Rao Objectives- RBF and GFR Flashcards
How many nephrons are in a kidney and what is their breakdown?
There are about 1 million per kidney.
15% are juxtamedullary nephrons.
85% are superficial nephrons.
What does a nephron consist of?
A glomerulus, proximal tubule, loop of hence, distal tubule and collecting duct.
What does the renal vasculature consist of?
Renal, interlobar, arcuate, and radial arteries and veins, and afferent and efferent arterioles.
What differentiates the renal vasculature from that of other organs?
The kidney has two capillary beds: the glomerular and the peritubular capillary beds.
How does renal vascular hydrostatic pressure change?
It drops in two steps from the arterial system to the venous system- once in the afferent arteriole and once in the efferent arteriole. This allows maintenance of high hydrostatic pressure in the glomerular capillary.
Are the afferent and efferent arterioles high or low resistance vessels?
HIGH
Does renal vascular oncotic pressure increase or decrease from afferent arteriole to efferent arteriole?
INCREASE
Describe the composition of glomerular filtrate:
It is the ultra filtrate of blood free of blood cells and large proteins.
It also has 4-5% more anions due to the Gibbs-Donnon Effect.
What is the GFR and what is it an indicator of?
It is the rate at which plasma is filtered through the glomerulus.
It is an indicator of renal function.
What is the filtrate fraction?
It is a ratio of GFR to renal plasma flow.
FF= GFR/RPF
**affected by things that reduce GFR (urethral obstruction)
**affected by things that reduce RPF (renal artery stenosis)
What are the three filtration barriers?
- Capillary Endothelium
- Basement Membrane
- Glomerular Epithelium (podocyte monolayer)
What is the function of the capillary endothelium?
It forms a barrier to blood cells and large proteins.
What is the function of the basement membrane?
It is a meshwork of connective tissues that forms a diffusion barrier for many molecules.
What is the function of the glomerular epithelium?
It prevents diffusion of large molecules.
Is the glomerular barrier size selective or charge selective?
SIZE
Is the filtration barrier size or charge selective?
CHARGE
What are the determinants of GFR?
- Filtration Coefficient
- Hydraulic Conductivity
- It is directly proportional to surface area of the glomerular capillary.
What promotes glomerular filtration?
- Glomerular Hydrostatic Pressure
2. Bowman’s Space Oncotic Pressure
What opposes glomerular filtration?
- Glomerular Oncotic Pressure
2. Bowman;s Space Hydrostatic Pressure
What are the three factors that affect net filtration pressure?
- Changes in capillary hydrostatic pressure
- Changes in Bowman’s space hydrostatic pressure
- Changes in capillary oncotic pressure
Define auto regulation of GFR:
It is maintenance of GFR in the face of change in arterial or venous pressures or obstructions.
What are the two main mechanisms of GFR auto regulation?
- Myogenic Mechanism
2. Tubuloglomerular Feedback Mechanism
Does the JGA have a role in auto regulation?
YES
What synthesizes and secretes renin?
Macula Densa
What stimulates renin release?
decrease in tubular fluid chloride concentration
What does renin do?
It converts alpha2 glob in into angiotensin I in circulation. Ang1 is then converted into AngII in the lung and the kidney. AngII induces renal arteriolar constriction and reduces GFR, thus opposing autoregulation.
What is the role of the SNS in regulation of GFR?
It induces constriction of the afferent arteriole and decreases GFR.
What is involved in the hormonal regulation of GFR?
- Adrenaline
- Endothelin I
- NO
- Prostaglandins
What does adrenaline do?
It causes constriction of arterioles, preferably the afferent arteriole.
What does Endothelin I do?
It causes constriction of arterioles, both afferent and efferent.
What does NO do?
It causes vasodialtion.
What do prostaglandins do
It cause vasodilaiton.
When does proteinuria occur?
when the glomerular barrier is interupted
What happens when visible barrier breakdown occurs with large pores?
Blood cells and proteins can be found in the urine.
What happens when barrier breakdown is only subtle?
Only proteins will be found in the urine- no RBCs.
Can proteinuria occur without glomerular barrier disruption?And if so, what causes this to occur?
YES. If abnormal proteins are produced in the body that are filtrable through the glomerular barrier, then this can occur.
What are the three processes involved in urine formation?
- Glomerular Filtration
- Tubular Reabsorption
- Tubular Secretion
What are the different types of substances?
- freely filtered + no reabsorption or secretion
- freely filtered, partially reabsorbed, no filtration
- freely filtered and completely reabsorbed
- freely filtered, no reabsorption, secreted from tubules
What is the wisdom behind filtering large amounts of body fluids and solutes and reabsorbing most of them back to the body?
- Allows the kidney to rapidly remove waste products form the body that primarily depend on glomerular filtration for excretion.
- Allows all body fluids to be filtered and processed several times a day.
What is the composition of filtrate?
- *Similar to plasma but without proteins
- low levels of some small molecules bound to proteins (calcium and fatty acids)
- 4-5% more anions and 4-5% less cations due to the Gibbs Donnan Effect
What is normal GFR?
130ml/min or 180L/day
**This decreases with age and renal disease.
What is the equation for GFR?
GFR= Kf x Net Filtration Pressure
where Kf= Filtration coefficient= hydraulic conductivity x glomerular surface area
How does diabetes mellitus affect Kf?
It reduces it due to increased thickness of the basement membrane and damaged capillaries.
What is the equation for net filtration pressure?
NFP= (Pg +Pibs) - (Pig + Pbs)
What happens if you increase resistance in the afferent arterioles?
GFR and RPF both decrease.
What happens if you decrease resistance in the afferent arterioles?
GFR and RPF both increase.
What happens if you increase resistance in the efferent arteriole?
Increase GFR and decrease RPF.
What happens if you decrease resistance in the efferent arteriole?
Decrease GFR and increase RPF.
Does a full bladder change GFR?
NO. It is independent of systemic influences.
What does high NaCl at the macula densa do?
It increases afferent arteriolar resistance therefore decreasing GFR.
What does low NaCl at the macula densa do?
It decreases afferent arteriolar resistance therefore increasing GFR.
***It is the chloride that is responsible for this.
