CMQ TS

Sexual reproduction is the production of offspring. First, here are some general facts:

Sexual reproduction involves two parents (unlike one-parent asexual reproduction); it increases variation of genetic traits among offspring of the same parents.

Gametes are sex cells that fuse at fertilization to form a one-celled zygote, the first cell of the offspring.

Sperm is the gamete from the male parent. The ovum is the gamete from the female parent.

Reproductive hormones regulate sexual characteristics that promote successful reproduction.

The ability to reproduce begins at puberty.

Some common general structures and functions can be identified between the systems in both sexes.

The reproductive systems are adapted for development of sperm or ova followed by successful fertilization, development, and birth of offspring.

Sex hormones in both sexes are important in the development of secondary sexual characteristics and normal reproductive system activity.

Now we’ll review the male reproductive system.

The reproductive tract in the male is also called the urogenital tract.

Reproductive organs are classified as essential or accessory.

Essential organs of reproduction are the gonads (or testes), which produce sex cells called sperm or spermatozoa.

Accessory organs of reproduction include the ducts, passageways that carry sperm from the testes to the exterior; sex glands that produce protective and nutrient solution for the sperm; and the external genitals.

Testes, the gonads of men, are located in the scrotum, which keeps them at a lower temperature.

The testes are covered by the tunica albuginea, a membrane that divides each testis into lobules containing seminiferous tubules.

Functions of the testes are spermatogenesis and production of testosterone.

Spermatogenesis is the process of sperm production.

Sperm precursor cells are called spermatogonia.

Meiosis produces the primary spermatocyte, which forms four spermatids with 23 chromosomes.

Spermatozoa are small, mobile cells.

The head of a spermatozoon contains genetic material.

The acrosome contains enzymes to assist sperm in penetration of the ovum.

Mitochondria in the midpiece provide energy for movement.

The tail is actually a flagellum.

Testosterone is produced by interstitial cells.

Testosterone “masculinizes” and promotes and maintains the development of male accessory organs.

It stimulates protein anabolism and development of muscle strength.

Reproductive ducts in the male are ducts through which sperm pass after exiting the testes until they exit from the body.

The epididymis is a single, coiled tube about 6 m in length; it lies along the top and behind each testis in the scrotum.

Sperm mature and develop the capacity for motility as they pass through the epididymis.

The vas deferens, also called the ductus deferens, receives sperm from the epididymis and transports them from the scrotal sac through the abdominal cavity.

It passes through the inguinal canal and then joins the duct of the seminal vesicle to form the ejaculatory duct.

Accessory glands produce components of semen.

Semen, also called seminal fluid, is a mixture of sperm and secretions of accessory sex glands. It averages 3 to 5 mL per ejaculation, with each milliliter containing about 100 million sperm, but is highly variable, even day to day.

The seminal vesicles are pouchlike glands that produce about 60% of seminal fluid volume. Their secretion is yellowish, thick, and rich in fructose to provide energy needed by sperm for motility.

The prostate gland is shaped like a doughnut and located below the bladder. The urethra passes through the prostate gland. Secretion from the prostate represents 30% of seminal fluid volume; it is thin and milk-colored. Prostatic secretion activates sperm and is needed for ongoing sperm motility.

The bulbourethral (or Cowper) glands, which resemble peas in size and shape, secrete mucus-like fluid constituting less than 5% of seminal fluid volume.

External genitals (also called genitalia) in the male are the penis and scrotum.

The penis has three columns of erectile tissue—two dorsal columns called corpora cavernosa and one ventral column surrounding the urethra called the corpus spongiosum.

The glans penis is covered by foreskin (called the prepuce).

Surgical removal of the foreskin is called circumcision.

Next, we will review the female reproductive system.

Female reproductive organs are classified as essential or accessory.

Essential organs of reproduction are the gonads (ovaries), which produce sex cells called ova.

Accessory organs of reproduction are the ducts or modified ducts—including oviducts, uterus, and vagina; sex glands—including the breasts; and external genitals.

The ovaries are paired glands that resemble large almonds and weigh about 3 g each.

They are attached to ligaments in the pelvic cavity on each side of uterus.

The microscopic structure of the ovaries reveals ovarian follicles.

Each ovarian follicle contains an oocyte, which is an immature sex cell. There are about 500 thousand present at birth.

Further development results in primary follicles surrounded by a layer of cuboidal cells, sometimes called follicular cells.

• With continued development, the layers of follicular cells increase in number and begin to secrete hormones. These cells are now called granulosa cells.

About 350 to 500 mature follicles ovulate during the reproductive lifetime of most women—they are sometimes called graafian follicles.

Secondary follicles have a hollow chamber called the antrum.

The corpus luteum forms after ovulation.

Functions of the female reproductive system are oogenesis and production of estrogen and progesterone.

Oogenesis involves meiotic cell division that produces daughter cells with equal chromosome numbers (23) but unequal cytoplasm.

The ovum is large; polar bodies are small and degenerate.

Granulosa cells surrounding the oocyte in the mature and growing follicles produce estrogen. Estrogen causes development and maintenance of secondary sex characteristics in females.

The corpus luteum produces progesterone. Progesterone stimulates secretory activity of the uterine epithelium and assists estrogen in initiating menses.

Both male and female reproductive ducts carry gametes from each (of two) gonads, join into a single passage, and exit the body.

Only the female ducts also function in receiving sperm, fertilization, and prenatal development.

Uterine (or fallopian) tubes are also called oviducts.

They extend about 10 cm from the uterus into the abdominal cavity.

The expanded distal end is surrounded by fimbriae.

The mucosal lining of the oviduct is directly continuous with the lining of the abdominal cavity.

The uterus is divided into a body, fundus, and cervix.

It lies in the pelvic cavity just behind the urinary bladder. The myometrium is the muscle layer; the endometrium (or uterine lining) is lost in menstruation.

Menopause is the end of repetitive menstrual cycles (at about 50 years of age).

The vagina is a distensible tube about 10 cm long. It is located between the urinary bladder and the rectum in the pelvis. It receives the penis during sexual intercourse and is the birth canal for normal delivery of a baby at the end of pregnancy.

Accessory glands include the greater and lesser vestibular glands and the breasts.

The vestibular glands secrete mucous fluid that may provide lubrication during sexual intercourse.

The ducts open between the labia minora.

They become clinically important when they become infected (as in gonorrhea).

Breasts are located over the pectoral muscles of the thorax.

Their size is determined by fat quantity more than the amount of glandular, milk-secreting tissue.

Lactiferous ducts drain at the nipple, which is surrounded by the pigmented areola.

Lymphatic drainage is important in the spread of breast cancer cells to other body areas.

External genitals, called vulva, include the mons pubis, clitoris, external urinary meatus, openings of vestibular glands, vagina, labia minora and majora, and hymen.

The perineum is the area between the vaginal opening and the anus; its surgical cut during childbirth is called an episiotomy.

The menstrual cycle involves many changes in the uterus, ovaries, vagina, and breasts.

The length of the cycle is about 28 days, and varies from month to month among individuals and in the same individual.

Menses is the first phase of the cycle; it lasts about the first 5 days of the cycle and varies somewhat.

It is characterized by sloughing of bits of endometrium with bleeding.

The first day of flow is day 1 of the menstrual cycle.

The proliferative phase lasts from the end of menses until the secretory phase; it varies in length. The shorter the cycle, the shorter the proliferative phase; the longer the cycle, the longer the proliferative phase. It is characterized by proliferation of endometrium.

The secretory phase occurs on the days between ovulation and the beginning of the next menses; it is usually about 14 days before the next menses. It is characterized by further thickening of endometrium and secretion by glands in preparation for implantation of a fertilized ovum.

Ovulation is the release of typically one ovum per cycle, 14 days before the next menses; the timing of ovulation is useful in timing sexual intercourse to maximize fertility. Combined actions of the anterior pituitary hormones follicle-stimulating hormone and luteinizing hormone cause ovulation; a sudden sharp decrease in estrogens and progesterone brings on menstruation if pregnancy does not occur.

Here is a brief summary of the chapter:

Organs of the reproductive system are adapted for the specific sequence of functions that permit development of sperm or ova, successful fertilization, and then normal development and birth of offspring.

The male system produces, stores, and introduces mature sperm into the female reproductive tract.

The female system produces ova, receives the sperm, and permits fertilization followed by fetal development and birth, with lactation afterward.

Men and women have analogous reproductive structures.

Production of sex hormones is required for the development of secondary sex characteristics and for normal reproductive functions in both sexes.

This concludes the audio review of Chapter 21.