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
visceral peritoneum
this layer of peritoneum covers the surfaces of internal organs* within the abdominal cavity
parietal peritoneum
this layer of peritoneum lines the internal surface of the abdominal cavity wall
What does parietal mean?
the term parietal means pertaining to a wall or partition
Pleura
comprised of a single layer of squamous epithelial cells; there are two layers of pleura in the thoracic cavity
visceral pleura
this layer of pleura covers surfaces of the internal organs within the chest (thoracic) cavity
parietal pleura
internal lining of the chest cavity
pericardium
double membranous sac that surrounds the heart
endothelium
inner lining of blood vessels
Simple cuboidal epithelium (where is it found?)
– the renal tubules are an example of one location where simple cuboidal epithelium is found
–in the kidneys it functions in absorption and secretion
Simple columnar epithelium (where is it found?)
i. lines the digestive tract – the simple columnar epithelium that lines the digestive tract has microvilli
ii. ciliated simple columnar epithelium is found in uterine tubes and in the small bronchi of lungs
Simple Columnar Epithelium (what are its functions?)
absorption and secretion in the digestive tract; ciliated type assists with movement of particles out of the lungs and with movement of the oocyte through the uterine tube.
Pseudostratified columnar epithelium (What is it?)
this epithelium has the false appearance of being stratified; every cell is attached to the basement membrane which makes it a single layer, not a stratified layer of cells
Pseudostratified columnar epithelium (where is it found?)
Respiratory tract (trachea and bronchi)
Pseudostratified columnar epithelium (what is its function?)
Functions as a mucociliary elevator to trap and remove debris that is in the air we
breath from the airways thereby preventing much of the debris that in inhaled air
form reaching the small airways and air sacs in the lungs
Stratified epithelium
this is epithelium that is comprised of several layers of cells.
Stratified squamous epithelium
several cell layers thick; the surface layer of cells is a layer of squamous cells.
Stratified squamous epithelium (Location)
Epidermis (keratinized); lining of the mouth, esophagus, and the
vagina (non-keratinized)
Stratified squamous epithelium (function)
Protects underlying tissues from abrasion, etc…
Stratified cuboidal epithelium
two layers of cuboidal cells
Stratified cuboidal epithelium (location)
Ducts of mammary glands, sweat glands, and salivary glands
Stratified cuboidal epithelium (function)
Secretion, absorption, and protection
Stratified columnar epithelium
this type of epithelium is <u>rare</u>
Stratified columnar epithelium (location)
Found in the urethra of some male animals
Stratified Columnar epithelium (function)
Functions in secretion and protection
Transitional epithelium
this is a special type of epithelium; it has the ability to stretch
Transitional epithelium (location)
Walls of the urinary bladder, the ureters, and the urethra
Transitional epithelium (function)
Stretches to increase the size of the urinary bladder as it is filling with urine
- when this type of epithelium is stretched it is thinner with fewer layers of cells;
when it is not stretched (as in a relaxed bladder that is empty) it is thicker with more layers of cells
What is an Oocyte?
Cell in an ovary that may undergo meiotic division to form an ovum
