7/26: Human Sex Determination and Hormonal Pathways

What four factors are required for a "complete-female" development?

No SRY gene, no testosterone, no anti-Mullerian hormone, and no DHT

What four factors are required for a "complete-male" development?

SRY gene, testosterone, anti-Mullerian hormone, and DHT

The bipotential gonad can form either ____ or _____.

Testes or ovaries

Out of the four factors (SRY gene, testosterone, AMH or DHT), which one influences the development of the gonads?

SRY gene

What would influence the bipotential gonad to form into ovaries?

Absence of SRY gene

What would influence the bipotential gonad to form into testes?

Presence of SRY gene

What hormones do the testes produce?

Testosterone and anti-Mullerian hormone

What duct is mainly influenced by testosterone?

Wolffian duct

What will the Wolffian duct form?

Internal male genitalia (seminal vesicle, vas deferens, epididymis)

Which word is true in this sentence? The (presence/absence) of testosterone causes the Wolffian duct to develop.

Presence

Which word is true in this sentence? The (presence/absence) of testosterone causes the Mullerian duct to develop.

NEITHER. Testosterone does not affect the Mullerian duct at all.

What duct is mainly influenced by anti-Mullerian hormone?

Mullerian duct

What will the Mullerian duct form?

Internal female genitalia (such as Fallopian tubes, uterus, upper part of vagina)

Which word is true? The (presence/absence) of AMH causes the Mullerian duct to develop.

Absence

Which word is true in this sentence? The (presence/absence) of AMH causes the Mullerian duct to disappear.

Presence

How can I remember which duct contributes to male vs. female internal genitalia?

Mullerian ducts are found in mothers who have uteruses, cervixes, etc to undergo pregnancy (this is a general biological description, there are plenty of examples in which this description of a mother does not adhere to this)

What two things do you need in order for a pathway to be fully functional (e.g. testosterone actively converting the Wolffian duct into internal male structures)?

Active forms of the hormone and functional receptors

What are the two hormones that testosterone can be converted into and how?

Estradiol through aromatase, DHT through 5alpha-reductase

Out of the four factors (SRY gene, testosterone, AMH or DHT), which one influences the development of external genitalia?

DHT

Presence of DHT will result in:

Development of male external genitalia (such as penis, scrotum)

Absence of DHT will result in:

Development of female external genitalia (such as clitoris, labial structures, etc)

How can I approach questions about the phenotypes of an individual based on their hormones/genes?

1. List out the four factors in sex determination:

- SRY gene

- Testosterone

- AMH

- DHT

2. Look at the information provided to you in order to determine the presence of the SRY gene and levels of each hormone.

3. Conclude how these levels will result in a person's phenotype.

Remember that testosterone, AMH, and DHT are dependent of each other, so you can have functional testosterone but there may be a mutation in the pathways for DHT/AMH that leads to low levels of these. Therefore, it's important to remember which hormone is associated with which structures!

What are the different phases in the uterine/menstrual cycle?

Menses, proliferative phase, and secretory phase

When does menses occur and what happens during this time?

0-5 days of the cycle. Endometrial lining is shedding and exiting the body

When does the proliferative phase occur and what happens during this time?

Days 6-14, endometrium is starting to regrow

When does the secretory phase occur and what happens during this time?

Between 15-28 days. Endometrium is at its thickest and is prepared for possible fertilization.

The start of the secretory phase (of the menstrual cycle) is correlated with the start of which phase of the ovarian cycle?

Luteal phase, or right after ovulation

What are the phases in the ovarian cycle?

Follicular phase, ovulation, and luteal phase

When does the follicular phase occur and what happens during this time?

Days 0-15. Follicular growth is stimulated, which helps prepare the egg for ovulation

When does ovulation occur and what happens during this time?

Day 14, most mature follicle opens to release its egg

What causes ovulation?

LH surge (due to high levels of estrogen)

When does the luteal phase occur and what happens during this time?

Days 15-28, ruptured follicle has formed a corpus luteum

Progesterone levels are highest during the ________ phase.

Luteal, as it is being produced by the corpus luteum

Estradiol levels are high right before _____ and during the ____ phase.

Ovulation (since this is what induces the LH surge) and luteal phase (since it is being produced by the corpus luteum)

LH and FSH levels are highest right before _____.

Ovulation, there are high levels of estrogen which works (only in this phase) to increase LH/FSH levels

How long do eggs usually live after ovulation?

24 hours

How long can sperm survive in the female reproductive tract?

5-7 days

What are the days in a normal cycle where unprotected sex with a person who produces sperm can highly result in conception?

Days 9-15

What are estrous cycles?

Cycles in which reproductive behaviors are occurring

When does proestrus occur?

Right before estrus (or in the follicular phase in humans)

What occurs in the proestrus phase?

Animals are demonstrating interest in reproductive behaviors, may not actually engage in these yet

When does estrus occur?

Right before ovulation (optimal for chances of fertilization)

What occurs in the estrus phase?

"All-consuming" reproductive behaviors

How long are estrous cycles?

Dependent on species, but many are seasonal

Does the blastocyst or the zygote attach to the endometrium?

Blastocyst

What is the outer layer of the blastocyst and what does this produce?

Chorion, which produces hCG

What is the function of the chorion?

Stimulates corpus luteum to continue progesterone secretion, will eventually become placenta

When can hCG be detected?

Only after implantation

What is the function of the placenta (after 7-8 weeks)?

Produces most of the estrogen, progesterone and hCG (corpus luteum is no longer producing E and P), also connects fetus to maternal bloodstream

What are some examples of hormonal or nonhormonal contraceptives that can prevent pregnancy?

Pills containing either only P or P + E, vaginal rings, barrier methods, IUDs, etc

What are some ways that contraceptives can prevent ovulation?

Hormonal contraceptives containing either only P or P + E can work to decrease FSH/LH levels and prevent ovulation

What are some ways that contraceptives can prevent fertilization?

Sperm entry is prevented by barrier methods or the thickening of cervical mucus through P, copper also inhibits/blocks sperm mitochondria

What are some ways that contraceptives can prevent implantation?

Copper blocks attachment to the endometrium, hormonal contraceptives prevent the thickening of the endometrium