Exam practice

Red blood cells contain a red pigment, hemoglobin, whose iron-containing part gives it its color. There are so many red cells (about 5 million in each cubic millimeter) that the whole blood looks red.

White blood cells defend the body: they find germs that get in, swallow and destroy them, and make antibodies against them. Like soldiers guarding a country, they protect the body from infection and give it immunity.

The auricles only push blood a short way down into the ventricles. The ventricles must pump blood out of the heart, to the lungs or all round the body, at high pressure. That needs much more force, so their walls have more muscle.

The right ventricle pumps blood only to the lungs, which are close by. The left ventricle pumps blood through the aorta to every part of the body, from head to toe, which needs a much higher pressure. So it has a thicker, stronger wall.

Blood in the arteries is under high pressure from the heart, which keeps it flowing forward, so no valves are needed. By the time blood reaches the veins its pressure is low and it flows slowly, often uphill (from the legs), so it could flow backwards. Valves in the veins let it flow only towards the heart.

An anemic person has too few red cells or too little hemoglobin, so the blood carries less oxygen. When they walk, their muscles need more oxygen to release energy from food, but don’t get enough. So they tire quickly and get out of breath.

Blood in arteries flows at high pressure, so a cut artery would lose a lot of blood very quickly; lying deep, protected by muscle, they are safer from injury. Veins have low pressure, so an injury to one is less dangerous, and many lie near the surface (where pressing muscles also help push their blood along).

If a patient gets red cells carrying an antigen (A, B or D) that their own cells don’t have, the patient’s antibodies attack those cells: they clump together and burst inside the blood vessels, which can block the vessels and kidneys and kill the patient. Testing the blood groups (and cross-matching) makes sure the donor’s blood is compatible.

In hemophilia, an inherited disease, the blood lacks one of the clotting proteins needed to turn fibrinogen into a net of fibrin. Without that net, a firm clot can’t form, so bleeding goes on for a long time. (A low platelet count also slows clotting, but that condition is called thrombocytopenia.)

1. Heart: a four-chambered muscular pump in the chest, between the lungs. Its right side pumps deoxygenated blood to the lungs; its left side pumps oxygenated blood to the body.
2. Blood vessels: arteries carry blood away from the heart, capillaries exchange substances with the cells, and veins bring blood back to the heart.
3. Blood: a liquid tissue of plasma (55 %) with red blood cells, white blood cells and platelets (45 %). It carries oxygen, food, hormones and wastes, fights germs and clots wounds.

1. Transport: carries oxygen from the lungs to the cells and carbon dioxide back; carries digested food, hormones, enzymes and wastes.
2. Regulation: keeps the body temperature, the amount of water and salts, and the pH steady.
3. Protection: white blood cells and antibodies fight germs; platelets and fibrinogen clot the blood to stop bleeding.

At a cut, the blood vessel narrows, and platelets stick to the damaged edge and to each other to form a plug. They release chemicals that turn the plasma protein fibrinogen into threads of fibrin. The fibrin forms a net that traps blood cells, making a clot that seals the wound, so the bleeding stops.

She probably has anemia: too few red blood cells or too little hemoglobin, often from a lack of iron in her diet. Her blood can’t carry enough oxygen, so when she walks her muscles run short of oxygen and tire quickly, and she breathes hard to try to get more. She should see a doctor, and eat iron-rich food (green leafy vegetables like saag, beans, meat, eggs).

130 mmHg is the systolic pressure, when the ventricles contract; 90 mmHg is the diastolic pressure, when they relax. The normal adult reading is about 120/80 mmHg, so both numbers are higher than normal. The systolic pressure (130) is raised but below 140; the diastolic pressure (90) has reached the limit for high blood pressure: doctors (and the WHO) count 140 or more or 90 or more as hypertension. If it stays like this when measured again, the person has high blood pressure and should see a doctor, eat less salt and oily food, and exercise regularly.

A sphygmomanometer: an inflatable cuff wrapped round the upper arm, with a gauge (or a digital meter) that reads the pressure in mmHg.

The patient’s plasma has antibodies against the A and B antigens their own red cells lack (and Rh-negative people can make anti-D). If the donor’s red cells carry such an antigen, the antibodies make them clump and burst inside the patient’s blood vessels, a reaction that can be fatal. Checking (and cross-matching) makes sure the blood is compatible.

These are the symptoms of diabetes: too much glucose in the blood (hyperglycemia), because her body makes too little insulin or doesn’t respond to it. The kidneys pass out the extra sugar with a lot of water (frequent urination, thirst); high sugar damages the nerves (numbness); and her cells can’t use the glucose for energy (tiredness). She should have her blood sugar tested.

Effects: the heart must work harder, and over time the walls of the arteries are damaged and narrowed. This can lead to heart attack, heart failure, stroke (a burst or blocked blood vessel in the brain), kidney damage and damage to the eyes. It can cause headaches, nosebleeds, breathlessness, tiredness and sleeplessness, though often there are no symptoms.

Prevention: eat less salt and oily food; eat a balanced diet with plenty of vegetables and fruit; exercise daily; keep a healthy weight; don’t smoke or drink alcohol; manage stress (yoga, meditation, pranayama, recreation); and have the blood pressure checked regularly.

• The digestive system breaks food into simple, soluble substances such as glucose, which are absorbed into the blood.
• The respiratory system takes oxygen into the lungs, where it passes into the blood.
• The circulatory system carries both glucose and oxygen to every cell. There, respiration uses them to release energy, and makes carbon dioxide, which the blood carries back to the lungs to be breathed out.

Without digestion there would be no food for the cells; without breathing, no oxygen to release its energy; and without circulation, neither would reach the cells. The systems depend on each other.

By measuring it with a sphygmomanometer (manual or digital). The cuff is pumped up round the upper arm to squeeze the artery shut, then let down slowly; the pressure when the pulse sounds start is the systolic pressure, and when they stop, the diastolic. A reading of 140/90 mmHg or more, found more than once, means high blood pressure; a reading below 90/60 mmHg means low blood pressure. Because high blood pressure often has no symptoms, regular checking is the only sure way to find it.

They show how a medicine taken by mouth reaches the place where it is needed: it is swallowed, absorbed from the stomach and small intestine into the blood (digestive system), and carried by the blood round the body to the knee (circulatory system). So the digestive and circulatory systems take part.
Without the circulatory system, the medicine could only spread by diffusion, the slow spreading of molecules from where there are many to where there are few. Diffusion works over a fraction of a millimeter, but over the distance from the stomach to the knee it would take years. In practice the medicine would not reach the knee in time to help. That is exactly why large animals need a circulatory system.

X is the red blood cell, Y the white blood cell, Z the platelet.

• i.A shortage of X, the red blood cells, causes anemia.
• ii.A large, abnormal rise in Y, the white blood cells, can mean leukemia (blood cancer), in which abnormal white cells crowd out the normal blood cells. (A smaller rise usually just means the body is fighting an infection.)
• iii.Z, the platelets, are below normal. A low platelet count is called thrombocytopenia. Some books call this hemophilia, but hemophilia is an inherited lack of a clotting protein, with normal platelets. An answer that is right either way: “Z, the platelets: thrombocytopenia. (Slow clotting with normal platelets is hemophilia, a missing clotting protein.)”

First an ECG: it is quick and shows whether the heart muscle is short of blood or has been damaged (along with a blood test for troponin). If it points to a heart attack, an angiogram (angiography) is done: a dye is put into the coronary arteries and an X-ray taken, which shows exactly which artery is narrowed or blocked and how badly. Then the doctors can open it at once with angioplasty and a stent, or plan bypass surgery.

Draw Figure 5.1. Blood flows through the heart twice in one round (double circulation):

1. Pulmonary circulation: the right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs; there it gives up carbon dioxide and takes in oxygen; the pulmonary veins bring the oxygenated blood to the left auricle, which passes it into the left ventricle.
2. Systemic circulation: the left ventricle pumps oxygenated blood into the aorta, which branches into arteries, arterioles and capillaries in every organ. In the capillaries the blood gives oxygen and food to the cells and takes their carbon dioxide and wastes. Venules and veins bring the deoxygenated blood to the vena cavae, which empty into the right auricle, which passes it to the right ventricle, and the cycle repeats.

Valves keep the blood moving one way.

1. Exercise regularly and keep a healthy weight.
2. Drink enough water, a little at a time, many times a day.
3. Avoid alcohol (especially beer) and smoking.
4. Eat less purine-rich food: fatty red meat, organ meat (liver, kidney), and seafood; avoid sugary drinks.
5. Eat cherries and other fruit, and plenty of vegetables.
6. Get diseases that harm the kidneys, like diabetes, treated.

Draw Figure 5.7 and label it. The heart has four chambers: two upper, thin-walled auricles (right and left) that receive blood, and two lower, thick-walled ventricles that pump it out. A muscular septum separates the right side (deoxygenated blood) from the left (oxygenated blood); the left ventricle has the thickest wall.

Vessels: the superior and inferior vena cava bring deoxygenated blood from the body to the right auricle; the pulmonary artery takes it from the right ventricle to the lungs; the pulmonary veins bring oxygenated blood from the lungs to the left auricle; the aorta takes it from the left ventricle to the body.

Valves: the tricuspid valve (right auricle → right ventricle), the bicuspid or mitral valve (left auricle → left ventricle), the pulmonary valve (right ventricle → pulmonary artery) and the aortic valve (left ventricle → aorta) keep blood flowing one way.

A heart attack happens when the blood supply to part of the heart muscle is cut off. Over years, plaque of fat and cholesterol builds up in the walls of the coronary arteries, narrowing them; if a plaque cracks, a blood clot forms on it and blocks the artery, and the muscle beyond it dies for lack of oxygen.
What makes this more likely: age (men over 45, women over 55), smoking and chewing tobacco, high blood pressure, high cholesterol and triglycerides, diabetes, a family history of heart attacks, lack of exercise and an unhealthy diet (trans fat, salt, sugar, animal fat, processed food), long-term stress, and drugs such as cocaine.

Blood vessels don’t show on an ordinary X-ray. In angiography, a thin tube (catheter) is passed through an artery in the wrist or groin up to the heart, and a dye that blocks X-rays (contrast medium) is injected into the coronary arteries while a live X-ray is taken. The X-ray picture of the arteries is the angiogram.
Importance: it shows exactly where an artery is narrowed or blocked, and how badly. This tells the doctors which treatment is needed (medicines, angioplasty with a stent, or bypass surgery), and the blockage can often be opened with a stent straight away, through the same tube.

Coronary artery bypass surgery is called open-heart surgery because the chest is opened. It is done when coronary arteries are badly blocked. The surgeon takes a healthy blood vessel from the patient’s own body (a vein from the leg or an artery from inside the chest wall) and sews one end to the aorta and the other to the coronary artery beyond the blockage. Blood then flows around the blockage through this new path (a bypass graft), and the heart muscle again gets oxygen and food. It is a major operation, usually planned, though sometimes done as an emergency during a heart attack.

The normal count is 4,000 to 11,000 per mm³.

• If his count is well above 11,000, his body is probably fighting an infection: he may have a fever, pain, swelling or pus where the infection is, and feel weak. A very high count of abnormal white cells could be leukemia, with tiredness, paleness, easy bruising and frequent infections, because the abnormal cells crowd out the normal blood cells.
• If his count is below 4,000 (leucopenia), he has fewer germ-fighters, so he will catch infections easily and take long to get better.

Yes. Fibrinogen is the protein that forms the fibrin net of a blood clot, and it also makes the blood thicker. Too much of it makes the blood clot too easily, even inside the blood vessels. A clot can block a coronary artery (heart attack) or a brain artery (stroke), or a deep vein in the leg. Thicker blood also flows less easily, so the heart has to work harder. So a high fibrinogen level raises the risk of heart and circulation problems.

• i.X. A shallow cut that won’t stop bleeding means the blood isn’t clotting.
• ii.Y. Blood coming out under high pressure (spurting) means an artery is cut; arteries lie deep and carry blood at high pressure.
• iii.Y’s. A cut artery loses blood very fast because of its high pressure, and a person can lose a dangerous amount in minutes. Z’s cut was shallow and clotted normally by itself.

• i.Systemic circulation: blood goes from the left ventricle to an organ of the body (the kidney) and back to the heart.
• ii.Arteries carry the blood from the left ventricle to the kidney (aorta → renal artery). Veins carry it from the kidney back to the heart (renal vein → inferior vena cava).

Note: the map has a mistake. Blood from the kidney returns to the right auricle, not the left auricle. The left auricle receives blood only from the lungs.

(i) 15 is the aorta; 18 is the superior vena cava.

• ii.11 is the bicuspid (mitral) valve: it lets blood pass from the left auricle into the left ventricle, and shuts when the ventricle contracts so blood can’t flow back into the auricle. 13 is the pulmonary valve: it opens to let blood from the right ventricle into the pulmonary artery, and shuts when the ventricle relaxes so blood can’t flow back into it.
• iii.4 is the pericardium. Without it, the heart would not be protected from shocks and injuries, and with no pericardial fluid it would rub against the lungs and chest wall with every beat.
• iv.6: right auricle; 7: left auricle; 8: right ventricle; 9: left ventricle.

Use these figures as your guide, and label every part:

• i.External structure: Figure 5.6.
• ii.Internal structure: Figure 5.7.
• iii.Arteries, veins and capillaries: Figure 5.13.
• iv.Pulmonary circulation: the top loop of Figure 5.1 (right ventricle → pulmonary artery → lungs → pulmonary veins → left auricle).
• v.Systemic circulation: the bottom loop of Figure 5.1 (left ventricle → aorta → body → vena cavae → right auricle).

Tips: draw the heart as you see it from the front, so its right side is on your left; color oxygenated blood red and deoxygenated blood blue; show the direction of flow with arrows; and draw the left ventricle’s wall thickest.