Membranes + epithelial tissues Flashcards
(35 cards)
Define diffusion
A function of concentration gradients as solutes move from a high conc. to a low conc.
State what molecules can undergo simple diffusion
Lipid soluble molecules
State what molecules undergo facilitated diffusion
Large/water soluble molecules/ions move through protein channels
-> leak channels enable free movement of ions
Explain the function of carrier proteins
Have specific receptor site that a molecule must bind to to open the protein + enable similar molecules to move across eg. glucose
-> must exhibit specificity
Define osmosis
Net movement of water molecules across a semi-permeable membrane to a higher solute concentration
-> moves through channels called aquaporins
State the osmolarity of normal plasma
285 osmol/L
Define tonicity
Effect of osmotic solutions on cells
Define active transport
Movement of molecules ‘up’ a concentration gradient, requiring ATP
Describe the sodium-potassium exchange pump
Moves Na+ out of cell + K+ in
-> b/c ions move down gradients therefore Na+ moves in -> cell X want Na+
Explain the process of secondary active transport
- glucose binds to protein / Na+ binds to carrier protein -> move across membrane
- Na+ pumped back out of cell
- enables glucose + amino acid absorption in digestion as moves specific substrate down conc. gradient then pumps Na+ back out
Explain the process of receptor-mediated endocytosis
- ligand binds to receptors in PM which migrate to clathrin coated pits
- ligand receptor areas form deep pockets in PM surface
- pockets pinch off, forming clathrin coated vesicles
- clathrin recycles back into PM + endosomes fuse w/ primary lysosomes to form secondary lysosomes
- ligands removed + absorbed into cytoplasm
- lysosomal + endosomal membranes separate
- endosomes fuse w/ PM, receptors again available for ligand binding
Describe the process of vesicular transport
- material is taken up by neuron at synapse -> transported to cell body (retrograde transport)
- material made at cell body released at axon terminal (anterograde transport)
Define exocytosis
Movement of material out of the cell
Define tissue
A collection of cells + cell products that perform specific, limited functions
Describe the 2 epithelial tissues
Epithelia = layers of cells covering internal/external surfaces
Glands = structures that produce secretions -> attached to/derived from epithelia
List 4 functions of epithelial tissues
- provide physical protection
- controls permeability
- provides sensation
- produce specialised secretions
Describe the structure + characteristics of epithelial tissues
- apical surface = exposed to internal/external environment -> have microvilli
- basal surface = bottom surface attached to basement membrane
- basement membrane = specialised form of extracellular matrix -> enables sticking together
Avascular
Describe the intercellular connection of cell adhesion molecules
- connects large areas of PM to adjacent cells via connecting basal surface w/ basement membrane
Describe the function of gasp junctions b/t cells
Permit free diffusion of ions + small molecules b/t 2 cells -> contain connexons
-> coordinate muscle contraction
Describe the function of tight junctions b/t cells
- prevents movement of water + solutes b/t cells
- protects basal surface from contents of lumen (enzymes, acids + wastes)
Describe the function of desmosomes b/t cells
Connections that resist stretching + twisting
-> link 2 cells via CAMs + proteoglycans to cytoskeleton
eg. superficial layers of skin
State how an epithelial cell attaches to the basement membrane
Via hemidesmosomes which attach the cell to extracellular filaments in basement membrane
State how epithelial cells are repaired/maintained
Structure maintained via division of stem cells located near the basement membrane
Describe the location + function of simple squamous epithelia
Location = lining of heart, blood vessels + alveoli
Function = reduce friction, controls vessel permeability, absorption + secretion
