S5) Epithelial Tissues and Glands Flashcards
What are mucous membranes?
Mucous membranes: line certain internal tubes which open to the exterior and bear mucus-secreting cells to varying degrees e.g. the alimentary tract, the respiratory tract, the urinary tract
What do mucous membranes consist of?
- Epithelium: lining the lumen of the tube
- Lamina propria: an adjacent layer of connective tissue
- Muscularis mucosae: a third layer consisting of a smooth muscle cells
What are serous membranes?
Serous membranes are thin, two-part membranes which line certain closed body cavities (spaces which do not open to the exterior)
What do serous membranes do?
Serous membranes secrete a lubricating fluid which promotes relatively friction-free movement of the structures they surround
Where can serous membranes be found?
- Line the peritoneum (envelopes many abdominal organs)
- Line the pleural sacs (envelopes the lungs)
- Line the pericardial sac (envelopes the heart)
What do serous membranes consist of?
- Visceral serosa – a simple squamous epithelium which secretes a watery lubricating fluid
- Parietal serosa – a thin layer of connective tissue which attaches the epithelium to adjacent tissues
What are epithelia?
Epithelia are sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body and line internal surfaces
Identify 3 types of surfaces which have epithelial linings
- Exterior surface: skin
- Open interior surfaces: gastrointestinal, respiratory & genitourinary tracts
- Closed interior surfaces: pleura, pericardium, peritoneum, lymphatic & blood vessels
What is a basement membrane?
Basement membrane is the thin, flexible, acellular layer which lies between epithelial cells and the subtending connective tissue
What are the three principal shapes associated with epithelial cells?
- Squamous epithelium
- Cuboidal epithelium
- Columnar epithelium
What are the three ways of describing the layering of epithelium?
- Simple
- Stratified
- Pseudostratified
What are the characteristics of simple epithelia?
- Single layer of cells
- Found where absorption, secretion and filtration occur
Describe the structure and function of simple squamous epithelium
- Structure: epithelium cells are flat in shape and arranged in a single layer
- Function: thinness facilitiates processes of lubrication, gas exchange, active transport
Identify 3 locations where simple squamous epithelium can be found
- Lining of blood and lymph vessels (endothelium)
- The lining of alveoli in the lungs
- Lining of closed body cavities (mesothelium)
- Bowman’s capsule
Describe the structure and function of simple cuboidal epithelium
- Structure: epithelium consists of a single layer cells that are as tall as they are wide
- Functions: secretion and absorption
Identify 3 locations where simple cuboidal epithelium can be found
- Small ducts of many exocrine glands (pancreas and salivary glands)
- Kidney tubules
- Germinal epithelium of the ovary
Describe the structure and function of simple columnar epithelium
- Structure: a single row of tall, closely packed cells, aligned in a row.
- Functions: absorption, secretion, lubrication (small intestine and colon), transport (oviduct)
Identify 3 locations where simple columnar epithelium can be found
- Areas with high secretory function (stomach lining and gastric glands)
- Absorptive areas (small intestine and colon)
- Oviducts
Describe the structure of pseudostratified epithelium
- Simple columnar epithelial cells with nuclei appearing at different heights, giving the misleading ‘stratified’ impression
- Can also possess cilia on their apical membrane
What are the functions of stratified squamous non-keratinised epithelium?
- Protection against abrasion
- Reducing water loss but maintaining moisture
What are the characteristics of keratinised epithelia?
- Apical layers of cells are dead and lose their nucleus & cytoplasm
- Cells contain keratin (tough & resistant) making the epithelium waterproof
What are the characteristics of transitional epithelia?
- Appear to be stratified cuboidal when the tissue is not stretched
- Appears to be stratified squamous when the organ is distended
What are the functions of transitional epithelia?
- Distensibility
- Protection of underlying tissue from toxic chemicals
Describe the structure, function and location of melanocytes
- Structure: dendritic cells of neural crest origin
- Function: produce melanin
- Location: occur at intervals along the basal layer of the epidermis
Describe the structure, function and location of Langerhans cells
- Structure: dendritic cells of bone marrow origin
- Function: antigen presentation and mediating immune reactions
- Location: scattered throughout the prickle cell layer
How do we classify glands according to their structure?
- Unicellular/multicellular
- Acinar/tubular
- Coiled/branched
How do we classify glands according to the method of secretion?
- Merocrine: exocytosis e.g most glands
- Apocrine: secreted droplets covered by plasma lemma e.g. fat droplets in milk
- -* Holocrine: whole cell breaks down e.g. sebaceous gland of skin
What is cystic fibrosis?
Cystic fibrosis is a condition resulting from the absence of the CFTR molecule in the apical membrane of the epithelial cells lining the duct of the sweat gland, resulting in poor reabsorption of chloride ions
What is psoriasis?
Psoriasis is a long-lasting autoimmune disease which is characterised by patches of abnormal skin (red, itchy, and scaly)
