THE CIRCULATORY SYSTEM

The Circulatory System

Circulatory System or cardiovascular system - the combined function of the heart, blood, and blood vessels to transport oxygen and nutrients to organs and tissues throughout the body and carry away waste products.

Functions:

1. To deliver food and oxygen to the cells and to pick up the cells’ waste materials and carbon dioxide
2. The circulatory system increases the flow of blood to meet increased energy demands during exercise and regulates body temperature.
3. When foreign substances or organisms invade the body, the circulatory system swiftly conveys disease-fighting elements of the immune system, such as white blood cells and antibodies, to regions under attack.
4. in the case of injury or bleeding, the circulatory system sends clotting cells and proteins to the affected site, which quickly stop bleeding and promote healing.

Components of the Circulatory System

The heart, blood, and blood vessels are the three structural elements that make up the circulatory system.

 

1. HEART - is the engine of the circulatory system.

   - the human heart is shaped like an upside-down pear and is located slightly to the left of center inside the chest cavity. About the size of a closed fist, the heart is made primarily of muscle tissue that contracts rhythmically to propel blood to all parts of the body. This rhythmic contraction begins in the developing embryo about three weeks after conception and continues throughout an individual’s life. The muscle rests only for a fraction of a second between beats. Over a typical life span of 76 years, the heart will beat nearly 2.8 billion times and move 169 million liters (179 million quarts) of blood.

Structures of the Heart

a.    Covering

1.    Pericardium - a tough, double-layered sac that surrounds the heart.

2.    Myocardium - wraps around a scaffolding of tough connective tissue to form the walls of the heart’s chambers.

3.    Endocardium - the inner surfaces of the heart’s chambers are lined with a thin sheet of shiny, white tissue. This lining helps blood flow smoothly and prevents blood clots from forming inside the circulatory system.

b.    Septum – it divides the heart into left and right sides

c.   Chambers – the heart is divided into four chambers: the right   atrium, the right ventricle, the left atrium, and the left ventricle.

1.     Atria – the 2 upper smaller chambers

2.     Ventricle – the 2 lower stronger chambers

d.    Valves – it directs the flow of blood and to prevent back flow of blood in the heart. The valves open easily in the direction of blood flow, but when blood pushes against the valves in the opposite direction, the valves close. These valves are known as atrioventricular valves and semilunar valves

·      Atrioventricular – are located between the atria and ventricles.

                                                           1. Tricuspid – the right atrioventricular valve is formed from three flaps of tissue and is called the tricuspid valve.

                                                  2. Mitral – the left atrioventricular valve has two flaps and is called the bicuspid or mitral valve.

·      Semilunar – the other two heart valves are located between the ventricles and arteries. They are called semilunar valves because they each consist of three half-moon-shaped flaps of tissue.

       1. Pulmonary - the right semilunar valve, between the    right ventricle and pulmonary artery, is also called the pulmonary valve.

        2. Aortic - The left semilunar valve, between the left ventricle and aorta, is also called the aortic valve.

Characteristics – Double Pump

1.    Systemic circulation - carries oxygenated blood from the heart to all the tissues in the body except the lungs and returns deoxygenated blood carrying waste products, such as carbon dioxide, back to the heart.

2.    Pulmonary circulation - carries this spent blood from the heart to the lungs. In the lungs, the blood releases its carbon dioxide and absorbs oxygen. The oxygenated blood then returns to the heart before transferring to the systemic circulation.

Heartbeat – Cardiac Cycle

The pumping action of the heart occurs in two stages for each heart beat: diastole and systole. During each heartbeat, typically about 60 to 90 ml (about 2 to 3 oz) of blood are pumped out of the heart. If the heart stops pumping, death usually occurs within four to five minutes.

1.  Diastole - when the heart is at rest

2.  Systole - when the heart contracts to pump deoxygenated blood toward the lungs and oxygenated blood to the body.

Path of Blood in the Heart

 

Deoxygenated blood (low in oxygen high in CO₂ ) from the arms and legs

Right atrium (superior vena cava and inferior vena cava)

Tricuspid valve

 I

Right ventricle

 I

Pulmonary SLV

I

Pulmonary artery (oxygenated blood)

I

Pulmonary veins

I

Left atrium

I

Bicuspid valve or Mitral valve

I

Left ventricle

I

Aortic SLV

I

Aorta

I

Arteries

I

All body cells

Electrocardiogram (ECG) – the recording voltage when the heart beat contracts

   Pacemaker - is a medical device that uses electrical impulses, delivered by electrodes contacting the heart muscles, to regulate the beating of the heart.

             Sphygmomanometer – a device used in measuring blood pressure

Blood Pressure – the pressure of the blood against the wall of the blood vessel

·  Blood pressure is measured during systole, the active pumping phase of the heart, and diastole, the resting phase between heartbeats.

·   Blood pressure varies between individuals and even during the normal course of a day in response to emotion, exertion, sleep, and other physical and mental changes. Normal blood pressure is less than 120/80 mm Hg, in which 120 describe systolic pressure and 80 describes diastolic pressure. Higher blood pressures that are sustained over a long period of time may indicate hypertension, a damaging circulatory condition. Lower blood pressures could signal shock from heart failure, dehydration, internal bleeding, or blood loss.

2.   BLOOD 

 

•       Body contains approximately 4 to 5 liters of blood, making up about 8% of the body’s weight

•       Functions include:

–      Transporting nutrients, oxygen, and hormones

–      Removing metabolic wastes and carbon dioxide

–      Providing immunity through antibodies

–      Maintaining body temperature and electrolyte balance

–      Clotting to prevent bleeding from a wound

Components of the Blood

a.          Red Blood Cells (Erythrocytes)

•  Erythrocytes contain a protein called hemoglobin that carries oxygen to all cells and removes carbon dioxide

•  Each red blood cell lives only 90 to 120 days

•  New cells are manufactured by the red marrow or myeloid tissue in bones

•  The liver and spleen remove dead red blood cells

 

b.          White Blood Cells (Leukocytes)

•  White blood cells remove foreign particles, fight infection, and help prevent  disease

•  There are fewer white blood cells than red

•  White blood cells are larger than red

•  Leukocytes live about 9 days

•  Pus consists of white blood cells mixed with bacteria

c.          Platelets (Thrombocytes)

•  Smallest blood cells 

•  Platelets promote clotting to prevent blood loss

•  Platelets can form a plug to seal small vessels by themselves or start the clotting process

•  Produced in red bone marrow

•  Live about 5 to 9 days  

Plasma

•       A pale yellow liquid that remains when elements are removed from blood

•       Whole blood is 55% plasma

•       Plasma is 90% water and approximately 10% proteins

•       It contains nutrients, electrolytes, oxygen, enzymes, hormones, and wastes

•       Helps fight infection and assists in the clotting (coagulation) of blood

Composition of Blood

Composition	Number per cubic mm	Function
RBC	4,500,000 – 5,500,000	Carries oxygen
WBC	7,000 – 10,000	Defends the body against harmful microorganisms
Platelets	300,000	Blood clotting

 

3. BLOOD VESSELS - any of the veins, arteries, and capillaries that transport blood through the body.

a. Arteries – are the blood vessels that carry blood away from the heart

- the tubular vessels that conveys blood from the heart to the tissues of the body.

- two arteries have direct connection with the heart: (1) the aorta, which, with its branches, conveys oxygenated blood from the left ventricle to every part of the body; and (2) the pulmonary artery, which conveys blood from the right ventricle to the lungs, whence it is returned bearing oxygen to the left side of the heart

- are stronger than veins, they have thicker walls because the blood that is pumped through them have much more force and pressure

b. Capillaries – derived from the Latin word capillus meaning hair

- are thin, delicate tubes that are only one-celled thick

- forms the connection between the arteries and the veins. These tiny vessels vary in diameter from 0.0127 to about 0.2032 mm (0.0005 to about 0.008 in) and are present in great numbers throughout the entire body.

c.     Veins – the large and thicker-walled blood vessels

- they carry non-oxygenated blood to the heart

 The Lymphatic System

1. This system consists of lymph vessels, lymph, lymph nodes, and lymph organs. Its primary function is to drain from tissue spaces, protein-containing fluid which escapes from blood capillaries
2. Lymphatic vessels are similar in structure to veins. All lymphatic deliver lymph to either the thoracic duct or right lymphatic duct.
3. Lymph nodes are oval-shaped structures located along lymphatic. Lymph passing through the node is filtered and it picks up antibodies and angular leucocytes.

Lymph – it is the clear, watery substance that forms the tissue fluid surrounding all body cells

Importance of Blood Clotting

-       to plug up ruptured blood vessels to stop bleeding and prevent loss of vital fluids in the body

HUMAN BLOOD TYPES

Blood contains:

1. Antigen – a foreign substance usually protein which elicits the formation of specific antibodies within an organism
2. Antibody – a protein produced in response to the presence of foreign substances in the blood or tissue
1. it makes vaccination effective
2. Prevents infections
3. Provides immunity and resistance to diseases

Type O – the universal blood donor because RBC has no antigens

Type AB – the universal recipient because blood plasma contains no antibodies

TRANSFUSION RELATIONSHIP

Blood Group	Can Donate To	Can Receive From
O	O, A, B, AB	O
A	B, AB	O, A
B	A, AB	O, B
AB	AB	O, A, AB, B

Disorders of the Circulatory System

•       Acquired immunodeficiency syndrome

–      Dysfunction of the immune system caused by a virus

•       Allergy

–      Hypersensitive response by the immune system to an outside substance

•       Anemia

–      The blood has an inadequate amount of hemoglobin, red blood cells, or both

•       Autoimmune

–      Conditions in which the immune system of the body turns against itself

·      Coronary artery disease also known as coronary heart disease

- is by far the most common disease of the circulatory system. It is caused due to accumulation of plaque in the coronary arterial walls, which indirectly impairs the blood supply to the heart. Coronary artery disease is the leading cause of death all over the world.

•       Elephantiasis

–      A massive accumulation of lymphatic fluid in body tissues, causing an abnormally large growth of tissue or hypertrophy

•       Hemophilia

–      A rare sex-linked genetic blood disease in which the blood is missing a clotting factor

•       Hepatitis

–      A viral infection of the blood

•       Hodgkin’s disease

-     A malignant cancer of the lymph system

·     Hypertension or High Blood Pressure
     - the common disorders of the circulatory system. Over here, the blood pressure (systolic and diastolic) reading remains higher than the recommended level. Hypertension increases the risk of heart attack and other heart diseases.

•       Leukemia

–      Also called blood cancer, is an abnormal malignant increase in the number and longevity of white blood cells

•       Lymphosarcoma

–      Is a group of malignant cancers of lymph tissues other than Hodgkin's disease

•       Polycythemia

–      An abnormal increase in the number of blood cells, making the blood thicker and slower flowing

•       Septicemia

–      Called blood poisoning, is an infection that occurs when pathogens enter the blood

•       Sickle cell anemia

–      A genetic condition that results in malformed red blood cells 

•       Splenomegaly

–      An enlargement of the spleen caused by an acute infection such as mononucleosis or anemia

•       Thrombocytopenia

–      A decrease in the number of platelets in the blood

•       Thrombosis

–      A condition in which a blood clot, called a thrombus, forms in the blood vessels