Regulation Of ECF Volume

Question 1

What happens when there is a Net increase in Total Body Na+? A Net decrease in Total Body Na+?

Answer 1

Increase Net Na+: Increased Osmolarity, and Body Fluid volume
Decreased Net Na+: Decreased Osmo. And Body Fluid Volume

Question 2

How do kidneys Regulate Total Body Na+?

Answer 2

Via Excretion of Na+:

Excretion = (GFR x Plasma [Na+]) - Na+ Reabsorbed

Question 3

What are the 3 ways to adjust Na+ Excretion?

Answer 3

1) Control Plasma Na+ (Eating and Drinking)
2) change in GFR
3) change in Na+ Reabsorption

Question 4

What are some Factors that control GFR?

Answer 4

Renal Sympathetic Nerves 
Renin-Angiotensin System 
Prostaglandins 
Glomerular Tubular Balance 
Autoregulation: Tubular Glomerular Feedback Mechanism

Question 5

What are the sensors that can detect Changes in Na+ Balance?

Answer 5

Extrarenal Baroreceptors: Carotid sinuses, arteries, cardiac chambers and great veins

Intrarenal Baroreceptors: Renal Juxtaglomerular Apparatus and Macula Densa Cells that control Renin Secretion

Question 6

How do Renal Sympathetic Nerves control GFR?

Answer 6

Increased Nerve Activation Causes:

Increased Constriction –> Decreased Pgc –> Decreased Renal BF -> Deceased GFR

Question 7

How does the Renin Angiotensin System Control GFR?

Answer 7

Increased Renin Release Causes:

Increased Plasma Ang II –> Decreased Renal BF –> Decreased GFR

Question 8

How do Prostaglandins Control GFR?

Answer 8

Prostaglandins such as: Prostacyclin, are vasodilator a that prevent platelet aggregation and Increase GFR.

Question 9

How does Glomerular Tubular Balance Control GFR?

Answer 9

1) Under normal conditions GTB allows for 60-65% Na+ Reabsorption
2) If there is an increase in GFR, there will be an increase in Glucose and Increase in a.a. Filtration which increases Na+ Reabsorption.

This balance is important to maintain proper Na+ balance in the event of GFR changes.

Question 10

How does Autoregulation: Tubular Glomerular Feedback Mechanism Control GFR?

Answer 10

Autoregulation allows GFR to remain relatively constant over a wide range of Perfusion pressures (systemic pressure)

Question 11

What Controls Na+ Reabsorption?

Answer 11

Aldosterone 
Renal Sympathetic Nerves
Angiotensin II 
Atrial Natriuretic Peptide (ANP) 
Antidiuretic Hormone (ADH)

Question 12

What is Aldosterone?

Answer 12

It is a hormone that is secreted by the Adrenal Cortex (Zona Glomerulosa)

Question 13

What stimulates The Adrenal Cortex and Aldosterone Secretion?

Answer 13

1) Increased Adrenocorticotropic Hormone (ACTH)
2) Increased Plasma K+
3) Increased Angiotensin II (due to stimulated Renin:low volume and low Na+)

Question 14

What is the Function of Aldosterone?

Answer 14

1) It increases the # of Na+ channels in Lumen (collecting ducts)
2) Increases # of Na+/K+ pumps in Basolateral membrane (Collecting Ducts)
3) Increases ATP generation

All of these lead to Na+ Reabsorption

Question 15

How Do Renal Sympathetic Nerves Control Na+ Reabsorption?

Answer 15

A) Via Alpha Adrenergic Receptors:
- Which Cause Vasoconstriction of Aff and Eff Arterioles
- Altering Starling Forces and FF (increased oncotic and decreased hydrostatic in PTC)
B) Via Beta Adrenergic Receptors:
- Stimulation of B Receptors in Granular Cells –> Renin Secretion –> DIRECT stimulation of Na+ Reabsorption in Prox. Tubules

Question 16

How Does Ang II effect Na+ Reabsorption in Proximal Tubules?

Answer 16

1) DIRECT EFFECTS:
- Stimulates Na+/H+ exchanger in Proximal Tubules & Na+ Reabsorption
- Increased FF & Na+ Reabsorption in Prox Tubules
2) INDIRECT EFFECTS:
- Increased Aldosterone Secretion

Question 17

How does Atrial Natriuretic Peptide (ANP) control Na+ Reabsorption?

Answer 17

• Atrial cells secrete ANP due to high volume stretching
  1) ANP Inhibits Na+ Reabsorption in the Collecting Ducts by
  2) Increasing cGMP
  3) Vasodilator of Renal Arterioles
  4) Inhibits Renin Secretion

Question 18

How does Antidiuretic Hormone (ADH) control Na+ Reabsorption?

Answer 18

ADH only has a MINOR effect on Na+ Reabsorpton

It Increases Na+ Reabsorption in Thick ALoH, Distal Tubules, and Collecting Duct

Question 19

What is the MAJOR control Factor of Water Excretion?

Answer 19

The RATE of Water Reabsorption, which is determined by ADH levels

Question 20

What is the MAJOR function of Antidiuretic Hormones (ADH)?

Answer 20

The MAJOR function is to Increase Permeability of the Cortical and Medullary Collecting Ducts to Water and Decrease Water Excretion.

Question 21

What Controls Antidiuretic Hormone (ADH) secretion?

Answer 21

Baroreceptors and Osmoreceptors.

Question 22

How do Baroreceptors Control ADH secretion?

Answer 22

Baroreceptors Detect Stretch, which is mediated by volume and Pressure.

HEMORRHAGE:
Decreased Cardiovascular pressure –> Decreased Baroreceptor Firing –> Increased ADH secretion –> Collecting Duct Permeability –> Increased H20 Reabs and Decreased H20 excretion.

**This Process helps to restore ECF volume via Increased H2O Reabsorption and increased BP **

Question 23

The Regulation of Na+ is directly tied to what?

Answer 23

Maintenance of Body Fluid Volume.

Question 24

How do Osmoreceptors Control ADH secretion?

Answer 24

Osmoreceptors react to changes in Osmolarity.
A) Thirst Response (high Osmo)
Decreased Blood Vol. –> Incr. ADH secret –> Incr Collecting Duct perm. To H2O –> incr.H2O reabs and thirst response

B) Excess H2O Ingested (low Osmo)
High [H2O] –> Decr ADH secret –> Decr Collecting Duct Perm. To H2O –> decr H2O reabs –> Incr H2O excretion

Question 25

What controls Na+/H2O Reabsorption/Excretion During Euvolumia?

Answer 25

Euvolumia (Normal ECF volume) 1. Proximal Tubules and LoH: Reabs 90% of Na+, and the other 10% gets deliver to distal tubules 2. Distal Tubules and Collecting Ducts: Reabsorbed Na+ will be regulated so that Na+ excreted = Na+ ingested

Question 26

What mechanisms constantly make sure that Na+ gets delivered to Distal Tubules?

Answer 26

``` Autoregulation Glomerular Tubular Balance Sympathetic Nerve Activation Angiotensin II Metabolites( Prostaglandins, NO-, Dopamine) ```

Question 27

What hormones Regulate Na+ Reabsorption in the Distal Tubules and Collecting Duct?

Answer 27

``` Aldosterone Atrial Natriuretic Peptide (ANP) ( vasodilator) Antidiuretic Hormone (ADH) (minor fun) ```

Question 28

How is Na+/H2O Reabsorption/Excretion Regulated during ECF Contraction?

Answer 28

Isovolumic Contraction occurs during: Diarrhea or Hemorrage. 1. A decrease in H2O and Na+ happens first 2. Decr Plasma Volume and Increase Arterial Oncotic Press 3. A series of events occurs that effect ( systemic pressure, Renal symp nerves, Renin, Ang II, and Constriction occurs) 4. Leading to Decr GFR 5. ***Ultimately leading to Decreased Na+ and H2O excretion and Increased Na+ and H2O Reabsorption ***

Question 29

What causes ECF Expansion?

Answer 29

1. Congestive Heart Failure | 2. Primary Hyperaldosteronism

Question 30

How does Congestive Heart Failure controls Na+/H2O during ECF Expansion?

Answer 30

During Congestive Heart Failure, Neurohumoral Compensatory Mechanisms Activate to Increase Na+ and H2O Retention and Edema . 1. Increased Sym. Nerve Stimulation 2. Increased Renin-Angiotensin system 3. Increased ADH release 4. Increased Aldosterone release 5. Increased Na+ and H2O retention

Question 31

What stimulates the sympathetic Nervous System?

Answer 31

Low CO Failing Heart Low Volume in Arterial System Low Perfusion Pressures --> Renin release

Question 32

How does Primary Hyperaldosteronism cause ECF expansion, and how is Na+/H2O regulated?

Answer 32

Hyperaldosteronism - is the over secretion of Aldosterone. - W/ the increased level of Aldosterone, there is an Initial increase Na+, but then a couple days later, that Na+ is excreted and Na+ levels return to normal despite the continued presence of Aldosterone. - The change in [Na+] "escapes" because there is an Increase in ECF, Increased GFR, Decreased Renal Symp. Nerve Activity, and Decreased Ang II

Question 33

What causes Hypernatremia?

Answer 33

A. Central Diabetes Insipidus - which is a decrease in ADH release in the pituitary gland, which causes an increase in H2O excretion in the urine. B. Nephron enact Diabetes Insipidus - which is when you have Normal levels of ADH, but the Tubules don't respond to circulating ADH, and there is an increased H2O excretion in the urine.

Question 34

What is the function of the Neurohumoral Compensatory Pathway?

Answer 34

It "overrides" the Autoregulatory Mechanisms during extreme situations such as Diarrhea or Hemorrhage. It causes Na+ and H2O retention and exacerbates Edema