Histology Terms
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adipose - A loose connective tissue made up of specialized cells called adipocytes, which store triglycerides. Adipose tissue is a major reserve of body energy and supports and protects various organs. T
anchoring junction - a cellular junction which serves to anchor sells to one another or to extracellular material; seen in tissues subjected to friction and stretching (e.g., muscle tissue of heart). T
apical surface - the free or unattached surface of an epithelial cell. T
apocrine - an exocrine gland which accumulates its secretory product at the apical surface of each cell. That part of each cell then separates from the remainder to from a secretion in the lumen of the gland. The cells then repair themselves (e.g., mammary glands). T
areolar - a widely distributed connective tissue made up of a number of different types of cells; combines with adipose tissue to form the subcutaneous layer of the body. T
basal lamina - the more superficial of two layers (along with the reticular lamina) making up the basement membrane. It is produced by the overlying epithelial tissue. T
basal surface - the surface of an epithelial cell which is attached to the underlying basement membrane. T
basement membrane - the thin extracellular layer which attaches the epithelium to the underlying connective tissue. It is made up of a superficial basal lamina and an underlying reticular lamina. T
-blast - a suffix which denotes a less differentiated precursor cell. It may or may not retain mitotic capability. Examples: myeloblast (white cell precursor), osteoblast (bone cell precursor). T
cilia - hairlike projections of lining epithelial cells which help move substances through the lumen by a coordinated waving motion. T
collagen - a protein which is the main component of connective tissue. T
collagen fiber - the most common of three types of fiber embedded in the matrix between cells of connective tissue. These lie in parallel rows, and add great strength. T
columnar - a type of epithelial tissue whose cells are shaped like columns. The tissue resembles a series of dominoes laid side by side. T
connective tissue - the most common of four basic tissue types in the human body. Functions as support for
epithelial tissues and as the binding (or "glue") of various organs. T
cuboidal - a type of epithelial tissue whose cells are shaped like cubes or blocks. T
cutaneous membrane - the membrane which covers the outer surface of the body (the skin). T
-cyte - a suffix which denotes a differentiated or mature cell. It has usually lost its mitotic potential. Examples: osteocyte (mature bone cell), adipocyte (mature fat cell). T
dermis - the
connective tissue layer of skin. T
desmosome - a type of anchoring junction which forms a firm attachment with other cells in a manner resembling a "spot weld." T
ectoderm - the outermost of the three primary embryonic germ layers, which gives rise to nervous tissue and the epidermis. T
elastic fiber - one of three types of fiber embedded in the matrix between cells of connective tissue. Smaller than collagen fibers, these allow tissues to stretch. Found in blood vessel walls and lung tissue. T
endocrine - a system of glands without ducts that deliver their secretions directly into the bloodstream. T
endoderm - the innermost of the three primary embryonic germ layers, which gives rise to the GI tract, urinary bladder and urethra, and respiratory tract. T
epidermis - the epithelial layer of skin. T
epithelial membrane - a membrane made up of an epithelial tissue layer as well as an underlying connective tissue layer. Examples include cutaneous, mucous, and serous membranes. T
epithelial tissue (epithelium) - the tissue which forms the superificial layer of skin and some organs. It also forms the inner lining of blood vessels, ducts, body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems. T
exocrine - glands that deliver their secretions through ducts into body cavities or to the outside. T
gap junction - a cellular junction which allows the two-way spread of action potentials from one cell to the next. T
goblet cells - specialized epithelial cells which secrete mucous for lubrication. T
ground substance - the chemical component of the matrix of connective tissue. T
holocrine - an exocrine gland in which entire cells and their secretions accumulate as the gland's secretory product. Discharged cells are replaced by new ones (e.g., sebaceous or oil glands). T
hyaluronic acid - a complex molecule (glycosaminoglycan) which is one of several types of ground substance. It is a thick, lubricating substance which binds cells together and lubricates joints. T
keratin - insoluble protein found in skin and epidermal appendages. T
lumen - the space within a blood vessel or hollow organ. T
Marfan’s syndrome - a hereditary disorder leading to a defect in elastic fibers. T
matrix - the intercellular material, or "glue" of connective tissue, made up of protein fibers and ground substance. T
membrane - a flexible sheet of tissue which may line cavities, or cover organs, joints, or the whole body. T
merocrine - an exocrine gland which secretes its product from intact cells (e.g., salivary glands). T
mesenchyme - the embryonic connective tissue from which all other connective tissue eventually arises. T
mesoderm - the middle of the three primary embryonic germ layers, which gives rise to connective tissue and most muscle. T
microvilli - microscopic projections of the plasma membrane of individual epithelial cells, to increase surface area in areas specialized for absorption or secretion (e.g., GI tract). Do not confuse these with villi (multicellular), or with cilia. T
mucous membrane (mucosa) - the type of membrane which lines body cavities which are open to the exterior. T
parenchyma - the functional tissue of an organ, as opposed to the supportive structures. T
parietal layer - a layer of serous membrane which lines the inside of a body cavity. T
pericardium - a loose serous membrane enclosing the heart. T
peritoneum - the serous membrane which lines the abdominal cavity and covers the abdominal organs. T
pleura - the serous membrane which lines the thoracic cavity and covers the lungs. T
pseudostratified columnar - epithelial tissue made up of simple columnar cells whose nuclei are situated at different levels, giving the appearance of stratification (e.g. lining of trachea). T
reticular fiber - one of three types of fiber embedded in the matrix between cells of connective tissue. Thinner than collagen fibers, this fiber forms branching networks, and helps form the stroma of many organs. T
reticular lamina - the deeper of two layers (along with the basal lamina) making up the basement membrane. It is produced by the underlying connective tissue. T
serous membrane (serosa) - the type of membrane which lines body cavities which do not open to the exterior. It also covers organs which lie within those cavities. T
simple - an epithelial tissue consisting of a single row of cells. T
simple columnar - an epithelial tissue consisting of a single row of columnar cells (e.g., inner lining of stomach). T
simple cuboidal - an epithelial tissue consisting of a single row of cuboidal cells (e.g., thyroid follicles). T
simple squamous - an epithelial tissue consisting of a single row of cells. T
squamous - flat, tile-like cells. T
stratified - consisting of many layers of cells. T
stratified squamous - an epithelial tissue consisting of multiple layers of squamous cells (e.g., skin). T
stroma - the supportive tissue of an organ, as opposed to the functioning tissue. T
subcutaneous layer (superficial fascia) - a sheet made up of connective tissue and adipose tissue which lies just below the dermis of the skin, but above the deep fascia of muscle. T
synovial membrane - a membrane which lines joints, which has only an areolar connective tissue layer.
tight junction - a cellular junction which forms a fluid-tight seal between cells (e.g., lining epithelial cells of large intestine). T
transitional - a stratified epithelial tissue consisting of cells which vary in appearance between squamous and cuboidal. This depends on whether the tissue is stretched or relaxed (e.g., urinary bladder). T
villus - a multicellular projection of lining epithelium in areas specialized for absorption or secretion. T
visceral layer - a layer of serous membrane which lines the outside of a body organ. T
Reference: Tortora GJ and Graboski SR, Principles of Anatomy and Physiology, 9th Ed., John Wiley, 2000.
