Anatomy and Physiology: Reproductive System

Reproductive System Lecture Notes

• Topic: Overview of the Reproductive System
• Speaker: Dr. Pugazhandhi Bakthavatchalam
• Institution: American University of Antigua
• Course: Anatomy and Physiology

Learning Outcomes

• Students should be able to describe the composition of semen.
• Students should be able to describe the physiology of ejaculation.
• Students should be able to describe male sex hormones (testosterone) during fetal life, puberty, and adulthood, including regulation and secretion.
• Students should be able to describe the female reproductive cycle (ovarian and uterine cycles), including hormonal changes.
• Students should be able to describe female sex hormones (estrogen and progesterone) and their regulation.

Sperm Production

• Each testis contains approximately 800 seminiferous tubules.
• Sperm begin as blob-like cells (spermatogonia).
• Sperm pass through stages (primary and secondary spermatocytes) becoming smaller and developing tails (spermatids).
• Spermatids mature into sperm with tails.
• Thousands of sperm are produced every second, taking about two months to mature.

Sperm Count

• Semen (seminal fluid) is more than just sperm.
• Sperm accounts for 5-10% of ejaculate.
• The remaining 90-95% consists of fructose, fatty acids, and proteins to nourish sperm.
• A man produces roughly 525 billion sperm in his lifetime and close to 1 billion per month.
• An average ejaculate contains 200-500 million sperm.

Sperm Structure

• Sperm consists of a head, midpiece, and tail.
• The head contains the nucleus (chromosomes) and acrosome (enzymes for penetrating the egg).
• The midpiece contains mitochondria to provide energy for movement.
• The tail propels the sperm forward.

Physiology of Erection and Ejaculation

• Normal male sexual function requires intact libido, the ability to achieve and maintain penile erection, ejaculation, and detumescence (return to a flaccid state).

Sexual Response Cycle

• Excitement Phase: Erection and heightened sexual awareness.
• Plateau Phase: Intensified bodily responses (increased heart rate, blood pressure, breathing rate, muscle tension).
• Orgasmic Phase: Ejaculation and other responses culminating in sexual excitement.
• Resolution Phase: Return to pre-arousal state.

Innervation

• Erections are mediated by central (psychogenic) and peripheral (reflexogenic) innervation.
• Central innervation (e.g., mental stimulation).
• Peripheral innervation (e.g., tactile stimulation).
• Tactile stimulation triggers parasympathetic nervous system (PSNS) vasodilation, releasing nitric oxide (NO), inducing vascular smooth muscle relaxation, and blood flow.
• Sympathetic nervous system (SNS) inhibition leads to erection.

Erection

• A vascular phenomenon involving three cylindrical vascular cords (corpora cavernosa and corpus spongiosum).
• Infact blood vessels constrict, allowing inflow, causing rigidity.

Ejaculation

• Emission: Mediated by sympathetic nervous system impulses (T11-L2 spinal segments). Contraction of epididymis, ductus deferens, seminal vesicles, and prostate. Internal vesicle sphincter closes, preventing semen from entering the bladder.
• Expulsion: Mediated by somatic motor impulses (pudendal nerve). Rhythmic contractions of bulbospongiosus and ischiocavernosus muscles increase pressure in the penis, expelling semen.
• Detumescence: Return to flaccid state mediated by norepinephrine (NA) from sympathetic nerves, endothelin from vascular endothelium, and smooth muscle contraction.

Spermatogenesis Maturation and Storage

• Sperm maturation occurs within the epididymis (18-24 hours, develops its capability of motility). Inhibitory proteins affect motility until after ejaculation.
• Mature sperm stored in the epididymis (most of them)maintain fertility for a month, in an inactive state by substances in the ducts' secretions.
• Adult human testes produce up to 120 million sperm daily.

Physiology of Mature Sperm

• Mature sperm are motile and capable of fertilizing an ovum in a slightly alkaline medium, becoming inactive in an acidic medium.
• Life expectancy in the female genital tract is 1-2 days.

Seminal Vesicle and Prostate Gland Function

• Seminal vesicles secrete a mucoid material containing fructose and prostaglandins.
• The prostate gland secretes a thin milky fluid containing Ca2+, citrate, phosphate, a clotting enzyme and profibrinolysin, and is important for fertilization success.

Effect of Sperm Count on Fertility

• Normal ejaculation volume averages 3-5 ml.
• Normal sperm count ranges from 35 to 200 million sperm per ml.
• Sperm count below 20 million per ml often leads to infertility.
• Sperm morphology and motility are also crucial for fertility; abnormal shapes or lack of motility can cause infertility even with a normal count.
• About half the sperm can be abnormal and still be infertile.

Hormonal Factors Stimulating Spermatogenesis

• Testosterone: Produced in the interstitial (Leydig) cells of the testes; crucial for growth and division of testicular cells.
• Luteinizing Hormone (LH): Secreted by the anterior pituitary; stimulates Leydig cells to produce testosterone.
• Follicle-Stimulating Hormone (FSH): Secreted by anterior pituitary; stimulates Sertoli cells, converting spermatids to sperm and crucial for spermatogenesis.
• Estrogen: Formed from testosterone; essential for spermatogenesis under FSH stimulation.
• Growth Hormone (GH): Necessary for controlling testis metabolic functions; crucial in spermatogonia division. Absence of GH is strongly linked to infertility.

Male Sexual Act

• Erection: Parasympathetic impulses from the sacral spinal cord, through pelvic nerves to the penis.
• Lubrication: Parasympathetic impulses to urethral and bulbourethral glands to secrete mucus.
• Emission: Sympathetic nerves stimulate vas deferens and ampulla. Prostate and seminal vesicles expel their fluids into the internal urethra. Mucous from bulbourethral glands form the semen along with the fluids.
• Ejaculation: Increased pressure forces semen out of the urethra.

Testosterone

• Secretion: Interstitial (Leydig) cells in the testes.
• Male Sex Hormones (Androgens): Testosterone, dihydrotestosterone, and androstenedione.
• Testosterone is the most abundant, but dihydrotestosterone is the most active form and found in target cells.
• Fetal Development: Stimulates the development of male genitalia, suppresses female genitalia development.
• Puberty: Enlargement of secondary sexual characteristics like penis, scrotum, hair and voice changes,.
• Adult Life: Maintains characteristics and is responsible for the body's masculine characteristics.

Cryptorchidism

• Failure of the testes to descend into the scrotum during fetal life.
• Treatment before puberty is crucial due to a higher risk of malignant tumors.

The Menstrual Cycle

• The body's way of preparing for pregnancy, controlled by hormones.
• Key phases:
  • Menstruation: Uterus lining breaks down.
  • Proliferation: Uterus lining repairs.
  • Ovulation: Release of an egg.
• Hormones involved: FSH, LH, estrogen, progesterone.

References

• List of textbooks and articles cited.

This quiz covers key concepts of the reproductive system as discussed in the Anatomy and Physiology lecture by Dr. Pugazhandhi Bakthavatchalam. Students will explore topics such as semen composition, ejaculation physiology, and hormonal regulation in both male and female reproductive cycles.