Kidney

Question 1

How much of the total body water is found in the ICF vs the ECF

Answer 1

ICF: 40%
ECF: 20%

Question 2

Where (and how much) water can be found in the ECF

Answer 2

Interstitial: 75% of water in the ECF
Intravascular: 25% of water in the ECF

Question 3

What separates the intracellular and extracellular compartments, vs the interstitial and intravascular compartments

Answer 3

Intra- and extracellular: the cell membrane
Interstitial and intravascular: vascular endothelium

Question 4

What is different (in terms of permeability) between the cell membrane and vascular endothelium

Answer 4

The cell membrane is freely permeable to water, but solutes (like electrolytes) need to be transported via a pump
The vascular endothelium is freely permeable to most ions and small molecules, but not colloid particles (e.g., albumin)

Question 5

What is osmotic pressure

Answer 5

The pressure made by particles in a fluid compartments causing fluid to move by osmosis to an area of higher solute concentration

Question 6

What is the average plasma osmolarity

Answer 6

300 mOsm/kg - 310 mOsm/kg

Question 7

Particles that can cross the semi-permeable membrane contribute to ___ but not ____

Answer 7

Osmolarity, NOT osmotic pressure

Question 8

What is oncotic pressure

Answer 8

The contribution of colloid particles and electrolytes towards plasma osmotic pressure

Question 9

Where is the concentration of sodium the highest: intravascular, interstitial or intracellular

Answer 9

Intravascular and interstitial

Question 10

Where is the concentration of potassium the highest: intravascular, interstitial or intracellular

Answer 10

Intracellular

Question 11

Where is the concentration of protein the highest: intravascular, interstitial or intracellular

Answer 11

Intracellular

Question 12

What are Starling forces

Answer 12

The oncotic and hydrostatic pressure gradients between the capillary and interstitial

Question 13

Briefly explain Starling forces as you move from the arteriole to venule end of a capillary

Answer 13

Arteriolar end: high hydrostatic pressure favors fluid movement OUT into interstitial space
Middle: hydrostatic pressure decreases as fluid volume is lost, oncotic pressure starts to increase
Venule end: Oncotic pressure is high as the remaining proteins are highly concentrated, and fluid moves back into the capillary

Question 14

Why is plasma colloid oncotic pressure so important to maintain fluid movement between the interstitium and intravascular space

Answer 14

The vascular endothelium is freely permeable to small molecules, so if not for the colloid particles inside the vascular space, the osmolality of the intravascular space and the interstitium would be identical and fluid would just keep moving out of the capillaries, causing oedema

Question 15

What is the basis of the modified Starling equation

Answer 15

The transcapillary fluid movement is determined by the glycocalyx and the sub-glycocalyx space

Question 16

What is a crystalloid

Answer 16

A fluid containing electrolytes and other solutes that can freely cross the capillary endothelium between intravascular and interstitial spaces

Question 17

What are the 3 classes of crystalloid fluids

Answer 17

1. Hypertonic
2. Isotonic
3. Hypotonic

Question 18

Why is hypertonic saline best for treating hypovolemic shock

Answer 18

It has such a higher osmolarity (8x higher) than normal plasma, so it causes water to be pulled rapidly out of the intracellular space and redistribute between the interstitial and intravascular spaces

Question 19

What are the insensible losses of water in the body

Answer 19

Feces, saliva, and evaporation

Question 20

How is fluid loss categorized in the body

Answer 20

By the tonicity of the fluid lost (hypotonic, isotonic or hypertonic)

Question 21

What is the difference between dehydration and hypovolemia

Answer 21

Dehydration: loss of fluid in the interstitial/intracellular space
Hypovolemia: loss of fluid in the intravascular compartment

Question 22

List 4 major electrolytes contributing to osmolarity

Answer 22

1. Sodium
2. Potassium
3. Glucose
4. Urea

Question 23

Define ineffective osmoles

Answer 23

Something that can move freely across a membrane (urea)

Question 24

Define effective osmoles

Answer 24

Something that cannot move freely across a membrane

Question 25

Define osmolarity

Answer 25

The number of particles (both effective and ineffective) contained in a solution

Question 26

What happens to the ECF/ICF following hypotonic fluid loss

Answer 26

Since the fluid lost is lower in osmolarity than the ECF (loss of water in excess of solute), ECF osmolarity will increase and water will move out of the ICF