The Male Reproductive System- Sperm Formation

Each testis is an oval structure about 5 cm long and 3 cm in diameter . A tough , white fibrous connective tissue capsule , the ____________________ ____________________ , surrounds each testis and extends inward to form septa that ____________________ the organ into lobules . There are about 250 lobules in each testis . Each lobule contains one to four highly coiled ____________________ tubules that converge to form a single straight tubule . The straight tubule leads into the ____________________ testis , a tubular network on one side of the testis . Short ____________________ ducts exit the testes . Interstitial cells , which produce male sex ____________________ , are located between the seminiferous tubules within a lobule .

Sperm are produced by the ____________________ within the seminiferous tubules . A transverse section of a seminiferous tubule shows that it is packed with cells in various stages of spermatogenesis . Interspersed with these cells , there are large cells that ____________________ from the periphery of the tubule to the ____________________ , These large cells are the supporting , or sustentacular , cells , which support and ____________________ the other cells .
Early in embryonic development , primordial germ cells enter the testes and differentiate into ____________________ , immature cells that remain dormant until ____________________ . Spermatogonia are ____________________ cells , each with ____________________ chromosomes ( 23 pairs ) , that are located around the periphery of the seminiferous tubules . At puberty , hormones ____________________ these cells to begin dividing by mitosis . Some of the daughter cells produced by mitosis remain at the periphery as spermatogonia . Others are pushed toward the lumen , undergo some changes , and become primary ____________________ , like spermatogonia , are diploid and have 46 ____________________ .

Each primary spermatocyte goes through the first meiotic division , meiosis I , to produce two secondary spermatocytes , each with 23 chromosomes . Just before this division , the ____________________ material is replicated so that each chromosome consists of two strands , called ____________________ , that are joined by a centromere . During meiosis I , one chromosome , consisting of two chromatids , goes to each secondary spermatocyte . In the second meiotic division , meiosis II , each secondary spermatocyte divides to produce two ____________________ . There is no replication of genetic material in this division , but the centromere divides so that a single - stranded chromatid goes to each cell . As a result of the two ____________________ divisions , each primary spermatocyte produces four spermatids . During spermatogenesis there are ____________________ cellular divisions , but only one ____________________ of DNA so that each spermatid has ____________________ chromosomes , one form each pair oin the original primary spermatocyte . Each sucessive stage in spermatogenesis is ____________________ toward the center of the tubule so that the more ____________________ cells are at the periphery and the more ____________________ cells are the nearer the center .

Spermatogenesis differs from mitosis because the resulting cells have only half the number of ____________________ as the original cell . When the sperm cell nucleus unites with an ____________________ cell nucleus , the full number of chromosomes is restored . If sperm and egg cells are produced by mitosis , then each successive generation would have ____________________ the number of chromosomes as the preceding one .
The final step in the development of sperm is called ____________________ . In this process , the spermatids formed from spermatogenesis become mature ____________________ , or sperm . The mature sperm cell has a head , midpiece , and tail . The head , also called the ____________________ region , contains the 23 chromosomes surrounded by the nuclear membrane . The tip of the head is covered by an acrosome , which contains ____________________ that help the sperm penetrate the female ____________________ . The midpiece , also called the ____________________ region , contains mitochondria that provides adenosine triphosphate . The tail , also called the ____________________ region , is typical flagellum for locomotion . The sperm are released into the lumen of the seminiferous tubule . Leaves the ____________________ , and enters the ____________________ , where they undergo their final ____________________ and become capable of ____________________ a female gamete .

Sperm production begins at ____________________ and continues throughout the ____________________ of a male . The entire process , beginning with a primary ____________________ , takes about ____________________ days . After ejaculation , the sperm can live for about ____________________ ____________________ in the female reproductive tract .