Epithelium (Part 1 of 3) Flashcards
Name the primary germ layers that epithelial tissue is derived from?
Derived from all three primary germ layers, depending on the type and location of the epithelial tissue.
Describe the characteristics of epithelium? (1)
(IPACHA)
Cellularity:
Epithelium contains cells that are tightly packed.
Polarity:
Apical surface faces external environment & Basal surface is anchored to the underlying connective tissue.
Attachment to a basement membrane:
Basal surface attaches to the basement membrane (produced by epithelial and connective).
Describe the characteristics of epithelium? (2)
(IPACHA)
Avascularity:
Epithelium lacks blood supply = blood supply via diffusion from the underlying connective tissue.
Innervation:
Epithelium is richly innervated by sensory nerves.
High regeneration capacity:
Deepest epithelial cells (closest to BM) undergo cell division to replace more superficial epithelial cells (damaged).
Describe the functions of epithelium?
(PSSS)
Physical protection:
From abrasion, dehydration + damage from physical, chemical or biological substances.
Selective permeability:
Essential substances can be absorbed & waste can be eliminated (traffic controller).
Describe the functions of epithelium?
(PSSS)
Secretion:
Produce secretions that aid in the lubrication of cavities and surfaces, the breakdown of substances and chemical communication.
Sensation:
Epithelium contains sensory receptors for general and special senses.
Describe how epithelium is classified, based on the number of cell layers?
Simple:
Single layer of cells + all cells are in direct contact with the basement membrane.
Stratified:
≥2 layers of cells + only the basal layer deepest layer of cells) is in direct contact with the basement membrane.
Describe how epithelium is classified, based on the shape of the cells?
Squamous Epithelium:
- Flat, irregularly shaped cells.
- Flattened, centrally located nucleus.
Cuboidal Epithelium:
- As tall as they are wide.
- Round, centrally located nucleus?
Columnar Epithelium:
- Taller than they are wide.
-Oval-shaped, basally located nucleus.
Describe the structure, function and location of simple squamous Epithelium?
Structure:
Composed of a single layer of squamous cells.
Function:
1. Diffusion and filtration (rapid movement of substances across its surface).
Location:
1. Lining the alveoli where gas exchange occurs.
2. Lining blood vessels where the movement of substances in and out of the blood occurs.
Describe the structure, function and location of simple cuboidal Epithelium?
Structure:
Single layer of cuboidal cells.
Function:
1. Absorption and secretion.
Location:
1. Lining the kidney tubules where substances are either reabsorbed into the blood or secreted into the tubular fluid.
2. Lining the ducts of glands which produce secretions.
Describe the structure, function and location of simple columnar Epithelium?
Structure:
Single layer of columnar cells.
1. Ciliated = have cilia on their apical walls.
2. Non-ciliated = do not have cilia on their apical walls (often have microvilli on their apical surfaces).
3. Often contain goblet cells on SCE (mucous-secreting cells).
Function:
1. Absorption and secretion.
Location:
1. Lining most of the GI tract, the uterine tubes in females and the bronchioles in the respiratory tract.
Describe the structure, function and location of pseudo stratified columnar Epithelium?
Structure:
Single layer of columnar cells, but varying levels of nuclei (appear stratified).
1. Ciliated & non-ciliated forms.
2. Goblet cells found throughout the ciliated form.
Function:
1. Protection (primary function).
Location:
1. Ciliated form: Lining most of the respiratory tract (more common).
*Cilia = move mucus out of the repisratory tract.
2. Non-ciliated form: Lining parts of the male urinary and reproductive tracts (less common).
Describe the structure, function and location of stratified squamous Epithelium?
Structure:
Multiple layers of cells –> apical cells being squamous & basal cells being cuboidal or polyhedral.
1. Keratinised (contains keratin): dead apical cells, lack both nuclei and other organelles.
2. Non-keratinised (does not contain keratin): all the cells are living, contain both nuclei and other organelles.
Function:
1. Protection (prevents the underlying tissue from damage caused by abrasion).
***Basal cells undergo division to produce new cells that migrate towards the surface to to replace the cells that have been damaged/lost.
Location:
1. Keratinised: Epidermis of the skin.
2. Non-keratinised: Lining the oral cavity, part of the pharynx, the oesophagus, the anal canal and the vagina.
***Provides protection for mechanical stress in these areas.
Describe the structure, function and location of stratified cuboidal Epithelium?
Structure:
A few layers of cells, with the apical cells being cuboidal.
Function:
1. Protection and secretion.
Location:
1. Lining the ducts of sweat and primary glands.
Describe the structure, function and location of stratified columnar Epithelium?
Structure:
A few layers of cells, with the apical cells being columnar.
Function:
1. Protection and secretion.
Location:
1. Lining the large ducts of some glands.
Describe the structure, function and location of transitional Epithelium?
Structure:
Multiple layers of cells that change shape depending on the degree of stretch.
1. Relaxed = basal cells resemble cuboidal cells and the apical cells are large and rounded.
2. Stretched = apical cells resemble squamous cells.
Function:
1. Specialised for distention.
Location:
1. Lining most of the urinary tract.
Label the flowchart on the types of Epithelium?
Identify and label both glands and their parts?
