Physiology Lecture 1 and 2 -- Kidney Function

Question 1

4 hormones secreted by the kidney

Answer 1

• Renin
• Angiotensin II
• Erythropoietin
• Activated vitamin D

Question 2

Renal blood flow

Answer 2

1 L/min (20% of CO)

Question 3

3 layers in the glomerular endothelium that separate the circulating blood from the capillary space

Answer 3

• Innermost = capillary endothelial cell
• Middle = collagenous basement membrane
• Outer = podocyte

Question 4

6 constituents of the ultrafiltrate

Answer 4

• Water
• Electrolytes
• Urea
• Cr
• Sugar
• Amino acids

Question 5

3 substances that should not appear in the ultrafiltrate

Answer 5

• Cells
• Proteins
• Fats

Question 6

Charges of the capillary basement membrane and podocytes

Answer 6

Negative

Question 7

2 conditions in which abnormal amount of albumin will cross the glomerular basement membrane

Answer 7

• Damage to the structure of the filtration barrier
• Loss of negative charge of the filtration barrier

Question 8

Define GFR

Answer 8

The amount of plasma filtered through the glomeruli per unit time (most often refers to all nephrons collectively)

Question 9

How to dose medication excreted by the kidneys if a patient has low GFR

Answer 9

Los GFR = less medication or simply avoid certain meds

Question 10

3 forces involved in glomerular filtration

Answer 10

• P_gc = capillary pressure
• P_t = tubular pressure
• π_gc = oncotic presusre (from unfiltered proteins in tubule)

Question 11

3 characteristics of creatinine that make it a good estimate of GFR

Answer 11

• Has stable plasma concentration
• Freely filtered at the glomerulus
• Stays in the tubule to be excreted (is not reabsorbed)

Question 12

Normal GFR

Answer 12

~100 mL/min

Question 13

Equation for creatinine clearance

Answer 13

Question 14

Relationship between plasma Cr concentration and GFR

Answer 14

Inverse

Question 15

If a patient’s GFR falls by 50%, what happens to the newly produced creatinine?

Answer 15

Newly produced creatinine accumulates until the filtered load again equals the rate of production (i.e. when the plasma Cr has increased by x2)

Question 16

4 formulae to estimate creatinine clearance in the hospital

Answer 16

• CKD epi
• MDRD
• COckroft Gault
• Schwartz

Question 17

Cockroft Gault equation

Answer 17

NOTE: GFR must be in a steady state to use formula

Question 18

What is a specific application for the Schwartz formula?

Answer 18

Can be used for children

Question 19

What is a specific application for CKD-epi?

Answer 19

Screening (can estimate GFR without taking any actual measurements like weight)

Question 20

What is a specific application for the Cockroft Gault equation?

Answer 20

More specific estimate of GFR since it takes into account body mass, so can use on patients who are amputees or have abnormal body weight (i.e. low BCM)

Question 21

How does Cr clearance overestimate GFR?

Answer 21

• It is secreted in the proximal tubule
• –> Cr excretion exceeds Cr filtration by 10 - 20%

Question 22

Perfect molecule to estimate GFR

Answer 22

Inulin (filtered, not reabsorbed, not secreted)

Question 23

2 limitations to creatinine clearance as an estimate of GFR

Answer 23

• Cr production varies with muscle mass (sarcopenia in older people ages 50 - 90)
• Varies with meat intake (may have high Cr due to eating steak 3x per day)

Question 24

Urea levels in hypovolemic states

Answer 24

Rises out of proportion to Cr, so can be useful in assessing patients with acute renal failure

Question 25

3 autoregulation mechanisms to maintain GFR

Answer 25

* Myogenic reflex = vasospasm of afferent arteriole (50% of autoregulation) * Tubuloglomerular feedback * Glomerular vasoconstrictors and vasodilators

Question 26

Describe the myogenic reflex

Answer 26

* BP too high = afferent arteriole sm contracts * BP low = afferent arteriole stretches/dilates

Question 27

Describe tubuloglomerular feedback

Answer 27

* Macula densa samples fluid (senses Cl concentration --\> low = glomerular blood flow is low) * Signals to arteriole to open up (possibly using adenosine) * Juxtaglomerular cells also release renin

Question 28

Describe the effect of glomerular vasoconstrictors and vasodilators

Answer 28

In situations of a major drop in systemic BP: * Activation of sympathetic nervous system * Increase production of angiotensin II Angiotensin II constricts efferent arterioles more than afferent arteriole to preserve glomerular capillary P

Question 29

Main purpose of the tubules

Answer 29

Reabsorb most of the water and solute of the filtrate back from the tubules into the circulation

Question 30

Define resorption

Answer 30

Move from urine back to the body (apical --\> basolateral)

Question 31

Define secretion

Answer 31

Moves from the blood to the urine (basolateral --\> apical)

Question 32

Define excretion

Answer 32

Leaves the body in the urine

Question 33

Only place in the body where a capillary does not drain into a vein

Answer 33

Glomerulus (drains into efferent arteriole)

Question 34

General effect of ADH on kidney

Answer 34

Induce collecting duct water permeability by insertion of aquaporins

Question 35

6 functions of the proximal tubule

Answer 35

* Na+ reabsorption * Reabsorption of almost all glucose, phosphate, amino acids * Reabsorption of bicarbonate * Secretion of uric acid and organic acids (i.e. drugs) * Water reabsorption * Calcium, potassium and chloride movement along their concentration gradients

Question 36

How does reabsorption occur in the proximal tubule?

Answer 36

Basically, it is all coupled to their respective Na+ cotransporters

Question 37

3 functions of the Loop of Henle

Answer 37

Separation of Na and water movement --\> countercurrent mechanism * Thin descending limb permeable to water * Thick ascending = Na+ out of lumen via Na-K-2Cl cotransporter in apical side + Ca and Mg reabsorption

Question 38

2 functions of the distal convoluted tubule

Answer 38

* Reabsorption of Na via Ca-Cl cotransporter * Calcium reabsorption (via channel in apical side and exchanger in basolateral side)

Question 39

4 functions of collecting duct

Answer 39

Principals cells * Na and water reabsorption * K+ secretion * Selective Na+ channels under aldosterone control Intercalated cells * Water transport (site of ADH action)