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Male Reproductive Physiology

Dr.Mohammed Sharique Ahmed QuadriAssistant professor physiology

Al Maarefa College

بسم الله الرحمن الرحيم

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Objectives • Describe the structure of the testis physiological functions

of the major components of the male reproductive tract. • Explain how the secretions of FSH and LH are regulated in

the male and describe the actions of these hormones on the testis.

• Describe spermatogenesis and the role of Sertoli cells, Leydig cells and the basement membrane in this process.

• Explain the hormonal control of spermatogenesis and describe the effects of androgens on the male accessory sex organs.

• Describe the composition of semen, • Discuss the various factors that affect male fertility.

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Male Reproductive Physiology

• Testes– Development of testis occurs in abdominal cavity, Descent

is usually complete by seventh month of gestation.– Descend into scrotum

• Location provides cooler environment essential for spermatogenesis

– Perform dual function• Produce sperm

– Occurs within seminiferous tubules• Secrete testosterone

– Produced by Leydig (interstitial) cells that lie in connective tissue between seminiferous tubules

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Structure of Testis

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Male Reproductive Physiology

• Testosterone – Steroid hormone derived

from cholesterol precursor molecule

– It is synthesized from the cholesterol in the Leydig cells and also from the androstenedione secreted by the adrenal cortex

– Testosterone secretion rate is 4-9mg/dL in normal adults and very small amount is secreted in women

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Male Reproductive Physiology

• Testosterone – Five categories of testosterone effects• Effects on Reproductive system before birth• Effects on Sex-specific tissues after birth• Other reproductive-related effects• Effects on Secondary sexual characteristics• Non-reproductive actions

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Effects of Testosterone• Effects before Birth

– Masculinizes the reproductive tract and external genitalia– Promotes descent of the testes into the scrotum

• Effects on Sex-Specific Tissues after Birth Promotes growth and maturation of the reproductive system at puberty

– Enlargement and maturation of gonads, – Development of secondary sexual characteristics, – Achievement of fertility(Is essential for spermatogenesis)– Growth and maturation of the reproductive tract, and

Maintains the reproductive tract throughout adulthood

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Effects of Testosterone(continues)

• Other Reproduction-Related Effects– Develops the sex drive at puberty– Controls gonadotropin hormone secretion by negative

feedback

• Effects on Secondary Sexual Characteristics– Induces the male pattern of hair growth (e.g., beard)– A deep voice because of thickening of the vocal folds.– Thick skin – Promotes muscle growth responsible for the male body

configuration.( as a result of protein-anabolic affect)

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Effects of Testosterone(continues)

• Nonreproductive Actions– Exerts a protein anabolic (synthesis) effect– Promotes bone growth at puberty– Closes the epiphyseal plates after being converted

to estrogen by aromatase– Stimulates oil secretion by sebaceous glands

(results in development of acne).– May induce aggressive behavior

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Does males also have Estrogen?

• Small amount produce by adrenal cortex

• A portion of the testosterone secreted by the testes is converted to estrogen outside the testes by the enzyme aromatase, which is widely distributed but most abundant in adipose tissue

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Spermatogenesis• Complex process by which diploid primordial germ cells

(spermatogonia) are converted into motile haploid spermatozoa (sperm).

• It takes 64 days for development of mature sperm from spermatogonium (several hundred million sperm may reach maturity daily)

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Spermatogenesis• Three major stages– Mitotic proliferation

• Spermatogonia divide mitotically to give rise to two daughter cells

• Sperm-forming daughter cell divides mitotically twice more to form four identical primary spermatocytes

– Meiosis• Each primary spermatocyte forms two secondary

spermatocytes yielding four spermatids after the second meiotic division

• Theoretically, sixteen spermatozoa result from each spermatogonium that goes through process

– Packaging • Production of motile spermatozoa from spermatids

(Spermiogenesis).

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Spermatogenesis

Spermiogenesis: Spermatids to Sperm

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Spermatozoa

Consists of four parts• Head

• Consists primarily of the nucleus (contains DNA)

• Acrosome• containing hydrolytic enzymes

that allow the sperm to penetrate and enter the egg

• Midpiece• Area where mitochondria are

concentrated • Tail

• Provides mobility for spermatozoa

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Functions of Sertoli cellslocated in seminiferous tubules

– Form blood-testes barrier– Provide nourishment– Phagocytic function– Secrete seminiferous

tubule fluid which flushes released sperm from tubule into epididymis for storage and additional processing

– Secrete androgen-binding protein

– Site of action for testosterone & FSH to control spermatogenesis• Release inhibin,Acts

in negative-feedback fashion to regulate FSH secretion• Also released

Mullerian inhibiting factor ( fetal development)

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Hypothalamic & pituitary Control on Testicular Function

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Role of Accessory Sex Glans & Reproductive Tract

• Epididymis and ductus deferens – Store and concentrate sperm

– Increase sperm motility and fertility prior to ejaculation

– Secret defensin , protect sperm from microorganisms

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Role of Accessory Sex Glans &• Seminal vesicles– Sperm and seminal fluid mix in the ejaculatory duct and enter the

prostatic urethra during ejaculation

– Supply fructose f(energy source for sperms)

– Contribute to 60% of the semen volume

– Secrete fibrinogen

– Supply prostaglandins• Promote smooth muscle contraction in both male and female

reproductive tracts (enhances sperm transport)

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Role of Accessory Sex Glans

• Prostate gland–Contributes alkaline fluid that neutralizes acidic

vaginal secretions( sperms are more viable in slightly alkaline environment)

–Provides clotting enzymes and prostate-specific antigen(PSA)-fibrin degrading enzyme

• Bulbourethral glands–Release lubricating mucus

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Semen• Milky white, sticky mixture of sperm and

accessory gland secretions• Viscous alkaline fluid containing fructose,

coagulating enzyme , and prostaglandins• Provides a transport medium and nutrients

(fructose), protects and activates sperm, and facilitates their movement

• Average volume is 2.5-3.5 ml per ejaculate • Normally 100 million sperm/ml of semen

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Location and Functions of the Components of the Male Reproductive System

Abnormalities of testicular functionCryptorchidism – descent of testes is incomplete one or less commonly both side, testes remain in the abdomen

Male hypogonadism: Clinical picture depends on whether testicular deficiency develops before or after puberty. causes:– Testicular disease(Hypergonadotrophic Hypogonadism)– Disorder of hypothalamus or pituitary (Hypogonadotrophic

Hypogonadism)

Androgen secreting tumors : Leydig cell tumors (a rare condition) leads to precocious pseudopuberty in prepubertal boys

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Don’t Forget the QUIZ on Saturday12/05/2012

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References

• Human physiology by Lauralee Sherwood, seventh edition

• Text book physiology by Guyton &Hall,11th edition

• Text book of physiology by Linda .s contanzo,third edition