4.1 Prenatal Development

1. After one has fertilized the egg, reactions occurs that repels other sperm

Anmerkungen:

• inability to get pregnant after trying for a year

1. Solutions
   1. Simple
      1. Men: looser pants
      2. Women: take temp. to see when ovulating
   2. More elaborate
      1. ART

         Anmerkungen:

         • Assisted Reproductive Techniques
         1. Prescription drugs for women to ripen ovaries and release several eggs
         2. Artificial Insemination

            Anmerkungen:

            • injecting sperm (woman's partner/donor) into uterus
         3. IVF

            Anmerkungen:

            • several eggs are removed from the ovary and manually combined with sperm in a lab dish before implanting into the uterus
2. Costly
3. Success rate for women to use their own eggs decreases with age

Anmerkungen:

• Lasts ~ 2 weeks 

1. Formation of the blastocyte

   Anmerkungen:

   • hollow ball of cells
   1. Around day 6 implants itself in the uterine wall
      1. Not all survive, some miscarried

Anmerkungen:

• 3rd-8th week of conception

1. Organogenesis

   Anmerkungen:

   • layers of blastocyte differentiate forming structures
   1. Outerlayer- Amnion

      Anmerkungen:

      • watertight membrane that fills with fluid that cushions and protects the fetus 
   2. Chorion

      Anmerkungen:

      • surrounds amnion and attaches villi to the uterine lining for nourishment for the embryo
      1. Eventually becomes the placenta

         Anmerkungen:

         • Tissue fed by blood vessels from the mother connected to the embryo by the umbilical chord 
         1. Exchanges materials btwn mother and fetus through the placental barrier
            1. Small substances but not large molecules can pass through
   3. Inner-layer
      1. Ectoderm
      2. Mesoderm
      3. Endoderm
   4. Brain Development

      Anmerkungen:

      • 3-4 weeks 
      1. neural plate folds to become neural tube
         1. Bottom becomes spinal chord
      2. Lower portions of the brain develop the first
         1. These parts make life possible
      3. Problems

         Anmerkungen:

         • 25-29 days after conception; occurs with deficiency in folic acid 
         1. Spina Bifida

            Anmerkungen:

            • part of the spinal chord is not fully encased in spinal column
         2. Anencaphaly

            Anmerkungen:

            • main portion of the brain above the brain stem fails to develop; lethal
   5. Sexual Differentiation

      Anmerkungen:

      • 7th/8th weeks 
      1. testes of male embryo secrete testosterone
         1. Stimulates male development
      2. Lack of testosterone allows female reproductive development

Anmerkungen:

• 9th week of pregnancy until birth 

1. Proliferation of neurons
   1. After birth, proliferation of glial cells

      Anmerkungen:

      • Support cells for neurons 
      1. Neurons use glial cells to migrate from their origin to particular locations in the brain
         1. "In to out" growth
2. Differentiation occurs
   1. Major malformations will not occur; organs have already formed
      1. But can stunt growth and interfere with the wiring of the nervous system
3. About 23 weeks, fetus reaches age of viability

   Anmerkungen:

   • survival out of uterus possible if the brain and respiratory system is formed well 
   1. Not a guarantee of life or health
4. Neurons develop a myelin sheath and connect to each other
5. Infant undergoes "infant states"

   Anmerkungen:

   • State of sleeping and waking