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Case 7 Hot and thirsty

6 important questions on Case 7 Hot and thirsty

Reabsorption in early proximal convoluted tubule

Glucose, AA, phosphate, lactate, citrate. With sodium co-transporters, but sodium cannot build up inside the epithelial cells of the wall. So sodium/potassium ATPase and sodium/proton exchanger are used.

Reabsorption in the late proximal convoluted tubule

Fluid that enters lacks essential substances.
Reabsorption of Cl ions, highly concentrated due to the water reabsorption.
- Chloride anion exchanges (driven by high conc. of Cl)
- Passive movement through thigh junctions.
Sodium continues to be reabsorbed.

Reabsorption in thick ascending limb

further 25% of sodium and potassium is reabsorbed via
- Three-ion cotransporter (sodium/potassium/chloride)
- Sodium/potassium ATPase.
Sodium is actively pumped out, potassium and chloride diffuse down electrochemical gradient
No reabsorbing of water

Reabsorption in distal tubule and collecting duct

These parts determine how much sodium will be excreted
There is a sodium/potassium ATPase
Also hormones which regulate the sodium reabsorption

Insensible water loss

Water loss we are not aware of (exhale for example)

Influence of ADH on water balance

Low ADH -> most water reaching the collecting duct can not be reabsorbed because the lack of aquaporins -> diluted urine and reduced volume of body fluids
High ADH -> Aquaporins are inserted in apical membranes -> nearly all the water is reabsorbed.
Osmoreceptors in hypothalamus sense ECF solute concentration and trigger/inhibit ADH release form the posterior pituitary.

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Homeostasis and Organ Systems

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