Regulation of Sodium Balance and Extracellular Fluid Volume Flashcards
(35 cards)
What are some important factors that are determined by ECFV regulation?
ECFV Determines:
• Plasma Volume which determines…
• Circulatory Filling Pressure
• Cardiac Output
How is ECFV calculated?
• What is the relationship between ECFV and sodium?
ECFV = Amount of ECF Na+ / Pna
At constant Plasma Na concentration ECFV is proportional to total body Na
**Note: Pna = Plasma Concentration of Na+; is pretty constant so ECFV is really only dependent on Amt. of ECF Na+
Why do we say that Pna (plasma sodium) is constant?
• when is this not true?
- Pna is kept constant by AVP(ADH)-mediated water regulation by the kidney
- Pna change only occurs when gain or loss of Na+ exceeds thirst Mechanism and Kidney’s ability to correct the situation
T or F: Plasma sodium is a god reflection of ECFV.
False, Plasma Na is always kept CONSTANT by ADH-mediated regulation of water reabsorption in the kidney
**ECFV is the main thing that changes with increased Na+
How do healthy individuals respond to changes in salt intake?
• what about someone with renal dysfunction?
Normally:
• We just increase salt output (takes 2-4 days for kidney to make adjustment)
Renal Pathology:
• They Cannot adjust to secrete more so they just increase ECFV to dilute salt in the body back to a normal level
How much salt do you have to retain to gain 1kg (2.2lbs)?
150 mEq
What are some condition that may lead to sodium imbalance?
Diarrhea
Excessive Sweating
Diuretics
How much Na+ passes through the glomerulus each day?
• what happens to it after that?
~ 25,000 mEq of Na/day
Reabsorption: Proximal Tubule: 16,000 mEq/day (64%) Ascending LOH: 7,000 mEq/day (28%) Distal CT: 2000 mEq/day (8%) Collecting Duct: 1750 mEq (7%)
Excretion:
150-250 mEq/day
**NOTE: the rate of excretion should be equal to our daily intake
What are some key causes of Hypovolemia?
• what are some key signs that you’re becoming hypovolemic?
Causes:
• Diarrhea/Vomiting
• Severe Burns
• Excessive Sweating
Signs:
• LOW SYSTOLIC and DIASTOLIC blood pressure
• ORTHOSTATIC HYPOTENSION
What are some key causes of Hypervolemia?
• associated signs?
Causes:
• Congestive Heart Failure (may be the cause or the 2º)
• Chronic Renal Failure
Signs:
• JVD - 2-3 liters of fluid
• S3 Gallop
• Pulmonary Edema
In what cases might you see edema with normal ECFV or even Low ECFV?
HYPOALBUMINEMIA
Caused by:
• Liver Disease - prot. never produced
• Nephrotic Syndrome - loss of prot. in urine.
• Burns (may loose lots of protein in add’n to fluid)
**Less protein in vessel means less fluid is in the vascular system and more is in the interstitial fluid (increased ISF)
How does your body compensate when you drink too much water?
- Increased Urination (diuresis)
* Solutes are conserved
What is the difference in response time of increased H2O in the system and increased Na+?
Ridding XS H2O:
• Happens in like 0.5 hrs
Ridding XS Na+:
• take 2-4 DAYS
**Water regulation is clearly much faster
What happens when a normal person ingests extra salt?
• what happens when they go off of this diet?
ADDITION:
• It takes 2-4 days for the output to catch up to and match the intake
**During this time of increased Na+ intake you will gain H2O wt. - this is corresponds with the adjustment of the kidney.
**Note: even in a properly functioning kidney you gain wt. because you are constantly putting in more Na+ at the same high rate
REMOVAL:
• When Na+ is removed, it take 2-4 days for balance to be restored as well
How does your therapy differ for salt sensensitive and salt insensitive hypertensive patients?
Salt Sensitive:
• Not Good at filtering salt so you MUST GIVE DIURETIC to help them clear salt
Salt Insensitive:
• Will reduce ECFV naturally as they excrete salt
What 3 types of receptors are involved in detection of ECFV?
• location
- Neural Stretch Receptors - Large Veins
- Atrial Stretch Receptors - Atrial Stretch Receptors
- Arterial Baroreceptors - Arterial Baroreceptors
What do the following receptors respond to?
• how do they modulate the bodies defense against stretch?
- Neural Stretch Receptors
- Atrial Stretch Receptors
- Arterial Baroreceptors
Neural Stretch Receptors:
• Responds to stretch due to VENOUS DISTENTION
• DOWNREGULATES ADH/AVP to increase water and Na+ excretion
Atrial Stretch Receptors:
• Parasympathetic fibers in VAGUS NERVE affect centers involved in:
–> AVP secretion
–> Sympathetic Firing to Kidney
–> CV centers
• ALSO ANP (atrial neurogenic peptid is released)
Arterial Baroreceptors:
• Arteries
• Controls AVP/ADH secretion
What does ANP do?
Stimulates Na Excretion from the kidney
What effect does Increased Glomerular Filtration have on Sodium Excretion?
• decreased?
High GFR:
• Rapid Na+ excretion
Low GFR:
• More Na+ Retention
What are 5 key factors that regulate SODIUM excretion in the kidney?
- Changes in GFR
- Aldosterone
- Natriuretic Hormone
- Renin-Angiotensin System
- Sympathetic nn. Prostaglandins, etc.
What effect does aldosterone have on the kidney?
• where does it act?
- Aldosterone Increases Reabsorption of Na+
* Acts in the Distal Tubule and Collecting Duct
What effect does Natriuretic hormone have on the kidney?
• Less Na+ reabsorption
What effect does RAAS have on the kidney?
• Decreases ECFV and Increases Na+ reabsorption
Would you be able to detect a 10% increase in GFR?
• what would this do to sodium excretion?
- 10% increase would not be detectable because serum creatinine is not a sensitive enough measure to see this change.
- Sodium excretion will still be bumped up big time because much you will be pushing much more fluid through the nephrons
E.g. Eating a lot of pizza will increase Na+ and ECFV and you will get thirsty. Increased arterial pressure will result and you’ll increase GFR and pee out Na+
