Lecture 25 3/19/24 Flashcards
What is the gonadal ridge?
undifferentiated primitive gonad during early embryonic development
What are the paramesonephric ducts?
part of a primitive kidney system during embryonic development
What is the yolk sac?
evolutionary remnant in mammals that still has functions in early embryonic development
What is the allantois?
part of the placenta involved in the formation of the umbilical cord and the exchange of nutrients/gas/metabolites
What are the characteristics of the primordial germ cells?
-migrate from the yolk sac to the gonadal ridge
-populate sex cords/cortical region of embryonic gonads
-become sperm or oocytes
What is the pronephros?
nonfunctional remnant of primitive kidney
What are the characteristics of the mesonephros?
-bilateral pair of intermediate kidneys
-replace the pronephros
-produce urine
-drained by the mesonephric ducts
What are the characteristics of the metanephros?
-final renal form
-develop functional nephrons
-functional form of kidney in the adult
What is the sexually indifferent stage?
when both the mesonephric and paramesonephric ducts are present, but the embryo is still undifferentiated in terms of sex
What is a true hermaphrodite?
individual with ovotestes or one ovary and one testis
What is a pseudohermaphrodite?
individual in which the gonads are consistent with the chromosomal sex, but the external genitalia is the opposite
Which substance controls the pathway towards being male or female?
testis determining factor/sex-determining region in the Y chromosome
How does testis determining factor (TDF) lead to a male individual?
-induces testicular development and differentiation of Sertoli cells
-Sertoli cells produce AMH (anti-Mullerian hormone)
-AMH induces Leydig cell differentiation and paramesonephric duct degeneration
-Leydig cells produce testosterone and DHT, leading to male duct system development
How does a lack of TDF lead to a female individual?
-absence of TDF allows gonads to develop into ovaries
-paramesonephric ducts give rise to female repro. tract
Which ducts are utilized in the male vs female?
male: mesonephric
female: paramesonephric
Which follicles form the cortex of the ovary?
primordial follicles
What are the characteristics of granulosa cells?
-surround gametes
-originate in sex cords
What are the characteristics of theca cells?
-form outer layer of follicles
-originate in gonadal ridge
How do the paramesonephric ducts give rise to the female repro tract?
-cranial part of duct develops into infundibulum
-uterus, cervix, and cranial vagina develop from fusion of the lower portion of the ducts
How do the mesonephric tubes play into the male repro tract?
-seminiferous tubules connect to rete testis and mesonephric tubes
-efferent ducts are derived from mesonephric tubes and give rise to epididymis and ductus deferens
What is the function of the gubernaculum?
-regression of the gubernaculum moves the testes into the scrotum
-remnant of the gubernaculum attaches testes to the bottom of the scrotum
When does testicular descent complete?
-before or around parturition in most species
-between days 3-45 of life for dogs
-movement between scrotum and inguinal canal until 2-4 months in cats
What is cryptorchidism?
failure of the testes to descend
What is inguinal herniation?
when a portion of intestine passes into the vaginal cavity and enters the scrotum
What are the characteristics of the pineal gland?
-involved in sleep patterns, circadian rhythms, and seasonal cycles
-produces melatonin
What are the characteristics of the hypothalamus?
-regulates metabolic processes of the ANS
-produces and secretes releasing hormones that act on pituitary gland
-main repro. hormone is GnRH
What are the repro. products of the pituitary gland?
-follicle stimulating hormone/FSH
-luteinizing hormone/LH
What is the function of the tonic center?
spontaneous, rhythmic basal secretion of GnRH
What are the characteristics of the surge center?
-responsible for preovulatory release of GnRH that stimulates LH and leads to ovulation
-releases basal levels of GnRH until appropriate stimulus is present
What is the stimulus for the surge center?
threshold level of estrogen in the absence of progesterone
Why do males only have a tonic center, and not a surge center?
testosterone from the fetal testis “defeminizes” the brain during development once it crosses the BBB and is converted into estrogen
Why does estrogen not defeminize the brain in females during development?
-estrogen produced by the ovaries binds to alpha fetoprotein (AFP)
-estrogen bound to AFP is too large to cross the BBB and act on the hypothalamus
What is the function of FSH?
responsible for growth and development of follicles during follicular phase
What is the function of LH?
responsible for ovulation
What is the positive feedback loop that acts on the female repro tract?
-FSH causes follicles to grow and mature
-granulosa cells in the follicle produce increasing concentrations of estradiol as they grow
-estradiol stimulates surge center to release GnRH, leading to LH secretion
What are the negative feedback loops that act on the female repro tract?
-presence of large quantities of estradiol inhibits further secretion of FSH
-presence of progesterone inhibits GnRH neurons
What are the processes associated with antral follicles?
-recruitment
-selection
-dominance
-atresia
What are the characteristics of recruitment?
-small follicles
-low estradiol
-high FSH and low LH
What are the characteristics of selection?
-medium follicles
-medium estradiol, inhibin
-decreased FSH, increasing LH
What are the characteristics of dominance?
-large follicle
-surge center
-high estradiol, inhibin
-high LH
Which negative feedback loop acts on the male repro tract?
testosterone inhibits both hypothalamus and pituitary gland
