Tissues Flashcards
1
Q
Define Tissue
A
Tissue: A group of cells performing similar functions
-vary in structure, function & content of their extracellular matrix (can contain protein fibres, salts, H20 & dissolved macromolcules)
2
Q
4 Types of Tissues
A
- Epithelial Tissue
- Connective Tissue
- Muscle Tissue
- Nervous Tissue
3
Q
Epithelial Tissue - 6 General characteristics
A
- Lines every body surface and all body cavities (organs lined on the outside and inside & majority of glands are derived from epithelial tissue)
1. Cellularity: composed almost entirely of cells - little extracellular matrix w/ cells bound together w/ intercellular junctions
2. Polarity - have apical suface & basal surface (i.e. lots of channels - one side of cell exposed, other not)
3. Attachment - Basal surface attached to thin basement membrane
4. Avascularity - lack blood vessels (nutrients via diffusion from underlying tissue)
5. Innervation - Richly innverated to detect changes in enviro
6. Regeneration - apical surface in constant contact w/ enviro (freq. damaged/die)- replaced quickly
4
Q
4 Functions of Epithelial Tissue
A
- Physical Protection: From dehydration & abrasion (phys. chem. bio.)
- Selective Permeability: needs to absorb certain things from enviro.
- Secretions: exocrine cells produce secretions such as sweat & oil (may be scattered amount other cell types in epithelium or may form a gland)
- Sensations: possess nerve endings that can detect light, taste, sound, smell & hearing
5
Q
Basement Membrane
A
- is a specialised structure of epithelium
- found between epithelium & underlying connective tissue
- provides physical support and anchoring of epithelial tissue
- acts as barrier to regulate passage of large molecules between epithelium & underlying connective tissue
*is actually composed of 3 layers that all strengthen attachment & form a selective barrier
6
Q
Intercellular Junctions - 4 types
A
*Epithelial cells strongly bound to each other by sharing membrane specialisations 4 types; 1. Tight junctions 2. Adhering Junctions 3. Desmosomes (or hemidesmosomes) 4. Gap junctions
7
Q
Tight Junctions
A
- Encircle cells near apical surface
- Prevents molecules from travelling between - must go through epithelial cells to reach basal membrane (are therefore gatekeepers)
- provides structure & support at apical surface.
-in small intestine, prevent digestive enzymes that degrade molecules from moving between epithelial & connective tissue
8
Q
Adhering Junctions
A
- Formed completely around the cell deep to tight junctions
- microfilaments act like a purse string to stabilise the apical surface (is a strengthening belt of the cell)
- provide a small space between neighbouring cells in direction of basal surface = passage between cells for materials that have already passed through epithelial cell
9
Q
Desmosomes
A
- Doesn’t totally encircle cell
- Like a button or snap between adjacent cells - joins cells together
- At places of mechanical stress between cells
- Have thickened protein plaque on each of apposed cell membranes w/ fine network of proteins spanning intercellular space
- On cytoplasmic side, intermediate filaments attach to plaques & provide suppot and stability
10
Q
Gap Junctions
A
- Fluid filled channels that directly connect the cytoplasms of apposed cells sharing these structures
- allow adjacent cells to communicate w/ each other by flow of ions & other small molecular messengers (i.e. glucose, a.a.)
i.e. muscle cells for contraction along muscle - might need communication along.
11
Q
Epithelia Classification
A
*classified based on shape of cells (at most superficial surface) & no. of cell layers
12
Q
Epithelial Cell Shapes (3)
A
- Squamous: flattened, wide, irregular w/ large nucleus (like a fried egg)
- Cuboidal: about same size on all sides - nucleus centrally located (but do NOT have edges)
- Columnar - taller than they are wide (nucleus is oval & located in basal region)
13
Q
Epithelium Cell Layers (3)
A
- Simple Epithelium: single layer of cells w/ all cells having apical surface & attached to basement membrane (apical often covered by thin layer of fluid or mucus for protection)
- found where stress minimal & absorption, filtration or secretion is primary function
- Stratified epithelium - 2+ layers (not all have apical surface or attach to basal membrane)
- areas subject to abrasive or mechanical stresses
- Pseudostratified epithelium - single layer - not all cells reach apical surface
- Nuclei give appearance of multilayered, stratified epithelium (those that do reach often have cilia to help move fluid along)
14
Q
Types of Epithelium & Location (Simple)
A
- Simple Squamous Epithelium: single layer of flat cells (allows rapid diffusion: lungs, blood vessels & membranes that cover body cavities)
- Endothelium (lines lumen of blood & lymphatic vessels & heart & its chambers
- Mesothelium (serous membrane that lines internal walls of pericardial, pleural & peritoneal cavities) - Simple Cuboidal: forms ducts of exocrine glands (gen. involved in absorption & secretion)
- Simple columnar: I.e. small intestine (involved in absorption & secretion
- Simple Columnar Ciliated - Possess cilia on apical surface such as in respiratory and reproductive systems
15
Q
Types of Epithelium & Location/function (Stratified)
A
- Stratified Squamous Cells - in areas w/ lots of stress as provide protection for underlying tissue
- either exists as nonkeratinized (remains alive w/ mucous or saliva) or keratin (apical = cells that are deal & lack a nucleus - such as outer layer of skin)
- Stratified Cuboidal Epithelium: Generally found in glandular tissue (i.e. sweat or semen), although function is mainly protective (serves to strengthen wall of gland ducts)
- Stratified Columnar - quite rare to fine (e.g. male urethra)
- Psuedostratified Columnar - not really stratified as all cells in contact w/ basement membrane - looks stratified as not all cells reach apical surface.
- often covered w/ cilia, generally involved in protection
- found in respiratory tract, naval cavity
16
Q
Transitional Epithelium - what it is, where found & distinct Feature
A
- Found in the lining of the urinary bladder
- Changes shape between squamous and cuboidal depending on whether bladder if full or empty (walls stretched or contracted)
- when stretched: resemble squamous cells
- When relaxed: polyhedral (many sided) - Distinct feature: presence of few binucleated cells
- Cells aren’t uniform - are bunched up
17
Q
Glands - Function
-2 Categories
Definition of Duct
A
- Perform secretory function
- produce mucin, hormones, enzymes & waste products
2 categories;
- Exocrine glands: possess ducts that cells secrete products into - almost all derived from epithelial tissue
- i.e. milk, sweat, mucous, saliva glands
- Endocrine Glands: do not possess ducts - cells secrete products into interstitial fluid or bloodstream - derived from multiple tissue
- i.e. hormones
Duct: epithelium lined tube through which secretions of glands are discharged to epithelial surface
