Figure 8.1 The female sex organs and reproductive structures
Figure 8.2 The menstrual cycle(a) In response to the hypothalamus, the pituitary gland releases the gonadotropins FSH and LH. Levels of FSH and LH stimulate the cycle (and in turn are affected by production of estrogen and progesterone).
(b) FSH does what its name says: It stimulates follicle development in the ovary. The follicle matures and ruptures, releasing an ovum (egg) into the fallopian tube.
(c) The follicle produces estrogen, and the corpus luteum produces estrogen and progesterone. The high level of estrogen at the middle of the cycle produces a surge of LH, which triggers ovulation.
(d) Estrogen and progesterone stimulate the endometrium, which becomes thicker and prepares to receive an implanted, fertilized egg. If a fertilized egg is deposited in the uterus, pregnancy begins. If the egg is not fertilized, progesterone production decreases, and the endometrium is shed (menstruation). At this point, both estrogen and progesterone levels have dropped, so the pituitary responds by producing FSH, and the cycle begins again.
Figure 8.3 Male sex organs and reproductive structures
Figure 8.4 A cross-sectional view of sexual intercourse
Sperm are formed in each of the testes and stored in the epididymis. When a man
ejaculates, sperm carried in semen travel up the vas deferens. (The prostate gland
and seminal vesicles contribute components of the semen.) The semen is expelled
from the penis through the urethra and deposited in the vagina, near the cervix.
During sexual excitement and orgasm in a woman, the upper end of the vagina
enlarges and the uterus elevates. After orgasm, these organs return to their normal
states, and the cervix descends into the pool of semen
Figure 8.6 How STIs spread
Most STIs are spread by viruses or bacteria carried in certain body fluids.
Figure 8.7 Continuum of risk for sexual relationships and behaviors
STI risks increase as relationships become less familiar and exclusive and as sexual
activities become unprotected and receptive.