Lecture 32 Flashcards
What are the three places where water is reabsorbed in the nephron?
PCT, descending limb on nephron loop, collecting duct
How much water is reabsorbed in the PCT?
67%
How much water is reabsorbed in the descending limb of the nephron loop?
25%
How much water is reabsorbed in the collecting duct?
2-8%
What is reabsorption of water in the collecting duct determined by?
Hydration level
How much water is excreted?
<1 - 6%
What type of water reabsorption occurs in the PCT and the descending limb of the nephron loop?
Bulk reabsorption via leaky epithelia
How much of the total water reabsorption occurs by bulk reabsorption?
92% (does not change)
What type of water reabsorption occurs in the collecting duct?
Regulated reabsorption via tight epithelia
How much of the total water reabsorption occurs in the collecting duct, what is this regulated by?
2-8% - regulated by antidiuretic hormone (ADH)
What are the four places where sodium is reabsorbed in the nephron?
PCT, ascending limb on nephron loop, DCT and collecting duct
How much sodium is reabsorbed in the PCT?
67%
How much sodium is reabsorbed in the ascending limb of the nephron loop?
25%
How much sodium is reabsorbed in the DCT?
5%
How much sodium is reabsorbed in the collecting duct?
2-3%
How much sodium is excreted?
<1%
What type of sodium reabsorption occurs in the PCT and the ascending limb of the nephron loop?
Bulk reabsorption via leaky epithelia
How much of the total sodium reabsorption occurs by bulk reabsorption?
92%
What type of sodium reabsorption occurs in the DCT and the collecting duct?
Regulated reabsorption via tight epithelia
How much of the total sodium reabsorption occurs by regulated reabsorption, and what is this regulated by?
7-8% - regulated by aldosterone
What drives and regulates body water homeostasis?
Distribution of water, osmolarity of solutions, chances in osmolarity, reabsorption of water and sodium in nephron and effects of osmotic & volume changes on the kidney
What is water reabsorption in the PCT driven by?
Na+ reabsorption
What transporter transports sodium across the apical membrane?
Sodium-glucose cotransporter
What is the driving force for the Sodium-glucose cotransporter?
Sodium gradient
How is chloride attracted across the epithelial cell?
The positive charge on the sodium attracts the negative charge on the chloride, allowing it to go down its concentration gradient via the paracellular pathway
How does Na+ facilitate water reabsorption?
Na+ and Cl- in the peritubular fluid increases the osmolarity, attracting water through aquaporins
What do juxtamedullary nephrons cause in the nephron loop?
A hyper-osmotic medullary gradient
What are changes in ECF osmolarity detected by?
Osmoreceptors in the hypothalamus
What do the osmoreceptors stilulate?
The posterior pituitary gland to secrete more/less ADH
What does ADH do?
Alters water permeability of the collecting duct cells by delivering/removing aquaporins in the apical membrane of CD cells
Explain what happens to water during dehydration
Increased osmolarity in ECF, stimulates more ADH secretion for kidneys to increase water reabsorption and increase ECF volume
Explain what happens to water during hyper-hydration
Decreased osmolarity in ECF, stimulates less ADH secretion for kidneys to decrease water reabsorption and decrease ECF volume
What is an increase in ECF volume detected by
Cardiac muscle cells (because e.g. increased volume (plasma) means more blood is being pumped into your heart per beat, therefore stretch receptors are stimulated)
What do the cardiac muscle cells stimulate?
The release of ANP
What does ANP do?
Acts on kidneys to increase Na+ and water loss in urine to decrease ECF volume
What is a decrease in ECF volume detected by?
Kidneys
What do the kidneys stimulate?
Activation of RAAS and an increased release of ADH
What does RAAS do?
Increases the release of aldosterone from the adrenal gland and therefore the delivery of more sodium channels to the apical membrane
What does the increased release of ADH and aldosterone cause?
Decreased Na+ and water loss in urine
What is found in normal urine?
Water, creatinin, urea, uric acid, H+, Na+, medications and toxins
What is found in pathological (abnormal) urine?
Glucose, protein, blood, haemoglobin, white blood cells and bacteria
What does normal urine look like?
Clear to light or dark amber (yellow) colours
What does pathological (abnormal) urine look like?
Orange, red, brown, blue/green colours
What could abnormal urine taste like?
Sweet from the presence of glucose
What would be the cause of ‘fruity’ smelling urine?
Ketones from fasting, diabetes, or chronic alcohol abuse
What could be the cause of ‘rotten’ smelling urine?
Bacterial infection of tumour
