Session 3 - Epithelial cells, tissues, organs & systems Flashcards
What are epithelia?
Sheets of contiguous cells that cover the external surface of the body & line internal surfaces including the body’s vessels
What is the embryonic origin of epithelial cells? (give examples)
Derived from all the embryological germ layers:
- ectoderm (eg epidermis)
- endoderm (eg inner & outer lining of gastrointestinal tract)
- mesoderm (eg inner linings of body cavities)
Why are dead cells able to be scrapped off the surface easily?
They are not held by desmosomes
Describe the structure of simple squamous epithelia. Which part of the body do they line and what are their functions?
One single layer of flattened cells
Line body cavities (mesothelium) => heart, blood vessels, pleural & peritoneal cavities.
Functions:
- Lubrication (pericardium, pleural membranes, peritoneum/viscera)
- Gas exchange
- Water, nutrient & waste exchange (eg endothelial cells lining heart & capillaries)
- Barrier ( skin, oesophagus, conjunctivae of eye, brain)
Describe the structure of simple cuboidal epithelia. Which part of the body do they line and what are their functions?
One single layer of polygonal cells whose height & width are approx equal
Line small ducts and tubules that may have excretory, secretory or absorptive functions eg kidney tubules, thyroid, exocrine gland
Functions:
- Absorption & secretion of materials into ducts/tubes
- Barrier (ovary)
- Hormone synthesis, storage & mobilisation
What is the basement membrane? What is it made up of?
A thin sheet-like layer of ECM
Made up of basal lamina + reticular layer
Where is the basement membrane found?
Located between most epithelium and deeper connective tissue
What are the functions of the basement membrane?
Acts as a filter for substances reaching epithelial tissue
Provides structural support for epithelial cells
Anchors the epithelial to connective tissue
What are serous membranes?
thin, two-part membranes which line most closed body cavities and envelop the viscera eg peritoneum (envelopes abdominal organs), pleural sacs (envelops lungs) & pericardial sac (envelops heart)
Why do serous membranes exude lubricating fluid?
for friction-free movement of structures that it surrounds
What do serous membranes consist of?
- simple squamous epithelium (mesothelium) => exudes watery lubricating fluid
- thin layer of connective tissue that attaches epithelium to adj tissues
- carries blood, lymphatic vessels & nerves
What are mucous membranes?
Moist inner lining of internal tubes which open up to exterior eg GI tract, respiratory tract & urinary tract
Why are mucous membranes coated with mucous gland secretions?
protects membranes & keep them moist
What do mucous membranes consist of?
- Epithelium lining the lumen of tube
- Adj layer of connective tissue (lamina propria)
- Third layer of smooth muscle cells (muscularis mucosae)
- Carries blood, lymphatic vessels & nerves
Describe the structure of simple columnar epithelia. Which part of the body do they line and what are their functions?
One single layer of column-like cells which are taller than they are wide
- Line stomach, gastric glands, SI, colon & gall bladder (most organs of the digestive tract)
Functions:
- Absorption (SI, colon & gall bladder)
- Secretion (stomach lining, gastric glands, SI & colon)
- Lubrication (SI & colon)
Describe the structure of pseudostratified epithelia. Which part of the body do they line and what are their functions?
consists of column-like cells of varying heights where all cells are in contact with the basement membrane not but all in contact with apical surface, nucleus all at diff levels
- Line nasal cavity, trachea, bronchi
Function:
- secretion & conduit
- mucus secretion
- particle trapping & removal (respiratory tract)
How does the composition of keratin render it the ability to be produce a waterproof surface?
tightly packed dead cells (keratinocytes) on the uppermost layer of the epidermis produces waterproof layer?
What are the functions of keratin (2)?
Reduce water loss
Protects against abrasion
Describe the structure of STRATIFIED SQUAMOUS KERATINISED EPITHELIUM. Which part of the body do they line and what are their functions?
Multiple layers of cells, outermost are squamous cells have lost their nuclei & cornified (squames of keratin)
- Lines surface of the skin (epidermis)
- Oral cavity (limited)
Functions:
- Protection against abrasion & physical trauma
- Preventing of water loss
- Preventing of microbial ingress
- Shielding against UV light damage
How do the outermost dead cells of stratified squamous keratinised epithelium protect the rest of the tissue?
- Reduces water loss & ingress
- Prevents ingress of toxins
- Protects against abrasion
- Reduces microbial colonisation
Describe the structure of the epidermis?
Made up of avascular EPIDERMIS & dense, irregular tissue consisting of collagen elastin bundles, DERMIS
Describe the structure of transitional urinary epithelium (urothelium). Which part of the body do they line and what are their functions?
Surface cells round & pear-shaped => cuboidal when relaxed & squamous when stretched
- Lines urothelium
Function: enable tissue to contract and expand eg allow the bladder to enlarge when the bladder is filled with urine.
- Protection of underlying tissue from toxic chemicals
Why are there tight junctions between urothelial cells (transitional urinary epithelium)?
prevents urine from entering body which will kill nerves & vessels
What are club cells? List their functions (3).
On the airway side of terminal bronchioles; club like apical surfaces; no cilia; no basal bodies
Functions:
- Protect bronchiolar epithelium => secretion of products eg uteroglobin & solution
- Detoxification of harmful substances inhaled in lungs
- Act as stem cells => multiplying & differentiation into diff ciliated cells to regenerated bronchiolar epithelium
