Introduction To Histology - Epithelium Flashcards
What is epithelia ?
Type of tissue.
Epithelia are a continuous sheet of cells covering the surfaces of the body.
Include both: surface epithelia + solid organs
What does epithelial tissue look like
Cells in close contact
Cells are polarised- supported by basement membrane
What does the basement membrane provide for epithelial tissue?
Provides site of attachment
Also separates the epithelium from underlying supporting tissues
Epithelial cells therefore polarised
Is epithelial tissue vascular or avascular ?
Avascular -> nourished by connective tissue which have blood vessels
What are the function of epithelial tissue ?
Covers and protects surfaces outside and inside of the body
Lines internal cavities, blood vessels and organs
Forms glandular structures
Forms barriers
Combines with nervous tissue to make special senses -> neuroepithelium
What are the two major types of epithelia ?
Covering epithelia and glandular epithelia
What is covering epithelia and what is its function ?
Covers/lines all body surfaces, cavities, tubes
What are glands ?
An organised collection of secretory epithelial cells
How are glands formed ?
Development of proliferation/invagination of epithelium -> project into underlying connective tissue
What are the two types of glands ?
Exocrine gland
Endocrine gland
What are exocrine glands ?
Retain continuity with surface- secrete via duct
What are endocrine glands ?
Lose contact with surface when their ducts degenerate during development
-> secrete directly into bloodstream
How can epithelia be classified ?
Number of layers
Shapes of cells
Surface specialisations
Explain simple in terms of layers
Single layer
Good for absorption/secretion fragile
Explain stratified in terms of layers ?
2 or more layers of cells, good for protection
Explain pseudostratified in terms of layers
One layer with mixture of cell shapes
Looks stratified as nuclei at different levels and not all cells reach surface
All cells in contact with basement membrane
What does a squamous cell look like ?
Squamous - flat shaped
What does cuboidal shape look like ?
Cube shaped
What does columnar shape of cell look like ?
Tall cylindrical shaped
What does a transitional shape cell look like ?
Readily changes shape, accommodates stretching
What are the classifications of epithelial tissue ?
Simple squamous
Simple cuboidal
simple columnar
Stratified squamous
Pseudostratified
Transitional
What is the structure of simple squamous epithelium
Single layer of flat cells
Irregularly shaped/hexagonal
Compared to scales on a fish
What is the function of simple squamous epithelium
Diffusion, filtration, some secretion and protection against friction
Due to delicate thin lining which allows easy passage of fluid
Where is simple squamous epithelium sound
Lining of blood vessels and the heart
Alveoli
Lining of serous membranes of the body cavities
Lining of some kidney tubules, etc
What is the structure o simple cuboidal epithelium ?
Single layer of cube shaped cells
Some cells which are kidney tubules have microvilli
What is the function of simple cuboidal epithelium
Good for diffusion
Lines small ducts that have excretory, secretory and absorptive functions
- good for secretion and absorption
Where are simple cuboidal epithelium found
Kidney tubules,
Glands and their ducts,
Lining of terminal bronchioles of the lungs,
Surfaces of the ovaries
What is the structure of simple columnar epithelium
Single layer of tall, narrow cells;
Nuclei are elongated
Some cells have cilia (bronchioles of lungs, auditory tubes, uterine tubes, and uterus) or microvilli (intestines)
What is the function of simple columnar epithelium
Movement of substances, absorption and Secretion
Offer more protection than flatter cells
Where can simple columnar epithelium be found
Location: Glands and some ducts, bronchioles of the lungs, auditory tubes, uterus, uterine tubes, stomach, intestines, gallbladder, bile ducts, ventricles of the brain
What is the structure of stratified squamous epithelium
Multiple layers of cells that are cube-shaped in the basal layer and progressively flattened toward the surface
The basal layer contains which type of cell ?
Continuously dividing stem cells
Explain keratinisation in stratified squamous epithelium
Stratified squamous epithelium cells can be nonkeratinized (moist) or keratinized;
What does stratified squamous look like
What is the function of stratified squamous
Protection against abrasion, a barrier against infection, reduction of water loss from the body
Where are stratified squamous epithelium found ?
Keratinized— skin
Nonkeratinized— mouth, throat, larynx, esophagus, anus, vagina, inferior urethra, cornea
What is the structure of pseudostratified epithelium
Technically single
layer - some cells reach the free surface others do not;
Nuclei at different levels so appears stratified
Almost always ciliated and associated with goblet cells (secrete mucus)
In a pseudo-stratified epithelium what do all cells do even though it seems stratified
All cells touch basal layer
What is the function of pseudo stratified epithelium
Synthesize and secrete mucus & move mucus (or fluid) that contains foreign particles over the surface
Due to goblet cells and cilia
Where are pseudostratified epithelium found
Lining of the nasal cavity, nasal sinuses, auditory tubes, pharynx, trachea, bronchi of the lungs
How would pseudostratified epithelium be found
Almost always has cilia and multiple rows of nuclei
What is the structure of transitional epithelium
Structure: Cuboidal/columnar when not stretched
Squamous/flattenend when stretched
Cell layers also decrease when stretched
Eg non distended 5/6 layers to 2/3 layers
What is the function of transitional epithelium
Accommodate fluctuations in the volume of
fluid in organs or tubes (tolerates stretching & recoil without damage)
Can withstand toxicity of urine
Where is transitional epithelium found
Lining of the urinary bladder, ureters, superior urethra, pelvis of the kidney (i.e. structures where considerable expansion occurs)
Hat does transitional epithelium look like
What is the difference between transitional epithelium between when organ is empty and filled
Empty - thicker epithelium
More layers
Cells have rounded borders
Filled organ- 2,3 layers
Cells have become flattened and no longer rounded
Resemble squamous epithelium
