Loop Of Henle, Countercurrent, ADH, And RAAS Flashcards
Major difference in Loop of Henle
Permeability to water varies extremely in the different segments, therefore osmolarity of the tubular fluid is not necessarily the same as the surrounding tissue
Countercurrent exchange
The key to the function of the Loop of Henle is that the tubular fluid enters the loop isoosmotic with systemic plasma and leaves it dilute
Solutes accumulate in the interstitial fluid of the medulla
Water diuresis
Large water consumption, dilutes plasma osmolarity, suppresses ADH, increased urine output
Antidiuresis
Water deprivation, increases plasma osmolarity, increases ADH, decreases water excretion, decreases urine output and increases urine osmolarity
Urea and osmotic regulation
Urea concentration increases due to decreased water
Allows urea to be reabsorbed in collecting duct
Sign of dehydration: increased BUN
Control of ADH secretion
Stimulated by increased plasma osmolarity, primarily sodium concentration
Inhibited by high blood volume, high BP, or decreased plasma Na concentration (stretch receptors)
Concept of effective circulating volume applies
Produced by supraootic and paraventricular in hypothalamus, stored in posterior pituitary
ADH Thirst mechanism
The receptors respond to increased plasma osmolarity, especially increased plasma sodium concentration
The same stimuli that increase secretion of ADH will also stimulate thirst
Osmolarity of Na dominates
Osmolality of glucose and urea follow
Disorders of Na regulation v water excretion
Na regulation: mainly affect fluid volume and distribution, not plasma sodium concentration, dilute urine
Water excretion: large effects on plasma sodium concentration, increased ADH
Look at ADH and RAAS levels
Increases in ADH tend to produce
Negative free water clearance (CH2O)
Causes conservation of water
Free access to water: lowers plasma osmolarity and sodium concentration
Water restricted: oppose or limit rate at which plasma osmolarity is increasing
Alcohol and ADH
Alcohol inhibits secretion of ADH
Rapid effect independent of volume
Consumption of beverages high in alcohol tend to cause urinary loss of several times the volume of water consumed
Control of water and solute excretion
Normal inverse relationship between urine flow and osmolarity
ADH controls volume of body water and key hormone in regulating osmolarity of ECF (NOT body sodium content)
RAAS
Re in secretion increased by decreased GFR, decreased TL of Sodium, and decreased renal artery blood pressure
Two principle control mechanisms for secretion of aldosterone are plasma K concentration (more sensitive) and plasma AII concentration (less sensitive)
Response to sodium intake
Increased sodium intake in normal has almost no effect on BP
Blood volume increases due to high ADH -> CO increases
High Na -> decreases renin/AII/aldosterone -> Na excretion increases -> reduces TPR -> so despite high CO, MAP does not increase
If renal function not normal then high Na intake increases BP
