2. WHAT IS REPRODUCTIVE SYSTEM?
-It’s basically a system in our bodies that includes our sex organs and certain parts of our
brain.
-The reproductive system is the human organ system responsible for the production and fertilization
of gametes (sperm or eggs) and, in females, the carrying of a fetus. Both male and female
reproductive systems have organs called gonads that produce gametes.
3. There are two forms of reproduction:
1. SEXUAL REPRODUCTION
-is a biological process by which higher organisms such as mammals, produce offspring.
-the production of new living organisms by combining genetic information from two individuals of different types
(sexes). In most higher organisms one sex(Male) produces a small motile gamete which travels to fuse with a larger
stationary gamete produced by the other (Female).
-In the sexual reproduction, male and female organs are involed in the process og propagation. The union of sex cells,
ovum and sperm cell are involved to form a new individual.
2. ASEXUAL REPRODUCTION
- Is a mode of production which only one parent is required, unlike sexual reproduction which needs two parents.
Since there is only one parent, there is no fusion of gametes and no mixing of genetic information.
- -In asexual reproduction, the offspring produced are exact copies of their parents. It is generally observed in every
small sized organisms. Binary fission, Budding, Fragmentation are examples of asexual reproduction.
4. The female reproductive system is a group of organs that
work together to enable reproduction, pregnancy, and
childbirth. It also produces female sex hormones,
including estrogen and progesterone. The system
consists of organs and tissues inside the body and some
that are visible outside the body.
Estrogen stimulates the development of the duct system;
and progesterone stimulates the development of the
lobulo-alveolar system.
Female reproductive system consists of internal and
external organs. It creates hormones and is responsible
for fertility, menstruation and sexual activity.
6. The principal sex organs of the female is the ovaries. The ovaries have two main
functions: (1) the production of sex cell or ovum; and (2) the production of female
sex hormone – estrogen.
The female reproductive system includes the pair of ovaries and the accessory
reproductive tract.
7. The ovaries are almond-shaped bodies attached by the
broad ligament to the dorsal wall in the sublumbar
region of the body cavity.
The outer layer (cortex) of the ovary is made up of
germinal epithelium with a very large number of primary
follicles each of which contains blood vessels, nerves,
ganglion cells, stroma and embryonic vestiges.
8. The accessory reproductive tract includes the infundibulum, oviducts, uterus (horn
and body), cervix, vagina and vulva.
The infundibulum is a funnel-shaped structure which picks up the egg when
released by the ovary. The “picking-up” of the egg is believed to evolve the
active participation of the celia-like structures at the rim of the infundibular
funnel which attract the eggs into the infundibulum.
9. The oviduct is a tubular structure connecting the infundibulum to the
horn of the uterus.
It serves as the passage way of the egg on its way to the uterus. It is
the site of fertilization and the beginning of embryonic development
after fertilization.
10. The horn of the uterus is the organ which serves as the
site of implantation for the fertilized egg.
This is where the fetus would develop during the stage
of pregnancy in gestating animals. The body of the
uterus unites the two horns of the uterus and connects
them to the cervix.
Your uterus is divided into two parts: the cervix
and the corpus.
Your corpus is the larger part of your uterus that
expands during pregnancy.
11. The cervix is sometimes considered as the neck of the uterus. Its
opening, os uteri, closes when the animal gets pregnant to protect
the uterine contents. It serves as sperm receptacle in certain
animals.
12. The vagina is the primary organ of copulation. It serves as the
receptacle of the sperm cells in many species. It also comprises a
part of the birth canal of the animal at parturition.
It can widen to accommodate a baby during
delivery and then shrink back to hold
something narrow like a tampon.
A lot of people mistakenly use the term “vagina” to
describe all female reproductive parts. However, your
vagina is its own structure located inside your body.
13. The vulva is a common passage way for the products of
reproduction and for urine.
The vulva of mammals is comparable to the ventral
portion of the cloaca of birds. It is also homologous with
the scrotum of the male, since both are derived from the
same embryological structure.
Your vulva is the collective name for all your external
genitals.
14. The clitoris is a rudimentary organ located in the ventral
commissure of the vulva in mammals. It is homologous to
the glans penis of the male.
Your two labia minora meet at your clitoris, a
small, sensitive protrusion that’s comparable
to a penis in men or people assigned male at
birth.
Your clitoris is covered by a fold of skin called
the prepuce and is very sensitive to
stimulation
15. The broad ligament suspends the female genital system
from the dorsolateral wall of the pelvic canal.
Three specialized regions of the broad ligament are
recognized:
(1) mesometrium is that portion of the broad ligament
which suspends the anterior portion of the vagina, the
cervix and the uterus and comprises the major portion
of the broad ligament;
(2) mesosalpinx is a lateral fold on the anterior portion of
the broad ligament which suspends the oviduct (Salpinx);
and
(3) mesovarium is a specialized portion of the anterior
edge of the broad ligament which suspend the ovary
proper.
18. The male reproductive system is to produce androgens
such as testosterone that maintain male reproductive
function and to promote spermatogenesis and transport
into the female reproductive system for fertilization.
-It has two main functions: (1) to produce sperm, the male
gamete, and (2) to release the male sex hormone,
testosterone, into the body.
19. The main sex organ of the male is the testes.
In birds, the two testes are located within the body cavity
in the dorsolumbar region.
In farm animals, the testes are located outside the body
cavity within the scrotum.
The scrotum is the cutaneous sac that serves as the
external covering of the testes. It protects the testes from
direct mechanical injuries and provides an environment
which is a few degrees (6-9oF) cooler than the body
temperature which is required for normal
spermatogenesis.
The scrotum is a sac-like structure that hangs in the
human body in front of the pelvis, between the two legs.
The scrotum consists of testicles and has two oval-shaped
glands that are involved in the production and storage of
sperm cells.
20. The thermoregulatory muscles of the testes are the
cremaster muscle and the dartos muscle.
Thermo" or "thermic" meaning heat or energy. And so
we're actually producing energy here by contracting our
skeletal muscle. This happens in our core muscle groups
that cause more of the heat that's being produced from
this reaction to be stored there, to help us respond to
these cold environments
21. What are the dartos and cremaster muscles?
Underneath the skin of the scrotum is a layer of involuntary
smooth muscle, the tunica dartos. Just under the tunica dartos is
another layer of muscle, the cremaster, which extends also to the
spermatic cord. This muscle contracts when the inner thigh is
stroked; the “cremasteric reflex”
22. During fetal development, the initial development of the testes starts
inside the body cavity. As the fetus grows, the testes start to descent to
the scrotum through the inguinal canal.
In certain instances, when both testes failed to descent to the
scrotal sacs, the individual is said to be a bilateral
cryptorchid, hence is sterile.
If only one of the testes failed to descend to the scrotal sac, the individual is said to be a
unilateral cryptorchid, but capable of fertilization. However, cryptorchid animals should
be culled and not allowed to mate because this condition is heritable.
23. The testes have two main functions:
(1) production of sperm cells; and (2) production of sex
hormone – testosterone.
Testosterone is the male sex hormone responsible for the
development of the secondary sex characters.
24. Male characteristics such as muscular development at the rear
quarters and shoulders, aggressiveness and libido when
confronted with an in-heat female animal of the same species are
governed or influenced by the hormone testosterone.
25. The seat of spermatozoa production in a testis is the
seminiferous tubules
The seminiferous tubules join together to form the rete
testis and come out of the testis as vasa efferentia.
The vasa efferentia converged to form the head of
epididymis, then the body and tail of the epididymis.
26. The convoluted epididymis straightens up to form the vas
deferens which then enters the inguinal canal and enlarges
to form the ampulla.
The ampulla joins with the urethra of the penis.
The penis is the male organ of copulation and serves to
introduce the spermatozoa into the female reproductive
tract.
27. There are three accessory glands which contribute to the
bulk of the semen ejaculate; these are the:
(1) seminal vesicles
(2) prostate gland
(3) Cowper’s glands or bulbo-urethral gland
28. Semen consists of the sperm cells plus the secretions of the three
accessory glands.
In vasectomized animals, the vas deferens are severed,
thus, the ejaculate consists only of the secretions of the
accessory glands – making the vasectomized male sterile
but without losing libido.
On the other hand, in castrated animals both testes are
removed, thus, rendering the male sterile with loss of
libido.
29. The secretions of the accessory glands serve as the vehicle
for the transport of the spermatozoa from the vagina to
the oviduct.
It stimulates also spermatozoa activity and served as the
lubricating substance during copulation particularly the
secretions of the bulbo-urethral gland.
30. The seat of spermatogenesis is the seminiferous tubules.
FSH stimulates the germinal epithelium lining the seminiferous
tubules to initiate spermatogenesis up to the secondary
spermatocytes stage.
On the other hand, LH stimulates the interstitial cells or
the cells of Leydig to secrete testosterone; and
testosterone is required for the final maturation of the
spermatozoa.
Therefore, both FSH and LH are required for normal
spermatogenesis.
31. FSH has a direct influence on spermatogenesis, whereas, the influence of LH on
spermatozoa production is through its stimulating effect on testosterone secretion,
which is required for the final stages of spermatogenesis.
The level of testosterone in circulation also serves as the negative feedback in
controlling LH production by the sertoli cells in the seminiferous inhibin, produced by
the sertoli cells in the seminiferous tubules, has a negative feedback effect on FSH
secretion.
32. Testicular and epididymal sperm cells are non-motile. They become motile only
when they are suspended in a fluid and this occurs when they come in contact
with the secretion of the accessory glands.
The normal spermatozoa consist of a head, neck or mid-piece and a tail.
The head is covered by a protoplasmic cap (galea capitis) and the shape is
flattened ovoid in bull, ram, boar and rabbit and rounded in man. It varies with
species like rat, rooster and salamander.
33. The mid-piece and the tail are composed of several
strands or fibrils which are covered by a sheath. At the
tip of the tail, these fibrils flare out into a naked brush.
Drawing of the reproductive tract of the bull
(from Nebraska Guide G80-536).
34. The common abnormalities encountered in a semen sample are sperm cells with
protoplasmic droplets at the mid-piece; headless or tailless; giant and miniature
heads; bent, coiled and shoe-hooked tailed sperm cells.
When sperm abnormalities in a semen ejaculate are about 50% of the total
sperm cell counts, the male is usually sterile.
Abnormal sperms are often seen in males suffering from fever, males used too
frequently for breeding, or too young males. In the same manner, if the number of
dead sperms in a semen ejaculate, as determined by a dead-alive staining
technique, is 50% or more, the male has impaired fertility if not sterile.
35. The life-span of ejaculated spermatozoa in the female reproductive tract is about 24
hrs (20-30 hrs) in most mammals and about 14 days in chickens.
Of so many million sperms per ejaculate, only a few thousand reach the oviduct and
few dozens actually reach the vicinity of the ovum.
Several may penetrate the zona pellucida, but only one sperm cell enters the ovum
proper and accomplishes fertilization.
36. Puberty and Estrous Cycle
The female reproductive tract starts to function when a
female reaches the age of puberty.
Puberty indicates that the female has reached sexual
maturity – capable of producing offsprings.
The age of puberty varies between breeds of animal and
among female animals of the same breed. The first
manifestation to indicate that the female animal has
reached the age of puberty is when it starts to show signs
of estrus.
In human, a girl does not show signs of heat, instead she
shows or manifests signs of menstruation to indicate that
she has reached the age of puberty.
37. When the animal reaches puberty, the anterior pituitary gland starts to
secrete gonadotrophic hormones which could affect the ovaries.
The first gonadotropin secreted in significant amount is follicle stimulating
hormone (FSH) with little luteinizing hormone or LH. FSH causes the growth
and development of the Graafian follicle (GF) in the ovary.
In turn, this developing follicle secretes a hormone known as estrogen. This
is the hormone which causes estrus in female. The presence of estrogen
stimulates the production of LH.
At the peak of estrogen production LH production increases which coincides
with the production if inhibin hormone from the ovary, which inhibits FSH
production.
38. Usually, LH is also produced with little FSH because the cells in the anterior
pituitary which secrete the former are the same cells that secrete the former are
the same cells that secrete the latter. These cells are the basophils of the
anterior pituitary.
LH is the hormone that causes ovulation of maturing follicles. It also initiates
the formation of corpus luteum (CL) by converting the cells of the stratum
granulosum into lutein cells.
Eventually, upon the action of LH, what used to be the GF will be filled up with
lutein cells and becomes the corpus luteum or CL. So, the GF with the action of
LH becomes the CL.
39. The CL secretes a specific hormone known as progesterone.
It has a strong inhibitory effect on FSH production. As long as the CL is
secreting progesterone, estrus is inhibited.
Progesterone prepares the endometrium of the uterus for implantation
of the fertilized egg. It also maintains normal pregnancy until birth.
Thus, CL also maintains normal pregnancy until birth.
Thus, CL persists if there is pregnancy; however, if there is no pregnancy,
the CL will regress.
It is now known that the uterus secretes prostaglandin F2 alpha which
could destroy the CL. In a normal cycle or if there is no pregnancy,
prostaglandin F2 alpha is secreted by the uterus and causes the
luteolysis or regression of the CL.
40. Animals may be classified based on the occurrence of their
estrus cycle as:
(1) Monoestrus, if the animal comes in heat only once a
year, such as dogs
(2) Seasonally polyestrus, if it comes in heat at certain
seasons only, such as sheep
(3) Polyestrus, if it comes in heat all throughout the year,
like cattle, swine and carabao.
41. An estrous cycle may be divided into four portions:
(1) Proestrus which is characterized by follicular growth;
(2) Estrus which is under the influence of estrogen;
(3) Metestrus is characterized by the formation of CL;
and
(4) Diestrus which is under the influence of progesterone
secreted by the CL.
42. To summarize, in an estrous cycle, the sequence of events are as follows:
the anterior pituitary secretes FSH which causes the formation of GF in the ovary. In turn,
the GF secretes estrogen which stimulates LH production and at the same time causes
heat or estrus in the female animal.
This is the best time to breed the animal. Then, the surge of LH released by the anterior
pituitary causes the ovulation of maturing GF. At the same time, LH would initiate the
formation of CL and causes the production of progesterone by the CL.
Progesterone would prepare the uterus for implantation of the fertilized egg if fertilization
had taken place. Also, progesterone maintains pregnancy, but if the animal is not
pregnant, the uterus then would produce prostaglandin which causes the destruction of
the CL, resulting in the cessation of progesterone production. When this happens, FSH
production would again continue and a new cycle begins.
The period from one estrus to the next estrus is known as the estrous cycle. In many farm
animals like carabao, cattle, pigs, and horses estrus comes every 21 days if the female
animal is cycling regularly, although it could vary from 12 to 30 days.
43. Signs of Heat or Estrus
Estrus is perceived through physiological manifestations that the female may
show or exhibit. The manifestations of heat are as follows:
(1) reddening and swelling of the vulva
(2) mucus discharges from the vagina
(3) frequent urination
(4) the animal becomes restless and lacks appetite
(5) mounting other animals in the herd
(6) the female stands still when mounted by the male.
44. The mucus discharge is watery at first and towards the end of estrus becomes
sticky. By taking a drop of the cervical mucus discharge and placing it on a glass
slide to dry, a ferning pattern will be observed under the microscope if the animal
is in heat. The vaginal lining of in heat animal is pinkish and it is pale when not in
heat. However, the best sign of heat is when the animal stands still when
mounted by a male animal of the same species.
45. When to Breed or Inseminate
In cattle and carabaos, ovulation takes place about 15-18 hours from the end of
estrus.
The best time to inseminate a female animal is towards the end of its estrus. But
since duration of estrus is variable and no one can tell exactly when the animal
started its heat, it is then recommended that once the animal is observed to be in
heat, then inseminate it immediately.
If the animal is observed to be in heat in the morning, inseminate immediately and
if it is still in heat in the afternoon, inseminate again. Likewise, if it is observed to
exhibit heat in the afternoon, inseminate immediately and if it is still in heat the
following morning, give the second insemination. This is the thumb rule that
should be followed. The duration of estrus in carabao lasts from 5 to 36 hours or
an average of 18 hours (less than a day).
46. In swine, the duration of estrus is about 2-3 days. The best time to breed or
inseminate a sow is on the second and third day of estrus.
In mares (female horse that has already given birth), estrus duration
is about 6-7 days. Mating or insemination is recommended on the fourth and
fifth day of estrus.
47. Parturition and Lactation
Parturition is defined as the physiologic process by which the pregnant uterus
delivers the fetus and placenta from the maternal organism.
Most signs of approaching parturition relate to changes in the pelvic ligaments, enlargement
and edema of the vulva, and mammary activity.
The signs are useful as a guide but they are too variable for an accurate prediction of the
date of parturition. Obvious enlargement of the mammary gland occurs in all farm species.
The teats becomes swollen and secretions may escape through the teat meatus.
Waxing occurs in most mares between 6-24 hours before parturition and is replaced by drips
of milk 12-24 hours later. Thus, presence of milk in the mammary gland is a strong indication
of approaching parturition.
48. Parturition is triggered by the fetus and is completed by complex interaction of endocrine,
neural and mechanical factors, but their precise roles and interrelationships are not fully
understood. Sequence of events leading to uterine contractions is triggered by hormonal
changes and myometrial stretch. An increase in estrogen, decrease in progesterone and an
increase in oxytocin plus myometrial stretch due to fetus development can stimulate the
production of prostaglandin from the maternal myometrium.
Myometrial contraction of low amplitude and frequency occur during the major part of
gestation, and at the onset of parturition, these are replaced by the expulsive form
characteristic of delivery.
At the time of parturition, fetal cortisol production increases which stimulates the placenta
to convert progesterone to estrogen, thus, descreasing progesterone and increasing
estrogen levels both at the placenta and maternal circulation. Estrogen stimulates
prostaglandin synthesis from the placental membrane and myometrium. Elevation of
prostaglandin lowers the threshold to oxytocin, and oxytocin and/or prostaglandin lead to
myometrical contractility. Also, prostaglandin destroys the CL thus, cutting off
progesterone secretion from the CL. It also stimulates the ovary to produce relaxin which
softens the cervix and the pelvic bones
49. Parturition may be divided into three stages:
(1) the dilation of the cervix
(2) expulsion of the fetus
(3) expulsion of the placenta
During the first stage, uterine contractions are painful causing restlessness and
signs of abdominal discomfort. At the fetus progresses through the cervix, the
allantochorion ruptures, releasing the urine-like fluid that marks the end of the
first stage of labor.
50. The distention of the cervix and vagina by the conceptus initiates the neurohumoral
reflex, which produces the expulsive force of abdominal muscular contractions
(straining) and the release of oxytocin, which in turn accentuates myometrial
contractions. The combined forces of intra-abdominal and intra-uterine pressure mark
the beginning of the second stage of labor.
Straining consists of a few contractions followed by a few minutes of rest. The fetus
enclosed in the amnion is propelled through the birth canal and appears at the vulva.
As straining continues, the amnion ruptures. The greatest effort is associated with the
emergence of the head, forelegs and chest. All farm species assume lateral
recombency with limbs extended during delivery. The umbilical cord breaks as the
neonate or the dam moves.
51. Rhythmic uterine contractions originating at the apex of the uterine horn continue
after birth (third stage) and cause the inversion of the chorioallantois in ruminants.
The presence of the detached placenta within the birth canal then initiates further
straining and expulsion of the placenta. The expulsion of the placenta is rapid in
the mare but is slower is ruminants due to the cotyledonary type of placentation.
The placentas of adjacent piglets are usually fused and often expelled as one or
more masses interspersed with the birth of piglets. The largest mass of placenta,
however, is usually expelled 3 to 4 hours after the delivery of the last piglet.
52. The onset of milk secretion follows parturition. In preparing the mammary gland for
lactation, hormonal interactions were needed even long before fertilization. It starts with
the development of the duct and the lobulo alveolar systems of the mammary gland
when the animal reached the age of puberty. The cyclic production of estrogen and
progesterone during the estrous cycle promotes the development of the mammary
gland.
Estrogen stimulates the development of the duct system; and progesterone stimulates the
development of the lobulo-alveolar system. With the onset of pregnancy, the sustained
production of progesterone by the CL and the placenta to maintain pregnancy until birth,
also maximize the development of the secretory units (alveoli) of the mammary gland.
Towards the end of pregnancy, there is a major surge in secretion of prolactin immediately
before parturition. Prolactin initiates milk secretion in the mammary gland. Thus, when the
fetus is born, the mammary gland is also ready to produce milk needed for the survival of the
newborn animal.
