PBL 2: Sarah Ablett -Fluid homeostasis Flashcards
Squamous Epithelia
- Thin cells that facilitate diffusion of gasses and nutrients
- Found lining blood vessels, lungs, bowman’s capsule
Cuboidal Epithelia
- Short, fat cells with sphrerical nuclei that facilitate secretion and absorption
- Found in prox and distal convolutedd tubules of the kidney, ovary surface
Columnar Epithelia
- Tall cells with round or oval nuclei that facilitate absorption, secretion and ciliated cells for propulsion of substances
- Non-ciliated types line the GI tract, cilliated types line the bronchi, uterine tubules and parts of the uterus
Intracellular Fluid Compartment
- Fluid within cells
- 25L, 40% body weight
- Low Sodium
- Low Chloride
- High Potassium
Extracellular Fluid Compartment
- External environment of all cells
- 15L, 20% body weight
- High Sodium
- High Chloride
- Low Potassium
What are the 3 divisions of the ECF?
- Plasma: fluid portion of blood, 3L, 20% ECF
- Interstitial Fluid: fluid in the spaces between tissue cells, 12L, 80%ECF
- Transcellular fluid: 1L includes other fluid compartments that are distinct from interstitial such as lymph, CSF, synovial fluid, serous fluid
How does Cholerae Vibrio disrupt normal fluid transport?
- Caiuses isosmotic dehydration
- Decreases Na+ uptake from the lumen and increased Cl= resulting in increased luminal osmolarity
- Water follows causing diarrhoea
- Pumps and channels on basolateral membrane continuously replenish lost solutes, dragging more water into lumen
What are the mechanisms of Cholera?
- Attaches to mucosal cells and releases Cholera Toxin
- Increases adenylate cyclase activity resulting in:
- Increase cAMP resulting in
- Increased PKA: increased activity and expression of Cl- channel, deactivation of NA+/H+ antiporter
- Increased osmolarity within lumen continuously draws water from the ECF causing diarrhoea
Describe the structure of biological membranes?
- Phospholipid bilayer
- Hydrophilic head, hydrophobic tail
What is the primary role of the lipid bilayer?
To separate the outside of the cell from the inside to maintain a homeostatic environment within. Selective permeability allows tramsfer of molecules beetween cells and cellular compartments without compromising the integrity of the cell.
What substances is the membrane permeable to?
- Small molecules
- Non-polar molecules
- Neutral molecules
Examples:
- FAs, steroid hormones
- Vitamins A/E/D/K
- Small alcohols
- NH3, N2, Water
- Urea
What substances is the membrane NOT permeable to?
- Large molecules
- Polar molecules
- Charged Molecules
Examples
- Ions
- Sugars, Proteins, AAs
- Nucleotides, Nucleic Acids
Describe the movement of water and soluted across membranes via movement down a concentration gradient?
- Some solutes cross the membranes through simple passive diffusion if they are lipid soluble and a concentration gradient exists, e.g. O2
- Trans-membrane channnels can allow facilitated diffusion of solute down its gradient. Protein opens passage between inside and outside of the cell e.g. CL- channels, leak channels
Describe the movement of water and solutes across the membrane via active transport mediated diffusion
- Primary: Pumps use ATP to pump soluted against their concentration gradient, e.g. Na+/K+ ATPase pumps
- Secondary: Use concentration gradients established by other soluted to co-transport the target solute against its gradient, e.g. Na+/Glucose co-transporters.
What are the two classes of proteins that allow transfer of solutes across the membrane?
- Carrier Proteins
- Channel Proteins
