Renal physiology Flashcards
What does GFR stand for?
glomerular filtration rate
What is glomerular filtration rate?
the volume of fluid filtered from the glomerulus to the Bowmann’s space per unit time
What is the average GFR is a 70Kg person?
125ml/min
What is the oncotic pressure into the bowmann’s space?
zero!
Why is the oncotic pressure into the bowmann’s space zero?
there are no proteins in the bowmann’s space
What is the renal blood flow per minute?
1 L
What is PGC?
hydrostatic pressure in the glomerular capillary
What is PBS?
hydrostatic pressure in the bowman’s space
What is πGC?
oncotic pressure into the glomerular capillary
What is KF?
the filtration coefficiant
What is the equation for glomerular filtration rate?
GFR= KF (PGC-PBS)-(πGC-πBS)
How can the afferemt and efferent arteriole decrease GFR?
constrict afferent arterioles
dilate efferent arteriole
How is GFR measured clinically?
creatinine used as a marker substance
What factors affect GFR?
blood pressure size of substance Charge of substance Surface area Attatchment to plasma proteins e.g albumin
If pressure within the afferent arteriole rises, how does it respond?
responds by constricting
When measuring GFR using a marker substance, what important qualities must the marker substance have?
be freely filtered
not be secreted or absorbed in the tubules
not metabolised
What equation do we use when calculating GFR from a marker substance?
GFR= Um x urinary flow rate /Pm Um= concentration of m in urine Pm= concentration of m in plasma
What is renal clearance?
the volume of plasma from which a substance is completely removed by the kidney per unit time
How do we calaculate renal clearance?
clearance= urine concentration x urine volume / plasma concentration
What is the filtration fraction?
GFR/ renal plasma flow
Describe the charge of the foot processes of podocytes
negative
What are the three basic layers of the filtration barrier in the kidneys?
- endothelium
- basement membrane
- epithelium
How much of the filtrate is reabsorbed in the proximal convoluted tubule?
2/3rds
Where in the kidney is most of the filtrate reabsobed?
proximal convoluted tubule
Where in the nephron does bulk reabsorption of glucose and amino acids occur?
the proximal convoluted tubule
Which tubule is the longest?
the proximal convoluted tubule
Does the proximal convoluted tubule have microvilli?
yes
What are the two parts of the loop of Henle? What do they do?
Ascending:
impermiable to ions, H2O reabsorption
Descending:
Na, K and Cl reabsorption
Where in the nephron does fine tuning occur?
the distal convoluted tubule
ADH acts on which type of cell at the collecting duct?
principal cells
The macula densa detects the concentration of which ion?
Na+
What happens if the macula densa detects low Na+ concentration?
a low Na+ concentration implies low GFR
macula densa sends signals to increase renin
renin causes an increase in blood pressure via RAAS
this increases GFR
What is the anion gap?
the difference between anions and cations
How do we calculate the anion gap?
cations- anions
describe the anion gap in a case of acidosis
acidosis- low anions
so wide anion gap
How do the kidneys control water and ultimately blood pressure?
ADH
RAAS
Atrial natriuretic peptide
Describe how a decrease in plasma volume is corrected for by ADH
decrease in plasma volume detected by baroreceptors
posterior pituitary increases ADH secretion
Increases collecting duct permeability to H2O
More H2O is absorbed at the collecting duct and less is excreted
