Biology of Sex Chromosomes and Hormones

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Questions and Answers

During which weeks does the medulla develop into a testis in a genetic male?

11-12 weeks

9-10 weeks

7-8 weeks (correct)

5-6 weeks

What is the primary function of Mullerian Inhibiting Substance (MIS)?

Induce the development of axillary and pubic hair

Regulate the secretion of adrenal androgens

Stimulate the development of breast tissue

Cause regression of Mullerian duct by apoptosis (correct)

What is the function of SRY protein in testicular differentiation?

To act as a transcription factor for many genes necessary for testicular differentiation (correct)

To stimulate the production of estrogen in the fetal period

To suppress the development of ovaries

To induce the regression of the medulla in the genetic female

What is the term for the first menstrual period in girls?

Menarche Signup and view all the answers

What is the chromosomal pattern of spermatogonium cells?

XY Signup and view all the answers

What is the primary effect of leptin on puberty?

Induces precocious puberty Signup and view all the answers

What is the effect of hormonal treatment of the mother on gonadal differentiation in human?

It has no effect on gonadal differentiation Signup and view all the answers

Why do young women who engage in strenuous athletics and lose weight stop menstruating?

Due to a decrease in leptin levels Signup and view all the answers

What is the chromosomal pattern of oogonia cells?

XX Signup and view all the answers

What happens when gonads are removed during adulthood?

A high increase in FSH secretion Signup and view all the answers

When does the cortex and medulla develop in the gonads?

Before 6 weeks of development Signup and view all the answers

What is the effect of testosterone secreted in the fetal period on gonadal differentiation?

It induces the formation of testes Signup and view all the answers

What is the term for the development of breast tissue in girls?

Thelarche Signup and view all the answers

What is the primary cause of hot flashes?

Ovaries losing their function Signup and view all the answers

What is the function of Leydig cells at puberty?

To secrete testosterone Signup and view all the answers

What is the pattern of the chromosomal sex in the female ovum?

X Signup and view all the answers

Why is recording basal body temperature in the morning before getting out of bed important?

To monitor changes in progesterone levels Signup and view all the answers

What triggers ovulation?

LH surge Signup and view all the answers

What percentage of estradiol is bound to plasma proteins?

98% Signup and view all the answers

What is the duration of the fertile period in relation to ovulation?

48 hours before ovulation Signup and view all the answers

What is the effect of estrogen on uterine blood flow?

It increases blood flow Signup and view all the answers

What is the function of estrogen in promoting fertilization?

It makes the cervix mucus thin and alkaline Signup and view all the answers

What is the result of estrogen's effect on vaginal epithelium?

It cornifies it, converting it to a stratified form Signup and view all the answers

What is the effect of estrogen on uterine smooth muscle?

It increases its sensitivity to oxytocin Signup and view all the answers

What is the primary cause of menopause?

Decline in the number of primordial follicles at the time of menopause Signup and view all the answers

What happens to estrogen production during menopause?

Estrogen is formed only in small amounts by androstenedione aromatization in peripheral tissues Signup and view all the answers

What is the average age of onset for menopause?

45 to 55 years of age Signup and view all the answers

What happens to the uterus and vagina during menopause?

They gradually become atrophic Signup and view all the answers

What is responsible for initiating hot flashes?

Estrogen-sensitive events in the hypothalamus Signup and view all the answers

What is the effect of menopause on the production of progesterone and 17β-estradiol?

They are no longer secreted in appreciable quantities Signup and view all the answers

What is the effect of estrogen and progesterone on FSH secretion?

They inhibit FSH secretion Signup and view all the answers

What is the relationship between LH secretion and hot flashes?

LH secretion is not responsible for hot flashing, but occurs in episodic bursts Signup and view all the answers

What is the primary source of estrogen in the body?

Ovary Signup and view all the answers

What is the effect of estrogen on LH secretion?

It inhibits LH secretion in some circumstances and increases it in others Signup and view all the answers

What is the role of estrogen in breast development?

It produces ductal growth and breast enlargement Signup and view all the answers

What is the effect of estrogen on implantation of the ovum?

It inhibits implantation Signup and view all the answers

What is the mechanism of action of estrogen receptors?

They act by gene transcription Signup and view all the answers

Which of the following tissues does not express ERα?

Ovaries Signup and view all the answers

What is the rate of estradiol secretion in men?

50 g/day Signup and view all the answers

What is the effect of estrogen on the body during puberty?

It produces female characteristics Signup and view all the answers

Study Notes

Sex Determination

Sex chromosomes are X and Y chromosomes
Y chromosome is necessary and sufficient for production of testes
Y chromosome contains the sex determining region that codes for SRY protein
SRY protein binds DNA and acts as a transcription factor for many genes necessary for testicular differentiation, including MIS
Spermatogonium cells (diploid cells) are of XY pattern
Male sperm can be either X or Y pattern
Oogonia cells (diploid cells) are of XX pattern
Female ovum is X pattern

Gonadal Differentiation

In genetic males, the medulla develops into a testis and the cortex regresses
In genetic females, the cortex develops into an ovary and the medulla regresses
Embryonic ovary does not secrete hormones
Hormonal treatment of the mother has no effect on gonadal differentiation in humans
Leydig and Sertoli cells appear and secrete testosterone and MIS in males

Testosterone

Testosterone causes regression of Müllerian duct by apoptosis
In boys, testosterone is secreted in bursts in the fetal period and again in the neonatal period

Puberty

Thelarche: development of breast
Pubarche: development of axillary and pubic hair
Menarche: first menstrual period
Adrenarche: increase in adrenal androgens (DHEA) at 8-10 in girls and 10-12 in boys

Leptin

Leptin is the satiety-producing hormone secreted by fat cells, linking body weight and puberty
Leptin treatment induces precocious puberty in immature female mice
Leptin restores fertility in obese ob/ob mice that cannot make leptin

Menopause

Definition: unresponsiveness of ovaries to gonadotropins with disappearance of sexual cycle with advancing age
Cause: decline in the number of primordial follicles at the time of menopause (loss of ovarian function)
During menopause, the ovaries no longer secrete progesterone and 17β-estradiol in appreciable quantities
Estrogen is formed only in small amounts by androstenedione aromatization in peripheral tissues
FSH secretion increases, and FSH plasma levels increase to high levels, and LH levels moderately high due to reduced negative feedback inhibition of estrogen and progesterone on the pituitary gland

Basal Body Temperature

Rise starts 1-2 days after ovulation
Temperature recording must be in the morning before getting out of bed
The rise is probably due to an increase in progesterone secretion (progesterone is a thermogenic hormone)

Recording Ovulation Time and Fertile Period

LH surge triggers ovulation
Ovulation occurs ~ 9 hours after the peak LH surge
The ovum lives ~ 72 hours after extrusion from the follicle
BUT the ovum is fertilizable for a much shorter time than 72 hours
Fertile period is 48 hours (2 days) before ovulation

Estrogens

Estrogen sources: ovary
Estradiol secretion rate in men: 50 μg/day
Estrogen functions:
- Ovarian follicle growth
- Increase uterine tube (oviduct) motility
- Cyclic change in endometrium (proliferation)
- Make the cervix mucus thin and alkaline to promote survival of sperm
- Cornified the vaginal epithelium (converted to hard tissue)
- Increase uterine blood flow (necessary for secretory phase)
- Promote more active excitation (contraction) of uterine smooth muscles (myometrium)
- Increase sensitivity of uterine smooth muscle to oxytocin
- Inhibit FSH secretion (-ve feedback)
- In some circumstances, inhibit LH secretion (-ve feedback) and in other cases, increase LH secretion (+ve feedback)
- Inhibit implantation of ovum when given in larger doses for 4-6 days (as morning-after contraceptives)
- Promote breast enlargement at puberty in girls
- Produce ductal growth in the breast
- Responsible for the pigmentation of areolas at puberty and during pregnancy
- Produce body changes characteristic of female
  - Enlarge breast (and uterus and vagina)
  - Narrow shoulders

Estrogen Receptors

Nuclear receptors
Act by gene transcription
There are two types: ERα and ERβ
ERα presents in uterus, kidney, liver, heart
ERβ presents in ovaries, prostate, lung, GIT, bone marrow, and CNS
Most effects of estrogen are genomic (production of mRNA)

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Description

This quiz covers the role of sex chromosomes, specifically the X and Y chromosomes, in determining sex and the production of hormones such as testosterone. It also explores the development of ovaries and testes.