Renal Physiology

Question 1

Massive blood loss as for a hemorrhage is often associated with…

Answer 1

Hyponatremia since Na+ ions most likely pulled the water out during fluid loss.

Question 2

List at least 3 things that cause renal hypo-perfusion.

Answer 2

Low Cardiac output, Volume depletion, Renal artery stenosis (can worsen the situation), Certain drugs

Question 3

What is the goal of maintaining GFR? What happens to this rate in a disease state?

Answer 3

Create optimal conditions for reabsorption. GFR and RBF is reduced in a disease state, such as in a severely low BP.

Question 4

How does Primary Hyperaldosteronism differ from Secondary?

Answer 4

Primary: an issue with the adrenal medulla gland, such as an adenoma causes an increase in Aldosterone levels; PRA:PAC ratio is high
Secondary: renal artery stenosis can be misinterpreted as low BP; both PRA and PAC are high

Question 5

What are some signs and symptoms that a patient with hyperaldosteronism can present?

Answer 5

Resistant Hypertension, hypernatremia and hypokalemia in blood labs; increased urine output due to pressure natriuresis to combat the Na+ load; elevated K/H+ in urine, reduced BUN and metabolic alkalosis.

Question 6

What is Pseudohypoaldosteronism and how might it present in a patient?

Answer 6

Hypotension, orthostasis, tachycardia and fatigue are signs of this ailment. It is associated with hyperkalemia, hyponatremia, antidiuresis and metabolic acidosis. The urine pH and Na+ would be higher than normal and K+ will be low.

Question 7

How does a relentlessly high BP correlate to a low PRA (plasma renin activity)?

Answer 7

Stimulated baroceptors tell SNS to shut off, so Renin is never too high in the first place. This shuts off the RAAS before a bad situation worsens.

Question 8

Why is maintaining proper Na+ concentration important?

Answer 8

To maintain electroneutrality and electrophysiology such as starting Action potentials.

Question 9

What is Diabetes Insipidus? What ion imbalance is it associated with?

Answer 9

A disorder of Na+ and water that is marked by heavy, DILUTE urination and thirst. This is due to insensible water loss (as compared to salt) leading to hypernatremia.

Question 10

What is SIADH?

Answer 10

Syndrome of Inappropriate ADH is a condition marked by polydipsia (extreme thirst) and hypotonic hyponatremia. This is due to XS water retention as compared to Na+ loss resulting in a euvolemic or hypervolemic state.

Question 11

Describe the mechanism of Hypovolemic hyponatremia.

Answer 11

Fluid loss = Na+ and water loss that is detected by baroceptors as low BP = causes AVP secretion = antidiuresis = negative free-water clearance = dilutional hyponatremia

Question 12

Describe the mechanism of Euvolemic hyponatremia.

Answer 12

SIADH = absorption of water > Na+ = negative free water clearance = Dilutional hyponatremia

Question 13

Describe the mechanism of Hypervolemic hyponatremia.

Answer 13

Cardiac failure or renal failure = low ECV = increased AVP secretion = activated RAAS = negative water clearance = dilutional hyponatremia (water > Na+)

Question 14

Name 2 ways Diabetes Insipidis differs from Diabetes Mellitus.

Answer 14

Hyper-dilute urine (with little to no glucose in it); Extreme thirst and no ketoacidosis

Question 15

How do the urine lab results between Diabetes Insipidis (DI) and SIADH differ?

Answer 15

DI has a low GFR and high BUN and effective osmolality (indicating dehydration) due to insensible water loss. Hypernatremia is paired with this condition.
SIADH presents as high GFR, low BUN and low effective osmolality due to insensible water retention. Hyponatremia is associated with this.

Question 16

What renal pathology is marked by an overall loss of function in the proximal convoluted tubule (PCT)?

Answer 16

Type 2 Renal Tubule Acidosis (RTA) = impairs NHE3, Na/K ATPase and Carbonic anhydrase at the PCT. Patient shows normal blood glucose and defective in HCO3, glucose, phosphate and Vitamin D.
“Come 2 Me”

Question 17

What renal pathology is marked by impaired distal acidification?

Answer 17

Type 1 RTA = where the DCT produces less H+ therefore reducing NH4+ excretion since ammonia usually buffers the H+ in urine. This is marked by an elevated urine AG.
“He’s D One”

Question 18

What renal pathology is marked by aldosterone deficiency or resistance?

Answer 18

Type 4 RTA = is associated with aldosterone deficiency which lowers plasma Na+ and increases K+ levels. This in turn impairs H+ ATPase which reduces NH4+ handling in DCT.

Question 19

Why is Type I Renal Tubule Acidosis associated with a high Urine AG?

Answer 19

Type I RTA involves impaired distal acidication, which is linked to less NH4+ produced from the buffer. This means less Cl- is excreted into the urine than normal = +++ Urine AG.

Question 20

Describe how a Primary Hyperaldosteronism can be associated with a Hypokalemic metabolic alkalosis?

Answer 20

XS aldosterone would increase Na+ reabsorption but H+ secretion as well. This would generate more HCO3- that increases the plasma pH. Metabolic alkalosis is associated with Hypokalemia due to H/K swapping mechanism.

Question 21

Describe how Hypoaldosteronsim can be linked to Hyperkalemic Metabolic acidosis?

Answer 21

Low levels of aldosterone would hinder H+ secretion reduce HCO3- made, thus lowering the pH. Metabolic acidosis is associated with hyperkalemia through the H/K swapping mechanism.

Question 22

How can Hyperkalemia be associated with Metabolic Acidosis?

Answer 22

Thiazide diuretics can promote K+ wasting. This can be coupled with the loss of aldosterone-mediated H+ secretion from taking an ACE inhibitor (Enalapril that lowers BP) which can result in the metabolic acidosis.

Question 23

Why is PRA low in Primary Hyperaldosteronism as compared to Secondary Hyperaldosteronism?

Answer 23

High aldosterone from a pituitary issue has a negative feedback effect on Renin, thus reducing its plasma levels. In Secondary Hyperaldosteronism, the high aldosteronism does not have much of an inhibitory effect since renin production from the kidneys is rampant.