Renal blood flow and glomerular filtration Flashcards
What percentage of cardiac output from the heart do the kidneys receive?
2 kidneys (0.5% body weight) receive ~20% of resting cardiac output.
What are the 4 functions of the kidney?
- Control volume & composition of body fluids
- To get rid of waste material from body
- Acid-Base balance
- As an endocrine organ – EPO, Renin & Vit D
What are the main 2 stages of urine production?
Urine is formed in 2 stages : glomeruli produce the liquid; tubules modifies its volume & composition
Refer to slides
Why such a huge filtration rate, namely 180 litre/day?
Answer; a high rate of formation of glomerular fluid is needed to wash out the waste products fast enough to keep their blood level low.
Example; a human produces 36 g urea per day:- yet normal plasma urea is only 0.2 g/litre.- To wash 36 g urea into the urine, 180litre of plasma have to be filtered per day (because 180L x 0.2 g/L = 36g).- This is a glomerular filtration rate (GFR) of 120 ml/min!
HOW is glomerular fluid formed?
By passive ultrafiltration of plasma across the glomerular membrane, as described by Starling’s principle of capillary fluid filtration.
What is the rate of glomerular filtration set by?
The glomerular filtration rate (GFR) is set by-
(i) autoregulation:
(ii) renal sympathetic vasomotor nerve activity
Describe the structure and contents of the Bowsman capsule
On slide
Describe the mechanisms for the glomerular fluid formation
What drives the ultrafiltration process?
The key features of glomerular filtration are therefore –
For small solutes, such as NaCl, glucose and urea, concentration in glomerular fluid = concentration in plasma.
For plasma proteins, concentration in glomerular fluid = almost zero. Hence, urine is routinely tested on wards for protein (proteinuria). Proteinuria is a sign of renal/urinary tract disease.
A net pressure drop across the glomerular membrane drives
the ultrafiltration process.
Describe the mass, radius and filtrate or urea, glucose and albumin in GF
On slides
What drives GF?
What pressures are in with GF?
An imbalance of starlings forces
Pc, capillary blood pressure, around 50 mmHg
PIp, plasma colloid osmotic pressure (25 mmHg)
Pu, pressure in Bowman’s space (10 mmHg)
How do we calculate the filtration fraction?
Describe the graph of pressure against distance along the capillary
GFR/ Plasma flow
on slides
Describe the Blood pressure profile in the kidney: Starling force balance is reversed (absorption) in peritubular capillaries.
On slides
Describe the 3D structure of the glomerular membrane
On slides
Describe the Electron micrograph of the glomerular barrier
On slides
Describe the surface view of filtration slits between foot processes, seen from urinary space
On slides