Lecture 4 - Na+ Balance

Question 1

The Na+ concentration in the ECF is THE MAJOR regulator of _____ regulation. That is, if Na+ concentration in EFC DECREASES, it results in _______ rather than Hyponatremia. If Na+ concentration in ECF INCREASES, it results in ________ rather than Hypernatremia.

Answer 1

HYPOvolemia

HYPERvolemia

Question 2

Fluid at the end of the ______ ______ _____ is isotonic with Blood plasma (keep in mind this is where most of the Na+ reabsorption in the nephron takes place).

Answer 2

Proximal Convoluted Tubule (PCT)

Question 3

In the Early PCT, Acetazolamide inhibits _______, which decreases the dissociation of CO2 into HCO3- and H+. How does this have diuretic action?

Answer 3

Carbonic Anhydrase

Less H+ produced in the cell –> Less can be exchanged with Na+ (so less Na+ and HCO3- comes in from the lumen of the PCT and less H+ goes out.)

Question 4

In the Early PCT, there is also a Na+ / ______ cotransporter (both are brought into the cell –> generates slight _____ charge in the lumen.)

Answer 4

Na+ / Glucose

Negative

Question 5

In the Early PCT, Na+ is preferentially reabsorbed along with _______, which effectively increases the lumenal concentration of _____.

Answer 5

HCO3-

Cl-

Question 6

In the Late PCT, H+ in the lumen combine with anions (other than HCO3-) to bring the H+ into the cells so they can then be exchanged with Na+ (H+ out, Na+ in). The anions from which the H+ dissociate once in the cell are transported back out to the lumen in an Antiport fashion with _____ (which ion?) –> movement of this ion into the cell will generate a slightly _____ charge in the lumen –> facilitates ______ transport of Na+ through tight junctions.

Answer 6

Antiport fashion with Cl-

Slightly POSITIVE charge in the lumen

Paracellular transport

Question 7

In the _____ of the loop of Henle, the ________ cotransporter (which diuretic blocks this?) brings all of these ions into the cell from the Lumen. Eventually, K+ would run out, as its Extracellular concentration is relatively low, so it moves back into the lumen via an Apical leak channel –> this generates a _____ charge in the lumen –> facilitates paracellular transport of _____ ions out of the lumen (particularly ____ and ____).

Answer 7

TAL

Na+/K+/2Cl- cotransporter

Furosemide blocks it

Positive charge

Positive

Ca++ and Mg++

Question 8

The TAL is responsible for ____% of Na+ reabsorption –> thus, _____ is the most potent diuretic.

Answer 8

25%

Furosemide

Question 9

_____ diuretics inhibit apical Na+ / Cl- cotransporters in the Early DCT.

Answer 9

Thiazide

Question 10

The Epithelial Na+ Channel (ENaC) of _____ cells is the main transporter of Na+ in Late DCT and _____ Collecting Duct. These ENaC channels are the target for _______, another diuretic. The flow of Na+ through these channels (and leak of K+ into the lumen) generates a -40mV charge in the lumen –> facilitates paracellular transport of _____.

Answer 10

Principal Cells

Cortical Collecting Duct

Amilioride

Cl-

Question 11

Renin release is stimulated by falls in BP detected by ______ cells which act as baroreceptors. It can also be stimulated directly by ______ innervation (via Beta 2 receptors). And it can also be stimulated by a decrease in the delivery of ____ and ____ to the Macula Densa.

Answer 11

Granular cells

Sympathetic innervation

Na+ and Cl-

Question 12

Renin release is Inhibited by negative feedback mech from _____ II. It is also inhibited by ____ from atrial myocytes.

Answer 12

Angiotensin II

ANP

Question 13

ACE inhibitors (“-pril”) indirectly increase ______ levels –> causes vasodilation and Cough.

Answer 13

Bradykinin

Question 14

______ is a Renin inhibitor.

Answer 14

Aliskiren

Question 15

Losartan is an _______ II receptor antagonist.

Answer 15

Angiotensin II

Question 16

Angiotensin II increases ______ reabsorption by REDUCING Peritubular Capillary ______ pressure and by increasing the FF which effectively INCREASES the Peritubular Capillary ______ presssure. These effects are most important where the majority of Na+ reabsorption takes place –> where is that?

Answer 16

Na+ reabsorption

Hydrostatic pressure

Oncotic pressure

It’s at the PCT (60% of Na+ reabsorption)

Question 17

Angiotensin II stimulates Na+ / H+ exchange in the _____ and _____. It also stimulates THIRST and ______ secretion from the zona glomerulosa of the adrenals.

Answer 17

PCT and TAL

Aldosterone

Question 18

Aldosterone is regulated by Angiotensin II, ACTH via stress, and ECF concentration of _____. Aldosterone increases ____ reabsorption and ____ and ____ secretion. What type of cell does it act mostly on?

Answer 18

K+

Na+

K+

H+

Principal cells

Question 19

ANP inhibits Na+ reabsorption at the _____ _____ Collecting Duct.

Answer 19

Inner Medullary Collecting Duct