Male reproductive physiology

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Male reproductive physiology:

Male reproductive physiology Dr.Gogoi Department of Physiology, University of Fiji

PowerPoint Presentation:

Male Reproductive System

TESTES: ONE PAIR:

HAS SEMENIFEROUS TUBULES: SERTOLI CELLS SPERMATOGONIA SPERM CELLS IN VARIOUS STAGES INTERSTITIAL CELLS OF LEYDIG: SECRETE TESTOSTERONE, THE MALE REPRODUCTIVE HORMONE TESTES: ONE PAIR

DUCTULAR SYSTEM:

RETE TESTIS EFFERENT DUCTULES EPIDIDYMIS VAS DEFERENS FUNCTION: TRANSPORT OF MATURE SPERMATOZOA. DUCTULAR SYSTEM

GLANDS:

SEMINAL VESICLES PROSTATE GLAND: BOTH SECRETING SEMEN BULBO-URETHRAL GLANDS: SECRETE A MUCOID SUBSTANCE GLANDS

Male reproductive system:

Male reproductive system Three major subdivisions: (1) spermatogenesis which means simply the formation of Sperm (2) performance of the male sexual act; and (3) regulation of male reproductive functions by the various hormones.

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During formation of the embryo, the primordial germ cells migrate into the testes and become immature germ cells called spermatogonia which lie in two or three layers of the inner surfaces of the seminiferous tubules .The spermatogonia begin to undergo mitotic division, beginning at puberty, and continually proliferate and differentiate through definite stages of development to form sperm.

Spermatogenesis I::

Spermatogenesis I: The immature germ cell in the male is referred to as the spermatogonium. These cells are located just under the basement membrane of the seminiferous tubules, between adjoining sustentacular (Sertoli) cells. Since sperm production continues throughout adult life and at the peak, 100-200 million sperm can be produced daily, the spermatogonia are constantly renewed. The first step in spermatogenesis is a mitotic division of the spermatogonium. One of the daughter cells remains, to replace the original spermatogonium, while the other cell (now called a primary spermatocyte) undergoes meiosis.

Spermatogenesis :

Spermatogenesis Spermatogonia: Replicate initially by mitosis. One of the 2 primary spermatocytes undergoes meiosis: 2 nuclear divisions: 1st meiotic division produces 2 secondary spermatocytes. 2nd meiotic division produces 4 spermatids.

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Cell divisions during spermatogenesis

Spermatogenesis II::

Spermatogenesis II: The first meiotic division yields two secondary spermatocytes. Usually, these secondary spermatocytes do not fully separate during cell division, leaving a direct cytoplasmic connection between the cells. Following the second meiotic division (again, an incomplete division), the cells are known as spermatids. As the germ cells are undergoing meiosis, they also migrate towards the lumen of the seminiferous tubule. As they approach the lumen, they shed much of their cytoplasm. They are attached to the Sustentacular cells, via specialized junctions, which provide nutrients. When the spermatids reach the lumen, they remain embedded within the sustentacular cells, where they undergo tail development, acrosome formation and nuclear condensation. Finally, the fully-formed spermatozoa are shed into the lumen of the seminiferous tubule, where they are carried to the epididymus. This whole process takes between 60 and 70 days.

Spermiogenesis:

Maturation of spermatozoa. Phagocytosis of cytoplasm by the Sertoli cells. Cytoplasm is eliminated. Spermiogenesis

Spermiogenesis :

Spermiogenesis Spermatid undergo change in shape and orientation of organelles:- nucleus undergo condensation and forms head. golgi apparatus forms the acrosome mitochondria forms the tail part provide energy for movement

Sertoli Cells:

Sertoli Cells Form blood-testes barrier: Prevents autoimmune destruction of sperm. Produce FAS ligand which binds to the FAS receptor on surface to T lymphocytes, triggering apoptosis of T lymphocytes. Prevents immune attack. Secrete inhibin. Phagocytize residual bodies: May transmit information molecules from germ cells to Sertoli cells. Secrete androgen-binding protein (ABP): Binds to testosterone and concentrates testosterone in the tubules.

Continued…:

Continued… Secrete mullerian inhibiting substance Secrete seminiferous tubular luminar fluid:- secrete watery ,solute rich (k+ and HCO3-) fluid into the lumen.

Structure of a spermatozoon:

Structure of a spermatozoon 55-65 µm in length Three parts head, neck and tail. On the outside of the anterior two thirds of the head is a thick cap called the acrosome that is formed mainly from the Golgi apparatus. It contains enzymes similar to those found in lysosomes hyaluronidase and powerful proteolytic enzymes . These play important roles in allowing the sperm to enter the ovum and fertilize it.

Continued..:

Continued.. The tail of the sperm, called the flagellum , has three major components: (1) a central skeleton constructed of 11 microtubules, collectively called the axoneme (2) a thin cell membrane covering the Axoneme (3) a collection of mitochondria surrounding the axoneme in the proximal portion of the tail (called the body of the tail ). Back-and-forth movement of the tail (flagellar movement) provides motility for the sperm. This movement results from a rhythmical longitudinal. The energy for this process is supplied in the form of adenosine triphosphate that is synthesized by the mitochondria in the body of the tail. Normal sperm move in a fluid medium at a velocity of 1 to 4 mm/min.

Hormonal control of spermatogenesis:

Hormonal control of spermatogenesis Testosterone - essential for growth of germinal testicular cells Luteinizing hormone - stimulates the Leydig cells to secrete testosterone. Follicle-stimulating hormone - for conversion of the spermatids to sperm (the process of spermiogenesis). Estrogens – essential for spermiogenesis. Growth hormone (as well as most of the other body hormones) is necessary for controlling background metabolic functions of the testes.

Male Accessory Organs:

Male Accessory Organs Epididymis responsible for: Maturational changes. Resistance to pH changes and temperature. Storage of sperm between ejaculations. Ductus (vas) deferens: Carries sperm from epididymis into pelvic cavity. Seminal vesicles secrete: Fructose. Prostate secretes: Alkaline fluid. Citric acid. Ca2+. Coagulation proteins.

Effect of temp. on spermatogenesis:

Effect of temp. on spermatogenesis Spermatogenesis requires a temperature considerably lower than that of the interior of the body. The testes are normally maintained at a temperature of about 32 °C. Applied:- Cryptorchidism i.e. failure or incomplete descent of testes they may lie in the lumbar region , in the iliac fossa,in inguinal canal, or the upper part of scrotum. incidence 10% at birth which falls to 0.3% at puberty. Effects –spermatogenesis fails to occur in undescended testis . testosterone secretion is normal. more likely to develop malignant tumor. Treatment – surgical correction and also testosterone administration.

Erection, Emission, and Ejaculation:

Erection, Emission, and Ejaculation Erection: Controlled by hypothalamus and spinal cord. Increased vasodilation of arterioles. Parasympathetic nervous system. NO is the NT. Blood flow into the erectile tissues of the penis. Emission: Movement of semen into the urethra. Stimulated by sympathetic nervous system. Ejaculation: Forcible expulsion of semen from the urethra out of the penis. Stimulated by sympathetic nervous system.

Semen : composition :

Semen : composition S emen contains sperms and the secretions of the seminal vesicles, prostate, Cowper's glands, and, probably, the urethral glands. An average volume per ejaculate is 2.5-3.5 mL after several days of abstinence. Even though it takes only one sperm to fertilize the ovum, there are normally about 100 million sperms per milliliter of semen. Fifty percent of men with counts of 20-40 million/mL and essentially all of those with counts under 20 million/mL are sterile. The presence of many morphologically abnormal or immotile spermatozoa also correlates with infertility.

Continued…:

Continued… Appearance :- is milky due to prostate secretions Specific gravity :- 1.028 Reaction :- is alkaline pH 7.5 helps to bring vaginal pH from 3.5-6.5 which aids in sperm motility Coagulant nature when ejaculated but liquefies after 15-20mins. Secretions of seminal vesicles have fructose, phosphorylcholine,ergothionine ,ascorbic acid and prostaglandins. These provide nutrition to sperm and help in fertilization. Prostate gland secretions help in maintaining pH etc.

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The bulbourethral glands are paired glands that secrete a small amount of thick clear mucus. This secretion is released prior to ejaculation and is believed to neutralize traces of acidic urine in the urethra. The prostate gland is a single gland, which secretes about one third of the semen volume. It secretes a milky, slightly acidic fluid containing citrate, acid phosphatase and several proteolytic enzymes. These enzymes are probably involved in breaking down the mucus plug in the cervix. They also appear to contribute to the motility and viability of the sperm

Sperm capacitance: :

Sperm capacitance: Freshly ejaculated sperm are incapable of fertilizing an egg. As the sperm travel up the female reproductive tract, they lose cholesterol from their membranes When the sperm reach the fallopian tubes, the membranes around the acrosome are fragile enough to allow the release of the acrosomal enzymes.

Male Fertility:

Male Fertility 60-150 million sperm/ml ejaculate. Oligospermia: Sperm count of < 20 million/ml ejaculate. Decreased fertility caused by heat, pharmaceuticals, and illicit drugs. Male contraception: Compounds that suppress gonadotropin secretion. Testosterone. Progesterone and GnRH antagonist. Vasectomy: Each ductus deferens is cut and tied. Interferes with sperm transport. May develop anti-sperm antibodies.

Testosterone :

Testosterone Interstitial Cells of Leydig in the Testes. Androgens, including testosterone, dihydrotestosterone, and Androstenedione. Production of Estrogen in the Male. one fifth the amount in the nonpregnant Female. The exact source of estrogens in the male is unclear, but the following are known: the concentration of estrogens in the fluid of the seminiferous tubules is quite high and probably plays an important role in Spermiogenesis. This estrogen is believed to be formed by the Sertoli cells by converting testosterone to estradiol. Much larger amounts of estrogens are formed from testosterone and androstanediol in other tissues of the body, especially the liver.

Control of testosterone secretion:

Control of testosterone secretion Negative feedback: Testosterone inhibits LH and GnRH production. Maintain relatively constant secretion of LH and FSH. Declines gradually in men over 50 years of age. Testosterone converted to DHT, which inhibits LH. Inhibin inhibits FSH secretion

Derivatives of Testosterone:

Derivatives of Testosterone

Endocrine Function of the Testes:

Testosterone and its derivatives are responsible for initiation and maintenance of body changes in puberty. Stimulate growth of muscles, larynx, and bone growth until sealing of the epiphyseal discs. Promote hemoglobin synthesis. Act in paracrine fashion, responsible for spermatogenesis. Endocrine Function of the Testes

PowerPoint Presentation:

1. INITIATION & MAINTAINANCE OF SPERMATOGENESIS 2.  GnRH FROM THE HYPOTHALAMUS 3. INHIBITS LH SECRETION VIA ANTERIOR PITUITARY. 4. DIFFERENTIATION & MAINTAINANCE OF MALE SECONDARY SEXUAL CHARACTERISTICS:Facial Hair & Body Habitus. TESTOSTERONE - FUNCTIONS 5. INDUCES DIFFERENTIATION & MAINTAINS ACCESSORY REPRODUCTIVE ORGANS. 6. STIMULATES PROTEIN ANABOLISM , BONE GROWTH & IT’S CESSATION. 7. ENHANCES LIBIDO & AGGRESSIVE BEHAVIOUR BY MASCULINIZING THE BRAIN. 8. STIMULATES SECRETION OF ERYTHROPOIETIN FROM THE KIDNEYS

Brain-testicular axis::

Brain-testicular axis:

Applied aspects:

Applied aspects Hypogonadism in males :- due to absent or deficient testicular functions Congenital nonfunctioning of testis Underdeveloped testis due to absence of HCG in fetal life Cryptochidism due to partial or total degeneration of seminiferous tubules Absence of androgen receptors in testis

Hypogonadism…:

Hypogonadism… Frohlich’s syndrome :- adipose genital syndrome or hypothalamic eunuchoidism this is hypogonadism which occurs due to hypothalamic disorders pituitary disorders genetic inability to secrete LHRH and GnRH

Hypergonadism :

Hypergonadism Due to excessive secretion of male sex hormones as in tumors of leydig cells. Features:- rapid growth of musculature and bones height is less due to early closure of epiphysis excessive development of sexual characters secrete estrogens which causes gynaecomastia

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