Renal Filtration & Blood Flow - Lecture 3 Flashcards
What is the first step in the production of urine?
Ultrafiltration of plasma by the glomerulus
Describe the ultra filtrate:
- What is it devoid of
- What concentrations are similar in ultra filtrate & plasma
- What drives ultrafiltration across the capillaries?
- What process holds GFR and RFP within their physiological ranges?
- No cellular elements or proteins (too large)
- Salt & Organic Compound concentrations are similar
- Starling forces drive ultrafiltration
- Autoregulation holds GFR and RFP within their physiological ranges
What does the glomerular filtration barrier filter molecules based on?
- Size
2. Charge (no anionic)
What molecules are permeable and impermeable to the GF Barrier?
Smaller than 20 A are filtered freely
Cationic (+) molecules are readily filtered
- greater than 42 are impermeable
- negative compounds are impermeable (Since the barrier is composed of negative glycoproteins itself)
Why is Albumin filtered poorly even though it has a size of 35 A?
It is an anionic protein, if any is filtered it is reabsorbed by the proximal tubule
The following describes what structure:
- Large filtration coefficient (K)
- Low Resistance
- Negative Charge
- Formation of ultra filtrate
- Exclusion of plasma proteins
Glomerular Capillaries
The filterability of Dextrans between 20 and 42 A depends on what?
Depends on charge
- larger than 42 do not get filtered REGARDLESS of charge
- smaller than 20 and cationic get filtered freely
What forces favor and impede filtration of the following:
- Glomerular Capillary Hydrostatic Pressure
- Glomerular capillary oncotic pressure
- Bowman’s space hydrostatic pressure
- Bowman’s space oncotic pressure
- = favors filtration
- = impedes filtration
- = impedes filtration
- = favors filtration
What changes in the following along glomerular capillaries:
- Pgc (glomerular capillary hydrostatic pressure)
- Pi gc (glomerular capillary oncotic pressure)
- PBs
- Net Ultrafiltration pressure
- Small decrease in Hydrostatic Pressure GC (low resistance)
- Oncotic pressures increase in the glomerular capillaries (due to the concentration of proteins that do not filter)
- Bowman’s Capsule Hydrostatic pressure DOES NOT CHANGE!
- Decrease in net ultrafiltration pressure!
What is the only force that does not change along the glomerular capillaries?
Bowman’s Capsule Hydrostatic Pressure
What is Kf?
The product of the intrinsic permeability of the glomerular capillary and glomerular surface area available for filtration
How does glomerular filtration compare in glomerular capillaries versus systemic capillaries? Why?
LARGER in glomerular capillaries due to the large Kf (approximately 100 times greater in glomerular capillaries)
How is the Pgc of glomerular capillaries compared to systemic capillaries?
Hydrostatic pressure is twice as great
How do the following affect Pgc and GFR:
- Increase in AFFERENT Arteriole Resistance
- Increase in EFFERENT Arteriole Resistance
- Increase in Renal Arteriole Pressure
- Afferent: Increase Resistance = decreases Pgc and GFR
- Efferent: Increase Resistance = increase in Pgc and GFR
- Increase in BP transiently increases Pgc , increasing GFR
How do the following renal diseases affect the Kidneys:
- Glomerulonephritis (early & late stages)
- Kidney Stones
- Nephritic Syndrome
- Early stages: decrease GC oncotic pressure and increase GFR
Late stages: increase Bowman’s Capsule Hydrostatic Pressure, and decrease GFR (reverse)
- Kidney Stones: Increase Bowman’s Capsule Hydrostatic Pressure (Pbc) and thus decrease GFR
- Nephritic Syndrome:
Increase Kf –> Proteinuria
What are the functions of blood flow in the kidneys? (5)
- Indirectly determines GFR
- Alters solute and water reabsorption rates by Proximal Tubule
- Urine Concentration
- Delivers O2, Nutrients, and hormones to the nephron & returns CO2 and reabsorbed fluid and solutes to the circulation
- Delivers substrates for excretion
What is total RBF?
1200 mL blood /min
or 4mL blood/min * gm of Tissue
Where is blood flow highest and where is it lowest? Why?
Inner medulla, outer medulla, cortex
- Blood flow highest in CORTEX - high vascularization
RBF = 90% - Outer Medulla: low vascularization, RBF = 8%
- Inner Medulla: very low vascularization, RBF = 2%
What is the ratio of cortical nephrons to juxtamedullary nephrons?
7:1
Where are the Glomerular and Peritubular Capillaries confined to?
What capillaries dive deep into the Renal Medulla?
- CORTEX
2. Vasa Recta
How does the Hydrostatic Pressure change from renal artery to renal vein?
Where is the P decrease largest? (Most resistance found here as well)
Where does oncotic pressure increase? Decrease?
- Hydrostatic Pressure (P) decreases from renal artery to renal vein
(filtration to reabsorption) - The largest decrease in Hydrostatic Pressure is across the Afferent & Efferent Arterioles, due to the high resistance
- Oncotic Pressure increases in the Glomerular Capillaries and Decreases in the Peritubular Capillaries
How do the following affect Pgc, GFR, and RBF?
Increased Resistance:
- Constriction of Afferent Arteriole
- Constriction of EFFERENT Arteriole
Decreased Resistance:
- Dilation of Efferent Arteriole
- Dilation of AFFERENT arteriole
- Constriction of Afferent Arteriole: INCREASES
Pgc decreases, GFR decreases, RBF decreases - Constriction of EFFERENT Arteriole:
Pgc INcreases, GFR increases, RBF DEcreases - Dilation of Efferent Arteriole:
Pgc decreases, GFR decreases, RBF increases - Dilation of AFFERENT arteriole:
Pgc increases, GFR increases, RBF increases
Constriction of either eff/afferent arterioles increases what? This causes a decrease in what?
Increases RESISTANCE! Thus is decreases FLOW (RBF)
What are some intrinsic auto regulation mechanisms of the Kidneys?
- Smooth Muscle Myogenic Theory
-If the pressure within a vessel is suddenly increased, the vessel responds by constricting
(opposite if pressure decreases) - Tubuloglomerular feedback theory
What are some intrinsic vasoconstriction factors? (2)
Vasodilating Factors?(4)
- Endothelin, Adenosine
2. NO, Prostaglandins, Dopamine, Kinins (4)
When does auto regulation fall out? What is the range for optimal auto regulation?
At very LOW and very HIGH pressures
100 - 180 = optimal
What happens to GFR & RBF at arterial pressures greater than 180 mmHg? At pressures less than 100 mmHg?
At pressures greater than 180 mmHg - GFR and RBF increase
At pressures less than 100 - GFR and RBF DECREASE
When does renal shutdown occur? What is ZERO here?
When does Renal Death occur? What value is zero?
Renal shutdown occurs when arterial pressure falls below 70 mm Hg
GFR = ZERO
Renal Death occurs when arteriole pressure falls to ZERO
RBF = Zero
What is tubuloglomular feedback?
- An increase in GFR
- Causes an increase in NaCl concentration in the tubule fluid of Henle’s Loop
- Increase in NaCl is sensed by the Macula Densa and converted to a signal
- INCREASE THE RESISTANCE IN AFFERENT ARTERIOLE
What resistance is increased in tubuloglomular feedback?
What senses the increase in NaCl concentration?
Afferent Arteriole! (want to decrease GFR)
Macula Densa senses NaCl increase and forms a signal
Do the afferent and efferent arterioles have sympathetic regulation?
YES!
Decreased blood pressure can be sensed by the Carotid Sinus & Aortic Arch Reflexes
What are some examples of stress factors that affect RBF and GFR?
- Decreased Central Blood Volume (Hemorrhage)
- Increased circulating renin & angiotensin (dehydration)
- Severe hypoxia (high altitude)
What affect does hemorrhage have on the renal system?
activates Renal Sympathetic Nerve activity & stimulates production of Angiotensin II
- Decrease in BP
- Increased Renin Secretion (granular cells)
- increase plasma and renal renin & angiotensin II
- increased tubular sodium & water reabsorption
- decreased excretion of Na and H20 - Increased Activity of Renal Sympathetic Nerves
- constriction of renal arterioles
- decrease RBF and GFR
What are the 3 major vasoconstrictors? How do they affect RBF and GFR?
- Sympathetic Nerves
- Angiotensin II
- Endothelin
- Decrease GFR and Decrease RBF
What are 4 major vasodilators? How do they affect RBF and GFR?
- Prostaglandins
- NO
- Bradykinin
- ANP, BNP (natriuretic peptides) - no change in RBF
- Increase GFR and Increase RBF (except for ANP/BNP = NO CHANGE IN RBF)
