Cross section of a vertebrate embryo in the neurula stage

Cross section of a vertebrate embryo in the neurula stage.

Human embryology is the study of the development of gametes, fertilization, and of the following developmental stages from human embryo to fetus. The MCAT fundamentals for the topic include the developmental narrative from ovulation through implantation and the development of tissues and structures during approximately the first two months of embryonic and fetal development. This descriptive level should be integrated with basic understanding of processes at the molecular, cellular and tissue level such as the behavior of morphogens on signaling pathways, gene expression, and cellular differentiation and how morphogenic movements can bring cell sheets into new spatial relationships making possible new phases of signaling and response between them.

WikiPremed Resources

Mammalian Tissues and Histology Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Human Embryology
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals


Understand how the major types of animal tissue are distinguished and characterized.

Be prepared to describe epithelial tissue in general and distinguish the different types of epithelial tissue.

Understand the derivation of the different types of epithelial tissue from the primary germ line tissues.

Be familiar with the contexts of connective tissue fitting the definition of this type of tissue as living cells within a non-living matrix.

Have a working familiarity with the standard paraffin technique of tissue processing from fixation, clearing, embedding, sectioning, and staining.

Be familiar with hematoxylin and eosin staining and understand the meaning of the terms basophilic and acidophilic in this context.

Suggested Assignments

Review the terminology for human embryology using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Read pp. 94-102 in ExamKrackers Biology II. Perform practice items 65-72 on pg. 103. (Concepts from both the reproductive system and human embryology)

Review the web resources for states of matter.

Conceptual Vocabulary for Human Embryology

A biological tissue is a collection of interconnected cells that perform a similar function within an organism.
Epithelium is a tissue composed of layers of cells which line the cavities and surfaces of structures throughout the body. It is also the type of tissue of which many glands are formed.
Connective tissue
Connective tissue is largely a category of exclusion rather than one with a precise definition, but most tissues in this category are involved in structure and support, derived from mesoderm, and characterized by the traits of non-living tissue.
Squamous epithelium
Squamous epithelium is an epithelium characterised by its most superficial layer consisting of flat, scale-like cells.
Cuboidal epithelia
Cuboidal epithelia are cube-shaped epithelial cells.
Simple cuboidal epithelium
Simple cuboidal eplithelia are epithelial cells with a cuboidal shape arranged in a single layer.
Stratified cuboidal epithelium
Stratified cuboidal epithelia is epithelial tissue composed of cuboidally shaped cells arranged in multiple layers.
Columnar epithelia
Columnar epithelia are epithelial cells whose heights are at least twice their width.
Simple columnar epithelium
Simple columnar epithelium is made up of one layer of cells that are relatively thick and protective of the underlying tissues due to its elongated shape.
Stratified columnar epithelia
Stratified columnar epithelia have several layers, with columnar cells as the outermost of these.
Goblet cell
Goblet cells are glandular simple columnar epithelial cells whose sole function is to secrete mucus.
Adipose tissue
Adipose tissue or fat is loose connective tissue composed of adipocytes.
Histology is the study of tissue sectioned as a thin slice, viewed under a microscope.
Basement membrane
The basement membrane is a structure that supports overlying epithelial or endothelial cells.
The endothelium is the thin layer of cells that line the interior surface of blood vessels.
A gland is an organ in an animal's body that synthesizes a substance for release, often into the bloodstream (endocrine) or onto a surface (exocrine).
Histopathology refers to the microscopic examination of tissue in order to study the manifestations of disease.
Fixation is a chemical process used in the fields of histology, pathology, and cell biology by which biological tissues are preserved from decay.
Antonie van Leeuwenhoek
Antonie van Leeuwenhoek (1632 - 1723) was a Dutch tradesman and scientist who is commonly known as the Father of Microbiology.
Transitional epithelium
Transitional epithelia is a type of tissue consisting of multiple layers of epithelial cells which can contract and expand.
Basal lamina
The basal lamina is a layer on which epithelium sits and which is secreted by the epithelial cells.
The endocardium is the innermost layer of tissue that lines the chambers of the heart.
Apical membrane
The apical membrane of a polarized cell is the part of the plasma membrane that forms its lumenal surface, distinct from the basolateral membrane.
Basolateral membrane
The basolateral membrane of a polarized cell is the part of the plasma membrane that forms its basal and lateral surfaces, distinct from the lumenal or apical surface.
Areolar connective tissue
Areolar connective tissue (or loose connective tissue) is the most widely distributed connective tissue type in the body. It can be found in the skin as well as in places that connect epithelium to other tissues.
Extracellular matrix
The extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the cells in addition to performing other functions. It is the defining feature of connective tissue in animals.
Dense connective tissue
Dense connective tissue has collagen fibers as its main matrix element.
Fibrous connective tissue
Fibrous connective tissue is a type of connective tissue which has relatively high tensile strength, due to a relatively high concentration of collagenous fibers.
Adipocytes are the cells that primarily compose adipose tissue, specialized in storing energy as fat.
White adipose tissue
White adipose tissue is one of the two types of adipose tissue found in mammals, in humans, composing as much as 20% of the body weight in men and 25% of the body weight in women.
Brown adipose tissue
Brown adipose tissue is present in many newborn or hibernating mammals as well as migratory birds. Its primary purpose is to generate body heat.
Optical microscope
The optical microscope, often referred to as a light microscope, is a type of microscope which uses visible light and a system of lenses to magnify images of small samples.
Olfactory epithelium
The olfactory epithelium is a specialized epithelial tissue inside the nasal cavity that is involved in smell.
Lamina propria
The lamina propria is a thin layer of loose connective tissue which lies beneath the epithelium and together with the epithelium constitutes the mucosa.
The microvilli are structures that increase the surface area of cells by approximately 600 fold, thus facilitating absorption and secretion.
Mucins are a family of large, heavily glycosylated proteins which are secreted on mucosal surfaces and in saliva.
The mesothelium is a membrane that forms the lining of several body cavities: the pleura, peritoneum and pericardium.
A fibroblast is a type of cell that synthesizes and maintains the extracellular matrix of many animal tissues.
Cell adhesion molecule
Cell adhesion molecules are proteins located on the cell surface involved with the binding with other cells or with the extracellular matrix.
Stroma refers to the connective, non-functional supportive matrix or framework of a biological cell, tissue, or organ.
Reticular connective tissue
Reticular connective tissue is a type of loose irregular connective tissue which has a network of reticulated fibers that form a soft skeleton to support the lymphoid organs.
Histological section
A histological section is a thin slices of tissue applied to a microscopic slide, usually around 5 to 10 micrometres thick, to be viewed under a microscope.
Pseudostratified epithelium
A pseudostratified epithelium is a type of epithelium that, though comprising only a single layer of cells, has its cell nuclei positioned in a manner suggestive of stratified epithelia.
Ground substance
Ground substance is a term for the non-collagenous components of the extracellular matrix.
Elastic fiber
Elastic fibers (or yellow fibers) are bundles of protein elastin found in connective tissue and produced by fibroblasts and smooth muscle cells in arteries.
Immunohistochemistry refers to the process of localizing proteins in the cells of a tissue section by exploiting the principle of the specific binding of antibodies to antigens.
Hematoxylin and eosin stain
Hematoxylin and eosin stain is a popular staining method in histology. It is the most widely used stain in medical diagnosis.
Advanced terms that may appear in context in MCAT passages
A counterstain is a histological stain with color contrasting to the principal stain, making the stained structure more easily visible.
Eosinophilic means loves eosin, and refers to the staining of certain tissues, cells, or organelles after they been washed with eosin, a dye.
Buccal mucosa
Buccal mucosa is mucous membrane of the inside of the cheek.
Germinal epithelium
The germinal epithelium of Waldeyer is a layer of columnar cells covering the surface of the ovary.
Hyaluronan, also called hyaluronic acid, is a non-sulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues.
A microtome is a mechanical instrument used to cut biological specimens into very thin segments for microscopic examination.
Immunofluorescence is the labeling of antibodies or antigens with fluorescent dyes.
In situ hybridization
In situ hybridization is a type of hybridization that uses a labeled complementary DNA or RNA probe to localize a specific DNA or RNA sequence in a portion or section of tissue.
Mucocutaneous zone
A mucocutaneous zone is a region of skin comprising both mucosa and cutaneous skin.
Selectins are a family of cell adhesion molecules that are single-chain transmembrane glycoproteins which share similar properties to C-type lectins due to a related amino terminus and calcium-dependent binding.
Fluorescein is a fluorophore commonly used in microscopy, as well as in forensics and serology to detect latent blood stains.
Green fluorescent protein
The green fluorescent protein is a protein of great use to fluorescence microscopy, comprised of 238 amino acids from the jellyfish Aequorea victoria that fluoresces green when exposed to blue light.
Van Gieson's stain
Van Gieson's Stain is a mixture of Picric Acid and Acid Fuchsin, which represents the simplest method of differential staining of Collagen and other Connective Tissue.
Periodic acid-Schiff stain
Periodic acid-Schiff is a staining method used in histology and pathology primarily to identify glycogen in tissues.