The structures and function of reproductive organs in males

1. Scrotum:

   • Structure: A sac of skin and superficial fascia that hangs outside the abdominopelvic cavity. It contains the testes, epididymis, and parts of the spermatic cords.
   • Function: Provides a cooler environment (about 2-3°C lower than body temperature) essential for viable sperm production. The cremaster and dartos muscles regulate testicular position in response to temperature changes.

2. Epididymis:

   • Structure: A comma-shaped organ attached to the posterior aspect of each testis, consisting of a head, body, and tail. It contains a highly coiled duct.
   • Function: Site of sperm maturation (acquiring motility and fertilizing ability) and temporary storage of sperm. Sperm can be stored here for several weeks.

3. Ductus Deferens (Vas Deferens):

   • Structure: A muscular tube that extends from the epididymis, ascends into the pelvic cavity, loops over the ureter, and joins the duct of the seminal vesicle to form the ejaculatory duct.
   • Function: Transports mature sperm from the epididymis to the ejaculatory duct during ejaculation via peristaltic contractions.

4. Ejaculatory Duct:

   • Structure: Formed by the union of the ductus deferens and seminal vesicle duct, it passes through the prostate gland.
   • Function: Mixes sperm with seminal fluid from the seminal vesicles and propels semen into the urethra.

5. Urethra (Male):

   • Structure: Extends from the bladder through the penis to the outside. It has three parts: prostatic urethra, membranous urethra, and spongy (penile) urethra.
   • Function: Conveys both urine and semen out of the body. During ejaculation, a sphincter at the base of the bladder closes to prevent urine from entering the urethra and semen from entering the bladder.

6. Accessory Glands: These glands produce seminal fluid, which mixes with sperm to form semen.

   • Seminal Vesicles (2):
     • Structure: Two pouch-like glands located posterior to the bladder.
     • Function: Secrete a yellowish, viscous alkaline fluid containing fructose (energy for sperm), prostaglandins (promote sperm motility and uterine contractions), and coagulating enzymes (to thicken semen post-ejaculation). Contributes about 60-70% of semen volume.
   • Prostate Gland (1):
     • Structure: A single, chestnut-sized gland inferior to the bladder, surrounding the prostatic urethra.
     • Function: Secretes a milky, slightly acidic fluid containing citrate (nutrient for sperm), prostate-specific antigen (PSA) and other enzymes (liquefy semen post-ejaculation), and seminalplasmin (an antibiotic). Contributes about 20-30% of semen volume.
   • Bulbourethral Glands (Cowper's Glands) (2):
     • Structure: Pea-sized glands inferior to the prostate, flanking the membranous urethra.
     • Function: Secrete a clear, thick, alkaline mucus before ejaculation. This mucus lubricates the urethra, neutralizes residual urine acidity, and lubricates the glans penis, protecting sperm.

7. Penis:

   • Structure: The male copulatory organ, composed of a root, shaft, and glans penis. Internally, it contains three cylindrical bodies of erectile tissue: two corpora cavernosa and one corpus spongiosum (which surrounds the urethra).
   • Function: Delivers sperm into the female reproductive tract during sexual intercourse. Erectile tissue engorges with blood during sexual arousal, causing an erection.

Female Reproductive System

The female reproductive system is designed for the production of eggs (female gametes), reception of sperm, fertilization, nurturing of the developing embryo/fetus, and production of female sex hormones.

Structures and Functions:

1. Ovaries (Gonads):

   • Structure: Two almond-shaped organs located in the pelvic cavity, lateral to the uterus. They contain ovarian follicles at various stages of development.
   • Function:
     • Oogenesis: Production of ova (eggs) through meiosis.
     • Hormone Production: Production of female sex hormones, primarily estrogens and progesterone, which regulate the menstrual cycle, support pregnancy, and develop secondary sexual characteristics.

2. Uterine Tubes (Fallopian Tubes or Oviducts):

   • Structure: Two tubes extending from the ovaries to the uterus. Each tube has fimbriae (finger-like projections near the ovary), an infundibulum, ampulla (site of fertilization), and isthmus (narrow portion joining the uterus).
   • Function:
     • Receive the ovulated oocyte.
     • Provide the primary site for fertilization (usually in the ampulla).
     • Transport the oocyte/zygote towards the uterus via ciliary action and peristaltic contractions.

3. Uterus:

   • Structure: A hollow, muscular, pear-shaped organ located in the pelvic cavity between the bladder and rectum. It consists of the fundus (domed superior part), body (main portion), and cervix (narrow inferior neck). The uterine wall has three layers: perimetrium (outer serous), myometrium (middle muscular), and endometrium (inner mucosal lining).
   • Function:
     • Receives, Retains, and Nourishes: Site of implantation for a fertilized egg.
     • Develops Fetus: Supports the development of the fetus throughout pregnancy.
     • Menstruation: Sheds its endometrial lining if pregnancy does not occur.
     • Labor and Delivery: Contracts vigorously to expel the fetus during childbirth.

4. Cervix:

   • Structure: The narrow neck of the uterus that projects into the vagina. Contains a cervical canal lined with mucus-secreting glands.
   • Function:
     • Provides a passageway for menstrual flow and sperm.
     • Produces cervical mucus that changes consistency during the menstrual cycle to either facilitate or block sperm entry.
     • Forms a protective barrier during pregnancy, retaining the fetus and protecting against infection.

5. Vagina:

   • Structure: A thin-walled, elastic fibromuscular tube extending from the cervix to the exterior of the body.
   • Function:
     • Receives the penis during sexual intercourse.
     • Serves as the birth canal during childbirth.
     • Passageway for menstrual flow.

6. External Genitalia (Vulva or Pudendum):

   • Mons Pubis: Fatty, rounded area overlying the pubic symphysis.
   • Labia Majora: Two large, fatty folds homologous to the male scrotum.
   • Labia Minora: Two thin, hair-free folds medial to the labia majora.
   • Clitoris: Small, erectile organ homologous to the male penis, rich in nerve endings, crucial for female sexual arousal.
   • Vestibule: Area enclosed by the labia minora, containing the vaginal and urethral orifices.
   • Greater Vestibular Glands (Bartholin's Glands): Located on either side of the vaginal opening, secrete mucus for lubrication during intercourse.
   • Function: Protection of internal structures, sexual arousal, and facilitation of intercourse.

Gametogenesis

Gametogenesis is the process of germ cell development into mature gametes (sperm in males, ova in females). It involves meiosis, a type of cell division that reduces the number of chromosomes by half.

Spermatogenesis (Male Gamete Formation):

• Location: Occurs in the seminiferous tubules of the testes.
• Timing: Begins at puberty and continues throughout a male's reproductive life.

Human Reproductive Systems

Male Reproductive System

The male reproductive system is designed for the production, maturation, storage, and transport of sperm (male gametes) and the production of male sex hormones.

Structures and Functions:

1. Testes (Gonads):

   • Structure: Two oval-shaped organs located in the scrotum, outside the abdominopelvic cavity. Each testis contains highly convoluted seminiferous tubules.
   • Function:
     • Spermatogenesis: Production of sperm within the seminiferous tubules.
     • Hormone Production: Production of androgens, primarily testosterone, by Leydig cells (interstitial cells) located between the seminiferous tubules. Testosterone is crucial for sperm maturation, development of secondary sexual characteristics, and maintaining libido.