Pregnancy and Placentation

Question 1

what is embryo implantation essential for? (2)

Answer 1

1. placental formation: to establish functional communication between fetal and maternal blood supply; develops from trophoblast and part of mom’s endometrium and is connected to the fetus by the umbilical cord
2. placenta function: as an essential transient endocrine organ, to support fetal development and maintain pregnancy

Question 2

know important early events in embryo development/implantation (5)

Answer 2

1. blastocyst hatching: breakdown of ZP by trypsin-like proteases from uterine and trophoblast cells, as well as altered pH for blastocysts to contact and adhere to uterine wall for implantation to begin
2. even spacing (ONLY WITH MULTIPLE OFFSPRING): promoted by uterine contractions and migration of embryos
3. attachment/adhesion of embryo to uterus
4. trophoblast differentiation into outer synctiotrophoblast (single giant cells with many nulei) and inner cytotrophoblast cells
5. trophoblast invasion into the endometrium, promoted by embryonic proteolytic enzymes

Question 3

what are clinical problems that can occur with blastocyst hatching? (2)

Answer 3

1. premature hatching: can lead to an ectopic pregnancy when embryo implants in the oviduct instead of uterus
2. failure to hatch: can lead to infertility

Question 4

describe formation of placenta and fetal membranes (4)

Answer 4

1. placenta develops from a network of villi that form on the outer surface of the chorion (an outer, extra-embyonic membrane)
2. villi project into the maternal uterine endometrium
3. as fetal circulatory system develops, fetal blood vessels then form the placental villi
4. these vessels then connect back through the umbilical cord, which attaches the fetus to the placenta

Question 5

describe the chorionic villi of the placenta

Answer 5

1. the functional unit of the placenta
2. projections from the chorion
3. functions as site for gas and nutrient exchange and waste removal from the fetus

Question 6

describe placental function (3)

Answer 6

1. provides nutrients to developing fetus via diffusion of nutrients from maternal to fetal blood
2. eliminates waste from fetus via diffusion
3. produces 4 hormones (transient endocrine organ):
   chorionic gonadotropin (primates and horses), progesterone, estrogen, and chorionic somatomammotropin

Question 7

what is the function of chorionic gonadotropin?

Answer 7

luteotropic effect on corpus luteum, important for maternal recognition of pregnancy in humans by stimulating growth and maintenance of the CL

Question 8

describe placental progesterone, including 3 functions and when levels drop

Answer 8

produced and secreted in high quantities from synctial trophoblast cells of the placenta

functions:
1. promote decidual cell development in uterine endometrium
2. decrease uterine contractility
3. promote mammary gland development in concert with estrogen

levels drop around time of parturition in every species!!

Question 9

describe placental estrogens, including 4 functions and how produced

Answer 9

produced by syncytial trophoblast cells of placenta; not formed de novo in placenta, need androgens produced by maternal and fetal adrenal glands as precursors!!

functions: proliferative!
1. enlargement of uterus
2. enlargement of mammary glands
3. relaxation of pelvic ligaments
4. affects fetal development

Question 10

describe the relative levels of estrogen during pregnancy for domestic species

Answer 10

cow, ewe, sow: estrogen INCREASE LATE in gestation; like right before parturtion in order to prepare for parturition (see google doc)

Question 11

describe placental somatotropin (2)

Answer 11

1. a protein hormone with a similar structure to GH
2. metabolic effects with nutritional implications for mother and fetus:
   2a. decrease insulin sensitivity and glucose utilization by mom to make glucose available to fetus
   2b. promote release of free fatty acids from fat stores in mom to provide an alternative energy source for maternal metabolic needs

Question 12

what are the 2 ways to classify placenta structure?

Answer 12

1. chorionic-villus pattern: describes placenta shape and distribution of contact sites between fetal membranes and endometrium
   includes:
   diffuse: pigs, horses
   cotyledonary: cow, sheep, giraffe
   zonary: dog and cat
   discoid: human, rodent
2. maternal-fetal barrier: the number of layers between maternal and fetal vascular systems based on degree of villi invasiveness into uterine endometrium
   includes:
   epitheliochorial
   endotheliochorial
   hemochorial

Question 13

describe a discoid placenta

Answer 13

a single disk shaped placenta seen in primates, rabbits, and rodents, the most invasive

Question 14

describe a zonary placenta

Answer 14

1. in dogs, cats, seals, bears, elephants (carnivores)
2. the placenta forms as a complete or incomplete band of tissue surrounding the fetus

Question 15

describe a cotyledonary placenta

Answer 15

1. in ruminants: cows and sheep
2. multiple discrete areas of attachment (placentomes) formed by interaction of patches of allantochorion (cotyledons) with endometrium (caruncles)
3. convex structure in cows, concave structure in ewes (peach rings)

Question 16

describe a diffuse placenta

Answer 16

1. in horse, pig, camelid
2. almost the entire surface of the allantochorion is involved in the formation of the placenta
3. there are numerous small contact sites called micro-cotyledons, so this is also called a microcotyledonary placenta

Question 17

describe equine endometrial cups (3)

Answer 17

1. transient structures in the mare placenta that develops from specialized trophectoderm cells (chorionic girdle) around day 25 of gestation
2. these cells attach to the endometrium and develop into endometrial cup cells around day 35 and produce equine chorionic gonadotropin (eCG)
3. cups regress around day 120-150 of gestation

Question 18

describe eCG

Answer 18

1. helps support the primary corpus luteum and promote development of accessory CLs by inducing ovulation of additional follicles
2. important for maintaining high levels of progesterone in pregnant mare until placenta can take over for P4 production

Question 19

what are the 6 layers that are possible to separate maternal and fetal blood

Answer 19

fetus: all 3 present in all placenta types!!
1. endothelial lining: allantoic capillaries
2. connective tissue: chorioallantoic mesoderm
3. chorionic epithelium: outermost layer of fetal membrane derived from trophoblast

maternal:
1. uterine endometrial epithelial cells
2. connective tissue of endometrium
3. endothelium lining endometrial blood vessels

number of retained maternal layers varies by species

MATERNAL AND FETAL BLOOD NEVER MIXES EVER EVER EVER

Question 20

describe epitheliochorial placenta

Answer 20

all 6 layers; cow, pig, horse, camelid

Question 21

describe endotheliochorial placenta

Answer 21

5 layers;
fetal chorion contacts endothelial cells of maternal/uterine blood vessels, no basement membrane on maternal side, more invasive breakdown by trophoblast cells

dog and cat

Question 22

describe hemochorial placenta

Answer 22

chorion in contact with maternal blood, lacks basement membrane and endothelial lining on mom side, in humans and rodents