Human reproduction is sexual, meaning that both a female and a male partner are required for reproduction. It is important to differentiate between gonads and gametes, and to indicate that both sexes have both gonads and gametes.
This is an overview of the roles of the male reproductive system. They will be discussed in detail on following slides.
Ask students to trace the path from the testes to the penis. The path should move from testes, to the epididymis, to the vas deferens, to the ejaculatory duct merging with the urethra and following the length of the penis.
Ask students to identify places where glandular secretions enter the genital ducts. Secretions from the seminal vesicles enter the ejaculatory duct and those from the prostate enter the urethra and the ejaculatory duct. The bulbourethral gland empties into the urethra.
Testes make both the sperm (in the seminiferous tubules) and testosterone (in the interstitial cells). Within the testes, testosterone is necessary for the maturation of sperm. Sperm move from the testes into the epididymis and follow the rest of the genital tract. Why are very tight jeans and underwear sometimes associated with male infertility? These garments may increase the temperature with the testes and adversely affect development of sperm. Undescended testicles cause sterility because of elevated temperature.
The primary purpose of meiosis is to reduce the chromosomal number in the sperm to 23 chromosomes. Upon fertilization of an ovum, the number of chromosomes in the zygote returns to 46, the normal number for humans.
At fertilization, only the head of the sperm (containing the genetic information) penetrates the ovum. The enzymes of the acrosome allow the head to penetrate the ovum. What is the purpose of the flagellum? It allows the sperm to swim up the female genital tract in search of the egg in the fallopian tube
At what point do the reproductive and urinary systems merge? They merge where the ejaculatory ducts connect to the urethra. Which segments of the genital ducts are exclusively reproductive? The epididymis, vas deferens and the ejaculatory ducts are exclusively reproductive structures. The vas deferens enters the pelvic cavity with the spermatic cord.
An enlarged prostate can interfere with urination; students are likely to mispronounce the name of the gland as “prostrate.” Ask students to show on the illustration why a digital rectal exam is used to diagnose an enlarged prostate gland. The prostate gland can be digitally probed against the wall of the rectum. The glandular secretions are alkaline to protect the sperm from the acidic environment of the vagina.
The shaft of body of the penis contains three columns of erectile tissue. The erectile tissue fills with blood causing an erection. The penis has two functions. It carries urine through the urethra and it is the organ of sexual intercourse or copulation. The glans penis is the enlarged tip of the shaft. Loose connective tissue called the foreskin or prepuce covers the glans. Part of the foreskin is removed during circumcision. Is circumcision necessary to maintain cleanliness? No, the foreskin can be retracted and the organ cleaned; however, circumcision is sometimes a religious ritual.
Erection is primarily controlled by the parasympathetic system. Emission is primarily controlled by the sympathetic system. Ejaculation results from the contraction of skeletal muscle at the base of the erectile columns in the penis. Ejaculation is not under autonomic control. Immediately after ejaculation, sympathetic nerve stimulation reduces blood flow to the penis. It becomes flaccid and returns to its unstimulated size.
Testosterone makes a male look male. Why does a vasectomy act as a contraceptive without disturbing secondary sex characteristics? After a vasectomy, no sperm moves into the penis. However, the interstitial cells continue to secrete testosterone and support the secondary sex characteristics. What effect does chronic steroid abuse have? It causes the testes to atrophy, and sterility often results.
Gonadotropins from the anterior pituitary control sperm production and the secretion of testosterone. FSH causes sperm to develop in the testes. LH causes the secretion of testosterone, which in turn causes sperm maturation. In the male, LH is more commonly called interstitial cell stimulating hormone or ICSH. The diagram shows testosterone exerting a negative feedback control on both the hypothalamus (releasing hormones) and the anterior pituitary.
The gonads (ovaries) produce the gametes (ova). The ovaries secrete estrogen and progesterone. In subsequent slides, the female reproductive system is presented in both the non-pregnant and pregnant states.
The cells surrounding the oocyte are called follicular cells. A woman is born with about 2 million ovarian follicles, nature’s way of insuring the continuation of the species. The broad and ovarian ligaments anchor the ovaries.. Several follicles mature each month, but usually only one fully matures. As the egg matures, meiosis reduces the number of chromosomes from 46 to 23. At the same time, the follicle enlarges, a fluid-filled center is formed, and the follicular cells begin to secrete estrogen. The mature ovarian follicle is known as the graafian follicle. The graafian follicle looks like a blister on the surface of the ovary.
The ovarian hormones (estrogen and progesterone) affect gamete production and secondary sex characteristics. At menopause, estrogen levels decline. What are some possible bodily changes accompanying menopause? Changes include absence of menses, weakening of ligaments supporting the breasts, and redistribution of fat.
Progesterone levels always need to be understood in relationship to estrogen levels. Progesterone is dominant in the luteal phase.
Using figure 26-4A on the slide, have students traced the path from the fimbriated edges of the fallopian tubes, to the uterus, to the vagina. The ovary is not directly connected to the fallopian tube. The genital tract opens directly into the pelvic cavity; therefore, a genital tract infection can also infect the pelvic cavity causing pelvic inflammatory disease (PID).
The infundibulum has fingerlike projections called fimbriae that hang over the ovary and sweep the egg from the surface of the ovary into the fallopian tube. Cilliated cells line the fallopian tubes. These cells and peristaltic action slowly move the egg through the fallopian tube.
STDs are often fairly asymptomatic in women, so considerable damage might be done to the tubes before diagnosis. Because the fallopian tubes cannot accommodate a growing fetus, an ectopic pregnancy will cause the tube to rupture unless the ectopic pregnancy is treated surgically.
Cervical cancer is easily diagnosed and successfully treated because of the Pap smear. The fundus is massaged after delivery to help control bleeding. Massage also facilitates involution. The endometrium responds to the ovarian hormones that cause the uterine cycle. Implantation of the early embryo occurs here. A placenta develops and the baby grows here for nine months. Endometrial tissue can leave the uterus, enter the pelvic cavity, and grow on the outside of pelvic and abdominal organs. This condition, endometriosis, is painful. The myometrium is the muscular layer which is important in labor.
A baby is usually delivered vaginally; unfortunately, there is a fairly high rate of caesarian delivery in the U.S. The vagina is lined with rugae to accommodate the baby’s head and shoulders during delivery. The vagina has a normal flora which is often disturbed by antibiotic therapy. This is a common cause of yeast infection. The vagina is usually acidic and hostile to the sperm; that is why the semen is alkaline.
Like the penis, the clitoris contains erectile tissue. The obstetric perineum is sometimes the site of episiotomy during delivery. The ancient term for the uterus, hystera, derives from the Greek word hysteria, reflecting the ancients’ belief that women were made irrational by empty wombs. Contemporary terms like hysterectomy are linked to this ancient history. The anus is close to the female’s short urethra, making females more prone to urinary tract infection.
The ovarian and uterine cycles are interdependent. It is essential to read the figure vertically and consider how all the elements of the figure interact: blood levels of gonadotropins (FSH and LH from the anterior pituitary), the ovary, the blood levels of ovarian hormones, the endometrial lining of the uterus. The next 5 slides are devoted to the ovarian and uterine cycles.
The ovarian cycle drives the uterine cycle. The ovarian cycle has both an early follicular phase and later luteal phase. Ovulation separates the two phases. During the follicular phase, the egg undergoes meiosis; both the egg and the follicle develop into the graafian follicle. Estrogen dominates the follicular phase; it nourishes the ovum and starts to build up the uterine lining. At the end of the follicular phase, there is a mid-cycle surge of LH causing ovulation. The extruded egg is sucked into the fallopian tube.
The luteal phase starts with ovulation and ends with menstruation if fertilization has not occurred. The follicular cells become the corpus luteum. The term corpus luteum means yellow body, and its presence on the ovary is shown in yellow on panel B of the figure. The corpus luteum secretes progesterone, which further builds up the endometrial lining of the uterus.
Fertilization determines whether the corpus luteum dies or lives. Dead: If the ovum is not fertilized, the corpus luteum deteriorates into the corpus albicans, which does not secrete hormones. Without hormonal support, the uterine lining sloughs off as menstrual flow (the period). Alive: If the ovum is fertilized, it secretes human chorionic gonadotropin (hCG). This hormone keeps the ovarian corpus luteum alive and secretory. The hormones maintain the uterine lining and no menstrual period occurs.
The uterine cycle is driven by the ovarian cycle. During the menstrual phase, the uterine lining is very thin, an unsuitable environment for implantation. Panel D also shows the thickening of the uterine lining under the influence of estrogen (ovary). The secretory phase is dominated by progesterone (ovary). During this phase, the uterine lining is ideal for implantation.
Why does menstruation occur only in the nonpregnant state? The endometrial lining loses its hormonal support as the corpus luteum decays into the dead corpus albicans. In the pregnant state, why doesn’t the anterior pituitary secrete FSH? Estrogen and progesterone levels remain high because the corpus luteum continues to secrete these hormones. As a result, the release of FSH is not triggered (negative feedback control). This is the basis for the birth control pill.
Menarche and menopause indicate the beginning and end of the female reproductive years.
How does each of these act as a contraceptive: the pill, vasectomy, and diaphragms? The pill contains estrogen and progesterone through negative feedback control it shuts off secretion of gonadotropins and prevents development of graafian follicle. Vasectomy prevents sperm from getting into the semen. Diaphragms prevent the sperm from reaching the egg. Mifepristone (RU-486) does not prevent fertilization; it prevents implantation.
The Human Body in Health and
Illness, 4th edition