Chapter 27: The Reproductive System – High Yield Study Guide

Male Reproductive Anatomy

Testes

The testes are the primary male reproductive organs, responsible for producing sperm and the hormone testosterone.

• Sperm production: Occurs in seminiferous tubules.

• Testosterone: Essential for male secondary sex characteristics and spermatogenesis.

Scrotum

The scrotum is a sac that supports and protects the testes, maintaining optimal temperature for sperm production.

• Cremaster muscle: Elevates the testes.

• Dartos muscle: Wrinkles scrotal skin to reduce heat loss.

Epididymis

The epididymis is the site of sperm maturation and storage.

• Microvilli: Provide nutrients and phagocytize degenerating sperm.

• Reabsorption: Reabsorbs testicular fluid.

Ductus (Vas) Deferens

The ductus deferens transports sperm from the epididymis to the urethra during ejaculation via peristalsis.

Urethra

The urethra serves as the terminal tract for both urinary and reproductive systems in males.

Ejaculatory Duct

The ejaculatory duct moves sperm into the prostatic urethra before ejaculation.

Accessory Glands

• Seminal glands: Secrete alkaline fluid with fructose, ascorbic acid, prostaglandins, and vesiculase. Coagulation keeps semen near cervix; enzymes later liquify semen for sperm migration.

• Prostate: Secretes milky, slightly acidic fluid containing nitrate, enzymes (phosphatase, fibrinolysin), and prostate-specific antigen (PSA).

• Bulbo-urethral (Cowper’s) glands: Secrete alkaline mucus-like fluid to lubricate urethra and neutralize acidic urine.

Hormonal Regulation: Hypothalamic-Pituitary-Gonadal (HPG) Axis

Overview

The HPG axis regulates gamete production and sex hormone secretion via hormonal interactions between the hypothalamus, anterior pituitary, and gonads.

• GnRH: Released from hypothalamus; stimulates FSH and LH release from anterior pituitary.

• FSH & LH: Gonadotropins; stimulate gamete production and sex hormone secretion in gonads.

• Sex hormones: Exert negative feedback on hypothalamus and anterior pituitary.

• Inhibin: Released from gonads; inhibits FSH release.

Puberty

Puberty marks the onset of reproductive capability, driven by increased GnRH release and subsequent FSH/LH secretion.

• Hypothalamus: Becomes less sensitive to inhibition by sex hormones.

• FSH/LH: Stimulate gonadal sex hormone production.

Meiosis and Gametogenesis

Meiosis

Meiosis is a specialized nuclear division in gonads, essential for sexual reproduction.

• Chromosome reduction: Reduces chromosome number by half.

• Genetic variability: Increases through crossing over and independent assortment.

• End product: Four haploid daughter cells.

Steps of Meiosis:

• Prophase

• Metaphase

• Anaphase

• Telophase

Meiosis I (Reduction Division)

Homologous pairs separate, reducing chromosome number from 2n to n (23 in humans).

Meiosis II (Equational Division)

Sister chromatids separate, each daughter cell receives equal chromosomes.

Key Terms

• Sister chromatids: Identical copies joined by a centromere.

• Homologous chromosomes: Paired chromosomes from each parent, carrying genes for same traits.

• Nonsister chromatids: Chromatids from different homologous chromosomes; exchange DNA via crossing over.

• Diploid (2n): Two sets of chromosomes (46 in humans).

• Haploid (n): One set of chromosomes (23 in humans).

• Independent assortment: Random alignment of homologous pairs during meiosis I.

Temperature Regulation of Testes

• Dartos muscle: Wrinkles scrotal skin.

• Cremaster muscle: Elevates testes.

Prostate Cancer

Overview

Prostate cancer is a common malignancy in males, often symptomless in early stages.

• Detection: Digital exam; PSA blood test (high false positives).

• Treatment: "Wait and see" for slow-growing cases; testosterone blockade for metastatic disease.

Male Sexual Response

Phases

• Erection: Parasympathetic control; engorgement of erectile bodies with blood.

• Ejaculation: Sympathetic control; propulsion of semen.

Erection Mechanism

• NO release: Relaxes smooth muscle, dilates arterioles.

• Corpora cavernosa: Compresses veins, maintains engorgement.

• Corpus spongiosum: Keeps urethra open.

Ejaculation Mechanism

• Emission: Ductus deferens, prostate, and seminal glands contract.

• Bladder sphincter: Prevents urine/semen reflux.

• Bulbospongiosus muscles: Contract to expel semen.

• Orgasm: Intense pleasure, muscle contraction, rapid heartbeat, elevated blood pressure.

• Resolution: Relaxation; refractory period follows.

Testicular Cells

• Interstitial endocrine cells (Leydig cells): Produce androgens (testosterone, small amounts of estrogens).

• Sustentocytes (nurse cells): Support sperm formation; form blood-testis barrier.

• Blood-testis barrier: Prevents immune response against sperm antigens.

Male Secondary Sex Characteristics

• Pubic, axillary, facial hair

• Enhanced body hair

• Larynx enlargement (deep voice)

• Thicker, oilier skin

• Increased bone and muscle mass

Testosterone: Boosts basal metabolic rate, influences behavior and libido.

Hormonal Regulation of Testicular Function

• GnRH: Released from hypothalamus; stimulates FSH and LH release.

• FSH: Stimulates sustentocytes to release androgen binding protein (ABP).

• LH: Stimulates Leydig cells to secrete testosterone.

• Testosterone: Maturation of sex organs, secondary sex characteristics, libido.

• Negative feedback: Testosterone inhibits FSH, LH, and GnRH release.

• Inhibin: Decreases FSH release.

Female Reproductive Anatomy

Mammary Glands

Mammary glands are modified sweat glands present in both sexes, functional in lactating females.

• Structure: 15-25 lobes, separated by connective tissue and fat.

• Lobules: Contain alveoli that produce milk.

• Lactiferous ducts: Carry milk to nipple; lactiferous sinus stores milk during nursing.

• Suspensory ligaments: Attach breast to muscle fascia and dermis.

Ovarian Cycle and Hormonal Regulation

Corpus Luteum

The corpus luteum is an endocrine structure formed from granulosa and theca cells after ovulation.

• Produces: Progesterone and estrogens during luteal phase.

• Degeneration: If no pregnancy, becomes corpus albicans after 10 days.

• Pregnancy: Persists until placenta takes over hormone production (~3 months).

Oogenesis

Oogenesis is the process of gamete production in the ovary, involving mitosis and meiosis.

• Oogonium: Pre-puberty cells, arrested.

• Primary oocyte: Completes meiosis I monthly after puberty.

• Meiosis I result: Secondary oocyte + first polar body.

• Meiosis II: Secondary oocyte completes division if fertilized, forming zygote + second polar body.

• Polar bodies: Nonfunctional, undergo atresia.

• End result: One fertilized zygote, several polar bodies.

Estrogen Effects

• Promotes oogenesis and follicle growth.

• Enlarges uterine tubes, uterus, vagina; thickens vaginal mucosa.

• Supports puberty growth spurt (females grow faster at 11-12 years).

• Induces secondary sex characteristics: breast development, fat deposition (hips, breasts), wider pelvis.

• Maintains low blood cholesterol, facilitates calcium uptake for bone density.

Regulation of Ovarian Cycle

• GnRH: Stimulates FSH and LH secretion.

• FSH: Stimulates granulosa cells to release estrogens.

• LH: Stimulates thecal cells to release androgens, converted to estrogens by granulosa cells.

• Estrogen: Negative feedback on hypothalamus and anterior pituitary, inhibiting FSH.

• Inhibin: Released by granulosa cells, inhibits FSH.

• Dominant follicle: Survives FSH dip; others undergo atresia.

• LH surge: Triggers ovulation and corpus luteum formation.

• Corpus luteum: Produces progesterone and estrogens; negative feedback inhibits LH and FSH.

• Cycle restart: Decline in hormones removes inhibition, FSH and LH secretion resumes.

Female Sexual Response

• Excitement: Clitoris, vaginal mucosa, bulbs of vestibule, breasts engorge with blood; clitoris and nipples become erect.

• Lubrication: Greater vestibular glands and vaginal walls secrete fluid (parasympathetic control).

• Orgasm: Rhythmic contractions of uterus and vagina; intense pleasure, relaxation.

• No refractory period: Females may experience multiple orgasms.

Summary Table: Key Male and Female Reproductive Structures and Functions

Structure	Function	Hormonal Regulation
Testes	Produce sperm and testosterone	FSH, LH, Testosterone
Ovaries	Produce oocytes and estrogens/progesterone	FSH, LH, Estrogen, Progesterone
Seminal glands	Secrete alkaline fluid for sperm	None
Prostate	Secretes milky fluid, PSA	None
Bulbo-urethral glands	Lubricate urethra, neutralize urine	None
Mammary glands	Produce milk (in females)	Prolactin, Oxytocin
Corpus luteum	Produces progesterone, estrogens	LH

Key Equations and Concepts

• Chromosome Number:

$\text{Diploid (2n) in humans} = 46$

$\text{Haploid (n) in humans} = 23$

• Meiosis:

$\text{Meiosis:} \, 2n \rightarrow n$

• Hormonal Feedback:

$\text{Negative feedback:} \, \text{Testosterone/Estrogen} \rightarrow \text{Inhibit GnRH, FSH, LH}$

$\text{Positive feedback:} \, \text{High Estrogen} \rightarrow \text{LH surge}$

• Example: During the ovarian cycle, a surge in LH triggered by high estrogen levels causes ovulation.

Additional info: Academic context was added to clarify hormonal regulation, gametogenesis, and sexual response mechanisms.