Pharmacology Flashcards
What are the most common drugs to increase urine flow?
Diuretics
Diuretics, simply work by one basic biochemical principle; what is it?
Where sodium goes, water must follow. Inhibiting sodium reabsorption reduces water reabsorption.
if we reduce sodium reabsorption what else decreases?
Chloride
Water
What is oedema?
Imbalance in rate of formation and reabsorption of interstitial fluid
What is interstitial fluid formation proportional to?
Forces favouring filtering - forces favouring reabsorption
What are the four starling pressures?
Capillary hydrostatic pressure Capillary oncotic pressure
Interstitial hydrostatic pressure
Interstitial oncotic pressure
Which of these two forces when changed with produce oedema? How do they change?
Capillary hydrostatic - increases
Capillary oncotic - decrease
Favouring filtration forces increase, favouring reabsorption forces decreases.
Give a few disease states in which the capillary hydrostatic pressure increases or oncotic pressure decreases.
Nephrotic syndrome
CHF
Hepatic cirrhosis + ascites where there is portal hypertension
What goes wrong in the nephrotic syndrome?
Disordered glomerular filtration
Protein in primary filtrate and so proteinuria.
If urine looks frothy think protein uria.
Decreases oncotic pressure and therefore oedema follows.
How does the nephrotic syndrome affect the rest of the body?
BP goes down, less preload, stroke volume decreases, overall less CO. RAAS activated - decreased renal blood flow starts it. Aldosterone production increases and increases sodium and water reabsorption. hydrostatic pressure goes up but oncotic is low; oedema worsens.
How is the nephrotic syndrome treated?
Diuretic!
How are congestive heart failure and the kidneys related?
CHF - reduced output.
Renal hypo perfusion.
RAAS activated. Blood volume expansion/vasoconstriction increase venous and cap. pressures, reduced plasma oncotic pressures and increased hydrostatic pressures worsen pulmonary and peripheral oedema, but especially pulmonary.
In hepatic cirrhosis, why does ascites occur?
Liver creates albumin normally. Cirrhosis, decreased albumin -> decreased oncotic capillary pressure. Increased hepatic portal pressure causes increased loss of fluid into the peritoneum. RAAS exacerbates problem; higher blood pressure, higher water loss into the peritoneum.
When a diuretic is used, blood leaving the nephron is ____
haemoconcentrated
How does haemoconcentration by a diuretic help with oedema?
There is a higher oncotic pressure in the capillary; water and sodium is drained out of the nephron and so oedema can be reabsorbed.
What risks are associated with diuretic use in oedema?
Thrombosis
Circulatory collapse
How likely are thrombosis and circulatory collapse due to oedema mobilisation using diuretics?
Very unlikely; huge hypovolaemia needed to decrease blood volume enough for collapse and concentrate platelets enough for thrombosis.
How many nephron does an average kidney have? How can this be changed?
1.4m
Decreases with age
1/2 with longstanding, uncontrolled HTN/
Two methods by which diuretics work are
Blocking sodium reabsorption
Blocking water reabsorption in water permeable nephron.
name the sites of the nephron sodium reabsorption may occur? give percentage of filtered sodium reabsorbed
PCT - 67%
TAL Loop of Henle - 25%
DCT - 10%
CD - 2%
Give a brief summary of the principle sodium reabsorption mechanism in the proximal tubule.
Sodium hydrogen exchanger.
Sodium in/hydrogen out
Hydrogen generated by carbonic anhydrase type II/IV, present on brush border and intracellularly. Needed to drive the reabsorption of sodium. CA blockers obsolete, lose effect over time. No longer used as diuretics
