Ch 17 Reproduction System

Reproductive Physiology

• Sexual reproduction requires a male and a female of the same species to copulate and combine their genes to produce a new individual who is genetically different from their parents.

Male Reproductive System

• The male reproductive system produces, sustains, and delivers sperm cells to the female reproductive tract.
• Testis: produces sperm in a process called spermatogenesis, and male sex hormones (testosterone).
• Each testis contains about 250 functional units called lobules; each lobule contains about 4 seminiferous tubules where spermatogenesis occurs.
• Scrotum: a pouch-like cutaneous extension that contains the two testes, located outside of the pelvic cavity to prevent overheating of testes.
• Epididymis: an expanded tubule from the rete testis where sperm is stored, matured, and becomes fully functional.

Regulation of Male Sex Hormone

• Negative feedback mechanism regulates testosterone concentration.
• As the concentration of testosterone rises, the hypothalamus is inhibited, and the anterior pituitary secretion of gonadotropins is reduced.
• As the concentration of testosterone falls, the hypothalamus signals the anterior pituitary to secrete gonadotropins.

Female Reproductive System

• Ovary: primary sex organ that produces egg cells in a process called oogenesis, and also produces female sex hormones such as estrogens and progesterone.
• Developed near the kidneys during fetal development, and descends into the pelvic cavity toward the end of pregnancy.
• Consists of ovarian cortex where the ovarian cycle occurs, and ovarian medulla where scar tissues and connective tissue are located.

Fertilization and Human Life Cycle

• Fertilization: the union of a sperm and an ovum to form a zygote.
• The human life cycle: a continuous process that involves multiple stages from fertilization to birth.

Mechanism of Penile Erection

• Sexual stimulation triggers the release of nitric oxide, causing dilation of small arterioles of the penis.
• Blood accumulates within the vascular spaces in erectile tissue of the penis, leading to penile erection.

Mechanism of Emission and Ejaculation

• 1. Intense sexual stimulation triggers sympathetic impulses that contract smooth muscles.
• 2. Peristaltic contractions in testicular ducts, epididymis, vas deference, and ejaculatory ducts occur.
• 3. Rhythmic contraction in bulbourethral, prostate, and seminal vesicles.
• 4. Emission: semen moves into urethra, followed by ejaculation, where semen is forcefully expelled from urethra.

Hormonal Control of Male Reproductive Function

• Hypothalamic and pituitary hormones regulate male reproductive function.
• GnRH (Gonadotropin-releasing hormone) stimulates the anterior pituitary gland to release gonadotropins (FSH, LH).
• FSH stimulates spermatogenesis, while LH (ICSH) stimulates the interstitial cells to produce male sex hormone (testosterone).

Hormonal Regulation During Pregnancy

• Aldosterone from the adrenal cortex promotes sodium reabsorption, leading to fluid retention.
• Parathyroid hormone from the parathyroid glands helps maintain a high concentration of maternal blood calcium due to high fetal demand.

Detecting Pregnancy

• Detecting HCG (human chorionic gonadotropin) in a woman's urine or blood is used to confirm pregnancy.

Factors Contributing to Labor

• As the time of birth approaches, progesterone secretion declines, and its inhibiting effect on uterine contractions may lessen.
• Decreasing progesterone concentration may stimulate the synthesis of prostaglandins, which may initiate labor.
• Stretching uterine tissues stimulates the release of oxytocin from the posterior pituitary gland.
• Oxytocin may stimulate uterine contractions and aid labor in its later stages.
• A positive feedback mechanism results in stronger and stronger uterine contractions and a greater release of oxytocin.
• Abdominal wall muscles contract with greater and greater force, forcing the fetus out through the birth canal.

Hormonal Control of Mammary Glands

• Before pregnancy, ovarian hormones secreted during menstrual cycles stimulate the development of alveolar glands and ducts in mammary glands.
• During pregnancy, estrogen causes the ductile system to grow and branch, while progesterone stimulates the development of alveolar glands.
• Placental lactogen promotes the development of the breasts.
• Prolactin from the anterior pituitary gland is secreted throughout pregnancy, but placental progesterone inhibits milk production until after birth.

Structure of Lactating Mammary Glands

• The blastocyst develops into an embryo, which continues to develop for the next two months until a fetus is formed.
• After implantation, layers of membrane begin to form outside the embryo, including the amnion, which secretes amniotic fluid, and the chorion, which produces HCG and forms the placenta.

The Placenta

• The placenta is made up of embryonic and maternal tissues, allowing for the exchange of nutrients and wastes between fetal and maternal blood.
• The placenta protects the embryo and fetus, and its outermost membrane is called the chorion.

Hormonal Changes During Pregnancy

• Following implantation, cells of the trophoblast (embryonic cells that help form the placenta) begin to secrete HCG.
• HCG maintains the corpus luteum, which continues to secrete estrogen and progesterone.
• As the placenta develops, it secretes large quantities of estrogen and progesterone, which:
  • Stimulate the uterine lining to continue development
  • Maintain the uterine lining
  • Inhibit secretion of FSH and LH from the anterior pituitary gland
  • Stimulate development of the mammary gland
  • Inhibit uterine contractions (progesterone)
  • Enlarge the reproductive organs (estrogen)

Uterus and Vagina

• The uterus is a pear-shaped cavity formed by the union of the two uterine tubes.
• It is composed of three layers of tissue: perimetrium, myometrium, and endometrium.
• The endometrium is stimulated by estrogens to thicken and become vascularized during the menstrual cycle.
• Myometrium, under the stimulation of oxytocin, contracts during labor to expel the fetus into the vagina.
• The cervix is a narrow passageway at the base of the uterus that prevents the entry of foreign substances.
• The vagina is an elastic channel inferior to the cervix that serves as the birth canal during parturition.

Oogenesis

• Oogenesis is the process of egg formation in the ovarian cortex.
• Before birth, several million cells called primordial oocytes exist in the ovaries, but most of them spontaneously degenerate.
• By puberty, only 400,000 primordial oocytes remain in the ovaries.

Birth Control

• Birth control is a voluntary regulation of conception.
• Contraception is any method used in birth control to prevent fertilization of the ovum.
• Common contraceptive methods include:
  • Abstinence (100%)
  • Vasectomy (99%)
  • Tubule ligation (99%)
  • Birth control pills (98%)
  • Intrauterine devices (IUDs) (95%)
  • Condoms (90%)
  • Diaphragm and/or foam (80%)
  • Withdrawal method (or coitus interrupts) (75%)