Transportation in human beings
Blood carries food, oxygen and wastes. In double circulation, blood passes through the four-chambered heart twice in each cycle, moving through arteries, veins and capillaries.
Draw it: double circulation
- back to Lungs
Blood passes through the heart twice in one cycle. The right and left sides are kept apart, so oxygen-rich and oxygen-poor blood never mix. Valves stop blood flowing backwards.
Arteries, veins and capillaries
| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| Carry blood | Away from the heart to the organs | From the organs back to the heart | Between arteries and veins, close to every cell |
| Walls | Thick and elastic | Thinner | One cell thick |
| Blood pressure | High | Low | Low |
| Valves | Absent | Present, to keep blood flowing one way | Absent |
Hearts of different animals
| Animal group | Chambers | Circulation |
|---|---|---|
| Fish | 2 | Single: blood passes through the heart once per cycle and picks up oxygen in the gills |
| Amphibians and many reptiles | 3 | Some mixing of oxygen-rich and oxygen-poor blood is tolerated |
| Birds and mammals | 4 | Double, with no mixing: needed for high energy use and a constant body temperature |
Blood, platelets, lymph and blood pressure
- Plasma carries food, CO₂ and nitrogenous wastes in dissolved form; red blood cells carry oxygen.
- Platelets help the blood to clot at a cut, plugging the leak so blood is not lost.
- Lymph (tissue fluid) leaks out through pores in capillary walls into the spaces between cells. It is like plasma but colourless and has less protein.
- Lymph flows in lymphatic vessels into large veins. It carries digested fat from the intestine and drains extra fluid back into the blood.
- Blood pressure is the force of blood on the wall of a vessel, measured with a sphygmomanometer: about 120 mm of Hg (systolic) and 80 mm of Hg (diastolic). Hypertension (high blood pressure) is caused by narrowing of arterioles.
How to draw the sectional view of the human heart
- Draw a heart shape and divide it down the middle by a wall, the septum. The heart's left side goes on your right, as if the person faces you.
- Divide each half into a smaller upper atrium and a larger lower ventricle. Draw the left ventricle wall the thickest.
- Draw small flaps, the valves, between each atrium and its ventricle.
- At the top, draw the aorta arching out of the left ventricle and the pulmonary artery leaving the right ventricle.
- Draw the vena cava entering the right atrium and the pulmonary veins entering the left atrium.
- Add arrows for the direction of blood flow and label every part.
Blood pressure checks with a sphygmomanometer are common at clinics and health camps across India. Less salt in pickles and papad, and regular exercise, help keep blood pressure normal.
2 marks: “Why is it necessary to separate oxygen-rich and oxygen-poor blood in mammals and birds?” Separation gives a very efficient supply of oxygen. Birds and mammals need a lot of energy and must keep a constant body temperature.
3 marks: “Give three differences between arteries and veins.” Arteries carry blood away from the heart, veins towards it; arteries have thick elastic walls, veins thinner; arteries have high pressure and no valves, veins low pressure and valves.
5 marks: “Draw a sectional view of the human heart and describe how blood flows through it in double circulation.” Labelled heart; lung circuit (right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins); body circuit (left atrium → left ventricle → aorta → body → vena cava); valves; why double circulation is useful.
Arteries go Away from the heart; Veins come back with Valves.