ch 27 reproductive

Anatomy and Physiology of the Male Reproductive Tract

  • Core Objectives

    • Describe the structure and function of the organs comprising the male reproductive system.

    • Describe the detailed structure and function of the human sperm cell.

    • Explain the specific events occurring during spermatogenesis that result in the production of haploid sperm from diploid cells.

    • Identify the critical importance of testosterone in the regulation of male reproductive function.

  • System Overview

    • The male gamete is the Sperm.

    • A sperm cell contains a haploid set of 2323 chromosomes.

    • The system is categorized into uncircumcised or circumcised states based on the presence of the Prepuce (foreskin).

  • Detailed Anatomical Components (Lateral and Anterior Views)

    • Prepuce (foreskin): Present in the uncircumcised penis.

    • Scrotum: The external muscular sack housing the testes.

    • Ductus (vas) deferens: The tube that transports sperm from the epididymis.

    • Suspensory ligament of penis: Anchors the penis to the pelvic structure.

    • Urinary bladder: Storage organ for urine, located superior to the prostate.

    • Pubic symphysis: The midline cartilaginous joint of the bony pelvis.

    • Corpus cavernosum: One of a pair of sponge-like regions of erectile tissue.

    • Corpus spongiosum: The mass of erectile tissue surrounding the male urethra.

    • External urethral opening: The exit point for both urine and semen at the tip of the glans penis.

    • Penis: The male organ of copulation.

    • Corona: The rounded edge of the glans penis.

    • Glans penis: The sensitive bulbous structure at the distal end of the penis.

    • Prostate gland: Secretes fluid that contributes to the volume of semen.

    • Spongy urethra: The portion of the urethra that passes through the penis.

    • Testis: The primary male reproductive organ where sperm and testosterone are produced.

    • Epididymis: A highly coiled tube where sperm undergo maturation.

    • Ampulla of ductus deferens: The terminal, dilated portion of the vas deferens.

    • Seminal vesicle: Glands that produce the majority of the fluid in semen.

    • Ejaculatory duct: Formed by the union of the vas deferens and the seminal vesicle duct.

    • Prostatic urethra: The segment of the urethra passing through the prostate.

    • Deep muscles of perineum: Provide structural support to the pelvic floor.

    • Bulbourethral gland: Also known as Cowper's gland; produces a lubricating fluid.

    • Membranous urethra: The short segment of the urethra between the prostate and the penis.

The Scrotum and Testes

  • The Scrotum

    • Structure: A muscular sack located outside the pelvic cavity.

    • Function: Helps to regulate the temperature of the testes (critical for sperm production).

    • Dartos muscle: A subcutaneous muscle layer that contracts to wrinkle the scrotal skin.

    • Scrotal septum: Divides the scrotum into two internal compartments.

    • Cremaster muscles: Muscles that cover the testes; they function to raise or lower the testes to maintain optimal temperature.

    • Raphae: The external ridge or seam that marks the division of the scrotum.

  • The Testes

    • Function: The male gonads and primary reproductive organs.

    • Dimensions: Typically 4−5 cm4-5\,cm in length.

    • Tunics (Protective layers):

      • Tunica vaginalis: The outer serous membrane covering.

      • Tunica albuginea: The dense, white fibrous connective tissue capsule.

    • Seminiferous tubules: The site of actual sperm development.

    • Primary Cell Types:

      • Sertoli cells: Support and nourish the developing sperm cells.

      • Germ Cells: The precursor cells that eventually become sperm.

Spermatogenesis and Sperm Structure

  • The Process of Spermatogenesis

    • Location: Occurs within the seminiferous tubules.

    • Duration: The entire process takes approximately ∼64\sim 64 days.

    • Cycle: A new cycle of spermatogenesis initiates every 1616 days.

    • Developmental Stages:

      1. Spermatogonia: Diploid stem cells.

      2. Primary spermatocyte: Formed after the first mitotic division.

      3. Secondary spermatocyte: Formed after the first meiotic division.

      4. Spermatids: Haploid cells resulting from the second meiotic division.

      5. Spermatozoa: Mature, motile sperm cells.

  • Sperm Statistics and Structure

    • Production: Between 100−300100-300 million sperm are produced daily.

    • The Head:

      • Contains the Nucleus (genetic material).

      • Acrosome: A cap-like structure containing enzymes to penetrate the egg.

    • Mid-piece:

      • Contains Mitochondria to provide energy for movement.

      • Contains the Centriole.

    • Tail:

      • Comprised of the Flagellum, Axial filament, and End piece.

      • Provides motility to move the sperm.

Sperm Transport and Accessory Glands

  • Epididymis and Duct System

    • Epididymis: Described as a "swim school" where sperm undergo maturation. If straightened out, it would be approximately 20 ft20\,ft long. It takes about 1212 days for sperm to move through its length.

    • Ductus deferens (vas deferens): The continuation of the epididymis; it is bundled within the spermatic cord.

  • Semen Composition

    • Semen: The final fluid that is ejaculated; sperm cells themselves make up only 5%5\% of the total volume.

    • Seminal vesicles: Produce fluid containing Fructose, which is utilized by sperm mitochondria for energy.

    • Prostate gland: Secretes a fluid that initially coagulates and then later decoagulates semen. The gland doubles in size during puberty and typically begins to enlarge further at the age of 2525.

    • Bulbourethral glands: Produce a thick, salty fluid known as "pre-ejaculate" that lubricates the urethra and the vagina.

The Penis and Testosterone

  • The Penis

    • Function: The organ of copulation.

    • States: Remains flaccid for nonsexual activities but becomes turgid (rod-like) during sexual arousal.

    • Internal Anatomy: Consists of three column-like chambers:

      • Two Corpora cavernosa.

      • One Corpus spongiosum.

    • Glans penis: Contains a high concentration of sensitive nerve endings.

    • Prepuce: The foreskin; also contains nerve endings.

    • Erection Mechanism: Can occur during REM sleep or due to sexual arousal. Triggered by Nitric Oxide, which acts as a vasodilator.

    • Dimension: The average length is 15 cm15\,cm.

  • Testosterone

    • Primary Functions:

      • Promotes the process of spermatogenesis.

      • Stimulates muscle development.

      • Promotes bone growth.

      • Responsible for the development of secondary sex characteristics.

    • Hormonal Control: Regulated by Gonadotropin-releasing hormone (GnRH), which stimulates the release of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).

Anatomy and Physiology of the Female Reproductive System

  • Core Objectives

    • Describe the structure and function of the organs of the female reproductive system.

    • List the sequential steps of oogenesis.

    • Describe the hormonal changes occurring during the ovarian and menstrual cycles.

    • Trace the physical path of an oocyte from the ovary to the site of fertilization.

  • External Female Genitals (Vulva)

    • Vulva: The collective term for external reproductive structures.

    • Mons pubis: A fat pad located over the pubic bone.

    • Labia majora: Folds of hair-covered skin located posterior to the mons pubis.

    • Labia minora: Thin skin folds extending medial to the labia majora.

    • Clitoris: The primary organ for sexual sensation.

    • Hymen: A thin membrane covering the vaginal opening.

    • Bartholin’s glands: Glands that provide lubrication.

  • The Vagina

    • Structure: A muscular canal approximately ∼10 cm\sim 10\,cm long.

    • Function: Serves as the entrance to the reproductive tract and the exit during menses and childbirth.

    • Tissue Layers:

      • Fibrous adventitia.

      • Smooth muscle.

      • Mucous membrane featuring rugae (folds).

    • Microbial Flora: Home to normal microbial flora, specifically Lactobacilli, which maintain health.

The Ovaries, Oogenesis, and Folliculogenesis

  • The Ovaries

    • Function: The female gonads.

    • Dimensions: Approximately 2−3 cm2-3\,cm in length.

    • Location: Situated within the pelvic cavity.

    • Support Structures: Supported by the Mesovarium, the Broad ligament, and covered by the Tunica albuginea.

  • Oogenesis and the Ovarian Cycle

    • Ovarian cycle duration: Approximately ∼28\sim 28 days.

    • Developmental Stages:

      • Oogonia: Diploid stem cells.

      • Primary oocytes: Development stops at this stage before birth. Meiosis I only resumes after the onset of puberty.

    • Ovulation: The release of the oocyte from the ovary.

    • Polar body: A smaller cell produced during meiosis that eventually disintegrates.

  • Folliculogenesis

    • Definition: The growth and development of ovarian follicles over a ∼28\sim 28-day period.

    • Primordial follicles: Present in newborns; these are the prevailing follicles in the adult ovary. They consist of a single layer of granulosa cells.

    • Primary follicles: Granulosa cells convert from flat to cuboidal shapes.

    • Secondary follicles: Cells divide further; connective tissue, blood vessels, nerves, and theca cells are added. The Zona pellucida is secreted (playing a vital role in fertilization). The Antrum begins to collect follicular fluid.

    • Tertiary follicles: Follicles where the antrum has become large and fully formed.

    • Atresia: The process of follicle death; 99%99\% of follicles undergo this process rather than reaching maturity.

Hormonal Control and the Menstrual Cycle

  • Hormonal Regulation of the Ovarian Cycle

    • GnRH (Gonadotropin-releasing hormone): Produced by the hypothalamus; signals the anterior pituitary to produce LH and FSH.

    • FSH (Follicle-stimulating hormone): Stimulates follicles to grow and develop.

    • LH (Luteinizing hormone): Stimulates granulosa and theca cells to produce estradiol.

    • The Cycle towards Ovulation:

      • One follicle typically survives and begins secreting estrogen.

      • Estrogen causes a further release of LH and FSH.

      • LH surge: Triggers ovulation and stimulates changes in the granulosa cells known as Luteinization.

      • Corpus luteum: Formed after ovulation; it releases Progesterone.

      • Corpus albicans: The degraded form of the corpus luteum if no pregnancy occurs.

  • The Uterine Tubes (Fallopian Tubes)

    • Function: Act as a conduit for the oocyte from the ovary to the uterus. They are not directly connected to the ovary.

    • Sections: Isthmus, Infundibulum, and Ampulla.

    • Oocyte Movement: Estrogen levels cause smooth muscle contractions in the tubes to move the oocyte.

  • The Uterus and Cervix

    • Uterus: A muscular organ designed to support a growing embryo. Dimensions: 5 cm5\,cm wide by 7 cm7\,cm long.

    • Regions: Fundus (top), Body (middle), and Cervix (bottom).

    • The Uterine Wall Layers:

      1. Perimetrium: Outer layer.

      2. Myometrium: Thick middle muscle layer.

      3. Endometrium: Inner lining that changes during the cycle.

  • The Menstrual Cycle Phases

    • The total cycle lasts approximately ∼28\sim 28 days.

    • Menses Phase: The uterine lining is shed; lasts between 2−72-7 days.

    • Proliferative Phase: The endometrium begins to proliferate (rebuild); occurs during days 7−147-14. Ovulation occurs specifically at day 1414.

    • Secretory Phase: Lasts 10−1210-12 days. The endometrium prepares for potential embryo implantation, and Glycogen is secreted. If no pregnancy occurs, the corpus luteum transitions into the corpus albicans.

The Breasts and Reproductive Development

  • Anatomical Features of the Breasts

    • Areola: The pigmented area surrounding the nipple.

    • Mammary glands: Produce milk.

    • Lactiferous ducts: Transport milk toward the nipple.

    • Lactiferous sinus: Storage areas for milk within the ducts.

    • Alveoli: Milk-producing clusters within the glands.

    • Suspensory ligaments: Connective tissue that supports the breast structure.

  • Development of Sexual Organs

    • The Fundamental Sex: Females are considered the "fundamental" sex because, without specific chemical/hormonal prompting, all fertilized eggs would develop as female.

    • SRY gene: The gene on the Y chromosome that directs male development.

    • Biopotential: The state in which the same group of embryonic cells has the potential to develop into either male or female gonads. However, not all tissues are bipotential.

    • Rudimentary Duct Systems:

      • Mullerian duct: Precursor to female internal sex organs.

      • Wolffian duct: Precursor to male internal sex organs.

  • Maturation at Puberty

    • Puberty involves the maturation of the sexual reproductive systems, controlled by GnRH, LH, and FSH.

    • Secondary Sex Characteristics in Men:

      • Increased larynx size (deepening of voice).

      • Increased muscular development.

      • Growth of facial and pubic hair.

    • Secondary Sex Characteristics in Women:

      • Deposition of fat in the breasts and hips.

      • Development of the breasts.

      • Broadening of the pelvis.

      • Growth of pubic hair.