Embryogenesis Flashcards
What is maternal recognition of pregnancy?
process by which an early conceptus signals its presence to the maternal system and prevents the lysis of the CL, thus ensuring a maternal milieu supportive of pregnancy continuation
What causes maternal recognition of pregnancy in cows/small ruminants, sows, mares/camelids, and dogs/cats?
COWS and SMALL RUMINANTS - interferon tau
SOWS - estradiol, possibly more
MARES and CAMELIDS - undetermined
DOGS and CATS - no proper mechanism, since length of diestrus will be the same whether they are pregnant or not
How does the fertilized embryo develop as it travels through the reproductive tract?
- INFUNDIBULUM - 4-celled
- AMPULLA - 16-celled
- ISTHMUS - morula
- UTERUS - blastocyst (which undergoes implantation)
What are the 3 layers that develop in the blastocyst inner cell mass? What do they become?
- ENDODERM - GIT, lungs, endocrine system
- MESODERM - muscle, skeleton, cardiovascular system, reproductive system
- ECTODERM - nervous system, skin, hair
What is responsible for gonad development in the embryo?
migration of primordial germ cells from the yolk sac toward the hindgut to settle at the gonadal/genital ridge
What stimulates male development? How is it different compared to female development?
Y CHROMOSOME has sex-determining region Y (SRY), which expresses TDF and SOX9 to stimulate male development (Sertoli cells secrete AMH)
X chromosomes lack an SRY gene = no AMH
How do the genes expressed during male and female development lead to the development of their gonads?
MALES = SRY, TDF, and SOX9 expression leads to the development of Sertoli cells that secrete AMH —> degeneration of paramesonephric duct —> leydig cells differentiate and secrete testosterone and ditestosterone (4)
FEMALES = lack of SRY, TDF, and SOX9 expression cause ovaries to develop lacking ADH —> paramesonephric ducts develop to eventually become oviducts, uterus, cervix, and part of the vagina (1)
How does the development of gonads differ in horse embryos?
gonads will initially be large early in the course of development and eventually shrink to normal sizes as they reach sexual maturity
What gender are all fetal brains? Describe how the development of gender differs in females and males.
female
FEMALES - fetal ovary produces estrogen that is bound to alpha-FP, making it unable to penetrate the BBB, which allows the GnRH surge center to develop
MALES - fetal testis produces testosterone that is not bound to alpha-FP, making it able to penetrate the BBB and be synthesized into estrogen by aromatase, which defeminizes the surge center (GnRH surge center does not develop)
What makes up the placenta?
endometrial tissues + fetal membranes
What are the 4 layers of extra-embryonic membranes?
- yolk sac - only layer that regresses into a remnant sac that can mineralize at the umbilicus
- amnion - surrounds fetus
- allantois - endodermal lined ventral outpocketing of the hindgut
- chorion - exchange of blood and gases between mother and fetus and develops into the fetal aspect of the placenta
What are the 4 types of placental based on gross shape?
- DIFFUSE - horse, pig, camelids
- COTYLEDONARY - bovine, small ruminants
- ZONARY - carnivores (dogs, cats)
- DISCOID - primates, rodents
What are the 4 major histological classifications of placenta?
- EPITHELIOCHORIAL - 6 layers makes Ig transfer impossible in horses and pigs
- SYNEPITHELIOCHORIAL - sheep, goats, cow
- ENDOTHELIOCHORIAL - dog, cat
- HEMOCHORIAL - primates, rodents
Histological classifications of placenta:
What are some examples of disorders of sex development in domestic species?
- freemartin calves
- polled gene intersex condition in goats
- formation of os clitoris in bitches
