EXAM III [Urine] and Dilution

Question 1

How much water can be excreted by the kidneys per day when there is a large excess of water in the body?

Answer 1

20 L/day with a [] as low as 50 mOsm/L

Question 2

What is the maximum [urine] that the kidneys can produce?

Answer 2

1200-1400 mOsm/L

Question 3

What is required by the kideny tubules for the formation of a concentrated urine?

Answer 3

ADH must be present - water reabsorption

High osmolarity of renal medullary interstitial tubule which establishes osmotic gradient necessary for water reabsorption to occur

Question 4

Explain why there is an obligatory volume of excreted urine of 0.5 L/day

Answer 4

A normal 70kg human must excrete ~600 mOsm of solute/day in order to rid of waste products of metabolism & ions that are ingested

1/2 of the max amount that can be concentrated (1200 mOsm)

Question 5

Where in the kidney tubule are most of the filtered electrolytes reabsorbed?

Answer 5

PCT ~ 65%

Tubular osmolarity = 300 mOsm/L

Question 6

What areas of the nephron are permeable/impermeable to water?

Answer 6

PCT - permeable (300 mOsm/L)

Thin Descending LOH - permeable (1200 mOsm/L)

Thin Ascending LOH - impermeable

Thick Ascending LOH - impermeable (100 mOsm/L)

DCT & Collecting Duct - impermeable (early 50 mOsm/L)

Question 8

What areas of the nephron reabsorb Na/Cl?

Answer 8

PCT - Y

Thin Descending LOH - Y; less permeable

Thin/Thick Ascending LOH - Y

Early/Late DCT & Collecting Tubule - Y

Question 9

The thin descending LOH is highly permeable to which of the following:

Sodium

Water

Urea

Amino Acids

Answer 9

Water

Question 10

Aldosterone is an important regulator of Na+ reabsorption and K+ secretion; one of its main targets is…?

Podocyte

Principal Cells

Intercalated Cells

Cells of macula densa

Answer 10

Principal Cells

Question 11

The macula densa is found in which of the following parts of the renal tubule?

PCT

Thin descending limb of Henle

Thick ascending limb of Henle

DCT

Answer 11

DCT

Question 12

Which of the following would be a result of increased levels of angiotensin II?

Decreased BP

Increased vasoconstriction

Increased natriuresis

Decreased aldosterone levels

Answer 12

Increased vasoconstriction

Question 13

Describe the pressure differences that cause oxygen to diffuse into the pulmonary capillary

Answer 13

O2 in the air = ~150mmHg, in the alveolus = 104mmHg, in the pulmonary capillary arterial end = 40mmHg; therefore there is a pressure difference

Diffusion Differential = 104 - 40 = 64mmHg that’s diffused

1/3 down the capillary, blood PO2 rises to that of alveolar

Question 14

What factors allow the diffusion capacity of oxygen to increase during exercise?

Answer 14

Increased Surface Area of capillaries involved in diffusion

An ideal V/Q ratio in upper portion of lungs

Question 15

Describe the effects of blood flow and metabolic rate on peripheral tissue PCO2

Answer 15

Greater metabolic rate causes greater interstitial CO2 at low blood flow

Lower metabolic rates results in less interstitial CO2 at fast blood flow

Question 16

Compare oxygen saturation in venous blood to that in arterial blood in relation to how much oxygen is bound to heme groups.

Answer 16

Venous Blood = PO2 = 40 mmHg therefore O2 saturation = 75% = about 1/3 heme is bound to oxygen

Arterial Blood = PO2 = 95 mmHg, therefore O2 saturation 97% = most heme groups are bound to oxygen

Question 17

Define oxygen utilization coefficient, provide an example on how to calculate it

Answer 17

Percentage of blood that gives up its oxygen

Greater during strenous exercise (75-85%); less at rest (25%)