# Anatomy and Physiology of Animals/Reproductive System

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## Objectives

After completing this section, you should know:

-   the role of mitosis and meiosis in the production of gametes (sperm
    and ova)
-   that gametes are haploid cells
-   that fertilization forms a diploid zygote
-   the major parts of the male reproductive system and their functions
-   the route sperm travel along the male reproductive tract to reach
    the penis
-   the structure of a sperm and the difference between sperm and semen
-   the difference between infertility and impotence
-   the main parts of the female reproductive system and their functions
-   the ovarian cycle and the roles of FSH, LH, oestrogen and
    progesterone
-   the oestrous cycle and the signs of heat in rodents, dogs, cats and
    cattle
-   the process of fertilization and where it occurs in the female tract
-   what a morula and a blastocyst are
-   what the placenta is and its functions

## Reproductive System

In biological terms sexual reproduction involves the union of
**gametes** - the sperm and the ovum - produced by two parents. Each
gamete is formed by **meiosis** (see Chapter 3). This means each
contains only half the chromosomes of the body cells (**haploid**).
Fertilization results in the joining of the male and female gametes to
form a **zygote** which contains the full number of chromosomes
(**diploid**). The zygote then starts to divide by **mitosis** (see
Chapter 3) to form a new animal with all its body cells containing
chromosomes that are identical to those of the original zygote (see
diagram 13.1).

Diagram 13.1 - Sexual reproduction

The offspring formed by sexual reproduction contain genes from both
parents and show considerable variation. For example, kittens in a
litter are all different although they (usually) have the same mother
and father. In the wild this variation is important because it means
that when the environment changes some individuals may be better adapted
to survive than others. These survivors pass their "superior" genes on
to their offspring. In this way the characteristics of a group of
animals can gradually change over time to keep pace with the changing
environment. This "survival of the fittest" or "**natural selection**"
is the mechanism behind the theory of **evolution**.

## Fertilization

In most fish and amphibia (frogs and toads) fertilization of the egg
cells takes place outside the body. The female lays the eggs and then
the male deposits his sperm on or at least near them.

In reptiles and birds, eggs are fertilized inside the body when the male
deposits the sperm inside the **egg duct** of the female. The egg is
then surrounded by a resistant shell, "laid" by the female and the
embryo completes its development inside the egg.

In mammals the sperm are placed in the body of the female and the eggs
are fertilized internally. They then develop to quite an advanced stage
inside the body of the female. When they are born they are fed on milk
excreted from the mammary glands and protected by their parents until
they become independent.

## Sexual Reproduction In Mammals

The reproductive organs of mammals produce the **gametes** (sperm and
egg cells), help them fertilize and then support the developing embryo.

## The Male Reproductive System

The male reproductive system consists of a pair of testes that produce
**sperm** (or**spermatozoa**), ducts that transport the sperm to the
penis and glands that add secretions to the sperm to make **semen** (see
diagram 13.2).

The various parts of the male reproductive system with a summary of
their functions are shown in diagram 13.3.

![](Male_repro_system_labelled.jpg "Male_repro_system_labelled.jpg")

Diagram 13.2. The reproductive organs of a male dog

![](Anatomy_and_physiology_of_animals_Diagram_summarizing_the_functions_of_the_male_reproductive_organs.jpg "Anatomy_and_physiology_of_animals_Diagram_summarizing_the_functions_of_the_male_reproductive_organs.jpg")

Diagram 13.3 - Diagram summarizing the functions of the male
reproductive organs

### The Testicles

Sperm need temperatures between 2 and 10 degrees Centigrade lower than
the body temperature to develop. This is the reason why the testes are
located in a bag of skin called the **scrotal sacs** (or **scrotum**)
that hangs below the body and where the evaporation of secretions from
special glands can further reduce the temperature. In many animals
(including humans) the testes descend into the scrotal sacs at birth but
in some animals they do not descend until sexual maturity and in others
they only descend temporarily during the breeding season. A mature
animal in which one or both testes have not descended is called a
**cryptorchid** and is usually infertile if both testicles have not
descended.

The problem of keeping sperm at a low enough temperature is even greater
in birds that have a higher body temperature than mammals. For this
reason bird's sperm are usually produced at night when the body
temperature is lower and the sperm themselves are more resistant to
heat.

The testes consist of a mass of coiled tubes (the **seminiferous**
or**sperm producing tubules**) in which the sperm are formed by meiosis
(see diagram 13.4). Cells lying between the seminiferous tubules produce
the male sex hormone **testosterone**.

When the sperm are mature they accumulate in the **collecting ducts**
and then pass to the **epididymis**before moving to the **sperm duct**
or **vas deferens**. The two sperm ducts join the **urethra** just below
the bladder, which passes through the **penis** and transports both
sperm and urine.

**Ejaculation** discharges the semen from the erect penis. It is brought
about by the contraction of the epididymis, vas deferens, prostate gland
and urethra.

![](Anatomy_and_physiology_of_animals_The_testis_&_a_magnified_seminferous_tubule.jpg "Anatomy_and_physiology_of_animals_The_testis_&_a_magnified_seminferous_tubule.jpg")

Diagram 13.4 - The testis and a magnified seminiferous tubule

### Semen

Semen consists of 10% sperm and 90% fluid and as sperm pass down the
ducts from testis to penis, (accessory) glands add various secretion\...

### Accessory Glands

Three different glands may be involved in producing the secretions in
which sperm are suspended, although the number and type of glands varies
from species to species.

**Seminal vesicles** are important in rats, bulls, boars and stallions
but are absent in cats and dogs. When present they produce secretions
that make up much of the volume of the semen, and transport and provide
nutrients for the sperm.

The **prostate gland** is important in dogs and humans. It produces an
alkaline secretion that neutralizes the acidity of the male urethra and
female vagina.

**Cowper's glands** (bulbourethral glands) have various functions in
different species. The secretions may lubricate, flush out urine or form
a gelatinous plug that traps the semen in the female reproductive system
after copulation and prevents other males of the same species
fertilizing an already mated female. Cowper's glands are absent in bears
and aquatic mammals.

### The Penis

The penis consists of connective tissue with numerous small blood spaces
in it. These fill with blood during sexual excitement causing erection.

#### Penis Form And Shape

Dogs, bears, seals, bats and rodents have a special bone in the penis
which helps maintain the erection (see diagram 13.2). In some animals
(e.g. the bull, ram and boar) the penis has an "S" shaped bend that
allows it to fold up when not in use. In many animals the shape of the
penis is adapted to match that of the vagina. For example, the boar has
a corkscrew shaped penis, there is a pronounced twist in bulls' and it
is forked in marsupials like the opossum. Some have spines, warts or
hooks on them to help keep them in the vagina and copulation may be
extended to help retain the semen in the female system. Mating can last
up to three hours in minks, and dogs may "knot" or "tie" during mating
and can not separate until the erection has subsided.

### Sperm

Sperm are made up of three parts: a **head** consisting mainly a
prominent haploid nucleus which carries the genetic material and also an
acrosome, a **midpiece** containing many mitochondria to provide the
energy and a **tail** that provides propulsion (see diagram 13.5).

![](Anatomy_and_physiology_of_animals_A_sperm.jpg "Anatomy_and_physiology_of_animals_A_sperm.jpg")

Diagram 13.5 - A sperm

A single ejaculation may contain 2-3 hundred million sperm but even in
normal semen as many as 10% of these sperm may be abnormal and
infertile. Some may be dead while others are inactive or deformed with
double, giant or small heads or tails that are coiled or absent
altogether.

When there are too many abnormal sperm or when the sperm concentration
is low, the semen may not be able to fertilize an egg and the animal is
infertile. Make sure you don\'t confuse infertility with impotence,
which is the inability to copulate successfully.

Sperm do not live forever. They have a definite life span that varies
from species to species. They survive for between 20 days (guinea pig)
to 60 days (bull) in the epididymis but once ejaculated into the female
tract they only live from 12 to 48 hours. When semen is used for
artificial insemination, storage under the right conditions can extend
the life span of some species.

### Artificial Insemination

In many species the male can be artificially stimulated to ejaculate and
the semen collected. It can then be diluted, stored and used to
**inseminate** females. For example bull semen can be diluted and stored
for up to 3 weeks at room temperature. If mixed with an antifreeze
solution and stored in "straws" in liquid nitrogen at minus 79^o^C it
will keep for much longer. Unfortunately the semen of chickens,
stallions and boars can only be stored for up to 2 days.

Dilution of the semen means that one male can be used to fertilise many
more females than would occur under natural conditions. There are also
advantages in the male and female not having to make physical contact.
It means that owners of females do not have to buy expensive males and
the possibility of transmitting sexually transmitted diseases is
reduced. Routine examination of the semen for sperm concentration,
quality and activity allows only the highest quality semen to be used so
a high success rate is ensured.

Since the lifespan of sperm in the female tract is so short and ova only
survive from 8 to 10 hours the timing of the artificial insemination is
critical. Successful conception depends upon detecting the time that the
animal is "on heat" and when ovulation occurs.

## The Female Reproductive Organs

The female reproductive system consists of a pair of **ovaries** that
produce egg cells or **ova** and **fallopian tubes** where fertilisation
occurs and which carry the fertilised ovum to the **uterus**. Growth of
the foetus takes place here. The **cervix** separates the uterus from
the **vagina** or birth canal, where the sperm are deposited (see
diagram 13.6).

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

Diagram 13.6. - The reproductive system of a female rabbit

Note that primates like humans have a uterus with a single compartment
but in most mammals the uterus is divided into two separate parts or
**horns** as shown in diagram 13.6.

### The Ovaries

Ovaries are small oval organs situated in the abdominal cavity just
ventral to the kidneys. Most animals have a pair of ovaries but in birds
only the left one is functional to reduce weight (see below).

The ovary consists of an inner region (**medulla**) and an outer region
(**cortex**) containing egg cells or ova. These are formed in large
numbers around the time of birth and start to develop after the animal
becomes sexually mature. A cluster of cells called the **follicle**
surrounds and nourishes each ovum.

### The Ovarian Cycle

The **ovarian cycle** refers to the series of changes in the ovary
during which the follicle matures, the ovum is shed and the **corpus
luteum** develops (see diagram 13.7).

Numerous undeveloped ovarian follicles are present at birth but they
start to mature after sexual maturity. In animals that normally have
only one baby at a time only one ovum will mature at once but in litter
animals several will. The mature follicle consists of outer cells that
provide nourishment. Inside this is a fluid-filled space that contains
the ovum.

A mature follicle can be quite large, ranging from a few millimetres in
small mammals to the size of a golf ball in large animals. It bulges out
from the surface of the ovary before eventually rupturing to release the
ovum into the abdominal cavity. Once the ovum has been shed, a blood
clot forms in the empty follicle. This develops into a tissue called the
**corpus luteum** that produces the hormone **progesterone** (see
diagram 13.9). If the animal becomes pregnant the corpus luteum
persists, but if there is no pregnancy it degenerates and a new ovarian
cycle usually.

![](Anatomy_and_physiology_of_animals_Ovarian_cycle_showing_from_top_left_clockwise.jpg "Anatomy_and_physiology_of_animals_Ovarian_cycle_showing_from_top_left_clockwise.jpg")

Diagram 13.7 - The ovarian cycle showing from the top left clockwise:
the maturation of the ovum over time, followed by ovulation and the
development of the corpus luteum in the empty follicle

### The Ovum

When the ovum is shed the nucleus is in the final stages of meiosis
(cell division). It is surrounded by few layers of follicle cells and a
tough membrane called the **zona pelluc**ida (see diagram 13.8).

![](Anatomy_and_physiology_of_animals_An_ovum.jpg "Anatomy_and_physiology_of_animals_An_ovum.jpg")

Diagram 13.8 - An ovum

### The Oestrous Cycle

The **oestrous cycle** is the sequence of hormonal changes that occurs
through the **ovarian cycle**. These changes influence the behaviour and
body changes of the female (see diagram 13.9).

![](Anatomy_and_physiology_of_animals_The_oestrous_cycle.jpg "Anatomy_and_physiology_of_animals_The_oestrous_cycle.jpg")

Diagram 13.9 - The oestrous cycle

The first hormone involved in the oestrous cycle is **follicle
stimulating hormone (F.S.H.),** secreted by the **anterior pituitary
gland** (see chapter 16). It stimulates the follicle to develop. As the
follicle matures the outer cells begin to secrete the hormone
**oestrogen** and this stimulates the mammary glands to develop. It also
prepares the lining of the uterus to receive a fertilised egg. Ovulation
is initiated by a surge of another hormone from the anterior pituitary,
**luteinising hormone (L.H.).** This hormone also influences the
development of the corpus luteum, which produces **progesterone**, a
hormone that prepares the lining of the uterus for the fertilised ovum
and readies the mammary glands for milk production. If no pregnancy
takes place the corpus luteum shrinks and the production of progesterone
decreases. This causes FSH to be produced again and a new oestrous cycle
begins.

For fertilisation of the ovum by the sperm to occur, the female must be
receptive to the male at around the time of ovulation. This is when the
hormones turn on the signs of "**heat**", and she is "**in season**" or
"**in oestrous**". These signs are turned off again at the end of the
oestrous cycle.

During the oestrous cycle the lining of the uterus (**endometrium**)
thickens ready for the fertilised ovum to be implanted. If no pregnancy
occurs this thickened tissue is absorbed and the next cycle starts. In
humans and other higher primates, however, the endometrium is shed as a
flow of blood and instead of an oestrous cycle there is a **menstrual
cycle**.

The length of the oestrous cycle varies from species to species. In rats
the cycle only lasts 4--5 days and they are sexually receptive for about
14 hours. Dogs have a cycle that lasts 60--70 days and heat lasts 7--9
days and horses have a 21-day cycle and heat lasts an average of 6 days.

**Ovulation** is spontaneous in most animals but in some, e.g. the cat,
and the rabbit, ovulation is stimulated by mating. This is called
**induced ovulation**.

### Signs Of Oestrus Or Heat

:\*When on heat a bitch has a blood stained discharge from the **vulva**
that changes a little later to a straw coloured one that attracts all
the dogs in the neighbourhood.

:\* Female cats "call" at night, roll and tread the carpet and are
generally restless but will "stand" firm when pressure is placed on the
pelvic region (this is the lordosis response).

:\* A female rat shows the lordosis response when on heat. It will
"mount" other females and be more active than normal.

:\* A cow mounts other cows (bulling), bellows, is restless and has a
discharge from the vulva.

### Breeding Seasons And Breeding Cycles

Only a few animals breed throughout the year. This includes the higher
primates (humans, gorillas and chimpanzees etc.), pigs, mice and
rabbits. These are known as **continuous breeders**.

Most other animals restrict reproduction to one or two seasons in the
year-**seasonal breeders** (see diagram 13.10). There are several
reasons for this. It means the young can be born at the time (usually
spring) when feed is most abundant and temperatures are favourable. It
is also sensible to restrict the breeding season because courtship,
mating, gestation and the rearing of young can exhaust the energy
resources of an animal as well as make them more vulnerable to
predators.

![](Anatomy_and_physiology_of_animals_Breeding_cycles.jpg "Anatomy_and_physiology_of_animals_Breeding_cycles.jpg")

Diagram 13.10 - Breeding cycles

The timing of the breeding cycle is often determined by day length. For
example the shortening day length in autumn will bring sheep and cows
into season so the foetus can gestate through the winter and be born in
spring. In cats the increasing day length after the winter solstice
(shortest day) stimulates breeding. The number of times an animal comes
into season during the year varies, as does the number of oestrous
cycles during each season. For example a dog usually has 2-3 seasons per
year, each usually consisting of just one oestrous cycle. In contrast
ewes usually restrict breeding to one season and can continue to cycle
as many as 20 times if they fail to become pregnant.

## Fertilisation and Implantation

### Fertilization

The opening of the fallopian tube lies close to the ovary and after
ovulation the ovum is swept into its funnel-like opening and is moved
along it by the action of cilia and wave-like contractions of the wall.

**Copulation** deposits several hundred million sperm in the vagina.
They swim through the cervix and uterus to the fallopian tubes moved
along by whip-like movements of their tails and contractions of the
uterus. During this journey the sperm undergo their final phase of
maturation so they are ready to fertilize the ovum by the time they
reach it in the upper fallopian tube.

High mortality means only a small proportion of those deposited actually
reach the ovum. The sperm attach to the outer **zona pellucida** and
enzymes secreted from a gland in the head of the sperm dissolve this
membrane so it can enter. Once one sperm has entered, changes in the
**zona pellucida** prevent further sperm from penetrating. The sperm
loses its tail and the two nuclei fuse to form a **zygote** with the
full set of paired chromosomes restored.

### Development Of The Morula And Blastocyst

As the fertilised egg travels down the fallopian tube it starts to
divide by mitosis. First two cells are formed and then four, eight,
sixteen, etc. until there is a solid ball of cells. This is called a
**morula**. As division continues a hollow ball of cells develops. This
is a **blastocyst** (see diagram 13.11).

### Implantation

Implantation involves the blastocyst attaching to, and in some species,
completely sinking into the wall of the uterus.

## Pregnancy

### The Placenta And Fetal Membranes

As the **embryo** increases in size, the **placenta**, **umbilical
cord** and **fetal membranes** (often known collectively as the
**placenta**) develop to provide it with nutrients and remove waste
products (see diagram 13.12). In later stages of development the embryo
becomes known as a **fetus**.

The placenta is the organ that attaches the fetus to the wall of the
uterus. In it the blood of the fetus and mother flow close to each other
but never mix (see diagram 13.13). The closeness of the maternal and
fetal blood systems allows diffusion between them. Oxygen and nutrients
diffuse from the mother's blood into that of the fetus and carbon
dioxide and excretory products diffuse in the other direction. Most
maternal hormones (except adrenaline), antibodies, almost all drugs
(including alcohol), lead and DDT also pass across the placenta.
However, it protects the fetus from infection with bacteria and most
viruses.

![](Anatomy_and_physiology_of_animals_Development_&_implantation_of_the_embryo.jpg "Anatomy_and_physiology_of_animals_Development_&_implantation_of_the_embryo.jpg")

Diagram 13.11 - Development and implantation of the embryo

![](Anatomy_and_physiology_of_animals_Fetus_and_placenta.jpg "Anatomy_and_physiology_of_animals_Fetus_and_placenta.jpg")

Diagram 13.12. The fetus and placenta

The fetus is attached to the placenta by the **umbilical cord**. It
contains arteries that carry blood to the placenta and a vein that
returns blood to the fetus. The developing fetus becomes surrounded by
membranes. These enclose the amniotic fluid that protects the fetus from
knocks and other trauma (see diagram 13.12).

![](Anatomy_and_physiology_of_animals_Maternal_and_fetal_blood_flow_in_the_placenta.jpg "Anatomy_and_physiology_of_animals_Maternal_and_fetal_blood_flow_in_the_placenta.jpg")

Diagram 13.13 - Maternal and fetal blood flow in the placenta

### Hormones During Pregnancy

The corpus luteum continues to secrete progesterone and oestrogen during
pregnancy. These maintain the lining of the uterus and prepare the
mammary glands for milk secretion. Later in the pregnancy the placenta
itself takes over the secretion of these hormones.

**Chorionic gonadotrophin** is another hormone secreted by the placenta
and placental membranes. It prevents uterine contractions before labour
and prepares the mammary glands for lactation. Towards the end of
pregnancy the placenta and ovaries secrete **relaxin**, a hormone that
eases the joint between the two parts of the pelvis and helps dilate the
cervix ready for birth.

### Pregnancy Testing

The easiest method of pregnancy detection is ultrasound which is
noninvasive and very reliable Later in gestation pregnancy can be
detected by taking x-rays.

In dogs and cats a blood test can be used to detect the hormone
**relaxin**.

In mares and cows palpation of the uterus via the rectum is the classic
way to determine pregnancy. It can also be done by detecting the
hormones **progesterone** or **equine chorionic gonagotrophin**
(**eCG**) in the urine. A new sensitive test measures the amount of the
hormone, **oestrone sulphate**, present in a sample of faeces. The
hormone is produced by the foal and placenta, and is only present when
there is a living foal.

In most animals, once pregnancy is advanced, there is a window of time
during which an experienced veterinarian can determine pregnancy by
feeling the abdomen.

### Gestation Period

The young of many animals (e.g. pigs, horses and elephants) are born at
an advanced state of development, able to stand and even run to escape
predators soon after they are born. These animals have a relatively long
gestation period that varies with their size e.g. from 114 days in the
pig to 640 days in the elephant.

In contrast, cats, dogs, mice, rabbits and higher primates are
relatively immature when born and totally dependent on their parents for
survival. Their gestation period is shorter and varies from 25 days in
the mouse to 31 days in rabbits and 258 days in the gorilla.

The babies of marsupials are born at an extremely immature stage and
migrate to the pouch where they attach to a teat to complete their
development. Kangaroo joeys, for example, are born 33 days after
conception and opossums after only 8 days.

## Birth

### Signs Of Imminent Birth

As the pregnancy continues, the mammary glands enlarge and may secrete a
milky substance a few days before birth occurs. The vulva may swell and
produce thick mucus and there is sometimes a visible change in the
position of the foetus. Just before birth the mother often becomes
restless, lying down and getting up frequently. Many animals seek a
secluded place where they may build a nest in which to give birth.

### Labour

Labour involves waves of uterine contractions that press the foetus
against the cervix causing it to dilate. The foetus is then pushed
through the cervix and along the vagina before being delivered. In the
final stage of labour the placenta or "afterbirth" is expelled.

### Adaptations Of The Fetus To Life Outside The Uterus

The fetus grows in the watery, protected environment of the uterus where
the mother supplies oxygen and nutrients, and waste products pass to her
blood circulation for excretion. Once the baby animal is born it must
start to breathe for itself, digest food and excrete its own waste. To
allow these functions to occur blood is re-routed to the lungs and the
glands associated with the gut start to secrete. Note that newborn
animals can not control their own body temperature. They need to be kept
warm by the mother, litter mates and insulating nest materials.

## Milk Production

Cows, manatees and primates have two mammary glands but animals like
pigs that give birth to large litters may have as many as 12 pairs.
Ducts from the gland lead to a nipple or teat and there may be a sinus
where the milk collects before being suckled (see diagram 13.14).

![](Anatomy_and_physiology_of_animals_reproduction_Mammary_gland.jpg "Anatomy_and_physiology_of_animals_reproduction_Mammary_gland.jpg")

Diagram 13.14 - A mammary gland

The hormones **oestrogen** and **progesterone** stimulate the mammary
glands to develop and **prolactin** promotes the secretion of the milk.
**Oxytocin** from the pituitary gland releases the milk when the baby
suckles. The first milk is called **colostrum**. It is a rich in
nutrients and contains protective antibodies from the mother. Milk
contains fat, protein and milk sugar as well as vitamins and most
minerals although it contains little iron. Its actual composition varies
widely from species to species. For example whale's and seal's milk has
twelve times more fat and four times more protein than cow's milk. Cow's
milk has far less protein in it than cat's or dog's milk. This is why
orphan kittens and puppies cannot be fed cow's milk.

## Reproduction In Birds

Male birds have testes and sperm ducts and male swans, ducks, geese and
ostriches have a penis. However, most birds make do with a small amount
of erectile tissue known as a **papilla**. To reduce weight for flight
most female birds only have one ovary - usually the left, which produces
extremely yolky eggs. The eggs are fertilised in the upper part of the
oviduct (equivalent to the fallopian tube and uterus of mammals) and as
they pass down it **albumin** (the white of the egg), the membrane
beneath the shell and the shell are laid down over the yolk. Finally the
egg is covered in a layer of mucus to help the bird lay it (see diagram
13.15).

Most birds lay their eggs in a nest and the hen sits on them until they
hatch. Ducklings and chicks are relatively well developed when they
hatch and able to forage for their own food. Most other nestlings need
their parents to keep them warm, clean and fed. Young birds grow rapidly
and have voracious appetites that may involve the parents making up to
1000 trips a day to supply their need for food.

![](Anatomy_and_physiology_of_animals_Female_reproductive_organs_of_a_bird.jpg "Anatomy_and_physiology_of_animals_Female_reproductive_organs_of_a_bird.jpg")

Diagram 13.15 - Female reproductive organs of a bird

## Summary

-   **Haploid** gametes (sperm and ova) are produced by meiosis in the
    **gonads** (testes and ovaries).
-   Fertilization involves the fusing of the gametes to form a diploid
    **zygote**.
-   The male reproductive system consists of a pair of **testes** that
    produce sperm (or **spermatozoa**), ducts that transport the sperm
    to the penis and glands that add secretions to the sperm to make
    semen.
-   Sperm are produced in the **seminiferous tubules**, are stored in
    the **epididymis** and travel via the **vas deferens** or **sperm
    duct** to the junction of the bladder and the **urethra** where
    various accessory glands add secretions. The fluid is now called
    **semen** and is ejaculated into the female system down the
    **urethra** that runs down the centre of the penis.
-   Sperm consist of a head, a midpiece and a tail.
-   **Infertility** is the inability of sperm to fertilize an egg while
    **impotence** is the inability to copulate successfully.
-   The female reproductive system consists of a pair of **ovaries**
    that produce **ova** and **fallopian tubes** where fertilization
    occurs and which carry the fertilized ovum to the **uterus**. Growth
    of the fetus takes place here. The **cervix** separates the uterus
    from the **vagina**, the birth canal and where the sperm are
    deposited.
-   The **ovarian cycle** refers to the series of changes in the ovary
    during which the follicle matures, the ovum is shed and the **corpus
    luteum** develops.
-   The **oestrous cycle** is the sequence of hormonal changes that
    occurs through the ovarian cycle. It is initiated by the secretion
    of **follicle stimulating hormone (F.S.H.),** by the **anterior
    pituitary gland** which stimulates the **follicle** to develop. The
    follicle secretes **oestrogen** which stimulates **mammary gland**
    development. **luteinising hormone (L.H.)** from the anterior
    pituitary initiates **ovulation** and stimulates the **corpus
    luteum** to develop. The corpus luteum produces **progesterone**
    that prepares the lining of the uterus for the fertilized ovum.
-   **Signs of oestrous** or heat differ. A bitch has a blood stained
    discharge, female cats and rats are restless and show the lordosis
    response, while cows mount other cows, bellow and have a discharge
    from the vulva.
-   After fertilization in the fallopian tube the **zygote** divides
    over and over by mitosis to become a ball of cells called a
    **morula**. Division continues to form a hollow ball of cells called
    the **blastocyst**. This is the stage that **implants** in the
    uterus.
-   The **placenta, umbilical cord** and **fetal membranes** (known as
    the **placenta**) protect and provide the developing fetus with
    nutrients and remove waste products.

## Worksheet

Reproductive System
Worksheet

## Test Yourself

1\. Add the following labels to the diagram of the male reproductive
organs below.

:   

    :   testis \| epididymis \| vas deferens \| urethra \| penis \|
        scrotal sac \| prostate gland

Diagram of the Male Reproductive System

2\. Match the following descriptions with the choices given in the list
below.

:   

    :   accessory glands \| vas deferens or sperm duct \| penis \|
        scrotum \| fallopian tube \| testes \| urethra \| vagina \|
        uterus \| ovary \| vulva

:   a\) Organ that delivers semen to the female vagina

:   b\) Where the sperm are produced

:   c\) Passage for sperm from the epididymis to the urethra

:   d\) Carries both sperm and urine down the penis

:   e\) Glands that produce secretions that make up most of the semen

:   f\) Bag of skin surrounding the testes

:   g\) Where the foetus develops

:   h\) This receives the penis during copulation

:   i\) Where fertilisation usually occurs

:   j\) Ova travel along this tube to reach the uterus

:   k\) Where the ova are produced

:   l\) The external opening of the vagina

3\. Which hormone is described in each statement below?

:   a\) This hormone stimulates the growth of the follicles in the ovary
:   b\) This hormone converts the empty follicle into the corpus luteum
    and stimulates it to produce progesterone
:   c\) This hormone is produced by the cells of the follicle
:   d\) This hormone is produced by the corpus luteum
:   e\) This hormone causes the mammary glands to develop
:   f\) This hormone prepares the lining of the uterus to receive a
    fertilised ovum

4\. State whether the following statements are true or false. If false
write in the correct answer.

:   a\) Fertilisation of the egg occurs in the uterus
:   b\) The fertilised egg cell contains half the normal number of
    chromosomes
:   c\) The morula is a hollow ball of cells
:   d\) The mixing of the blood of the mother and foetus allows
    nutrients and oxygen to transfer easily to the foetus
:   e\) The morula implants in the wall of the uterus
:   f\) The placenta is the organ that supplies the foetus with oxygen
    and nutrients
:   g\) Colostrum is the first milk
:   h\) Young animals often have to be given calcium supplements because
    milk contains very little calcium

/Test Yourself Answers/

## Websites

-   <http://www.anatomicaltravel.com/CB_site/Conception_to_birth3.htm>
    Anatomical travel. Images of fertilisation and the development of
    the (human) embryo through to birth.
-   <http://www.uchsc.edu/ltc/fert.swf> Fertilisation. A great animation
    of fertilisation, formation of the zygote and first mitotic
    division. A bit advanced but still worth watching.
-   <http://www.uclan.ac.uk/facs/health/nursing/sonic/scenarios/salfordanim/heart.swf>
    Sonic. An animation showing the foetal blood circulation through the
    placenta to the changes allowing circulation through the lungs after
    birth.
-   <http://en.wikipedia.org/wiki/Estrus> Wikipedia. As always, good
    interesting information although some terms and concepts are beyond
    the requirements of this level.

## Glossary

-   Link to
    Glossary

