Lec 5 - GFR and Filtrations Flashcards
What is Renal plasma flow (RPF)?
- This is haematocrit or erythrocyte volume fraction (EVF) is the volume percentage of RBC in blood.
- –> normally is approx 0.45
- –> RBF is 1.1 L/min
Describe the passage of blood from and to the heart.
- aorta
- renal artery
- segmental artery
- lobular artery
- arcuate artery
- Interlobular artery
- afferent arteriole
- glomerulus
- efferent arteriole
- peritubular capillaries
- Interlobular vein
- arcuate vein
- lobular vein
- segmental vein
- renal vein
- IVC
- Back to heart.
Instead of the efferent arteriole passing blood into the peritubular capillaries where does it go?
To the vasa recta
—> This then feeds blood either into the interlobular vein or the arcuate vein.
What are peritubular arteries?
These are a second specialised capillary bed, which are unique to the kidney.
How can the appearance of the peritubular arteries indicate which type of nephron it is?
Juxtamedullary nephron —> The peritubular arteries are structured.
Cortical nephron —> The peritubular arteries are spaghetti like.
What are the differences between the Cortical nephron and juxtamedullary nephron In terms of location, glomerulus size, loop of henle and the diameter of the afferent artery compared to the efferent artery?
- Location
- –> The cortical nephron is in the outer part of the cortex.
- –> The juxtamedullary nephron is in the inner part of the cortex next to the medulla. - Glomerulus size
- –> In cortical nephron it is small.
- –> In the juxtamedullary nephron it is big. - Loop of Henle
- –> In cortical nephron it is short next to outer cortex and just into the medulla.
- –> In the juxtamedullary nephron it is longer and goes into the inner part of the medulla. - Diameter of AA/EA
- –> In cortical nephron, AA > EA
- –> In juxtamedullary nephron, AA = EA
What are the differences between the cortical nephron and the juxtamedullary nephron In terms of efferent artery, sympathetic nerve innervation, concentration of renin and ratio?
- EA
- –> Cortical nephron, EA goes to form the peritubular capillary.
- –> Juxtamedullary nephron, EA goes to form the vasa recta. - Sympathetic nerve innervation
- –> The cortical nephron is rich - has a lot of sympathetic nerve innervation.
- –> The juxtamedullary nephron is poor - not much sympathetic nerve innervation. - Concentration of Renin
- –> High in the cortical nephron.
- –> Almost none in the juxtamedullary nephron. - Ratio
90% of nephrons are cortical and 10% are juxtamedullary.
What is the end product of filtration like?
- It is identical to plasma without the large proteins and cells.
Where is the glomerulus found and what are the components of the filter?
- The glomerulus is found only in the cortex.
- 20% of blood from the renal artery is filled at any one time.
- The normal total glomerular filtrate per day is 140 - 180 L/ day
- 80% of the blood arriving at the glomerulus exits via the efferent arteriole and is unfiltered.
What are the three layers of the filtration barrier?
- endothelium
- acellular gelatinous basement membrane
- pedicel.
How is the structure of the basement membrane related to its function?
- The basement membrane is charged as it has glycoproteins in it which carry a negative charge on it.
- –> When other small proteins that may fit through, come to the basement membrane are are repelled by that -ve charge.
what happens in proteinuria which allows the proteins to be filtered?
- The proteins are more readily filtered because the negative charge on the filtration barrier is lost.
Describe the effect of charge on the filtration in terms of the types of dextrans.
- Cationic dextrans –> these are positively charged and small sizes can fit through.
- Neutral dextrans –> these have positive charge but small can not get through.
- Anionic dextrans –> negatively charged so no matter the size none can get through.
What does PGC mean?
This is the hydrostatic pressure in the capillary.
What does PBC mean?
This is the hydrostatic pressure in the Bowman’s capsule.
What does piGC mean?
This is the oncotic pressure difference between the capillary and tubular lumen.
—> This is exerted by oncotic proteins that are within the plasma within the glomerulus.
What would cause the net filtration pressure to decrease?
- decrease PGC
- Increase in piGC
- Increase in piGC
How is PGC regulated?
By autoregulation or myogenic regulation.
What is auto regulation used for?
- autoregulation is able to maintain GFR when blood pressure is within physiological limits (80 - 180 mmHg)
- auto - regulatory mechanisms keep GFR within its normal limits.
What are the auto-regulatory mechanisms to increase blood pressure?
- To increase blood pressure
- afferent arteriole is constricted.
- GFR is unchanged.
What are the auto-regulatory mechanisms to decrease blood pressure?
- To decrease blood pressure
- afferent arteriole is dilated
- GFR is unchanged.
Describe the properties of myogenic regulation in PGC.
- Arterial smooth muscle responds to increases and decreases in vascular wall tension.
- It contributes to total auto-regulatory mechanism.
- It happens rapidly —> from 3-10 seconds.
- It is a property predominantly of the preglomerular resistance vessels including the:
- –> accurate
- –> Interlobular
- –> Afferent arteriole
Describe the myogenic regulation of PGC to cause a decrease in GFR.
Method 1
- Constrict AA
- PGC decreases
- GFR decreases.
Method 2
- Dilate EA
- PGC decreases
- GFR decreases.
Describe the myogenic regulation of PGC to cause an increase in GFR.
Method 1
- Constrict EA
- PGC increases
- GFR increases.
Method 2
- Dilate EA
- PGC increases
- GFR increases.
