Epithelia Flashcards
(28 cards)
What are the 2 types of epithelia?
- Covering epithelia
2. Glandular epithelia
What is the difference between endocrine and exocrine glands?
Exocrine glands have ducts. Endocrine glands don’t have ducts but secrete hormones directly into the bloodstream
Example of exocrine gland
Sweat gland, salivary gland
In the classification of epithelia, what is one layer of cells called?
Simple epithelium
What are multiple layers of cells called?
Stratified epithelium
What is benefit of stratified epithelium?
Protective: the higher the number of layers the more protective it is at withstanding abrasion
What is pseudo-stratified?
Single layer of cells but the nuclei are at different heights, so it looks like more than one layer
What are transitional epithelia?
The cells can alter their shape
How do squamous cells look?
Cells are flat: width is much greater than the height
How do cuboidal cells look?
Cells appear approx square
How do columnar cells look?
Cells are tall: height is greater than width
What is shape and structure of epithelia involved in gas exchange? Why?
Single layer of squamous cells i.e. simple. squamous
Minimal distance for gaseous diffusion
Some cells have specialisations. What is purpose of microvilli?
Increase the surface area of epithelium available for absorption.
Where are microvilli most developed?
In cells specialised for absorption e.g. intestinal cells
What is purpose of keratin?
In the skin, basal cells start to divide and move out into layers above where they start to lose their nuclei and degenerate. These cells finally flake off from apical surface
Where is keratin mostly found?
In areas susceptible to abrasion and water loss (skin). Layers of the immediate protein keratin are found on the apical surface
What is classification of cells found in oesophagus?
Non-keratinised stratified squamous epithelium
- Does not need layer of keratin for protection against drying out
- Many layers: protective
What is purpose of cilia and where are they found?
Beat synchronously. Found on cells lining upper respiratory tract, rhythmic beating moves mucus upwards
What are the 3 methods of secretion of exocrine secretion?
Merocrine, Holocrine, Apocrine
What happens during holocrine?
Secretory product accumulates in cytoplasm. Whole cell ruptures to release product
What is example of holocrine secretion?
Sebum in sebaceous glands
What happens during merocrine secretion?
Most common form of secretion
- Product produced inside intra-cellular vesicle which travels up to surface
- Fusing with cell membrane. 3. Product released by exocytosis
- Fused plasma membrane recycled by endocytosis
What is example of merocrine secretion?
Most sweat glands, pancreas
What happens during apocrine?
- Product in vesicle
2. Vesicle approaches apical membrane which pinches off with some loss of apical membrane
