Physiology 2 Renal Blood Flow

Question 1

Renal Blood flow avereages what percentage of the cardiac output

Answer 1

20% (1000 ml/min)

Question 2

Discuss the perfusion of kidneys relative to their metabolic needs. What is the significance

Answer 2

Over perfused for their metabolic needs - important in filtration function and cleansing the palsms

Question 3

Renal oxygen consumption

Answer 3

linear relationship between renal oxygen consumption and Na+ reabsorption (90% of renal energy expenditure is devoted to the reabsorption of Na)

Question 4

What is the principle transport system of Na in the kidney

Answer 4

Na K ATPase - located in the basolateral membranes of tubules (3Na out 2 K in )Important for maintaining low intracellular sodium concentrations (establishes Na gradient for the transport of other molecules)

Question 5

Glomerular and Peritubular Capillaries are arranged in series/parallel

Answer 5

Series- glomerular capillaries arise from afferent arterioles and are continuous with efferent arterioles which give rise to the peritubular capillaries

Question 6

Glomerular capillary starling forces

Answer 6

Favors filtration (capillary pressure >oncotic pressure)

Question 7

Peritubular capillary starling forces

Answer 7

Favors reabsorption (oncotic pressures > hydrostatic pressure)

Question 8

Autoregulation of RBF and GFR

Answer 8

60-100 mmHg. INTRINSIC PROPERTY. Uncouples changes in flow and GRF due to changes in arterial pressure (allows kidney to do its job despite flux in arterial pressure) Because blood flow is regulated so is GFR

Question 9

Pressure diuresis

Answer 9

as the arterial pressure increases urination increases

Question 10

Myogenic Vasoconstriction

Answer 10

Afferent arterioles. Increased pressure causes vessel to stretch resulting in myogenic vasoconstriction (protects the glomerular capillaries and decreases glomerular pressure) aka INTRA-RENAL BARORECEPTOR

Question 11

Tubuloglomerular Feedback

Answer 11

Macula Densa in the distal nephron senses changes in flow and solute (Cl-) delivery- if GRF is too high the increased CL- flow results in vasoconstriction of the afferent arteriole to decrease RBF and GFR also inhibits renin release via ATP . If GFR is too low: leads to vasodilation to increase RBF and GFR and increase renin release via prostaglanding and NO

Question 12

after the loop of henle how much of the filtrate has been reabsorbed

Answer 12

85%

Question 13

Autoregulation of GFR with respect to autoregulation of blood flow

Answer 13

autoregulation of GFR is secondary to the autoregulation of blood flow

Question 14

importance of extrinsic control of RBF and GFR

Answer 14

can override the intrinsic control

Question 15

Extrinsic control of RBF and GFR: Neural control

Answer 15

Resting sympathetic tone is low. Constriction of the afferent arterioles decreases BOTH GRF and RBF. SHUNTS BLOOD AWAY FROM THE KIDNEY to help maintain arterial pressure and tissue perfusion

Question 16

Extrinsic control of RBF and GFR: Humoral control

Answer 16

Vasoconstrictors (catecholamnes, angiotensin II, ADH, adenosine) are modulated by vasodilators (prostaglandns, kinins, APT, NO) to protect the kidney from extreme vasoconstriction resulting in ischemia and decreased GFR

Question 17

What is the importance of vasodilators in extrinsic humor control of RBF and GFR

Answer 17

modulates areterial tone in the face of vasoconstriction to protect the kidney from extreme ischemia and decreased GFR. CLINICAL COMMENT: Problem for patients in a chronic hypovolemic state (causes SNS vasoconstriction) who take NSAIDS (inhibits prostaglandins) - can lead to renal failure

Question 18

What is the limiting element on the glomerular filtration barrier

Answer 18

the basement membrane

Question 19

Why doesn’t albumin get through the Glomerular Capillary

Answer 19

Negatively charged membrane repels the negatively charged plasma protein. CLINICAL COMMENT: Nephrotic Syndrome causes loss of negative membrane and results in loss of plasma protien through the urine

Question 20

Ultrafiltrate

Answer 20

“Everything except the plasma proteins”

Question 21

Ultrafiltration

Answer 21

High glomerular hydrostatic pressure (PG) results in high rates of fluid filltration (GFR) BULK FLOW NOT DIFFUSION. Ultrafiltrate enters Bowman’s capsule and flows into the proximal tubule

Question 22

What is not filtered in ultrafiltration

Answer 22

Plasma proteins, substances bound to proteins(50% of Ca is bound to protein) , and formed elements (platelets)

Question 23

Determinants of Glomerular Capillary Barrier Permeability

Answer 23

1.) The size and numer of membrane pores 2.) Presence of fixed negative charges on glomerular capillaries (negatively charged glycoproteins)

Question 24

Average GFR

Answer 24

125 ml/min (~180 L/day)

Question 25

How does glomerular capillary oncotic presure change

Answer 25

starts at 25 mmHg (same as systemic) and then increases along the capillary - due to the amount of fluid filtration from the glomerular capillaries causes plasma protiens to become more concentrated

Question 26

What happens to GFR as you increase renal plasma flow

Answer 26

increase GFR

Question 27

glomerular capillary filtration coefficient compared to systemic capillaries

Answer 27

50-100 times greater than systemic (a lot leakier) - due to resistance on either side of the capillary bed

Question 28

what is the driving force for flow through the nephron

Answer 28

The Hydrostatic pressure in Bowman’s space (PB)

Question 29

Peritubular capillaries

Answer 29

specialized for uptake of reabsorbed fluid and solutes from interstitium. Close proximity to renal tubules. Low Capillary pressure and high onoctic pressure favors reabsorption (as filtration fraction increases the oncotic pressure in peritubular capillaries increases more)

Question 30

What is the effect of Efferent aretriolar vasoconstriction on the peritubular capillaries

Answer 30

increase in plasma oncoti and decrease in plasma hydrostatic in the peritubular capillaries = becomes more favorable for the absorption of fluid (imprtant for enhancing net proximal tubular reabsorption in hypovolemic states)

Question 31

Back- leak

Answer 31

Seen in hypervolemic states when there is affernet and efferent arteriolar vasdilation leading to decreased FF (GFR/RPF). Reabsorption becomes less favorable - not taken up by peritubular capillaries and there is a progresisve rise in interstitial hydrostatic pressure causing fluid to leak BACK into the proximal convoluted tubule by bulk flow (possible due to relatively leaky junctions in the PCT)

Question 32

Changes in GFR and RBF (relative to one another)

Answer 32

Tend to change in the same direction. Magnitudes of chane will be differnet- typically GFR changes LESS than RBF due to changes in the efferent arteriole

Question 33

Hypovolemia (GFR and RBF)

Answer 33

1.) Decreased MAP will decrease RBF and GFR (small due to autoregulation) 2.) Constriction of the afferent and efferent arterioles (increased synpathetic nervous system) 3.) increased plasma oncotic pressure in sympathetic capillaries (eg: dehydration) 4.) Decreased Kf (decreased surface area, contraction of mesangial cells and podocytes- reach filtration equilibrium sooner- less “effective surface area” ) = result: decrease in GFR and large decrease in RPF resulting in and increased filtration fraction

Question 34

Changes in filtration fraction in hypovolemic states

Answer 34

constriction of BOTH the afferent and efferent arterioles leads to large decrease in RPF and smaller decrease in GRF resulting in an increased FF

Question 35

What is the significance of an increased Filtration fraction

Answer 35

Filtration fraction is the proportion of fluid reaching the kidneys that passes into the renal tubules. When blood flow is reduced the filtration must increase in order to perform the normal tasks of the kidney in balancing fluid and electrolytes in to body (higher filtration fraction = kidney has to do more work with the fluid they are recieving)

Question 36

Hypervolemia (GFR and RBF)

Answer 36

1.) Increased MAP will increas RBF and GFR (small due to autoregulation 2.) Dilation of afferent and efferent arterioles 3.) Decreased systemic plasma oncotic pressure (dilution) 4.) Increased Kf (relaxation of mesangial cells, increasd RBF causes equilibrium to be reached later- more surface area) Result= Increased RPF, Increased GFR and decreased FF

Question 37

How does filtration equilibrium change with renal blood flow

Answer 37

increased renal blood flow causes equilibrium to be reached later. Decreased renal blood flow causes equilibrium constant to be reached sooner