Glomerular Filtration Flashcards
What is the advantage of the glomerular filtration rate being high?
It means that the kidney has ample opportunity to precisely regulate ECF volume and composition
What parts of the kidney does blood flow through?
None of the red cells and very little of the plasma is filtered through into Bowman’s capsule. The rest passes via the efferent arterioles into the peritubular capillaries and then into the renal vein
What factors is glomerular filtration dependent on?
The balance between the hydrostatic forces favouring filtration and the oncotic pressure forces favouring reabsoprtion
What factors determine the filterability of solutes across the glomerular filtration barrier?
Molecular size
Electrical charge
Shape
Why is glomerular capillary pressure higher than most other capillaries?
The afferent arteriole is short and wide and offers little resistance to flow so the blood arriving at the capillaries still has a high hydrostatic pressure
Also, efferent arteriole is long and narrow and so gives a high post-capillary resistance
What factors can effect GFR?
Subject to intrinsic control via:
- Sympathetic VC nerves giving afferent and efferent constriction and greater sensitivity of afferent arteriole
- Circulating catecholamines, constriction primarily afferent
- Angiotensin II, constriction of efferent at low concentrations and both at high concentrations
How is BF and GFR kept constant in the kidneys?
Through intrinsic control of the renal vasculature to adjust its resistance
How does blood flow to the kidneys alter in haemorrhage?
In situations where blood volume/BP face serious compromise (ie haemorrhage) activation of sympathetic VC nerves and angiotensin II can override autoregulation liberating blood for more immediately important organs
Why is the pressure in the peritubular capillaries so low?
Hydrostatic pressure is overcoming frictional resistance in the efferent arterioles
What factors allow for reabsorption of fluid?
Low Ppc and high oncotic forces means that the balance of Starlings forces in the peritubular capillaries is in favour of reabsorption
What molecules have low and high filtration rates?
Simple molecules have higher filtration rates whereas more complex molecules such as proteins have a lower filtration rate
What is GFR controlled by?
Vasoconstriction of the afferent and efferent arterioles
What is the zone for autoregulation of GFR?
60-130mmHg
