles are
    significant in animals.

#### Tumors

-   Benign tumors of the skin: Squamous cell papilloma
-   Skin cancer
-   Acne
-   Keratosis pilaris
-   Fungal infections such as athlete\'s
    foot
-   microbial infections
-   calcinosis cutis
-   ulcer

## Hair

### Types of hair

Humans have three different types of hair:

-   Lanugo, the fine, unpigmented hair that covers nearly the entire
    body of a fetus, although most has been replaced with vellus by the
    time of the baby\'s birth
-   Vellus hair, the short, downy, \"peach fuzz\" body hair (also
    unpigmented) that grows in most places on the human body. While it
    occurs in both sexes, and makes up much of the hair in children, men
    have a much smaller percentage (around 10%) vellus whereas 2/3 of a
    female\'s hair is vellus.
-   Terminal hair, the fully developed hair, which is generally longer,
    coarser, thicker, and darker than vellus hair, and often is found in
    regions such as the axillary, male beard, and pubic.

### Pathological impacts on hair

Drugs used in cancer chemotherapy frequently cause a temporary loss of
hair, noticeable on the head and eyebrows, because they kill all rapidly
dividing cells, not just the cancerous ones. Other diseases and traumas
can cause temporary or permanent loss of hair, either generally or in
patches.

The hair shafts may also store certain poisons for years, even decades,
after death. In the case of Col. Lafayette Baker, who died July 3, 1868,
use of an atomic absorption spectrophotometer showed the man was killed
by white arsenic. The prime suspect was Wallace Pollock, Baker\'s
brother-in-law. According to Dr. Ray A. Neff, Pollack had laced Baker\'s
beer with it over a period of months, and a century or so later minute
traces of arsenic showed up in the dead man\'s hair. Mrs. Baker\'s diary
seems to confirm that it was indeed arsenic, as she writes of how she
found some vials of it inside her brother\'s suit coat one day.

## Nails

{{-}}

### Parts of the fingernail

!The parts of a finger
nail{width="200"}

The fingernail is an important structure made of keratin. The fingernail
generally serve two purposes. It serves as a protective plate and
enhances sensation of the fingertip. The protection function of the
fingernail is commonly known, but the sensation function is equally
important. The fingertip has many nerve endings in it allowing us to
receive volumes of information about objects we touch. The nail acts as
a counterforce to the fingertip providing even more sensory input when
an object is touched.

### Nail Structure

The structure we know of as the nail is divided into six specific
parts - the root, nail bed, nail plate, eponychium (cuticle),
perionychium, and hyponychium.

**Root** The root of the fingernail is also known as the germinal
matrix. This portion of the nail is actually beneath the skin behind the
fingernail and extends several millimeters into the finger. The
fingernail root produces most of the volume of the nail and the nail
bed. This portion of the nail does not have any melanocytes, or melanin
producing cells. The edge of the germinal matrix is seen as a white,
crescent shaped structure called the lunula.

**Nail Bed** The nail bed is part of the nail matrix called the sterile
matrix. It extends from the edge of the germinal matrix, or lunula, to
the hyponychium. The nail bed contains the blood vessels, nerves, and
melanocytes, or melanin-producing cells. As the nail is produced by the
root, it streams down along the nail bed, which adds material to the
undersurface of the nail making it thicker. It is important for normal
nail growth that the nail bed be smooth. If it is not, the nail may
split or develop grooves that can be cosmetically unappealing.

**Nail Plate** The nail plate is the actual fingernail, made of
translucent keratin. The pink appearance of the nail comes from the
blood vessels underneath the nail. The underneath surface of the nail
plate has grooves along the length of the nail that help anchor it to
the nail bed.

**eponychium** The cuticle of the fingernail is also called the
eponychium. The cuticle is situated between the skin of the finger and
the nail plate fusing these structures together and providing a
waterproof barrier.

**Perionychium** The perionychium is the skin that overlies the nail
plate on its sides. It is also known as the paronychial edge. The
perionychium is the site of hangnails, ingrown nails, and an infection
of the skin called paronychia.

**Hyponychium** The hyponychium is the area between the nail plate and
the fingertip. It is the junction between the free edge of the nail and
the skin of the fingertip, also providing a waterproof barrier.

!Nails: left hand, adult human
male{width="200"}

### Nail Diseases

Nail diseases are in a separate category from diseases of the skin.
Although nails are a skin appendage, they have their own signs and
symptoms which may relate to other medical conditions. Nail conditions
that show signs of infection or inflammation require medical assistance
and cannot be treated at a beauty parlor. Deformity or disease of the
nails may be referred to as **onychosis**.

There are many disease that can occur with the fingernails and toenails.
The most common of these diseases are ingrown nails and fungal
infections.

#### Ingrown Nails

**Onychocryptosis**, commonly known as \"ingrown nails\" (unguis
incarnatus), can affect either the fingers or the toes. In this
condition, the nail cuts into one or both sides of the nail bed,
resulting in inflammation and possibly infection. The relative rarity of
this condition in the fingers suggests that pressure from the ground or
shoe against the toe is a prime factor. The movements involved in
walking or other physical disturbances can contribute to the problem.
Mild onychocryptosis, particularly in the absence of infection, can be
treated by trimming and rounding the nail. More advanced cases, which
usually include infection, are treated by surgically excising the
ingrowing portion of the nail down to its bony origin and cauterizing
the matrix, or \'root\', to prevent recurrence. This surgery is called
matricectomy. The best results are achieved by cauterizing the matrix
with phenol. Another method, which is much less effective, is excision
of the matrix, sometimes called a \'cold steel procedure\'

#### Nail Fungus

An infection of nail fungus (onychomycosis) occurs when fungi infect one
or more of your nails. **Onychomycosis** generally begins as a white or
yellow spot under the tip of the fingernail or toenail. As the nail
fungus spreads deeper into the nail, it may cause the nail to discolor,
thicken and develop crumbling edges --- an unsightly and potentially
painful problem.

Infections of nail fungus account for about half of all nail disorders.
These infections usually develop on nails continually exposed to warm,
moist environments, such as sweaty shoes or shower floors. Nail fungus
isn\'t the same as athlete\'s foot, which primarily affects the skin of
the feet, but at times the two may coexist and can be caused by the same
type of fungus. Topical steroid misuse is one of the most common cause
now a days.

An infection with nail fungus may be difficult to treat, and infections
may recur. But medications are available to help clear up nail fungus
permanently.

### Clinical Application

Nail inspection can give a great deal of information about the internal
working of the body as well, and like tongue or iris inspection, has a
long history of diagnostic use in cantraditional medical practices such
as Chinese medicine.

**Pliability:**

Brittleness is associated with iron deficiency, thyroid problems,
impaired kidney function, circulation problems\[2\], and biotin
deficiency\[3\] Splitting and fraying are associated with psoriasis,
folic acid, protein and/or Vitamin C deficiency. Unusual thickness is
associated with circulation problems. Thinning nails and itchy skin are
associated with lichen planus\[4\].

**Shape and texture:**

Clubbing, or nails that curve down around the fingertips with nail beds
that bulge is associated with oxygen deprivation and lung, heart, or
liver disease. Spooning, or nails that grow upwards is associated with
iron or B12 deficiency. Flatness can indicate a B12 vitamin
deficiency\[5\] or Raynaud\'s disease\[6\] Pitting of the nails is
associated with Psoriasis. Horizontal ridges indicate stress, and
Beau\'s lines are associated with many serious conditions. Vertical
ridges are associated with arthritis\[7\]. Vertical grooves are
associated with kidney disorders, aging, and iron deficiency\[8\].
Beading is associated with rheumatoid arthritis\[9\]. Nails that
resemble hammered brass are associated with (or portend) hair
loss\[10\]. Short small beds are associated with heart disease\[11\].

**Coloration of the nail bed:**

Mee\'s lines are associated with arsenic or thallium poisoning, and
renal failure. White lines across the nail are associated with heart
disease, liver disease, or a history of a recent high fever\[12\].
Opaque white nails with a dark band at the fingertip are associated with
cancer, cirrhosis, congestive heart failure, diabetes and aging\[13\].
Paleness or whitening is associated with liver or kidney disease and
anemia\[14\]. Yellowing of the nail bed is associated with chronic
bronchitis, lymphatic problems, diabetes, and liver disorders. Brown or
copper nail beds are associated with arsenic or copper poisoning, and
local fungal infection. Grey nail beds are associated with arthritis,
edema, malnutrition, post-operative effects, glaucoma and
cardio-pulmonary disease\[15\]. redness is associated with heart
conditions. dark nails are associated with B12 deficiency. Stains of the
nail plate (not the nail bed) are associated with nail polish\[16\],
smoking, and henna use.

**Markings:**

Pink and white nails are associated with kidney disease\[17\]. Parallel
white lines in the nails are associated with hypoalbuminemia. red skin
at the base of the nail is associated with connective tissue
disorders\[18\]. blue lunulae are associated with silver poisoning or
lung disorder\[19\]. blue nail beds are (much like blue skin) associated
with poor oxygenation of the blood (asthma, emphysema, etc)\[20\]. small
white patches are associated with zinc or calcium deficiency or
malabsorption, parasites, or local injury\[21\]. receded lunulae (fewer
than 8) are associated with poor circulation\[22\], shallow breathing
habits or thyroid dysfunction\[23\]. large lunulae (more than 25% of the
thumb nail) is associated with high blood pressure.

## Glands

### Sudoriferous(Sweat Glands)

!A diagrammatic sectional view of the skin (magnified). Sweat gland
labeled as \"sudoriferous gland\" at center
right.. Sweat gland labeled as "sudoriferous gland" at center right."){width="350"}
In humans, there are two kinds of sweat glands which differ greatly in
both the composition of the sweat and its purpose: Also \"**click**\"
here\[<http://health.howstuffworks.com/adam-200101.htm>\|\"How our body
Sweats\"\] to see a short movie on sweat glands.

#### Eccrine (a.k.a. merocrine)

**Eccrine sweat glands** are exocrine glands distributed over the entire
body surface but are particularly abundant on the palms of hands, soles
of feet, and on the forehead. These produce sweat that is composed
chiefly of water (99%) with various salts. The primary function is body
temperature regulation.

Eccrine sweat glands are coiled tubular glands derived leading directly
to the most superficial layer of the epidermis (outer layer of skin) but
extending into the inner layer of the skin (dermis layer). They are
distributed over almost the entire surface of the body in humans and
many other species but are lacking in some marine and fur-bearing
species. The sweat glands are controlled by sympathetic cholinergic
nerves which are controlled by a center in the hypothalamus. The
hypothalamus senses core temperature directly, and also has input from
temperature receptors in the skin and modifies the sweat output, along
with other thermoregulatory processes.

Human eccrine sweat is composed chiefly of water with various salts and
organic compounds in solution. It contains minute amounts of fatty
materials, urea, and other wastes. The concentration of sodium varies
from 35--65 mmol/l and is lower in people acclimatized to a hot
environment. The sweat of other species generally differs in
composition.

#### Apocrine

Apocrine sweat glands only develop during early- to mid-puberty
(approximately age 15) and release more than normal amounts of sweat for
approximately a month and subsequently regulate and release normal
amounts of sweat after a certain period of time. **Apocrine sweat
glands** produce sweat that contains fatty materials. These glands are
mainly present in the armpits and around the genital area and their
activity is the main cause of sweat odor, due to the bacteria that break
down the organic compounds in the sweat from these glands. Emotional
stress increases the production of sweat from the apocrine glands, or
more precisely: the sweat already present in the tubule is squeezed out.
Apocrine sweat glands essentially serve as scent glands.

In some areas of the body, these sweat glands are modified to produce
wholly different secretions, including the cerumen (\"wax\") of the
outer ear. Other glands, such as Mammary glands, are greatly enlarged
and modified to produce milk.

### Sebaceous Glands

!Schematic view of a hair follicle with sebaceous
gland.{width="200"}
The **sebaceous glands** are glands found in the skin of mammals. They
secrete an oily substance called **sebum** (Latin, meaning *fat* or
*tallow*) that is made of fat (lipids) and the debris of dead
fat-producing cells. These glands exist in humans throughout the skin
except in the palms of the hands and soles of the feet. Sebum acts to
protect and waterproof hair and skin, and keep them from becoming dry,
brittle, and cracked. It can also inhibit the growth of microorganisms
on skin.

Sebaceous glands can usually be found in hair-covered areas where they
are connected to hair follicles to deposit sebum on the hairs, and bring
it to the skin surface along the hair shaft. The structure consisting of
hair, hair follicle and sebaceous gland is also known as **pilosebaceous
unit**. Sebaceous glands are also found in non haired areas of lips,
eyelids, penis, labia minora and nipples; here the sebum reaches the
surface through ducts. In the glands, sebum is produced within
specialized cells and is released as these cells burst; sebaceous glands
are thus classified as holocrine glands.

Sebum is odorless, but its bacterial breakdown can produce odors. Sebum
is the cause of some people experiencing \"oily\" hair if it is not
washed for several days. Earwax is partly sebum, as is mucopurulent
discharge, the dry substance accumulating in the corners of the eye
after sleeping.

!A hair follicle with associated
structures.{width="360"}
The composition of sebum varies from species to species; in humans, the
lipid content consists of about 25% wax monoesters, 41% triglycerides,
16% free fatty acids, and 12% squalene.

The activity of the sebaceous glands increases during puberty because of
heightened levels of androgens.

Sebaceous glands are involved in skin problems such as acne and
keratosis pilaris. A blocked sebaceous gland can result in a sebaceous
cyst. The prescription drug isotretinoin significantly reduces the
amount of sebum produced by the sebaceous glands, and is used to treat
acne. The extreme use (up to 10 times doctor prescribed amounts) of
anabolic steroids by bodybuilders to prevent weight loss tend to
stimulate the sebaceous glands which can cause acne.

The sebaceous glands of a human fetus *in utero* secrete a substance
called Vernix caseosa, a \"waxy\" or \"cheesy\" white substance coating
the skin of newborns.

The preputial glands of mice and rats are large modified sebaceous
glands that produce pheromones.

### Ceruminous glands

!Wet-type human earwax on a cotton
swab.{width="200"}

**Earwax**, also known by the medical term **cerumen**, is a yellowish,
waxy substance secreted in the ear canal of humans and many other
mammals. It plays a vital role in the human ear canal, assisting in
cleaning and lubrication, and also provides some protection from
bacteria, fungus, and insects. A comprehensive review of the physiology
and pathophysiology of cerumen can be found in Roeser and Ballachanda.
Excess or impacted cerumen can press against the eardrum and/or occlude
the external auditory canal and impair hearing.

#### Production, composition, and different types

Cerumen is produced in the outer third of the cartilaginous portion of
the human ear canal. It is a mixture of viscous secretions from
sebaceous glands and less-viscous ones from modified apocrine sweat
glands.

Two distinct genetically determined types of earwax are distinguished
\-- the wet-type which is dominant, and the dry type which is recessive.
Asians and Native Americans are more likely to have the dry type of
cerumen (grey and flaky), whereas Caucasians and Africans are more
likely to have the wet type (honey-brown to dark-brown and moist).
Cerumen type has been used by anthropologists to track human migratory
patterns, such as those of the Inuit.

The difference in cerumen type has been tracked to a single base change
(an single nucleotide polymorphism) in a gene known as \"ATP-binding
cassette C11 gene\". In addition to affecting cerumen type, this
mutation also reduces sweat production. The researchers conjecture that
the reduction in sweat was beneficial to the ancestors of East Asians
and Native Americans who are thought to have lived in cold climates.

#### Function

!Wet-type earwax fluoresces weakly under ultraviolet
light..jpg "Wet-type earwax fluoresces weakly under ultraviolet light."){width="200"}
**Cleaning.** Cleaning of the ear canal occurs as a result of the
\"conveyor belt\" process of epithelial migration, aided by jaw
movement. Cells formed in the center of the tympanic membrane migrate
outwards from the umbo (at a rate equivalent to that of fingernail
growth) to the walls of the ear canal, and accelerate towards the
entrance of the ear canal. The cerumen in the canal is also carried
outwards, taking with it any dirt, dust, and particulate matter that may
have gathered in the canal. Jaw movement assists this process by
dislodging debris attached to the walls of the ear canal, increasing the
likelihood of its extrusion.

**Lubrication.** Lubrication prevents desiccation and itching of the
skin within the ear canal (known as *asteatosis*). The lubricative
properties arise from the high lipid content of the sebum produced by
the sebaceous glands. In wet-type cerumen at least, these lipids include
cholesterol, squalene, and many long-chain fatty acids and alcohols.

**Antibacterial and antifungal roles.** While studies conducted up until
the 1960s found little evidence supporting an antibacterial role for
cerumen, more recent studies have found that cerumen provides some
bactericidal protection against some strains of bacteria. Cerumen has
been found to be effective in reducing the viability of a wide range of
bacteria (sometimes by up to 99%), including *Haemophilus influenzae*,
*Staphylococcus aureus*, and many variants of *Escherichia coli*. The
growth of two fungi commonly present in otomycosis was also
significantly inhibited by human cerumen. These antimicrobial properties
are due principally to the presence of saturated fatty acids, lysozyme
and, especially, to the relatively low pH of cerumen (typically around
6.1 in normal individuals).

### Mammary Glands

!Cross section of the breast of a human
female.{width="200"}
**Mammary glands** are the organs that, in the female mammal, produce
milk for the sustenance of the young. These exocrine glands are enlarged
and modified sweat glands and are the characteristic of mammals which
gave the class its name.

#### Structure

The basic components of the mammary gland are the *alveoli* (hollow
cavities, a few millimetres large) lined with milk-secreting epithelial
cells and surrounded by myoepithelial cells. These alveoli join up to
form groups known as *lobules*, and each lobule has a *lactiferous duct*
that drains into openings in the nipple. The myoepithelial cells can
contract, similar to muscle cells, and thereby push the milk from the
alveoli through the lactiferous ducts towards the nipple, where it
collects in widenings (*sinuses*) of the ducts. A suckling baby
essentially squeezes the milk out of these sinuses.

!Dissection of a lactating breast.\
1 - Fat\
2 - Lactiferous duct/lobule\
3 - Lobule\
4 - Connective tissue\
5 - Sinus of lactiferous duct\
6 - Lactiferous
duct{width="250"}
One distinguishes between a *simple mammary gland*, which consists of
all the milk-secreting tissue leading to a single lactiferous duct, and
a *complex mammary gland*, which consists of all the simple mammary
glands serving one nipple.

Humans normally have two complex mammary glands, one in each breast, and
each complex mammary gland consists of 10-20 simple glands. (The
presence of more than two nipples is known as polythelia and the
presence of more than two complex mammary glands as polymastia.)

Also, **\"click\"**
this;\[<http://health.howstuffworks.com/adam-200040.htm>\|\"Breast
tissue\"\], to this a movie visual of the breast.

#### Development and hormonal control

The development of mammary glands is controlled by hormones. The mammary
glands exist in both sexes, but they are rudimentary until puberty when
in response to ovarian hormones, they begin to develop in the female.
Click this \<http://health.howstuffworks.com/adam-200042.htm%5Dto> see
what breast tissue does in a female during menstruation. Estrogen
promotes formation, while testosterone inhibits it.

At the time of birth, the baby has lactiferous ducts but no alveoli.
Little branching occurs before puberty when ovarian estrogens stimulate
branching differentiation of the ducts into spherical masses of cells
that will become alveoli. True secretory alveoli only develop in
pregnancy, where rising levels of estrogen and progesterone cause
further branching and differentiation of the duct cells, together with
an increase in adipose tissue and a richer blood flow.

Colostrum is secreted in late pregnancy and for the first few days after
giving birth. True milk secretion (lactation) begins a few days later
due to a reduction in circulating progesterone and the presence of the
hormone prolactin. The suckling of the baby causes the release of the
hormone oxytocin which stimulates contraction of the myoepithelial
cells.

#### Breast cancer

As described above, the cells of mammary glands can easily be induced to
grow and multiply by hormones. If this growth runs out of control,
cancer results. Almost all instances of breast cancer originate in the
lobules or ducts of the mammary glands.

**Types of breast cancer**

-   [DCIS: Ductal Carcinoma in Situ
-   LCIS: Lobular Carcinoma in Situ
-   Invasive ductal carcinoma
-   Invasive lobular carcinoma
-   Inflammatory breast cancer
-   Paget\'s disease

center\|framed\|Early Signs of Breast
Cancer

## Homeostasis

As a whole, the integumentary system plays a big part in maintaining
homeostasis. The integumentary system is the outermost organ system of
the body and many of its functions are related to this location. The
skin protects the body against pathogens and chemicals, minimizes loss
or entry of water, and blocks the harmful effects of sunlight. Sensory
receptors in the skin provide information about the external
environment, helping the skin regulate body temperature in response to
environmental changes and helping the body react to pain and other
tactile stimuli. The large surface area of the skin makes it ideal for
temperature regulation. The rate of heat loss can be regulated by the
amount of blood flowing through the blood vessels in the dermis close to
the surface of the skin. When the body temperature rises, as for example
during exercise, sympathetic tone is reduced and this brings about
dilation of the blood vessels supplying the skin. The increase in skin
blood flow allows heat to be lost more rapidly so that body temperature
does not rise above the normal homeostatic range. The rate of heat loss
can also be boosted by the production of sweat, which takes up
additional heat as it evaporates. Conversely, if heat production is less
than required, the dermal vessels constrict, sweating stops, and heat is
conserved by the body.

## Glossary

Areolar:Areolar connective tissue is a pliable, mesh-like tissue with a fluid matrix and functions to cushion and protect body organs. It acts as a packaging tissue holding the internal organs together and in correct placement.

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Basal lamina :Basal lamina (often erroneously called basement membrane) is a layer on which epithelium sits. This layer is composed of an electron-dense layer (lamina densa) between two electron-lucid layers (lamina lucida), and is approximately 40-50 nm thick (with exceptions such as the 100-200 nm glomerular basement membrane).

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Dermis : The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane.

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Epidermis : The epidermis is the outermost layer of the skin. It forms the waterproof, protective wrap over the body\'s surface and is made up of stratified squamous epithelium with an underlying basal lamina.

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Fibroblasts :A fibroblast is a cell that makes the structural fibers and ground substance of connective tissue.

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Hair follicle :A hair follicle is part of the skin that grows hair by packing old cells together.

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Hypodermis : The hypodermis (also called the hypoderm), is the lowermost layer of the integumentary system in vertebrates. It is derived from the mesoderm, but unlike the dermis, it is not derived from the dermatome region of the mesoderm.

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Impetigo: This is a superficial skin infection most common among children age 2--6 years. People who play close contact sports such as rugby, American football and wrestling are also susceptible, regardless of age. The name derives from the Latin impetere (\"assail\"). It is also known as school sores.

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Melanocytes :These are cells located in the bottom layer of the skin\'s epidermis and in the middle layer of the eye, the uvea. Through a process called melanogenesis, these cells produce melanin, a pigment in the skin, eyes, and hair.

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Melanoma : A melanoma is a malignant tumor that originates in melanocytes. It is a highly malignant form of skin cancer, and, though rare, is responsible for the majority of skin cancer-related deaths.

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Onychosis :Deformity or disease of the nails

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Papillary : The papillary layer is outermost and extends into the epidermis to supply it with vessels. It is composed of loosely arranged fibres. Papillary ridges make up the lines of the hands.

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Recticular Layer : The reticular layer is more dense and is continuous with the hypodermis. It contains the bulk of the structures (such as sweat glands). The reticular layer is composed of irregularly arranged fibres and resists stretching.

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For more fun pictures of other skin diseases and skin problems \"click\" to this cool website: \[<http://tray.dermatology.uiowa.edu/Home.html>\|\"Dermatology Image Database\"\]. Note: From this link then click \"Clinical Skin Diseases Images\".

## Review Questions

Answers for these questions can be found here

1\. Name all of the parts of the integumentary system.

2\. Name the cells that produce melanin and describe its function.

3\. Name and describe the importance of the cutaneous senses.

4\. Explain how sweating helps maintain normal body temperature.

5\. Explain where on the body hair has important functions and describe
these functions.

6\. What is a melanoma?

A\) The outermost layer of skin

B\) A type of nail disease

C\) A malignant tumor that originates in melanocytes

D\) The lower most layer of skin

## References

:   Brannon, Heather (2006). \"Nail Anatomy\" About, Inc., A part of The
    New York Times Company.

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:   American Academy of Dermatology - Nail
    Health

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:   Cobb, Judith. Fingernails, Jewels or
    Tools? *Nature\'s
    Field* - Nail diagnosis

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:   Graaff, Van De (2002). *Human Anatomy, Sixth Edition*. New York:
    McGraw-Hill.

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:   Mader, Sylvia S. (2004). *Human Biology*. New York: McGraw-Hill.

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:   Sorrentino, Sheila A. (2004). *Mosby\'s textbook for Nursing
    Assistants, 6th Edition*. St. Louis, Missouri: Mosby.
