Lesson 1, Topic 1
In Progress

Reproductive Ducts

July 2, 2023

Overview

The reproductive ducts in the male and female reproductive tract are similar in some fundamental ways. First, both sets of ducts lead from each of the paired gonads, then join into a single passage that leads out of the body. Second, both male and female ducts carry gametes away from the gonads.

However, because humans are placental mammals, the female reproductive ducts also have central roles in receiving sperm from the male, fertilization, and prenatal development—functions not needed in the male reproductive tract. Keep these unique reproductive functions in mind as we now learn how structure fits function in the female reproductive tract.

Uterine tubes

The two uterine tubes, also called fallopian tubes or oviducts, serve as ducts for the ovaries, even though they are not attached to them. The outer end of each tube terminates in an expanded, funnel-shaped structure that has fringelike projections called fimbriae along its edge. This part of the tube curves over the top of each ovary (Figure 23-12) and opens into the pelvic cavity. The inner end of each uterine tube attaches to the uterus, and the cavity inside the tube opens into the cavity in the uterus. Each tube is about 10 cm (4 inches) in length.

FIGURE 23-12​Uterus. ​Sectioned view shows muscle layers of the uterus and its relationship to the ovaries and vagina.

After ovulation, the discharged ovum first enters the pelvic cavity and then enters the uterine tube assisted by the wavelike movement of the fimbriae and the beating of the cilia on their surface. Once in the tube, the ovum begins its journey to the uterus. Some ova never find their way into the oviduct and remain in the pelvic cavity where they are reabsorbed. In Chapter 24 the details of fertilization, which normally occurs in the outer one-third of the uterine tube, are discussed.

The mucosal lining of the uterine tubes is directly continuous with the lining of the pelvic cavity on one end and with the lining of the uterus and vagina on the other. This is of great clinical significance because infections of the vagina or uterus such as gonorrhea may pass into the abdominopelvic cavity, where they may become life threatening.

Uterus

The uterus is a small organ—only about the size of a pear—but it is extremely strong. It is almost all muscle, or 631myometrium, with only a small cavity inside. During pregnancy the uterus grows many times larger so that it becomes big enough to hold a full-term fetus and a considerable amount of fluid.

The uterus is composed of several major regions. The upper portion of the uterus is the body. Just above the level where the uterine tubes attach to the body of the uterus, it rounds out to form a bulging prominence called the fundus (see Figure 23-12). The lower, narrow neck section is called the cervix.

Except during pregnancy, the uterus lies in the pelvic cavity just behind the urinary bladder. By the end of pregnancy, it has become large enough to extend up to the top of the abdominopelvic cavity. It then pushes the liver against the underside of the diaphragm—a fact that explains a comment such as “I can’t seem to take a deep breath since I’ve gotten so big,” made by many women late in their pregnancies.

Hysterectomy is surgical removal of the uterus. It may be excised and removed through a typical incision in the abdomen (abdominal hysterectomy), through the vagina (vaginal hysterectomy), or laparoscopically (laparoscopic hysterectomy). In total hysterectomy both the body and cervix are removed; in subtotal hysterectomy only the body of the uterus is removed, sparing the cervix.

The uterus functions in three processes—menstruation, pregnancy, and labor. The corpus luteum stops secreting progesterone and decreases its secretion of estrogens about 11 days after ovulation. About 3 days later, when the progesterone and estrogen concentrations in the blood are at their lowest, menstruation starts. Small pieces of the mucous membrane lining of the uterus, or the endometrium pull loose, leaving torn blood vessels underneath. Blood and bits of endometrium trickle out of the uterus into the vagina and out of the body.

CLINICAL APPLICATION

ECTOPIC PREGNANCY

The term ectopic pregnancy is used to describe a pregnancy resulting from the implantation of a fertilized ovum in any location other than the uterus. Occasionally, because the outer ends of the uterine tubes open into the pelvic cavity and are not actually connected to the ovaries, an ovum does not enter an oviduct but becomes fertilized and remains in the pelvic cavity.

Although rare, if implantation occurs on the surface of an abdominal organ or on one of the mesenteries, development may continue to term. In such cases, delivery by cesarean section is required. Most ectopic pregnancies involve implantation in the uterine tube and are therefore called tubal pregnancies. If a tubal pregnancy is not terminated, catastrophic rupture of the uterine tube and death of both fetus and mother is likely to occur.

Immediately after menstruation, the endometrium starts to repair itself. It again grows thick and becomes lavishly supplied with blood in preparation for pregnancy.

If fertilization does not take place, the uterus once more sheds the lining made ready for a pregnancy that did not occur. Because these changes in the uterine lining continue to repeat themselves, they are spoken of as the menstrual cycle (see pp. 633-635).

If fertilization occurs, pregnancy begins, and the endometrium remains intact. The events of pregnancy are discussed in Chapter 24.

Menstruation first occurs during puberty, often around the age of 12 to 13 years but sometimes even earlier. Normally it repeats itself about every 28 days or 13 times a year for some 30 to 40 years before it ceases at the time of menopause, when a woman is somewhere around the age of 50 years.

Vagina

The vagina is a distensible tube about 10 cm (4 inches) long made mainly of smooth muscle and lined with mucous membrane. It lies in the pelvic cavity between the urinary bladder and the rectum, as you can see in Figure 23-9. As the part of the female reproductive tract that opens to the exterior, the vagina is the organ that receives the penis during intercourse and through which sperm enter during their journey to meet an ovum.

The vagina is also the organ from which a baby emerges to meet its new world, and so it is also called the birth canal.

Accessory glands

Vestibular glands

Two pairs of exocrine glands lie imbedded in tissue to the left and right of the vaginal outlet and release mucous fluid into the vestibule of the vulva (described later in Figure 23-14).

One pair of these small glands are called the greater vestibular glands, and the other pair are called the lesser vestibular glands. The greater vestibular glands are also called Bartholin glands, and the lesser vestibular glands may be called Skene glands or female prostate.

Mucus from these glands may contribute to lubrication during sexual intercourse.

The vestibular glands have clinical importance because they may become infected. For example, Neisseria gonorrhoeae—the bacteria that cause gonorrhea—are often hard to eliminate once they infect a vestibular gland (see Table 23-4).

Breasts

The breasts lie over the pectoral muscles and are attached to them by fibrous suspensory ligaments (of Cooper). Breast size is determined more by the amount of fat around the glandular (milk-secreting) tissue than by the amount of glandular tissue itself. Hence the size of the breast has little to do with its ability to secrete adequate amounts of milk after the birth of a baby.

Each breast consists of 15 to 20 divisions or lobes that are arranged radially (Figure 23-13). Each lobe consists of several lobules, and each lobule consists of milk-secreting glandular cells. The milk-secreting cells are arranged in grapelike clusters 632of small hollow chambers called alveoli (see Figure 23-13, inset). Small contractile cells surround the alveoli and push milk into ducts when stimulated by oxytocin (OT) released from the posterior pituitary gland—an event called “milk let-down.”

FIGURE 23-13​Female breast. ​Sagittal section shows the gland fixed to the overlying skin and the pectoral muscles by the suspensory ligaments (of Cooper). Each lobule of secretory tissue is drained by a lactiferous duct that opens through the nipple. The inset (left) shows one of the milk-producing alveoli of the mammary gland.

Small lactiferous ducts drain the alveoli and converge toward the nipple like the spokes of a wheel. Only one lactiferous duct leads from each lobe to an opening in the nipple. Each lactiferous duct widens into a lactiferous sinus just before reaching the nipple. Each sinus acts like the bulb at the end of an eyedropper, pumping milk out of the nipple as an infant rhythmically squeezes its jaws as it nurses.

The colored surface area around the nipple is the areola. It contains many tiny bumps called areolar glands. Areolar glands are large sebaceous glands that secrete skin oils that condition the skin while nursing an infant. The areola also has a network of smooth muscles that contract to cause the nipple to become erect—which often helps an infant latch on to the breast at the most efficient location.

Cancerous cells from breast tumors often spread to other areas of the body through the lymphatic system. This lymphatic drainage is discussed in Chapter 16 (see also Figure 16-8).

Females and males both have breasts—and either can get breast cancer. For more information on male and female breast health, check out the articles Male Breast Health and Breast Self-Examination at Connect It! at evolve.elsevier.com.

CLINICAL APPLICATION

FIBROCYSTIC DISEASE

The terms fibrocystic disease and mammary dysplasia are just two of the many names for a group of conditions characterized by benign lumps in one or both breasts. It is common in adult women before menopause, occurring in half of all women at some time, and is considered the most frequent breast lesion.

The lumps that characterize fibrocystic disease are often painful, especially during the secretory phase of the reproductive cycle. Treatment is usually aimed at relieving pain or tenderness that may occur. Although it is commonly called a disease, most experts agree that fibrocystic disease is simply a collection of normal variations in breast tissue. Even though the lumps associated with fibrocystic disease are benign, any suspicious lump or other change in breast tissue should be regarded as possibly cancerous until determined otherwise by a physician.

QUICK CHECK

  1. What is another name for the uterine tubes?
  2. What three major functions does the uterus perform?
  3. What substance is conducted through lactiferous ducts?
  4. Describe the function of the areolar glands.