Male reproductive system

I. Introduction

- role: production of sex cells and production of offspring -- in the male specific function is to produce gametes and deliver them to the female reproductive tract for fertilization.

- reproductive system consists of :

• primary sex organs (gonads): produce sex cells or gametes and secrete sex hormones.
• accessory reproductive organs: ducts, glands, external genitalia.

II. Anatomy of male reproductive system.

- sex organs (gonads): testes, produce sperm

- system of ducts to deliver sperm to exterior: epididymis, ductus deferens, urethra

- accessory sex glands: empty contents into ducts during ejaculation, materials to nourish, protect, activate sperm

• seminal vesicles
• prostate gland
• bulbourethral glands

A. Scrotum

- sac of skin and fascia that hangs outside abdominopelvic cavity

- testes suspended in scrotum by cremaster muscle

- to produce viable sperm testes temperature must be at 3 degrees C below body temp; cremaster raises or lowers testes to keep them at this optimal temp.

B. Testes

- male gonads

- surrounded by two layers connective tissue, innermost divides testes into 250-300 wedges or lobules, each lobule contains 1-4 sets of highly coiled tubules, seminiferous tubules (site of spermatogenesis).

- between seminiferous tubules are the interstitial cells of Leydig, produce testosterone.

- seminiferous tubules converge to form rete testis prior to epididymis.

- rich blood supply -- testicular arteries and veins

- innervated by PS and SYM divisions of ANS.

C. Duct system

1. sperm move from seminiferous tubules ---> rete testis ---> epididymis

2. epididymis on top, posterior aspect of each testis -- location where sperm mature and become mobile; can remain there for several months

- during ejaculation epididymis contracts, sperm moved to ductus deferens

3. ductus deferens propels sperm from epididymis storage site into urethra -- during ejaculation they contract vigorously

4. urethra conveys both urine and semen (sperm and secretions of accessory glands, see below

• prostatic urethra: enclosed by prostate
• membranous urethra: prostate ---> penis
• penile urethra: in penis

D. Accessory glands

1. seminal vesicles: secretion make up 60% of semen

- contents (enter prostatic urethra during ejaculation):

• ascorbic acid
• coagulating enzyme: coagulates semen in vagina to form a big clump and protect sperm from acidity of vagina.
• prostaglandins: cut viscosity of cervical mucus and cause uterine contractions
• fructose: nutrition for sperm

2. prostate gland: surrounds urethra, secretion makes up 13-33% of semen

- alkaline secretion with enzymes -- activate sperm, neutralize acidity of urethra, vagina.

3. bulbourethral glands: pea sized glands

- produce thick, clear mucus prior to ejaculation, neutralize acidity of urethra.

E. Penis

- cylindrical organ -- deliver sperm to female reproductive tract.

- cross section shows three long bodies of erectile tissue each surrounded by a fibrous CT; during sexual excitement, arousal, vascular spaces in erectile tissue fill with blood, penis enlarges and becomes rigid.

F. Semen: sperm and accessory gland secretions.

III. Physiology of male reproductive system.

A. Spermatogenesis: sperm formation in seminiferous tubules -- basal cells are immature, more luminal cells are more mature

- begins at puberty

- involves reduction of number of chromosomes by 1/2, production of haploid cells (46 (2n)- 23 (n) chromosomes): spermatogonium (2n)---> primary spermatocyte (2n) ---> secondary spermatocytes (n) ---> spermatids (n) ---> sperm (n) (only mature in epididymis).

- role of sustentacular cells (Sertoli cells): supporting cells in tubules -- nutrition of developing sperm cells?

B. Hormone regulation

a. hypothalamus produces gonadotrophin releasing hormone (GnRH) ---> goes to anterior pituitary, stimulates AP cells to produce follicle stimulating hormone (FSH) and luteinizing hormone (LH)

- FSH: stimulates Sertoli cells to produce a protein (androgen-binding protein) that aids testosterone binding to spermatogenic cells

- LH: stimulates Leydig cells to produce testosterone

- testosterone in turn causes negative feedback of GnRH, FSH, LH

b. development hormone patterns

- GnRH and testosterone levels in infant or midpubertal boy similar; levels drop until mid puberty as very small amounts of testosterone inhibit GnRH release.

- at puberty GnRH release only inhibited by much greater testosterone levels -- thus testosterone levels increase dramatically, testosterone and GnRH levels cycle dramatically; eventually stable adult levels of both hormones achieved.

c. other roles of testosterone

- maintenance of all accessory ducts and glands

- development of male secondary sex characteristics: pubic and facial hair, deepening of voice, thickening of skin, increased bone size and density, increased muscle mass.