Unit A Reproduction

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Male Reproductive Structures The male reproductive system is shown in Figure 2. During puberty, these primary sexual characteristics mature and enable males to reproduce. There are two testes that hang outside the abdominal cavity. The testes are enclosed in a protective sac, called the scrotum. The testes produce and nourish the developing sperm, and also produce testosterone. Each testis contains a mass of coiled tubes called seminiferous tubules, which contain diploid cells that undergo meiosis to produce haploid sperm cells. Sitting above each of the testes is the epididymis, where mature sperm are stored. Did You KNOW? Cool Sperm Most mammalian sperm cells, including human sperm cells, cannot be produced at normal body temperature. Therefore, the testes in the scrotum hang outside the abdominal cavity, where the temperature is about two degrees cooler. Whales and bats are the only mammals that permanently retain the testes in the abdominal cavity. bladder seminal vesicle vas deferens prostate urethra Cowper’s gland (bulbouretheral gland) penis epididymis testis seminiferous tubules Figure 2 The male reproductive system The Path of the Sperm Cell Mature sperm travel to the outside through two tubes. Attached to the epididymis is the vas deferens, a tube that carries the sperm to the urethra. The urethra, which is part of both the excretory and reproductive systems, transports both sperm and urine outside the body. Note that urine from the bladder cannot travel through the urethra at the same time as sperm. The penis is the organ that contains the urethra. It enters the female during sexual intercourse. Muscular contractions propel the sperm cells along. The sperm cells, together with other fluids, are ejaculated out of the erect penis when it is inside the female. LEARNING TIP Diagrams help you clarify information visually. As you study Figures 2 and 3, look back and forth between the figures and the boldface words in the text. NEL 4.1 The Male Reproductive System 109
LEARNING TIP Did you notice that Section 4.1 includes many new terms? To help you with your studying, try using index cards. On one side of a card, write a term. On the other side, write a brief definition. Male Accessory Glands Sperm cells need a fluid in which to swim, as well as nutrients to provide energy for the journey. The seminal vesicles, prostate gland, and Cowper’s glands (also called bulbourethral glands) (Figure 2) are accessory glands that secrete seminal fluid. Seminal fluid provides sugar for energy, protects the sperm from the acidic female reproductive tract, and provides the fluid for swimming. The sperm and the seminal fluid together make up semen. Sperm Production and Development Sperm cells start out as diploid cells on the inside surface of a seminiferous tubule (Figure 3). They increase in numbers by undergoing mitosis several times. These cells are gradually pushed closer to the centre of the tubule. They then undergo meiosis to become haploid cells. Even though they are haploid, they don’t yet look like mature sperm. In order to develop into sperm, they need lots of nutrients. Special support cells provide nourishment to the developing sperm. When the sperm cells are almost mature, they have reached the centre of the tubule. The sperm cells then move to the epididymis, where they finish maturing. Sperm cells have a short life cycle. It takes from 65 to 75 days for a sperm cell to mature. Males with a healthy reproductive system can produce 200 to 300 million sperm each day. Even though only one sperm cell fertilizes an egg, millions of sperm are needed because many die on the way. Sperm that are not released die within a few days and are broken down by white blood cells. New sperm cells continually replace the old sperm cells. Males can produce sperm even into old age, but the number of mature sperm decreases with age. Only mature sperm can reach and fertilize an egg. scrotum epididymis vas deferens mature sperm cell immature sperm cell testis seminiferous tubules support cell Figure 3 Sperm cells are produced in the testes, stored in the epididymis, and travel through the vas deferens. 110 <strong>Unit</strong> A <strong>Reproduction</strong> NEL
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CHAPTER 2 Cell Growth and Reproduct
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Unit A Reproduction

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