Circulatory System – The Heart (part 3 of 4)

Cells must be constantly supplied with the materials necessary for life. The blood in humans is the transport system of these materials and this system must be constantly moving materials to and from the cells.

The heart is a muscular pump and the major organ of the circulatory system. It keeps the blood moving in its’ constant motion.

The human heart is about the size of a clenched fist.

The heart lies in the chest cavity, behind the breast bone and slightly to the left.

The heart is a bundle of cardiac muscles specialized for rhythmic contractions and relaxations, also know as the HEARTBEAT.

The rate of the average heartbeat is 72 beats per minute. Over an average lifetime of about 70 years, the heart beats about 2.5 billion times and pumps 200 million liters of blood.

The heart re-circulates the entire volume of blood, about 5 liters, every minute.

The heart is a strong, muscular organ that has two sides and contains four chambers.

Both sides of the heart beat simultaneously.

The walls are thicker on the one side than on the other.

The upper chambers are called the ATRIA/ARTIUM. The atrium are thin-walled and receive the blood from the veins. They are the receiving chambers of the heart.

The lower chambers are called the VENTRICLES. The ventricles are larger and receive the blood from the atrium above it. They are the pumping chambers of the heart.

Each atrium is separated from the ventricles by a VALVE.

The atrium and ventricles on the right are separated from the left atrium and ventricles by a thick wall of muscle called a SEPTUM.

Blood leaves the ventricles and flows through arteries.

Blood flows one way through the heart with the help of valves. ARTERIES CARRY BLOOD AWAY FROM THE HEART, VEINS CARRY BLOOD TO THE HEART.

PATH OF THE BLOOD
The heart is a double pump.

1. PULMONARY CIRCULATION
– The right ventricle represents the 1st pump. It is the pump for the PULMONARY CIRCULATION.
– Blood that is low in oxygen returns from the upper and lower parts of the body and enters the right atrium of the heart and then the right ventricle.
– The right ventricle pumps the DEOXYGENATED blood into the PULMONARY ARTERIES that bring the blood to the lungs where it receives oxygen and gives up waste products, including carbon dioxide, which is exhaled.
– The blood returns from the lungs by way of the PULMONARY VEINS to the left atrium and the left ventricle of the heart. This begins the SYSTEMIC CIRCULATION, which carries blood from the heart to the rest of the body.

2. SYSTEMIC CIRCULATION
– The left side of the heart is the pump for the systemic circulation.
– Oxygenated blood enters the left atrium and then the left ventricle. The left ventricle contracts and pumps the blood through the largest artery in the body, the AORTA, to all parts of the body.
– The oxygenated blood passes through arteries that lead to smaller arteries, them to arterioles, then to capillaries, where oxygen, nutrients, hormones and other substances move from the blood to the cells.
– It is through the capillary walls that waste products, like carbon dioxide are picked up.
– Other substances such as nutrients and hormones enter the blood through the capillary walls.
– Due to the pumping action of the heart, blood is continuously circulating throughout the body, maintain the constant exchange of materials necessary for life to continue.
– The blood eventually returns to the right atrium of the heart to complete the cycle.

CORONARY CIRCULATION
– The surface of the heart is covered with a number of small arteries and veins.
– Even though the heart has blood flowing through it internally all the time, it is unable to obtain the materials it needs from this blood.
– These small vessels are the CORONARY ARTERIES AND VEINS that carry blood full of oxygen and nutrients to the muscle fibers of the heart and remove waste from the heart tissue.
– These coronary vessels are essential for the health of the heart.
– A heart attack occurs when these vessels become blocked and do not allow the heart tissue to receive oxygen and nutrients.
– This causes death of the heart tissue and the chest pain associated with a heart attack.

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Circulatory System – Blood (Part 1 of 4)

The Circulatory System is made up of 4 parts:
1. Blood
2. Blood Vessels
3. Heart
4. Lymphatic System

1. BLOOD
Blood is the only liquid connective tissue in the body.

Human adults have 4.7 liters of blood in their bodies.

Blood has roles in transport, regulation and protection.
– It transports oxygen, carbon dioxide, nutrients, hormones, heat and waste.
– It is involved in the regulation of body temperature, PH and the water content of cells.
– The body is protected from blood loss through clotting and against disease by PHAGOCYTIC WHITE BLOOD CELLS and ANTIBODIES.

PLASMA
– Plasma makes up 55% of the blood.
– It is a clear; straw-colored liquid, which is mostly water.
– It is the bloods SOLVENT (able to dissolve substances).
– It transports nutrients, waste products of metabolism, respiratory gases and hormones.
– There are 3 main PLASMA PROTEINS:
1. ALBUMIN
– Is the smallest and most numerous protein.
– It helps recover water that has been lost.
– It transports some of the steroid hormones.
2. IMMUNOGOBULIN (antibodies)
– Aids the immune system by attacking bacteria and viruses.
– Other globulins help in the transport of iron, lipids and fat-soluble vitamins.
3. FIBRINOGEN
– It plays an essential role in the clotting of blood, by providing the necessary protein network.
– Various ions act as solutes in plasma; they play key roles in osmotic balance, PH buffering and the regulation of membrane permeability.

BLOOD CELLS
Blood cells make up about 45% of the blood.

There are 3 main types of blood cells:
1. RED BLOOD CELLS (ERYTHROCYTES)
– They transport oxygen to all cells.
– The oxygen-carrying protein HEMOGLOBIN is the pigment that gives blood its red color.
– They are the simplest cells in the body; mature red blood cells lack a nucleus, ribosomes and mitochondria.
– They are also the most numerous cells in the body; 5 million/ml of blood.
– About 2.5 million are made every second in the red bond marrow.
– Mature cells are flattened and disc-shaped with a central depression.
– They are non-reproducing sacks of oxygen binding hemoglobin.
– The hormone, ERYTHROPOIETIN, triggers transformation of skin cells in the marrow to produce red blood cells.
– After circulating for 3 to 4 months in the blood, red blood cells are engulfed by liver and spleen SCAVENGER CELLS.

2. WHITE BLOOD CELLS (LEUKOCYTES)
– They contain a nucleus.
– Most live only a few days, although some, particularly LYMPHOCYTES can live for several months or longer.
– During infections white blood cells may only live for a few hours.
– The shape of their nuclei and the staining properties of their granules distinguish white blood cells from each other.
– The number and type of white blood cells can indicate a person’s health. Most infections stimulate an increase in circulating white blood cells.
– There are 5 classes of white blood cells:
1. NEUTROPHILS and 2.MACROPHAGES
– Are active in PHAGOCYTOSIS (the engulfing of particles by phagocytes); ingesting bacteria and cellular debris.
– Certain chemicals released by bacteria and inflamed tissue attract the white blood cells to the site.
– After engulfing the bacteria, neutrophils lysozymes are released that destroy the bacteria.
– Strong oxidants are then released, like peroxide and proteins called DEFENSINS that have antibiotic activity.
– Monocytes arrive after the neutrophils and enlarge to become macrophages, which clean up cellular debris and bacteria after an infection.
3. EOSINOPHILS
– They enter tissue fluid from the capillaries and release enzymes to combat allergic reactions.
4. BASOPHILS
– Intensify the inflammatory response when they enter the tissue from the capillaries.
5. LYMPHOCYTES
– They are the major combatants in the immune response.
– They are the B-CELLS, T-CELLS and the natural killer cells.
– These cells are active in fighting infections caused by viruses, bacteria and fungi.
– They are also responsible for transfusion reactions, allergies and the rejection of transplanted organs.

3. PLATELETS
– They are the small cell-like fragments that come from special white blood cells, called MEGAKARYOCYTES.
– They have no nucleus and live for about 5 to 9 days.
– Aged and dead platelets are removed by macrophages in the liver and spleen.
– Platelets release chemicals in blood clotting.

BLOOD TYPE
Humans have highly individualized blood that is credited to proteins and other genetically determined factors located on the surface of red blood cells and the plasma bathing the red blood cells.

The main types of blood are A, B, AB, and O.

Transfusions of blood are possible only when the blood types of the donor and recipient are compatible.

If the blood types are not compatible, proteins in the plasma will recognize foreign antigens and respond by causing the cells to AGGLUTINATE (clump) which will block the small vessels.

Type AB is considered the UNIVERSAL RECIEPENT (this person can receive blood from any type in the ABO blood group).

Type O is considered the UNIVERSAL DONOR (this type of blood can be given to any blood type in the ABO blood group).