Human Biology Quiz: Hormones and Menstrual Cycle

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Questions and Answers

What role does dihydrotestosterone (DHT) primarily play in the body?

Promotes the formation of gonads during embryogenesis (correct)

Stimulates spermatogenesis in the testes

Influences sex drive in the brain

Regulates the menstrual cycle in females

Which of the following statements about the menstrual cycle is incorrect?

Ovulation typically occurs on day 14 of the cycle

The average duration of menses is between 2-7 days

The normal menstrual cycle has a range of 21-35 days

The mean duration of the menstrual cycle is 28 days for all women (correct)

What primarily drives the cyclic changes in hormone levels throughout the menstrual cycle?

Local changes in the endometrium

Estrogens and progesterone only

Paracrine signaling within the ovaries

Hypothalamic-pituitary-gonads axis regulation (correct)

Which phase of the menstrual cycle is characterized by the thickening of the endometrium?

Secretory phase Signup and view all the answers

At what age does female puberty typically begin?

10-11 years old Signup and view all the answers

What major event marks the end of the follicular phase?

Ovulation occurs Signup and view all the answers

Which statement accurately describes the role of FSH during the follicular phase?

It promotes the maturation of a cohort of ovarian follicles Signup and view all the answers

What feedback mechanism is observed when estrogen levels rise during the preovulatory period?

Negative feedback on pituitary FSH secretion Signup and view all the answers

During the luteal phase, which hormone primarily supports the development of the uterine lining?

Progesterone Signup and view all the answers

What happens to the corpus luteum if pregnancy does not occur?

It disintegrates Signup and view all the answers

Which role does hCG play during early pregnancy?

It prevents the deterioration of the corpus luteum Signup and view all the answers

What physiological change is primarily responsible for the onset of menstruation?

Reduction in progesterone levels Signup and view all the answers

Which of the following processes occurs during the recruitment stage of the follicular phase?

Only one follicle matures while others become atretic Signup and view all the answers

What happens when GnRH is administered continuously?

It leads to a decrease in FSH and LH levels. Signup and view all the answers

Which of the following hormones is primarily responsible for stimulating spermatogenesis?

Testosterone Signup and view all the answers

How does high estrogen levels affect LH secretion?

It induces a surge in LH secretion. Signup and view all the answers

What role do aromatase enzymes play in female sex hormone biosynthesis?

They facilitate the conversion of androgens to estrogens. Signup and view all the answers

During male puberty, which of the following is NOT a characteristic change?

Increase in body fat percentage. Signup and view all the answers

Which cells are primarily responsible for the production of estrogen in females?

Granulosa cells Signup and view all the answers

What effect does progesterone typically have on GnRH secretion?

It decreases GnRH pulse frequency. Signup and view all the answers

What initiates the process of puberty?

Hormonal signals from the brain to the gonads. Signup and view all the answers

Which hormone negatively regulates GnRH secretion?

Testosterone Signup and view all the answers

What is a key role of luteinizing hormone (LH) in males?

Stimulates interstitial cells to produce testosterone. Signup and view all the answers

Study Notes

Sex Hormones

GnRH (Gonadotropin-Releasing Hormone) is the initial step in sex hormone production.
GnRH is released in a pulsatile manner from the hypothalamus.
GnRH pulse rate impacts subsequent FSH/LH release patterns.
Continuous GnRH administration decreases FSH/LH release.

Pituitary Factors: Gonadotropins

The anterior pituitary responds to GnRH by releasing gonadotropins.
FSH (Follicular Stimulating Hormone) is a gonadotropin.
LH (Luteinizing Hormone) is a gonadotropin.
FSH and LH's effects differ in males and females, though both utilize a two-cell system.

Males

LH stimulates Leydig cells, leading to testosterone synthesis.
FSH stimulates Sertoli cells, aiding in spermatogenesis.
Testosterone directly promotes spermatogenesis.

Females

LH stimulates Theca cells, enabling androgen synthesis.
FSH stimulates Granulosa cells.
Aromatase activation converts androgens to estrogens.
Estrogen is produced from androgen precursors.
Progesterone is a precursor to androgens.
Both theca and granulosa cells produce estrogen under LH influence.
The menstrual cycle is a continuous, cyclic process in females.

Female Reproductive Cycle

The female reproductive cycle involves follicular maturation, ovulation, and corpus luteum formation.
Follicles mature into primary, secondary, mature stages.

Ovarian Phases of Cycle

Follicular Phase.
- Recruitment and maturation of ovarian follicles occur.
- FSH prompts follicular development.
- Typically only one follicle reaches maturity.
Ovulatory Phase.
- Follicular growth and maturation conclude in ovulation.
- LH surge is a key trigger.
Luteal Phase.
- The empty follicle transforms into a corpus luteum.
- Progesterone is produced.
Menstruation occurs if no fertilization.

Biosynthesis of Sex Hormones

The biosynthesis of sex hormones involves enzymatic conversions starting with cholesterol.
Key enzymes are CYP11A1, 3βHSD, 17α-hydroxylase, and others.
Specific pathways lead to testosterone, estrogens, and other hormones.

Negative Feedback

Testosterone inhibits hypothalamic GnRH and pituitary FSH/LH secretion.
High estrogen and progesterone levels can increase LH, with high estrogen increasing hormone effects.
Progesterone alone diminishes GnRH pulse rate and anterior pituitary responsiveness to GnRH.

Puberty

Puberty is initiated by hormonal signals from the brain to the gonads via the Hypothalamic-Pituitary-Gonadal (HPG) axis.
The hypothalamus becomes less sensitive to gonadal steroids during puberty.
Puberty is not a single event but a process spanning years.

Male Puberty

Male puberty begins between ages 11-12.
It generally ends between ages 16-17.
It is characterized by androgen secretion (e.g., testosterone).

Androgens

Testosterone is the primary androgen.
Other androgens include androstenedione and dihydrotestosterone (DHT).
Androgens are precursors to estrogens.

Actions of Androgens

Testosterone stimulates spermatogenesis (sperm production).
Testosterone promotes development of secondary sexual characteristics in males.

Male Secondary Sexual Characteristics

Height and weight increase.
Shoulders broaden.
Muscle development improves.
Sexual organs grow.
Pubic and facial hair growth.
Voice deepens.
Body odor and acne increase.

Hypothalamic-Pituitary-Gonadal (HPG) Axis (Males)

LH stimulates testosterone production by interstitial cells in the testes.
Testosterone promotes secondary sex characteristics and spermatogenesis.
Testosterone produces sex drive in the brain.

Hypothalamic-Pituitary-Gonadal (HPG) Axis (General).

GnRH (Gonadotropin-Releasing Hormone) released by the hypothalamus, regulates the release of LH and FSH from the anterior pituitary.
LH or FSH stimulate the gonads (testes or ovaries).
The gonads release sex steroids (e.g., testosterone, estrogen).
These hormones regulate secondary sexual characteristics, growth and other functions.

Dihydrotestosterone (DHT)

DHT is a potent androgen converted locally from testosterone.
DHT plays a role in male embryogenesis and gonadal formation.
DHT leads to hair follicle development.
DHT is implicated in androgenetic alopecia (male pattern baldness).
Oestradiol plays a role in brain regulation of sexual drive, and in the development and maintenance of genitalia.

hCG (Human Chorionic Gonadotropin)

hCG is initially secreted by the developing trophoblast.
Acts like LH and FSH but not inhibited by progesterone.
hCG maintains the corpus luteum in early pregnancy.
Supports continued pregnancy.

Menstruation

If no embryo develops, the corpus luteum deteriorates.
Progesterone levels decrease.
The uterine lining detaches, leading to menstruation.
Blood and unfertilized egg are discharged.
Menstruation typically lasts 3-7 days.

Menstruation Cycle (Hallmarks)

The menstrual cycle is marked by periodic endometrial shedding (desquamation).
Prostaglandins (hormones) peak just before menstruation, causing arteriole constriction and ischemia.
This process is followed by arteriolar relaxation, leading to bleeding and tissue breakdown.

Follicular Phase (Recruitment, Maturation, Selection)

FSH stimulates a cohort of ovarian follicles' maturation.
Only one follicle matures fully.
Estrogen plays a negative feedback role.
The least successful follicles undergo atresia (breakdown).

Preovulatory Period (Negative & Positive Feedback)

Estrogen (estradiol) exerts negative feedback on pituitary FSH release.
Rising estrogen concentration triggers positive feedback, stimulating LH surge.
LH surge initiates ovulation.

Preovulatory Period (LH Surge)

LH surge lasts for approximately 48 hours, culminating in ovulation at about 36 hours.
Rapidly falling estrogen levels accompany the surge.
Granulosa cells transform into luteal cells, causing progesterone synthesis.
The follicular wall ruptures, releasing the oocyte.

Luteal Phase

The remaining follicle becomes the corpus luteum.
The corpus luteum produces estrogen and progesterone.
Progesterone prepares the uterine lining for pregnancy.
If fertilization occurs, hCG maintains the corpus luteum.

Oral Contraceptives

Combined oral contraceptives (COCs) contain estrogen and progesterone.
Progesterone-only pills (POPs) are another option for contraception.
These medications inhibit GnRH release, preventing FSH and LH surges thereby blocking ovulation.
Both COCs and POPs are highly effective methods of contraception when used correctly.

Mechanism of Action (Oral Contraceptives)

Estrogen and progesterone prevent GnRH, FSH and LH, preventing ovulation.
The lack of ovulation prevents fertilization from occurring.

Pregnancy Tests

hCG (human chorionic gonadotropin) is a key indicator for pregnancy.
hCG is a hormone produced by the placenta during pregnancy.
hCG levels increase rapidly after conception and peak in the 8-11 weeks of pregnancy;
The hormone's presence can be detected in urine using pregnancy tests.

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Description

Test your knowledge on human biology focusing on hormones and the menstrual cycle. This quiz covers the roles of dihydrotestosterone, the phases of the menstrual cycle, and puberty in females. Challenge yourself with questions about hormonal changes and reproductive health.