Reproductive System of the Male Mammal Help
Introduction to Reproductive System of the Male Mammal Help
In order to fully understand internal fertilization, we must first study the reproductive system of the male and female mammal (in particular, of human beings).
Figure 20.4 reveals the basic anatomy of the reproductive system in the human male. A scrotum ( SKROH -tum) or “leathery bag of skin” (scrot) suspends the two testes ( TES -teez) outside of the abdominal cavity. Each testis ( TES -tis) is a rather oval, whitish, “eggshell” (test) -like structure that contains the seminiferous (sem-ih- NIF -er-us) tubules. The seminiferous tubules are a collection of tiny, highly coiled tubes that carry out the process of spermatogenesis (sper-mat-uh- JEN -eh-sis) – the “production of” (-genesis) “sperm” (spermat) cells.
From the time of puberty (age 12–13 years) onward, mature sperm cells are continually produced by a germinal ( JER -muh-nal) epithelium, which is located in the thick walls of the seminiferous tubules. This germinal epithelium undergoes a constant process of “sprouting” (germin) new sperm cells by mitosis, followed by meiosis.
You may recall that meiosis is literally “a conditioning of lessening.” This implies that division of a parent cell by meiosis lessens or reduces the number of chromosomes in each resulting daughter cell by one-half. In the human male, each primitive sperm cell contains 46 chromosomes within its nucleus. But after meiosis, the developing sperm cell has this reduced by half, to a total of just 23 chromosomes. Eventually, a mature spermatozoon (sper- mat -uh- ZOH -un) or “seed” (sperm) “animal” (-zoon) with only 23 chromosomes results.
Thousands of mature spermatozoa ( sper -mah-tah- ZOH -ah) or “seed animals” leave the germinal epithelium of the seminiferous tubules, and are temporarily stored within the epididymis (eh-pih- DID -ih-mus). The epididymis is a curved, comma-shaped pouch that literally lies “upon” (epi-) each testis or “eggshell” (didym). The thousands of spermatozoa are ejected from the epididymis during each ejaculation (ih- JACK -yuh- lay -shun). Ejaculation is literally the “throwing out” (ejacul) of semen ( SEE -mun) and spermatozoa from the urinary orifice at the tip of the penis.
Accessory Reproductive Organs In The Male
The semen is a thick, milky, sugar-rich, very basic fluid that suspends the spermatozoa and gives them nutrition. When the male has an orgasm ( OR -gaz-um), or is literally “swollen and excited,” he ejaculates spermatozoa suspended in a fluid of semen. The stored spermatozoa are actively sucked out of the epididymis by strong peristalsis (ring-like muscular contractions) of the walls of the vas (vas) deferens ( DEF -er-enz).
The vas deferens, or “carrying away” (deferens) “vessel” (vas), is not actually a blood vessel at all. More appropriately, it is alternately called the ductus ( DUCK -tus) deferens or “carrying away duct.” During male orgasm, the walls of the vas deferens (ductus deferens) powerfully and rhythmically constrict or narrow. This negative pressure (suction) event draws the stored spermatozoa out of the epididymis, carrying them over the top of the urinary bladder and out into the urethra.
Semen is added to the spermatozoa from a number of accessory male reproductive organs. These accessory male reproductive organs include the two seminal ( SEM -ih-nal) vesicles, the two bulbourethral ( BUL -boh-you- REE -thral) glands, and the single prostate ( PRAH -state) gland.
Practice problems for these concepts can be found at: Urine and Sex in Animals Test