In epithelial tissue, cells are closely packed with little or no extracellular matrix except for the basal lamina that separates the epithelium from underlying tissue. The main functions of epithelia are protection from the environment, coverage, secretion and excretion, absorption, and filtration. Cells are bound together by tight junctions that form an impermeable barrier. They can also be connected by gap junctions, which allow free exchange of soluble molecules between cells, and anchoring junctions, which attach cell to cell or cell to matrix. The different types of epithelial tissues are characterized by their cellular shapes and arrangements: squamous, cuboidal, or columnar epithelia. Single cell layers form simple epithelia, whereas stacked cells form stratified epithelia. Very few capillaries penetrate these tissues.
Glands are secretory tissues and organs that are derived from epithelial tissues. Exocrine glands release their products through ducts. Endocrine glands secrete hormones directly into the interstitial fluid and blood stream. Glands are classified both according to the type of secretion and by their structure. Merocrine glands secrete products as they are synthesized. Apocrine glands release secretions by pinching off the apical portion of the cell, whereas holocrine gland cells store their secretions until they rupture and release their contents. In this case, the cell becomes part of the secretion.
Cells closely packed together; tight junctions; little intercellular material; very few capillaries.
Basement membrane (lamina) anchors epithelial cells.
Functions:
protects underlying tissues
absorbs nutrients
secretes hormones, mucus, and enzymes
excretes waste like urea in sweat.
Epithelial tissue can be named according to shape, arrangement, or function.
Squamous epithelial cells are flat; protective function eg lining of mouth, skin.
Cuboidal epithelial cells are shaped like cubes; function in protection and secretion.
Columnar epithelial cells are tall and rectangular; function in secretion and absorption.
Simple epithelium is one cell layer thick.
Stratified epithelium is several layers of cells thick.
Pseudostratified epithelium looks like several layers thick, but all cells extend from the basement membrane to the outer surface.
Transitional epithelium consists of several layers of closely packed, easily stretched cells. When stretched they appear flat; when relaxed they look ragged or saw-toothed.
1. Mucous membrane produces mucus. It protects, absorbs nutrients, and secretes enzymes and bile salts in addition to mucus.
2. Glands are secretory tissues and organs:
Exocrine glands secrete through ducts.
2 types by structure:
Simple - single unbranching ducts, eg. sweat and sebaceous glands
Compound - branching lobules and ducts, eg. mammary glands and salivary glands
3 types by type of secretion
Merocrine glands secrete products as they are synthesized.
Apocrine glands release secretions by pinching off the apical portion of the cell
Holocrine gland cells store their secretions until they rupture and release their contents.
Endocrine glands are ductless and secrete hormones directly into the bloodstream.
5. Endothelium lines the blood and lymphatic vessels. The endothelium of the heart is called the endocardium.
6. Mesothelium or serous tissue lines the great cavities of the body:
pleura lines the thoracic cavity
peritoneum lines the abdominal cavity
pericardium covers the heart.
anchoring junction
mechanically attaches adjacent cells to each other or to the basement membrane
apical
that part of a cell or tissue which, in general, faces an open space
apocrine secretion
release of a substance along with the apical portion of the cell
basal lamina
thin extracellular layer that lies underneath epithelial cells and separates them from other tissues
basement membrane
in epithelial tissue, a thin layer of fibrous material that anchors the epithelial tissue to the underlying connective tissue; made up of the basal lamina and reticular lamina
cell junction
point of cell-to-cell contact that connects one cell to another in a tissue
endocrine gland
groups of cells that release chemical signals into the intercellular fluid to be picked up and transported to their target organs by blood
endothelium
tissue that lines vessels of the lymphatic and cardiovascular system, made up of a simple squamous epithelium
exocrine gland
group of epithelial cells that secrete substances through ducts that open to the skin or to internal body surfaces that lead to the exterior of the body
gap junction
allows cytoplasmic communications to occur between cells
goblet cell
unicellular gland found in columnar epithelium that secretes mucous
holocrine secretion
release of a substance caused by the rupture of a gland cell, which becomes part of the secretion
merocrine secretion
release of a substance from a gland via exocytosis
mesothelium
simple squamous epithelial tissue which covers the major body cavities and is the epithelial portion of serous membranes
mucous gland
group of cells that secrete mucous, a thick, slippery substance that keeps tissues moist and acts as a lubricant
pseudostratified columnar epithelium
tissue that consists of a single layer of irregularly shaped and sized cells that give the appearance of multiple layers; found in ducts of certain glands and the upper respiratory tract
reticular lamina
matrix containing collagen and elastin secreted by connective tissue; a component of the basement membrane
serous gland
group of cells within the serous membrane that secrete a lubricating substance onto the surface
simple columnar epithelium
tissue that consists of a single layer of column-like cells; promotes secretion and absorption in tissues and organs
simple cuboidal epithelium
tissue that consists of a single layer of cube-shaped cells; promotes secretion and absorption in ducts and tubules
simple squamous epithelium
tissue that consists of a single layer of flat scale-like cells; promotes diffusion and filtration across surface
stratified columnar epithelium
tissue that consists of two or more layers of column-like cells, contains glands and is found in some ducts
stratified cuboidal epithelium
tissue that consists of two or more layers of cube-shaped cells, found in some ducts
stratified squamous epithelium
tissue that consists of multiple layers of cells with the most apical being flat scale-like cells; protects surfaces from abrasion
tight junction
forms an impermeable barrier between cells
transitional epithelium
form of stratified epithelium found in the urinary tract, characterized by an apical layer of cells that change shape in response to the presence of urine
Watch this video to find out more about the anatomy of epithelial tissues. Where in the body would one find non-keratinizing stratified squamous epithelium?
The inside of the mouth, esophagus, vaginal canal, and anus.
1. In observing epithelial cells under a microscope, the cells are arranged in a single layer and look tall and narrow, and the nucleus is located close to the basal side of the cell. The specimen is what type of epithelial tissue?
A) columnar
B) stratified
C) squamous
D) transitional
A
2. Which of the following is the epithelial tissue that lines the interior of blood vessels?
A) columnar
B) pseudostratified
C) simple squamous
D) transitional
C
3. Which type of epithelial tissue specializes in moving particles across its surface and is found in airways and lining of the oviduct?
A) transitional
B) stratified columnar
C) ciliated non-stratified columnar
D) stratified squamous
C
4. The ________ exocrine gland stores its secretion until the glandular cell ruptures, whereas the ________ gland releases its apical region and reforms.
A) holocrine; apocrine
B) eccrine; endocrine
C) apocrine; holocrine
D) eccrine; apocrine
A
1. The structure of a tissue usually is optimized for its function. Describe how the structure of individual cells and tissue arrangement of the intestine lining matches its main function, to absorb nutrients.
Columnar epithelia, which form the lining of the digestive tract, can be either simple or stratified. The cells are long and narrow. The nucleus is elongated and located on the basal side of the cell. Ciliated columnar epithelium is composed of simple columnar epithelial cells that display cilia on their apical surfaces.