Lecture Notes, Biology 203

Lecture Notes, Biology 203, Human Sexuality and Reproduction

Introductory Material

Anatomy and Physiology
1. Definitions
  1. Anatomy: location, shape, size, appearance of structures
  2. Physiology: function of structures--how they work, when they work, in relation to each other
2. Male reproductive tract anatomy and physiology
  1. Testis
    1. Sperm originate in wall of seminiferous tubules
    2. Cells near outer edge of wall differentiate into more mature cells closer to center of wall
    3. Nearly mature sperm are released into hollow center of tubule and travel to epididymis
    4. Interstitial cells between tubules produce testosterone, which promotes sperm maturation
  2. Epididymis
    1. Sperm continue to mature in epididymis
    2. Complete maturation of sperm requires about 45 days in the testis and about 18 days in the epididymis (about 63-65 days total)
    3. Mature sperm are composed of head (acrosome with enzymes, DNA), midpiece (mitochondria -> energy), and tail (motility)
  3. Vas deferens, ampulla of vas deferens
  4. Seminal vesicles
    1. Produce much of fluid in semen
    2. Nutritional chemicals: fructose, amino acids, lipids
  5. Prostate gland
    1. Secretes an alkaline fluid that enters urethra through pores in urethral walls
    2. Components: buffering chemicals, citrate, calcium, spermine
    3. Sperm are both viable and motile at pH 7-8.5, and begin to be less motile and viable below pH 7.0; since normal vaginal pH is 3.8-4.5, sperm must be protected from acidic pH by components of semen
  6. Bulbourethral gland (Cowper's gland) (secrete viscous alkaline fluid)
  7. Ejaculatory duct
  8. Urethra
  9. Semen components and normal characteristics
    1. Volume: 2.5 to 5 ml per ejaculation
    2. Sperm (from epididymis, testis)-- 50 to 150 million per ml (less than 20 million suggests infertility)
    3. Nutrients and fluid (from seminal vesicles)
    4. Protective, buffering chemicals (from prostate gland)
    5. Thick, alkaline fluid (from bulbourethral glands)
    6. Color: milky appearance (due to secretions from prostate)
    7. Motility: at least 60% active, showing good forward motion)
    8. pH: slightly alkaline (pH of 7.2 and 7.6 or 7.8)
    9. Specific gravity: 1.028 (slightly denser than water)
    10. Morphology: at least 80% normal
  10. Penis
    1. Shaft, glans, coronal ridge
    2. Erectile tissues: corpora cavernosa, corpus spongiosum
    3. Urethra passes through corpus spongiosum to urethral opening
  11. Nervous system control of erection and ejaculation
    1. Brain communicates sexual stimulus to erection reflex center in sacral part of spinal cord
    2. Spinal cord nerves send signals to erectile tissue in penis, arteries dilate, blood pools in erectile tissues, leading to erection
    3. Spinal cord nerves send signals that result in contraction of inner structures (epididymis, vas deferens, seminal vesicles, prostate)
    4. Semen washes past bulbourethral glands into the lower urethra (emission); sensation of urethral filling is returned to erection complex
    5. Spinal cord nerves send signals that result in contraction of muscles at base of penis, leading to rhythmic contractions (ejaculation)
3. Female reproductive tract anatomy and physiology
  1. Production of ova
    1. A female embryo, at two month postconception (about seven months before birth): ovary has 600,000 germ cells in her ovaries(ancestors of eggs or ova)
    2. By 5 months postconception, the fetus has 6-7 million germ cells, which will develop into 5 million primary oocytes (peak number of oocytes for her lifetime)
    3. At the time of birth, 700,000 to 2 million primary oocytes will remain in the ovaries
    4. By puberty, 40,000 to 400,000 are left
    5. At each ovulation from menarche to menopause, one ovum is released from an ovary each month (ovulation)
    6. At 12 ovulations per year, for 40 years, a woman releases about 480 ova, therefore most are redundant
  2. Ovarian cycle
    1. Hormones stimulate development of primary ovum in primary follicle (usually only one)
    2. Mature ovum is surrounded by zona pellucida and corona radiata, inside Graafian follicle just before follicle ruptures
    3. Hormonal surge triggers rupture of mature Graafian follicle (ovulation)
    4. Enclosed ovum leaves ovary (moves into abdominal cavity but is rapidly collected in Fallopian tube)
    5. Follicle remnant becomes corpus luteum, which secretes hormones
    6. Eventually corpus luteum degenerates into corpus albicans
  3. Fallopian tube
    1. End of tube near near ovary has fimbriae, fingerlike extensions that move around ovary surface
    2. Cilia inside tube wave fluids toward uterus--ovum (itself nonmotile) is drawn into tube and floats downstream toward uterus
    3. Fertilization, if any, usually occurs in Fallopian tube
  4. Uterus
    1. If fertilization occurs, first few cell divisions occur in tube before pre-embryo reaches uterus, where it will implant in uterine lining (endometrium)
    2. If there is no fertilization, ovum is washed away with the loss of the endometrium in menstruation
    3. Uterus has three layers
      1. Endometrium (inside layer)--uterine lining, thickens during menstrual cycle and is shed during menstruation
      2. Myometrium (middle layer)--muscle layer, contracts during menstruation and childbirth
      3. Perimetrium (outer covering)
    4. Top of uterus (farthest inside body) is called the fundus
    5. Narrowing at bottom of uterus (closer to outside of body) is cervix (dilates and thins during childbirth)
    6. Cervix opens into vagina
  5. Vagina
    1. Walls have same three layers as uterus, but thinner
    2. Usually is collapsed or flattened hollow tube
    3. Important in sexual intercourse--outer 1/3 is most sensitive to sexual stimulation
    4. Acts as the birth canal in vaginal deliveries
    5. Vaginal opening in front of anus (opening from rectum and large intestine) and behind urethral opening
  6. Bladder
    1. Collects urine from kidneys
    2. Urine leaves body through urethra and urethral opening
  7. Pubococcygeal muscle--forms triple figure 8 around urethral opening, vaginal opening, and anus, good muscle tone important for support of pelvic organs, esp. during pregnancy and childbirth
  8. Clitoris
    1. Embryonic/fetal analog of penis--contains erectile tissues
    2. Very sensitive to stimulation---many nerve endings
    3. May retract and become less evident when erect
    4. Located in front of urethral opening
  9. Labia
    1. Labia majora (outer lips)--swell during sexual stimulation
    2. Labia minora (minor lips)--swell and change color during sexual stimulation
  10. Breasts
    1. Have both erotic and reproductive roles
    2. Contain variable amount of fatty tissue that provide size and shape
    3. Contain mammary glands involved in lactation
      1. Milk sacs, alveoli, are where milkis produced
      2. Milk ducts deliver milk to 6-8 nipple openings
    4. During sexual stimulation, breasts may enlarge and nipple and surrounding areola (usually darker than surrounding tissue) may become erect, but have no erectile tissue