Fluid compartments

Question 1

List the main fluid compartments, recall approximate sizes and composition of each compartment

Answer 1

Intracellular (IC) – 55% of body water ( main cation K⁺, Cl^-) having low calcium levels allows for a big change in concentration

Extracellular (EC) – 45% of body water ( main cation Na⁺ ,Ca⁺)

1. Intestinal fluid 36%
2. blood plasma 7%
3. Transcellular 2%

Question 2

Define osmosis, diffusion and permeability; explain mechanisms of solute exchange across cell membranes, recall examples and explain whether the process is active or passive

Answer 2

Osmolarity is the measure of concentration of all the particles in a solution.

Osmosis moves water to the area of higher osmolarity (=area of lower water concentration)

Diffusion moves solutes to an area of lower solute concentration

Permeability: how easily a solute crosses a membrane.

Mechanism of solute exchange;

1. Passive (down the conc.. gradient) via
   
   • Lipid // pores/channels // carriers
2. Active
   
   • Primary active transport (against conc. gradient)
   • Secondary active transport (energy from passive used to move solute against conc.)
3. Exocytosis – peptide hormones from endocrine glands
4. Endocytosis – nerve growth factors entering

Question 3

Explain the difference between tonicity and osmolarity, and explain how this may impact on the integrity of cells

Answer 3

Osmolarity is the concentration of all the particles in a solution

Tonicity defines the “strength” of a solution as it affects final cell volume.

• Tonicity depends on both cell permeability and osmolarity.
• Osmolarity does not depend on cell permeability.
• Tonicity depends on both the extracellular solution and also on the cell types.

HYPERTONIC –> in>out and cell explodes

HYPOTONIC–> out>in and cell shrinks

ISOTONIC–> in=out

Question 4

Define oedema, recall the causes of oedema, and explain the main types of exchange across the capillary wall

Answer 4

Plasma leak-out;

Each day 8L of blood plasma leak out.

Osmotic pressure; due to plasma proteins (colloid osmotic pressure COP)

Hydrostatic pressure; due to blood pressure (HP)

HP>COP–>leak out

HP<cop--> flow into vessels</cop-->

HP=COP–> normal vessel

Oedema; is defined as the swelling of tissue due to accumulation of excess interstitial fluid

• Imbalance of forces causing fluid to move between blood plasma, interstitium and lymphatic vessels and being drained from lymphatic vessels. When likage exceeds the capacity of the lymphatics–> excess likage
• Increased permeability of capillary walls to plasma proteins (endothelial cells and clefts between)

1. Inflammatory oedema; due to inflamation (ex. mosquito bite)
2. Hydrostatic oedema; due to high blood pressure

Main types of exchange through capillary wall;

1. Small, water-soluble substances pass through the clefts between cells
2. Lipid-soluble substances pass through the endothelial cells
3. Exchangeable proteins are moved across endothelial cells by vesicles