CHAPTER TWENTY-SEVEN
The Reproductive System
27.1 Anatomy & Physiology of the Male Reproductive System A. Function: manufacture gametes (sperm) and to deliver them to the female reproductive tract, where fertilization can occur. B. It consists of gonads (which produce the gametes and hormones), accessory glands and organs (that secrete fluids into ducts), and perineal structures that form the external genitalia. 1. Scrotum = pouch of skin containing the testis, or gonad of the male. a. Divided into two scrotal cavities by a scrotal septum marked externally by a raised ridge called the raphe. b. Allows testicles to descend outside the body cavity where they can remain cooler and proper sperm production can occur. Proper sperm production occurs at three degrees lower than body temperature. c Two muscles are associated with the scrotums ability to change size and shape during temperature changes: Dartos muscle=smooth muscle layer that wrinkles the scrotal sac trapping warm air. ii. Cremaster muscle=skeletal muscle layer that pulls testicles close to the body thus regulating temperature. 2. Testes = paired, oval-shaped gonads of the male located in the scrotum. a. Descend through the inguinal canal during development. b. Produce sperm within the seminiferous tubules via spermatagonia and their helper cells sertoli cells or sustentacular cells. While the interstitial cells produce androgens, specifically testosterone. C. Surrounded by two connective tissue layers: the tunica vaginalis (both parietal and visceral layers) as well as the tunica albuginea = an tough, inner fibrous capsule that extends internally to divide the testes into 250-300 lobules which each contain one to four seminiferous tubules (site of sperm production). d. From the seminiferous tubules of the testis, the sperm is transported via the tubulus rectus (straight tubule) into the rete testis and then out the efferent ductules into the epididymis e. Testes descend through the abdominal musculature into the scrotal cavity during the 7th month of development. Cryptorchidism is when 1 or both of the testes fail to descend out of the abdominal cavity. Spermatogenesis = sperm formation begins during puberty and continues throughout life. Occurs in the seminiferous tubules of the testes and generally takes 9 weeks ii. Requires three steps: 1) mitosis of the spermatogonia followed by 2) one of the daughter cells undergoing meiosis to form the gametes and 3) differentiation of immature male gametes into physically mature sperm called spermiogenesis. a. Mitosis of spermatogonia = each division of a diploid spermatogonium produces two daughter cells. One is a spermatogonium that remains in contact with the basal lamina of the tubule, and the other is a primary spermatocyte that is pushed towards the lumen of the tubule. b. Meiosis I = as meiosis I begins, each primary spermatocyte contains 46 individual chromosomes. At the end of meiosis I, the daughter cells are called secondary spermatocytes. Every secondary spermatocyte contains
23 chromosomes, each of which consists of a pair of duplicate chromatids
c. Meiosis II = the secondary spermatocytes soon enter meiosis II, which yields four haploid spermatids, each containing 23 chromosomes. Fo