Body Fluids and Circulation

The formed elements of blood are:

- Erythrocytes (RBCs) – they mainly transport respiratory gases like oxygen and carbon dioxide.
- Leucocytes (WBCs) – they mainly defend the body against infections.
- Platelets (thrombocytes) – they help in blood clotting.

Plasma proteins have important functions:

- Fibrinogen: needed for blood clotting.
- Globulins: involved in defense mechanisms of the body.
- Albumins: help in maintaining osmotic balance of blood.

| Column I | Column II |
|---|---|
| (a) Eosinophils | (iii) Resist Infections |
| (b) RBC | (v) Gas transport |
| (c) AB Group | (ii) Universal Recipient |
| (d) Platelets | (i) Coagulation |
| (e) Systole | (iv) Contraction of Heart |

Blood is called a connective tissue because it has a fluid matrix, plasma, in which the formed elements are suspended. It connects different parts of the body by transporting nutrients, oxygen, hormones and wastes from one place to another.

Differences between lymph and blood:

- Blood is red in colour because it contains haemoglobin in RBCs, whereas lymph is colourless.
- Blood contains RBCs, WBCs and platelets; lymph mainly contains lymphocytes and lacks RBCs and platelets.
- Blood carries oxygen, nutrients and wastes through blood vessels; lymph helps in transport of nutrients, hormones and fats, and returns tissue fluid to veins.
- Blood has a higher protein content; lymph has less protein than blood.

Double circulation means that blood passes through the heart twice in one complete cycle: once through the pulmonary circulation and once through the systemic circulation.

Significance:
- It keeps oxygenated and deoxygenated blood separate.
- This allows efficient supply of oxygen to body tissues.
- It helps maintain a high pressure in systemic circulation, making transport of substances more effective.

The question asks for differences between four pairs:

### (a) Blood and Lymph
- Blood is red and contains RBCs, WBCs and platelets; lymph is colourless and mainly contains lymphocytes.
- Blood transports gases, nutrients and wastes; lymph transports nutrients, hormones and fats and returns tissue fluid to blood.

### (b) Open and Closed System of Circulation
- In an open system, blood is pumped into body cavities or sinuses.
- In a closed system, blood always flows through blood vessels.
- Closed circulation allows more precise regulation of flow.

### (c) Systole and Diastole
- Systole means contraction of heart chambers.
- Diastole means relaxation of heart chambers.

### (d) P-wave and T-wave
- P-wave represents depolarisation of the atria, leading to atrial contraction.
- T-wave represents repolarisation of the ventricles, i.e. return of ventricles to normal state.