The Circulatory System

In The Amazingly Designed Human Body – Part 3 we started with the structural frame of the human body in the skeletal system.  Then in Part 4 we started adding the muscles to our frame in the muscular system.  This week we are taking a look at the system that carries all of the essential elements to these other two systems and to systems we will look at in forthcoming installments.

The circulatory system, also referred to as the cardiovascular system is a closed system composed of one main organ, the heart, with the supporting roles of the blood vessels, and blood.

The Heart

Long considered to be the symbol of love, the heart is one of the most important organs in the entire human body.  While the sentiment may be true, the primary function of the heart is not love but one of a pumping station.

Located just off to the left side of the center of the chest, the human heart consists of four chambers: the right and left atrium, and the left and right ventricle.

  • Left Ventricle – The left ventricle is the largest and strongest chamber of the heart.  It receives oxygen rich blood from the left atrium and pumps it out through the aortic valve through the aorta (the largest artery in the human body) where it is carried to the rest of the body.
  • Right Atrium – The right atrium receives the deoxygenated blood from the superior and inferior vena cava.  It then pumps the blood on to the right ventricle.
  • Right Ventricle – The ventricle receives the deoxygenated blood from the right atrium and pumps it through the pulmonary artery to the lungs where the blood is re-oxygenated.
  • Left Atrium – The left atrium receives the newly oxygenated blood from the lungs and pumps it into the left ventricle where the cycle is repeated over and over throughout our entire lifetime.

Blood Vessels

Blood vessels in the human body are basically divided into five types: arteries, arterioles, capillaries, venules and veins.  Think of it as the water and plumbing system in your home.  Plumbing carries clean water from the water main to your house.  That main water line branches off to the various locations in the house where the water is used for a multitude of purposes.  Then the drains in your sinks, tubs, showers, toilets and washing machines collect the water which is now filled with a number of different waste products, away from the house to the sewer lines where they are cleaned out and eventually returned to the house again as clean water.

  • Arteries – Arteries are primarily responsible to carry the oxygenated blood away from the heart to the rest of the body except for the pulmonary and umbilical arteries which carry deoxygenated blood back to the heart.  Arteries are found in all parts of the body, except the hair, nails, epidermis, cartilages, and cornea of the eye.  The walls of the arteries are thicker and stronger than veins as the blood being pumped through them is under greater pressure than the blood returning through the veins.
  • Arterioles – Arterioles are smaller branches of the arterial system that lead from the larger arteries to the capillaries.  As blood passes through the arterioles, the blood pressure and speed are decreased in preparation for the blood’s passage into the tiny capillaries.
  • Capillaries – Capillaries are the smallest of all blood vessels.  Their walls are only one cell thick.  The thinness of their walls along with the reduction in blood pressure and speed, allows for the greatest exchange of oxygen, nutrients and waste products.
  • Venules – Venules arise where capillaries join together to form a larger vessel.  They collect the deoxygenated and waste loaded blood from the capillaries and carry it to the veins.
  • Veins – Veins form where venules join together to form even larger vessels.  Basically veins are hollow collapsible tubes designed to carry deoxygenated blood back to the heart, except for the pulmonary and umbilical veins which carry oxygenated blood back to the heart.  Veins have one way valves in them to prevent blood from flowing back or down to the lower extremities.

The Blood

While the heart is the pumping station and the blood vessels are the plumbing, it is the blood itself that carries life throughout the body.  Not only does blood carry oxygen, but it also transports food, nutrients, hormones, lymph and waste materials.  The blood is composed of the liquid plasma, red blood cells, a number of different white blood cells and platelets.

  • Plasma – Blood plasma is the fluid component of blood.  It is usually yellowish in color and consists of about 55% water.  Besides the red and white blood cells and platelets, the plasma carries the rest of the vital compounds needed through the body.  It carries sugars, proteins, hormones, clotting agents, carbon dioxide, and a number of mineral ions such as calcium and potassium that are so vital to the muscles.
  • Red Blood Cells – Red blood cells called erythrocytes are red because of a protein called hemoglobin.  Hemoglobin is an iron based protein that readily adheres to oxygen molecules, but not so strongly as to permanently keep them.  When the red blood cells reach the thin walled capillaries they readily give up their oxygen which passes through the capillary wall into the tissue that needs it.  They are concave in shape and lack a nucleus and most typical cell organelles.
  • White Blood Cells – White blood cells, also called leucocytes, compose approximately 1% of the blood.  In general, white blood cells play an important role in the body’s immune system.  White blood cells are divided into two main groups: granulocytes and agranulocytes. 

Granulocytes – White blood cells that contain membrane bound enzymes that appear as small granules when stained, are referred to as granulocytes.  There are three types of granulocytes: basophils, eosinophils and neutrophils.

Basophils – Basophils contain the anti-coagulant heparin which prevents blood from clotting and histamine that dilates the vessels to increase blood flow.  They are generally found in the vicinity of an allergic inflammation or bites such spiders and ticks.

Eosinophils – Eosinophils are involved with the immune systems response to allergies, asthma and some parasite and viral infections.

Neutrophils – Neutrophils are the most numerous of the different types of while blood cells.  They respond to a number of different infections and illnesses including cancers and bacterial infections.  Neutrophils are so abundant at the sites of infection and inflammation that they are responsible for the whitish or yellowish feature of pus.

Agranulocytes – As the name would imply, agranulocytes are white blood cells that lack the membrane bound enzyme granules that appear with specific staining.  They do contain a non-specific type of granule known as a lysosome.  Like granulocytes, there are three types of agranulocytes: lymphocytes, monocytes and macrophages.

Lymphocytes – There are several types of lymphocytes: large lymphocytes which contain natural killer cells and smaller lymphocytes that consist of T cells and B cells.

Natural Killer Cells – They play a major role in the immune system battle against tumors and viral infection.  They are named natural killer cells because when they locate a cell that has been altered by tumor or virus, they release a cytotoxin that kills the infected cell.

T Cells – T cells are so designated because they mature in the thymus gland.  There are a variety of T cells that perform various immune system functions.

B Cells – B cells principally produce antibodies that are used against antigens.

Monocytes – Monocytes are stored in the spleen and respond to inflammation anywhere in the body.  Once they reach the infected site, they convert to macrophages and dendritic cells.

Macrophages – Macrophages seek out and devour pathogens and cellular fragments.  The term macrophage means ‘large eater.’

  • Platelets – Platelets, also known as thrombocytes, are small clear, non-nucleated cell fragments.  Platelets are an important part of the clotting process.  If the platelet count is too low, a person may have difficulty getting a cut or abrasion to stop bleeding.  Platelets are also a source of growth factors.

Fun facts concerning the circulatory system;

  • The heart beats an average of 30 million times in a year.
  • On the average, the heart pumps between 430 to 460 gallons of blood every day.
  • A baby’s body contains about a quart of blood at birth and the average adult contains about 1.3 gallons.
  • It only takes about 20 seconds for blood to completely circulate through the human body.
  • One drop of blood contains approximately 10-13 thousand white blood cells and 5 million red blood cells.
  • Every second, approximately 10 million red blood cells die and another 10 million are produced.
  • Depending upon what source one uses, it is estimated that if all of the arteries, arterioles, capillaries, venules and veins were laid end to end that they would measure somewhere between 50,000 to 100,000 miles in length.
  • Most blood cells are produced in the bone marrow and the plasma is produced in the liver.

After 6,000 years of the Curse, a number of genetic mutations and diseases affect the heart and circulatory system.  Among those are angina, aneurism, arrhythmia, atherosclerosis, cardiomyopathy, congenital heart defect, coronary artery disease, cycle cell anemia, hemophilia, hypertension, peripheral vascular disease to name a few.

Although the circulatory system seems like a simple system of just pumping blood throughout the body, that is hardly the case.  From the intricate network of vessels to the life giving substances in the blood, the circulatory system is another marvel of God’s design.  It reminds of Leviticus 17:14 that states:

For the life of every creature is its blood: its blood is its life.

And the words of Jesus Christ as record in Matthew 26:27-28:

And he took a cup, and when he had given thanks he gave it to them, saying, “Drink of it, all of you, for this is my blood of the covenant, which is poured out for many for the forgiveness of sins.

Additional Resources

Fearfully & Wonderfully Made (DVD)

When does life begin?

Take a journey from conception to birth with Dr. David Menton, former professor of anatomy at the prestigious Washington University School of Medicine in St. Louis. Dr. Menton provides both a biblical and scientific answer to the question of when life begins.

Taken from one of Dr. Menton’s lectures, this video will reveal the wondrous design of the womb along with the numerous miracles involved along every step of the development of the unborn child.

Following the tragic starvation induced death of Terry Schiavo, Dr. Menton clearly shows the value and sanctity of human life.

With grace and sensitivity Dr. Menton concludes with a salvation message and explanation of the second birth process as described in John 3.

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