Module 5.7 Renal Handling of Sodium

Question 1

______\_ is the primary solute in the extracellular fluid (ECF)

Answer 1

Sodium (Na+) is the primary solute in the extracellular fluid (ECF)

Question 2

The homeostatic maintenance of Na+ concentration is critical for two reasons:

Answer 2

The homeostatic maintenance of Na+ concentration is critical for two reasons:

1. to achieve normal osmotic pressure
2. for the functioning of excitable cells

Question 3

Define hypernatremia

Answer 3

A high plasma concentration of Na+

• is accompanied by water retention and increased blood pressure (hypertension)

Question 4

Define hyponatremia

Answer 4

A low plasma concentration of Na+

• accompanied by low plasma volume and decreased blood pressure (hypotension)

Question 5

Normally, 99.4% of the filtered Na+ is reabsorbed, with the majority of it being reabsorbed in the ______\_(about 67%), some in the _____________\_(about 25%), and the remainder in the ______\_(about 8%).

Answer 5

Normally, 99.4% of the filtered Na+ is reabsorbed, with the majority of it being reabsorbed in the proximal tubule (about 67%), some in the ascending loop of Henle (about 25%), and the remainder in the distal tubule (about 8%).

Question 6

Reabsorption of Na+ in proximal tubule is important for the reabsorption of other solutes, such as ______\_, _________\_, ______\_, ______\_, ______\_, and ____\_.

Answer 6

Reabsorption of Na+ in proximal tubule is important for the reabsorption of other solutes, such as glucose, amino acids, water, chloride (Cl^-), hydrogen ions (H⁺), and urea.

Question 7

On the apical membrane of the tubular epithelial cells, Na+ is transported into the cell by _____\_or by _____\_, both of which are carried out through ______ ______ ______ _____\_

Answer 7

On the apical membrane of the tubular epithelial cells, Na+ is transported into the cell by cotransport or by countertransport, both of which are carried out through secondary active transport proteins

Question 8

The coupling of Na+ reabsorption is ______\_favourable because the reabsorption of the coupling solute is driven by Na+ moving ___\_ its ______\_gradient. This ______\_ gradient for Na+ is maintained by the_________ located in the basolateral membrane, which pumps Na+ out of the cell in exchange for K+.

Answer 8

The coupling of Na+ reabsorption is energetically favourable because the reabsorption of the coupling solute is driven by Na+ moving down its electrochemical gradient. This electrochemical gradient for Na+ is maintained by the Na+/K+-ATPase located in the basolateral membrane, which pumps Na+ out of the cell in exchange for K+.

Question 9

Na+ reabsorption in the ascending loop of Henle is important for the regulation of ______\_

Answer 9

Na+ reabsorption in the ascending loop of Henle is important for the regulation of water balance

Question 10

Na+ reabsorption in the distal tubule is important for the regulation of ______\_and ultimately for _____________\_

Answer 10

Na+ reabsorption in the distal tubule is important for the regulation of ECF volume and ultimately for mean arterial pressure (MAP)

Question 11

In the apical membrane of the tubular epithelial cells, Na+ moves into the cell through a _____\_, or by cotransport with ___, which is mediated by a ___________\_

Answer 11

In the apical membrane of the tubular epithelial cells, Na+ moves into the cell through a Na+ channel, or by cotransport with Cl–, which is mediated by a secondary active transport protein

Question 12

In the basolateral membrane, Na+ is pumped out of the cell by the _________\_

Answer 12

In the basolateral membrane, Na+ is pumped out of the cell by the Na+/K+-ATPase.

Question 13

Na+ reabsorption in the distal tubule is regulated by the hormones ____\_ and _____ _____ _____ (_____).

Answer 13

Na+ reabsorption in the distal tubule is regulated by the hormones aldosterone and atrial natriuretic peptide (ANP).

Question 14

What is aldosterone?

How does it increase Na+ reabsorption?

Answer 14

• a steroid hormone secreted from the adrenal cortex
• increases Na+ reabsorption by increasing the number of Na+ channels in the apical membrane (A) and the number of Na+/K+-ATPases in the basolateral membrane (B) of the principal cells of the distal tubules,

Question 15

Aldosterone is a ___\_hormone secreted from the ___ __\_ which increases Na+ reabsorption by increasing the number of _____\_in the apical membrane (A) and the number ________\_ in the basolateral membrane (B) of the _____\_cells of the __\_ tubules

Answer 15

Aldosterone is a steroid hormone secreted from the adrenal cortex which increases Na+ reabsorption by increasing the number of Na+ channels in the apical membrane (A) and the number of Na+/K+-ATPases in the basolateral membrane (B) of the principal cells of the distal tubules

Question 16

Aldosterone secretion is regulated by the _________\_, as outlined in the following figure.

Answer 16

Aldosterone secretion is regulated by the renin-angiotensin-aldosterone system (RAAS), as outlined in the following figure.

Question 17

Describe the steps of the Renin-Angiotensin-Aldosterone-System

1. Granular cells of the _________\_secrete _____\_ into the blood in response to decrease in ______/______ ______/__\_
2. Secretion of Renin into blood activates _____\_into ________\_ which passes through the pulmonary circuit where it is converted into _____\_
3. Which is the main stimulant for the release of the hormone _____\_ from the adrenal cortex
4. This hormone ^ increases _____\_reabsorption by the distal and collecting tubular cells by promoting the insertion of ______ _____\_ into luminar membranes and ______-______ _____\_ into basolateral membranes

Answer 17

Describe the steps of the Renin-Angiotensin-Aldosterone-System

1. Granular cells of the Juxtaglomerular Apparatus secrete renin into the blood in response to decrease in NaCl/ECF Volume/BP
2. Secretion of Renin into blood activates angiotensinogen into Angiotensin I which passes through the pulmonary circuit where it is converted into Angiotensin II
3. Which is the main stimulant for the release of the hormone aldosterone from the adrenal cortex
4. This hormone ^ increases sodium reabsorption by the distal and collecting tubular cells by promoting insertion of sodium channels into luminar membranes and sodium potassium pumps into basolateral membranes

Question 18

Unlike aldosterone, ANP is a hormone released from specialized ____________ in response to stretching

Answer 18

Unlike aldosterone, ANP is a hormone released from specialized cardiac atrial muscle cells in response to stretching

Question 19

How does ANP differ from aldosterone?

• Secreted from?
• Effect?

Answer 19

• ANP is secreted from specialized cardiac atrial muscle cells while aldosterone is secreted by the adrenal cortex.
• decreases Na+ reabsorption by decreasing the number of Na+ channels in the apical membrane of the principal cells of the distal tubule

Question 20

In addition to directly influencing Na+ reabsorption, ANP inhibits secretion of ___\_and _______\_, inhibits _______\_of smooth muscle cells in the afferent arterioles, and inhibits activity of the ___\_ ___\_____\__.

Answer 20

In addition to directly influencing Na+ reabsorption, ANP inhibits secretion of renin and aldosterone, inhibits contraction of smooth muscle cells in the afferent arterioles, and inhibits activity of the sympathetic nervous system.

Question 21

Atrial natriuretic peptide (ANP) mechanism of action: In response to stretch, such as that caused by increased ____\_, _____ _____ ____\_, or increased _____ _____ ____\_, cardiac atria secrete the hormone _________\_ which acts on the body to increase ____\_and ____\_ excretion in urine and _______\_ arterial blood pressure.

Answer 21

Atrial natriuretic peptide (ANP) mechanism of action: In response to stretch, such as that caused by increased NaCl, extracellular fluid (ECF) volume, or increased arterial blood pressure, cardiac atria secrete the hormone atrial natriuretic peptide (ANP) which acts on the body to increase sodium (Na+) and water (H2O) excretion in urine and decrease arterial blood pressure.