Regulation of Plasma Sodium & ECF Volume - RR

Question 1

What primarily regulates the ECF volume?

Answer 1

Amount of sodium

Question 2

How is the amount of sodium different than the concentration of sodium?

Answer 2

Amount= mmoles
Amount is found by multiplying the concentration by the volume
Concentration= moles/L

Question 3

What are the two compartments of the ECF?

Answer 3

Intravascular ( RBC/WBC/platelets/plasma) and extravascular (interstitial)

Question 4

The regulation of RBC, WBC, plasma or platelets allows you to regulate the volume of blood?

Answer 4

Plasma

Question 5

What is a sensor for a change in osmolarity?

Answer 5

Osmoreceptors in the hypothalamus

Question 6

What are some sensors to a change in volume? Is this a direct or indirect measure of volume?

Answer 6

Carotid sinus, aortic arch, renal afferent arteriole, atria

-this is an indirect measure: these are baroreceptors that can determine volume by responding to stretch

Question 7

What are the effectors (the organs that elicit a response) to a change in osmolarity?

Answer 7

1. Brain- induces thirst (increased water will decrease the osmolarity), also releases ADH which acts on kidney
2. Kidney- changes water clearance depending on the plasma osmolarity (negative water clearance when hyperosmotic)

Question 8

What are the effectors (the organs that elicit a response) to a change in volume?

Answer 8

1. Heart and blood vessels
   - a decrease in volume will decrease mean arterial pressure which causes a sympathetic response with an increase in HR and an increase in TPR
   - this is a short term response
2. kidney
   - can increase or decrease sodium reabsorption (aldosterone would cause an increase in reabsorption)
   - takes longer to respond

Question 9

Altering the free water clearance is used to regulate osmolarity or volume?

Answer 9

Osmolarity

Question 10

What are the short term and long term alterations that are used to regulate volume?

Answer 10

Short term: changing BP

Long term: changing renal sodium excretion

Question 11

You eat a ton of sodium, increasing the amount of sodium that gets absorbed and in your plasma and increases the osmolarity. What happens next?

Answer 11

The increased osmolarity is detected by hypothalamus which then releases ADH from the posterior pituitary. This causes an increase in water reabsorption at the collecting duct and a decrease in plasma osmolarity. Over time, the kidney matches excretion of Na to the consumption, which reduces the volume (decrease the reabsorption of sodium)

Question 12

You’re in a desert with only water, which decreases your sodium in your plasma. How is this related to volume and how does your body respond?

Answer 12

Detected as a decrease in volume (as well as a decrease in osmolarity)
ADH secretion is decreased, decreasing the water retention(increasing positive free water clearance) and the renin-angiotension-aldosterone system is activated to increase sodium reabsorption in the distal tubule and collecting duct

Question 13

How does the kidney respond to an ECF volume expansion? Does GFR change?

Answer 13

Decreasing the reabsorption of sodium and water without changing GFR

Question 14

How does the kidney respond to an ECF volume contraction?

Answer 14

Increasing the reabsorption of sodium and water. In extreme cases like hemorrhage can decrease GFR

Question 15

The kidneys increase sodium excretion in response to an increase in ECF volume OR in response to an increase in sodium consumption?

Answer 15

ECF volume

Question 16

How is the effective circulating volume defined? How does it relate to the total ECF volume?

Answer 16

The functional volume that reflects the extent of perfusion where blood pressure can be sensed- generally parallels the total ECF

Question 17

Is the amount of sodium excreted dependent on the effective circulating volume or the total ECF?

Answer 17

Effective circulating volume

Question 18

What are some circumstances where the effective circulating volume does not parallel the total ECF volume?

Answer 18

Congestive heart failure (have an increase in hydrostatic pressure which causes edema and effective circulating volume will be lower than the total ECF)
Pulmonary edema (increased hydrostatic pressure in lung)
Liver disease (decreased synthesis of albumin so decreased capillary oncotic pressure)
Nephrotic disease (glomerulus allow albumin through which decreases the oncotic pressure)

Question 19

A decrease in the effective volume influences four different effector systems. What are they?

Answer 19

1. Renin- Angiotensin-Aldosterone system
2. Sympathetic NS
3. Post. pituitary with ADH
4. ANP (from heart)– decreases in activity

Question 20

What does ANP cause?

Answer 20

Naturesis- more sodium in urine

Question 21

What is the renin-angiotensin-aldosterone system? Where is each made and what is the effect of each one?

Answer 21

Renin—> cleaves angiotensinogen (made in liver) to angiotensin I—> ACE in the lungs converts to angiotensin II–> angiotensin II acts on the adrenal cortex to stimulate aldosterone release—> addition of Na/K ATPase which effectively increases the absorption of sodium

Question 22

Besides activating aldosterone, angiotensin II has other functions. What are some of these functions?

Answer 22

Vasoconstriction (increases TPR and MAP)

Goes to the hypothalamus and increases ADH release as well as stimulating thirst

Question 23

What are the three mechanisms that regulate renin release from the juxtaglomerular apparatus?

Answer 23

1. Local renal baroreceptors in afferent arteriole will respond to a decreased pressure by releasing renin
2. Decrease in MAP leads to activation of SNS which stimulates renin release
3. Cells of macula densa sense the tubular fluid sodium concentration and if low will release renin

Question 24

Where in the nephron does aldosterone work?

Answer 24

Late distal tubule and the early collecting duct in the cortex

Question 25

How much of the sodium filtered load is reabsorbed in the proximal tubule? In the TAL?

Answer 25

Proximal tubule= 67%

TAL= 25%

Question 26

What is the difference between the sodium reabsorption in the medullary part of the TAL versus the cortical part of the TAL?

Answer 26

The sodium reabsorbed in the medullary TAL contributes to the countercurrent multiplication, while the sodium reabsorbed in the cortical portion joins with the renal vein and is returned to the circulation

Question 27

How does aldosterone influence potassium? What is the mechanism behind this?

Answer 27

The presence of sodium will cause increased excretion of potassium
This is because aldosterone works by increasing the amount of Na/K ATPase therefore more K will be in the cell and will go down the gradient into the tubular fluid

Question 28

What are three factors that cause aldosterone secretion?

Answer 28

1. Angiotensin II
2. ACTH (from ant. pituitary)
3. High concentrations of potassium in the plasma

Question 29

What are the values for hypernatremia? How is this related to water?

Answer 29

Above 135-145 mEq/L
Hypernatremia isn’t a problem with sodium, but rather is a problem with water balance– dont have enough water to bring down the osmolarity

Question 30

What are some causes of hypovolemic hypernatremia?

Answer 30

Inadequate water consumption, extreme sweating, severe diarrhea, polyuria (as seen in DM or DI)

Question 31

What are some causes of hypervolemic hypernatremia?

Answer 31

Excessive hypertonic fluid consumption (like salt water) or hyperaldosteronism

Question 32

What are the values for hyponatremia? How is this related to water balance?

Answer 32

Below 135-145mEq/L

Caused by a gain of water in excess of solute

Question 33

What are some causes of hypervolemic hyponatremia?

Answer 33

Inappropriate reabsorption of water in excess of solute, CHF (sensed as decreased circulating effective volume so increase ADH), kidney failure where can’t reabsorb sodium, liver failure where can’t make protein so oncotic pressure and effective volume decreases, hemorrhage, Addison’s disease, severe vomiting/diarrhea