lecture 3a: introduction to embryology

Ontogeny

The life history of an organism, from fertilized egg to its death.

Embryology

The study of the early stages of ontogeny, particularly from the fertilized egg to the formation of the embryo.

Cleavage

The division of the zygote into smaller cells, resulting in the formation of the blastula.

Blastula

A hollow ball of cells formed after the zygote undergoes several rounds of mitosis.

Gastrulation

The process during early embryonic development that forms the three germ layers: ectoderm, mesoderm, and endoderm.

Ectoderm

The outer germ layer that develops into the skin and nervous system.

Mesoderm

The middle germ layer that develops into muscles, bones, and the circulatory system.

Endoderm

The inner germ layer that develops into the gut and internal organs.

Holoblastic cleavage

A cleavage pattern where the cell division furrows go all the way through the egg, seen in eggs with little to no yolk.

Meroblastic cleavage

A cleavage pattern where the cell division is restricted to a portion of the egg, seen in eggs with a large amount of yolk.

Microlecithal

An egg type with a small amount of yolk, found in species like amphioxus and eutherian mammals.

Mesolecithal

An egg type with a moderate amount of yolk, found in amphibians and lampreys.

Macrolecithal

An egg type with a large amount of yolk, typically seen in reptiles, birds, and some fish.

Blastocoel

The fluid-filled cavity inside the blastula.

Primitive gut

The early stage of the gut formed during gastrulation.

Neural tube

The structure that develops from the ectoderm and eventually forms the nervous system.

Somite

Blocks of mesoderm that form along the developing embryo, giving rise to vertebrae and skeletal muscle.

Splanchnic mesoderm

The inner layer of the hypomere that contributes to the formation of internal organs.

Somatic mesoderm

The outer layer of the hypomere that contributes to the body wall.

Dermatome, Myotome, Sclerotome

The three divisions of the somite, giving rise to skin, muscle, and vertebrae respectively.