• The human circulatory is a part of the body which works together to ensure the circulation of oxygen, digested food substances, as well as the transportation of waste products from one part of the body to another.

Parts of the Human Circulatory System

The Human Circulatory System (Photo Credit: BiologyDictionary.net)

• The circulatory system is made up of the blood, heart, and blood vessels.
• The Blood: In human beings, blood is a liquid medium that carries materials around the body. The materials include: oxygen from the lungs, digested food substances, such as glucose, mineral salts, amino acids, and waste products such as carbon IV oxide, urea, and excess salts.

Structure of the Blood

The Components of Blood (Photo Credit: StanfordChildrens.org)

• The human blood consists of two parts, the liquid part and the solid part.
• The liquid part is called the plasma. The solid part is made up of red blood cells, white blood cells, and platelets.
• Plasma – The plasma is watery. It contains foods substances and waste products in solution.
• Red Blood Cells (Erythrocytes) – Erythrocytes are small and circular in shape. They contain a protein called hemoglobin. They are red in color when they are in large numbers.
• White Blood Cells (Leukocytes) – Leukocytes are of different shapes and sizes. They are larger in size than red blood cells but fewer in number. They have irregular shapes and are colorless.
• Platelets (Thrombocytes) – These are not cells. They are round bodies in blood. They are fewer and smaller than red blood cells and have no nuclei.

Function of the Blood

• The main function of the blood is the circulation of substances in the body.
• The functions of the components of blood include:
  • Plasma
    • They transport end products of the digested food, especially glucose and amino acids.
    • They transport waste products, hormones, heat from every activity, respiring tissue, antibodies, amino acids, and mineral salts.
    • They participate in blood clotting.
    • They transport oxygen.
  • Erythrocytes
    • They transport oxygen as oxyhemoglobin.
    • They transport carbon IV oxide.
    • They take part in blood clotting.
  • Leukocytes
    • They defend the body against disease-causing organisms.
    • They provide antibodies or immunity for the body.
  • Thrombocytes
    • They aid blood clotting.

The Heart

Sectional View of the Human Heart (Photo Credit: Nia.Nih.Gov)

• The human heart is muscular. It is conical in shape and is made up of four chambers.
• The four chambers consist of two upper chambers called auricles and two lower chambers called ventricles.
• The left ventricle is the most muscular.
• There are two small openings, called valves, between the left ventricle and the left auricle; the bicuspid valve.
• There also are two small openings, called valves, between the right ventricle and the right auricle; the tricuspid valve.
• The heart is located in the chest cavity of the body and is connected to all the parts of the body by the means of blood vessels.
• The major function of the heart is to pump the blood that is circulated in the body.
• Blood leaves the heart through the left ventricle to all the parts of the body and comes back to the heart through the right auricle.
• The valves between the auricles and ventricles control the direction of blood flow.
• The heart pumps blood so that the blood takes food, oxygen, and other materials to all parts of the body and collect waste products from all cells.
• The heart communicates with the lungs for the exchange of gases.
• There are three major types of blood vessels in the human circulatory system. They are:
  • Arteries.
  • Veins.
  • Capillaries.
  • Their walls vary in thickness and size.
  • The capillary is the tiny permeable blood vessel. It allows direct passage of solutions through tiny permeable cells.
  • The veins carry blood from the body to the heart.
  • Arteries carry blood from the heart to other parts of the body.
    

    Differences between Arteries and Veins

    Arteries	Veins
    They carry blood away from the heart	They carry blood to the heart
    Blood pressure is usually high	Blood pressure is usually low
    They have elastic walls	Their walls are inelastic
    They are thick-walled	They are thin-walled
    Valves are absent	Valves are present
    They are deeply sited in the body	They are superficially sited in the body
    Blood flows in the arteries under the pressure from the heart beat and pulse	Blood flows in the veins with assistance from contracting muscles and gravity
    Blood in the artery is bright red	Blood in the vein is dark or dull red
    Arteries carry oxygenated blood except the pulmonary artery	All veins carry deoxygenated blood except the pulmonary vein

Diseases of the Blood

• Sickle Cell Anemia: is a hereditary disease of the red blood cells in which they do not have the normal shape and do not contain normal hemoglobin. They are shaped like a sickle and are therefore unable to carry oxygen made in the body cells quickly, making the patient weak most of their life.
• Leukemia – is a cancer of the blood. Patients have excess white blood cells. The red blood cells are reduced abnormally and the patient usually dies of weakness.
• Hemophilia – is a blood disease in which the patients easily bleed to death from injuries since their blood cannot clot like normal blood.