• Fertilization: gametes meet, generating a 1-celled diploid organism called a zygote
• Cleaveage: cell division
• Gastrulation: first migration of cells to form the gut
• Neurulation: differentiation and migration of cells to form the beginnings of the nervous system
• Organogenesis: development of the organs

• Both an endocrine gland and a reproductive organ
• Egg develops within a follicle
• Follicle producs hormones

Precursors to tissues that form in the embryo

• Endoderm(inner layer): becomes the lining of organs and cardiovascular system
• Mesoderm(middle layer): becomes skeleton, muscle, CV system, bottom of skin
• Ectoderm(outer layer): becomes top layer of skin, nervous system and germ cells

• Error in the neural tube closure
• Most common debilitation birth defect in US

1. Determination: cells are committed to a fate
2. Differentiation: cells go through the genetic and morphological changes to become specialized

• Factors within the cell itself (autonomous specification)
• Factors from outside the cell, usually signaling (conditional specification)

• Regional specificities
• Certain risk groups (advanced maternal age)
• Certain behaviors (maternial use of alcohol and drugs)

• Cell division without cell growth
• ball of cells (blastula) stays roughly the same size, but increasing cell number
• Cells alternate between M and S phase, no G₁ or G₂

• Process of cell migration and dramatic reorganization
• paves the way for tissue differentiation
• 3 germ layers from after gastrulation

• Starts with neurulation (formation of the nervous system)
• Posterior mesoderm cells pinch off to become a rod called notochord, then ectoderm cells above this site change shape and curve inward, neural plate invaginates and pinches off becoming neural tube

• Made up of skin, mucus, white blood cells, and lymph nodes
• protects you from infection of all sorts of pathogens and cancer

1. Self vs. Non-self: some cells are educated to recognize all self molecules. These cells do not make a reaction against these self molecules. Anything else is considered non-self and a reaction takes place.
2. Common features of the enemy: Other cells are able to detect and react to a few conserved features of pathogens

• Immediate and always
• Barriers
• Epithelium
•                    Skin, gut, respiratory system
• Example: your skin prevents bacteria from entering

• Innate
• Immediate upon infection
• Inflammation
• Chemicals
• Non-specific cells
• Example: Immediate inflammatory response, brings blood to site of infection, wound get swollen and red, chemicals send signals to respond and cause pain sensitivity, bring antigen to lymph nodes

• Acquired
• Takes 5 days to kick-in
• Leukocytes that are specific to pathogens and are able to develop memory (antibodies)
• Cells of acquired response reside in lymph nodes
• Example: B and T cells become activated, reproduce and kill infected cells at infection site

• Helper: talk to macrophages and learn about pathogen. Coordinate entire acquired immune response including telling B cells when to make antibodies
• Killer: kill cells that are infected with intracellular pathogens

• Produce antibodies that are specific to pathogen
• can last for decades

• Virus infects Helper T cells
• immune response is comprised
• AIDS is defined as T cell count below a certain level