Testes, Spermatogenesis, Ovaries and Oogenesis: Summary Notes

Testes and Spermatogenesis

  • Gametes: Specialized sex cells with 23 chromosomes (haploid).
  • Male gamete (sperm) combines with female gamete (ovum) during fertilization.
  • Testes produce sperm and androgens (e.g., testosterone).
  • Accessory organs and ducts aid sperm maturation and transport.

Gross Anatomy of the Testes

  • Testes: Male gonads that produce sperm and androgens.
  • Located within the scrotum.
  • Tunica vaginalis: Outer serous membrane.
  • Tunica albuginea: Tough, white connective tissue that divides the testis into lobules.
  • Lobules contain seminiferous tubules where sperm develop.
  • Descent of the testis: Testes move into the scrotal cavity during fetal development.
  • Cryptorchidism: Failure of one or both testes to descend.

Seminiferous Tubules and Cell Types

  • Seminiferous tubules: Site of sperm production.
  • Sertoli cells (sustentacular cells): Support sperm development, secrete signaling molecules, and form the blood-testis barrier.
  • Germ cells: Developing sperm cells (spermatogonia, spermatocytes, spermatids, spermatozoa).
  • Spermatogonia: Stem cells that differentiate into sperm cells.

Spermatogenesis

  • Spermatogenesis: Process from spermatogonia to sperm.
  • Occurs in seminiferous tubules.
  • Begins at puberty and continues throughout life.
  • Takes approximately 64 days for one cycle.
  • Sperm counts decline after age 35.
  • Mitosis of diploid spermatogonia (2n) produces two identical diploid cells.
  • One cell remains a spermatogonium, the other becomes a primary spermatocyte.
  • Meiosis I: Primary spermatocyte divides into two secondary spermatocytes (haploid, 1n).
  • Meiosis II: Secondary spermatocytes divide into four spermatids.
  • Spermiogenesis: Spermatids transform into spermatozoa (formed sperm).

Structure of Formed Sperm

  • Sperm: Smaller than most cells, produced at 100-300 million per day.
  • Head: Contains compact haploid nucleus and acrosome (enzymes for fertilization).
  • Mid-piece: Filled with mitochondria to power the flagellum.
  • Tail: Flagellum for movement.

Hormonal Control of the Testes

  • Testosterone: Steroid hormone produced by Leydig cells (interstitial cells).

Functions of Testosterone

  • In male embryos, testosterone causes anatomical differentiation of sexual organs.
  • Necessary for spermatogenesis.
  • Promotes muscle development, bone growth, secondary sex characteristics, and libido.

Control of Testosterone

  • Hypothalamus releases GnRH, stimulating the pituitary gland.
  • Pituitary releases LH and FSH.
  • LH stimulates Leydig cells to produce testosterone.
  • FSH stimulates Sertoli cells to promote spermatogenesis and produce inhibins, which inhibit FSH release.
  • Negative feedback loop: Testosterone and inhibin inhibit GnRH, LH, and FSH production.
  • Dihydrotestosterone (DHT): Development of male secondary sexual characteristics.
  • Androgen-binding protein (ABP): Concentrates testosterone in the testes.

Further Sexual Development Occurs at Puberty

  • Puberty: Individuals become sexually mature.
  • LH release at night precedes physical changes.
  • Decreased sensitivity in the hypothalamus and pituitary to negative feedback.
  • Increased sensitivity of the gonads to FSH and LH signals.
  • Multiple factors affect puberty onset: genetics, environment, and nutrition.
  • Growth of testes and scrotum, followed by growth of penis and hair.
  • Testosterone stimulates larynx growth and voice deepening.

Sperm Transport

  • Sperm move from seminiferous tubules to epididymis for maturation.

Role of the Epididymis

  • Epididymis: Coiled tube where sperm mature.
  • Sperm acquire the ability to move.
  • Stored in the tail of the epididymis until ejaculation.

Duct System

  • Ductus deferens (vas deferens): Carries sperm during ejaculation.
  • Spermatic cord: Contains ductus deferens, blood vessels, and nerves.

Vasectomy

  • Vasectomy: Surgical sterilization by cutting and sealing the ductus deferens.

Seminal Vesicles

  • Seminal vesicles: Contribute approximately 60% of semen volume.
  • Fluid contains fructose for sperm ATP production.

Prostate Gland

  • Prostate gland: Secretes alkaline, milky fluid to coagulate and decoagulate semen.
  • Benign prostatic hyperplasia (BPH): Enlargement can cause urinary symptoms.
  • Prostate cancer: Second most common cancer in males.

Bulbourethral Glands

  • Bulbourethral glands: Release a thick, salty fluid that lubricates the urethra and vagina and cleans urine residues.
  • Pre-ejaculate may contain sperm.

The Penis

  • Penis: Male organ of copulation.
  • Shaft: Contains three columns of erectile tissue (corpora cavernosa and corpus spongiosum).
  • Glans penis: Sensitive skin with nerve endings.
  • Prepuce (foreskin): Covers the glans penis.
  • Erections: Vasocongestion due to increased arterial blood flow and reduced venous drainage.
  • Nitric oxide (NO) release causes smooth muscle relaxation and vasodilation.

Male External Genitalia

  • Scrotum: Contains testes and regulates temperature for sperm production.
  • Dartos and cremaster muscles: Elevate testes in cold and relax in heat.

Male Sexual Response

  • Four stages: excitement, plateau, orgasm, and resolution.
  • Excitement: Erection due to parasympathetic stimulation.
  • Plateau: Penis gradually fills with more blood.
  • Orgasm: Ejaculation of semen via sympathetic nervous system.
  • Resolution: Return to normal state, refractory period.

Anatomy of the Ovary

  • Ovaries: Female gonads that produce oocytes and reproductive hormones.
  • Located within the pelvic cavity.
  • Supported by the mesovarium, suspensory ligament, and ovarian ligament.
  • Ovarian surface epithelium, tunica albuginea, cortex (ovarian stroma), and inner ovarian medulla.

Ovarian Follicles

  • Ovarian follicles: Oocytes and their supporting cells.
  • Folliculogenesis: Growth and development of ovarian follicles.
  • Atresia: Death of ovarian follicles.
  • Follicles progress from primordial to primary to secondary and tertiary stages.
  • Primordial follicles: Single layer of granulosa cells.
  • Primary follicles: Granulosa cells become cuboidal.
  • Secondary follicles: Add outer layer of connective tissue (theca cells) and secrete zona pellucida.
  • Tertiary follicles: Large antrum filled with follicular fluid.

Oogenesis

  • Oogenesis: Gametogenesis in females.
  • Oogonia: Ovarian stem cells formed during fetal development.
  • Primary oocytes: Formed in fetal ovary and arrested in meiosis I.
  • Ovulation: Release of a secondary oocyte from the ovary.
  • Meiosis I resumes, forming a secondary oocyte and a first polar body.
  • Meiosis II completes only if a sperm penetrates the secondary oocyte, forming a haploid ovum.

Development of the Sexual Organs in the Embryo and Fetus

  • Sex determination: Determined by X and Y chromosomes (XX = female, XY = male).
  • SRY gene: On the Y chromosome, triggers testes development.
  • Bipotential gonads: Can develop into either male or female gonads.
  • Testosterone influences tissues to become male reproductive structures.
  • Müllerian duct degrades in males, Wolffian duct develops.
  • Wolffian duct degrades in females, Müllerian duct develops.

Development of the Secondary Sexual Characteristics

  • Breast tissue development, growth of axillary and pubic hair.
  • Growth spurt.
  • Menarche: Start of menstruation.

Female Reproductive Tract

  • Female reproductive tract: Ovaries, uterine tubes, uterus, and vagina.

Ovaries and Uterine Tubes

  • Uterine tubes (fallopian tubes): Conduit for oocyte from ovary to uterus.
  • Isthmus, infundibulum, and ampulla (where fertilization often occurs).
  • Oocytes move via smooth muscle contractions and cilia.

The Uterus

  • Uterus: Nourishes and supports the growing embryo.
  • Fundus, body, and cervix.
  • Broad ligament, round ligament, and uterosacral ligament support the uterus.
  • Perimetrium, myometrium (smooth muscle), and endometrium (stratum basalis and stratum functionalis).
  • Endometrium sheds during menstruation.

The Vagina

  • Vagina: Muscular canal serving as entrance to the reproductive tract.
  • Fornix, rugae, hymen.
  • Bartholin’s glands and lesser vestibular glands secrete mucus.
  • Lactobacillus bacteria maintain acidic pH to protect against pathogens.

External Female Genitals

  • Vulva: External female reproductive structures.
  • Mons pubis, labia majora, labia minora, clitoris, hymen.

Breasts and Mammary Glands

  • Breasts: Accessory organs of the female reproductive system.
  • Mammary glands produce milk.
  • Nipple, areola, lactiferous ducts, lactiferous sinuses, alveoli.
  • Myoepithelial cells contract to push milk to the sinuses.

Female Sexual Response

  • Four stages: excitement, plateau, orgasm, and resolution.
  • Excitement: Increased blood flow to genitals, vaginal lubrication.
  • Plateau: Blood flow to the lower part of the vagina reaches its maximum.
  • Orgasm: Contraction of the lower part of the vagina.
  • Resolution: Return to normal state, may experience further orgasms.

Hormonal Control of the Ovarian Cycle

  • Female reproductive cycle: Events in the ovaries and uterus regulated by hormones.
  • Ovarian cycle: Changes in oocytes and ovarian follicles.
  • Uterine cycle: Events in the uterus.
  • GnRH, LH, FSH, estradiol, progesterone, and inhibin.
  • Follicular phase: Tertiary follicles grow and secrete estrogen.
  • LH surge triggers ovulation.
  • Luteinization transforms follicle into corpus luteum, producing progesterone and inhibin.
  • Luteal phase: Progesterone secretion.
  • Corpus luteum degrades if pregnancy does not occur.

Phases of the Uterine Cycle

  • Menses phase: Lining is shed when progesterone levels are low.
  • Proliferative phase: Endometrium begins to proliferate again due to increased estrogen.
  • Secretory phase: Endometrial lining prepares for implantation due to progesterone.