Lecture 6- Body Water And Cell Membranes

Question 1

Define the major compartments of body water

Answer 1

Water makes up 60% of total body weight
-66% of TBW is the intracellular fluid (fluid inside cells)
-33% of total body water is in the extracellular fluid (fluid outside cells)
20% of above is plasma in the ECF
80% of extracellular fluid is in the interstitial fluid ECF outside the blood. Refer to slide 12 of PowerPoint

Question 2

Substances dissolved in liquid are called?

Answer 2

Solutes

Question 3

Liquid in which they dissolve are called?

Answer 3

Solvents

Question 4

Combination of solutes dissolved in solvents are called?

Answer 4

Solution

Water acts as a solvent for the many solutes found in the body

Question 5

Solutes can be electrolytes or non electrolytes

What is the difference between electrolytes and non-electrolytes?

Answer 5

Electrolytes:
-dissociate into charged ions in water
-ionic bonds
-can conduct electricity
-include inorganic salts, inorganic and organic acids and bases, some proteins Na+ Cl-
Non-Electrolytes
-don't dissociate in water
-covalent bonds
-aren't electrically charged 
-mostly organic molecules 

In an animal electrolytes have more osmotic activity than non-electrolytes because each electrolyte dissociates into at least two ions

Question 6

How do you work out the osmolarity of a solution

Also why can’t you often refer to it as concentration

Answer 6

Osmolarity= total no. Of particle/liters of solution

Question 7

What is the 4 functions of the cell membrane?

Answer 7

1. Physical isolation
2. Regulation of exchange with environment eg movement of ions, gases and water
3. Communication between cell and environment eg changes in ECF detected by receptors
4. Structural support- maintains cell shape via intracellular proteins (cytoskeleton)

Question 8

Describe the structure of the cell membrane and draw it

Answer 8

Fluid mosaic model

• thin phospholipid bilayer (7-8nm)
  
  • polar phosphate heads face the outer surfaces of membrane
  • non polar tails of lipid face inwards
• other membrane lipids and proteins are inserted partly/completely throughout the membrane (mosaic)
• imbedded elements can move laterally in the membrane-it is a dynamic fluid structure
• there are peripheral and integral proteins

Question 9

Which out of red blood cells, myelin membrane (nerve cells) or inner mitochondrial membrane has the most protein in their structure, the most lipid in their cell and the most cholesterol in their structure?

Answer 9

Red blood cells have more protein than lipid but have the most cholesterol out of the three.
Nerve cells have the most lipid
Mitochondria have most protein
In general, more metabolically active cells have more protein in their membranes.

Question 10

What are the major types of membrane proteins and what are their functions?

Answer 10

1. Integral proteins
   - tightly bound in phospholipid bilayer
   - extended into and through layers
   - include membrane channels and transporters
2. Peripheral proteins
   - attach loosely to integral proteins or phospholipid head
   - can be removed without disrupting membrane integrity
   - include enzyme and structural proteins

Question 11

Membrane proteins main functions are:

Answer 11

1. Transporters: allows molecules that can’t diffuse across membrane to enter cell eg kidneys to reabsorb water via aquaporins and glucose
2. Structural components: connects membrane and cytoskeleton to maintain shape of cell
3. Receptors: activate biomechanical pathways in response to binding of chemicals called ligands (transmitters or hormones)
4. Enzymes: catalyst reactions on internal or external surface of the cell

Question 12

What are glycocalyx cells? What do they function as?

Answer 12

• carbohydrate containing molecules, with branching sugar groups, they form a layer called the glycocalyx on the extracellular membrane surface.
• carbohydrate chains form on either membrane lipids (glycolipids) or integral membrane proteins (glycoproteins)
• the have an important function which is cell recognition ie immune response to bacteria. The pattern of sugars is cell type specific

Question 13

There is significant structural variation between different regions of the same membrane. Eg lips rafts, explain this.
What is homeoviscous adaptation?

Answer 13

Lipid rafts are thickened regions of membrane containing higher density of cholesterol, glycolipids and integral proteins.
Homeoviscous adaptation means that the lipids in the membrane can change their composition and position which keeps membrane fluidity relatively constant in changing conditions

Question 14

Explain the clinical applications of liposomes

Answer 14

• new advance in drug delivery
• centre of liposomes filled with drugs, antibodies, or DNA fragments
• liposomes act to reduce toxicity and improve efficacy of drug
• they release the drug in a pulsatile manner

Question 15

If you have a saline drip put into your arm, which body compartment will saline enter first?

Answer 15

?

Question 16

Tissue dehydration involves loss of fluid from which body compartments

Answer 16

The 10% loss of body weight caused a decrease in TBW by 17% from the control value; 41% of this loss was from ICF, 47% from ISF, and 12% from
Answer: interstitial fluid

Question 17

Identify one difference in the solute composition of plasma and interstitial fluid?

Answer 17

Plasma and interstitial fluid have similar composition except plasma has more proteins (plasma proteins)