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22 Cards in this Set
- Front
- Back
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MEMBRANE TRANSPORT PROTEINS |
- Ion channels (let molecules through a pore, 10^7-10^8 ions/s) - Pumps (a primary active transport, use ATP to pump molecules across, 10^0-10^3 ions/s) - Transporters (flip holding onto ions and let them across, 10^2-10^4) |
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ROLES OF PUMPS AND TRANSPORTERS |
- Uptake of molecules and ions - Extrusion of molecules and ions - Maintenance of intracellular pH - Generation and use of ion gradients - Regulation of cell volume |
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CLASSIFICATION OF TRANSPORTERS |
- Uniport (facilitated diffusion) - Symport + antiport (secondary active transport, coupled transport) |
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PRIMARY ACTIVE TRANSPORT |
- Energy from hydrolysis of ATP to ADP liberating energy from high energy phosphate bond - Moving against a concentration gradient - e.g. Na+ transport out of kidneys |
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FACILITATED DIFFUSION/PASSIVE TRANSPORT |
- High concentration to low concentration - Powered by the potential energy of a concentration gradient and does not require the expenditure of metabolic energy - e.g. Cl- entry into kidneys |
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SECONDARY ACTIVE TRANSPORT |
- Co-transporters - Function dependent on another primary active transporter |
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PROPERTIES OF PUMPS AND TRANSPORTERS |
- Integral membrane proteins - Can carry molecules/ions - Are specific (selective) - Are regulated - Are passive or active |
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KIDNEY NEPHRON 3 MAIN FUNCTIONS |
- Filtration of blood to produce a filtrate - Reabsorption of water, ions and organic nutrients from filtrate - Secretion of waste products into tubular fluid |
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TRANSCELLULAR MOVEMENT |
Movement through cells |
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PARACELLULAR MOVEMENT |
Movement between cells |
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KIDNEY FILTRATION |
- Occurs at the glomerulus, the initial step of urine production - ALL small molecules are filtered (electrolytes inc Na+, amino acids, glucose, metabolic waste, most drugs) - Cells and large molecules (red blood cells, lipids, proteins and some drugs) remain in blood |
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KIDNEY REABSORPTION |
- More than 99% of water, electrolytes and nutrients are reabsorbed - Some solutes (e.g. Na+) are reabsorbed down concentration/electrochemical gradients - Others (glucose) undergo active transport - Water follows passively along the osmotic gradient created by solute uptake |
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Na+-K+-ATPase REABSORPTION |
- Pumps out Na+ into blood against concentration and electrochemical gradient - Active transport so requires ATP - Accompanied by entry of K+ which rapidly diffuses out of the cell - 3 Na+ leaving: 2 K+ entering |
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SODIUM (Na+) REABSORPTION FROM THE PROXIMAL TUBULE (PT) |
- Na+ is actively transported out of PT cell (ATP required) - Cl- follows Na+ out by passive (facilitated) diffusion - Glucose is co-transported into the PT cell with Na+. This is an example of SYMPORT and CO-TRANSPORT |
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SODIUM-GLUCOSE TRANSPORTER (SGLT2) INHIBITORS |
- New drug for controlling type 2 diabetes (usually end in -flozin) - Not so much glucose reabsorbed into blood - Idea is to make diabetic patients excrete more glucose leading to an overall hypgoglycaemic effect |
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SOLUTE TRANSPORT IN THE LOOP OF HENLE |
The Na+/K+/2Cl- (NKCC2) co-transporter (electroneutral) out of urine into blood |
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LOOP DIURETICS |
- Most effective diuretics available, often called 'high-ceiling diuretics' lead to 'torrential urine flow' - Inhibit NKCC2 transporter in the thick ascending limb of the loop of henle: this reduces the reabsorption of N+, K+ and Cl- - Reduced Na+ reabsorption leads to rapid and profound diuresis (excessive production of urine) , increase urine volume from 300-1200mL in 3 hours - Can be used for treatment for hypertension, CHF and water retention |
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THIAZIDE DIURETICS |
- Act in the distal tubule to inhibit the Na+/Cl- transport system - Cause moderate but sustained Na+ extretion with increased water extretion - Moderately powerful diuresis but considerably lower than loop diuretics - Well absorbed from GI tract and long duration of action: up to 24 hours - Leads to a reduction of high blood pressure (hypertension treatment) |
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RENAL ACTIONS OF ALDOSTERONE |
Overall effect: More Na+ reabsorbed so more water moves into plasma so blood pressure increases |
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ALDOSTERONE ANTAGONISTS |
- Spironolacetone, competitive antagonist of aldosterone, reduces Na+ channel formation - Therefore reduces Na+ absorption from distal tubule - Limited diuretic action (not as potent as loop diuretics or thiazides) - Mechanism depends on protein expression in distal tubular cells so effects may take several days to develop |
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NORADRENALINE |
- Stimulatory neurotransmitter, increased brain levels lead to stimulation - Released from presynaptic nerve terminals to postsynaptic nerve terminals - Levels reduced by reuptake into presynaptic terminal and breakdown into metabolites |
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TRANSPORTER FALSE SUBSTRATES: AMPHETAMINE |
Amphetamine increases levels of noradrenaline around postsynaptic cells in 2 ways: - transporting into presynaptic cell as a false substrate where it increases levels of noradrenaline - reducing noradrenaline reuptake in presynaptic cell (cocaine also does this) Can be used to treat narcolepsy, also produces and appetite suppression |
