Embryogenesis

Question 1

What is maternal recognition of pregnancy?

Answer 1

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

Question 2

What causes maternal recognition of pregnancy in cows/small ruminants, sows, mares/camelids, and dogs/cats?

Answer 2

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

Question 3

How does the fertilized embryo develop as it travels through the reproductive tract?

Answer 3

• INFUNDIBULUM - 4-celled
• AMPULLA - 16-celled
• ISTHMUS - morula
• UTERUS - blastocyst (which undergoes implantation)

Question 4

What are the 3 layers that develop in the blastocyst inner cell mass? What do they become?

Answer 4

1. ENDODERM - GIT, lungs, endocrine system
2. MESODERM - muscle, skeleton, cardiovascular system, reproductive system
3. ECTODERM - nervous system, skin, hair

Question 5

What is responsible for gonad development in the embryo?

Answer 5

migration of primordial germ cells from the yolk sac toward the hindgut to settle at the gonadal/genital ridge

Question 6

What stimulates male development? How is it different compared to female development?

Answer 6

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

Question 7

How do the genes expressed during male and female development lead to the development of their gonads?

Answer 7

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)

Question 8

How does the development of gonads differ in horse embryos?

Answer 8

gonads will initially be large early in the course of development and eventually shrink to normal sizes as they reach sexual maturity

Question 9

What gender are all fetal brains? Describe how the development of gender differs in females and males.

Answer 9

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)

Question 10

What makes up the placenta?

Answer 10

endometrial tissues + fetal membranes

Question 11

What are the 4 layers of extra-embryonic membranes?

Answer 11

1. yolk sac - only layer that regresses into a remnant sac that can mineralize at the umbilicus
2. amnion - surrounds fetus
3. allantois - endodermal lined ventral outpocketing of the hindgut
4. chorion - exchange of blood and gases between mother and fetus and develops into the fetal aspect of the placenta

Question 12

What are the 4 types of placental based on gross shape?

Answer 12

1. DIFFUSE - horse, pig, camelids
2. COTYLEDONARY - bovine, small ruminants
3. ZONARY - carnivores (dogs, cats)
4. DISCOID - primates, rodents

Question 13

What are the 4 major histological classifications of placenta?

Answer 13

1. EPITHELIOCHORIAL - 6 layers makes Ig transfer impossible in horses and pigs
2. SYNEPITHELIOCHORIAL - sheep, goats, cow
3. ENDOTHELIOCHORIAL - dog, cat
4. HEMOCHORIAL - primates, rodents

Question 14

Histological classifications of placenta:

Answer 14

Question 15

What are some examples of disorders of sex development in domestic species?

Answer 15

• freemartin calves
• polled gene intersex condition in goats
• formation of os clitoris in bitches

Question 16

What description system is preferred for categorizing disorders of sex development?

Answer 16

chromosomes affected + presence of SRY + gonads

78, XY, SRY +, testicular DSD = Persistent Mullerian Duct Syndrome, common in Schnauzers, causing males to be able to develop pyometra

Question 17

What is the difference between chimeras, mosaics, and aneuploidy?

Answer 17

CHIMERA - organism or tissue that contains at least two different sets of DNA, most often originating from the fusion of different zygotes

MOSAIC - mitotic error in a single zygote, resulting in two or more genetically different sets of cells

ANEUPLOIDY - incorrect number of copies of chromosomes (monosomy, trisomy)

Question 18

What determines normal development of gonads?

Answer 18

SRY gene and SOX9 gene

• presence = male
• absence = female
• abnormal = ovotestes

Question 19

What determines the phenotypic appearance of genitalia?

Answer 19

testosterone and AMH

• presence = male genitalia
• absence = female genitalia
• abnormal = freemartin