Medical brain notes 27

  MEIOSIS   The cell division process of  meiosis  produces the gametes—sperm or egg cells. In meiosis, one cell with the diploid number of chromosomes (46 for humans) divides twice to form four cells, each with the haploid number of chromosomes.  Haploid  means half the usual diploid number, so for humans the haploid number is 23. Although the process of meiosis is essentially the same in men and women, there are some important differences.   SPERMATOGENESIS   Spermatogenesis  is the process of meiosis as it takes   place in the testes, the site of sperm production. Within each testis are seminiferous tubules  that contain spermatogonia, which are stem cells that gen-erate sperm. A spermatogonium divides by mitosis to form two cells, one of which will remain in place as a stem cell, while the other differentiates (specializes) to become a primary spermatocyte that will undergo meiosis (Fig. 20–1). As you may recall, gamete formatio...

  MALE REPRODUCTIVE SYSTEM   The male reproductive system consists of the testes and a series of ducts and glands. Sperm are produced in the testes and are transported through the repro-ductive ducts: epididymis, ductus deferens, ejaculatory duct, and urethra (Fig. 20–3). The reproductive glands produce secretions that become part of semen, the fluid that is ejaculated from the urethra. These glands are the seminal vesicles, prostate gland, and bul-bourethral glands.   TESTES   The  testes  are located in the  scrotum , a sac of skin between the upper thighs. The temperature within the scrotum is about 96 8 F, slightly lower than body temperature, which is necessary for the production of viable sperm. In the male fetus, the testes develop near the kidneys, then descend into the scrotum just before birth.  Cryptorchidism  is the condition in which the testes fail to descend, and the result is sterility unless the testes are surgically placed i...

  FEMALE REPRODUCTIVE SYSTEM   The female reproductive system consists of the paired ovaries and fallopian tubes, the single uterus and vagina, and the external genital structures (Fig. 20–5). Egg cells (ova) are produced in the ovaries and travel through the fallopian tubes to the uterus. The uterus is the site for the growth of the embryo-fetus. Figure 20–5.  Female reproductive system shown in a midsagittal section through the   pelvic cavity. QUESTION:  Where is the uterus with respect to the urinary bladder, and why is this impor-tant?   OVARIES   The  ovaries  are a pair of oval structures about 1.5 inches (4 cm) long on either side of the uterus in the pelvic cavity (Fig. 20–6). The ovarian ligament extends from the medial side of an ovary to the uter-ine wall, and the broad ligament is a fold of the peri toneum that covers the ovaries. These ligaments help keep the ovaries in place.   Figure 20–6.  Female reproductive system...