Renal Function Flashcards
Name the 2 types of nephrons. Explain the difference
Cortical (in cortex)
Juxtamedullary (long loops into medulla)
Juxtaglomerular apparatus (between glomerular and thick ascending limb). Name the functions.
- autoregulation
2. renin release (salt & water balance)
Describe the two capillary beds in series.
- Glomerulus (high hydrostatic pressure- filtration)
2. Peritubular capillaries (low pressure- reabsorption, secretion)
What is the vasa recta?
Thin walled capillary that follows the loop of Henle
Describe the formula for urinary excretion.
Urinary excretion = filtered - reabsorbed + secreted
Cardiac output of kidneys?
Filtration fraction?
Glomerular filtration rate?
25% cardiac output
20% of plasma is filtered
120 ml/min GFR
Which arteriole is smaller? What drives filtration?
Efferent is smaller than afferent. hydrostatic pressure is the driving force.
Where is glucose reabsorbed?
Proximal tubule, provided it doesn’t exceed the maximum reabsorptive capacity.
Define GFR
Volume of fluid entering Bowman’s capsule per unit time.
What cells make up bowman’s capsule?
Epithelial cells
Podocytes
Mesangial cells - structural support
What separates podocytes from endothelium?
basement membrane
What are mesangial cells and function?
structural support
What are the gaps between endothelial cells called?
fenestrations
Gaps in between podocytes called?
slit pores
have foot-like processes called pedicels
What are on basement membranes that repel negatively charged things? Why is this important?
glycoproteins. repels negatively charged things like proteins
aids filtration
Normally, all constituents in plasma filtered except what 2 things?
size and charge
RBCs +cells and plasma proteins
3 symptoms of nephrotic syndrome
proteinuria
hypoalbuminaemia
oedema
What kind of modules pass through the bowman’s capsule easily?
water
small positively charged molecules passes through easily
Forces influencing filtration - name 4. Which one is negligible and why? What is the driving force?
Capillary hydrostatic pressure (driving force)
Colloid osmotic pressure
Bowman’s space pressure
Net filtration pressure
Give an example where Kr (filtration coefficient) would change and how it changes.
decrease in kidney diseases, no glomeruli or change in membrane thickness/pore area.
What is PGC? If afferent arteriole constricts, how does PGC change? What if the efferent constricts? And dilation of each.
Pressure within glomerular capillaries
arteriole constricts - reduce PGC (GFR drops)
efferent constricts - increase PGC (GFR up)
How does GFR change if filtration forces change? Colloid osmotic pressure?
Bowman’s capsule?
Kr?
Colloid osmotic pressure (increases = dec in GFR)
Bowman’s space pressure (dec in GFR)
Kr (increase = inc in GFR)
What is the gold standard of measuring GFR?
Measure inulin
freely filtered, not reabsorbed, not secreted, not met by kidney, no effect on renal function
easily measured
Easier way of measuring eGFR? Equation?
creatinine clearance as inulin needs to be injected.
gives an estimation
eGFR = [U]CR x V
/[P]CR
U-urine conc
P-plasma conc
V-urine flow rate
In what populations should the eGFR equations not be used for?
Other equations: Cockroft-Gault, MDRD, CKD-EPI
Shouldn’t be used in children, malnourished, pregnancy, acute renal failure or oedema.
