1.3 and on Flashcards
Most common problem in beef cows, estrous related
nutritional anestrus
phases of estrus cycles
follicular: proestrus & estrus
luteal: metestus, diestrus
Pro - maturation of follicles; E2
Estrus - sexual receptivity, peak E2
Met - CL formation, P4
Di - sustained CL; P4 secretion
cow and mare cervical/uterine tone during estrus
-cow has increased tone during estrus
-mare has decreased tone/ is flaccid during estrus
cause of seasonal anestrus
hypothalamic dormancy of GnRH secretion
short day breeders, feedback response resulting in anestrus
in the summer/ when there is a lot of light:
>increased firing of retinal neurons
>increased secretion from inhibitory neurons in SCG
>inhibition of pineal gland
>decreased melatonin release
>decreased GnRH release
>decreased LH, FSH release
»anestrus
=>melatonin causes GnRH release in these animals
short day breeders, feedback response resulting in cyclicity
during short photoperiods of fall/winter:
>decreased light
>decreased firing of retinal neurons
>less excitation of SCG inhibitory neurons
>pineal gland not inhibited
>increased melatonin release
>increased GnRH release
>increased FSH, LH release
>cyclicity
in long day breeders, what effect does melatonin have on GnRH?
less melatonin > more GnRH
more melatonin > less GnRH
=>melatonin inhibits GnRH release
which domestic animal does not have lactational anestus?
mare
how much can cyclicity be delayed after parturition in the suckled cow
60d
influence of suckling on estrus
if suckling occurs >2x per day, LH levels remain low, no return to estrus
reasons for pathological anestrus
pyometra, cystic ovaries, ovarian aplasia, etc.
pathological process underlying pyometra in dogs
- may occur in any sexually intact young to middle-age dog, but most common in older dogs
- secondary infection as a result of hormonal changes in the female’s reproductive tract. Following estrus (heat), the hormone progesterone remains elevated for up to two months and causes the lining of the uterus to thicken in preparation for pregnancy. If pregnancy does not occur for several consecutive estrus cycles, the uterine lining continues to increase in thickness until cysts form within the uterine tissues (cystic endometrial hyperplasia).
- The thickened, cystic lining secretes fluids that create an ideal environment for bacterial growth.
- Uterine muscle cannot contract properly either due to thickening of the uterine wall or the high levels of the hormone progesterone. Bacteria that enters the uterus and accumulated cannot be expelled.
The dominant hormone responsible for luteolysis is _____ produced by _____
The dominant hormone responsible for luteolysis is PGF2a produced by endometrium.
-oxytocin also can have a role
what must occur before follicualr phase can begin
luteolysis
what regulates the lifespan of CL?
uterus - esp. ipsilateral horn. contralateral horn not really important. > uterus controls CL lifespan through local mechanisms.
what is required to initiate timely PgF2a synthesis
- Exposure to P4 required to initiate timely PgF2a synthesis
what hormone stimulates pulsatile secretion of PgF2a?
-oxytocin
>oxytocin receptors somehow increased by progesterone from CL?????
death of luteal cells is via???
apoptosis, via cytokine etc.
>final cleanup by macrophages
will PGF2a exposure always lyse a CL?
no, eg
If a single injection of PGF2a is given between cycle day 0-6, luteolysis will not occur because CL must reach certain stage of development before it is sensitive to PGF2a.
when should we inject with PGF2a to induce return to estrus?
- If PGF2a is injected on day 6-17, luteolysis will occur. Progesterone will drop and the animal will return to estrus in about 3 days.
- Such a strategy is used for estrus synchronization in large groups of animals.
what mediates maternal recognition of pregnancy?
- A mechanism whereby the regression of CL is prevented early in gestation
- Protecting the CL from exposure to luteolysin PgF2a (domestic animals)
where does spermatogenesis occur?
seminiferous tubules
what is the purpose of the seminal fluid that is deposited with sperm in the upper vagina (in some species)?
*During copulation seminal fluid in deposited in the upper vagina
*Its composition and buffering capability protect spermatozoa from the
acidity of the upper vagina
*In 10 seconds, pH from 4.3 to 7.2
*Buffering effect last only few minutes, enough for sperm to approach the cervix in a pH (6 to 6.5) optimal for sperm motility
what is the interaction of the cervix with sperm?
- Cervix is a major barrier to spermatozoal transport and serves as a spermatozoal reservoir
- During estrus, copious mucus is produced under the influence of estrogen that regulates the transport of spermatozoa
- Composition and viscosity of cervical mucus vary through the menstrual cycle. During days 9-16 of the human menstrual cycle its water content increases, facilitating passage of sperm through the cervix at time of ovulation
function of the cervix as relates to sperm
a) it is receptive to sperm penetration and inhibits sperm migration during other phases of estrus cycle
b) It protects sperm from hostile environment in the vagina
c) it filters defective and immotile spermatozoa
rapid transport phase for sperm transport
- Immediately after insemination/ejaculation, spermatozoa penetrate the cervical mucus and some are quickly transported through the cervical canal and reach the uterine tubes within one hour of ejaculation
- Muscular movements of the female reproductive tract
- It is still unclear whether the first spermatozoa entering the oviduct participate in fertilization of ovum
slow transport phase for sperm transport
- Swimming of spermatozoa through cervical mucus (2-3 mm/hr)
- Storage of spermatozoa in the cervical crypts and release sequentially for a prolonged period (passage through the cervical canal as long as 3-4 days after ejaculation)
- This slow release ensures the continued availability of spermatozoa for entry to the oviduct to effect fertilization
- Various anatomical and physiological barriers help in preventing polyspermy
what is the overall process of fertilization? where does it occur?
Series of processes beginning with the spermatozoa penetrating the corona radiata and ending with the intermingling of maternal and paternal chromosomes after the spermatozoon entered the egg
>It usually occurs in the ampullary part of the uterine tube
how does a sperm penetrate the corona radiata?
*Approximately 12 spermatozoa surround the corona radiata
*Hyaluronidase emanating from the acrosome of the sperm head might play a role in penetration: rooster spermatozoa
*Sperm motility surely play major role in penetration of corona radiata
Role of zona pellucida:
*Allows ONLY sperm of the same species to enter the egg
*After fertilization prevent any other spermatozoon to enter the egg
*During first cleavage divisions, acts as a filter and allows substances from the uterine tubes to enter the egg
*Prevent premature implantation of embryo
what is the acrosomal reaction?
- Acrosomal reaction is an orderly fusion of the spermatozoal plasma membrane and the outer acrosomal membrane
- Release of acrosomal enzymes allows the spermatozoon to digest its way through the zona pellucida
- Acrosomal reaction releases hyaluronidase and acrosin
- In several species the trigger for the acrosome reaction has been identified in zona pellucida
why and how is polyspermy prevented?
Once sperm-egg fusion occurs, entry of other spermatozoa into the egg must be avoided to prevent abnormal development
Fast block
*Rapid depolarization of the egg plasma membrane.
*Occurs 2-3 seconds after fusion
Slow block
(Cortical reaction)
what is the cortical reaction that prevents polyspermy?
- Propagation of Ca++ wave from the site of sperm-egg fusion.
- Cortical granules fuse with plasma membrane and release hydrolitic enzymes and polysaccharides into the perivitelline space
- The cortical granules content hydrolize the sperm receptor molecules in the zona: ZONA BLOCK
Cleavage: Events. what is the blastomere?
- Initial division of zygote to form embryo
- Involves rapid mitotic divisions with no growth phases
- Blastomeres - resulting daughter cells
- Blastomeres are smaller with each division since there is no overall growth
- Blastomeres up to 8-cell stage are totipotent → important in twinning
Cleavage and blastocyst formation:
- A cavity appears within the morula converting it into a cystic structure called blastocyst.
- The cells become arranged into an :
1. Inner mass (embryoblast) which will form all the tissues of the embryo
2. Outer layer called trophoblast which invade the uterine wall.
what is blastocyst hatching and when does it occur?
- Occurs just prior to implantation
- Embryo breaks through ZP due to proteases secreted by blastocyst
- Inability to hatch is one cause of infertility
hormones produced by the placenta
- Progesterone
- Estrogen
- Relaxin (NOT in the cow)
- Placental Lactogen
effect of fetal cortisol on progesterone and progesterone block
Fetal cortisol activates
17a-hydroxylase,
17-20 desmolase,
and aromatase that convert progesterone to estradiol
-this removes the “progesterone block” that is inhibiting strong myometrial contractions
effect of fetal cortisol on CL
stimulates PGF2a which causes luteolysis
Fergusson Reflex
- Pressure is created on the cervix as fetus moves into the birth canal
- This stimulates the afferent sensory neurons and PVN (paraventricular nucleus)
- Oxytocin is secreted from posterior pituitary lobe
- Oxytocin stimulates myometrial contractions
Summary of Cortisol Actions (Fetus)
Promotes adaptations necessary for extra-uterine existence
Lung: increased Surfactant production by Type II pneumocytes
Blood: Conversion of fetal to adult hemoglobin
Liver: increased Glycogen deposition
Pancreas: increased Pancreatic islet cell response to glucose
Thyroid: increasedActivation of T3-generating enzymes
Summary of Cortisol Actions
(Placenta)
Terminates progesterone block and initiates estrogen production leading to the onset of lactation
Decrease:
1. The presence or activity of the placental factors
2. Progesterone synthesis and secretion
increase:
1. Placental estrogen synthesis and secretion
2. Prostaglandin synthesis and secretion from
placenta and endometrium
Events Occurring Just Prior to Parturition:
- Softening of pelvic ligaments
>estrogen and relaxin - Cervix softens and begins secreting mucus
- Swelling of the vulva
- Udder swells, fills with first milk
>prolactin, estrogens and glucocorticoids - Fetus moves into proper position
Stages of Parturition
- dilation of the cervix - ends with breaking water
- expulsion of fetus or active labor
-more oxytocin released, to peak levels
* Ends with delivery of the fetus or fetuses - expulsion of afterbirth
summary of parturition key points:
- Fetal corticoids initiate parturition
- Removal of progesterone block is a key event
- Parturition consist of 3 stages:
Stage I: Cervical dilation/myometrial contractions
Stage II: Expulsion of the fetus
Stage III: Expulsion of fetal membranes
Puerperium:
Period when uterus returns to its non-pregnant condition. It begins immediately after parturition and lasts until another pregnancy occurs.
Involution:
Process of reduction of the uterus to its non-pregnant size and state following birth of the offspring.
Lochia:
The normal uterine discharge of blood, tissue, and mucus from the vagina after birth.
Normal Vulval Discharge (Lochia)
- Fluid and cellular debris that is expelled by the cow’s reproductive tract, particularly the uterus.
- Appearance changes over time. The amount is greatest during the first 48 h after calving.
- At Day 4, discharge changes to dark yellow or brown. By day 10, it changes to red or reddish grey, due to the presence of blood and sloughed uterine tissue.
Abnormal Discharge postpartum:
- Defined as a discharge which continues well past 20 days post-partum, has an unpleasant odor and/or contains purulent material (infection).
- More common after difficult calving, maybe an indicator of potentially serious problems.
uterine involution process length
- Process depends upon the extent of uterine damage, the fitness of the uterus prior to parturition, and other factors (nutrition, disease, infection, age).
- Time ranges from 2 to 8 weeks, with an average of 5 to 6 weeks.
- Process involves the dying and sloughing of the endometrium. Aided by uterine contractions and extensive tissue reorganization and re-growth.
how long does it take the uterus to restore itself after parturition
Most restoration of the uterine lining occurs by 20 to 30 days after calving, though regression to normal size will not be complete until 50 to 60 days postpartum.
- Regenerative phase begins almost immediately in intercaruncular areas.
- Within 8 days, the lining cells have formed in the areas between the caruncles, but complete restoration of deeper layers, the mucosa and gland cells, may take up to 35 days.
- The caruncular surface sloughs by day 15 to 20 post-partum, and the caruncles are then covered with a new lining that also grows in from the periphery.
Post-partum bacterial infection
Conditions that predispose the uterus to infections are? best cure?
- Retained fetal membranes
- Dystocia
- Delay in lochial espulsion
Pharmaceutical treatment is controversial, best cure is return to cyclicity
how do the mammary glands grow?
Isometric Growth
(between birth and puberty)
Allometric Growth
(between puberty and pregnancy)
- Under influence of estrogens during the first estrous cycles after puberty the mammary ducts begin to branch and diameter increases
- Under influence of progesterone during the luteal phase of estrous cycle the branches begin forming the alveoli
- Alveoli form the functional secretory unites of the mammary gland
physiology of milk ejection
- suckling stimulates sensory neurons in mammary gland
- signal to hypothalamus
- PVN stimulates pituitary to release oxytocin
- oxytocin causes contraction of myoepithelial cells causes squeezing out milk
pressure atrophy of mammary glands
- As the need for milk as the sole nutritional source begins to decrease > less suckling
- Secretory cells become less functional because of a buildup pressure within the mammary gland
- Mammary involution > allows the gland to recovery and develop new secretory tissue for a subsequent lactation
how many cows show behavioural estrous during first post-partum ovulation?
50%
normal post partum timeline summary:
- The placenta is usually expelled within the first 6h after calving.
- Normal vulval discharge continues for up to 20 days after calving.
- Uterine involution is not complete until 5 to 6 weeks after parturition.
- Many cows have ovulated by three weeks after calving.
- In one-half of all cows, estrus is not expressed at the first post-partum ovulation.
