The Circulatory System

The Main Body Systems

The table below shows the seven main body systems:-

The Circulatory System

The first main body system we will look at is the circulatory system.

The diagram below shows the main features of the circulatory system:-

Where:-

  1. Heart - Main organ of the circulatory system, contracts to pump blood around the body.

  2. Arteries - Large blood vessels which carry blood away from the heart.

  3. Veins - Large blood vessels which carry blood to the heart.

  4. Capillaries - Very small blood vessels (too small to be seen above) which are present in all body tissue, Oxygen and Carbon Dioxide transfer takes place between the capillaries and the cells of the body.


The Heart and Blood Vessels

The heart is the main organ within the circulatory system. The heart is a very strong muscle that contracts on a regular basis to pump blood around the body.

The diagram below shows the main parts of the heart:-

The heart is the main organ of the circulatory system, consisting of four chambers, which contract in sequence to pump the blood around the body.

The right side of the heart pumps deoxygenated blood to the lungs.

The left side of the heart pumps oxygenated blood to the rest of the body.

There are three main blood vessels within the body, each perform a different job and are specialised in different ways:-

The table below shows a summary of the three different blood vessels:-

Pulse Rate

The heart pumps blood around the body with such a large force that it can be felt in the blood vessels as a pulse.

A Doctor can listen to your heart (and lungs) using a Stethoscope. A stethoscope is a device that amplifies sounds to allow the doctor to hear them clearly.

The diagram below shows the main parts of a stethoscope:-

The stethoscope works by sound being received at either the drum or the diaphragm. This causes the air within the thin tubing to vibrate, carrying the sound to the earbuds.

In order to hear different sounds within the body, either the diaphragm or the bell can be used:-

  1. Closed diaphragm - High frequency lung sounds.

  2. Open Bell - Low frequency heart sounds.

Note - An easy way to remember which way round to use the stethoscope is open bell - open heart surgery...


Pulse Rate and Exercise

When you exercise, your muscles need more oxygen and nutrients than they would normally use. In order to keep up with this demand, your heart will beat faster and with greater force.

After exercise, your body has to remove the waste substances from your muscles, and so your pulse rate will take some time to return to normal.

The peak pulse rate, and the recovery time depend upon your fitness level:-

The Circulatory System

The circulatory system works as part of a figure 8 cycle, with the blood passing through the heart twice in each cycle.

The diagram below shows the path of blood through the circulatory system:-

Keeping the Beat

In order to keep the heart beating at the correct rate, all the heart muscle has to work together at the same time. In order to do this, the heart uses a pacemaker.

The diagram above shows the location of the heart's pacemaker, a small group of cells called the SAN node. This small group of cells in the right atrium generate an electrical pulse which causes both atrium to contract. This electrical pulse then triggers a second pulse that causes the ventricles to contract.

The diagram below shows the stages of the cardiac cycle:-

Blood Pressure

When the above cardiac cycle occurs, blood is forced into the arteries at high pressure. This pressure is required to force the blood through the hundreds of thousands of tiny blood vessels, ensuring Oxygen and nutrients reach where they are needed.

Blood pressure is measured using a device called a Sphygmomanometer. This consists of a cuff that tightens around the arm to measure the blood pressure. The image below shows a sphygmomanometer in use:-

Image result for sphygmomanometer in use

As can be seen from the display in the above image blood pressure is given normally as a ratio of two numbers, in the example above this is shown as 132 / 90 .

  1. The top number is the systolic value, the highest pressure when the heartbeats.

  2. The bottom number is the diastolic value, the lowest pressure between the heartbeats.

The Video below shows an introduction to the Biology of Blood Pressure:-

Blood Pressure Problems

There is a range of safe values for blood pressure. If a person's blood pressure is too high or low, it can cause severe health risks.

The diagram below shows the safe range of blood pressures:-

If a person's blood pressure is outside of the green section, the person is an increased risk of illness, especially if it falls within the red zone:-

  1. Low blood pressure - Can cause dizziness or cause the person to collapse.

  2. High blood pressure - Increases the risk of heart attacks or strokes.


Cardiovascular Disease

As can be seen above, the heart is vital to the survival of a person. However, by having a poor diet or unhealthy lifestyle, a person's heart can be put at risk. One of the main risks to the heart is Cardiovascular Disease.

Worldwide, cardiovascular disease is the cause behind ~30% of all deaths, many of which could be prevented.

Cardiovascular disease is caused by the buildup of fatty deposits within the walls of the arteries, due to too much fat in the bloodstream. These deposits take decades to form, so care should be taken from a young age to reduce their growth.

The diagram below shows the blocking of an artery due to the build up of a fatty deposit called a plaque or atheroma:-

In the above diagram, the plaque has grown over several decades to a size at which it has nearly blocked the entire artery. If this plaque becomes damaged, blood will clot around it, blocking the whole artery, causing a heart attack.

These plaques can be treated before they cause a heart attack by a type of surgery called an angioplasty.

The diagram below shows the treatment of a plaque:-

  1. Stage A - Advanced growth of a plaque is restricting blood flow through the artery, the person is at extreme risk of a heart attack.

  2. Stage B - A small catheter is inserted into the artery, tipped with a small inflatable balloon with a wire cage called a stent around it.

  3. Stage C - The balloon is inflated, compressing the plaque to allow greater blood flow. The stent remains within the artery to hold the artery open and the catheter is then removed.

The video below shows a dramatisation of a heart attack, highlighting the causes and effects of the arteries of the heart becoming blocked.

Note - This dramatisation should be viewed before showing a class. It contains scenes that some students may find distressing, and as such may not be appropriate for all classes. Also, only show first 24 minutes as the video continues on a different topic.