L4: Epithelium Flashcards
what are the main types of tissues in our bodies?
-epithelial
-connective
-muscular
-nervous
what are the characteristics of epithelial tissue?
1- The cells are close to each other with minimal intercellular substance.
2- The cells rest on a basement membrane.
3- The cells are supported by underlying connective tissue.
4-High rate of degeneration and regeneration (can divide and form new cells).
5- Nerves can enter between the epithelial cells.
6- No blood vessels enter between the cells.
7-from 3 embryonic origins (mesodermal-ectodermal-endodermal).
how are epithelial tissues classified functionally?
-covering:- covers the body and lines the cavities.
-glandular:- secretion
-neuro:- perception of stimuli
what are the types of covering epithelium?
-simple
-stratified
what are the types of simple epithelium?
-squamous
-cuboidal
-columnar
-pseudostratified
squamous simple epithelium
-1 layer
-flat cells
-flat and bulging nuclei
-in the lung alveoli, the lining of the heart, lining of blood vessels(endothelium), and external layer of the bowman’s capsule.
cuboidal simple epithelium
- 1 layer
-cuboidal cells
-central and rounded cells
-medium ducts of glands and kidney tubules.
columnar simple epithelium
-1 layer
-tall, elongated cells
-the nucleus is basal and oval
-non-modified in large ducts of glands
what are the sites of modified columnar epithelium?
-stomach—-contain vacuolated cytoplasm
-intestine—-where the cells have microvilli on their free side (brush border) for increasing the surface area and consequently absorption and it is associated with goblet cells for secretion of mucous
-uterus and fallopian tube (with cilia).
what is the shape of cells in pseudostratified epithelium?
tall and short
what is the shape of the nuclei in pseudostratified cells of epithelium?
they are arranged at different levels.
what is the site of pseudostratified epithelium?
ciliated with goblet cells: upper respiratory passages (nose-trachea-bronchi)
non-celiated: large ducts of glands
why are pseudostratified epithelium called by this name
-because cells are arranged at different levels even though they rest on the same basement membrane.
why are the nuclei arranged at different levels even though they rest in the same basement membrane?
-Due to the crowding during development.
How are stratified epithelium classified?
according to the shape of top layer cells
what are the types of stratified epithelium?
-Transitional
-columnar
-squamous
what is the structure of squamous stratified epithelium?
-has a thick wavy basement membrane.
-base layer is composed of columnar cells with basal, oval nuclei and is responsible for the regeneration of cells.
-middle layer is composed of polyhedral cells with central, rounded nuclei and is responsible for junctions between cells.
-top layer is from flat cells and flat nuclei
what is the number of layers in squamous stratified cells?
30
what are the types and sites of squamous stratified epithelium?
keratinized: is dry found in the epithelial layer of skin with horny covering scales
non-keratinized: wet and found in the mouth cavity, esophagus, anal canal, vagina, and terminal urethra.
what is the structure of transitional stratified epithelium?
-thin ill-defined basement membrane.
-base layer is composed of low columnar cells with basal, oval nuclei
-middle layer is composed of polyhedral cells with central, rounded nuclei and is separated by mucous-like substance that helps in the gliding of cells
-superficial layer consists of the top layer and the underlying layers.
top:composed of cuboidal layer which is dome-like and binucleated which is responsible for protecting underlying layers from the bad effect of urine.
underlying layers are flask-shaped
how many layers are there in transitional squamous epithelium?
6-8 layers
what are the sites of transitional stratified epithelium?
-ureter
-urinary bladder
-prostatic urethra
-pelvis of the kidney
what are the forms of transitional stratified epithelium and what does it depend on?
-it depends on the degree of distention of viscus
-in the case of full bladder it consists of two layers the upper is flat and the underlying is cuboidal
-in the case of an empty bladder it returns back to normal.
What is glandular epithelium?
It is a modified type of epithelium specialized for secretion.
How are glands classified?
-presence of ducts or not
-no. Of cells
-Branching and shape of ducts and secretory parts.
-mode of secretion
-Type of secretion
What are glands classified into according to the presence or absence of ducts?
Exocrine: salivary glands
Endocrine: suprarenal-pituitary-thyroid
Mixed: liver and pancreas
What are glands classified into according to no. of cells?
Mono like goblet cells and multi-like liver and salivary glands.
What are glands classified Into according to branching and shape of ducts and secretory parts?
Simple: no branching
Simple branched: branching in secretory part
Compound branched:Branching in both
What are types of simple glands?
Simple tubular: Have tubular secretory part
Simple alveolar: Have an alveolar (flask-shaped) secretory part.
Simple tubualveolar: Have both tubular and alveolar secretory part
What are the types of simple branched glands?
1- simple branched tubular
2- simple branched alveolar
3- simple branched tubualveolar
What are the types of compound branched glands?
1- compound branched tubular
2- compound branched alveolar
3- compound branched tubualveolar
What is the classification of glands according to the mode of secretion?
Merocrine glands:
- The cells of the glands are intact at the time of secretion
E.g. Salivary glands
Holocrine glands:
- The cells are shed at the time of secretion and then replaced by new cells
E.g. Sebaceous glands
Apocrine glands:
- The apical portions of the cells are pinched off at the time of secretion
E.g. Mammary glands
What is the Classification of glands according to Nature of secretion?
What is the structure of neuroepithelium?
1- sensory cells:
apical part: hairlets (microvilli)
basal part: surrounded by nerve fibrils
2- supporting cells
3- basal cells (can give the other two types)
What are the sites of neuroepithelium?
- Taste buds (tongue)
- Organ of corti (inner ear)
- Olfactory epithelium (nose)
What is the definition of intracellular junctions?
The lateral membranes of the epithelial cells show several specialized structures called intercellular junctions that contribute to adhesion and communication between the cells
What are the types of intracellular junctions?
Types
1- Tight junction
2- Adherens junction
3- Gap junction
What is the structure of occludens (tight) junctions?
The 2 adjacent cell membranes fuse completely at certain points (ICS=0) to form a seal between I.C & luminal fluids
What are the sites & types of occludens (tight) junctions?
- Epithelial cells of the intestine
- Proximal convoluted tubules of the kidney
- Capillary endothelial cells
What is the function of occludens (tight) Junctions?
Forming a complete seal that prevent passage of materials (water & other fluids) from the lumen to the I.C.S
What is the structure of adherens junctions?
The 2 adjacent cell membranes are separated by wide I.C.S filled with binding (adhesive) material
What are the sites of adherens junctions?
Firm adhesion between the cells that fix them strongly and preventing their separation
What is the structure of gap junctions?
The 2 adjacent cell membranes are separated by 2nm gap to allow cell communication
What are the sites & functions of gap junctions?
1- In the heart, rapid transmission of nerve impulse between the cells so heart contract as one unit (coordinated heart beat)
2- In smooth muscle: transmission of wave of contraction to act in coordination
3- Between the bone cells for rapid exchange of small molecules
