6. Development of the Embryo What is an embryo??? Embryo – Early stages of development immediately following implantation of the zygote; body parts are forming Zygote Egg Sperm

How does a Zygote develop into a fully developed multi-celled organisms? Cleavage: Series of rapid mitotic cell divisions that increases # of cells (not size)

EARLY STAGES OF DEVELOPMENT Zygote 2 Cell Stage 8, 16, 32 Cell Stage 4 Cell Stage Blastula – hollow ball of cells Gastrula Morula – solid ball of cells

A = zygote B= 2 cell stage C= 4 cell stage D,E = 8-16 cell stage F= Blastula ( ball of cells w/hollow center) Note: Up until this point, all the cells are identical to one another!

Differentiation – To become different body parts; specialized Gastrulation - formation of gastrula; cell begins to indent; differentiation occurs Differentiation – To become different body parts; specialized Ectoderm (outer) Mesoderm - Middle Endoderm - Inner

The organ systems of a human develop from the following germ or embryonic layers: Ectoderm Mesoderm Endoderm Skin Circulatory Respiratory Hair Muscles Digestive Nails Bones Nervous Sys. Excretory Reproductive

Stem Cells Undifferentiated cells that have the ability to become ANY specialized cell when given the proper signal. Stem cells can be retrieved from cells of: 1. The embryo (highly controversial) 2. From “deprogrammed” adult cells (no embryo involved = no controversy)

Development For an embryo to develop, the following conditions are needed: a. Food b. Warmth c. Protection d. Oxygen e. Waste Removal

Two Types of Development External Development – development of the young occur OUTSIDE the mother’s body 1. In Water (External Fertilization) ex: fish, frog - Food – in yolk of egg - Oxygen + wastes – diffuse from water

(Internal Fertilization) A featherless Chicken!!! On land (Internal Fertilization) Ex: Birds, Reptiles a. Shell – Protection b. Amnion – fluid filled sac around embryo (or fetus). Fluid is for protection, cushioning, and shock absorber c. Yolk Sac – sac filled with food d. Allantois – sac to store solid wastes and acts as a respiratory membrane e. Chorion – outer most membrane

B. Internal Development (Internal Fertilization) Placental Mammals: Embryo develops in the uterus Nutrients are obtained from the placenta (temporary organ) by the process of DIFFUSION Umbilical cord contains blood vessels that carry nutrients, water and oxygen TO the fetus and wastes away from the fetus Amnion provides protection Fewer offspring and a lot Parental Care

Ways a mother can have a healthy pregnancy Avoid drugs and alcohol Eat healthy Prenatal vitamins exercise

Non-placental mammals Marsupials: Kangeroo, Koala Bear Embryo is born undeveloped Development is completed inside a pouch which has mammary glands