Embryology and Human Development

Flashcards covering the stages of prenatal and postnatal development, fertilization processes, cell cleavage, implantation, and the formation of the three primary germ layers and extra-embryonic membranes.

Differentiation

The process by which initially similar cells become specialized, adopting unique structures and functions to form diverse cell types like muscle cells, neurons, or epithelial cells.

Prenatal development

The developmental period from conception (fertilization) to childbirth (parturition).

Postnatal development

The period of development that occurs after birth and continues until maturity, generally occurring around $15$ to $20$ years of age.

Pre-embryonic period

The first two weeks of prenatal development, lasting from fertilization to implantation in the uterine wall.

Embryonic period

The stage of prenatal development spanning from implantation to the end of the eighth week of pregnancy, focusing on the formation of major organs.

Fetal period

The prenatal stage from the ninth week of pregnancy until birth, characterized by the growth and maturation of specialized organs.

Zygote

A single diploid cell formed by the union of two haploid gametes (sperm and oocyte).

Mitochondrial DNA

Genetic material that follows a maternal lineage because the oocyte provides the essential organelles and cytoplasm for the developing embryo.

Ampula

The specific region of the uterine tube, located approximately the distal two-thirds of the tube, where fertilization typically occurs.

Capacitation

A functional maturation of sperm within the female reproductive tract that increases motility and enables the sperm to fertilize the egg.

Corona radiata

A layer of cells surrounding the ovulated oocyte that acts as a cellular barrier the sperm must penetrate.

Hyaluronidase

An enzyme released by sperm that breaks down the extracellular matrix holding the cells of the corona radiata together.

Ooplasm

The cytoplasm of the oocyte.

Polyspermy

The fertilization of an egg by more than one sperm, which results in an abnormal number of chromosomes.

Male pronucleus

The haploid nucleus from the sperm carrying paternal genetic material.

Female pronucleus

The haploid nucleus of the mature ovum containing maternal genetic material.

Gestation period

The entire nine-month period from fertilization to birth, divided into three roughly equal trimesters.

Organogenesis

The process by which major organs and organ systems begin to form, primarily occurring during the first trimester.

Cleavage

A sequence of rapid mitotic cell divisions of the zygote without an increase in overall size, leading to smaller cells called blastomeres.

Morula

A solid ball of cells formed after several rounds of cleavage, typically around day 3 or 4 post-fertilization.

Blastocyst

A hollow ball of cells consisting of an inner cell mass, a trophoblast, and a fluid-filled blastocoele.

Inner cell mass

A cluster of pluripotent cells in the blastocyst that have the potential to develop into all the tissues of the embryo.

Trophoblast

The outer layer of cells in the blastocyst responsible for providing nutrients and attaching the blastocyst to the uterine lining.

Ectopic pregnancy

A condition where implantation occurs outside the uterine wall, such as in the fallopian tube.

Syncytiotrophoblast

A multi-nucleated mass of cytoplasm from the trophoblast that erodes maternal tissues to allow the blastocyst to burrow into the endometrium.

Blastodisc (Bilaminar disc)

A flattened disc-like structure formed by the inner cell mass, composed of the hypoblast and epiblast layers.

Gastrulation

A fundamental event in embryogenesis that establishes the three primary germ layers: ectoderm, mesoderm, and endoderm.

Primitive streak

A thickened line formed by epiblast cells migrating towards the center of the blastodisc during gastrulation.

Ectoderm

The outermost primary germ layer formed from the epiblast cells that remain on the surface.

Mesoderm

The middle primary germ layer formed by epiblast cells that migrate inward through the primitive streak.

Endoderm

The innermost primary germ layer formed by hypoblast cells that are displaced during gastrulation.

Amnion

The extra-embryonic membrane that forms a fluid-filled cavity surrounding the embryo to provide protection from mechanical shocks.

Allantois

An extra-embryonic membrane derived from endoderm and mesoderm that contributes to the development of the urinary bladder.

Yolk sac

An extra-embryonic membrane that serves as an early site of blood cell formation.

Chorion

The outermost extra-embryonic membrane that forms blood vessels connecting the embryo to maternal tissues via the placenta.

Chorionic villi

Finger-like projections of the chorion that invade the endometrium to establish the network for substance exchange.

Umbilical arteries

Vessels that carry deoxygenated blood and fetal waste products from the fetus to the placenta.

Umbilical veins

Vessels that carry oxygenated, nutrient-rich blood from the placenta to the fetus.

Embryogenesis

The process by which the embryo takes shape and separates from extra-embryonic membranes, characterized by the formation of head and tail folds.

Uterine expansion

The increase of the uterus in length from $7\,\text{cm}$ to approximately $30\,\text{cm}$ by the end of gestation to accommodate the fetus.