UNIT 8 GPT

What is the primary purpose of reproductive endocrinology?

To produce gametes that combine to create a new organism through meiosis regulated by hormones.

What are chromosomes?

Long strands of DNA packaged around histone proteins forming nucleosomes, which organize into chromosomes shaped like an 'X', with paternal and maternal halves.

What does diploid (2N) mean?

A cell with 46 chromosomes—23 from sperm (paternal) and 23 from oocyte (maternal).

What is a haploid cell?

A cell with half the number of distinct chromosomes (23), formed after meiosis, containing recombined genetic material.

What are gametes?

Haploid cells involved in fertilization, sperm from testes and oocytes from ovaries.

What are germ line cells?

Cells in testes or ovaries that give rise to gametes through meiosis.

How is biological sex determined?

At fertilization: XX (female) if sperm carries X chromosome; XY (male) if sperm carries Y chromosome.

What distinguishes meiosis from mitosis?

Meiosis produces 4 genetically different haploid cells, mitosis produces 2 identical diploid cells.

How many divisions occur in meiosis?

Two rounds of division (Meiosis I and Meiosis II).

What happens during DNA replication before meiosis?

The cell copies DNA, temporarily doubling chromosomes with sister chromatids.

What occurs in Prophase I?

Homologous chromosomes pair up, and crossing over (recombination) occurs, exchanging DNA segments between chromatids.

Why is recombination important?

It increases genetic variability, ensuring gametes are genetically unique.

What happens in Metaphase I?

Homologous chromosomes align in the middle of the cell, preparing for separation.

What occurs in Anaphase I?

Homologous chromosomes are pulled to opposite sides of the cell.

What happens during Telophase I and Cytokinesis?

The cell divides into two daughter cells, each with 23 chromosomes (each chromosome still has sister chromatids).

Does DNA replicate before Meiosis II?

No, DNA replication does not occur before Meiosis II.

What happens in Prophase II?

Chromosomes condense and spindle fibers form in each daughter cell.

What occurs in Metaphase II?

Sister chromatids line up in the center of the cell.

What happens during Anaphase II?

Sister chromatids are pulled apart to opposite sides of the cell.

What occurs in Telophase II and Cytokinesis?

Each daughter cell splits, forming 4 genetically distinct haploid cells with 23 chromosomes each.

What role do feedback loops play in gamete production?

They regulate hormone levels to control the timing and quantity of gamete production.

How does negative feedback regulate reproduction?

It reduces secretion of GnRH, LH, and FSH when hormone levels are high to prevent overproduction of gametes.

What role does positive feedback play in the female menstrual cycle?

Rising estrogen triggers an LH surge causing ovulation and release of a mature egg.

What can disruptions in feedback loops cause?

Reproductive issues like infertility or hormone imbalances.

What is the basic principle of a negative feedback loop?

The effect of a reaction loops back to shut off its own production.

What are the external genitalia of the male reproductive system?

Penis and scrotum.

What structures make up the penis?

Urethra, erectile tissue, and the penis itself.

Where are sperm and testosterone produced?

In the testes, which are housed in the scrotum.

What is the pathway sperm takes during ejaculation?

Testes → Epididymis → Vas deferens → Seminal vesicle → Prostate → Bulbourethral gland → Urethra → Penis → Out of the body.

What is the function of the seminal vesicle fluid?

Provides fructose and enzymes to nourish and maintain sperm.

What does the prostate gland secrete and why?

Enzymes and fluid to neutralize the acidic environment of the urethra and vagina, protecting sperm.

How is growth and maintenance of the prostate regulated?

By testosterone.

What does the bulbourethral gland do?

Releases alkaline lubricating fluid to neutralize urethra acidity before and during ejaculation.

What dual function does the urethra serve?

Conducts both urine and sperm out of the body through the penis.

What is the scrotum’s role?

Houses the testes.

What is the seminiferous tubule?

The site of spermatogenesis and meiotic events in the testes.

How long does sperm maturation take in the epididymis?

2 to 3 weeks.

How long would the seminiferous tubules stretch if laid out?

Up to 1600 meters.

How many sperm are produced per ejaculate?

40 to 80 million.

How many gametes are produced from one spermatogonia?

Four.

What are Sertoli cells?

Nurse cells that support spermatogenesis and form the blood

What is the blood-testes barrier?

A protective barrier formed by Sertoli cells’ tight junctions shielding spermatocytes from the immune system.

What hormone receptor do Sertoli cells have?

Follicle stimulating hormone (FSH) receptor.

What hormone do Sertoli cells produce?

Inhibin, which inhibits gonadotropin release.

What are Leydig cells and their function?

Cells between seminiferous tubules that produce testosterone in response to LH.

What happens when spermatogonia divide?

One cell replaces the spermatogonia; the other becomes a primary spermatocyte (2N).

What is the chromosome count of a primary spermatocyte?

46 chromosomes (2N).

What occurs in meiosis I during spermatogenesis?

Primary spermatocyte becomes two secondary spermatocytes (each 23 chromosomes, 2 copies).

What occurs in meiosis II?

Secondary spermatocytes divide into four spermatids (each 23 chromosomes, 1 copy).

What is spermiogenesis?

The morphological maturation of spermatids into spermatozoa.

How long does the process from spermatogonia to spermatozoa take?

64 to 72 days.

What is the function of the sperm tail?

Propels sperm through the female reproductive tract.

Why is the mitochondrial spiral important in sperm?

Provides energy for tail movement.

What is in the sperm head?

The nucleus with 23 condensed chromosomes.

What is the acrosome?

An organelle containing enzymes to penetrate the oocyte.

How is testosterone regulated?

Via negative feedback involving the hypothalamus, anterior pituitary, Sertoli cells, and Leydig cells.

What hormone stimulates the anterior pituitary to release FSH and LH?

Gonadotropin releasing hormone (GnRH) from the hypothalamus.

What does FSH do in the testes?

Acts on Sertoli cells to promote spermatogenesis and release inhibin.

What does LH do in the testes?

Stimulates Leydig cells to produce testosterone.

What does inhibin do?

Provides negative feedback to reduce FSH and LH secretion.

What role does testosterone play in feedback?

Inhibits GnRH, FSH, and LH production via negative feedback.

How do levels of GnRH, FSH, LH, inhibin, and testosterone interact?

They fluctuate in a feedback loop to maintain hormone balance.

Do biological females produce testosterone?

Yes, primarily from adrenal glands affecting muscle, blood production, and more.

What is testosterone’s biosynthesis starting molecule?

Cholesterol.

Why is testosterone structurally similar to cholesterol?

Because it's synthesized through multiple steps from cholesterol.

When does testosterone rise during fetal development?

To develop male reproductive tract and external genitalia.

What happens to testosterone levels at birth?

Brief increase with unknown function.

When does testosterone increase during puberty?

GnRH increases, stimulating FSH and LH → more testosterone.

When is peak testosterone and sexual maturity typically reached?

Around ages 16–18.

What happens to testosterone levels in adulthood?

Stable until ~40, then gradual decline.

What is andropause?

Around age 50; decline in testosterone and sperm causing low libido, fatigue, and muscle loss.

Name key functions of testosterone in the body.

Male reproductive development, secondary sex traits, sex drive, spermatogenesis, muscle/bone growth, aggression.

What is the relationship between spermatogenesis, testosterone, and the hypothalamic-pituitary-gonadotropin axis?

Spermatogenesis is regulated by this axis; testosterone supports it and influences other tissues under feedback control.

What is the role of the fimbriae?

Finger

Where does fertilization typically occur?

In the uterine (fallopian) tube.

What helps move the oocyte or embryo along the uterine tube?

Cilia and movement regulated by progesterone.

What are the functions of the ovary?

Site of female gamete development, responsive to FSH and LH, secretes estrogen and progesterone, and releases oocyte at ovulation.

What is the function of the uterus?

Muscular organ where embryo implants; maintains pregnancy.

Which hormones regulate the endometrium?

Estrogen regulates development; progesterone regulates maturation.

What is the cervix and its function?

Connects vaginal canal to uterus; secretes mucus that changes during the cycle to either facilitate or prevent sperm entry.

How do estrogen and progesterone affect cervical mucus?

Estrogen → thinner mucus; Progesterone → thicker mucus.

What are the functions of the vagina?

Receives penis and sperm, allows menstrual fluid discharge, and passage of the baby during birth.

When does the oocyte you came from first develop?

When your biological mother was in your biological grandmother’s womb.

How many oocytes are present at birth and puberty?

~1–2 million at birth; ~300,000 at puberty.

Why does the ovary stockpile oocytes before birth?

Possibly to ensure enough healthy oocytes throughout reproductive life.

What signals menopause?

Depletion of the oocyte pool.

At what stage are most oocytes arrested for years?

Diplotene stage of prophase I.

When does oocyte meiosis resume?

At puberty, for oocytes that are recruited to mature.

How long can oocytes remain dormant?

50–55 years depending on the oocyte pool.

How does oocyte division differ from sperm cell division?

Oocyte divides unequally into one oocyte and one small polar body.

What triggers completion of meiosis II in oocytes?

Fertilization.

What is produced when meiosis II finishes?

One fertilizable haploid oocyte and another polar body.

What is syngamy?

The fusion of sperm and oocyte DNA to form a zygote.

What is folliculogenesis?

The maturation process of ovarian follicles alongside oocyte development.

What is the zona pellucida?

Gelatinous layer between oocyte and follicle cells, forms during oogenesis.

Which cells nurse and support the oocyte?

Granulosa cells and theca cells.

What hormones do granulosa and theca cells produce?

Estrogen and progesterone.

What hormones regulate folliculogenesis via the HPG axis?

FSH and LH, in response to GnRH.

What is a primordial follicle?

An oocyte with a single layer of flattened granulosa cells, present at birth.

How many primordial follicles are recruited during a cycle?

30–50 follicles.