D) Mammary Glands

Areola, Lobules, Alveoli, Nipple, Lactiferous ducts, Lobes, Lactiferous sinus

The mammary glands or breasts exist, of course, in both sexes, but they have a reproduction-related function only in females. Since the function of the mammary glands is to produce milk to nourish the newborn infant, their importance is more closely associated with events that occur when reproduction has already been accomplished. Periodic stimulation by the female sex hormones, especially estrogens, increases the size of the female mammary glands at puberty. During this period, the duct system becomes more elaborate, and fat is deposited---fat deposition being the more important contributor to increased breast size.

Figure 10.17

Figure 10.18

The rounded, skin-covered mammary glands lie anterior to the pectoral muscles of the thorax. Slightly below the center of each breast is a pigmented area, the areola, which surrounds a centrally protruding nipple.

Internally each mammary gland consists of 15 to 20 lobes which radiate around the nipple and are separated by fibrous connective tissue and adipose, or fatty, tissue. Within each lobe are smaller chambers called lobules, containing the glandular alveoli that produce milk during lactation. The alveoli of each lobule pass the milk into a number of lactiferous ducts, which join to form an expanded storage chamber, the lactiferous sinus, as they approach the nipple. The sinuses open to the outside at the nipple.

Make a list of the different methods of female contraception:
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FEMALE CONTRACEPTIVE LIST

As with male contraception the prevention of male and female gametes from uniting is the goal in female contraception. Abstention, or refraining from intercourse, is the most effective method of birth control. Other methods involve oral contraceptives or hormonal implants, tubal ligation, use of barrier methods such as the condom or diaphragm and use of spermicidal foams. The use of oral contraceptives which are synthetic estrogens and progesterone’s decrease the levels of LH and FSH in the pituitary thus preventing ovulation from occurring. Progesterone implants elevate hormone levels, which also prevent ovulation.

Stroma, Secondary follicles, Corpus albicans, Ovarian follicles, Primary oocytes, Corpus luteum, Primordial follicles, Secondary oocytes, Primary follicles

Examine a prepared slide of the ovary under the microscope. Locate the background substance of the ovary, which is known as the stroma. Look for circular structures in the ovary. These are the ovarian follicles. Locate the primordial follicles and the primary and secondary follicles.

Some of the follicles may contain oocytes. Primary follicles contain primary oocytes, secondary follicles contain secondary oocytes. The largest follicles in the ovary are the mature ovarian follicles, and you may be able to see one if it is present in your slide. One of these secondary oocytes is shed from the ovary during ovulation.

After ovulation the remains of a mature ovarian follicle become a corpus luteum, which primarily secretes progesterone. If pregnancy does not occur the corpus luteum decreases in size and becomes the corpus albicans.

Gonadotropic hormones produced by the anterior pituitary influence the development of ova in the ovaries and their cyclic production of female sex hormones. Within an ovary, each immature ovum develops within a saclike structure called a follicle, where it is encased by one or more layers of smaller cells called follicle cells (when one layer is present) or granulosa cells (when there is more than one layer).

The process of oogenesis, or female gamete formation, which occurs in the ovary, is similar to spermatogenesis occurring in the testis, but there are some important differences. The process begins with primitive stem cells called oogonia, located in the ovarian cortices of the developing female fetus. During fetal development, the oogonia undergo mitosis thousands of times until their number reaches 700,000 or more. They then become encapsulated by a single layer of squamouslike follicle cells and form the primordial follicles of the ovary. By the time the female child is born, most of her oogonia have increased in size and have become primary oocytes, which are in the prophase stage of meiosis I. Thus at birth, the total potential for producing germ cells in the female is already determined; the primitive stem-cell line no longer exists or will exist for only a brief period after birth.

From birth until puberty, the primary oocytes are quiescent. Then, under the influence of FSH, one or sometimes more of the follicles begin to undergo maturation approximately every 28 days.

As a follicle grows, its epithelium changes from squamous to cuboidal cells and it comes to be called a primary follicle. The primary follicle begins to produce estrogens, and the primary oocyte completes its first maturation division, producing two haploid daughter cells that are very disproportionate in size. One of these is the secondary oocyte, which contains nearly all of the cytoplasm in the primary oocyte. The other is the tiny first polar body. The first polar body then completes the second maturation division, producing two more polar bodies. These eventually disintegrate for lack of sustaining cytoplasm.

As the follicle containing the secondary oocyte continues to enlarge, blood levels of estrogens rise. Initially, estrogen exerts a negative feedback influence on the release of gonadotropins by the anterior pituitary. However, approximately in the middle of the 28-day cycle, as the follicle reaches the mature vesicular, or Graafian, follicle stage, rising estrogen levels become highly stimulatory and a sudden burstlike release of LH (and, to a lesser extent, FSH) by the anterior pituitary triggers ovulation. The secondary oocyte is extruded and begins its journey down the uterine tube to the uterus. If penetrated en route by a sperm, the secondary oocyte will undergo meiosis II, producing one large ovum and a tiny second polar body. When the second maturation division is complete, the chromosomes of the egg and sperm combine to form the diploid nucleus of the fertilized egg. If sperm penetration does not occur, the secondary oocyte simply disintegrates without ever producing the female gamete in human females.

Thus in the female, meiosis produces only one functional gamete, in contrast to the four produced in the male. Another major difference is in the relative size and structure of the functional gametes. Sperm are tiny and equipped with tails for locomotion. They have few organelles and virtually no nutrient-containing cytoplasm; hence the nutrients contained in semen are essential to their survival. In contrast, the egg is a relatively large nonmotile cell, well stocked with cytoplasmic reserves that nourish the developing embryo until implantation can be accomplished. Essentially all the zygote's organelles are "delivered" by the egg.

Once the secondary oocyte has been expelled from the ovary, LH transforms the ruptured follicle into the corpus luteum, which begins producing progesterone and estrogen. Rising blood levels of the two ovarian hormones inhibit FSH release by the anterior pituitary. As FSH declines, it stimulatory effect on follicular production of estrogens ends, and estrogen blood levels begin to decline. Since rising estrogen levels triggered LH release by the anterior pituitary, falling estrogen levels result in declining levels of LH in the blood. Corpus luteum secretory function is maintained by high blood levels of LH. Thus as LH blood levels begin to drop toward the end of the 28-day cycle, progesterone production ends and the corpus luteum begins to degenerate and is replaced by scar tissue (corpus albicans).

Figure 10.19	Figure 10.20	Figure 10.21	Figure 10.22	Figure 10.23