Human Embryology: From Zygote to Organogenesis

Zygote

Single cell formed after sperm and egg fusion.

Embryo

Developing human from 6-8 weeks post-conception.

Pythagoras

Greek philosopher who discussed sperm's role in development.

Aristotle

Philosopher who described sperm as sculpting menstrual fluid.

Preformation

Theory that sperm contains a mini human being.

Pangenesis

Darwin's theory of gemmules transmitting traits.

Cytoplasmic determinants

Molecules in egg influencing cell development.

Cell differentiation

Specialization of cells in structure and function.

Morphogenesis

Process by which an organism takes shape.

Cleavage

Cell division forming a blastocyst from zygote.

Gastrulation

Rearrangement of cells into a three-layered gastrula.

Organogenesis

Formation of organs from three embryonic layers.

Diploid zygote

Result of haploid sperm and egg fusion.

Acrosomal reaction

Sperm's release of enzymes to penetrate egg.

Polyspermy

Fertilization by multiple sperm, lethal to zygote.

Zona pellucida

Egg's outer coat preventing polyspermy.

Cortical granules

Structures in egg that modify outer coat post-fusion.

Calcium ions (Ca2+)

Increase in egg's cytosol activating metabolic processes.

First cell division

Occurs 12-36 hours after sperm binding in mammals.

Morula

Solid ball of cells formed during cleavage.

Blastocyst

Fluid-filled ball of cells after morula stage.

Metabolic activation

Rapid changes in egg metabolism post-fertilization.

Sperm-binding receptors

Egg surface proteins that recognize sperm.

Fertilization envelope

Protective layer formed around egg post-fertilization.

Fertilized egg

The initial cell formed after sperm-egg fusion.

Four-cell stage

Embryonic stage with four cells post-cleavage.

Early blastula

Stage where blastocyst begins to form.

Later blastula

Advanced stage of blastocyst before implantation.

Inner cell mass

Group of cells developing into the embryo.

Trophoblast

Outer layer of blastocyst initiating implantation.

Gastrula

Three-layered embryo formed during gastrulation.

Ectoderm

Outer germ layer forming skin and nervous system.

Endoderm

Inner germ layer lining digestive tract.

Mesoderm

Middle germ layer forming muscles and organs.

Neurulation

Formation of neural tube from ectoderm.

Notochord

Mesodermal structure guiding spinal cord development.

Somites

Blocks of mesoderm forming vertebrae and muscles.

SRY gene

Y chromosome gene determining male sex characteristics.

Amniotes

Organisms developing embryos in fluid-filled sacs.

Chorion

Extraembryonic membrane for gas exchange.

Amnion

Membrane enclosing amniotic fluid around embryo.

Yolk sac

Membrane providing nutrients to the developing embryo.

Allantois

Membrane for waste disposal and gas exchange.

Totipotent

Cells capable of forming any cell type.

Differentiation

Process where cells express different genes.

Inductive signals

Chemical signals influencing cell fate decisions.