Recognition and Maintenance of Pregnancy

Question 1

identify the timing of embryo transport into the uterus

Answer 1

humans, primates, rodents: develop to the blastocyst stage within the oviduct before entering the uterus

most domestic species: enter the uterus earlier, somewhere between the 16 cell to morula stage

Question 2

describe the 3 key functions of progesterone

Answer 2

1. in hypothalamus and pituitary:
   negative feedback
   a. decreases GnRH secretion from hypothalamus
   b. decreases GnRH receptors in the pituitary
   c. decreases LH and FSH secretion
   d. decreases estrus behavior
2. in uterus:
   a. decreases myometrial tone (contractions)
   b. increases uterine gland development and secretion
3. in mammary gland: increases alveolar development

Question 3

how does the uterus change to support early embryonic development? (hormonally and physically)

Answer 3

1. after ovulation, ovarian granulosa cells luteinize to luteal cells for formation of corpus luteum that secretes high levels of progesterone that promote decidual cell development in the uterus
2. mucosal layer undergoes essential changes and is referred to as the decidua, with increased cell thickness and vascularity and cells enlarge with glycogen and lipid accumulation that provide essential nutrition for developing embryo before implantation

Question 4

know the different developmental strategies of early embryos of domestic animals

Answer 4

the time during which an embryo will implant into uterine endometrium varies greatly between species, in some species the embryo can enter diapus and temporarily arrest at the blastocyst stage for some time until mom is done with lactation for another baby

Question 5

know the different developmental strategies of early embryos of bovine and sheep embryos

Answer 5

1. embryos reach uterus at 16-cell stage
2. blastocyst then undergoes dramatic elongation of trophoblastic tissues, allowing for a 300-fold increase in size
3. embryos then actively synthesis interferon-tau for maternal recognition of pregnancy by the blastocyst stage

Question 6

know the different developmental strategies of early embryos of pigs

Answer 6

1. embryos enter uterus between 8 to 16-cell stage
2. between days 8-11 the embryos migrate and become spaced throughout the uterine horns (FOR PIGS!! establishment of pregnancy requires at least 4 embryos)
3. these embryos can be at different stages of development, and those farther along have an advantage
4. pig embryos then secrete estrogen by day 11-12 for maternal recognition of pregnancy

Question 7

know the different developmental strategies of early embryos of equines

Answer 7

1. horse embryo enters uterus at morula stage and develops and unique glycoprotein capsule that surrounds it completely by days 7-12 and absorbs nutrients from uterus and provides physical integrity to the embryo
2. embryo develops within the capsule as it migrates within the uterine horns before fixation in one horn around day 17; this migration may be important for maternal recognition
3. embryo implants around day 35-36
4. embryo secretes estrogens, PGE2 and PGF2a, which could be potential maternal recognition factors but we are still unsure

Question 8

describe each species’ signal from conceptus to maintain the corpus luteum

Answer 8

ruminants: IFN-t
pigs: estrogen
horses: unknown

1. communication between mom and baby in uterus is essential to maintain preg
2. conceptus establishes physical and nutritional contact with maternal endometrium at implantation
3. conceptus signals its presence to maintain the CL and prevent luteolysis
4. CL= high levels of P4 in maternal circulation, which promotes decidualization of uterine endometrium and fetal survival

Question 9

how is luteolysis prevented? generally, in humans and primates, in ruminants, and in pigs

Answer 9

generally: a signal from the conceptus suppresses endometrial PGF2a

humans and primates: secrete hCG from trophoblast cells of conceptus, which maintaisn CL and stimulates steroid secretion by CL early in preg to maintain high P4

ruminants: secrete IFN-t, which suppresses oxytocin receptor expression in endometrium (cannot stimulate PGF2a and prevent luteolysis) and promotes implantation by stimulating uterine gland protein secretion

pigs: trophoblast secretes estrogen, which redirects PGF2a into uterine lumen for degradation

Question 10

how is luteolysis encouraged?

Answer 10

oxytocin promotes PGF2a secretion from uterus, which acts on ovary to promote CL regression in a cycling female

Question 11

describe the timing of embryo fixation and attachment (implantation) for the development of the placenta

Answer 11

bovine: IFN-t 15 days post fertilization prevents uterine synth of PGF2a

ovine: IFN-t day 12 days post fertilization

equine: embryonic factors unknown, but uterine migration around day 12-17 is essential

pigs: embryonic estrogen day 10-12 and day 14-30 post fertilization causes intrauterine sequestration of PGF2a