Male Reproductive System

TestosteroneSynthesized mainly by leydig cells in the

testes, other sources (adrenal cortex and ovarian stroma).

Transported bound to plasma proteins (albumin, globulin and other proteins).

Converted in the tissue (by binding to 5 α reductase) to dihydrotestosterone (active form).

Metabolized in the liver and excreted in the urine and bile.

ActionsMaintain and develop

the male primary and secondary sex characteristics.

FSH with testosterone is required for spermatogenesis.

Has protein anabolic effect causes growth spurt at puberty and closure of epiphysis.

Spermatogenesis (primary sex characteristic)Definition: formation of the male germ cell or

mature sperm.Spermatogenesis is a sign of reproductive

maturity.It takes 74 days to form mature sperm from a

primitive germ cell.

The first phase – the primitive germ cells (spermatogonia) divide by mitotic division to form primary spermatocytes The second phase – the primary spermatocytes undergo meiotic division (reduction division) reducing the number of chromosome to half into secondary spermatocytes, the secondary spermatocytes divide to give spermatids

The third phaseSpermatids develop and changes to spermatozoa.Spermatozoa mature around the sertoli cell

before they reach the lumen of the seminiferous tubules.

Spermatids mature into spermatozoa in the cytoplasm of the sertoli cells.

Mature spermatozoa are released from the sertoli cells and become free in the lumens of the tubules.

Sertoli cells secrete androgen-binding protein (ABP), inhibin and MIS (mullerian inhibiting substance). The stages from spermatogonia to spermatids androgen independent. Maturation from spermatid to mature spermatozoa is androgen dependent, ABP to maintain a high stable supply of androgen in the tubular fluid.

Inhibin inhibits FSH secretion.MIS causes regression of the mullerian ducts

in males during fetal life.

Endocrine control of spermatogenesis by LH and FSH from the pituitary.LH acts on the leydig cells to stimulate the production

of testosterone (primary and secondary sexual characteristics).

FSH acts on the sertoli cells.Both FSH and testosterone act on sertoli cells to

produce a high affinity androgen-binding protein (ABP) which maintain high concentration of androgen in the seminiferous tubule essential for normal spermatogenesis.

Sertoli cells secrete inhibin which control FSH release by negative feedback,

Composition of seminal fluid different from the plasmaHigh concentration of K+, glutamic acid,

aspartic acid and inositol, androgens and estrogens

Low levels of glucose and protein

The blood testes barrierDue to tight junctions between the sertoli

cells near the basal lamina of the seminiferous tubules.

This barrier prevents harmful substances e.g., drugs in the blood from reaching the lumen. Also it prevents antigenic products that formed during cell division from reaching the blood stream (autoimmune reaction).

Development of secondary sex characteristicsExternal genitalia – enlargement of penisInternal genitalia – enlargement of seminal

vesicles which begin to secrete fructose. Enlargement of prostate and bulbourethral glands.

Voice – larynx enlarges, vocal cords increase in length and thickness and voice becomes deeper

Mental – more aggressive, active attitude, interest in opposite sex develops.

Hair growth – beard appears, hairline on scalp recedes anterolaterally, pubic hair grows with male pattern (triangle with apex up towards the umbilicus), also hair appears in axillas, chest and around the anus and there increase in general body hair.

Body conformation – shoulders broaden and muscles enlarge.

Skin – sebaceous gland secretion thickens and increases (predisposing to acne). Sweat glands become more active.

Composition of human semen60% of the seminal fluid comes from the

seminal vesicles, the rest comes from prostate, vas deferens and mucous glands of the urethra.

Volume – 3.5 mL and pH = 7.5 (alkaline) coagulates dues to fibrinogen secreted from vas deferens. Prostate secrete fibrinotrypsin which causes the clot to dissolve.

Sperm count = 35-200 million/mL (male fertility), sperm count = <20 million/mL (infertility).

range(120 million)