3.7.3. Body Fluid Compartments

Question 1

What are the five functions of the kidneys?

Answer 1

1. Regulate total body fluid composition
2. Regulation of BP long term
3. Excrete waste products
4. Acid Base balance
5. Endocrine and metabolic functions like RBC creation, gluconeogenesis and bone homeostasis

Question 2

What is the major blood test that focuses on the kidneys? What are a few of its components (what it tests for)?

Answer 2

1. With Kidneys we focus on the BMP, Basic Metabolic Panel
   
   1. Electrolytes
   2. BUN, Cr, GFR, CO2

Question 3

What is the 60/40/20 rule?

Answer 3

1. 60/40/20 rule
   
   1. 42L of water in the body = 60% of body weight
   2. Intracellular is ⅔ of the body of water, ⅓ is extracellular
   3. Thus, total water is 60% of body weight, 40% intracellular, 20% extracellular

Question 4

What are the different locations for extracellular water in the body? What percentage is interstitial and plasma?

Answer 4

1. Extracellular = 17L
   
   1. Plasma 3L, Interstitial fluid 8L, Bone/Dense Connective tissue 5L, Transcellular water 1L
   2. Thus in extracellular water, Interstitial fluid = 75%, plasma = 25% roughly

Question 5

How does body fluid composition change between newborns and females? How much is stored in adipocytes (like in obesity)?

Answer 5

Females have <60%, newborns have >60%, obesity only 10-15% in adipocytes

Question 6

How much water are we supposed to drink per day? How much can the kidneys excrete?

Answer 6

1. Formation of body water
   
   1. Intake - Ingest 2L, 200mL/day by carb catabolism
   2. Excrete - 0.5 - 20L/day, skin and resp tract = 800mL/day, sweat and feces = 200mL/day

Question 7

What is a positive water balance? A negative one?

Answer 7

1. Positive water balance = weight gain = Get more water than you release
2. Negative water balance = opposite

Question 8

What is osmolarity? What is the difference between osmolarity and osmolality?

Answer 8

1. Osmolarity
   
   1. Osmole = solute particle that contributes to osmotic pressure
   2. Osmolarity = #osmoles/L of solution
   3. Osmolality = #osmoles/kg of solvent
      
      1. Usually equivalent because 1L H20 = 1kg H20, but in differing temperatures, osmolarity may alter

Question 9

What happens to cells when they are isotonic, hypotonic, or hypertonic?

Answer 9

1. Tonicity
   
   1. Isotonic solution = cells don’t change
   2. Hypotonic solution = Cells will swell
   3. Hypertonic Solution = Cells will shrink

Question 10

What two general principles cause water to move?

Answer 10

1. Osmosis - H20 shifts until
   
   1. Water/solute concentration are equal OR
   2. Hydrostatic pressure is equal and opposite to osmotic pressure

Question 11

What is an effective osmole? What is an ineffective one?

Answer 11

Both are in solutions where the osmolarity is the same inside and outside the cell.

Question 12

What is the calculation for plasma osmolarity?

Answer 12

OR (a shortcut)

Question 13

How do we calculate the physiologically relevant sodium concentration in water?

Question 14

Why do we care about the “physiologically relevant” sodium concentration?

Question 15

What are the water compartments in the body (broadest categories)?

Question 16

What are the water compartments in the body (more specifically)?

Question 17

What are the compartments of transcellular fluid?

Question 18

Why do we typically ignore the dense connective tissue and bone and transcellular fluid compartments?

Answer 18

We normally ignore the Dense and Trans compartments because water exchange is not readily done here, but they are still very important!

Question 19

What assumptions do we make about water moving between the compartments?

Answer 19

1. Assumptions we make:
   
   1. All changes to the body fluid will occur through the extracellular compartments
   2. Water will move between the compartments but solutes do not move

Question 20

What are Darrrow-Yanet Diagrams?

Answer 20

These plot plasma osmolarity against body fluid volume. They help us understand how the body water compartments will respond to changes in their composition.

Question 21

Describe the steady state that will be achieved with the introduction of water into the ECF.

Question 22

What steady states will be achieved when we add water, NaCl, or Isotonic NaCl?

Question 23

What steady states will be achieved when we LOSE water, NaCl, or Isotonic NaCl?

Question 24

Discuss how fluid goes from plasma to the interstitium

Question 25

Give a description of water movement at the level of the capillary involving the terms for hydrostatic pressure and osmotic pressure as they pertain to the capillary and interstitium

Answer 25

Normal function of the lymphatics is to keep interstitial hydrostatic and interstitial colloid osmotic pressures constant

Blood pressure, protein concentration, and fluid filtration all drive the capillary hydrostatic and capillary colloid osmotic pressures

Question 26

What is Starling’s Law (of the capillaries)?

Question 27

What can cause an increase in capillary hydrostatic pressure?

Question 28

How do we decrease capillary colloid osmotic pressure?

Question 29

What increases K, the constant in the Starling equation that represents capillary permeability?

Question 30

How can lymphatic blockage occur and what does it lead to?

Question 31

What is the relationship between the kidneys at EPO (erythropoietin)?

Answer 31

1. Kidney senses low oxygen, as in Anemia, and we get renal hypoxia. Kidney releases erythropoietin out of the peritubular cells in the kidney
2. Goes through blood, hits bone marrow and causes stimulation for RBC synthesis (so the proerythroblast and basophillic erythroblast) which will solve the problem.
3. Dysfunction in this system is a common complication of chronic kidney disease