deck_752436 Flashcards

1
Q

How do small polar uncharged molecules pass though the bilayer?

A

down their concentration gradient by diffusion.

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2
Q

How do hydrophobi molecules move across the bilayer?

A

Hydrophobic molecules (O2 and CO2) diffuse across easily.

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3
Q

How do large, uncharged polar molecules pass through the bilayer?

A

Large, uncharged polar molecules and ions must pass through by transport proteins, again down a concentration gradient.

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4
Q

The smaller the membrane coefficient …

A

… the larger the net rate of transport

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5
Q

Define secondary transport

A

transport of a substance is linked to the concentration gradient and transport of another. Usually uses sodium gradient.

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6
Q

What are symports?Give an example of a symport

A

two molecules move from the same side to another e.g. glucose cotransporter in small intestine

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7
Q

What are antiports and give an example

A

molecules move to opposite sides e.g. Na/Ca exchange.

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8
Q

What is the purpose of the Na/K/ATPase?

A

It is necessary for setting up the membrane potential but does not produce the membrane potential – sets up the Na conc gradient that drive the majority of particle transport

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9
Q

Describe some characteristics of Na/K/ATPase

A

antiport, 3Na for 2K, uses ATP hydrolysis, primary AT = ATP hydrolysis, inhibited by digoxin and ouabain (cardiac glycosides)

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10
Q

Describe PMCA characteristics and what its purpose is

A

antiport, high affinity, low capacity for Ca, Ca in H out, primary AT = ATP hydrolysis, maintains low intracellular calcium

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11
Q

Describe SERCA characteristics and what its purpose is

A

antiport, high affinity low capacity for Ca, increase Ca in SR/ER in exchange for H, primary AT = ATP hydrolysis, maintains stores of Ca in SR/ER to prevent cell death

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12
Q

What cellular response does NCX have in ischaemia?

A

Low ATP levels due to low O2. Na pump inhibited, NCX reverses to lower Ns a conc, high Ca is toxic and activates potent enzymes causing cell death

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13
Q

Describe the characteristics of NCX

A

secondary AT, 3Na in 1Ca out, current follows Na so not dependent on ATP hydrolysis, involved in ischaemia

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14
Q

Describe the characteristics of NBC

A

Na and HCO3 into cell and Cl out, follows Na gradient

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15
Q

Describe the characteristics of NHE

A

uses Na gradient to move H out of the cell, increasing the intracellular pH

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16
Q

How is cell volume controlled?

A

Efflux or influx of ions. Water will follow.

17
Q

What happens in response to cell swelling?

A

– cells extrude ions and water follows– usually efflux K, Na, Cl or solute molecules

18
Q

What happens in response to cell shrinkage?

A

– cells influx ions and water follows– influx K, Na, Cl

19
Q

How is bicarbonate resorbed in the kidneys?

A

Starts as NaHCO3 in lumen of kidney. Splits into Na+ and HCO3-Na+ taken up by NHE (exchanges H+)HCO3- + H+ –> H2CO3 (carbonic anhydrase)H2CO3 –> H20 + CO2 which diffuse acrossH20 + CO2 –> H2CO3 (carbonic anhydrase)H2CO3 –> H+ + HCO3-HCO3- moved into capillary by anion exchanger (exchange Cl-)Na into capillary by Na pump (exchange K)

20
Q

How much bicarbonate is reabsorbed by the kidneys and why is it resorbed?

A

All of it in order to retain a base for the buffers

21
Q

Where does Na resorption take place in the kidneys?

A

Thick ascending limb, distal convoluted tubule and cortical collecting duct.

22
Q

What is the mechanism for Na resorption in the thick ascending limb?

A

Na moves out of kidney lumen via NKCC2 (Na,K,2Cl)K is filtered back into lumen via ROMKKClCT moves K & Cl into capillariesClC-Kb moves Cl into capillariesNa/K/ATPase transports 3Na into capillaries and 2K in exchange

23
Q

What inhibits resorption at the thick ascending limb and what does it treat?

A

Loop diuretics – inhibit NKCC2Limits Na resorption, more Na stays in lomerular filtrate reducing blood volume which treats hypertension

24
Q

What is the main cotransported used for Na resorption in the distal convoluted tubule and what is its inhibitor drug?

A

NCC2 is inhibited by thiazides

25
Q

What is the main cotransported used for Na resorption in the cortical collecting duct and what is its inhibitor drug?

A

ENaC and AquaporinsInhibited by Spironolactone