Embryological Development Flashcards

Vocabulary flashcards covering core embryology terms, cellular division types, germ layer derivatives, and early embryonic structures based on Dr. Gentry-Apple's lecture.

Embryogenesis

The formation of body structures and organs through cell division (proliferation) and cell differentiation (specialization).

Embryonic Period

The developmental timeframe extending from fertilization to the earliest stages of organ development (organogenesis), lasting ~30 days in dogs, cats, sheep, and pigs, and ~60 days in horses, cattle, and humans.

Fetal Period

The phase of development between the embryonic period and parturition during which organs grow and begin to function.

Chromosome

An organized structure containing an organism's DNA, composed of nucleic acids and proteins, translated literally as "body of color."

Diploid

A cellular condition of containing the full amount of chromosomes ($2n$), found in most body cells such as skin, liver, and muscle cells.

Haploid

A cellular condition of containing half of the total number of chromosomes ($n$), characteristic of gametes such as spermatocytes and oocytes.

Fertilization

The process initiated by gamete fusion and completed with the beginning of zygotic cell division (mitosis).

Zygote

A single pluripotent cell formed by the union of haploid gametes that is capable of developing into a complete individual.

Cleavage

An initial series of mitotic divisions that fraction a large single-celled zygote into numerous normal-sized blastomeres without increasing overall embryo size.

Blastomere

An individual daughter cell produced during early cleavage divisions of a zygote.

Morula

A solid ball of compacted blastomeres surrounded by a zona pellucida.

Holoblastic Cleavage

A cleavage pattern with division planes that completely divide the egg into separate blastomeres.

Meroblastic Cleavage

Incomplete cleavage in which only a portion of the egg divides due to a large accumulation of yolk.

Cell Differentiation

The process by which cells express specific genes while suppressing others within a shared genome, producing diverse specialized proteins, enzymes, and cell types.

Blastulation

The morphogenic phase during which blastomeres organize into a hollow, fluid-filled, spherical or cylindrical structure called a blastocyst.

Trophoblast

The outer blastomeres of a blastocyst that flatten, gain fluid-secreting capacity, and form the fetal membranes (chorion and amnion).

Inner Cell Mass (Embryoblast)

The inner cluster of blastomeres within a blastocyst that form gap junctions to maximize intercellular communication and give rise to the embryo.

Blastocyst

A hollow developmental stage consisting of an outer trophoblast layer, an inner cell mass, and a fluid-filled cavity (blastocoel).

Gastrulation

The morphogenic process that reorganizes the blastocyst/embryonic disc into the three primary germ layers: ectoderm, mesoderm, and endoderm.

Embryonic Disc

A thickened group of cells formed by the proliferation of the inner cell mass beneath degenerating trophoblast cells.

Epiblast

The upper cellular layer formed by the differentiation of the inner cell mass within the embryonic disc.

Hypoblast

The lower cellular layer of the differentiated inner cell mass that detaches to line the yolk sac, which later develops into the gastrointestinal tract.

Primitive Streak

A longitudinal depression flanked by ridges formed on the epiblast surface that establishes the longitudinal body axis of the embryo.

Ectoderm

The outer primary germ layer that gives rise to the epidermis, hair, nails, brain, spinal cord, and peripheral nervous system.

Mesoderm

The middle primary germ layer that gives rise to muscle, bone, connective tissue, notochord, kidneys, gonads, and the circulatory system.

Endoderm

The inner primary germ layer that gives rise to the epithelial lining of the digestive tract (stomach, colon, liver, pancreas), bladder, and lungs.

Monozygotic Twins

Twins that originate from a single fertilization event (one zygote) and share the same genetic composition.

Dizygotic Twins

Twins that originate from two separate fertilization events occurring within the same pregnancy.

Veratum californicum

A plant associated with inducing the embryological midline developmental defect known as "cyclopia".

Notochord

A rod-shaped aggregate of mesodermal cells along the primitive streak midline that induces neurulation and somite formation and marks the future location of the vertebral column.

Neurulation

The process induced by the notochord in which neuroectoderm transforms into nervous tissue, forming the neural plate, groove, tube, and crest.

Neural Tube

A closed dorsal tubular structure formed by the fusion of neural folds during neurulation that develops into the Central Nervous System (CNS).

Neural Crest Cells

Multipotent cells detaching during neural tube closure that migrate to form skin pigment cells, peripheral nervous system cells, adrenal medulla, meninges, cranial bones, fascia, and teeth.

Somites

Paired cuboidal blocks of mesoderm aligned laterally along the notochord and neural tube that create the vertebral column and associated tissues.

Sclerotome

The region of a somite that differentiates into vertebrae, ribs, and endochondral bones at the base of the skull.

Myotome

The region of a somite that differentiates into the skeletal muscles of the body.

Dermatome

The region of a somite that differentiates into the dermis layer of the skin.