WEEK 6.1 GIE Reproduction Study Notes
Endocrinology of Reproduction Study Notes
Physiological Control of Reproduction
Instructor: Dr. Alex Cheong
Subjects Covered
Anatomy
Male Reproductive Physiology
Spermatogenesis
Hormonal Control
Female Reproductive Physiology
Oogenesis
Menstrual Cycle
Hormonal Control
Male Reproductive System Anatomy
Components:
Urinary bladder
Ureter
Bulbourethral gland
Ductus deferens
Bulb
Epididymis
Testis
Urethra
Glans of penis
Seminal vesicle
Prostate gland
Key Points About Male Reproductive Anatomy
Testes:
Contain Sertoli and Leydig cells for testosterone production.
Composed of lobules with sperm-producing tubes.
Spermatogonium:
Cells responsible for sperm production.
Epididymis and Ductus Deferens:
Sites for maturation, storage, and exit of sperm.
Prostate Gland:
Secretes a thin milky white seminal fluid to alkalinize the vagina and enhance sperm motility.
Seminal Vesicles:
Store seminal fluid rich in fructose, prostaglandins, and clotting factors.
Detailed Anatomy of the Testes
Components:
Vas deferens: transports sperm.
Efferent ductules: connect seminiferous tubules to epididymis.
Rete testis: Network of tubules that transport sperm.
Seminiferous tubules: Site of spermatogenesis.
Leydig Cells: Interstitial cells that secrete testosterone.
Sertoli Cells: Support and nourish developing sperm and form the blood-testis barrier through tight junctions.
Functions of Sertoli Cells
Form the blood-testis barrier.
Provide nourishment to developing sperm.
Phagocytose dead spermatogenic cells.
Secrete fluid that flushes sperm into the epididymis.
Produce androgen-binding protein (ABP) to maintain high testosterone levels in the testes.
Act in response to follicle-stimulating hormone (FSH) and testosterone.
Leydig Cells Overview
Site: Located within connective tissue between seminiferous tubules.
Function: Distinct from spermatogenesis; they secrete testosterone.
Hormonal Control: Stimulated by luteinizing hormone (LH).
Testosterone:
A steroid hormone derived from cholesterol.
Secreted into the blood, often bound to plasma proteins, including ABP from Sertoli cells.
Testosterone Actions
Refer to textbooks for detailed physiological actions of testosterone.
Hormonal Control of Testicular Function
Diagram showing control by the hypothalamus and pituitary, including the role of Gonadotrophin-releasing hormone (GnRH) from the hypothalamus:
Activates the pituitary to produce LH and FSH.
Sertoli Cells respond to these hormones to stimulate sperm production.
Spermatogenesis
Duration: Continuous process, with a single sperm taking approximately 64 days to mature.
Volume: 200 million sperm present at any one time.
Spermatogenesis Process
Initial Stage: Spermatogonium undergoes mitosis.
Primary Spermatocyte undergoes meiosis I to form two secondary spermatocytes.
Secondary spermatocytes undergo meiosis II to yield four spermatids.
Summary of Meiosis and Mitosis
Meiosis: 1n results in gametes, producing genetic variability through two rounds of division.
Mitosis: 2n leading to cloning of cells for growth and repair.
Prostate Gland Anatomy
Location: Positioned near the bladder and surrounding the sperm duct.
Function: Important in secretion of seminal fluid for sperm viability.
Male Fertility Factors
Seminal fluid improves sperm viability by alkalinizing the acidic environment of the vagina.
Challenges for sperm: Must travel through cervical mucus and face immune cells that may attack sperm.
Average sperm swim speed is approximately 5 mm/min, attributed in part to muscular movements in the female reproductive tract.
Female Reproductive Anatomy
Components:
Ovary (active endocrine organ)
Fallopian tubes
Uterus
Cervix
Vagina
Female Reproductive Cycle
Follicular Phase: Developing follicle secretes estrogen.
Luteal Phase: Corpus luteum secretes progesterone, essential for maintaining uterine lining.
Menstrual Cycle Phases
Hypothalamus releases GnRH, stimulating the anterior pituitary for FSH/LH release.
FSH stimulates follicle growth; LH surge triggers ovulation.
Follicular phase increases estrogen levels, thickening the endometrial lining.
Post-ovulation: Corpus luteum secretes hormones to prepare for potential implantation.
Folliculogenesis Control
Initiation by FSH, which stimulates estrogen production from developing follicles.
Positive feedback loop enhances more FSH secretion.
Mid-cycle LH surge triggers ovulation and formation of the corpus luteum.
Post-Ovulation Hormonal Changes
Corpus luteum secretes progesterone and estrogen, along with inhibin to regulate FSH and LH secretion.
Former corpus luteum, if not successful in implantation, degenerates into corpus albicans.
Charts and Hormonal Levels
Hormone Levels and phases related to follicular and luteal cycles shown in graphical format.
Basal body temperature changes throughout menstrual cycle phases as influenced by hormone levels.
Fertilization and Pregnancy Process
Fertilization: Sperm and egg nuclei fusion creates zygote, followed by cell division.
Implantation: Blastocyst adheres to endometrial lining; trophoblast secretes enzymes to facilitate embedding into endometrium for nutrient access.
HCG: Human chorionic gonadotropin is secreted after implantation, preserving the corpus luteum and hormonal production.
Not Pregnant Scenario
Absence of implantation results in corpus luteum degeneration, decreased progesterone levels, and resets hormonal regulation for a new cycle.
Comparison of Female and Male Reproduction
Females release about 400 eggs over their lifetime, whereas males produce around 200 million sperm continuously.
Female reproductive activity is cyclical, while male spermatogenesis is a continuous process.
Contraception and Manipulation of Reproductive Physiology
Understanding reproductive physiology aids in the development of reliable contraceptive methods.
Future Lectures
Introduction to contraception and infertility.
Discussion on menopause.
Overview of common gynecological disorders.