Chapter 26

Chapter 26: The Reproductive System

Intro

  • The human body operates with complexity, yet cannot function indefinitely due to the inevitability of aging and biological degeneration.

  • The genes pass onto future generations, representing continuity. This final chapter addresses the mechanisms of reproduction via male and female reproductive systems.

26.1a The Chromosomal Sexes

  • Sexual Reproduction: Involves biparental contribution—offspring receive genetic material from two parents, resulting in genetic diversity.

  • Gametes: Male and female sex cells (sperm and ovum) that enable fertilization leading to zygote formation.   * Required:     * 1. Motility: Ability to move to meet each other.     * 2. Sufficient Cytoplasm: Allows for multiple cell divisions to form the embryo.

  • Definitions:   * Sperm (spermatozoon): Small, motile gamete.   * Egg (ovum): Large gamete containing enough cytoplasm for embryo development.

  • Chromosomal Makeup: Males have one X (from mother) and one Y (from father); females possess two X chromosomes (one from each parent).

26.1b Overview of the Reproductive System
Functions of the Reproductive System

  • Male: Produces sperm and introduces it into the female body.

  • Female: Produces eggs, receives sperm, serves as the site for fertilization, gestation, and lactation.

Primary Sex Organs (Gonads)

  • Testes: Male gonads that produce sperm.

  • Ovaries: Female gonads that produce eggs.

Secondary Sex Organs

  • Male: Ducts (epididymis, ductus deferens), glands (seminal vesicles, prostate), penis.

  • Female: Uterine tubes, uterus, vagina.

External vs. Internal Genitalia

  • External Genitalia: Located externally in the perineum.

  • Internal Genitalia: Situated within the pelvic cavity (exceptions noted for the testes and some ducts).

Secondary Sex Characteristics

  • Develop during adolescence and contribute to sexual attraction:   * Hair distribution (pubic, axillary, facial).   * Body composition variations (muscularity, fat distribution).   * Breast development in females.   * Vocal pitch differences between sexes.

26.2 The Male Reproductive System
26.2a The Testes

  • Testes (testicles): Dual-function endocrine and exocrine glands producing sex hormones and sperm.

  • Covered by tunica vaginalis and encapsulated by tunica albuginea.

  • Histology: Contains lobules featuring seminiferous tubules where sperm is produced.     * Interstitial endocrine cells: Located between tubules, responsible for testosterone production.     * Seminiferous tubules: Lined with germinal epithelium featuring developing sperm and nurse cells that protect and promote sperm development.     * Blood-Testis Barrier (BTB): Comprised of tight junctions between nurse cells, preventing immune reaction to developing sperm.

Important Note

  • No Blood Capillaries in Seminiferous Tubules: Blood vessels are situated in interstitial areas to protect developing germ cells from potential harm by blood-borne molecules.

The Testes Pathway

  • Seminiferous tubules connect to rete testis, facilitating sperm maturation, which then moves to the epididymis for full development and storage.

  • Vascular Supply: Supplied by testicular artery and drained by testicular vein.

  • Testicular Nerves: Mixed composition; sensory for pain, autonomic motor for regulating blood flow.

26.2b The Scrotum

  • Scrotum: A skin pouch containing the testes, featuring:     * Sebaceous glands     * Sparse hair     * Rich sensory innervation     * Darker pigmentation than other skin areas.   * Dartos fascia and dartos muscle beneath the skin.   * Median septum divides the scrotum into two halves, marked by the perineal raphe.   * Spermatic cord: Comprises connective tissue, ductus deferens, and blood vessels.   * Pampiniform plexus: A network of veins surrounding the testicular artery, crucial for maintaining testicular temperature.   * Cremaster muscle: Muscle strips surrounding the spermatic cord.

Temperature Regulation

  • Optimal sperm development occurs at a temperature of 35°C, lower than the body's internal 37°C. Mechanisms include:   * Cremaster Muscle: Elevates or lowers testes based on temperature.   * Dartos Muscle: Reduces surface area when cold.   * Pampiniform Plexus: Cools arterial blood entering the testes through heat exchange.

26.2c The Spermatic Ducts

  • After production, sperm pass through a series of ducts to reach the urethra:   * Efferent Ductules: Convey sperm from rete testis to epididymis.   * Epididymis: A coiled duct where sperm fully mature and stored (disintegration occurs after 40-60 days).   * Ductus Deferens: Travels through the spermatic cord to the pelvis and back of the bladder, widening to form the ampulla.   * Ejaculatory Duct: Merges from ductus deferens and seminal vesicle, passing through the prostate into the urethra.

26.2d The Accessory Glands

  • Accessory Glands: Three primary sets which contribute to semen volume:   * Seminal Vesicles: Produce 60-70% of semen volume; secrete alkaline fluid containing fructose, prostaglandins, and clotting factors for sperm nourishment, protection, and transportation.   * Prostate Gland: Surrounds the urethra and ejaculatory ducts; contributes 25-30% of semen fluid, aiding fertility.   * Bulbourethral Glands: Produce lubricating secretions and neutralize urethral and vaginal acidity.

Sperm Pathway and Components

  • Pathway from Sperm Production to ejaculation includes:   * Seminiferous tubules (testes) → Rete testis → Efferent ductules → Epididymis → Ductus deferens → Ejaculatory duct → Urethra.

  • Components of Semen (Seminal Plasma): Composed of approximately 2-5% sperm and various fluid contributions from accessory glands (notably prostate and seminal vesicles).

26.2e The Penis

  • Functions: Deposits semen into the vagina.

  • Anatomic Structure: Consists of:   * Internal root: Establishes connection internally.   * Shaft: The long body extending externally.   * Glans: The sensitive tip;     * Covered by prepuce (foreskin).

  • Erectile Tissues:   * Corpus Spongiosum: Encloses the urethra, engorges during erection.   * Corpora Cavernosa: Paired structures on dorsal side.

  • Blood Supply: Originates from internal pudendal arteries, with intricate drainage via deep and superficial dorsal veins.

26.2f Sperm and Semen

  • Gametogenesis Process: Involves meiosis to ensure gametes (sperm) are haploid.   * Result: Male meiosis yields four sperm cells; female meiosis produces one functional egg and polar bodies.

  • Structure of Sperm:   * Head: Contains nucleus and acrosome; the acrosome facilitates egg penetration.   * Tail: Composed of middle piece, principal piece, and end piece; the middle piece houses mitochondria for energy.

  • Semen Composition: Predominantly fluid with sperm concentration around 2-5%, prostate contributes approximately 25-30%, seminal vesicles comprise 65-75%.

26.2g Male Sexual Response

  • Response involves:   * Arousal: Parasympathetic stimulation leads to dilation of deep arteries; results in increased blood flow and erection.   * Ejaculation: Initiated through sympathetic stimulation, initiating peristaltic contractions in ducts driving sperm to the urethra.   * Expulsion Reflex: Reflexive muscular contractions through the bulbospongiosus muscle allow semen expulsion.

  • Refractory Period: Post-orgasm, males typically cannot attain another erection or orgasm for a period of time ranging from 10 minutes to hours.

26.2h Male Reproductive Disorders

  • Common disorders affecting males include:   * Benign Prostatic Hyperplasia (BPH): Leads to urethral compression.   * Prostate Cancer: Second most prevalent cancer. Diagnosed by digital rectal examination and elevated PSA levels.   * Testicular Cancer: Occurs more frequently in younger males, high curability if detected early.   * Other disorders: Cryptorchidism, infertility, penile cancer.

Clinical Applications
Clinical Application 26.1: Varicocele

  • Description: Abnormal dilation of veins in the pampiniform plexus, resembling a "bag of worms."

  • Symptoms: Can range from asymptomatic to sharp pain, may lead to testicular swelling, low sperm counts, and infertility.

Clinical Application 26.2: Reproductive Effects of Pollution

  • Endocrine disrupting chemicals (EDCs) negatively impact reproductive health.

  • Common sources include industrial solvents, plastics, and pesticides, potentially leading to developmental and reproductive disorders in both sexes, including infertility and various cancers.

26.3 The Female Reproductive System
26.3a The Ovaries

  • Ovaries: Female gonads that produce ova and sex hormones.

  • Positioned in ovarian fossae of the posterior pelvic wall, encapsulated by a tunica albuginea.

  • Histology:   * Outer cortex with ovarian follicles and connective tissue, containing developing ova and follicular cells.   * Inner medulla consists of connective tissue and blood vessels.

Structure and Support

  • Ligaments: Ovarian ligament (attaches to uterus), suspensory ligament (attaches to pelvic wall), mesovarium (peritoneal fold connection).

  • Blood Supply: Receives blood primarily from ovarian and uterine arteries.

26.3b Follicle Development and Egg Production

  • Oogenesis: Egg production occurring rhythmically as part of the ovarian cycle, initiated during embryonic development.   * Oogonia evolve into primary oocytes by birth; meiosis plays a critical role.

  • Folliculogenesis: Changes in ovarian follicles occur alongside oogenesis, progressing from primordial follicles to mature (graafian) follicles.

26.3c The Uterine Tubes

  • Function: Ciliated tubes responsible for moving the ovulated egg from ovary to uterus.

  • Histological Structure: Mucosa has longitudinal folds, with ciliated epithelium aiding egg transport via mucosal activity.

26.3d The Uterus

  • Uterus: Muscular chamber where fetal development occurs, with distinct anatomical regions (fundus, body, and cervix).

  • Histological Layers: Perimetrium (outer), myometrium (muscle), and endometrium (inner mucosal layer).   * The endometrium has two sublayers:     * Functional Layer: Shed during menstruation.     * Basal Layer: Persistent layer providing regeneration.

26.3e The Vagina

  • Vagina: Tubular organ for menstruation, sexual intercourse, and childbirth.

  • Structure includes a mucosa, muscularis, and adventitia layers with friction ridges aiding in stimulation.

26.3f The External Genitalia

  • Collectively Known As: Vulva, includes:   * Mons Pubis: Fatty tissue mound.   * Labia Majora: Thick outer skin folds.   * Labia Minora: Thinner inner folds.

  • Other components include: Vestibule, clitoris, and various glands providing lubrication.

  • The clitoris has similar structure and function to the penis in males.

26.3g The Breasts and Mammary Glands

  • Mammary glands develop during pregnancy; the structure includes secretory acini surrounded by myoepithelial cells assisting in lactation.

  • Each lobe drains via a lactiferous duct leading to the nipple.

26.3h Female Sexual Response

  • Vasodilation results in engorgement of genital tissues, secretion in the vagina, and elevated sensitivity to stimulation.

  • Orgasm involves rhythmic contractions without a refractory period affecting sexual response.

26.3i Female Reproductive Disorders

  • Common disorders include:   * Breast cancer (notably BRCA gene-related).   * Cervical cancer (HPV related).

  • Detection through self-examination, mammograms, and Pap smears.

Summary of Important Concepts

  • Meiosis: Two rounds of division producing haploid gametes.

  • Hormonal Changes: Regulate reproductive functions through puberty, menstruation, and aging.

  • Clinical Issues: Recognize the impact of pollutants, hormonal health, cancers, and reproductive disorders affecting both genders.