Veterinary Developmental Anatomy Basics

Study Notes

Embryology refers to the process of prenatal development and differentiation of an organism.
Germ layers are sheets of cells that form all tissues and organs, consisting of three primary layers: ectoderm, mesoderm, and endoderm.
Epithelium is a tissue with one or several layers of cells closely joined together, supported by a base membrane; it may differentiate into mesenchyme.
Mesenchyme consists of loosely arranged embryonic cells within an extensive extracellular matrix, capable of differentiating into various adult structures or epithelium.
Connective tissues are responsible for connecting and supporting other tissues in the body.

Gametogenesis is the maturation process of sex cells (gametes), involving ovum and spermatozoon.
There are three types of ova based on yolk quantity: microlecithal (mammals), mesolecithal (amphibians), macrolecithal (birds).
Ova are classified by yolk distribution into isolecithal and telolecithal categories.

The nucleus of the spermatid compacts to form the spermatozoon's head.
The centrosome develops into the motile axial filament of the tail.
Cytoplasm reduces, forming an envelope around the head and middle piece of the tail.
The Golgi apparatus transforms to create the acrosome.
Mitochondria arrange in a spiral for energy production in the middle piece.

In mammals, sex is determined by the Y chromosome of the sperm (XY for male, XX for female).
In birds, sex is determined by the W chromosome of the female (ZZ for male, ZW for female).

Fertilization involves several key steps: insemination, sperm capacitation, migration, acrosome reaction, formation of the fertilization cone, and penetration of the ovum.
Following penetration, the fertilization membrane forms, and both male and female pronuclei are established.

Cleavage immediately forms blastomeres, starting during the anaphase stage of cell division.
There are two cleavage types: holoblastic and meroblastic.
Morula refers to the early compact ball of cells, while blastula indicates the sphere of blastomeres.

Meroblastic cleavage occurs as the egg travels through the oviduct, starting gastrulation by the time the egg is laid.
Cleavage is focused at the whitish blastoderm on the yolk's surface, involving central and marginal blastomeres.

Gastrulation leads to the formation of primary germ layers and involves ordered cell rearrangement.
Cells acquire the ability to undergo morphogenetic movements and display a degree of differentiation during this stage.