Renal Blood Flow and Glomerular Filtration Flashcards
What is the percentage of the Juxta medullary nephrons and superficial nephrons?
15% - Juxta medullary nephrons
85% - Superficial Nephrons
How much of the cardiac output is recieved by the kidney?
More than 20%
What is the order vessels from renal arteries to renal veins?
- Renal Artery
- Interlobar Artery
- Arcuate Artery
- Interlobular Artery
- Afferent Arteriole
- Glomerulus
- Efferent Arteriole
- Peritubular Capillary Bed
- Renal Vein
What gives rise to the two unique capillary beds in the kidney?
Afferent Arteriole =>Glomerular Capillary Bed
Efferent Arteriole => Peritubular Capillary Bed
***Note: these are both resistance arterioles
What is the difference in the vasa recta and the peritubular capillaries?
Vasa Recta => Medulla
Peritubular Capillaries => Cortex
What happens to the following as you move from the afferent to the efferent arteriole?
• Hydrostatic Pressure
• Oncotic Pressure
Afferent —–> Efferent
Hydrostatic Pressure REMAINS constant
ONCOTIC pressure of blood INCREASES as you push fluid into bowman’s space
What two substances don’t go through the glomerulus?
- Proteins - don’t pass because they are too large or are negatively charged
- Calcium - attaches to proteins to maintain charge balance - Dannon Effect
What are some substances that are freely filtered by the glomerulus with not reabsorption or secretion?
•Inulin
What are some substances that are freely filtered by the glomerulus and are partially reabsorbed but NOT secreted?
- Na+
* Cl-
What are some substances that are freely filtered by the glomerulus, then completely reabsorbed in the tubule?
- Glucose
* Amino Acids etc.
What is the purpose of filtering plasma 60x per day?
- Most waste products are poorly reabsorbed with rapid filtration and excretion so they they are removed from the blood quickly
- ALSO allows the kidney to respond RAPIDLY to changes in plasma composition
What prevents albumin from crossing the basement membrane despite the fact that its small enough to pass through the fenestrations?
Negative Charge of Albumin and Basement membrane repels this protein that might otherwise pass
What is the difference in Nephritic and Nephrotic Syndrome?
Nephritic Syndrome:
• There is Structural Damage to glomerulus
• BOTH cells and protein pass through
Nephrotic Syndrome:
• There is ONLY DAMAGE TO SLITS in fenestrations
• ONLY proteins leak through
**Why do diabetics get proteinurea?
- Thickening of the Basement Membrane
* Less Charge on the Basement Membrane
What is the major difference in plasma and filtrate composition?
Plasma Contains Proteins, FIltrate does not
*Calcium and Fatty Acids that are bound to proteins also do not come through = Gibbs Donnan effect
***What is the filtration fraction?
• how is it calculated?
Tells you how much of the plasma is filtered out with a pass through the glomerulus
FF = GFR/RPF
**Filtration Fraction = glomerular filtration rate / Renal plasma Flow
What are the 3 barriers to filtration in the glomerulus and what do they filter?
- Epithelial Layer of Capillary - filters out only large proteins
- Basement Membrane - filters out negatively charged proteins
- Podocytes - Filter out any remaining proteins
T or F: Nephritic syndrome essentially leaves a big hole in the membrane while nephrotic syndrome causes loss of selectivity.
True, Nephrotic Syndrome is more of an invisible barrier breakdown
What is the equation for GFR?
• what factors promote filtration?
GFR = Kf x Net filtration pressure
or
GFR = Kf + [(Pg + πbs) - (πg + Pbs)]
Factors increasing Filtration:
• Increased Glomerular Pressure
• Increased Oncotic Pressure in Bowman’s space
What is the oncotic pressure in Bowman’s Space?
~0 mmHg
What are the only two situations involving afferent and efferent arterioles where GFR and RPF (renal plasma flow) have an inverse relationship?
When the EFFERENT arteriole acts ALONE
•Constriction - INcreased GFR but DEcreased RPF
• Dilation - DEcreased GFR but INcreased RPF
What factors control Pg in the Net Filtration equation (Pg + πbs) - (πg + Pbs)?
Pg = Glomerular Hydrostatic Pressure
Affected by:
• Changes in Tone of the Afferent and Efferent Afterioles
What factors control πbs in the Net Filtration equation (Pg + πbs) - (πg + Pbs)?
πbs = the Oncotic Pressure in Bowman’s Capsule
Affected by:
• Nothing Really….its pretty much always at a level of 0mmHg because proteins can’t cross
What factors control πg in the Net Filtration equation (Pg + πbs) - (πg + Pbs)?
πg = Glomerular Oncotic Pressure
Affected by:
• Changes in concentration of the Glomerular Capillary blood
*Slow Flow (Efferent Arteriolar Resistance Increase) causes more filtration and concentration of Blood inside glomerulus. At some point Hydrostatic and Oncotic Pressure equalize and there is no net movement of Fluid
What factors control Pbs in the Net Filtration equation (Pg + πbs) - (πg + Pbs)?
Pbs = Pressure in Bowman Capsule
Affected by:
•ANYTHING that causes a downstream blockage (e.g. Tumor, Kidney Stone, Benign Prostatic Hypertrophy)
How does increasing the filtration fraction lead to a decrease in GFR?
High Pressure flow through glomerulus will allow lots of Fluid to be pulled out of Glomerulus into Bowman’s Capsule the Oncotic pressure will then increase by a lot in the Glomerulus and GFR will decrease
What are some factors that could change Glomerular Oncotic pressure?
- Diabetes
* Medications
What is Auto Regulation of GFR?
• Role of Neurohumoral Factors?
- Maintainance of constant GFR in the face of changes in mean arterial pressure, venous pressure, obstructions
- This is INDEPENDENT of systemic influences
- Neurohumoral Factors Play NO ROLE HERE
What are the 2 methods of autoregulation?
• Explain how they work.
- Myogenic Mechanism
• Increases Resistance in Response to increased flow - Tubuloglomerular Feedback Mechanism
• Macula Densa sense chloride concentrations and send signals (via ATP and Arachidonic Metabolites) to JXG cells, these smooth muscle cells respond accordingly
T or F: reduction in intracellular Ca2+ stimulates renin release.
True, but this is not important in autoregulation
What myogenic changes occur when the Macula Densa cells detect high chloride?
- High [Chloride] in tubule
- Na / K / 2Cl cotransporter detects high [Cl-]
- ATP or Arachiodonate metabolites are synthesized
- Smooth Muscle/JXG cells contract
- Arteriole resistance increases
Neurohumoral Note:
Don’t Forget that
• Adrenaline, Endothelin-1 vasoconstrict
• NO and PGs vasodilate
