Medical brain notes 44

  Physiologic Anatomy of the Male Sexual Organs Figure 80–1 A  shows the various portions of the male reproductive system, and Figure 80–1 B  gives a more detailed structure of the testis and epididymis. The testis is composed of up to 900 coiled  seminiferous tubules,  each averaging more than one half meter long, in which the sperm are formed. The sperm then empty into the  epididymis , another coiled tube about 6 meters long. The epididymis leads into the  vas deferens , which enlarges into the  ampulla of the vas deferens  immediately beforethe vas enters the body of the prostate gland.          Two  seminal vesicles , one located on each side of the prostate, empty into the pro-static end of the ampulla, and the contents from both the ampulla and the seminal vesicles pass into an  ejaculatory duct  leading through the body of the prostate gland and then emptying into the  intern...

  Spermatogenesis 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  (a cross section of one is shown in Figure 80–2 A ). The spermatogonia begin to undergo mitotic division, beginning at puberty, and continually proliferate and differentiate through definite stages of development to form sperm, as shown in Figure 80–2 B. Steps of Spermatogenesis Spermatogenesis occurs in the seminiferous tubules during active sexual life as the result of stimulation by anterior pituitary gonadotropic hormones, begin-ning at an average age of 13 years and continuing throughout most of the remainder of life but decreasing markedly in old age. In the first stage of spermatogenesis, the spermatogonia migrate among  Sertoli cells  toward the central lumen of the seminiferous tubule. The Sertoli...

  Steps of Spermatogenesis Spermatogenesis occurs in the seminiferous tubules during active sexual life as the result of stimulation by anterior pituitary gonadotropic hormones, begin-ning at an average age of 13 years and continuing throughout most of the remainder of life but decreasing markedly in old age. In the first stage of spermatogenesis, the spermatogonia migrate among  Sertoli cells  toward the central lumen of the seminiferous tubule. The Sertoli  cells are very large, with overflowing cytoplasmic envelopes that surround the developing spermatogo-nia all the way to the central lumen of the tubule. Meiosis.  Spermatogonia that cross the barrier into theSertoli cell layer become progressively modified and enlarged to form large primary spermatocytes  (Figure 80–3) .  Each of these, in turn, undergoes meiotic division to form two  secondary spermatocytes . After another few days, these too divide to form  spermatids  that are ev...

  Function of the Seminal Vesicles Each seminal vesicle is a tortuous, loculated tube lined with a secretory epithelium that secretes a mucoid material  containing an  abundance  of   fructose ,  citric  acid , and  other nutrient  substances, as  well  as large quantities of  prostaglandins  and  fibrinogen .  During the process of emission and ejaculation, each seminal vesicle empties its contents into the ejacula-tory duct shortly after the vas deferens empties the sperm. This adds greatly to the bulk of the ejaculated semen, and the fructose and other substances in the seminal fluid are of considerable nutrient value for the ejaculated sperm until one of the sperm fertilizes the ovum. Prostaglandins are believed to aid fertilization in two ways: (1) by reacting with the female cervical mucus to make it more receptive to sperm movement and (2) by possibly causing backward, reverse peri-staltic contraction...

  Function of the Prostate Gland The prostate gland secretes a thin, milky fluid that contains calcium, citrate ion, phosphate ion, a clotting enzyme, and a profibrinolysin. During emission, the capsule of the prostate gland contracts simultaneously with the contractions of the vas deferens so that the thin, milky fluid of the prostate gland adds further to the bulk of the semen. A slightly alkaline characteris-tic of the prostatic fluid may be quite important for successful fertilization of the ovum, because the fluid of the vas deferens is relatively acidic owing to the presence of citric acid and metabolic end products of the sperm and, consequently, helps to inhibit sperm fertility. Also, the vaginal secretions of the female are acidic (pH of 3.5 to 4.0). Sperm do not become opti-mally motile until the pH of the surrounding fluids rises to about 6.0 to 6.5. Consequently, it is probable that the slightly alkaline prostatic fluid helps to neu-tralize the acidity of the other semi...

  Semen Semen, which is ejaculated during the male sexual act, is composed of the fluid and sperm from the vas deferens (about 10 per cent of the total), fluid from the seminal vesicles (almost 60 per cent), fluid from the prostate gland (about 30 per cent), and small amounts from the mucous glands, especially the bulbourethral glands. Thus, the bulk of the semen is seminal vesicle fluid, which is the last to be ejaculated and serves to wash the sperm through the ejaculatory duct and urethra. The average pH of the combined semen is about 7.5, the alkaline prostatic fluid having more than neutral-ized the mild acidity of the other portions of the semen. The prostatic fluid gives the semen a milky appearance, and fluid from the seminal vesicles and mucous glands gives the semen a mucoid consistency. Also, a clotting enzyme from the prostatic fluid causes the fibrinogen of the seminal vesicle fluid to form a weak fibrin coagulum that holds the semen in the deeper regions of the vagina...

  Abnormal Spermatogenesis and Male Fertility The seminiferous tubular epithelium can be destroyed by a number of diseases. For instance, bilateral orchitis of the testes resulting from  mumps causes sterility in some affected males. Also, some male infants are born with degenerate tubular epithelia as a result of strictures in the genital ducts or other abnormalities. Finally, another cause of sterility, usually temporary, is  excessivetemperature of the testes . Effect of Temperature on Spermatogenesis.  Increasing thetemperature of the testes can prevent spermatogenesis by causing degeneration of most cells of the semini-ferous tubules besides the spermatogonia. It has often been stated that the reason the testes are located in the dangling scrotum is to maintain the temperature of these glands below the internal temperature of the body, although usually only about 2°C below the inter-nal temperature. On cold days, scrotal reflexes cause the musculature of the scr...

  Neuronal Stimulus for Performance of the Male Sexual Act The most important source of sensory nerve signals for initiating the male sexual act is the  glans penis . The glans contains an especially sensitive sensory end-organ system that transmits into the central nervous system that special modality of sensation called  sexualsensation . The slippery massaging action of intercourseon the glans stimulates the sensory end-organs, and the sexual signals in turn pass through the pudendal nerve, then through the sacral plexus into the sacral portion of the spinal cord, and finally up the cord to undefined areas of the brain. Impulses may also enter the spinal cord from areas adjacent to the penis to aid in stimulating the sexual act. For instance, stimulation of the anal epithe-lium, the scrotum, and perineal structures in general can send signals into the cord that add to the sexual sensation. Sexual sensations can even originate in internal structures, such as in areas of...