Circulatory System

Blood and the Circulatory system The circulatory system is composed of blood + blood vessels + the heart.

Blood: plasma + suspended solids (red blood corpuscles, white blood cells, platelets)

Blood vessels: arteries, capillaries, veins.

Heart: double pump keeping the blood flowing without stop

Functions of the blood circulatory system

1. Transport: O2 and food nutrients to all cells & transport of wastes (CO2, urea) to the lungs, kidneys.

2. Defence: protection against disease-causing organisms and cancer.

3. Temperature control: by altering blood flow through the skin.

4. Communication: transport of hormones to their target tissues.


The plasma is the liquid part of the blood making up 50% of the volume of the blood.

Plasma is a complex protein solution with nutrients, vitamins, minerals, hormones and wastes also in solution.

Red blood corpuscles are tiny biconcave discs. No nucleus. Loaded with haemoglobin. Red colour. Pick up oxygen at the lungs & transport the oxygen to the other tissues and organs. Made in bone marrow. Survive for 120 days. Recycled by liver & spleen. 5 million per mm3 .Iron (Fe) is needed to make haemoglobin.

White blood cells have no colour. A Nucleus. Defence against disease-causing organism and cells that have turned cancerous. Kill the disease-causing organisms and cancer cells by engulfing them and by secreting defence proteins called antibodies. Made in bone marrow and special glands. Live for several hours to many years. About 8,000 per mm3.

Platelets are fragments of special bone marrow cells. Loaded with blood clotting chemicals. Seal breaks in blood vessels to stop blood loss and seal wounds to prevent entry of disease causing organisms. About 250,000 per mm3 and survive for about 10 days.

Blood vessels

Arteries Capillaries Veins

carry blood Away from the heart

Thicker wall than a vein – more connective tissue and muscle.

No valves along their length.

The pulmonary artery carries deoxygenated blood from the right side of the heart to the lungs for the excretion of carbon dioxide and the uptake of oxygen.

The aorta carries oxygenated blood from the left side of the heart to the organs of the body to deliver oxygen and food nutrients plus pick up carbon dioxide.

connect arteries to veins

Very thin-walled one cell thick only) and extremely narrow. No valves. Exchange between tissue cells and blood takes place at the capillaries. The capillaries are where the real work of the blood system is done.

Thinner wall than an artery Wider lumen. Valves along their length.

Valves prevent the backflow of blood so the blood can only move in one direction

The pulmonary veins carry oxygenated blood from the lungs to the left side of the heart for pumping to all the organs of the body.

The two vena cava carry deoxygenated blood from all the organs of the body to the right side of the heart for pumping to the lungs.

The Heart

The heart is a double pump in the chest cavity between the lungs.

1. Right side: collects deoxygenated blood and drives it to the lungs.

Left side: collects oxygenated blood from the lungs and drives it to all parts.

LORD – left oxygenated, right deoxygenated.

2. Composed of tireless cardiac muscle.

3. Each side is composed of two chambers – smaller atrium and larger ventricle. The ventricles can hold from three to four times the amount of blood as the atria.

4. Pulmonary artery from right ventricle carries deoxygenated blood to the lungs.

5. Pulmonary veins carry oxygenated blood from the lungs to the left atrium.

6. Aorta carries oxygenated blood from the left ventricle to all areas of the body.

7. Vena Cava carries deoxygenated blood from everywhere to the right atrium.

8. Cuspid Valves: prevent blood returning to the atria when the ventricles contract –

so all the blood enters the arteries.

9. Semilunar Valves: prevents blood returning to the ventricles when the arteries expanded with blood recoil elastically – so the blood continues to move along the artery away from the heart.

10. Much thicker left Ventricle wall: more muscle because the blood needs a push 8

times stronger to force it the greater distance and through more blood vessels.

Passage of Blood Through the Heart

The left and right sides of the heart fill and empty at the same time and collect and pump the same volume of blood.

Blood flows from the veins into the atria, push open the cuspid valves, flow into and fill the ventricles and then fill the atria. The atria then contract topping up the ventricles with extra blood. Then the ventricles contract pumping blood out of the heart into the arteries. The right ventricle pumps deoxygenated blood towards the lungs in the pulmonary arteries. The aorta carries the oxygenated blood from the left ventricle to all the organs of the body.

To Demonstrate the Effect of Exercise and Rest on the Pulse Rate

Method: measure the pulse rate in an artery close to the body surface e.g. pulse in the wrist.

1. When relaxed and at rest place the index and middle finger of one hand on the inside of the wrist close to the base of the thumb of the other hand.

2. Feel the rhythmic beat against your finger.

3. Each ‘beat’ is a pressure wave ,each wave is caused by a contraction of the left ventricle.

4. The pulse rate is the same as the heart rate.

5. Measure the pulse rate: count the ‘beats’ in 15 seconds and multiply by 4. This is the pulse rate - pulses per minute.

6. Repeat the measurement twice more and take the average.

7. Carry out gentle exercise for three minutes e.g. jogging on the spot and then measure and record the pulse rate. Each minute after the exercise record measure and record the pulse rate to discover the effect of rest on the pulse rate.

8. Repeat step 7 twice more and take the average of the pulse rate due to gentle exercise.

9. Now do more vigorous exercise measuring and recording the pulse rate as before for gentle exercise and the rest stage after exercise. Again, three bouts of exercise must be recorded and the average results calculated.

Exercise increases the pulse rate, the harder the exercise the higher the pulse. Rest reduces the pulse back to normal.

Why Exercise Increases Pulse and Breathing Rate

Exercise needs more energy and so the rate of respiration of the muscles must increase. The harder working muscles need more oxygen, make more carbon dioxide and produce more heat. Therefore breathing has to increase to take in the extra oxygen, excrete the extra carbon dioxide at the alveoli of the lungs and carry away the excess heat to the skin for heat loss to prevent the body temperature rising beyond 40°C. The pulse rate increase indicates that the heart rate increases to increase the supply of oxygen to the muscles and increase the removal of carbon dioxide. The increased blood flow also increases the supply of glucose the major fuel of the muscle cells.

Pulse Rates The average adult resting pulse rate is about 70 beats per minute. With increased physical fitness the resting pulse rate reduces. Pulse rates below 60 are normal for physically fit people and some elite athletes may have pulse rates as low as 30.

Factors Affecting Human Pulse Rate

Increased heart rate is caused by: physical exercise, fear or anxiety, smoking, infection, caffeine in coffee, tea and certain drinks. Decreased heart rate is caused by: physical rest, mental relaxation (meditation), sleep, high level of physical fitness.

Age is also a factor: from infancy to adulthood the pulse rate gradually declines from 140 to 70.

Body Temperature

Normal body temperature is 37°C. even during strenuous physical exercise. The body responds to changes inside and outside to keep the temperature at 37°C. But infection or illness can cause the body temperature to rise. The higher temperature is known as fever and it improves our ability to overcome the disease-causing organisms. Therefore a constant temperature over 37°C often is taken as an indication of infection.

Heart Care

Regular physical exercise. 

Stay cool – avoid negative stress.

Healthy diet avoid excess fat & sugars.

Do not smoke.

Maintain a healthy body fat percentage –

females 25%, males 15%.