Session 5 Flashcards
What does an issue with Na+ balance effect?
The volume
What does an issue with water balance effect?
Osmolarity
What causes plasma osmolarity to increase?
When water intake is less than water excretion
What causes plasma osmolarity to decrease?
When water intake is more than water excretion
What detects changes in plasma osmolarity?
Hypothalamic Osmoreceptors
What are the 2 efferent pathways for plasma osmolarity?
ADH
Thirst sensation
What is the effector for when ADH pathway is activated?
The kidney. Water excretion is effected
What is the effector for when thirst is activated?
Brain. Water intake is effected
Where, specifically, are osmoreceptors?
In the OVLT of the Hypothalamus
When is ADH activated?
When there is water loss
When is thirst activated?
When the person is already at least 10% dehydrated
Where is ADH released from?
The posterior pituitary gland
Where is ADH made?
In the Hypothalamus
What stimulates ADH?
Increase is osmolarity (i.e loss of water)
What inhibits ADH?
Decreased osmolarity (i.e lots of water)
What stimulates osmoreceptors?
Increased osmolarity
What is important to remember about the thirst reflex?
The water does not correct osmolarity immediately, but the brain recognises that it will be fixed so reduces the thirst sensation
When does the body stop trying to correct osmolarity?
When there is severe fluid loss (i.e drop in blood volume) the body will compromise and have dilute plasma to keep the volume correct
What are the effects of ADH on the kidney?
Causes vasoconstriction in the Glomerulus
Increases Na+, Cl- and K+ reabsorption in ascending limb
Water reabsorption in the the DCT and CD (by causing Aquaporin 2 to insert into the apical membrane of cells - allows for subtle changes)
How does osmolarity effect renal water excretion?
Decreased osmolarity = Increased excretion
Increased osmolarity = Decreased excretion
How much urine is excreted when it is Hypo-osmotic?
Large amounts of dilute urine (diuresis)
What does hyper-osmotic urine cause?
The kidney to reabsorb as much water as possible, but this requires a hyper-osmotic intersitium (Achieved by counter current multiplier by Loop of Henle and vasa recta acting as counter current exchanger)
What is the arrangement of Peritubular capillaries around Juxtamedullary nephrons?
Vasa recta. (Hair pin shape) Blood runs in an opposite direction to the filtrate
What does the Vasa recta maintain? (It is needed for reabsorption)
The Corticopapillary Osmotic gradient (Gradient of increasing osmolarity)
What is the Descending limb of the Loop of Henle permeable to?
Water
What is the Ascending limb of the Loop of Henle permeable to?
Solutes
