Epithelium Flashcards
Epithelium
body and organ coverings, lining of body cavities and tubular structures, glandular epithelium
Epithelial tissue serves to:
- cover organs such as the lungs
- lines tubular structures such as blood vessels and the intestinal tract
- lines body cavities such as the mouth, thoracic cavity, and abdominal cavity
Name some General Characteristics of Epithelium
- The cells of epithelial tissue are tightly packed together into one or more layers of cells
- There is little or no room for extracellular matrix between epithelial cells
- Epithelial tissue is composed of either a single layer of cells called simple epithelium
or a multiple layer of cells known as stratified epithelium - All epithelial is avascular and relies on the blood supply of the underlying connective tissue for oxygen and nutrients
What are the functions of epithelium?
- Some epithelium serves to provide a protective covering for other tissues or organs
- In some locations it acts as a filter of biochemical substances
- Some epithelia is absorptive and/or secretive
Glandular epithelium
- This type of epithelium produces substances that are secreted or excreted
- Hormones, enzymes, milk, and sweat are all examples of substances produced by glandular epithelia
Secretions vs. excretions
- Excretions are substances that ultimately leave the body (eg., sweat)
- Secretions are substances that remain within the body (eg., insulin)
Basement membrane
- A nonliving meshwork of fibers that cements the epithelium to the underlying connective tissue
microvilli
- Some epithelium is covered with a surface specialization called microvilli
– Microvilli greatly increases the surface area of the epithelium
– Microvilli functions in absorption and secretion
Cilia
– Found on the free surface of the epithelium that lines the respiratory tract
– Cilia are very short hair like structures that constantly move in a coordinated wave-like manner
– It functions to move the mucus that is produced by the Goblet cells* that are located in the layer of epithelium that lines the respiratory tract
Goblet Cells
Goblet cells are specialized epithelial cells that produce mucus – the purpose of the mucus is to trap debris such as the dust, bacteria, viruses, etc.. that is in the air we breath so that it does not get into the small airways and air sacs of the lungs
Mucocilary Elevator
The mucus produced by Goblet cells is moved up the trachea to the throat where it can be coughed out of the windpipe (trachea) into the pharynx (throat) thereby expelling the debris trapped by the mucus so that it does not get into the lungs. It only moves up
How much does microvilli increase the absorptive and secretive capacity of the simple columnar epithelium that lines the intestinal tract?
20x (absorption is still possible, but not as efficient)
Epithelial tissue is classified according to what three characteristics?
- The number of layers of cells
- The shape of the cells – squamous, cuboidal, and columnar.
- The presence or absence of surface specializations, ie., microvilli or cilia
Simple epithelia
- comprised of a single layer of epithelia cells
- provides little protection to the underlying connective tissue
- it is found in protected areas of the body such as body cavities (chest and abdomen), ducts (bile duct) vessels (blood and lymphatic vessels), and passageways (intestinal tract)
Stratified epithelia
- comprised of more than one layer of cells which makes it thicker than simple epithelia
- the increased thickness of stratified epithelium makes it stronger and tougher than simple epithelia making it more resistant to mechanical stresses (eg., the act of chewing and swallowing
food causes abrasive force against the lining of the oral cavity and the esophagus) - it is found in areas that are subjected to mechanical stress
(eg. , the skin, mouth, esophagus, etc…)
Simple squamous
found where a smooth surface is required to reduce
friction such as the coverings of viscera and the linings of body cavities and blood vessels.
In addition to reducing friction it may also serve in filtration, secretion, and absorbtion.
What does viscera mean?
means internal organs – the term visceral means pertaining to the internal organs
peritoneum
comprised of a single layer of squamous epithelial cells; thereare two layers of peritoneum in the abdominal cavity