Renal Blood Flow and Glomerular Filtration
Key Points:
An overview of how urine is formed
The blood supply of the glomerulus
The structure of the glomerular membrane, fenestrae, basement membrane,
podocytes and nephrin-based filtration slits
The Starlings forces that act at the glomerular membrane to determine
glomerular filtration rate (GFR)
Relation between GFR or renal blood flow and blood pressure – the
autoregulation of GFR and renal blood supply in the face of changing perfusion
pressures
How the levels of GFR and renal perfusion at which autoregulation operates in
vivo can be adjusted by sympathetic nervous tone e.g. exercise, hypotension,
shock
How failure of glomerular function can lead to acute/chronic renal failure
How increased glomerular permeability can lead to nephrotic syndrome (i.e. loss
of proteins in urine, deficiency of plasma proteins and oedema)
Introduction
We have two kidneys that are only 0.5% of body weight, but they receive around 20%
of resting cardiac output. This large blood flow is hence not related to the metabolic
needs of the kidney, but instead it is related to the kidneys function.
The main functions of the kidney include:
- To control volume and composition of body fluids
- To get rid of waste material from the body
- Acid-base balance
- As an endocrine organ – EPO, renin, vitamin D
The functional unit of the kidney is the nephron (average around 4cm long) and the
nephron has two elements to it, the glomerulus and a tubule.
The glomerulus (a tuft of blood vessels) is contained within the Bowmans capsule. The
glomerulus is unusual in that is has an artery entering (the afferent arteriole) and also
the vessel leaving is also an artery (efferent arteriole) before becoming the peritubular
capillaries the surround/are adjacent to the tubule.
Importantly, the blood and tubule meet again through the peritubular capillaries.
Each kidney contains about 1 million nephrons.
, Urine is formed in two stages, the glomeruli produce the liquid and the tubule
modifies its volume and composition.
Blood flowing through the renal artery enters into the afferent arteriole, goes into the
ball shaped glomerular capillaries. Here fluid is filtered out (by ultrafiltration) into the
tubule at a relatively fast rate of normally about 120ml/min.
As blood leaves the glomerular capillaries it leaves via another arteriole, the efferent
arteriole. The efferent arteriole leads on to the peritubular capillaries and here a lot of
reabsorption takes place.
Key Points:
An overview of how urine is formed
The blood supply of the glomerulus
The structure of the glomerular membrane, fenestrae, basement membrane,
podocytes and nephrin-based filtration slits
The Starlings forces that act at the glomerular membrane to determine
glomerular filtration rate (GFR)
Relation between GFR or renal blood flow and blood pressure – the
autoregulation of GFR and renal blood supply in the face of changing perfusion
pressures
How the levels of GFR and renal perfusion at which autoregulation operates in
vivo can be adjusted by sympathetic nervous tone e.g. exercise, hypotension,
shock
How failure of glomerular function can lead to acute/chronic renal failure
How increased glomerular permeability can lead to nephrotic syndrome (i.e. loss
of proteins in urine, deficiency of plasma proteins and oedema)
Introduction
We have two kidneys that are only 0.5% of body weight, but they receive around 20%
of resting cardiac output. This large blood flow is hence not related to the metabolic
needs of the kidney, but instead it is related to the kidneys function.
The main functions of the kidney include:
- To control volume and composition of body fluids
- To get rid of waste material from the body
- Acid-base balance
- As an endocrine organ – EPO, renin, vitamin D
The functional unit of the kidney is the nephron (average around 4cm long) and the
nephron has two elements to it, the glomerulus and a tubule.
The glomerulus (a tuft of blood vessels) is contained within the Bowmans capsule. The
glomerulus is unusual in that is has an artery entering (the afferent arteriole) and also
the vessel leaving is also an artery (efferent arteriole) before becoming the peritubular
capillaries the surround/are adjacent to the tubule.
Importantly, the blood and tubule meet again through the peritubular capillaries.
Each kidney contains about 1 million nephrons.
, Urine is formed in two stages, the glomeruli produce the liquid and the tubule
modifies its volume and composition.
Blood flowing through the renal artery enters into the afferent arteriole, goes into the
ball shaped glomerular capillaries. Here fluid is filtered out (by ultrafiltration) into the
tubule at a relatively fast rate of normally about 120ml/min.
As blood leaves the glomerular capillaries it leaves via another arteriole, the efferent
arteriole. The efferent arteriole leads on to the peritubular capillaries and here a lot of
reabsorption takes place.
