February 5, 2015

Senior Inter Zoology Human Reproduction Chapter Summary

1. Testes: There is a pair of oval, pinkish testes, that lie outside the abdominal cavity, in special pouch called scrotum [because in scrotum the temperature is less than (2°C - 2.5°C) that of abdomen, which is necessary for spermatogenesis]. The cavity of scrotum is connected to the abdominal cavity through inguinal canal. Tests are held in position in scrotum by spermatic cords (extends between testes and abdomen) and gubernaculum. Each spermatic cord is formed by an artery, a vein, a nerve and other tissues.

A testis is enclosed by a tunica vaginalis. Below the tunica vaginalis is a fibrous sheath called tunica albuginea. It projects inwards as septa and divides the testis into many lobules. Each lobule contains 1 - 3 highly coiled seminiferous tubules. They are lined by germinal epithelium. Germinal epithelial cells divide and form spermatogonia (sperm mother cells). They divide further and produce primary spermatocytes. These primary spermatocytes undergo meiotic divisions and form the sperms/ spermatozoa [The process of formation of sperms is known as spermatogenesis].

Among the germinal epithelial cells, sertoli cells. They provide nutrition for developing sperms and secrete a hormone called inhibin, which inhibits the secretion of FSH. Among the seminiferous tubules, there are Leading cells, or interstial cells. They secrete testosterone. It is necessary for the development of secondary sexual characters in male. Seminiferous tubules open into the vasa efferentia. Through a network of minute tubules called rete testis.

2. Epididymis: It is a long, narrow and highly, coiled present along the posterior surface of each kidney. In epididymis, sperms are stored, where the mature epididymis is divisible into three parts, namely, caput epididymis (receives sperms through vasa efferentia), corpus epididymis (connects caput epididymis and cauda epididymis) and cauda epididymis (it is attached to the scrotum through gubernaculum).

3. Vasa deferentia: The long narrow, muscular tube arising from the cauda epididymis is the vas deferns. The inner lining of vas diferens is formed by pseudostratified epithelium and lamina propria (areolar tissue). Vas deferens passes through the inguinal canal, loops over the urinary bladder, receives a duct from seminal vesicle and become an ejaculatory duct. The ejaculatory ducts of both sides converge and opens into the urethra.

4. Urethra: It is the common passage for urine and sperms. It originates in the urinary bladder, receiver the ejaculatory ducts, passes through the penis and opens out through urethral meatus.

5. Penis: Penis is the copulatory organ that transfers the sperms to the vagina of female. It is formed by two dorsal (corpora cavernosa) and a ventral (corpus spongiosum) columns of special tissue that helps in erection. The enlarged tip of the penis is called glans penis, which is covered by loose skin called prepuce. Urethra lies in corpus spongiosum.

6. Accessory glands:

a. Seminal vesicles: Near the posterior part of urinary bladder there is a pair of simple tubular glands known as seminal vesicles. Each seminal vesicle opens into the corresponding vas deferens. Seminal vesicles secrete about 60% of the seminal fluid. It is an alkaline, viscous fluid that contains prostaglandins, fructose, proteins, citric acid, inorganic phosphorus and potassium. Prostaglandins cause the mucus lining of cervix to be more receptive to the sperms and activate sperms fructose is the energy source for sperms.

b. Prostate gland: It lies beneath the urinary bladder. It surrounds the urethra and sends its secretions into it. Prostate secretion forms 15 - 30% of seminal fluid. It activates the sperms and provides nutrition.

c. Bulbo urethral glands/ Cowper's glands: Behind the prostate gland, at the beginning of penis, is a pair of Cowper's glands. The secretions of these glands are alkaline, lubricates the urethra and makes it alkaline by fluship out the acidic urine residues.

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