Urine + Renal Function Flashcards
When do we make dilute urine?
When there is too much water or too little ions (concentrates the blood)
When do we make concentrated urine?
When there is too little water or too many ions (dilutes the blood)
Are the collecting ducts permeable when creating dilute urine?
No
Where does most of the reabsorption occur?
In the PCT
How does the osmotic gradient get set up?
By the thick ascending LOH pumping out ions but not water
Why does water leave the descending LOH?
Because of the salty interstitial fluid - set up by the ascending limb pumping out ions
Are the collecting ducts permeable when making concentrated urine?
Yes
How do diuretics work?
Inhibit Na-K-Cl pumps in the ascending LOH therefore decreased water re-uptake and more dilute urine
Hormonal regulation of tubular reabsorption (x2)
ADH and angiotensin
How does ADH cause permeability in CDs?
Leads to the fusion of aquaporin-2 to the basolateral membrane of the collecting ducts
Where is ADH made + stored?
- Hypothalamus
2. Posterior pituitary gland
How is high osmolarity detected?
Osmoreceptors in the hypothalamus detect high osmolarity in the plasma and interstitial fluid
Causes neurosecretory cells in hypothalamus to release ADH
ADH and Na-K-Cl symporter
ADH increases the activity of the symporter (allows for more concentrated urine –> saltier in the medulla)
Also increases BP
Angiotensin II and BP
Decrease in BP/sympathetic stimulation –> juxtaglomerular apparatus releases renin –> angiotensin II –> constriction of afferent arterioles –> increase in blood pressure and decrease in GFR
Aldosterone and filtration
Aldosterone increases Na+ and Cl- reabsorption in collecting ducts (increased BP) –> increased BV –> increased blood pressure
What does urinalysis look at?
Volume, colour, turbidity, odor, pH
Ways to do blood analysis (tells you how well kidneys are working, x2)
- Blood urea nitrogen: measure of urea nitrogen produced due to protein breakdown (this is filtered by the kidney)
- It increases in the blood when the GFR decreases & urine production is low
- Plasma creatinine: waste product form the breakdown of creatinine phosphate in skeletal muscle (high levels = poor kidney function)
Renal function tests (x2)
- Renal clearance
2. Glomerular filtration rate (GFR)
What is renal clearance?
Determines how effectively the kidneys are removing a given substance
High plasma clearance = efficient excretion of a substance in urine (penicillin)
Glucose is the opposite
Renal clearance formula
Conc. in urine x rate of urine output = conc. in plasma
What is GFR?
Measure of the rate in which glomeruli filter the blood
To measure this, you need a substance that is not reabsorbed or secreted by tubules (e.g. creatinine or inulin)
