Chapter 17, Clinical
Anatomy and Physiology for Veterinary Technicians
Chapter 12, An Illustrated Guide to Veterinary Medical Terminology (might be
The Female Reproductive Tract
The female tract consists of paired ovaries, ovaducts and uterine horns. The
uterine horns merge to form the body of the uterus which continues on as the cervix and
then the vagina. It ends at the external opening the vulva. The broad
the female reproductive tract from the body wall.
Graphics reprinted with
permission by the copyright owner, Hill's Pet Nutrition Inc.
a) ovary b) ovarian artery and vein c) suspensory ligament
d) uterine horn
e & f) colon and rectum g) urinary bladder h)
Parts of the female reproductive tract:
The ovaries produce the ova (eggs) and hormones. They are located caudal to the kidneys
and are suspended from the body wall by part of the broad ligament. The ovarian pedicle
contains the ovarian artery and vein. That part of the broad ligament that suspends the
ovaries is termed the suspensory ligament.
The oviduct is the small tube which extend from the ovary to the uterine
horns. The oviduct carries the ova into the uterine horn. At the end nearest the ovary a funnel like structure, the infundibulum catches the
ovum when it "drops" from the ovary.
The uterine horns:
The uterine horns are lined with a vascular and glandular mucosa and contain smooth muscle.
There is species variation in the relative size of the uterine horns, species having
"litters" often have larger and longer horns. The embryo is implanted here.
Species variation in uterine
A) cat B) cow C) horse D) human
(notice the less distinct horns in species normally giving birth to one or two
The body of the uterus:
The body of the uterus is formed by joining of the two uterine horns.
The cervix contains connective tissue and muscle which forms a firm tube
like sphincter. The cervix is usually "closed", because the muscular
sphincter contracts and closes the cervix. The cervix acts as a barrier to foreign substances except during
fertilization and birth when the sphincter is relaxed or opened.
The vagina extends caudally from the uterus and is located within the pelvic canal. This is the
area where sperm are deposited during breeding, in many species this is also the area
where the urinary tract opens via the urethra.
The vulva is the external opening of the female reproductive tract.
a) What structures are removed for the
Hormones involved in the female reproductive
Several hormones regulate estrus, the reproductive cycle in female animals.
The time of hormone secretion and their actions vary slightly among species.
the female cat is a "reflex or induced ovulator"
- she does not drop an egg
(ovulate) until after breeding, thus her hormonal timetable is somewhat different than
Follicle stimulating hormone:
Follicle stimulating hormone (FSH) initiates the growth of the follicle
(the ova and its support cells). It is secreted from the anterior pituitary gland.
Luteinizing hormone (LH) also stimulates the growth of the follicle, in
addition it stimulates the rupture of the ova from the ovary.
It assists in the
conversion of the area where the ova ruptured (on the ovary) into the
"temporary" endocrine gland the corpus luteum. This
process is termed luteinization. LH is also secreted by the anterior pituitary.
Estrogen is secreted by the ovary. It functions to prepare the uterus
for pregnancy and causes the female secondary sexual characteristics.
b) What are female secondary sexual characteristics?
Progesterone is secreted from the corpus luteum or "yellow body",
the area that the ova was ruptured from the ovary, early in pregnancy. Later in pregnancy
progesterone is secreted by the placenta. Progesterone is responsible for maintaining
Certain prostaglandins are essential in the reproductive
cycle at specific points. The lysis (destruction) of the corpus luteum, rupture of the
follicle, and uterine contractions at birth are all also stimulated by reproductive
prostaglandins, such as F2Alpha.
Control of the female reproductive cycle:
A complex sequence of secretions regulates the estrus cycle in the female.
The FSH and LH levels are controlled by a feedback loop involving estrogen and
progesterone. Basically, FSH and LH production is decreased when progesterone levels
This is logical because during pregnancy progesterone is high and there is no need
for estrus cycling or production of ova.
Although there is considerable difference between species regarding the levels
and times that the various hormones are secreted the following graph demonstrates the
basic relationship between the blood levels of the four hormones.
The small vertical line
on the horizontal axis represents ovulation.
a) estrogen b) FSH c) LH d)
The phases of the estrus cycle:
The estrus cycle is divided into four different phases, the length of the
various phases is different between species. The species variations are studied in Animal
Breeds and Behavior (VET 116).
This phase involves the development of the reproductive tract and follicle
and the secretion of estrogen, this "get ready" phase is regulated by FSH and
This phase also termed "heat" is the period of sexual receptivity. Ovulation
occurs here, when the egg is dropped from the ovary and fertilization also occurs.
At ovulation FSH drops and
LH surges or increases.
In this phase progesterone is secreted from the corpus luteum.
If fertilization and implantation occur then the normal reproductive cycle is suspended during pregnancy.
This is a period of hormonal inactivity between the next estrus cycle.
"Without" estrus, this is a prolonged period of hormonal inactivity.
Oocysts developing at
peripheral area of ovary
a) enlarged fluid filled follicle
b) ovum rupturing from follicle
c) corpus luteum "yellow body"
Oogenesis is the development of the ova or egg inside the ovary.
Only a small number of ovum
mature in the female lifetime, compared to sperm production in the male. It is estimated
that about 400 ova mature in the lifetime of a human female, compared to approximately 5
million sperm that are produced in one ejaculate of the human male.
Oogenesis occurs after puberty and involves cellular sexual reproduction,
During meiosis, (unlike mitosis), four
cells are formed.
In females only one viable cell (ova) results, that particular ova has
most of the cytoplasm during meiosis and it is able to nourish the developing embryo
until it is implanted in the uterus.
The number of unfertilized ova is probably decreased in species that are "reflex ovulators."
The rupture of the ovum in these species occurs after breeding due to a neuroendocrine
reflex that stimulates the release of L.H. from the anterior pituitary. This occurs in the
cat, ferret, and rabbit and reduces the number ova dropped.
There is a continual secretion of progesterone from the
corpus luteum to "maintain" pregnancy. (See the
unit on embryology for description of early pregnancy).
During later gestation the progesterone
is produced by the placenta. The attachment of the fetus to the
uterus varies among species.
In the dog and cat the fetal placenta is attached to
the uterus only around the middle (in a belt like fashion) of the fetus.
This is termed zonary
In the horse and hog the entire placenta is attached throughout its surface,
this is diffuse placentation.
In cattle and other ruminants the placenta and uterus are
fused together at "buttons" (the fetal cotyledeons and maternal caruncles.)
is termed cotyledonary placentation.
Near the end of pregnancy the fetus secretes A.C.T.H. (Adrenocorticotropic hormone)
which stimulates increased cortisol levels in both the fetus and the mother. The cortisol is
believed to then stimulate prostaglandin and estrogen secretion from the uterus.
This in turn
stimulates the secretion of oxytocin which causes uterine contractions and birth. Oxytocin
also causes milk letdown and passing of the afterbirth.
Mammary glands and milk production
Cross section of mammary gland
Mammary glands are modified sweat glands. There is species variation in the
numbers, location and anatomy of the glands.
Mammary glands are composed of connective tissue (to provide support
and structure ),
blood vessels, lymphatic vessels and glandular tissue. The mammary gland contains alveoli
(somewhat like the lungs) where milk is stored and secreted. The alveoli are connected by
a duct system and empty into the teat.
Milk is composed of:
Specialized enzyme systems in the mammary glands transform blood components to
milk (milk fat, sugars, and proteins). The actual mechanisms of this transformation not
The variation between species in different components of the milk can be seen
protein% lactose% ash%
c) What does this tell us about substituting different milk sources
What is mastitis?
with permission by the copyright owner, Hill's Pet Nutrition Inc.
a) urinary bladder b) testicular vessels c) ureter d)
colon e) rectum
f) prostate gland g) pelvic symphysis h) spermatic cord
i) ductus deferens
j) testicle k) penis l) bulbus glandis m)
The male reproductive system consists of:
The paired testicles, surrounded by a "skin sac" the scrotum.
The epididymis which extends from each testicle. It is a long tubule where the sperm mature
and are stored.
The ductus deferens (also called the vas deferens) is the tubular continuation of the
epididymus into the urethra. The urethra is the common passageway for both
urine and semen.
The accessory sex glands (these vary among species) including the prostate gland (present
in all domestic animals), the bulbourethral gland and the vesicular glands.
The penis, which carries the semen into the female reproductive tract, and the protective
skin surrounding the penis, the prepuce.
The testicles are composed of tightly coiled tubes, the seminiferous tubules.
There are about 900
per testicle, which are separated by connective tissue septa.
The tubules produce the spermatozoa or "sperm". Millions of
spermatozoa are produced daily in most healthy, young male mammals.
The spermatozoa develop
from "stem cells" which line the seminiferous tubules.
These cells first
divide by mitosis, then later some cells will undergo meiosis to become
spermatocytes, which finally divide to form the sperm.
After the sperm are formed in the tubules they are carried to the epididymis in fluid.
There are also "support cells" inside the tubules, the sertoli and leydig cells.
The testicle is surrounded by two layers of connective tissue, the tunics.
Cross section of
a) center of the tubule with formed spermatocytes
b) stem cells
During development of the male the testicles "descend" from inside
the abdomen, through an opening (the inguinal canal) into the scrotum. In livestock most
males are born with descended testicles; in dogs the testicles descend shortly after birth
When the testicles do not descend the animal is termed cryptorchid. If the
testicle remains inside the abdomen the animal is usually sterile, since the high
temperature inside the body inhibits the development of the sperm. Sometimes the testicles
will descend only partially and stop at the inguinal canal.
These animals are usually
Various shapes of sperm
#1) bull #2) dog #3) rat #4) avian
The scrotal temperature is about 2 degrees C cooler than the body temperature.
d) What significance does this have for male animals with undescended
head of epididymus
b) testicular vessels
c) spermatic cord (vas deferens and testicular vessels)
The epididymis is divided into three portions, the head, body and tail, which are easily
visible attached to the testicle. In the male human the coiled epididymus is about 18 feet
in length. It is the storage and maturation area for sperm (for about one month)
The spermatic cord:
The spermatic cord (which is severed and ligated during castration) contains the
testicular artery and vein, nerves, lymphatic vessels, the cremaster muscle, and the ductus deferens.
Accessory sex glands:
The accessory sex glands secrete fluid which contain sugars and vitamins to nourish the
spermatozoa. About 90% of the ejaculate is fluid from the accessory glands.
The penis is the tube-like structure which contains a common passageway for the urinary and
reproductive tract, the distal "free" part of the penis is called the glans. The
penis contains erectile tissue which fills with blood and becomes enlarged during
breeding. There is considerable variation among species in the shape, size and even
location of the penis.
From the hypothalamus, the gonadal releasing factor travel to the pituitary
gland which secretes FSH and LH.(Yes, males do secrete
follicle stimulating hormone)
The FSH stimulates the development of the sperm. The LH stimulates the production of
The Leydig cells of the testicles produce testosterone. It is secreted in small amounts in
fetus and neonate, then increases greatly at puberty.Testosterone (also called androgen) causes the typical male sexual characteristics
including: increase muscle mass (up to 50% more than female), increase calcium (in the
bone) and bone thickness, increase numbers of red blood cells and increase metabolic rate.
In the dog, the enlarged part of the penis the bulbus glandis, assists in the
"tying" process during breeding. This is the unique feature of canine copulation
when the male is trapped inside the female vagina.
Clinical Textbook for Veterinary Technicians by Bassert and
Please answer these questions and return answers by e-mail to Dr.
abidwell @nvcc.edu Assignment will be “spot checked” and logged in and answered e-mailed
back to student after receiving assignment. The student is responsible
for noting the correct. The questions might be included on exams
Reproduction – chapter 17
1. What makes the reproductive system very
different in its function compared to other body physiological systems?
2. What are the 2 ways that animals can have the
exact same genetic make up?
3. Why don’t the ova and sperm have diploid numbers
of chromosomes in their nuclei?
4. If the interstitial cells of a stallion were
nonfunctional what would he lack?
5. What is the function of the cremaster muscle?
6. Define orchiectomy.
7. What is the heat exchange mechanism of the
8. How many layers of tissue surround the
9. Which cells “nurse” the developing spermatozoa?
10. List 4 structures inside the spermatic cord.
11. Which common domestic species doesn’t have
12. Which species has the largest prostate gland?
13. From looking at diagram 17-14, which species
has a uterus that appears to support multiple embryos (liters)?
14. Define multiparous.
15. Explain induced ovulation and list 3 species
that are induced ovulators.
16. What does the statement “the cervix is open at
both ends of the cycle” mean?
17. Name a monoestrus female.
Answers to italized questions.
a) What structures are removed for the
ovariohisterectomy (spay)? The ovaries, oviducts and horns of the uterus
b) What are female secondary sexual
characteristics? Breast development, increased deposits of fat etc.
c) What does this tell us about
substituting different milk sources for newborns?
What is mastitis? It is not giving the young animal a balanced diet. Mastitis
is inflammation of the mammary glands, a common disease in dairy cattle.
d) What significance does this
have for male animals with undescended testicles? These animals are usually
sterile, since the higher temperature within the body
causes death of the sperm.