Repro New Units for Exam 1

What does HPG axis stand for?

Hypothalamic–Pituitary–Gonadal axis.

Which hormone from the hypothalamus stimulates the anterior pituitary?

GnRH

Which cells in the hypothalamus act as the GnRH pulse generator?

KNDy (Kisspeptin/Neurokinin B/Dynorphin) cells

What kind of feedback do KNDy cells have? 

Positive and negative feedback

What cells in the hypothalamus are responsible for the LH surge in response to estradiol?

Kisspeptin only cells

What kind of feedback do kisspeptin only cells have?

Positive feedback

T/F: GnRH neurons have receptors for estradiol, progesterone, and testosterone

False — they only have receptors for kisspeptin

Which two gonadotropins does the anterior pituitary release?

LH and FSH

What type of hormone are LH and FSH?

Glycoproteins

What does the pulse frequency of GnRH determine?

Whether more LH (fast pulses) or FSH (slow pulses) is secreted

High frequency GnRH pulses cause:
a) High LH, low FSH
b) High FSH, low LH
c) No gonadotropin release

a) High LH, low FSH

(Females): In the two-cell, two-gonadotropin model, which cells respond to LH and FSH?

Theca cells → LH; Granulosa cells → FSH

(Females): What is required for estradiol production?

LH stimulates androgen production in theca cells → FSH stimulates aromatase in granulosa cells to convert androgens into estradiol → estradiol

(Males): Which cells have LH receptors and what do they produce?

Leydig cells → testosterone

(Males): Which cells have FSH receptors and what do they support?

Sertoli cells → spermatogenesis

T/F: Sex steroids normally exert positive feedback on LH/FSH

False — they normally exert negative feedback on the hypothalamus and pituitary, suppressing GnRH, LH, and FSH secretion

What triggers the LH surge in females?

High, sustained estradiol → positive feedback on kisspeptin neurons → GnRH surge → LH surge

Negative feedback keeps hormone levels at a ________, not at zero

Set point

A patient has a tumor in gonadotroph cells causing unregulated LH and FSH secretion. Predict LH, FSH, testosterone, and GnRH levels

LH/FSH = High, Testosterone = High, GnRH = Low (negative feedback)

Mutation in Kiss1 receptor leads to what condition?

Hypogonadotropic hypogonadism (low FSH/LH, absent puberty, infertility)

What is the hypothalamic–pituitary portal system?

A blood vessel network that transports hypothalamic hormones directly to the anterior pituitary

Where is the hypothalamus located?

Base of the brain, between optic nerve and brainstem, above anterior pituitary

T/F: Pulses of gonadotropin secretion cause ovulation

False, LH surge causes ovulation 

T/F: There are two populations of kisspeptin, only kisspeptin and KNDy 

True

A 31 year old man was diagnosed with a pituitary cell cancer, specifically causing unregulated gonadotroph cell growth and hormone secretion. Would you expect LH and FSH levels to be high, low or typical? 

High because unregulated gonadotroph cell growth = unregulated LH/FSH secretion and synthesis

A 31 year old man was diagnosed with a pituitary cell cancer, specifically causing unregulated gonadotroph cell growth and hormone secretion. Would you expect testosterone levels to be high, low or typical? 

High, because LH regulates leydig cells which produces testosterone and with excess LH there is excess leydig activity and therefore excess testosterone 

A 31 year old man was diagnosed with a pituitary cell cancer, specifically causing unregulated gonadotroph cell growth and hormone secretion. Would you expect GnRH levels to be high, low or typical?  

Low, high GnRH is the negative feedback for testosterone, testosterone suppresses KNDy cells leading to low GnRH 

• A typical person would have low LH/FSH response to high GnRH

T/F: Reproductive cyclicity in cows is the menstrual cycle 

False, In cows, it's the estrous cycle

T/F: The luteal phase of an estrous cycle is day 0 and is characterized by presence of CL as the dominant structure of the ovary

False

In estrous animals, day 0 is the beginning of behavioral estrous (the follicular phase), not an estrous cycle

The luteal cycle is indeed characterized by the presence of the CL

What hormone is rising during proestrus?

Estradiol (from developing follicles)

What changes happen in the uterus during proestrus?

Endometrium proliferates, increased blood supply, uterine glands enlarge

Is the female sexually receptive in proestrus?

No, receptivity begins in estrus

Which hormone dominates estrus?

High estradiol (E2)

What major event is triggered at estrus?

LH surge → ovulation

True/False): Estrus is the period of sexual receptivity in animals (“heat”)

True

What structure forms after ovulation in diestrus?

Corpus luteum (CL)

Which hormone dominates diestrus?

Progesterone (P4)

What is the function of progesterone in diestrus?

Prepares and maintains uterus for implantation

What happens to the CL if no pregnancy occurs?

Luteolysis (degeneration), progesterone falls

Match the stage with the hormone:

• Proestrus = ___

• Estrus = ___

• Diestrus = ___

Proestrus = Decreasing progesterone, increasing estradiol

Estrus = Peak estradiol and LH surge

Diestrus = Peak progesterone