Lecture 6- Hemodynamics

Question 1

How much blood flow goes to the kidneys and describe the distribution

Answer 1

20-25% of cardiac output goes to kidneys

90% of that goes to cortex and 10% goes to medulla

Question 2

What are some ways renal blood flow is controlled

Answer 2

Through blood pressure

Intrinsic autoregulation (myogenic and tubuloglomerular feedback)

Extrinsic innervation (sympathetic nervous system)

Hormones (renin/angiotensin)

Question 3

Myogenic mechanism

Answer 3

Related to vascular smooth muscle

When the smooth muscle is stretched due to increase in blood pressure, the vessel constricts to reduce blood flow

Question 4

Tubuloglomerular feedback

Answer 4

Increases in NaCl at macula densa results in release of vasoconstrictors (adenosine?) and a decrease in RBF and GFR

Question 5

Renal plasma flow equation

Answer 5

RPF = RBF (1-hematocrit)

Question 6

Measurement of RPF

Answer 6

At low plasma levels, you can estimate RPF by measuring the clearance of PAH because PAH is almost completely cleared after a single circuit of filtration

Question 7

Describe the net clearance of substances in relation to the clearance of inulin

Answer 7

Substances that have a net reabsorption will have a lower clearance than inulin while substances with a net secretion will have a higher clearance than inulin.

Question 8

Filtration fraction (FF)

Answer 8

The amount of plasma that flows through Bowman’s capsule from glomerular capillaries

FF = GFR/RPF

Only about 20% of the total plasma- if 100% was filtered there would be no fluid in the veins

Question 9

What type of energy metabolism in cortex

Answer 9

Oxidative- uses fatty acids

Question 10

What type of energy metabolism in medulla

Answer 10

Anaerobic- glucose is primary substrate