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age at which an animal can support pregnancy without harm to herself.
horns of the uterus
layers of uterus
- mucous membrane lining interior is endometrium (glandular, everywhere except at caruncles in bovine)
- muscular portion is smooth muscle (myometrium)
mushroom-like projections from inner surface that provides attachment for the fetal membrane in bovine uterus.
has horns, no body, double cervix (duplex uterus)
Blood supply to female reproductive system
- overy and oviduct (ovarian artery)
- vagina (vaginal artery)
- uterus (uterine artery, crainal ovarian, caudal vaginal)
stages of ovarian follicles
- primordial follicles (immature, most primitive)
- growing follicles, secondary follicles
- graafian follicles (mature. visible antrum)
- primary follicle
- single oocyte surrounded by single layer of follicular cells (granulosa)
- When primary oocyte is surrounded with follicular cells, form basement membrane. Can stay suspended with no meiosis for years.
- secondary follicles
- begun growth from resting stage, no antrum yet.
- granulosa cells surround oocyte, add layers as older
- granulosa cells secrete glycoproteins
- zona pellucida (pores through which processes of granulosa cells can interact with oocyte surface). Sperm must get past this to fertilize.
- a theca (layer of cells immediatly surrounding the granulosa)
mature. Identified by antrum (empty space). Two layers of theca cells (theca interna and theca externa)
- process by which oocytes are formed.
- begins in fetal ovary with mitosis. Near birth oogonia begin meiosis and become primary (haploid) oocytes. All oocytes are formed by birth.
- development PAUSED during first meiotic prophase--stays this way into primordial follicle. Resumes meiosis near ovulation--only one cell formed. Rest are polar bodies.
- concurrently with oogenesis. When primary oocyte is surrounded with follicular cells, form basement membrane = primordial follicle. suspended in this state (no meiosis) for years.
- Then they wait, die (atresia) or resume.
- If resume, they die (atresia) or develope and ovulate.
- Multiple develop during each ovulation, one develops more, rest die (in single-litter). Several at a time for litters.
- Hormone independant until secondary-graafian phase.
- multiple primordial follicles begin further development during a single estrus cycle
- one follicle develops more rapidly than others
- rest regress and form atretic follicles
- only one ovum released at ovulation.
- (mare and cow)
- (carnivores and swine)
- multiple primordial follicles typically bein further development during a single estrus cycle
- several follicles develop and ovulate at approximately the same time
- ova may all come from one ovary or some may come from the other
Hormone dependance/independance of folliculogenesis
- primary-secondary follicles are hormone-independant.
- secondary-graafian follicles is hormone dependant and begins at puterty when LH and FSH begin to rise and fall with estrus cycle
Follicle-stimulating hormone function
promotion of the growth of follicles. Secreted by anterior pituitary after gonadotropin-releasing hormone is released from the hypothalamus (pulsatile)
Luteinizing hormone function
important for ovulatory process and the luteinization of the granulosa, which is essential in formation of a corpus luteum. Secreted by anterior pituitary after gonadotropin-releasing hormone is released from the hypothalamus (pulsatile)
granulosal cells in secondary follicles contain ____________ receptors
theca cells in secondary follicles contain __________ receptors
major identifier of graafian follicle
antrum full of cellular secretions of FSH and paracrine agents.
Hormone produced by granulosa cells
Estrogen's effect on developing follicles
- increases FSH receptors and add LH receptors to the granulosa layer. Promotes relication, growth and secretion.
- Granulosa cells are producing the estrogens, local positive feedback effect.
- Peak in estradiol causes LH surge which initiates ovulation
Circulating estrogen effect on folliculogenesis
negative feedback, estrogens stop FSH secretion so that non-dominant follicles that cannot make their own estrogen regress
- peptide hormone secreted by granulosa cells of developing follicle
- negative feedback effect on FSH release from pituitary. Helps to suppress all but most dominant follicle.
Consist of estradiol and estrone. Female sex hormones
- secreted by fetal membranes (placenta)
- predominant estrogen in pregnant animal
Secreted by granulosa cells of ovarian follicles. predominant estrogen of non-pregnant animals.
Effects of estradiol
- Increases granulosal cell proliferation
- stimulates endometrial gland growth, maturation and maintinence of uterus, uterine tubes, cervix and vagina, development of mammary gland tissue
- Regulates LH and FSH secretion
- increases libido
- stops long bone growth
Effects of progesterone
- stimulates secretory activity of oviduct
- stimulates glandular development of endometrium
- causes thickening of myometrium
- prevents development of further ovarian follicles
- in female dog, necessary for sexual receptivity
- promotes mammary gland development
- in pregnancy, necessary for INPLANTATION of fertilized ovum and nourishment of developing embryo, inhibits uterine contractions
action of the oocyte during ovulation
completion of first meiotic division to produce a secondary oocyte and first polar body (just before in most, just after in horses
- LH level increases seven to tenfold during the 24 hours before ovulation
- caused by estradiol peak secreted by granulosa cells in developing follicle. Depends on changes in the hypothalamus-pituitary axis
- Promotes final development of primary oocyte.
- Reduces number of FSH receptors on the granulosa cells so the rate of conversion of androgens to estrogen diminishes.
- transformation of granulosa cells to luteal cells (cells of the corpus luteum).
- LH attaches to granulosa cell LH receptors and begins the convrsion of the granulosa from estrogen-producing cells in the follicular phase to progesterone-producing cells in the luteal phase.
prostaglandin, thromboxanes and leukotriene effect in ovulation
After LH surge, granulosal cells synthesize these. They induce a local response similar to inflammation that weakens the follicle wall promotes the rupture to release the oocyte.
when is second meiotic division of the oocyte completed?
- LH surge and ovulation occur in most domestic species independant of copulation (mare, cow, ewe, sow, dog).
- LH surge is due to increase in estradiol produced by preovulatory follicle that acts on the hypothalamus and pituitary gland producing a positive feedback effect.
Induced ovulators, nonspontaneous ovulators
- no mating, no ovulation
- If no mating occurs, follicle undergoes atresia.
- LH surge is caused by stimulation of cervix
- animals that express estrus continuously throughout the year
- cattle and swine
express only one estrus annually (long anestrous cycle). (wild canids, wolves, coyotes)
express estrous cycles continuously but only during particular times of the year. (sheep, goats, horses, cats). Birth occurs when environmental conditions are more conducive to survival of the young. (PHOTOPERIOD)
- relative lengths of alternating periods of lightness and darkness.
- Most important factor associated with seasonal breeding.
Breeding season of horse and cat
estrous when days get longer/brighter
breeding season of goat and sheep
estrous as days get shorter/darker
- Sometimes after ovulation a corpus hemorrhagicum is formed. A blood vessels bursts into corpus luteum.
- Does not always occur.
granulosa cells under the influence of LH develop into a corpus luteum. "yellow bodies". Formed from remaining follicle cells in/on ovary after ovulation.
regressed corpus luteum. Regression caused by prostaglandin F2alpha released from uterus if animal is not pregnant. Diffuses from uterine vein to ovarian artery in some species. Other animals must go through systemic system.
Proestrus, estrus, metestrus, diestrous (anestrous)
- period of follicular development when, under stimulation of FSH and LH, ovary secretes increasing quantities of estradiol.
- Begins with onset of blood-tinged vulvar discharge
- ends with onset of sexual receptivity
- period of sexual receptivity in the female.
- Begins first day female accepts male, ends as soon as she is no longer receptive
- In most sponaneous ovulators, LH surge and therefore ovulation occurs during or shortly after estrus
- Early post-ovulatory period.
- Corpus luteum is formed and secretes progesterone.
- Roughly approximates the rest of the luteal period of the ovarian cycle.
- Corpus luteum continues to secrete progesterone.
- Animals with long periods between cycle or polyestrous animals that stop cycling (season, etc) enter a long period of inactivity.
- Begins when the corpus luteum regresses (stops secreting progesterone)
- Uterine tubes, uterus, and vagina shrink and remain small until the next breeding cycle.
the condition of a female animal while young are developing within her uterus.
from fertilization of the ovum to the birth of the offspring. It includes fertilization (union of sperm and ova), early embryonic development, implantation (nidation) (attachment of embryo in the uterine wall), placentation (development of fetal membranes), continued growth of fetus, parturition (act of giving birth).
tip of sperm head full of hydrolytic enzymes that eat away at the zona pellucida to facilitate fertilization.
- usually occurs in uterine tube next to ovary. Sperm move to site of fertilization by muscular activity of the tubular genitalia/uterus
- Fusion of pronuclei
physiologic changes to sperm which make it capable of fertilization.
a semipermeable membrane that helps protect the ovum and has receptor sites for attachment of spermatozoa during fertilization
- detection of the developing embryo, which prevents regression of the progesterone-secreting corpus luteum (no secretion of prostaglandin F2alpha).
- Sometimes embryo travels around the uterus for a while before implantation to ensure maternal recognition.
- attachment of a blastula to the uterine epithelium and penetration of the epithelium by embryonic tissue. Degree of penetration varies among species. Noninvasive in domestic animals, primarily result of a cell to cell junctions between embryonic tissue and uterine epithelium.
- endometrial glands secrete "uterine milk" to provide nutrients.
- development of extraembryonic membranes, or placenta
- Allows for exchange between maternal and fetal circulation for exchange of nutrients and wastes.
Fetal placental membranes
- Chorion (outermost membrane, in contact with endometrium)
- Allantois (first water bag) outer layer fused to chorion, inner layer fused to amnion. Filed with allantioc fluid
- amnion (second water bag) innermost membrane enveloping fetus, filled with amniotic fluid.
- protects the fetus from external shock
- prevents adhesions of fetal skin with amniotic membrane
- assists in dilating the cervix and lubricating the birth passage at parturition
- made of fetal urine, respiratory and oral secretions and from maternal circulation
originates from fetal urine and from secretory activity of the allantoic membrane. Between two allantoic membranes
Where are veins and arteries in the fetus?
Umbilical arteries and umbilical veins occupy the space between outer allantois and chorion
- canal connecting fetal urinary bladder with allantoic sac
- passes through umbilical cord
- normally closes at birth
- persistent urachus is a failure of urachus to close at birth
nutrition source during development. Connected to fetal intestine
Blood of the fetus and blood of the dam
don't mix, though they are close enough that oxygen and nutrients can cross
- 6 layers between fetus and mother.
- Cow, horse, pig
dog and cat. Only endothelial cells between mother and fetal membranes.
most deeply embedded fetus. Mother's blood runs directly against chorionic epithelial cells. human and rodents.
mare and sow. site for exchange between the placenta and the uterus are scattered over all of the entire endometrium
ruminants. scattered attachments, structures called placentomes made up of cotyledons and caruncles (mom)
connection in one place. Humans and rodents
carnivore. Takes the form of a band that encircles the fetus. Complete in dogs and cats, two halves in ferret and raccoon.
progesterone secretion during gestation
- in all domestic species, corpus luteum needed to secrete progesterone early in pregnancy. Corpus luteum needed for secretion. Different for different species.
- in mare and ewe secondary sources take over prostaglandin production.
Equine chorionic gonadotropin
- equine protein hormone that acts similarly to the luteinizing hormone. Secretion begins after a month of gestation and continues until four months of gestation.
- Follicular development occurs on ovary and ECG promotes luteinization. Secondary corpora lutea provide progesterone. Can diagnose early pregnancy
- Progesterone (progestins to support endometrium to help fetus survive and suppression of contractility in uterine smooth muscle)
- Estrogen (estrogens in maternal blood rises to max toward end of gestation. Stimulate growth of myometrium, stimulate mammary gland development)
- relaxin (prepares pelvic canal for passage of fetus, produced from day 20 of pregnancy in c/d, to about day 70 in horse. Secreted by corpus luteum in pig and cow
process by which pregnant uterus delivers fetus and placenta from mother.
signs of approaching parturition
- a few days prior- mammary glands begin secreting milky material
- vulva swells, discharges mucus
- pelvic ligaments relax
- in bitch body temperature drops 2 degrees C within 24 hours
- Animal becomes restless, lies down and gets up frequently, attempts to urinate often
- sow and bitch try to build nest
Stages of parturition
- 1) dilation of cervix (uterine contractions force water bags against proximal side of cervix, causing dilation)
- 2) delivery of fetus (presence of part of fetus in cervix along with rupture of one or both water bags reflexively initates contraction of abdominal muscle. Combination of contractions forces fetus through birth canal
- 3) delivery of placenta (in litter bearing, almost immediatly after fetus. In single-bearing, immediatly or within a few hours)
fetal hormones that trigger labor
- Uterine wall releases prostaglandin F2alpha
- cow, ewe, doe (goat) and sow, fetus secretes cortisol
- Stimulates placenta to increase estrogen, decrease progesterone, oxytocin receptors form on myometrium
central hormone in initiating parturition. Released in uterine wall, stimulates strong uterine contractions. In cow, goat, dog, and cat initiates regression of corpus luteum.
entry of fetus into birth canal triggers oxytocin secretion. Oxytocin is synergistic with prostaglandin F2alpha, stimulating uterine contractions
calf and foal are normally presented feet-first with feet extended and the nose between the front feet.
hind feet first, hocks up, occurs frequently enough in cattle to be considered normal.
uterine contractions force the fetal placenta (water bags) against the cervix of the uterus and they rupture. At the same time the abdominal muscles begin to contract forcefully to expel the fetus.
fetal presentation of pigs and dogs
young are carried in both horns of uterus and may be presented either cranially or caudally with equal facility
the process by which the uterus returns to its nonpregnant size after parturition
most important hormone involved in the process of milk synthesis or lactogenesis
Oxytocin release during suckling
- in order for lactogenesis to be maintained, milk must be removed from mammary gland by suckling or milking.
- If not removed within 16 hours in dairy cow the synthesis begins to be suppressed.
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