Renal Excretory Function Flashcards
What are the three layers of the filtratrion membrane of glomerulus? [3]
Fenestrated capillary endothelium [1]
Basement membrane [1]
Podocyte foot processes [1]
Name 4 factors that determine filtrate that goes into glomerulus
- Net filtration pressure
- Podocyte slit pores
- Size of molecule (urea / creatinine can make it through)
- Charge of molecule: (albumin is negatively charged and so is BM - creates repulsion)
Which molecules are filtered through the glomerulus? [3]
Small molecules:
* Water
* Electrolytes eg Na, K, Cl, phosphate, glucose
* Urea, small amino acids
Large molecules such as albumin have a too big molecular weight to do pass through
What is the most important parameter of kidney function?
GFR
Define GFR
GFR = Clearance of substance
Total amount of fluid that is filtered through the glomerulus
What molecule do you use to measure GFR in specialised clinic? [1]
What molecule do you use to measure GFR in normal clinic? [1]
What molecule do you use to measure GFR in specialised clinic? [1]
Inulin
What molecule do you use to measure GFR in normal clinic? [1]
Creatinine
What is creatinine a breakdown product of? [1]
creatine phosphate: found in muscle
Found at a steady-state concentration in the blood
What are 4 disadvantages of using creatinine to eGFR? [3]
using creatinine to estimate GFR underestiamtes GFR by 10-20%
underestimated in black ethnicities
malnourished patients have low muscle mass so overestimates eGFR
muscular individuals have raised muscle mass so underestimates GFR
How is creatinine clearance measured?
Cr Clearance = ( [U] / [P] ) x Volume
(Urine conc / plasma conc) x volume of urine
How do you measure eGFR using the 4 variable MDRD equation?
Need:
Cretinine
Age
Gender
Ethnicity
What is the function of the PCT? [3]
Reabsorption of:
Solutes: up to 80%
Water – up to 65%
Amino acids, low molecular weight proteins – up to 100%
Explain the MoA of Kidney absorption
Reduce volume of water and solutes within urine but without changing the concentration: make a hypertonic medulla
MoA:
At thin descending loop
* Water pumped out via aquaporins due to increased osmolality produced by thick ascending limb pumping out Na+
At thick ascending limb
* Na is actively pumped into medullary space via Na/K channel
* Paracellular transport of Na, Ca and Mg down a electrochemical gradient
* This wall is impermeable to water.
At distal convoluted tubule:
* Aldosterone works to increase Na absorption
At collecting duct:
- ADH opens aquaporins to reabsorb more water
- Fluid passes down from here to ureter and ladders
In th kidney, osmotic gradient is maintained by the countercurrent exchange by the which structures?
Osmotic gradient is maintained by the countercurrent exchange by the vasa recta
Which parts of LoH action are active transport and which a passive transport?
Blue: passive
Red: AT
Which parts of LoH action are active transport and which a passive transport?
Blue: passive
Red: AT
Which transporter do loop diuretics (such as Furosemide) inhibit? [1]
Where is this transporter located? [1]
Loop diuretics inhibit NaKCl2 on the thick ascending limb
Results in Na & water remaining in tubular lumen and being excreted in urine:
Which transporter do thiazide diuretics inhibit? [1]
Where is this transporter located? [1]
Block Na+/Cl− cotransporter at distal convoluted tubules
Explain MoA of Spironolactone
Binds to mineralocorticoid receptor: an aldosterone antagonist
The concentration/osmolality of the urine is determined by []
The concentration/osmolality of the urine is determined by Anti diuretic hormone (ADH, Vasopressin)
ADH acts via which receptor to cause aquaporin insertion? [1]
ADH acts via V2 receptor to cause aquaporin 2 insertion and fluid movement from collecting duct to intersitium down osmotic gradient.
Explain what the renal threshold of a substance is?
What happens when renal threshold of a substance is exceeded?
Renal threshold is the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine
When the renal threshold of a substance is exceeded, reabsorption of the substance by the proximal renal tubule is incomplete and some of the substance remains in the urine.
The most common reason for the glucose renal threshold ever being exceeded is [].
The most common reason for the glucose renal threshold ever being exceeded is diabetes.
What plasma concentration of glucose exceeds renal threshold, so glycosuria occurs / glucose threshold?
At a plasma glucose level of about 10 mmol/L
The rate of glucose reabsorption reaches a constant maximal value called the []
The rate of glucose reabsorption reaches a constant maximal value called the transport maximum for glucose (TmG)
A low GFR leads to an [] glucose threshold:
filtering rate []
[] in glucose load \ [] glucose reabsorbed.
A low GFR leads to an elevated threshold:
filtering rate reduced
decrease in glucose load \ more glucose reabsorbed.
Explain why glycosuria leads to thirst sensation?
- Glucose in urine induces osmotic diuresis: excess solute present in tubular fluid, this will attract water and increases urine volume
- This leads to increased plasma osmolality and causes thirst
`Label the class of drugs found at A, B & C [3]
A: Carbonic anhydrase inhibitors
B: Loop diuretics
C: Thiazides
Name and explain which transport protein in the thick ascending loop of Henle assists NaKCl2 transporter
Renal Outer Medullary potassium channel or ROMK
- K is AT pumped into the tubular lumen / urine to generate positive voltage within the cell (because less K+ in)
- This creates an overall voltage gradient of +80mV; from +10mV in the tubular lumen to -70mV in the tubular cell
- This voltage difference drives Na into the tubular cell via NaKCl2 transporter
