Chapter 29 Notes
Development and Inheritance

Fertilization

1. Union of two haploid cells: spermatozoan and secondary oocyte

• species specific due to acrosome enzymes
• depolarization and Ca++ block entry of more sperm
• secondary oocyte completes meiosis II
• fusion of two nuclei restore 46 chromosomes
• Human Karyotype online
• fraternal twins: two secondary oocytes and two sperm
• identical twins:  one secondary oocyte and one sperm

Cleavage and Blastocyst Structure

2. Formation of  the morula

• first cell divisions is called cleavage
• rapid mitotic divisions with little time for growth
• morulla is a ball of cells moving through the uterine tubes

3. Formation of the blastocyst

• within 5 days a hollow ball of cells appear
• fluid inside a cavity called a blastocele
• outer layer of cells is called a trophoblast will become the chorion
• inner cell mass adds to chorion and becomes the embryo

Implantation and Germ Layers

4. Blastocyst implants in endometrium

• by day 22 of Menstrual Cycle statum functionalis rich with glands and blood supply
• blastocyst imbeds in this inner uterine lining
• ectopic pregnancy is implantation in an area other than the uterus

5. Development of three germ layers

• cells in inner cell mass move into a position where they can differentiate into the organ systems
• the systems are derived from three germ layers
• a fouteen day old embryonic disk has three distinct layers
• ECTODERM
  - cells close to a space called the amniotic cavity
  - develop into epidermis and nervous system
• ENDODERM
  - cells close to the blastocele
  - lining of the digestive and respiratory tracts
• MESODERM
  - scattered cells
  - dermis, muscle, cartilage, bone, blood, epithelium of kidneys testes, and ovaries

Embryonic Membranes and Placenta

6. Formation of embryonic membranes

• yolk sac
  - derived from endoderm
  - early blood formation
  - cells form the oogonia and spermatogonia
• amnion
  - a fluid filled cavity surrounding embryo
  - amniotic fluid is a cushion
  - amniocentesis examines the fetal cells that slough off into the fluid
  - ruptures before birth
  - is adjacent to ectoderm
• chorion
  - derived from mesodern and trophoblast
  - a system of blood capillaries that penetrate into maternal blood sinuses
  - chorionic villi sampling removes cells from the blood capillaries for genetic analysis
  - becomes principle part of the fetal placenta surrounding fetus
  - secretes the hormone hCG, which maintains a functioning corpus luteum and is the basis of  
    pregnancy tests
  - surrounds embryo and later fuses with amnion
• allantois
  - endodermal growth toward wall of blastocyst
  - becomes part of umbilical cord

7. Placenta

• site of nutrient/waste exchange between fetus and mom
• endometrium contains blood sinuses (blood filled cavities) in which chorionic villi infiltrate
• maternal and fetal blood do not mix
• the lifeline is the umbilicus containing two umbilical arteries and one umbilical vein
• your naval was once the site of  your umbilical cord
• Placenta Previa results when the placenta grows near the internal os of the cervix

Fetal Growth and Parturition

8. Eight week old fetus

• fetal membranes fill the uterine cavity
• eyes fused
• internal organs present
• human form becomes apparent

9. Parturition

• at full term head rests against cervix
• high levels of estrogen cause the secretion of oxytocin which stimulates uterine contractions
• First stage of labor - dilation
  - cervix widens
  - uterus contracts
  - amnion ruptures
• Second stage of labor- expulsion
  - normally the birth of the head is first followed by the birth of the body
• Third stage of labor - placental stage
  - placenta is expelled