Functions of the Reproductive System

• The male reproductive system produces sperm cells, provides nutrients for the sperm cells and secretions, transfers the sperm cells to the female, and makes male sex hormones.

• The female reproductive system produces female sex cells, receives sex cells from the male, provides nourishment for the developing infant before and after birth, and produces female sex hormones.

Formation of Sex Cells

• The reproductive organs in males and females produce sex cells by meiosis.

Male Reproductive System

Scrotum

• The scrotum is a two-chambered sac that contains the testes.

• The dartos and cremaster muscles help to regulate testes temperature.

Testes

• The testes are divided into lobules containing the seminiferous tubules and interstitial cells.

• During development the testes pass from the abdominal cavity through the inguinal canal to the scrotum.

Spermatogenesis

• Spermatogenesis begins in the seminiferous tubules at the time of puberty.

• Sperm cells are produced in the seminiferous tubules.
  • Germ cells divide (mitosis) to form primary spermatocytes.

  • Primary spermatocytes divide by meiosis to produce sperm cells.

  • Sertoli cells nourish the sperm cells and produce small amounts of hormones.

• Spermatids develop a head, midpiece, and flagellum to become a sperm cell. The head contains the acrosome and the nucleus.

Ducts

• The epididymis is a coiled tube system, located on the testis, that is the site of sperm maturation.

• The seminiferous tubules lead to the rete testis.

• The rete testis opens into the efferent ductules that extend to the epididymis.

• The ductus deferens passes from the epididymis into the abdominal cavity.

• The ejaculatory duct is formed by the joining of the ductus deferens and the duct from the seminal vesicle.

• The ejaculatory ducts join the urethra in the prostate gland.

• The urethra extends from the urinary bladder through the penis to the outside of the body.

Penis

• The penis consists of erectile tissue.
  • The two corpora cavernosa form the dorsum and the sides.

  • The corpus spongiosum forms the ventral portion and the glans penis, and it encloses the spongy urethra. The prepuce covers the glans penis.

Glands

• The seminal vesicles empty into the ejaculatory duct.

• The prostate gland consists of glandular and muscular tissue and empties into the urethra.

• The bulbourethral glands are glands that empty into the urethra.

Secretions

• Semen is a mixture of gland secretions and sperm cells.

• The bulbourethral glands and the urethral mucous glands produce mucus that neutralizes the acidic pH of the urethra.

• The testicular secretions contain sperm cells.

• The seminal vesicle fluid contains nutrients, prostaglandins, and proteins that coagulate.

• The prostate fluid contains nutrients and proteolytic enzymes, and it neutralizes the pH of the vagina.

Physiology of Male Reproduction

Regulation of Sex Hormone Secretion

• GnRH is produced in the hypothalamus and is released in surges.

• GnRH stimulates release of LH and FSH from the anterior pituitary.
  • LH stimulates the interstitial cells to produce testosterone.

  • FSH binds to Sertoli cells and stimulates spermatogenesis.

Puberty

• Before puberty small amounts of testosterone inhibit GnRH release.

• During puberty testosterone does not completely suppress GnRH release, resulting in increased production of FSH, LH, and testosterone.

Effects of Testosterone

• Testosterone causes enlargement of the genitals and is necessary for spermatogenesis.

• Testosterone is responsible for the development of secondary sex characteristics.

Male Sexual Behavior and the Male Sex Act

• Testosterone is required for normal sex drive.

• Stimulation of the sexual act can be tactile or psychological.

• Afferent impulses pass to the sacral region of the spinal cord.

• Efferent stimulation causes erection, mucus production, emission, and ejaculation.

• The most common cause of infertility is a low sperm cell count.

Female Reproductive System

Ovaries

• The ovaries are covered by the visceral peritoneum.

• Follicles consist of an oocyte surrounded by granulosa cells and a thecal layer.

• As follicles mature in response to FSH they enlarge, an antrum forms, and the oocyte increases in size. Granulosa cells form a cumulus layer that surrounds the oocyte, and a zona pellucida (a thin noncellular layer) forms around the oocyte.

• About the time of ovulation the first meiotic division is completed.

• Ovulation is the release of the oocyte from the ovary.
  • In response to LH the follicle completes its growth and ruptures, and the oocyte is released from the ovary.

  • The second meiotic division is completed when the oocyte unites with a sperm cell to form a zygote.

• Fate of the follicle.
  
  
• The ovulated follicle becomes the corpus luteum.

• If fertilization occurs, the corpus luteum persists. If there is no fertilization, it degenerates.

Uterine Tubes

• The uterine tubes transport the oocyte or zygote from the ovary to the uterus.

• The ovarian end of the uterine tube is surrounded by fimbriae.

• Cilia on the fimbriae move the oocyte into the uterine tube.

• Fertilization usually occurs in the upper part of the uterine tube.

Uterus

• The uterus is a pear-shaped organ. The uterine cavity and the cervical canal are the spaces formed by the uterus.

• The wall of the uterus consists of the perimetrium or serous layer, the myometrium (smooth muscle), and the endometrium.

Vagina

• The vagina connects the uterus (cervix) to the vestibule.

• The vagina consists of a layer of smooth muscle and an inner lining of moist stratified squamous epithelium.

• The hymen covers the vestibular opening of the vagina.

External Genitalia

• The vestibule is a space into which the vagina and the urethra open.

• The clitoris is composed of erectile tissue and contains many sensory organs important in detecting sexual stimuli.

• The labia minora are folds that cover the vestibule and form the prepuce.

• The greater vestibular glands produce a mucous fluid, and lubricating fluid is produced by the wall of the vagina.

• The labia majora cover the labia minora, and the pudendal cleft is a space between the labia majora.

• The mons pubis is an elevated area superior to the labia majora.

Mammary Glands

• The mammary glands are modified sweat glands that consist of glandular lobes and adipose tissue.

• The lobes connect to the nipple through ducts. The nipple is surrounded by the areola.

Physiology of Female Reproduction

Puberty

• Puberty begins with the first menstrual bleeding (menarche).

• Puberty begins when GnRH, LH, and FSH levels increase.

Menstrual Cycle

• The cyclical changes in the uterus are controlled by estrogen and progesterone produced by the ovary.

• Cyclical changes in the uterus.
  • Menses (day 1 to days 4 or 5). Menstrual fluid is produced by degeneration of the endometrium.

  • Proliferative phase (day 5 to day of ovulation). Epithelial cells multiply and form glands.

  • Secretory phase (from day of ovulation to day 28). The endometrium becomes thicker, and endometrial glands secrete. The uterus is prepared for implantation of the developing blastocyst by day 21.

  • Estrogen stimulates proliferation of the endometrium, and progesterone causes thickening of the endometrium. Decreased progesterone causes menses.

• FSH initiates the development of the follicles.

• LH stimulates ovulation and formation of the corpus luteum.

• A positive-feedback mechanism causes FSH and LH levels to increase near the time of ovulation.
  • Estrogen produced by the follicles stimulates GnRH, FSH, and LH secretion.

  • FSH and LH stimulate more estrogen secretion, and the cycle repeats.

Menopause

• The cessation of the menstrual cycle is called menopause.

Female Sexual Behavior and the Female Sex Act

• Female sex drive is partially influenced by testosteronelike hormones (produced by the adrenal cortex) and estrogen produced by the ovary.

• Autonomic nerves cause erectile tissue to become engorged with blood, the vestibular glands to secrete mucus, and the vagina to produce a lubricating fluid.

• Causes of infertility in females include malfunctions of the uterine tubes, reduced hormone secretion from the pituitary or ovary, and interruption of implantation.