Epithelial Tissue Flashcards
List principle features of epithelial tissue
Features:
- Avascular i.e. they rely on diffusion alone
- Lie on layer of connective tissue known ad the basal lamina
- Cells lie close to each other i.e. very small gaps between them
- Derived from all parts of the germ layers: mesoderm, ectoderm and endoderm
- Line all body surfaces
- Have a rapid turnover rate
- Have a polarity
List the principle functions of epithelia
- Protection
- Sensation
- Absorption
- Gas exchange
- Surface movement
- Secretion of substances
- Surface lubrication
Explain the nature of cell-cell adhesion complexes with relation to epithelial function.
Tight junction: Control movement at the top
Desosomes: Control movement but are connected to intermediate filaments which facilitate communication
Hemidesomsomes: Glue the cells to the basal lamina
Adherens junction: Control communication between the cells but keep them glued together
Gap junction: Control movement of ions across cells
How do you name epithelia?
- Look at the number of layers.
If single layer = simple
If have multiple layers = stratified
If has one layer that looks like many due to different sized cells = pseudostratifed. The cells are arranged densely and the nuclei are at different layers. - Look at the shape of the cells. Can be cuboidal, columnar or squamous (flat). If stratified, look at the shape of the cells on the top layer. Transitional epithelial are epithelia that have multiple layers and the cells have different shapes e.g. in the bladder.
- Do the cells have any specialisation/adaptions. For example keratinisation, ciliated or secretory.
What is the difference between exocrine and endocrine glands?
Exocrine glands secrete their substances into ducts. Endocrine glands secrete substances directly into the blood.
What is the structure of the basement membrane?
It is made from the basal lamina and the reticular connective tissue. It is a thin, extracellular matrix of tissue that operates the lining of an internal or external body surface from underlying connecting tissue.
Give the functions of endothelium.
- Produces Prostocylin. Prostocylin prevents the adhesion of platelets `and avoid blood clot formation. Also acts as a vasodilator.
- Cells secrete smooth muscle relaxing/contracting factors. e.g. nitric acid
- Controls vascular cell growth. Epithelial cells secrete factors that stimulate angiogenesis.
- Trigger blood coagulation. Endothelial cells release tissue factors that bind to factor Vila to convert Factor X to Factor Xa and initiate the common blood clotting cascade.
- Regulate trafficking of inflammatory cells. Endothelial cells facilitate trans-epithilial migration of cells involved in an inflammatory reaction in the surrounding extravascular connective tissue,.
What is mesothelium? Give an example of a cavity lined by mesothelium.
Mesothelium is a type of simple epithelium in which the cells secrete a substance that stops the surfaces rubbing together. An example of this is the pleural cavity and the pericardial sac.
How do you name exocrine glands?
Look at the duct.
If the excretory gland is unbranched = simple.
If the excretory gland is branched = compound.
Then describe the gland: is it tubular? Alveolar/acinar? Is it coiled?
What is the mechanism of exocrine glandular secretion?
There are three main types:
Merocrine secretion: The substance is secreted by exocytosis and the membrane remains intact, and so can be recycled.
Apocrine: The secretory substance is also carried in vesicle. The vesicle again fuses with the membrane but some of the membrane is lost when released as part of the excretion process
In the breast, merocirne and aporcrine is used.
Holocrine: The cell fills up with the secretory substance and explodes when it releases the secretion. This kills the cell. e.g. sebaceous glands.
What is Epidermolysis bulls?
The cells are not stuck down onto the basal lamina. There is an abnormality in the adhesion molecules. It affects young children. It is a blistering skin disorder.
What is the biochemical cause of cystic fibrosis? What are the symptoms?
Results in the mutation of chloride channels in the apical surface of the cell to do with secretion. The mucus secreted does not have enough water and so is very thick and not easily dispelled. Leads to an increased risk of infection and infertility. Affects not only the lungs but also exocrine glands in the pancreas.
