Physiology L2 - Membrane Transport

Question 1

What is the transitional compartmemt of the cells and what does this mean? Also how does it relate to oral hygiene?

Answer 1

ECF if the transitional compartment. This means it is where water goes into and out of the body. This depends on osmotic gradients across the cell membranes.
- ADA states that oral hygiene is compromised when people are dehydrated due to a lack of saliva and mineral support for the teeth

Question 2

What is the role of the Na+/K+ ATPase and what are the resting concentrations of ions in ECF and ICF?

Answer 2

• This pump sets up and maintains the relative concentration gradients of Na+ and K+ between the intracellular and extracellular fluid.
• 3Na+ ions out and 2K+ ions in for every ATP used (primary active transporter)
• However the membrane is more permeable to K+ than Na+ so K+ leaks out of cells. This is where Na+/K+ ATPase balances the charges

ICF:
- Na+ = 15mM
- K+ = 150mM

ECF:
- Na+ = 145 mM
- K+ = 5 mM

Question 3

Which part is the chemical gradient and which part is the electrical gradient that the Na+/K+ ATPase sets up?

Answer 3

• set up for the chemical gradient for Na+ (145mM -> 15mM)
• set up of the electrical gradient (inside cells is more negative, outside of cell is more positive) RMP = -70mV

Question 4

Describe the absorption of solutes and water across the small intestine’s leaky epithelium

Answer 4

• SGLT1 on luminal surface of cell pumps glucose into cell using Na+ conc gradient (secondary active transport). Na+ is then pumped out of cell in exchange for K+ using the sodium potassium ATPase. Glucose builds up in the cell and then when it reaches a certain concentration it diffuses out of the cell down its concentration gradient through the GLUT2 transporter.
• due to the large buildup of sodium and glucose in the interstitium this drives the trans- and para- cellular absorption of water (osmotic gradient).

Question 5

Describe the themes and examples of ion movement

Answer 5

• the depolarisation of cells straits with the opening of a cation channel that can, in some cases, be a receptor (NMDA receptor, glutamate/Ca2+ receptor)
• the depolarisation of cells needs a reversal back to the RMP, which involves, besides many other channels and transporters, the Na+/K+ ATPase

Eg. signalling between neurons, signalling at the neuromuscular junction (chewing), release of insulin, enzymes

Question 6

Describe how diuretics (loop diuretics and thiazides) control blood pressure

Answer 6

• these diuretics are sodium transporter inhibitors so no sodium can be reabsorbed and therefore water isn’t reabsorbed either (decreases BP_

Question 7

describe how anaesthesia interrupts ion movement

Answer 7

local anaesthetic: lignocaine
1. to pass through the membrane the lignocaine loses a hydrogen
2. it can than diffuse into the cell
3. once inside the cell it regains the hydrogen
4. it can then bind within open VG Na+ channels preventing depolarisation

ie. anaesthesia inhibits ion channels

Question 8

how is exocytosis a type of membrane transport?

Answer 8

• allows the release of cellular contents needing to cross cell membrane
• it is also a method by which proteins embedded in the cell membrane can be presented on the cell surface (eg. receptors, transporters and channels)

Question 9

how does vesicle fusion work?

Answer 9

v-SNARE on vesicle
t-SNARE on cell membrane or organelle (target)
SNARE proteins allow vesicles to dock with the larger membrane. once calcium binds to synaptotagmin the membranes can fuse.

Question 10

describe endocytosis as a type of membrane transport

Answer 10

• allows for the intake of extracellular contents
• can be receptor mediated
• can involve clathrin or other proteins (such as caveolin)
• recycling of transporters and channels from the plasma membrane

Question 11

describe signalling using G-proteins as a type of membrane transport

Answer 11

• the binding of the ligand to the receptor activated the G-protein
• different alpha subunits lead to different intracellular responses

Activated Galpha-s stimulates membrane bound adenylyl cyclase (AC):
- AC converts ATP to cAMP
- cAMP activated protein kinase A (PKA)
- PKA phosphorylates proteins
(Galpha-i does the opp. and inhibits)

Activated Galpha-q stimulates membrane bound phospholipase C (PLC):
- PLC cleaves PIP2 into IP3 and DAG
- IP3 causes Ca2+ release from ER
- DAG and Ca2+ activate protein kinase C (PKC)
- PKC phosphorylates proteins eg. H+/K+ ATPase (which makes gastric acid in the stomach)
- basically QALPHA-Q INCREASES INTRACELLULAR CA2+ CONCENTRATION