Reproductive System Anatomy

The Reproductive System

• Primary sex organs:
  • Testes (male)
  • Ovaries (female)
• Accessory sex organs:
  • Glands
  • External genitalia

The Male Reproductive System

• Testes: Located within the scrotum.
• Scrotum:
  • Skin and superficial fascia surrounding the testes.
  • Positioning provides an environment approximately 3 degrees Celsius cooler than body temperature. This lower temperature is essential for proper sperm development.
• Dartos Muscle:
  • A layer of smooth muscle in the scrotum.
  • Responsible for wrinkling the scrotal skin, which reduces the surface area for heat loss.
• Cremaster Muscle:
  • Bands of skeletal muscle surrounding the testes.
  • Elevates the testes, bringing them closer to the body for warmth when needed.

The Testes (Detailed Structure)

• Enclosed in a serous sac called the tunica vaginalis.
• Tunica Albuginea: Fibrous capsule of the testes.
  • divides each testis into 250-300 lobules.
• Lobules:
  • Contain 1-4 coiled seminiferous tubules where sperm production occurs.
• Epididymis:
  • Comma-shaped structure on the posterior testis.
  • This is where sperm mature and are stored.

Structure of the Testis

• Spermatic Cord: Contains blood vessels and nerves.
• Ductus Deferens: Transports sperm during ejaculation.
• Epididymis: Site of sperm maturation and storage.
• Testis: Produces sperm and testosterone.

Microscopic Structure of the Testis

• Areolar Connective Tissue: Surrounds the seminiferous tubules.
• Interstitial Endocrine Cells (Leydig Cells): Produce testosterone, which is crucial for male sexual development and function.
• Myoid Cells: Contractile cells that surround the seminiferous tubules and help move sperm and fluids through the tubules.
• Seminiferous Tubules: Site of sperm production.
• Sustentocytes (Sertoli Cells): Support and nourish developing sperm cells.
• Spermatogenic Cells: Cells in the tubule epithelium that differentiate into sperm.

Nerves and Vessels of the Testes

• Arterial Supply: Testicular arteries provide blood to the testes.
• Venous Drainage:
  • Testicular veins arise from the pampiniform plexus, a network of veins that surrounds the testicular artery.
  • The pampiniform plexus helps cool arterial blood before it enters the testes, aiding in temperature regulation.
• Innervation: Testes are innervated by parasympathetic and sympathetic divisions of the autonomic nervous system (ANS).

Microscopic Anatomy of Seminiferous Tubules

• Seminiferous Tubules:
  • Separated by areolar connective tissue.
• Epithelium consists of:
  • Spermatogenic Cells: Sperm-forming cells.
  • Columnar Sustentocytes: Support cells (also known as Sertoli cells).

Sustentocytes (Sertoli Cells) Details

• Surround spermatogenic cells, providing support and nutrients.
• Extend from the basal lamina to the lumen of the seminiferous tubules.
• Tight Junctions:
  • Form the blood-testis barrier, which protects developing sperm from the immune system.
• Functions:
  • Assist in sperm production.
  • Secrete testicular fluid and androgen-binding protein (ABP).

Myoid and Interstitial Cells

• Myoid Cells:
  • Surround seminiferous tubules and contract rhythmically to help move sperm and fluids.
• Interstitial Endocrine Cells (Leydig Cells):
  • Secrete testosterone.
  • Secretion is regulated by luteinizing hormone (LH) from the pituitary gland.

The Epididymis

• Duct of the epididymis is approximately 6 meters long when uncoiled.
• Epithelium:
  • Dominated by pseudostratified columnar epithelium.
  • Bears tufts of stereocilia (immotile, long microvilli) that increase surface area for absorption and secretion.
• Sperm Maturation:
  • It takes about 20 days for sperm to move through the epididymis.
  • During this time, sperm gain the ability to swim and to fertilize an egg through the acrosomal reaction.

The Ductus Deferens

• Stores and transports sperm during ejaculation.
• Histology:
  • Epithelium: Pseudostratified columnar epithelium.
  • Muscularis: Thick layer of smooth muscle that facilitates peristaltic contractions to move sperm.
  • Adventitia: Outer connective tissue layer.

The Spermatic Cord

• Contains:
  • Ductus deferens
  • Testicular blood vessels
  • Nerves
• Course:
  • The superior portion of the ductus deferens runs through the inguinal canal.

The Urethra (Male)

• Carries sperm and urine from the ejaculatory ducts to the outside of the body.
• Three Parts:
  • Prostatic urethra: Runs through the prostate gland.
  • Intermediate part of urethra (membranous urethra): Short segment between the prostatic and spongy urethra.
  • Spongy urethra (penile urethra): Runs through the penis and opens at the external urethral orifice.

Accessory Glands (Male)

• The Prostate:
  • Encircles the prostatic urethra.
  • Consists of 20-30 compound tubuloalveolar glands.
  • Secretes approximately 25-30% of seminal fluid.
• Secretions Contain:
  • Substances that enhance sperm motility.
  • Enzymes that clot and then liquefy semen, aiding in sperm transport.

The Bulbo-Urethral Glands (Cowper's Glands)

• Pea-sized glands inferior to the prostate gland.
• Secretion:
  • Produce a mucus that enters the spongy urethra prior to ejaculation.
• Functions:
  • Neutralizes traces of acidic urine in the urethra.
  • Lubricates the urethra to ease the passage of semen.

The Penis

• External Anatomy:
  • Shaft (body): The main portion of the penis.
  • Glans penis: Distal expanded end.
  • Prepuce (foreskin): Cuff of skin covering the glans, which may be removed during circumcision.

The Male Perineum

• Contains: Scrotum, root of penis, and anus.
• Boundaries:
  • Pubic symphysis anteriorly
  • Coccyx posteriorly
  • Ischial tuberosities laterally

Spermatogenesis (Sperm Production)

• Divided into three stages:
  • Stage 1: Spermatogonia divide by mitosis
    • Type A: Maintain the germ cells.
    • Type B: Differentiate into primary spermatocytes.
  • Stage 2: Meiosis I and Meiosis II
    • Meiosis I: Forms two secondary spermatocytes.
    • Meiosis II: Each spermatocyte forms two spermatids.
  • Stage 3: Spermiogenesis
    • The four spermatids differentiate into spermatozoa (sperm).
    • Spermatozoa shed superfluous cytoplasm and develop a head, midpiece, and tail.

Spermatogenesis and Sustentocytes

• Sustentocytes surround spermatogenic cells.
• Tight Junctions:
  • Divide seminiferous tubules into:
    • Basal compartment: Contains spermatogonia and early primary spermatocytes.
    • Adluminal compartment: Contains later-stage spermatocytes and spermatids.

Blood-Testis Barrier

• Tight junctions between sustentocytes form the blood-testis barrier.
• This barrier protects developing sperm from the immune system, which recognizes sperm as foreign.

Hormonal Control of Spermatogenesis

• Spermatogenesis is controlled by:
  • Follicle-stimulating hormone (FSH) from the pituitary gland.
  • Testosterone from interstitial endocrine cells.
• Sustentocyte Secretions:
  • Androgen-binding protein (ABP) concentrates testosterone near spermatogenic cells.
  • Inhibin inhibits FSH secretion when sperm production is high, providing negative feedback.

The Female Reproductive System

• Produces gametes (ova).
• Prepares to support a developing embryo.
• Undergoes changes according to the menstrual cycle.
  • The menstrual cycle is the monthly cycle as it affects all female reproductive organs.
• Includes:
  • Ovaries
  • Uterine tubes, uterus, and vagina

The Ovaries

• Small, almond-shaped organs.
• Produce ova (eggs).
• Support:
  • Held in place by ligaments and mesenteries:
    • Broad ligament
    • Suspensory ligament
    • Ovarian ligament
• Vascular Supply:
  • Ovarian arteries provide the arterial supply.
• Innervation:
  • Innervated by both divisions of the autonomic nervous system (ANS).

Internal Structure of the Ovaries

• Tunica Albuginea:
  • Fibrous capsule of the ovary.
  • Covered in simple columnar epithelium.
• Ovarian Cortex:
  • Houses developing oocytes within follicles.
  • Follicles are multicellular sacs housing oocytes.
• Ovarian Medulla:
  • Loose connective tissue containing blood vessels, lymph vessels, and nerves.

The Uterine Tubes (Fallopian Tubes)

• Receive ovulated oocyte from the ovary.
• Parts:
  • Infundibulum: Distal end of uterine tube, surrounded by fimbriae that help capture the oocyte.
  • Ampulla: Middle third of uterine tube; the usual site of fertilization.
  • Isthmus: Medial third of uterine tube.

Supports of the Uterus

• Uterus is supported by:
  • Mesometrium: Anchors the uterus to the lateral pelvic walls.
  • Cardinal ligaments: Horizontal ligaments from the cervix and vagina to the pelvic walls.
  • Round ligaments: Bind the uterus to the anterior pelvic wall.

Uterine Wall

• Wall of the uterus composed of:
  • Perimetrium: Serous layer; the peritoneum.
  • Myometrium:
    • Interlacing bundles of smooth muscle.
    • Contracts during childbirth to expel the fetus.
  • Endometrium:
    • Mucosal lining of uterine cavity.
• Layers of Endometrium
  *Functionalis layer
  *Basal layer

Endometrium Layers

• Embryo burrows into the endometrium during implantation.
• Endometrium has two layers:
  • Functional layer (stratum functionalis): Undergoes cyclic changes in response to ovarian hormones and is shed during menstruation.
  • Basal layer (stratum basalis): Forms a new functional layer after menstruation ends.

Uterine Arteries

• Uterine arteries send branches to the uterine wall and divide into arcuate arteries.
• Arcuate Arteries:
  • Radial arteries reach the endometrium and branch into:
    • Straight arteries: Supply the basal layer.
    • Spiral arteries: Supply the functional layer and undergo degeneration and regeneration with each menstrual cycle.

The Female Menstrual Cycle and Oogenesis

• Menstrual Cycle:
  • Monthly cycle due to hormonal fluctuations in ovaries and uterus.
• Ovarian Cycle:
  • Stimulates production of ovarian follicles and oocytes.
• Uterine Cycle:
  • Prepares uterine wall for implantation.

The Ovarian Cycle Phases

• Has three successive phases:
  • Follicular phase
  • Ovulation
  • Luteal phase

The Ovarian Cycle: Follicular Phase

• Antrum Formation:
  • A fluid-filled cavity forms between granulosa cells.
• Follicle Development:
  • Primary follicles become secondary follicles.
• Corona Radiata:
  • A coat of granulosa cells surrounding the oocyte.
• Vesicular (Graafian) Follicle:
  • Secondary follicle enlarges and becomes a vesicular follicle, ready to be ovulated.

The Ovarian Cycle: Ovulation

• Occurs about halfway through each ovarian cycle (day 14).
• One mature oocyte exits from one ovary.
• Enters peritoneal cavity and is swept into the uterine tube.
• Trigger:
  • Sudden increase in luteinizing hormone (LH) is the signal for ovulation.

The Ovarian Cycle: Luteal Phase

• Occurs after ovulation in the last half of the ovarian cycle.
• Corpus Luteum Formation:
  • The remaining follicle becomes a corpus luteum.
• Progesterone Secretion:
  • The corpus luteum secretes progesterone, which acts to prepare for implantation of an embryo.
• Fate of Corpus Luteum:
  • If no implantation occurs, the corpus luteum dies and becomes a corpus albicans.

Oogenesis (Egg Production)

• Takes many years to complete.
• Meiosis I Arrest:
  • Primordial follicles are arrested (stalled) in meiosis I.
• Meiosis I Completion:
  • The surge of LH also causes the primary oocyte to complete meiosis I.

Oogenesis Outcomes

• Oogenesis produces only one ovum and three polar bodies.
• Polar Bodies:
  • Do not contribute to the developing embryo.
• Meiosis II:
  • Completed only if sperm penetration occurs.

The Uterine Cycle (Menstrual Cycle)

• Series of cyclic phases of the endometrium.
• Phases coordinate with the ovarian cycle.
• Endometrial phases are directed by follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• Phases;
  *Menstrual phase-days 1–5
  *Stratum functionalis is shed
  *Proliferative phase-days 6–14
  *Secretory phase-days 15-28

The Vagina

• Consists of three coats:
  • Adventitia: Fibrous connective tissue.
  • Muscularis: Smooth muscle.
  • Mucosa: Marked by transverse folds; consists of lamina propria and stratified squamous epithelium.
• Hymen:
  • An incomplete diaphragm at the vaginal opening.
• Fornix:
  • Recess formed at the superior part of the vagina around the cervix.

External Genitalia and Female Perineum

• Clitoris:
  • Anterior to vestibule.
  • Erectile tissue homologous to the penis.
• Female Perineum:
  • Anterior boundary: Pubic arch.
  • Posterior boundary: Coccyx.
  • Lateral boundaries: Ischial tuberosities.

The Mammary Glands (Breasts)

• Modified sweat glands.
• Glandular Structure:
  • Undeveloped in nonpregnant women.
• Milk Production (Lactation):
  • Starts at or after childbirth.

Implantation

• Timing:
  • Blastocyst begins implantation about 6 days after conception.
• Blastocyst Structure:
  • Consists of an inner cell mass (future embryo) and outer trophoblast.
• Trophoblast Layers:
  • Cytotrophoblast: Inner layer.
  • Syncytiotrophoblast: Outer layer, which erodes into the endometrium.

Placenta Formation

• Embryonic and maternal tissues contribute to the placenta.

Anatomy of the Placenta

• Exchanges Across Chorionic Villi:
  • Occur between maternal and fetal blood.
• Functions:
  • Provide the fetus with nutrients and oxygen.
  • Dispose of fetal wastes.
  • Allow hormonal signals to be sent to the mother.
• Formation:
  • By week 13, the placenta is fully formed.

Placental Anatomy Details

• Placental Barrier Consists Of:
  • All three layers of the chorionic villi.
• Diffusion
  *Sugars, fats, and oxygen diffuse from mother to fetus
  *Urea and carbon dioxide diffuse from fetus to mother

Placental Function

• Syncytiotrophoblast:
  • Secretes substances that regulate events of pregnancy.
• Transport:
  • Maternal antibodies are transported across the placenta, providing passive immunity to the fetus.
• Harmful Substances:
  • Viruses, alcohol, and heroin can cross the placental barrier.

Childbirth (Parturition)

• Parturition: Occurs approximately 266 days after fertilization.
• Labor:
  • Events that expel the infant from the uterus.

Reproductive System Cancers in Males

• Testicular Cancer:
  • Affects 1 of 50,000 males.
  • Commonly originates from early-stage spermatogenic cells.
  • Increase of 50% from 1974 to 1990.
  • Cured in 95% of cases with early detection and treatment.
• Prostate Cancer:
  • Slow-growing cancer.
  • Arises from peripheral glands of the prostate.
• Risk Factors:
  • Fatty diet
  • Genetic predisposition

Reproductive System Cancers in Females

• Ovarian Cancer:
  • Arises from cells in the germinal epithelium of the ovary.
• Endometrial Cancer:
  • Arises from the endometrium of the uterus.
• Cervical Cancer:
  • Slow-growing cancer.
  • Arises from epithelium at the tip of the cervix.
  • Often caused by human papillomavirus (HPV); preventable with vaccination and screening.
• Breast Cancer:
  • Second most common cause of cancer deaths in women.
  • 97% of cases occur in women over 50.

Treatment of Breast Cancer

• Surgical removal of the mass (lumpectomy).
• Radiation therapy.
• Administration of selected hormones (hormone therapy).
• Chemotherapy.

Embryonic Development of the Sex Organs

• Embryo at 5-6 weeks is sexually indifferent.
• Mesonephric Ducts (Wolffian Ducts):
  • Future male ducts.
• Paramesonephric Ducts (Müllerian Ducts):
  • Future female ducts.

Male Sexual Differentiation

• Male embryos: sexual differentiation begins in week 7.
• Mesonephric Duct Development:
  • Becomes the epididymis, ductus deferens, and ejaculatory duct.
• Paramesonephric Duct Fate:
  • Degenerate.

Female Sexual Differentiation

• Female embryos: sexual differentiation begins in week 8.
• Ovary Development:
  • Cortical portion of immature ovaries forms ovarian follicles.
• Paramesonephric Duct Development:
  • Becomes the uterus, uterine tubes, and superior part of the vagina.
• Mesonephric Duct Fate:
  • Degenerate.

Puberty

• Period of life between ages 10 and 15.
• Reproductive organs grow to their adult size.
• Events of puberty occur in the same sequence in all individuals, but the age at which these events occur varies widely.

Male Puberty

• Secondary Sex Characteristics:
  • Enlargement of the scrotum and testes (about age 13).
  • Appearance of pubic, axillary, and facial hair.
  • Lengthening of vocal folds, leading to a deepening voice.
  • Musculoskeletal system increases in mass.
• Sexual Maturation:
  • Mature sperm appear in semen.

Female Puberty

• Secondary Sex Characteristics:
  • Budding breasts (around age 11).
  • Menarche: The first menstruation.

Other Female Puberty Characteristics

• Increase in subcutaneous fat.
• Widening and lightening of the bones of the pelvic girdle.
• Appearance of axillary and pubic hair.
• Growth Spurt:
  • Estrogen-induced growth spurt from age 12 to 17.

Menopause

• Female reproductive peak: Late 20s.
• Follicle Degeneration:
  • Around age 35, the rate of follicle degeneration increases.
• Cessation of Ovulation and Menstruation:
  • Typically occurs between ages 46 and 54.
• Ovarian Hormone Secretion:
  • Ovaries stop secreting estrogen.
• Reproductive Organ Changes:
  • Reproductive organs and breasts begin to atrophy.