ANATOMY

Reproductive System Study Guide Notes

General Overview

• The reproductive system is not essential for individual homeostasis but is crucial for species survival.
• Primary Sex Organs (Gonads):
  • Males: Testes
  • Females: Ovaries
  • Functions:
  • Produce gametes: sperm and ova
  • Secrete steroid sex hormones:
    • Androgens (males)
    • Estrogens and Progesterone (females)
• Accessory Reproductive Organs: Ducts, glands, and external genitalia.

Male Reproductive System Overview

• Gonads:
  • Testes (located in scrotum) produce sperm.
• Sperm Delivery Pathway:
  • Epididymis → Ductus deferens → Ejaculatory duct → Urethra

The Scrotum

• Structure: A sac of skin outside the abdominopelvic cavity that holds paired testes at approximately (3^{ ext{o}}C) lower than core body temperature (essential for sperm production).
• Muscles for Temperature Regulation:
  • Dartos muscle: Smooth muscle; wrinkles skin and pulls the scrotum close.
  • Cremaster muscle: Skeletal muscle; elevates testes.

The Testes

• Produce sperm (~3% of semen).
• Structure:
  • Surrounded by two tunics:
  • Tunica vaginalis (outer)
  • Tunica albuginea (inner fibrous capsule)
  • Divided into lobules, each containing (1-4) seminiferous tubules (sperm-forming factories).
• Interstitial Endocrine (Leydig) Cells: Produce androgens.

Important Testicular Cells

Male Duct System

• Pathway: Epididymis → Ductus deferens → Ejaculatory duct → Urethra.

Epididymis

• Length: (~6) meters long.
• Function: Absorbs testicular fluid, nourishes sperm.
  • Sperm enter nonmotile and become motile gradually.
  • Stored for months and contracts during ejaculation to move sperm.

Ductus Deferens (Vas Deferens)

• Carries sperm from epididymis to ejaculatory duct.
  • Forms an ampulla and joins with the seminal vesicle duct.
  • Vasectomy: Cutting and sealing ductus deferens (birth control).

Urethra

• Extends from bladder to tip of the penis.
• Carries urine and sperm (at different times).
• Regions:
  • Prostatic urethra: Surrounded by prostate
  • Membranous urethra: Through urogenital diaphragm
  • Spongy (penile) urethra: Through the penis.

Accessory Glands

Semen Composition

• Volume: 2–5 mL ejaculated.
• Concentration: (20-150) million sperm/mL.
• Contents:
  • Fructose (energy)
  • Alkalinity (neutralizes acidity)
  • Relaxin, enzymes (motility)
  • Prostaglandins (reduce cervical mucus viscosity)
  • Antibacterial action
  • Coagulation (initial thickening), fibrinolysin (liquefaction).

Male External Genitalia and Sexual Response

• Erection:

  • Blood fills erectile tissues:
  • Corpus spongiosum (surrounds urethra)
  • Corpora cavernosa (paired)
  • Parasympathetic activation releases Nitric Oxide (NO) causing vasodilation.

• Ejaculation:

  • Sympathetic spinal reflex:
  • Internal urethral sphincter closes (no urine).
  • Ducts/glands contract.
  • Bulbospongiosus muscles expel semen (at (~5) m/s).

Viagra and Erectile Function

• Increases cGMP levels by preventing its breakdown.
• Enhances NO pathway for erection maintenance.
• Warning: Seek help if erection lasts longer than 4 hours.

Female Reproductive System Overview

• Ovaries:
  • Produce ova (eggs)
  • Secrete estrogen and progesterone.

Other Structures

• Uterine tubes (fallopian tubes)
• Uterus
• Vagina
• Vulva
• Clitoris

Vagina

• Extends from cervix to exterior, located between the bladder and rectum.
• Functions:
  • Receives penis
  • Birth canal
  • Hymen partially covers vaginal opening (at birth).

Vulva and Clitoris

• Vulva: External genitalia.
• Glands:
  • Bartholin’s glands: Lubrication (equivalent to male bulbourethral glands).
  • Paraurethral glands: Female prostate (secretes mucus).
• Clitoris:
  • Somatosensory nerve-rich
  • Contains erectile tissue (corpus cavernosum).

Uterus

• Regions:
  • Cervix (neck)
  • Body
  • Fundus (top)
• Functions: Receives, retains, and nourishes the fertilized egg.
• Wall Layers:
  • Endometrium: Inner layer; sheds during menstruation.
  • Myometrium: Middle layer; smooth muscle.
  • Perimetrium: Outer layer (visceral peritoneum).

Uterine Tubes (Fallopian Tubes/Oviducts)

• Site of fertilization and transport ovulated oocyte to the uterus.
• No direct contact with the ovary; fimbriae catch oocyte.

Pre-Embryonic Development

• Cleavage Stages:
  • Zygote → Morula (solid ball) → Blastocyst (hollow ball) → Gastrula (with invagination).

Implantation and Ectopic Pregnancy

• Fertilized egg implants in endometrium.
• Ectopic Pregnancy: If the egg implants outside the uterus, it becomes a medical emergency.

Pregnancy and Trimesters

• Full lung maturation (surfactant production) occurs by the third trimester.

Female Reproductive Differentiation

• Genetic: XX → Female
• Gonadal: No SRY gene → Ovary development.
• Phenotypic: Estrogen and progesterone guide external genitalia differentiation.

Hormone Production by Ovaries

Oogenesis vs. Spermatogenesis

Ovarian and Menstrual Cycles (~28 days)

• Ovarian Cycle Phases:

  • Follicular Phase (Day 1–14): Follicle growth.
  • Ovulation (~Day 14): Release of oocyte.
  • Luteal Phase (Day 14–28): Corpus luteum active (secretes progesterone).

• Menstrual Cycle (Uterus):

  • Prepares uterus for implantation.
  • If no fertilization occurs → menses (endometrium sloughs off).