1.1. Basic Renal Process - Filtration Flashcards
What is the process if the filtration?
The formation of an essentially protein-free filtrate of plasma
Where does the process of filtration occur?
At the glomerular capillaries
How much of the plasma, from the afferent arterioles, is filtered through the glomerular capillaries?
20%
Where is the plasma filtered from / into?
From - The glomerular capillaires
Into - Bowman’s capsule
What happens to the remainder of the plasma, which isn’t filtered into the Bowman’s Capsule?
It passed into the efferent arterioles
Where does the blood, which passes into the efferent arterioles, travel to?
The peritubular capillaries
What are the three layers of the glomerular capillary wall?
- Endothelial Cells
- Basal Lamina
- Podocytes
What is special about the Glomerular Endothelial Cells?
It is fenestrated as to prevent blood cells from being filtered, but allowing smaller components of plasma
What is special about the Glomerular Basal Lamina?
This prevents larger proteins from being filtered, but allowing smaller components of plasma
What is special about the Glomerular Podocytes?
They form a Slit Membrane between Pedicles of the Podocytes, which prevent medium sized proteins from being filtered, but allowing smaller components of plasma
How does glomerular filtration occur?
Through the balance of:
1. Hydrostatic Forces
2. Oncotic Pressure
Note - This is the same method as fluid filters through capillaries
What force favours filtration?
Hydrostatic forces
What force favours reabsorption?
Oncotic pressure (Starling’s Forces)
Is the pressure in the Glomerular Capillaries high or low?
High
What is responsible for the high glomerular capillary pressure?
- The afferent arteriole
2. The efferent arteriole
- How are the afferent arterioles described?
2. What is the result of this?
- Short and Wide
- This offers little resistance to Flow, allowing for a high hydrostatic pressure to arrive at the glomerular capillaries
- How are the efferent arterioles described?
2. What is the result of this?
- Long and Narrow
2. This offers high resistance to Flow, allowing for increased pressure upstream (in the Glomerular Capillaries)
What happens as a result of the high glomerular capillary pressure?
The hydrostatic forces exceed the oncotic pressure - favouring filtration
- What is the Glomerular Filtration Rate?
2. Is this high or low?
- 125ml/min
2. High
What does the Glomerular Filtration Rate allow the kidneys to do?
Precisely regulate Extra-Cellular Volume
What percentage of the renal plasma will become Glomerular Filtrate?
19%
What equation which can show the percentage of renal plasma which will become glomerular filtrate?
Plasma = 55% of the total blood volume
Total blood volume = 1200ml/min
Therefore Renal Plasma Flow = 55% of 1200 = 660ml/min
Glomerular Filtration Rate = 125ml/min
Therefore the Filtration Fraction = 125/660 x 100 = 19%
What is responsible for regulating the Glomerular Filtration Rate?
- Afferent Arteriolar Diameter
2. Efferent Arteriolar Diameter
What are the extrinsic controls of the Afferent / Efferent Arteriole Diameter?
- Sympathetic Vaso-Constricting Nerves
- Circulating Catecholamines
- Angiotensin II
What are the Sympathetic Vaso-Constricting Nerves responsible for?
The constriction of both the afferent and efferent arterioles, but there is a greater sensitivity for the afferent
What are the circulating Catecholamines responsible for?
The constriction of primarily the afferent arterioles
What is Angiotensin II responsible for?
- Constriction of the efferent arteriole at low concentrations
- Constriction of both afferent and efferent arterioles at high concentrations
What is a special feature of renal vasculature? And what is it’s name?
It exhibits a well-developed intrinsic ability to adjust its resistance in response to changes in arterial blood pressure - Autoregulation
What is the function of Autoregulation?
This keeps the blood flow, and therefore the Glomerular Filtration Rate constant over a range of mean blood pressure
Over what mean blood pressure can autoregulation keep the Glomerular Filtration Rate constant?
60mmHg - 130mmHg
How is autoregulation related to nerves and hormones?
It isn’t - it works independently of these and so will occur at the same time
What happens below a mean blood pressure of 60mmHg?
Glomerular Filtration Rate falls
What happens below a mean blood pressure of 50mmHg?
Glomerular Filtration Rate ceases all together
What happens if there is an increase in mean arterial pressure?
There is an automatic increase in afferent arteriolar constriction, preventing a rise in Glomerular Capillary Pressure
What happens if there is severe volume compromise (i.e. haemorrhage)?
There is an interaction between intrinsic and extrinsic controls
What happens in the interaction between intrinsic and extrinsic controls in situations of severe volume compromise?
- There is an activation of vaso-constricting nerves and Angiotensin II. This overrides autoregulation
What is the purpose of the vaso-constriction and release of Angiotensin II in times of severe volume compromise?
This overrides autoregulation, liberating more blood for more immediately important organs
How much blood is freed up by the overriding of autoregulation?
800mls per minute
What happens if the blood is diverted away from the kidneys over long periods of time?
Renal damage occurs
