Transport in humans

Circulatory system

The main transport system of human is the circulatory system; a system of tubes (blood vessels) with a pump (the heart) and valves to ensure one-way flow of blood.


Its functions:

  • To transport nutrients and oxygen to the cells.
  • To remove waste and carbon dioxide from the cells.
  • To provide for efficient gas exchange.

The right side of the heart collects deoxygenated blood form the body and pumps it to the lungs.

The left side collects oxygenated blood from the lungs and pumps it to the body. \

  1. Blood and its compositions.

Human blood consists of plasma and blood cells. Functions of blood – Transports oxygen, continuous circulation of blood lowers body temperature, distributes food from intestines throughout the body, waste products such as carbon dioxide/mineral salts and urea are transported to organs responsible.


  • Plasma – The liquid part of the blood Contains – Water, proteins, minerals, end products of digestion, hormones.
    Functions of plasma – Transports carbon dioxide, waste matter, hormones, digested food, heat, ions and water, white blood cells and platelets.
  • Blood Cells – Red, white, platelets

Red Blood Cells (Erythrocytes) – Disc shaped cells containing hemoglobin which transport oxygen from the lungs to the body tissue.
Function of red blood cell– the uptake of oxygen and to transport it to round the body
White Blood Cells (Leucocytes) – The name for a number of colorless cells in blood e.g. phagocytes and lymphocytes, they attack and engulf bacteria and produce antibodies.

Function of white blood cell- they carry out phagocytosis- ingestion of harmful bacteria to prevent or overcome the infections and also they produce antibodies which stick to the bacteria and clump them together making ready for bring indigested by phagocytes.

Platelets (Thrombocytes)- Particles in the blood which are used in the formation of blood clots to stop bleeding of wounds.

Function of platelets- plays an important role in blood clotting and helps to block holes in damaged capillary walls.


  1. Blood vessels

There are three types of blood vessels:

  1. Arteries
  • Arteries are vessels which transports bloodaway from the heart. They branch repeatedly to form arterioles (small arteries), the smallest and thinnest branches of arteries.
  • Have thick muscular walls and small passageways for blood (internal lumen).
  • Contain blood under high pressure.


  1. Veins
  • Veins are vessels which transportsblood to the heart. From the capillaries the blood drains into very small veins called venules, which unite into larger veins along which the blood returns to the heart.
  • Have thin walls and larger internal lumen.
  • Contain blood under low pressure.


  1. Capillaries
  • Arteries and veins are connected byblood capillaries, microscopically small tubes which form a network, the capillary bed in different tissues.
  • The blood capillaries are so small that red blood corpuscles can only move in a single file through it. The exchange of all substances takes place in these capillaries.
  • Microscopic – one cell thick also control very low blood pressure.
  • Where gas exchange takes place. Oxygen passes through the capillary wall and into the tissues, carbon dioxide passes from the tissues into the blood.


  1. Heart

External structure of heart

The heart is surrounded by two layered tissue membrane called pericardium. The space between the two layers is filled with fluid called pericardial fluid. This fluid protects the heart from external pressure, push, shock and reduces friction during the heart beat and facilitates free heart contraction.

Internal Structure of heart


Aorta – The largest artery in the body which originates from the left ventricle and extends down the abdomen distributing oxygenated blood to all parts of the body.

Pulmonary Artery – Arteries which carry blood from the heart to the lungs

Pulmonary Vein – A large blood vessel which carries blood from the lungs to the left atrium of the heart

Ventricle – One of the large thick walled lower chambers of the heart that pumps blood into arteries Four chambers of the heart – Left atrium, right atrium, left ventricle, right ventricle

 Right Atrium – Receives deoxygenated blood from the superior and inferior vena cava and pumps it into the right ventricle through the tricuspid valve

Left Atrium – Receives oxygenated blood from the pulmonary veins and pumps it into the left ventricle

Left Ventricle – Receives oxygenated blood from the left atrium vial the bicuspid (mitral) valve and pumps it into the aorta via the aortic valve

Right Ventricle – Receives deoxygenated blood from the right atrium via the tricuspid valve and pumps it into the pulmonary artery via the pulmonary valve

Double Circulation

In a double circulatory system there are two circuits for blood passing through the heart:

  • Pulmonary Circulation
    Deoxygenated blood is pumped from the heart to the lungs, oxygenated blood returns to the heart from the lungs.
  • Systemic Circulation
    Oxygenated blood is pumped from the heart around the body. That blood returns to the heart deoxygenated because much of the oxygen it contained when it left the heart has been supplied to tissues in the body


Blood flow

The right side of the heart accepts blood that has been circulated throughout the body and pumps it at a relatively low pressure to the lungs. In the lungs, the blood is replenished with oxygen. Once the blood has been completely circulated through the lungs, it returns to the heart. Arriving at the much larger left side of the heart, the blood is then pumped out to the entire body. As this side must push the blood though a greater amount of tissue, it squeezes much harder than the right, creating a greater amount of pressure. After the blood has been fully circulated throughout the body, it returns to the right side of the heart, where the process is repeated.


Blood pressure

Blood pressure is a measure of how hard your blood is pushing against the sides of your arteries. It is a force exerted by the blood on the walls of blood vessels as a result of contractions and relaxation of heart.



The high blood pressure exerted on the elastic and muscular walls of the aorta during ventricular contraction causes a wave of contractions to pass along the main arteries of the body. This series of waves can be felt s pulses in many places where the arteries are sufficiently superficial such as the wrist and the neck. Heartbeats can be measured by counting the pulse rate.


Effects of physical exercise on pulse rate

The amount of exercise someone does will affect the pulse rate. For example, more exercise means more movement so more energy will be needed. In order to get more energy, respiration takes place at a faster rate. More oxygen is used so more Carbon Dioxide is produced. Carbon Dioxide is a waste product and must be removed, as it is a toxin. Because of the extra Carbon Dioxide being produced, blood is pumped faster around the body to transport it. This process will give you a faster pulse rate.


Heart diseases

Heart diseases can occur when animal fats and cholesterol are deposited on the walls of the arteries.

Coronary heart disease
Coronary heart disease refers to the disease of the arteries to the heart and their resulting complications, such as angina, heart attacks and heart failure. It is caused by blockage in coronary arteries which provide blood to the heart muscles. The blockage stops supply oxygen and soluble food substances to the heart muscles. Therefore heart cannot function well. This blockage of coronary artery is caused under 2 conditions.

  • Atheroma
It’s an abnormal mass of fatty or lipid material with a fibrous covering, existing as a discrete, raised plaque within the intimae of an artery. atheroma can make an artery narrower, which can restrict and reduce the blood flow through the artery.  If a blood clot forms over a patch of atheroma in a coronary artery it can cause a heart attack.
  • Coronary thrombosis

Coronary thrombosis is a term used to describe the blockage of a coronary artery secondary to blood clotting within the artery.

Thrombosis of coronary arteries occurs when the opening, or lumen, of the artery becomes so small that the blood flow through the narrowed segment slows, allowing the blood to clot in the artery. Thrombosis of a coronary artery can lead to a heart attack if not treated.

Coronary thrombosis

Possible causes of the heart diseases

  1. Smoke: cigarette smoke contains two harmful substances, nicotine and carbon monoxide.
  2. Diet: taking diet rich in cholesterol and fats results high blood pressure. Obesity also leads to high blood pressure
  3. Stress: it triggers reduced blood flow to the heart, promotes your heart to beat irregularly and increases the likelihood of your blood clotting.  All of these can trigger the development of cardiovascular disease.

Preventive measures of heart diseases

  • Restriction the intake of animal’s fat and cholesterols.
  • Avoid obesity.
  • Refrain from smoking.
  • Lead a less stressful life.
  • Do regular exercise.