Renal function: glomerular filtrate and its control Flashcards
What is a nephron
Where urine is formed
Where is urine drained
Collecting ducts into renal pelvis
How does urine leave kidney
Via ureter into the bladder ready for excretion
HOwdoes blood enter and leave kidneyb
Renal artery
Renal vein
What are the two nephron types in the kidney and what are the differences
Cortical nephrons (have most of their structures in the cortex)
Juxtamedullary nephron which has most of its structure in the medulla
Where does urine formed in the nephron go
Intio common collecting duct then into renal pelvis then leaves the kidney via the ureter
Structure of a single nephron
1) Bowman’s capsule. Comprised of glomerular capillaries and both together make the renal corpuscle
2) Proximal convoluted tubule
3) Descending and ascending limbs of loop of henle
4) DCT
5) collecting duct
6) renal pelvis –> ureter
What are the main function of the nephron
Filter blood in the renal corpuscle
Control the concentration and content of urine in the tubular system
What re the two capillary beds in a single nephron
1) glomerulus which have a high hydrostatic pressure for ultrafiltration
2) Peritubular capillaries which have a low pressure and wrap around the remainder of the nephron
What do the peritubular capillaries around loop of Henley do and what are these called
Wrap around the loop of henle and provide oxygen and nutrients to the medulla of the kidney.
-Called the vasa recta
What re the different processes which modify urine composition and volume
FIltration- movement of fluid from blood, to lumen of nephron in renal corpuscle
Reabsorption- movement of filtered material from lumen of nephron back into blood through peritubular capillaries
Secretion- removal of deleted molecules from blood and their addition to fluid in lumen of nephron
Excretion- removal of substance from body
What is the filtration fraction
Only 20% of blood entering the glomerulus is filtered. The other 80% is returned via the efferent arteriole into the systemic circulation.
What is the GFR
Glomerular filtration rate - volume of fluid entering the Bowmans capsule per unit time
How much urine is excreted per day
1.5L
How does glomerular filtration occur
Efferent arteriole has smaller diameter than afferent arteriole. There is also a high capillary hydrostatic pressure. Fluid is driven fro capillaries into Bowman’s capsule across glomerular filtrate
What are mesangial cells
Provide structural support in the bowman’s capsule
Layers if the glomerular capillary membrane
Endothelial cell (next to capillary lumen)
Basement membrane
Podocytes (specialised epithelial cells) next to the Bowman’s space
How do things pass from capillary lumen to bowman’s space
Through fenestrations (gaps) in the capillary endothelium and slit pores in the podocyte cells
What can pass through fenestration and slit pores
Non-ionised compounds and very small proteins
What is the oncotic pressure in the Bowman’s space and why
0 because it is protein-free
What is the colloid osmotic pressure
Pressure exerted from bowman’s space
What can GFR be altered by
Changing Kf (filtration coefficient. intrinsic permeability x filtration area)
Changing any of the Starling forces
Drugs
What happens to GFR and RPF (renal plasma flow) if afferent arteriole decreases in size
GFR decreases
RPF decreases
What happens to GFR and RPF If efferent arteriole decreases in size
GFR increases
RPF decreases
If there are changes in protein metabolism, what will change
Change in colloid osmotic pressure
how will hyperproteinaemia change GFR
Increase GFR
What will changes in Bowman’s space pressure do to GFR e.g. renal stone occluding ureter
Reduce GFR
Why measure GFR
Assessing patients with kidney disease by providing info on severity and course of kidney disease and how much drug you can provide.
how to measure GFR
Inulin clearance
Formula for measuring GFR
(Urine flow rate x urine concentration of inulin) / plasma concentration of inulin
Why can inulin be used to measure GFR
Inulin clearance is constant
How can eGFR be estimated and why would you do this
Measure creatinine clearance because you don’t need to inject inulin and also creatinine is pretty much constant
