Protective and Glandular epithelium Flashcards
Define epithelium
Epithelium is a tissue composed of cells tightly bound together structurally and functionally to form a sheetlike or tubular structure with little extracellular matrix that line cavities of organs and cover body surfaces( internal and external)
Epithelium is functionally grouped into;
- Protective
- Secretory or glandular
List the features of epithelial cells
- Epithelial cells exhibit polarity
- They have basal and apical poles
- Poles differ in structure and function
- The basal surface of epithelial cell rest on a basement membrane
- Epithelial cells adhere strongly to neighboring cells and basal lamina
- The apical poles of some epithelial cells exhibit specialization features such as microvilli, stereocilia, cilia
- They have lateral surface modifications such as tight junctions,adherens junction,gap junction and desmosomes
- Have basal surface modification, hemidesmosome
What are the functions of the basement membrane?
- It is a semipermiable filter for substances reaching the cell from below.
- Provides structural support for epithelium
- Attaches epithelial cells to connective tissue
- Helps to organize proteins in the plasma membrane of epithelial cells
- Helps to maintain polarity
- Aids in signal transduction
- Scaffold for rapid epithelial repair and regeneration
What are the functions of tight or occluding junctions?
- Form a seal between adjacent cells
- Ensures that molecules pass by transcellular paths
- Restricts movement of membrane lipids and proteins between apical and lateral surfaces
What are the functions of adherens junction?
- Enhances the function of the tight junction
- Aids surface polarization
What is the function of gap junctions?
- They mediate intercellular communication
…………… anchor cell-cell
Desmosomes
…………. anchor cell-basement membrane
Hemidesmosomes
Features of the microvilli include;
- They are cytoplasmic projections
- Numerous in epithelia specialized for absorption
- Average size,1microm long and 0.1microm wide
- They increases total surface area
The microvilli, stereocilia, and cilia are collectively called ………..?
Apical surface modifications
Where are stereocilia usually found?
male reproductive system and inner ear sensory cells
Stereocilia and microvilli have similar functions; what are their structural differences
Stereocilia are longer, branching and less motile than microvilli
Features of cilia include;
- Usually larger than micrvilli
- About 5-10microm long and 0.2microm wide
- Exhibit rapid beating pattern
- Moves fluid and suspended matter in one direction along the epithelium
Define squamous
a layer of epithelium that consists of very thin flattened cells
Stratified refers to …………
Two or more layers of cells
What is pseudo-stratified epithelium?
“Pseudo” means fake.
Pseudo-stratified epithelium appears to be stratified, but is not.
They consist of cells with nuclei at different levels. All the cells may not reach the surface but they all adhere to the basal lamina.
Describe keratinized epithelium briefly.
Keratinized epithelium has keratin deposited on the surface which makes it impermeable and dry.
What’s a special feature of transitional epithelium?
They can undergo a change in their shape and structure
The distributions of simple squamous epithelium include
Lining of vessels (endothelium)
Serous lining of cavities
Pericardium
Pleura
Peritoneum (mesothelium)
The distributions of simple cuboidal epithelium include
Covering the ovary and thyroid
The distributions of simple columnar epithelium include
Lining of intestine
Gallbladder
stratified squamous keratinized epithelium is found in the ………….?
Epidermis
The distributions of stratified squamous non-keratinized epithelium include
Mouth
Vagina
Anal canal
Larynx
Esophagus
The distributions of stratified cuboidal epithelium include
- Sweat glands
- developing ovarian follicles
The distributions of stratified transitional epithelium include;
-Bladder
-Uterus
-Renal calyces
Where can stratified columnar epithelium be found;
Conjunctiva
The distributions of pseudo-stratified epithelium include
Lining of the trachea
Bronchi
Nasal cavity
Define glandular epithelia.
They are epithelial cells with principal function of producing and secreting various macromolecules.
They develop from covering epithelium
Differentiate between endocrine and exocrine.
Exocrine maintains its connection with original epithelium (duct) while endocrine does not.
Transport across epithelium occurs through?
- Mostly by active transport via transcellular paths aided by ion pumps
- Endocytosis
Describe tubular and acinar secretory portions.
Tubular glands – these have secretory units that resemble a tube-like shape and are found in the uterus, alimentary tract and sweat glands.
Acinar (alveolar) glands – these have a more rounded secretory unit and are found in the breast
What are compound glands?
They have branching ducts and multiple types of secretory portions
Classify glands according to their secretion mechanism.
Merocrine glands are the most common and release their secretory products via exocytosis. The major secretory products of these glands are usually proteins.
Apocrine glands release their secretory products contained within membrane-bound vesicles. This type of secretion is rare and these glands are found in the breast and constitute some sweat glands.
Holocrine glands release whole secretory cells, which later disintegrate to release the secretory products. This type of secretion is seen in sebaceous glands associated with hair follicles.
Define simple and compound glands, include examples
An unbranched duct is referred to as a simple gland, whereas a branched duct is known as a compound gland. An example of a simple gland is a sweat gland, whereas the pancreas is an example of a compound gland.
Serous cells stain intensely with basophillic and acidophillic stains, how can mucous cells be distinguished?
Mucous cells are distinguished by PAS method
PAS (periodic-acid-Schiff) staining is used for detection of structures that contain high concentrations of carbohydrate macromolecules (eg. glycogen, glycoprotein, proteoglycan) typically found in connective tissue, mucus, and basal laminae.
Classify exocrine glands into 3 subtypes according to their type of secretory product:
Serous glands produce serous fluid, a watery substance containing enzymes.
Mucous glands are involved in the production of mucus, a viscid (sticky) glycoprotein.
Mixed glands -seromucous- are comprised of both serous and mucous glands and secrete a mixed substance containing both serous fluid and mucus.`
Glandular epithelia usually contain myoepithelial cell, what are their functions;
They function by aiding in the secretion of fluid from the gland and synthesize basement membrane elements such as fibronectin, laminin, collagen IV, and nidogen
What is the implication of the disruption of tight junction in the GI epithelia ?
Disruption of the tight junction in the gastrointestinal epithelia by activities of micro-organisms or toxins causes fluid loss and in some gastric ulcers
What causes blistering diseases?
Abnormal desmosome junctions causes blistering diseases
What disease is associated with the loss of the microvilli?
Celiac disease
…………… is associated with male infertility due to cilia akinesia
Kartagener syndrome
Metastasia in habitual smokers causes ……………..
Chronic bronchitis
Bronchial pseudostratified ciliated epithelium becomes ……………….. in response to cigarette smoke
Stratified squamous epithelium
What happens to the stratified squamous epithelium of the oesophagus when it is exposed to persistent acid reflux?
Stratified squamous epithelium in the oesophagus becomes gastric epithelium when exposed to persistent acid reflux (Barrett’s oesophagus)
All epithelia are highly vascularised. true or false
False
