L40,41 and 42

Reproductive System Overview

• The lecture covers the reproductive system, focusing on male and female aspects.
• The learning objectives include understanding semen composition, ejaculation physiology, male sex hormones (testosterone), female reproductive cycles, and female sex hormones (estrogen and progesterone).

Sperm Production

• Each testicle contains seminiferous tubules, crucial for sperm production.
• Sperm develop from spermatogonia through primary and secondary spermatocytes, eventually becoming spermatids and then sperm.
• Sperm maturation takes approximately two months.
• Thousands of sperm are produced every second.

Semen Composition

• Semen comprises sperm (5-10%) and a nutrient-rich fluid (fructose, fatty acids, proteins) essential for sperm survival.
• A healthy ejaculate contains 200-500 million sperm.
• A man produces roughly 525 billion sperm throughout his lifetime.

Sperm Structure

• Sperm consists of a head (containing the nucleus with chromosomes and the acrosome with enzymes), a midpiece (with mitochondria for energy), and a tail (for motility).
• The acrosome contains enzymes necessary for penetrating the female egg.
• The midpiece contains mitochondria for energy to move the tail and thus the sperm.

Physiology of Erection and Ejaculation

• Normal male sexual function requires intact libido, the ability to achieve/maintain erection, ejaculation, and detumescence (return to flaccid state).
• The autonomic nervous system (ANS) plays a key role in these processes.

Sexual Response Cycle

• The cycle comprises excitement, plateau, orgasmic, and resolution phases.
• Excitement encompasses erection and heightened sexual awareness.
• Intensification and body responses (increased HR, BP, RR, muscle tension) occur during the plateau phase.
• Ejaculation and other culminatory responses occur during the orgasmic phase.
• The resolution phase involves the return to the pre-arousal state.

Innervation of Erection

• Erection is mediated by central (psychogenic) and peripheral (reflexogenic) innervation.
• The central nervous system (CNS) stimulates or antagonizes spinal pathways for erection and ejaculation.
• Peripheral input (reflexogenic) is involved in tactile stimulation to generate CNS response in achieving and maintaining erection.

Sexual Arousal

• Tactile stimulation from the skin or glans penis initiates tactile stimulation, which reflexively triggers ↑ PSNS (parasympathetic) vasodilator activity.
• This leads to the release of NO from endothelial cells and the relaxation of smooth muscle, leading to vasodilation.
• Prostaglandins also play a role in smooth muscle relaxation, aiding erection.
• SNS (sympathetic) inhibition contributes to erection.

Erection Mechanism

• Erection involves three cylindrical vascular cords (corpora cavernosa and corpus spongiosum) that engorge with blood.
• Blood flow into the erectile tissue increases, constricting outflow.
• The penis becomes rigid, and the emissary veins draining the penis, are compressed, preventing blood from escaping and maintaining erection.

Ejaculation

• Ejaculation, mediated by somatic motor impulses via the pudendal nerve and SNS impulses, involves rhythmic contractions of the bulbospongiosus and ischiocavernosus muscles.
• Emission (expulsion of seminal fluid into the urethra), as well as semen mixing with mucous from the bulbourethral glands are vital steps.
• Detumescence (return to flaccid state) is due to increased venous outflow, with NA (norepinephrine) and endothelin's role.

Sperm Maturation in Epididymis

• Sperm requires several days in the epididymis to mature.
• After 18-24 hours, they develop motility.
• Inhibitory proteins in the epididymal fluid prevent final motility until ejaculation.

Sperm Storage

• The testes produce up to 120 million sperm daily.
• The majority is stored in the epididymis, maintaining fertility for up to a month.
• Sperm is kept in an inactive state by multiple inhibitory substances in the ducts.

Maturation of Mature Sperm

• Mature sperm are motile and capable of fertilization in a neutral/alkaline medium.
• Their life expectancy within the female genital tract is short (1-2 days).

Seminal Vesicle and Prostate Gland Function

• Seminal vesicles secrete a mucoid fluid containing fructose, citric acid, nutrients, and prostaglandins/fibrinogen.
• The prostate gland secretes a fluid containing Calcium (Ca2+), citrate, phosphate, and enzymes essential for successful fertilization of the egg.

Effect of Sperm Count & Morphology on Fertility

• Sperm count below 20 million/ml is associated with infertility.
• Even with normal sperm count, abnormal morphology or motility can impact fertility negatively.

Hormonal Factors Stimulating Spermatogenesis

• Testosterone, crucial for testicular growth and germinal cell division, is secreted by Leydig cells.
• Luteinizing hormone (LH) stimulates Leydig cells to secrete testosterone.
• Follicle-stimulating hormone (FSH) stimulates Sertoli cells and spermatid maturation into sperm.
• Estrogen is crucial for spermatogenesis.
• Growth hormone (GH) is vital for spermatogenesis and overall testis function.

Cryptorchidism

• Cryptorchidism is the failure of the testes to descend into the scrotum.
• Treatment is recommended before puberty due to the higher incidence of malignant tumors.

Menstrual Cycle

• The menstrual cycle is the body's way of preparing for pregnancy, controlled by hormones.
• The phases include menstruation, proliferation, and ovulation.
• The cycle involves FSH, LH, estrogen, and progesterone, which regulate the maturation and release of an egg and preparation of the uterus for implantation.

Male Sexual Act

• Male sexual act comprises erection, lubrication, emission, and ejaculation.
• Erection is a parasympathetic process affecting the penis.
• Lubrication involves secretion of mucus from bulbourethral glands.
• Emission involves sympathetic stimulation of sperm and seminal fluid ducts and muscles, passing them into the urethra.
• Ejaculation involves rhythmic contractions of the muscles to propel semen out of the body.

Testosterone Function

• Testosterone is a crucial male sex hormone, responsible for the development and maintenance of male secondary sexual characteristics. These include increased body hair distribution on the face, chest, etc., baldness, voice thickening, and acne.
• Testosterone is also responsible for muscle development.
• It plays a crucial role in bone matrix formation and Ca2+ retention.
• It's essential for the descent of testes into the scrotum during fetal development.

Test your knowledge on human reproductive biology, focusing on the anatomy and physiology related to sperm production and function. Explore topics such as hormones influencing spermatogenesis and the components of semen. Ideal for students studying biology or health sciences.