Epithelia Flashcards
What are the common functions of epithelia
protection, sensation, absorption, digestion, secretion (glands), excretion and cleaning
What separates epithelia from underlying connective tissue
basement membrane that varies in thickness depending on the type of epithelium
What functions/roles does the basement membrane have
- anchor down the epithelium to its loose CT (in dermis)
- The basement membrane has a supportive function
What is the basement membrane formed of
proteoglycans and collagen types 3 and 4
What kinds of cells are found in simple epithelia
- Comprise a single layer of cells which all rest on the basement membrane
- Consist of cells that vary in shape from flattened to columnar according to their function.
- may have microvilli and cilia
Where can simple epithelia be found
- Are found lining absorptive or secretory surfaces (e.g. intestines)
- Where minimum barrier to passive diffusion is required (e.g. alveoli, vessels)
What cells are found in simple squamous epithelia
Consists of a single layer of flattened cells and are found lining surfaces
What kind of surface does simple squamous epithelia line
Surfaces involved in the transport of : - gases (e.g. lung alveoli) - fluids (e.g. lymphatics, blood vessels) - Series body cavities
What cells are in simple cuboidal cells
Consists of a single layer of square shaped cells.
What kinds of things does simple cuboidal epithelia line and give examples
- Line small ducts and tubules that have secretory, excretory or absorptive function
- eg. bile duct, renal medulla, salivary glands
What cells are in simple columnar cells
Are similar to cuboidal epithelium except that the cells are taller and have elongated nuclei usually at the base of the cell.
What surfaces do simple columnar cells line
- absorptive surfaces (eg. small intestine)
- secretory surfaces (eg. stomach)
What cells are found in the stratified epithelia
Consist of two or more layers of cells
Can be keratinised, e.g. in skin in order to resist friction, bacteria infection and to be waterproof
What is used to classify stratified epithelia
only the surface layer of cells
What is the main function of stratified epithelia
Protection
What determines the degree and nature of the stratification
the type of stress to which the surface is exposed
What kind of cells are usually found in stratified squamous epithelia
- Usually several layers, thick (eg. skin)
- Matures progressively from the basal layer which has cuboidal-shaped cells through to the surface layer where the cells are flattened
Give an example of non-keratinised stratified squamous epithelia
oral mucosa
What kind of cells are found in the stratified cuboidal epithelia
Consists of two or three layers of cuboidal cells
What does the stratified cuboidal epithelia line and give examples
Is found lining larger excretory ducts, such as those of
the salivary glands, sweat glands and pancreas
What functions do the stratified cuboidal provide
Does not have an absorptive or secretory function but provides a more robust lining than that of simple epithelium
Describe the cells found in the pseudo-stratified epithelium
- All cells rest on the basal lamina but not all reach the surface and thus nuclei are at different levels giving the appearance of a stratified epithelium
- May be ciliated (trachea/upper respiratory tract) or non-ciliated
Where can transitional epithelium be found
Is a special form of stratified epithelium found in the urinary tract
Why is the transitional epithelium found in the urinary tract
- Is specialised to withstand the toxicity of urine
- Can accommodate to distension, a high degree of
stretching
Why is transitional epithelium termed “transitional”
Has an appearance intermediate between that of stratified cuboidal epithelium and stratified squamous epithelium, hence “transitional”
What is a tight epithelial junction
seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them
What is a gap epithelial junction
Cell-Cell junction allowing the passage of small water soluble ions and molecules
What is the mucous membrane made of
- Epithelium
- Basement membrane
- Lamina propria (loose
CT) - smooth muscle
What specialised cells can be found in the mucous membrane
- Mucus secreting goblet cells
- Absorptive enterocytes
What are the different portions of a gland
Composed of a secretory portion and a non- secretory or excretory portion (exocrine glands).
What are the 2 types of gland
- Exocrine glands discharge their secretory product via
a duct onto an epithelial surface - Endocrine glands secrete hormones directly into the bloodstream and are composed of highly specialised epithelial cells.
What are the sections of the exocrine glands
- excretory ducts
- secretory portions
In exocrine glands what can the secretory portions be
Tubular or acinar (alveolar)
What are the 3 secretory mechanisms of exocrine glands
- Eccrine/Merocrine
- Apocrine
- Holocrine
What can be the 4 secretion contents of exocrine glands
- Sweat-water
- Mucous-Mucous
- Serous-proteins/enzymes
- Sebum-lipids
Describe the mechanism of Eccrine/merocrine secretion
- Secretory granules fuse to plasma membrane and are secreted-exocytosis
- e.g. eccrine sweat gland (thermoregulation)
Describe the mechanism of Apocrine secretion
- Unbroken, membrane-bound vesicles accumulated in apical cytoplasm, which then pinched off, the cell losing part of cytoplasm in the process
e. g. apocrine sweat gland (body odour)
Describe the mechanism of Holocrine secretion
- The whole cell lysis and entire contents secreted, thus the cells are lost in the process
- e.g. sebaceous gland
Describe the features of endocrine glands
- Much simpler than exocrine (no duct)
- Supporting tissue is thin and sparse (reticular CT)
- and associated with a very rich blood capillary
What are the 2 types of endocrine gland
Cord and clump - most common
Follicle - thyroid glands
