CH. 4 - Vertebrate Embryology

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1. 1. Keywords

1. Allantois - sac-like structure that's involved in respiration and excretion and contains blood vessels to transport gas, and waste

2. Amnion - encloses the amniotic fluid.  Provides the aqueous environment that protects the developing embryo

3. Blastocoel - when morula develops the cavity

4. Blastula - hollow sphere of cells evolved from blastocoel

5. Blastulation - process of morula developing a fluid-filled cavity

6. Chorion - lining of inside the shell.  A moist membrane that permits gas exchange.  Envelops the amnion

7. Determinate cleavage - cells whose future pathways are determined early

8. Ectoderm - outer layer.  Integument, hair, nails, skin, lens of eye, retina, CNS

9. Endoderm - inner outer layer.  Lining of digestive and respiratory tracts, parts of liver, pancreas, thyroid, and bladder lining.

10. Fraternal Twins - more than one egg fertilized during fertilization

11. Gastrulation - process of 1 layer blastulat to 3 layered structure called gastrula

12. Identical Twins - results of indeterminate cleavage

13. Indeterminate cleavage - cells maintain ability to develop into complete organism

14. Mesoderm - musculoskeletal, circulatory, excretory systems.  Gonads, connective tissues, and portions of digestive and respiratory organs.

15. Morula - solid ball of embryonic cells that hasn't developed a fluid-filled cavity

16. Yolk sac - encloses the yolk.  The yolk sac blood vessels gives food to developing embryo

  

Early Developmental Stages

1. General

1. Embryology is the study of development of zygote into complete cellular organism.

2. Fertilization

1. Happens within 12-24 hours following ovulation

3. Cleavage

1. Rapid divisions without growth in cell protoplasm

1. Results in smaller and smaller cells

2. Increasing ration of nuclear to cytoplasmic material

3. Increases surface-to-volume ratio

2. First complete cleavage happens 32 hours after fertilization, then second at 60, third at 72.

3. At 72 hours, the 8 celled embryo will reach uterus

4. With more cell division, it'd be called morula, which is right before development of fluid filled cavity

5. Next comes blastulation where the morula develops the cavity, which turns it into blastocoel and soon turns into blastula.

4. Gastrulation

1. The process is the transformation of a single cell layer of blastula into 3-layered structure

2. Each of the three layers develops into different parts of the body.

3. The ectoderm forms the "outer layer" of the body like the skin, hair, nails, lense of the eye, retina, nervous system, surface of nose, mouth, and anal canal

4. The endoderm forms the "inner outer layer" of the body, like the lining of the digestive and respiratory tracts, and parts of the liver, pancreas, thyroid, and bladder lining

5. The mesoderm forms the guts like the musculoskeletal system, circulator system, excretory system, gonads, connective tissue, and portions of digestive and respiratory systems.

5. Development

1. There are different types of development for zygote, external, non-placental internal, and placental internal

2. External development

1. Occurs outside of the body in fish and amphibians

1. Basically, females lay eggs and male comes around to fertilize them

2. Reptiles, birds, and some mammals would have internal fertilization then the eggs are laid

3. Egg structure

1. Chorion - lining of inside the shell.  A moist membrane that permits gas exchange.  Envelops the amnion

2. Allantois - sac-like structure that's involved in respiration and excretion and contains blood vessels to transport gas, and waste

3. Amnion - encloses the amniotic fluid.  Provides the aqueous environment that protects the developing embryo

4. Yolk sac - encloses the yolk.  The yolk sac blood vessels gives food to developing embryo

3. Non-placental internal development

1. Happens in marsupials and some tropical fish

2. Basically develops in mother without placenta thus the transfer of food and oxygen between mother and embryo is limited

4. Placental internal development

1. The fetus receives oxygen, nutrients and expels CO2 and wastes via a special circulatory system between mother and embryo.

1. Placenta and the umbilical cord are responsible

1. Outgrowths of 4 extra-embryonic membranes formed during development

1. Amnion

2. Chorion

3. Allantois

4. Yolk sac

2. Placenta development begins with the chorion

3. Allantois develops as an outpocketing of the gut

1. The blood vessels develops into umbilical vessels that connects the fetus and the plaenta

4. Yolk sac is associated with the umbilical vessels

6. Birth and Maturation

1. Childbirth happens with labor, a series of strong uterine contractors

2. Labor has three distinct stages

1. Stage 1 -

1. Cervix thins and dilates and amniotic sac ruptures (water broke!)

2. Contractions are mild

2. Stage 2 -

1. Rapid contractions, baby is expelled along with umbilical cord

3. Stage 3 -

1. The uterus contracts and placenta and umbilical cords are fully expelled

3. Maturation

1. In some animals, maturation can be suspended

2. Mammals develop uninterrupted