Pregnancy and Parturition Flashcards
What is pregnancy?
The condition when the female animal develops offspring in the uterus
What is gestation
The period from fertilization to parturition that occurs in four main phases
What are the four phases of gestation?
1.) Fertilization and early embryonic development
2.) Implantation of the embryo to the uterine wall
3.) Placentation/development of the placenta
4.) Fetal growth
Where does the first step of gestation (fertilization and early embryonic development) occur?
Lumen of the female reproductive tract
What does the second step of gestation (implantation of the embryo to the uterine wall) require?
Appropriate development/thickening of the endometrial layer
What does the third step of gestation (placentation, or development of the placenta) involve?
Development of fetal membranes
When do spermatozoa become motile?
After ejaculation
What is the fate of the first arriving spermatozoa?
They typically aren’t the ones to accomplish fertilization
What can result in oxytocin release in natural and artificial insemination?
Tactile stimulation of the female reproductive tract
What is oxytocin release a result of and what does oxytocin do?
It’s released as a result of a neural reflex and it promotes contraction of smooth muscle in the female tubular genitalia to help transport spermatozoa
Nontactile stimuli can release oxytocin from what location?
Posterior pituitary gland
What can release and effects of oxytocin be dampened by?
Stressors that increase sympathetic tone (sympathetic impulses = fight or flight)
What does presence of semen in the female reproductive tract result in?
An immunologic reaction and inflammation
Why is an immunologic reaction present when sperm is in the reproductive tract?
To clear the remaining debris as the sperm become nonviable
What is the timeframe for viability and survival times of spermatozoa under normal conditions?
They are only viable for a matter of hours and are correlated to the period of sexual receptivity of the female
When does insemination most often occur and why?
It most often occurs prior to ovulation so the viable sperm are present when the ova arrive for fertilization
What does the zona pellucida surround?
Vitelline membrane (cell membrane/plasma membrane of the ovum)
What is the number of granulosa cells surrounding the zona pellucida called?
Cumulus oophorous
How many haploid spermatozoa does the male produce for every stem cell?
4
How many mature gametes does the female develop per cycle?
1
What is the genetic material that is discarded during ova maturation called?
Polar body
What is the zona pellucida?
A semipermeable membrane made of glycoproteins
What does the zona pellucida contain?
Receptor sites for attachment of sperm and Zona Protein 3 (ZP3)
What does the sperm do after binding to the zona pellucida?
The acrosome reaction occurs, which releases enzymes that break down the zona pellucida and allow the passage of sperm to the vitelline membrane
What does the sperm do after penetrating the zona pellucida?
The cell membrane of the sperm that will accomplish fertilization fuses with the vitelline membrane of the ovum
What does the fusing of the sperm and the vitelline membrane cause and what does it form?
The initiation of the second meiotic division of the ovum, which forms the second polar body
What is polyspermy?
Entry of more than one spermatozoon into the ovum
Fusion of the gametes stimulates what?
The ovum releases cytoplasmic granules, which depolarizes the plasma membrane of the egg
What is a fast block and what is an example?
A fast block stops more sperm from fertilizing as soon as the first sperm attachment
An example is the depolarizing of the plasma membrane
What is an example of a fast and a slow block?
An example of a fast block is depolarizing the vitelline membrane to prevent further attachment
An example of a slow block is when depolarization also stimulates an increase in Calcium, which causes vesicles to move toward the cell surface, which causes the release of cytoplasmic granules and ZP3 to become inactive
What is the typical result of polyspermic fertilization?
Early embryonic death
What are the three layers of the uterus
Perimetrium, myometrium, and endometrium
Where is the perimetrium found?
Outside the uterus, but covered by the visceral peritoneum
What is the myometrium and what is it made of?
It’s the middle muscular layer of the uterus and it’s made of smooth muscle wall that grows with the fetus
Why are ovary hormones important to the myometrium?
It is responsive to ovary hormones. It decreases tone and relaxes with progesterone and increases tone and contracts with estrogen
What does contraction of the myometrium allow?
Expulsion of the fetus
What is the endometrium?
The innermost mucosal layer of the uterus
What is unique about the endometrium?
It thickens and changes under the influence of hormones and provides the attachment site for placental membranes
What are the three stages of the spermatozoa in the fertilization process?
Epididymal, Ejaculated, and Capacitated
What does the sperm look like in the epididymal stage?
The plasma membrane contains surface proteins and carbohydrates
What does the sperm look like in the ejaculated stage?
The surface proteins and carbohydrates from the epididymal stage are coated in seminal plasma proteins that mask parts of the proteins and carbohydrates on the surface
What does the sperm look like in the capacitated stage?
The seminal plasma coatings and parts of the surface proteins and carbohydrates are released when in the female tract, exposing the parts of the surface proteins and carbohydrates that can bond to the zona pellucida
What stage of the spermatozoa is not understood very well?
The capacitated stage
What do sperm have to do before they are capable of fertilization?
Remain in the female reproductive tract for a period of time after ejaculation
What is capacitation?
The physiologic process that conveys the capacity to fertilize the ovum by changing or removing parts of the outer acrosome
What are the 6 steps of fertilization through the generalized acrosomal process?
1.) Sperm makes contact with the egg at the Zona Protein 3
2.) The acrosome reacts with the zone pellucida to break it down with hydrolytic enzymes
3.) The acrosome reacts with the perivitelline space through protein receptors
4.) Plasma membrane of sperm and egg fuse
5.) Sperm nucleus enters the gg
6.) Cortical granules in the egg fuse with the egg’s plasma membrane which makes the vitelline layer impenetrable to sperm
What is implantation?
Attachment of the blastula to the uterine epithelium and penetration of the epithelium by embryonic tissue
What happens before implantation?
The ovulated and then fertilized ovum migrates through the lumen of the uterine tubes
What does migration through the uterine tubes permit in litter-bearing animals and how is this achieved?
Spacing of embryos so each has enough space for development and the insurance that each uterine horn has some embryos
This is achieved through contact or paracrine communication between embryos
Implantation is not ________
Invasive
What is formed during implantation?
Cell-to-cell junctions between embryonic tissues and uterine epithelium
What is involved in implantation between the mother and the embryo?
Binding of membrane proteins in embryonic tissues to receptors on maternal epithelium
After fertilization, when does attachment occur in the sow, ewe, cow, and mare?
Sow- 11 days
Ewe- 16 days
Cow- 35 days
Mare- 55 days
What is placentation?
The development of the extraembryonic membranes, called the placenta
What is shed along with the placenta at parturition (birth) in some species?
A portion of the endometrium
What allows for the exchange of nutrients between the fetus and the mother?
Areas of attachment between the dam and the fetus
What is the relation between fetal and maternal blood vessels?
They are separated, but in close proximity
What are the three layers of the placenta?
Amnion, allantois, and chorion
What does the amnion consist of?
The amniotic sac surrounding the fetus
What does the allantois consist of?
The allantoic sac
What does the chorion consist of?
The outer layer of the placenta that attaches to the lining of the uterus
What is the chorion?
The outermost placental membrane that is in contact with the maternal uterine endometrium
What is the allantois?
The middle placental membrane that is a continuous layer that encloses a sac (similar to the pleural and cardiac potential spaces), which is called the allantoic cavity
What is the amnion?
The innermost membrane that is closest to the fetus. It is a fluid filled cavity that contains the fetus and is fused with the inner layer of the allantois
What are the first and second water bag?
Fetal membranes at the time of parturition. The allantoic sac is expelled first, so it’s the first bag, and the amniotic sac is expelled second, so it’s the second bag
After the embryo reaches the uterus, about how long does it take for attachment to occur?
Around 5-7 days
What type of placenta do cows have and how does it attach?
Cows have a cotyledonary placenta that attaches through button like structures called placentomes.
What is the fetal side of the cotyledonary placenta attachment called and what is the maternal side called?
The fetal side is called the cotyledon and the maternal side is called the caruncle
What type of placenta do horses and pigs have and how does it attach?
They have a diffuse placenta that attaches uniformly throughout the placenta and uterus
What type of placenta do dogs have and how does it attach?
They have a zonary placenta that attaches through a banded region
What type of placenta do primates have and how does it attach?
They have a discoidal placenta that attaches via a distinct disc shaped region
What are the three functions of progesterone during pregnancy?
1.) Providing negative feedback to the hypothalamus to inhibit further estrous cycles
2.) Inhibiting smooth muscles in the uterus to permit attachment and development of the fetus
3.) Assisting with the maintenance of the contractility of the cervix to protect the uterine environment
When is relaxin present?
The last stages of pregnancy
What does relaxin do?
Stimulates the mammary glands and relaxes the cervix and ligaments to help with birth
What type of hormone is relaxin?
A protein hormone
What species secrete relaxin from what locations?
The cow and the sow secrete it from the corpus luteum and the bitch and the mare secrete it from the placenta
What is the primary function of relaxin?
To prepare for parturition and ultimately lactation by relaxing the ligaments between bones around the birth canal
How does relaxin relate to the cervix and birth canal?
It contributes to the opening of the cervix and the relaxing of the muscles and ligaments in the birth canal to allow the fetus to pass through
When does peak secretion of relaxin occur in some species?
Just before parturition
What does a gradual increase of relaxin during late gestation do?
Facilitates mammary gland development to prepare for lactation
What is parturition?
The act of giving birth to young that marks the end of a successful pregnancy
What are the three steps of parturition?
1.) Uterine contractions
2.) Delivery of the newborn
3.) Delivery of the placenta
What happens during the uterine contractions stage of parturition
Myometrium of the uterus contracts as the cervix relaxes, which presses the fetus into the cervix and causes the cervix to dilate
What happens during the delivery of the newborn stage of parturition?
In the first stages there are strong uterine contractions and when very close to birth there are strong abdominal contractions
What happens to contractions as time proceeds?
The increase in frequency and strength, which causes the water bags to rupture
What happens during the delivery of the placenta stage of parturition?
The placenta separates from the wall of the uterus and is expelled by weaker uterine contractions
What happens if the placenta stays in?
It causes infection
Plasma levels of what type of hormone increase shortly before parturition?
Glucocorticoids
What types of glucocorticoids are secreted from what organs?
Cortisol is secreted from the fetal adrenal cortex and ACTH is secreted from the fetal anterior pituitary gland
What do glucocorticoids do?
Affect the placenta and the maternal uterus by causing changes to the uterine smooth muscle
They also increase estrogen production by the placenta so estrogen increases relative to progesterone
What do glucocorticoids and estrogen act together to do?
Promote uterins synthesis and secretion of PGF2a
What does PGF2a do?
In species where the corpus luteum remains, it causes leutolysis to remove this source of progesterone
Why does progesterone need to be removed for parturition?
It suppresses activity of uterine smooth muscle, which prevents the fetus from being expelled
Besides leutolysis, what else does PGF2a do?
Stimulates contraction of uterine smooth muscles to move the fetus to the birth canal, where it promotes dilation of the cervix
How do hormones in the blood contribute to a positive feedback regulation loop?
Rising blood concentrations of a hormone produce increased release of that hormone
What is a positive feedback loop not designed to do?
Maintain homeostasis
What are the steps of cervix dilation and oxytocin relations during parturition
1.) Oxytocin is secreted, which causes uterine contraction
2.) The baby is pushed toward the cervix
3.) Fetal movement and pressure increase cervix dilation
4.) Increased cervix dilation sends nerve impulses to the brain
5.) These nerve impulses stimulate the pituitary gland to release more oxytocin
What is uterine involution?
The shrinking and contraction of the uterus
When does uterine involution begin?
Immediately after parturition
What helps decrease blood loss after parturition?
Myometrium contraction
After parturition, what happens at the former placental attachment sites?
The endometrium dies, detaches, and sloughs into the lumen of the uterus
How long does complete uterine involution take?
Weeks to a month
When is peak lactation?
A month to 3 months after parturition
What is hypocalcemia associated with?
Decreased uterine involution and a retained placenta
