Renal and Acid-Base Physiology

Question 1

What percentage of body weight is water?

Answer 1

60% of body weight is water, it is the highest in newborns and adult males, lowest in adult females and adults with a high ammount of adipose tissue.

Question 2

What fraction of total body weight is made up by extracellular fluid and intracellular fluid?

Answer 2

Intracellular fluid makes up 2/3 mostly of potassium and magnesium.

Extracellular fluid makes up 1/3 of the weight with mostly sodium in the plasma and chloride and bicarb.
Plasma makes up 1/4 of the ECF

Question 3

What is the 60-40-20 rule?

Answer 3

60% bw is water
40 percent is intracellular
20 percent is extracellular fluid.

Question 4

How would the infusion of isotonic NaCl effect the fluid compartments?

Answer 4

It would expand the ECF and would not effect the ICF. It would not change the osmolarity as it is isotonic however it would increase blood pressure as the ECF is increasing.

Question 5

How would diahrrea effect the water compartments of the body?

Answer 5

Would lower ECF but would not cause an ion shift as no change occurs in the osmolarity.

Plasma concentration and hematocrit would increase because the loss of ECF would concentrate blood proteins and arterial blood pressure would decrease.

Question 6

How would excessive salt intake effect the water compartments of the body?

Answer 6

The ECF osmolarity would increase. The ICF would shift water into the ECF until the osmolarity of both compartments were equal. As a result, ECF volume increases and ICF volume decreases.

This is known as volume expansion!

Question 7

What is syndrome of innapropriate antidiuretic syndrome?

Answer 7

causes hypoosmotic gain in volume expansion.

Excess water is retained filling the ECF and causing its osmolarity todrop. Thus water from the ECF shifts into the ICF decreasing its osmolarity as well.

Question 8

What occurs in adrenocortical insufficiency?

Answer 8

Excessive loss of salt leading to hyposomotic volume contraction.

Hematcrit increases here as ECF fluid moves from the ECF into the ICF.

Arterial blood pressure also decreases.

Question 9

What is the equation for clerance?

Answer 9

Urine concentration * Urine volume / Plasma concentration

Question 10

Which two systems will cause arteriole constriction of the efferent renal arteries?

Answer 10

Sympathetic nervous system and Angiotensin II

Question 11

What effect do ACE inhibitors have at the renal arterioles?

Answer 11

Dialates renal efferent arteries resulting in a decrease in GFR.

Question 12

What effects do prostaglandins have at the renal arterioles?

Answer 12

Prostaglandins dialate the renal arterioles, specifically via E2 and I2.

Question 13

What effects does dopamine have on the renal arterioles?

Answer 13

Dialates the renal arterioles.

Question 14

What effect does atrial natriueretic peptide *(ANP) have on the kidneys?

Answer 14

Dialates the afferent arteriole and constricts the efferent arteriole.
Overall it increases renal blood flow.

Question 15

What is the tubuloglomerular feedback at the kidney?

Answer 15

The macula densa cells feel an increase in blood volume and constrict the afferent arteriole to maintain consistant GFR.

Question 16

When would you use para-aminohippuric acid PAH?

Answer 16

PAH is completely filtered and secreted by the renal tubules thus it measures renal plasma flow.

Question 17

When would you use inulin?

Answer 17

Inulin can be used to detect the GFR of the kidney as it is filtered but not reabsorbed or secreted.

So again it would be concentration of inulin in urine multiplied by the volume of urine and divided by the total plasma concentration of inulin to determine GFR.

Question 18

How do BUN and serum creatinine relate to GFR?

Answer 18

When GFR decreases both BUN and Serum Creatinine increase.

Question 19

When would BUN levels increase faster than creatinine levels?

Answer 19

BUN levels would increase faster than creatinine in prerena azotemia (hypovolemia)

Question 20

Why does serum creatinine remain constant in the body even though GFR decreases with age?

Answer 20

Because the body loses muscle mass appropriately with age as well.

Question 21

What keeps the anions out of the urine normally?

Answer 21

Negatively charged podocytes. In kidney damage, these charges are interupted and albumin and other negatively charged molecules can pass through to the urine.

Question 22

What increases GFR in the arterioles?

Answer 22

Dialation of the afferent arteriole or constriction of the efferent arteriole.

Question 23

What would cause an increase in the hydrostatic pressure of bowmans capsule?

Answer 23

Anything blocking or constricting the ureters would cause back flow and increase in glomerular hydrostatic filtration pressures.

Question 24

What plasma glucose levels will result in excretion of glucose through the kidneys?

Answer 24

Any blood glucose levels higher than 250 assuming the kidneys are functioning correctly. at levels of 350 all of the glucose/sodium channels are saturated.

Normally glucose is uptake at the proximal convuluted tubule via a glucose/sodium channel. However, there are only so many of these channels. Hyperglycemia causes excess loss in urine glucose.

Question 25

What is uniqueabout measuring GFR with PAH?

Answer 25

PAH isnt just filtered, it is also secreted and this has to be taken into account.
This is why it is important to saturate the patient with a known ammount of PAH to ensure that all of the secretion has remained constant while measuring GFR.

Inulin however is only excreted and filtered thus it perfectly matches GFR.

Question 26

How can one increase the excretion of a weak acid from the kidneys?

Answer 26

By eliciting basic materials, the weak acid can be stuck in its A- charged form and will not be able to back flow.

The acidic form HA can back flow and is uncharged.

Question 27

How is HCO3- reabsorbed in the proximal convuluted tubule?

Answer 27

Na+/H+ channels directly interact to reabsorb bicarbonate at the PCT.

Question 28

How does the drug Acetazolamide work?

Answer 28

This is a carbonic anhydrase inhibitor present at the proximal convuluted tubule.
It prevents HCO3- from being reabsorbed.

Question 29

Which portion of the tubule is impeneratable to water and thus reabsorbes sodium without water?

Answer 29

The thick ascending limb of henle where the Na/K/Cl pump works its magic.

The distal convulted tubule is impermeable to water as well and uses the Na/Cl pumps.

Question 30

Which segment of the kidney is coined the diluting segment?

Answer 30

The thick ascending loop of henle.

Question 31

Where in the tubule is sodium absorbed via the Na/Cl channel?

Answer 31

The distal convuluted tubule.

Thiazides work here.

Question 32

How do principle cells work?

Answer 32

At the distal convuluted tubule these reabsorb sodium and water while secreting potassium.

Aldosterone increases Na+ reabsorption and K+ excretion through these cells. “ENaC cells”

Question 33

How does ADH work?

Answer 33

This hormone works by inserting aquaporins into the collecting duct.

Question 34

How do alpha interculated cells of the tubule work?

Answer 34

These secrete H+ via ATP and are effected by aldosterone.
In exchange they reabsorb K+ by a H/K ATPase.

Work to secrete under acidic conditions.