Reproduction & Development

Reprise: What is LIFE?

A. Modes of reproduction

1. Asexual reproduction - lower invertebrates
   • Fission
   • Budding
   • Fragmentation & regeneration
   • Parthenogenesis - e.g. rotifers, whiptail lizards
2. Hermaphroditism - e.g. earthworms, sponges
3. Sequential hermaphroditism - some fish
4. External fertilization
   • Aquatic invertebrates, amphibians, fish
   • Large number of offspring
   • Moist environment
5. Internal fertilization
   • Most terrestrial animals
   • Complex behaviors/copulation required
   • Complex reproductive organs
   • Fewer offspring
   • More nurturing
6. Development of embryo
   • Oviparous: within an egg
   • Viviparous: live birth

B. Male reproductive system

External genitalia

1. Penis
   1. Urethra
   2. Erectile tissue
2. Scrotum
   • Cremaster muscle 

Internal genitalia

1. Testes
   1. Seminiferous tubules: Spermatogenesis
      • Spermatocytes go thru meiosis I
      • Spermatids go thru meiosis II
      • Sperm cells mature: flagella, acrosome
   2. Leydig cells
      • Testosterone production
2. Epididymis
   • Sperm maturation
3. Vas deferens
   • Sperm storage & ejaculation
4. Seminal vesicles
   • Nutrient-rich fluid (fructose)
5. Prostate gland
   • Adds 'alkaline' fluid (pH ~ 6.5)
6. Bulbourethral gland
   • Lubricating fluid

C. Female reproductive system

External genitalia

1. Labia majora & minora
2. Clitoris

Internal genitalia

1. Vagina
   • Smooth muscle
2. Uterus
   • Cervix
   • Endometrium
   • Myometrium (smooth muscle)
3. Oviducts (Fallopian tubes)
   • Ciliated epithelium
4. Ovaries: oogenesis
   1. Oocytes (stuck in prophase I of meiosis)
      • surrounded by a follicle
   2. Follicles (400,000 are left at puberty)
      • stimulated to grow by FSH
      • only one follicle matures per month (Graafian follicle)
   3. Corpus luteum
      • LH causes ovulation
      • Remaining cells of follicle become corpus luteum

D. The female reproductive cycle

1. The ovarian cycle
   1. Follicular phase: FSH stimulates growth of follicle
   2. Ovulation: LH surge causes rupture of follicle
   3. Luteal phase: LH causes corpus luteum to secrete Estrogen + Progesterone
2. The menstrual cycle
   1. Menstrual phase: Lack of E+P = uterine lining shed
   2. Proliferative phase: Rise in Estrogen causes growth of uterine lining
   3. Secretory phase: Rise in Progesterone causes thickening/secretion of lining

E. Pregnancy

1. Fertilization
   • Sperm penetration (only 1 sperm allowed)
   • egg & sperm nuclei fuse = zygote
2. Implantation
   • Blastocyst (~ 16 cells) reaches endometrium
   • Trophoblast (outer layer of cells) becomes placenta
     • produces hCG (detectable by day 6)
3. Embryonic growth
   • Gastrulation
     • Ectoderm becomes nervous system + epidermis
     • Endoderm: Linings of intestinal tract, liver, pancreas
     • Mesoderm: internal organs (heart, kidney)

      

     

F. Human Development

• Neural tube forms ~ 1 week-old
• Rapid differentiation of CNS  ~2 week-old
• Fetal heartbeat begins ~ 3 week-old
• Mouth & eyes; muscles & movement ~ 5 week-old
• Brainwaves present, arms/legs/fingers ~ 6 week-old
• Heart almost complete; AV shunt ~ 8 week-old
• Brain fully formed; pain sensation present ~ 10 week-old
• Taste buds present ~ 13 week-old
• Eyebrows, eyelashes, hair; 
  grasping, kicking movements ~ 14 week-old
• Child can suck thumb! see photo here >>>>>>>
• Gender easily seen; fingernails & fingerprints ~ 18 week-old
• Lungs develop; fetus 'inhales' amniotic fluid ~ 22  week-old
• I can stick my tongue out! ~ 24 weeks
• Indications of REM sleep present ~ 30 week-old

5. Labor 
   1. Oxytocin & prostaglandins

Application topics

1. STDs
2. Contraception
3. In vitro fertilization
4. Infertility