Question

QUESTION 4
A. Write about the following:
i. Cell membranes are composed primarily of phospholipids and proteins.
ii. The refractory period in action potential
iii. The role of body water
B. Explain the following causes of Edema
iv. Malnutrition and Capillary wall damage
v. Fluid accumulation in the lungs
vi. Left ventricular heart failure and Congestive heart failure
vii. Glomerulonephritis and Nephrotic syndrome
(All 7 points x 5= 35Marks)

Answer 1

1) Cell membrane is composed of phospholipids and protein. The head end of the phospholipids is positively charged and quite soluble in water that is polar or hydrophilic. The tail end consists of two chains of fatty acids or steroid radical of cholesterol. It is quite insoluble in water therefore it is nonpolar or hydrophobic. This lipid molecules are arranged as bilayer in such a way that their nonpolar hydrophobic tail ends are directed towards the centre of the membrane whereas their polar hydrophilic head ends are directed outwards on either side of the membrane. This lipid bilayer of the cell membrane makes it a semi permeable membrane which constitutes a major barrier for the water soluble molecules like electrolytes urea and glucose. set syllabus substances like oxygen carbon dioxide fatty acids can pass through the membrane with ease.

Proteins are arranged as:

• Transmembrane proteins: which function as G protein coupled receptors or Na K ATPase pump.
• Peripheral proteins: Proteins on inner side of membrane function as enzymes. Outer surface proteins can serve as cell adhesion molecules.

2) The refractory period is the period in which the cell actually rests and don't undergo any other action potential. It is of two types:-

• Absolute refractory period: It ranges from onset of firing to the 1/3 of repolarization. In this period, whatever strength or whatever stimulus is given, the cell will not be stimulated.
• Relative Refractory period: it ranges from 1/3 of repolarization till the acquirement of resting membrane potential. In this period, only supramaximal strength of stimulus can generate an action potential.

3) The human body is composed of 60% water in males and 50% water in females due to greater amount of adipose tissue in females. It is divided into two compartments:- intracellular fluid compartment and extracellular fluid compartment.

Compartment	Volume (L)	Body weight (%)	Body water (%)
Total body water	42	60	100
Intracellular fluid	28	40	67
Extracellular fluid Plasma (25%) Interstitial fluid, transcellular fluid and mesenchymal tissue (75%)	3.5 10.5	5 15	8 25

Total body water volume can be measured by injecting a marker which will be evenly distributed in all the compartments of a body fluid. Such markers include Deuterium oxide (D2O), Tritium oxide and Aminopyrine.

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