Transportation in humans: heart, blood, lymph and blood pressure
The four-chambered heart pumps blood through arteries, veins and capillaries. Blood carries food, oxygen, hormones and wastes; lymph returns tissue fluid and fights germs.
Arteries, veins and capillaries
| Feature | Arteries | Veins | Capillaries |
|---|---|---|---|
| Carry blood | Away from the heart to the body | From the body back to the heart | Between arteries and veins, close to every cell |
| Kind of blood | Oxygen-rich, except the pulmonary artery | Oxygen-poor, except the pulmonary vein | Give oxygen and food to cells, and take away wastes |
| Walls | Thick and elastic, to bear high pressure | Thinner | Very thin, one cell thick |
| Valves | Absent | Present, to keep blood flowing one way | Absent |
Blood and lymph: the parts and their jobs
| Part | What it is like | Job |
|---|---|---|
| Plasma | The pale yellow fluid part of blood | Carries dissolved food, carbon dioxide, hormones, wastes and medicines |
| Red blood cells (RBC, erythrocytes) | Round, with no nucleus; contain the red pigment haemoglobin | Carry oxygen to the tissues and bring back carbon dioxide |
| White blood cells (WBC, leucocytes) | Colourless, irregular in shape | Fight germs by eating them or by making antibodies |
| Platelets (thrombocytes) | Tiny pieces of cells, with no nucleus | Help blood to clot at a cut |
| Lymph | Light yellow fluid in lymph vessels; flows one way, from the tissues towards the heart | Its lymphocytes fight germs; it returns tissue fluid and proteins from the tissues to the blood (one line of your NIOS lesson puts this the other way round) |
ABO blood groups and blood transfusion
| Blood group | Antigen on RBC | Antibody in plasma | Can give blood to | Can receive blood from |
|---|---|---|---|---|
| A | A | b | A, AB | A, O |
| B | B | a | B, AB | B, O |
| AB | A and B | None | AB only | A, B, AB, O (universal recipient) |
| O | None | a and b | A, B, AB, O (universal donor) | O only |
Heartbeat, blood pressure and disorders
- The heart's chambers contract and relax in a rhythm, the heartbeat, about 72 times a minute. An ECG (electrocardiogram) shows if the beat is abnormal.
- The left ventricle pumps oxygen-rich blood into the largest artery, the aorta, which carries it to the whole body.
- Blood pressure is the push of blood on the walls of arteries. It is highest, about 120 mm of Hg, when the ventricles contract, and about 80 mm of Hg when they relax.
- Blood transfusion (giving blood from a donor) works only when the groups match. Wrong blood makes the red cells clump together (agglutination), which can kill.
- Heart attack: the arteries that feed the heart muscle grow thick with age or too much fatty food, so the heart cannot beat in rhythm. It needs urgent medical help.
- Hypertension is high blood pressure. It causes headache, dizziness and tiredness. A proper diet, exercise, medicines and a calm mind help.
- Anaemia: too little haemoglobin, so the person looks pale and weak; iron in the diet helps. Leukaemia is blood cancer: the bone marrow makes too many WBCs and few RBCs.
Activity: count your pulse rate
Each heartbeat sends a jerk along the arteries. This jerk is the **pulse**. Feel it where an artery lies near the skin: the **radial artery** at the wrist, or the artery in the neck below the jaw.
- 1Sit quietly for five minutes.
- 2Turn one palm up. Press two fingers, not the thumb, gently on the thumb side of the wrist until you feel the beat.The thumb has a pulse of its own, which can confuse the count
- 3Using a watch with a seconds hand, count the beats for 15 seconds.
- 4Multiply by 4 to get beats per minute. For example, 18 beats in 15 seconds gives 18 × 4 = 72 beats a minute.
- 5Skip or climb stairs for one minute, then count again and compare.
- 6★Observe: the pulse is about 72 a minute at rest and rises after exercise. The pulse rate is the same as the heart rate.
★ key step
How to draw 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 (auricle) and a larger lower ventricle. Draw the left ventricle wall the thickest.
- Draw small flaps, the valves, between each atrium and its ventricle: the tricuspid valve on the right and the bicuspid valve on the left.
- 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 path of blood: vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body. Label every part.
Blood pressure checks at clinics and health camps across India catch hypertension early. Less salt in pickles and papad, a daily walk and a calm mind help keep the heart healthy.
2 marks: “Explain why a person of group O can give blood to all groups, while a person of group AB can receive blood from all groups.” O red cells carry no A or B antigen, so the receiver's antibodies do not clump them: O can be given to all groups. AB plasma has no a or b antibody, so an AB person can receive blood of any group.
2 marks: “Write two differences between arteries and veins.” Arteries carry blood away from the heart and have thick, elastic walls. Veins carry blood back to the heart, have thinner walls and have valves. Arteries mostly carry oxygen-rich blood, except the pulmonary artery.
5 marks: “Draw a labelled diagram of the human heart. Trace the path of blood through it, and state the normal blood pressure of a healthy young adult.” Labelled heart: atria, ventricles, septum, valves, aorta, pulmonary artery and veins, vena cava. Path: vena cava → right atrium → right ventricle → pulmonary artery → lungs → pulmonary veins → left atrium → left ventricle → aorta → body. Normal pressure about 120/80 mm of Hg.
Arteries go Away from the heart; Veins come back with Valves.