Renal Nephron

Question 1

The _____ transporter found in the thick ascending loop of Henle is responsible for K+ cycling and drives Na+, Cl- and ____ reabsorption.

Answer 1

ROMK2 transporter (TAL)
Facilitates NKCC and Ca++ reabsorption

Question 2

This hormone plays a role in regulation of blood pH through H+ secretion, Na+ retention and indirectly helps form HCO3-. It acts on ____________ cells in the CCT.

Answer 2

Aldosterone;

Intercalated cells

Question 3

How might aldosterone help alleviate hyperkalemia? Does hypervolemia occur?

Answer 3

When there are high K+ levels in plasma, aldosterone activates protein-kinase pathaway to activate ROMK2 and help excrete K+ as well as reabsorb Na+ (normal function). If BP goes up, kidneys pressure natriurese, so hypervolemia DOES NOT OCCUR.

Question 4

This hormone is a vasoconstrictor that increases water reabsorption at the distal nephron. The hyponatremia that this hormone can cause is countered by ___________ which increases plasma Na+ levels.

Answer 4

Arginine Vasopressin (AVP or ADH);
Tolvaptan (V2 receptor antagonist)

Question 5

Describe the mechanism behind how AVP increases water reabsorption.

Answer 5

AVP binds to V2R receptors on the plasma side of the peritubular cell. This couples to the aquaporins on the lumenal and basolateral membrances, enabling water to flow down it’s osmotic gradient and be reabsorbed into the blood stream.

Question 6

This hormone is secreted in the presence of high BP. Right atrium distension leads to the secretion of this hormone that causes vasodilaton, inc GFR, and inc pressure natriuresis at the kidneys. The result is lower BP.

Answer 6

Atrial Natriuretic Peptide (ANP.

Question 7

Describe signs and symptoms behind Diabetes Insipidis.

Answer 7

Excess hyper-DILUTE urine (no glucose), High plasma Na+ (hypernatremia), and extreme thirst/

Question 8

What is SIADH? What are the 2 types and how do they differ?

Answer 8

Syndrome of Inappropriate ADH can be neurogenic (where the pituitary gland persistently pumps out AVP) or nephrogenic (due to constituent activation of mutant V2R receptors).

Question 9

What are some signs and symptoms associated with SIADH?

Answer 9

Excess dark, CONCENTRATED urine; Low plasma Na+ (hyponatremia); neuromuscular symptoms due to hyponatremia; Elevated BP

Question 10

What ion buffers H+ in the urine. What is the significance of this

Answer 10

Ammonia (NH3) binds with free-floating H+ in the urine to be excreted as NH4+. This enables us to get rid of toxic ammonia byproduct from protein catabolism and is why urine pH should be lower than that of blood.

Question 11

Most of the body’s water is found where?

Answer 11

Within the intracellular fluid (ICF) ~67%

Question 12

What physiologic compartment holds most of the fluid of the ECF? Why is this significant for normal function.

Answer 12

Interstitial fluid holds more fluid in the ECF but this is variable depending on the more important blood volume that must be maintained for ECV and perfusion (BP).

Question 13

GFR lower than < 15-20 (mL/min/1.73 m^2) is a clinical marker for _____. Normal ranges for GFR are between what values?

Answer 13

Normal GFR = 60 - 100;

GFR < 20 is an indication of kidney failure.

Question 14

What type of pressure is the driving factor for glomerular filtration? Where does this change the most in renal circulation?

Answer 14

Hydrostatic pressure; changes most at afferent arteriole then at the efferent arteriole.

Question 15

For each of the numbered scenarios, indicate what change occurs in GFR and renal blood flow (RBF).

1. Constriction of afferent arteriole
2. Constriction of both afferent and efferent arterioles
3. Constriction of efferent arteriole

Answer 15

1. GFR dec & RBF dec
2. GFR constant & RBF dec
3. GFR inc & RBF dec

Question 16

A man presents to the office feeling lightheaded and slightly exhausted. A urine analysis presents elevated BUN and normal Creatinine levels, as well as a BUN/Creatinine level of 25. What is he most likely experiencing?

Answer 16

Intravascular Volume Depletion (hypovolemic status), possibly due to dehydration.

Question 17

What effects would occur from a loss in NKCC function within the proximal tubule of the nephron? These effects are similar to what type of drug?

Answer 17

Calcium wasting, reduced Na+, K+ and Cl- reabsorption. These effects are brought upon by Loop Diuretics such as furosemide.

Question 18

What effects would happen from a loss of NCC function in the distal tubule of the nephron? What drug causes similar effects?

Answer 18

Promotion of Calcium reabsorption, loss in Na+ and Cl- reabsorption, as well as a decrease in K+ reabsorption (wasting). This is similar to the effects from Thiazides such as HCTZ.

Question 19

How would a gain of function mutation of ENaC channel in the CCT present in a patient?

Answer 19

High plasma Na+ levels (hypernatremia) and resistant hypertension would result. This is similar to the effects of aldosterone but without the K+ wasting (normal kalemic status).

Question 20

What is the significance of the Na/K ATPase on the basolateral side of the PCT?

Answer 20

If Na+ accumulates in the tubule cell, there is no gradient driving the SGLT symporter. Therefore, when Na+ comes into the peritubular cell, get it reabsorbed ASAP, otherwise glucose is not reabsorbed too.

Question 21

What events occur at the Loop of Henle (TAL) and why are they significant?

Answer 21

Na+ is fully reabsorbed, but H2O is not allowed to pass through resulting in a HYPO-OSMOLAR filtrate compared to that of the PCT. K+ is leaked out via ROMK2 and comes in via NKCC.

Question 22

What ions move across the DCT and what channels are they transported through?

Answer 22

Na+, Cl- and Ca++ reabsorption occurs via the NCC channel that can be inhibited by Thiazides, such as HCTZ. Na+ also can be reabsorbed by ENaC transporter.

Question 23

What is the specific gravity of urine in the CCT and what hormone plays a role in the affect of this condition?

Answer 23

Urine should physiologically have a high specific gravity by the time it reaches the CCT as compared to the filtrate of the DCT. AVP hormone works by increasing expression of AQPs to increase water reabsorption and make urine more concentrated.

Question 24

How does HCO3- get back into serum by increased Aldosterone activity?

Answer 24

Aldosterone causes Na+ reabsorption via ENaC that helps drive the gradient to move H+ out in exchange for HCO3- generation.

Question 25

What channels are affected by Aldosterone in the nephron?

Answer 25

All Na channels, ENaC, Na/K ATPase and the K/H antiporters in the nephron.