PBL 2: Sarah Ablett -Fluid homeostasis

Question 1

Squamous Epithelia

Answer 1

1. Thin cells that facilitate diffusion of gasses and nutrients
2. Found lining blood vessels, lungs, bowman’s capsule

Question 2

Cuboidal Epithelia

Answer 2

1. Short, fat cells with sphrerical nuclei that facilitate secretion and absorption
2. Found in prox and distal convolutedd tubules of the kidney, ovary surface

Question 3

Columnar Epithelia

Answer 3

1. Tall cells with round or oval nuclei that facilitate absorption, secretion and ciliated cells for propulsion of substances
2. Non-ciliated types line the GI tract, cilliated types line the bronchi, uterine tubules and parts of the uterus

Question 4

Intracellular Fluid Compartment

Answer 4

• Fluid within cells
• 25L, 40% body weight
• Low Sodium
• Low Chloride
• High Potassium

Question 5

Extracellular Fluid Compartment

Answer 5

• External environment of all cells
• 15L, 20% body weight
• High Sodium
• High Chloride
• Low Potassium

Question 6

What are the 3 divisions of the ECF?

Answer 6

1. Plasma: fluid portion of blood, 3L, 20% ECF
2. Interstitial Fluid: fluid in the spaces between tissue cells, 12L, 80%ECF
3. Transcellular fluid: 1L includes other fluid compartments that are distinct from interstitial such as lymph, CSF, synovial fluid, serous fluid

Question 7

How does Cholerae Vibrio disrupt normal fluid transport?

Answer 7

1. Caiuses isosmotic dehydration
2. Decreases Na+ uptake from the lumen and increased Cl= resulting in increased luminal osmolarity
3. Water follows causing diarrhoea
4. Pumps and channels on basolateral membrane continuously replenish lost solutes, dragging more water into lumen

Question 8

What are the mechanisms of Cholera?

Answer 8

1. Attaches to mucosal cells and releases Cholera Toxin
2. Increases adenylate cyclase activity resulting in:
3. Increase cAMP resulting in
4. Increased PKA: increased activity and expression of Cl- channel, deactivation of NA+/H+ antiporter
5. Increased osmolarity within lumen continuously draws water from the ECF causing diarrhoea

Question 9

Describe the structure of biological membranes?

Answer 9

1. Phospholipid bilayer
2. Hydrophilic head, hydrophobic tail

Question 10

What is the primary role of the lipid bilayer?

Answer 10

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.

Question 11

What substances is the membrane permeable to?

Answer 11

1. Small molecules
2. Non-polar molecules
3. Neutral molecules

Examples:

1. FAs, steroid hormones
2. Vitamins A/E/D/K
3. Small alcohols
4. NH3, N2, Water
5. Urea

Question 12

What substances is the membrane NOT permeable to?

Answer 12

1. Large molecules
2. Polar molecules
3. Charged Molecules

Examples

1. Ions
2. Sugars, Proteins, AAs
3. Nucleotides, Nucleic Acids

Question 13

Describe the movement of water and soluted across membranes via movement down a concentration gradient?

Answer 13

1. Some solutes cross the membranes through simple passive diffusion if they are lipid soluble and a concentration gradient exists, e.g. O2
2. 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

Question 14

Describe the movement of water and solutes across the membrane via active transport mediated diffusion

Answer 14

1. Primary: Pumps use ATP to pump soluted against their concentration gradient, e.g. Na+/K+ ATPase pumps
2. Secondary: Use concentration gradients established by other soluted to co-transport the target solute against its gradient, e.g. Na+/Glucose co-transporters.

Question 15

What are the two classes of proteins that allow transfer of solutes across the membrane?

Answer 15

1. Carrier Proteins
2. Channel Proteins

Question 16

Carrier Proteins

Answer 16

Bind specific soluted before undergoing a conformational change and releasing the solute on the other side

Question 17

Uniporter

Answer 17

Moves one type of solute down its concentration gradient

Question 18

Symporters

Answer 18

Moves two or move different solutes across the membrane in the same direction simultaneously or sequentially

Question 19

Antiporters

Answer 19

Move two different types of solutes in opposite directions across a membrane

Question 20

Channel Proteins

Answer 20

Allow solutes to move through an aqueous pore across the membrane

Question 21

Leak Channel

Answer 21

Continuously open ion channels

Example: water, Na, KK

Question 22

Gated ion channels

Answer 22

Have open and closed conformations

Voltage-gated: electrical potential across membrane

Ligand-gated: specific regulator molecule

Mechanosensitive: stretch regulated