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PinkMonkey Online Study Guide-Biology

24.1 Human Reproduction

(A) Male reproductive system (Figures 24.1)

It consists of following structures:


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Figure 24.1 Male reproductive system (Position in the body)

(1) Testes : The paired oval testes lie outside the abdominal cavity in man, in a skin-covered special sac called the scrotum. The main functions of the testes are the production of sperm and the synthesis of male sex hormones. Since temperature is an important factor in sperm production, the position of testes within the scrotum provides a lower temperature (at least 2-3oC lower) than within the abdominal cavity.


(2) Ducts and glands

Ducts, rete testis and epididymis. The spermatozoa from the seminiferous tubules are transported to the exterior by ducts. The seminiferous tubules open by number of vasa-efferentia that join to form a network known as the rete testis. About 20 tubes from the rete testis lead into the long (about 20 feet) coiled tube, the epididymis, located on the surface of each testis. The epididymis stores sperm before ejaculation, and secretes a small portion of the semen. As the epididymis emerges from the testes, it forms the vas deferens (ductus deferens). Each vas deferens enters the abdominal cavity through the inguinal canal, arches over the bladder and opens into the back side of the urethra. Since the urethra carries both urine and semen (sperm) it is also called the ureto--genital canal.

SEMINIFEROUS

TUBULES

(1) Sometimes the testes do not descend down into the scrotum during development and no functional sperm are produced. This condition is to known as cryptorchidism and results in sterility. In elephants and whales, temperature is not a critical factor for functional sperm and the testes are permanently located in the abdominal cavity.

(2) The human penis does not contain a bone, though it is common in many mammals. The penis bone is called a baculum.

Each testis is covered by a connective tissue covering (tunica albuginea), and send partitions inside, dividing it into lobules. Each lobule contains many seminiferous tubules, lined by germinal epithelial cells. These cells undergo the process of spermatogenesis (forming spermatogonia, primary and secondary spermatocytes, spermatids and sertoli or nurse cells), to produce spermatozoa. Between the seminiferous tubules are numerous microscopic interstitial cells (Leydig cells) which produce the male hormone, testosterone. The main functions of testosterone are development of male secondary sex characteristics, stimulation of protein anabolism and inhibition of anterior pituitary secretions of gonadotropins.


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Figure 24.3 Transverse section through a Testis

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Table of Contents


24.0 Introduction
24.1 Human reproduction
24.2 Female reproductive cycle
24.3 Embryonic Development

Chapter 25





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