Epithelium Flashcards
What are tissues?
A group of closely associated cells that perform related functions and are similar in structure.
-Between cells: non living extracellular material
What are the 4 basic types of tissue?
- epithelium -covering
- connective tissue- support
- muscle tissue - movement
- nervous tissue - control
What is epithelium?
Sheet of cells that covers a body surface or lines a body cavity; also form most of the body’s glands
What are the roles and functions of epithelia?
Roles: as interfaces and as boundaries
Functions:
- protection
- sensory reception
- secretion
- absorption
- ion transport
- filtration
- formation of slippery surfaces for movement.
What are the special characteristics of epithelia?
- cellularity
- specialized contacts cell junctions
- polarity
- free upper (apical) surface
- Lower (basal) surface contributing basal lamina to basement membrane
-support by connective tissue
- Avascular but innervates
- without vessels
- with nerve endings
-regeneration
How can epithelia be classified according to shape?
Squamous- wider than tall (flattened appearance)
Cuboidal- as tall as wide
Columnar- taller than wide
How can epithelia be classified according to thickness?
Simple- one cell layer
Stratified- more than one layer of cells (which are named according to the shape of the cells in the apical layer)
Which epithelial cell classification is important for diffusion?
Squamous
Which epithelial classification is important for secretion and absorption ? Why ?
Cuboidal and columnar
Larger cells because of machinery of production, packaging, and energy requirements
What are the 6 type of epithelial tissue?
- simple squamous epithelium
- simple cuboidal epithelium
- simple columnar epithelium
- pseudostratified epithelium
- stratified squamous epithelium
- transitional epithelium
Where would simple squamous epithelium be located?
Simple squamous epithelium may be located at sites of rapid diffusion, such as:
- lining of the lung alveoli
- lining of blood vessels
- in the lining of major body cavities
What is endothelium?
A simple squamous epithelium that lines the interior of the circulatory vessels and the heart
What is the mesothelium?
Simple squamous epithelium that lines the peritoneal, pleural and pericardial cavities and covers the viscera
Which body parts require for simple cuboidal epithelium?
Ducts of glands
- small ducts - simple cuboidal epithelium
- large ducts - stratified cuboid
- N.B. deeper cells may also be cuboidal
Pigmented layer of retina
Surface of Ovary
Follicular cells of thyroid
Which body parts use simple columnar epithelium?
Some usual locations
- gall bladder
- epithelium of digestive system
- epithelium of uterus
- uterine glands
What is pseudostratified epithelium?
Appears stratified, typically with nuclei located in at least two more-or-less distinct levels. But in fact every cell rests on the basement membrane, so the epithelium is technically “simple”, in spite of appearances
Where is pseudostratified epithelium found?
Found lining the respiratory system and in the excretory ducts of the male reproductive system
What kind of pseudostratified epithelium is in the respiratory system?
Pseudostratified epithelium with goblet cells
What are the stratified squamous epithelium?
Surface cells are squamous
Deeper cells may be cuboidal in nature and can regenerate
What is the usual function of stratified squamous epithelium?
Usually protective in function. The outer layer may or may not be keratinized
Also used where transport is important
Where are the stratified squamous epithelium found?
Gastrointestinal tract e.g. oesophagus, anus- non-keratinized
- Vagina - non-keratinized
- Skin - keratinized
What are transitional epithelium?
Urothelium
Lines the distensible walls of the urinary tract
Glands are formed from
Epithelial cells
Describe the functioning of glands
- production and secretion of needed substances
- Aqeous (water-based) products
- the protein product is made in rough ER, packed into secretory granules by Golgi apparatus, released from the cell by exocytosis
What the classification of glands ?
Exocrine: external secretion onto body surfaces (skin) or into body cavities
Endocrine: secrete messenger molecules (hormones) which are carried by blood to target organs; “ductless” glands
By cell count: unicellular or multicellular
Give an example of a unicellular exocrine glands
Unicellular: goblet cell scattered within epithelial lining of intestines and respiratory tubes
Product: mucin
Mucus is mucin and water
What is distinctive about multicellular exocrine glands?
Epithelium-walled duct and a secretory unit
Give some examples of exocrine gland products
Many types of mucus secreting glands
- sweat glands of skin
- oil glands of skin
- salivary glands of mouth
- liver(bile)
- pancreas (digestive enzymes)
- mammary glands (milk)
Describe endocrine glands
Ductless glands
- release hormones into extracellular shape
- hormones are messenger molecules
-Hormones enter blood and travel to specific target organs
List the epithelial surface features
- lateral surfaces
- basal surfaces
- apical surfaces
Describe the lateral epithelial cell surfaces
- adhesion
- tongue and groove wavy contours
- cell junctions
Describe the basal epithelial surface
Basal lamina: noncellular sheet of protein together with reticular fibers form basement membrane
List the type of cell junctions
- tight junctions
- adherents junctions
- desmosomes
- gap junctions
What are the functions of gap junctions?
Allow small molecules to move between cells
What are the functions of desmosomes ?
- anchoring junctions
- filaments anchor to the opposite side
What are the functions of adherents junctions?
Transmembrane linker proteins
What are the function of tight junctions?
Impermeable
List the features if the apical features
Microvilli
Cilia
Flagellum
What are cilia?
Whiplike motile extensions of the apical surface membranes
What are flagellum?
- long isolated cilium
- only found as sperm in human
What are microvilli?
Maximize surface
- finger like extensions of the plasma membrane of apical epithelial cells
- on moist and mucus secreting epithelium
- longest in epithelia that absorb nutrients (small intestine) or transport ions (kidneys)
