Human Biology Quiz: Hormones and Menstrual Cycle

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.

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.