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Circulatory system

Circulatory system: The circulatory system is that system which is related with the blood circulation in body.

The circulatory system contain following parts:

  1. Blood
  2. Heart
  3. Blood vessels


Blood: The blood is special fluid connective tissue which contains the plasma, RBC, WBC & platelets. The healthy person contains about 1/12th blood of the total body.

Blood composition: The blood contains about 55% plasma, 45% essential elements or formed elements, RBC, WBC & platelets.


Plasma: The 55% part of the blood is plasma. The plasma contains about 90% water and important plasma proteins; prothrombin + fibrinogens, globulin and albumin.

  1. Prothrombin + fibrinogens: It helps in blood clotting.
  2. Globulin: It provides the defense function.
  3. Albumin: It helps to maintain the osmotic balance in the body.

The plasma also contain the salts like sodium chloride, NaHCo3, Ca2+, Mg2+, Fe 2+ etc. It also contains the glucose, fats, urea, uric acid, cholesterol and amino acid etc.

The plasma also contains the gases like O2 and CO2.

It also contains the internal secretions, hormone and antigens.

The plasma without the clotting factor is called the serum.

Formed / Essential elements:

Formed / Essential elements: It is 45% of the blood. It contains the RBC, WBC and platelets.


  1. RBC: These are called as the red blood cells. This is the main part of the blood. The healthy person contains 5000000/Cubic mm.
  • The RBC originates in the short bone, Long bone, flat bones, irregular bone, sesamoid bone and in the shaft of ribs and sternum.
  • The maximum RBC is formed in the ends of the long bones.
  • The diameter of RBC is 7 microns.
  • During the process many stages at first they are large and contain a nucleus but no hemoglobin, Finally the get the hemoglobin and loss the nucleus and then pass in the blood circulation.
  • The average life period of RBCs is 120 days. They are destroyed in the liver and spleen. The RBC contain the hemoglobin which is a complete protein rich in iron it has the affinity for O2.

The normal hemoglobin value is 15gm per 100ml. The RBC provides the red color to the blood the cells are rounded or bi-concave disc like structure.


  1. WBC: The WBCs are the colorless cells. WBC contain the nucleus, it secrete the anti-bodies to kill the harmful micro-organism and toxins. They are less in number as compared to the RBC. It is about 6000-10000 per cubic mm. The cells are irregular in shape. They are also called as the leucocytes.

Type of WBC

  1. Granulocytes
  2. Agranulocytes

The granulocytes are of three types

  • Eosinophils
  • Basophiles
  • Neutrophils

Eosinophils: These cells reduce the inflammatory reaction. These are anti-histaminic.

Basophiles: These cells secrets histamine and heparin.

Neutrophils: These cells kill the bacteria by phagocytosis (kill the bacteria). This is never ending function even in a healthy person.


  1. Platelets: They are 150,000 cubic per mm in a normal human. They also called thrombocytes. They do not contain the nucleus, they are round or oval in shape. Their life period is about 7 days they help in the blood clotting .

Extra for knowledge:-

Jaundice: The Old RBCs are destroyed by the liver. It releases the hemoglobin. The global portion separates from the hemoglobin. This is a protein finally the heam breaks and produces the bilirubin pigments, the enzymes of liver mix with this pigment. These mixed pigment of bilirubin come in the intestine by the bile juice. In the intestine the bilirubin pigment is modified by bacterial enzymes which give the brown color to the feces (excreta) some pigments are absorbed by the blood vessels and enter in the blood circulator. It gives the yellowish urine. When there is excess of bilirubin pigment it causes the jaundice.

Test for jaundice – Serum bilirubin

Erythropoiesis: The development of erythrocytes is called erythropoiesis.

Formation of RBC in the fetal life: The formation of RBC during the fetal life takes place by the spleen, liver and after the birth this function is performed by bone narrow.

Factors affecting Erythropoiesis:

  1. Vitamin B12
  2. Vitamin C
  3. Iron
  4. Protein
  5. Formic acid
  6. Erythropoietin ( Name of the hormone secreted by kidney)

Antigen: It is a substance that produces the antibodies.

Antibodies: It is a substance capable of reacting with antigen.

Hemoglobin: It binds the CO to form carboxyl hemoglobin. Hemoglobin has high affinity for O& COthe pH value of the blood is 7.35-7.45. It is slightly alkaline.

Blood clotting:

Blood clotting: whenever there is some cut or injury the blood starts coming out. It sets into gel after sometime this is called as the blood clotting.

  • The process of clotting takes place as following:-
  1. Prothrombin + calcium (Ca2+) + thrombokinase = thrombin
  2. Thrombin + fibrinogen = Fibrin
  3. Fibrin + blood cells = clot

Factors affecting blood clotting.

  • The blood clotting is faster by
  1. Heat a little higher than the body’s temperature.
  2. Contact with a rough surface for example: Surgical dressing the blood clotting is slower by:
  • The blood clotting is retarded by

1. Blood vessels coated by Vaseline / wax.

2. by Cold

3. It will be slow by the addition of potassium citrate or sodium citrate which removes the calcium salt.

Blood functions:

Blood functions:

  1. Transportation: The blood functions as the transport in the body it supplies the food and other materials to the complete body.
  2. Respiration: The blood help in the respiration in the body. It supplies the oxygen to all parts of the body and collects the COfrom all parts of the body.
  3. Body Temperatures: The blood maintains the body temperature 98.4F by the blood circulation.
  4. Defense function: Due to the presence of WBC the blood helps in the defense function it kills the harmful micro-organisms.
  5. Balance of pH Value: The blood maintains the water balance in the cells and tissues of the body by the circulation.
  6. Excretion of toxic materials: The blood helps in the excretion of the toxic materials like urea and Coby the kidney and the lungs.
  7. Carrier of hormones, vitamins and enzymes: The blood carries the important materials like hormones, enzymes and vitamins to the complete body.
  8. Clotting of blood: The blood helps in the blood clotting due to the presence of plasma proteins prothrombin and fibrinogens.
  9. Anti-clotting: Due to the presence of the chemical heparin produced by the liver the blood helps in anticlotting.

Blood Groups:

Blood Groups: The blood groups are different chemically from person to person. When two different type of blood are mixed, the RBCS run together form a clamp. The clamping of RBCis called agglutination.

The agglutination is due to the content of 2 types of proteins:-

  1. Antigen
  2. Antibodies

These antigens and antibodies are present in the plasma. There are the antigens of two types.

  1. A & B – Two types of antigen
  2. a & b – Two types of antibodies

In a person the RBC may contain only A or B or both A and B or neither A nor B and the plasma may contain ‘a’ or ‘b’ or both ‘ab’ or neither ‘a’ not ‘b’ antibodies.

The antigen A can mix with antibodies b and antigen B with antibody a.

Therefore every person contains two factors AB & ab on the basis of this.

There are four blood groups in the humans.

  1. Group A: This group contain the blood corpuscle factor A and plasma factor b.
  2. Group B: It contains the blood corpuscle factor B and plasma factor a.
  3. Group AB: This blood group contains the both A & B blood corpuscle factor but no plasma factor.
  4. Group O: These blood groups having no blood corpuscle factor but plasma factors a, b are present.

RH factor: It is a protein at surface of RBC in many persons 95-99% of person contains the RH positive factor and 1-5% is RH negative.

The blood group O is the universal donors and AB is universal acceptors / receptors.

Transfusion: The first transfusion of Rh positive blood to Rh negative person causes no harm because the Rh negative person develops the anti Rh factors or antibodies in his body. In 2nd person, the person’s anti RH factors attack and destroys the donors RBCs.

BOMBAY blood group: This is extremely rare ABO group called so because it uses first discovered among some people in Bombay though the group is more likely to occur in east Indians. It is a very rare group in Bombay also, it is not limited to east Indians but in Japanese also, this RBCs lack ABH antigens and the serum contains the ABH.


External structure of heart



The heart is a hollow muscular organ roughly the size is 12cms from apex to base and 8cm from left to right and 6cm from front to back. The weight is approximately 300gms in the males and 260gms in females. It is reddish brown in color and conical in shape. It is situated almost in the middle of the thoracic cavity.

The broad base faces in the upward direction and open in the downward direction slightly to the left side, it rests on diaphragm. The heart is present in a protective covering pericardium. It has two layers inner and outer. The pericardial fluid is filled between the two layers. It gives protection to the heart during the heartbeat.

The organs related with the heart.

  1. Inferiorly the apex of the heart rests on the central tendon of diaphragm.
  2. Superiorly related with the great blood vessels e.g. aorta-superior vena cava and pulmonary arteries and veins.
  3. Posteriorly it is related with the esophagus trachea left and right branches descending aorta inferior vena cava and thoracic vertebral.
  4. Laterally with the lungs the left lung overlaps the left side of the heart.
  5. Anteriorly it is related with the sternum, ribs and intercostal muscles.

The heart is divided by septa into two equal parts right and left each half part contains the two collecting chambers the upper two are called as the auricles and the lower two are called as the ventricles the heart contains the four chambers.

Blood Supply to heart: The right and left coronary arteries divided into smaller arteries which encircle the heart and supply the blood to all parts of the organ heart. The return of blood is by the coronary veins which open by the coronary sinus in the right auricle just above the inferior vena cava this is called as the coronary circulation.

The normal blood flow is 250ml/min within the walls of the heart.

Nerve supply to heart- VAGUS nerve.

Internal structure of heart



Internally the heart can be divided into two parts right and left part each part contain the two chambers the upper chambers are called as the auricles and the lower chambers are called as the ventricles. The right and left part are separated by the common wall intra auricular and intra ventricular septum.

The right auricle is connected with the right ventricles by a small pore called as the A-V aperture.

There is present a tricuspid valve which presents the back entry of the blood. The right auricle receives the superior and inferior vena cava which brings the blood from the upper and lower parts of the body. The walls of the auricles are thin because they pump the blood to the ventricles which are present just below them.

From the right ventricle arises the large blood vessel which is called as the pulmonary arch which takes the deoxygenated blood to the right and left lungs for purification. There is present the pulmonary value below the pulmonary arch (artery).

The left side of heart contains the oxygenated blood in the left auricles the oxygenated blood enters by the four pulmonary veins just below the left auricle there is present the left ventricle there also present the bicuspid valve, which presents the back flow of blood.

From the left ventricle arises the large blood vessel which is called as the aortic arch which supplies the oxygenated blood to the complete body except the lungs. There is present the aortic valve & the base of the aortic arch therefore these are four valves in the heart.

The wall of the left ventricles is approximately five times thicker than the right ventricle because it forces the blood to the further path of body from head to toe. The blood entering in the aortic arch from left ventricle has much more high blood pressure than the blood entering from right ventricle to pulmonary arch.

The length of the bicuspid valve mitral valve is about 3cms in diameter.

Tricuspid valve is 4cms in diameter.

The size of pulmonary valve is 2.5cm in diameter.

Aortic valve is 2.5cm in diameter

Coronary sinus: This is the largest venous channel about 2.3cms in length. This is present in the posteriors auricles ventricular groove called coronary sinus.

It opens into the right auricle in the lower part of inter auricular septum between the inferior vena cava and auricle ventricular opening.

Heart beat: The contraction and relaxation of the heart chambers to pump out and to receive the blood to the body and from the body is called heartbeat.

Blood Pressure: The pressure of flowing blood against the walls of the blood vessels.

Blood pressure is of two types:-

  1. Systolic blood pressure: Maximum blood pressure recorded in the arteries during left ventricular systole, normal valve-120mmhg.
  2. Diastolic blood pressure: Minimum blood pressure recorded in arteries during ventricular diastole, normal valve-80mmhg.

Cardiac output: It is the volume of blood send by both ventricles into the arterial system. In a normal resting person the heart beats about 72/min and pumps 70ml each time the amount of blood pumped each minute is about 5 liter/min. This is also called stroke volume.

Functions of Heart:

  1. It functions as a pumping station for blood.
  2. As the heart contracts it supplies the blood to all parts of the body.
  3. As it relaxes it collects the blood from all parts of the body.
  4. It maintains the circulation of blood with the body.
  5. It maintains the blood pressure in arteries and veins.
  6. It controls the flow of blood in different parts of body.

Resting phase of heart: – The ventricular contraction is for 0.3 seconds. The relaxation period is longer= 0.5 sec. The resting phase for the heart is more it is 0.5 – 0.3 sec = 0.2 sec

Blood Circulation:

Exchange of gases

Heart sound: is produced during the systolic and diastole blood pressure.

Blood circulation: The blood circulation takes place in the body as results of heart beat during the first phase. There is the relaxation of all the four chambers as a result of this the maximum oxygenated blood enter in the left auricle by these four pulmonary veins.

The maximum blood also enters from the superior and inferior vena cava (deoxygenated blood) in the right auricles Very little quantity of the blood also comes in the right and left ventricles through the A-V aperture.

During the phase two there is maximum contraction of the auricles as a result of this the maximum blood is forced in the ventricles which are also relaxed and are present just below the auricles.

During the phase three there is the maximum contraction of the ventricles as a result of this the auricles but due to the presence of bicuspid and tricuspid valve blood cannot go back but there is continuous pressure due to this the maximum blood from left ventricle passes in the aortic arch which supplies the oxygenated blood to the complete body parts, similarly the maximum blood enter in the pulmonary arch from the right ventricle and is taken to the lungs for purification.

When the oxygenated blood reaches the different parts of the body tissue as a result of the metabolism the Ois used the energy are produced which is used by the body and the waste products like urea & COare produced. The CO2 is takes by the superior and inferior vena cava to the right auricle of the heart from right auricle to right ventricle from right ventricle to the lungs by the pulmonary arch.

In the lungs as a result of respiration the air is purified the oxygenated blood is taken to the left auricle from left auricle to left ventricle then to aortic arch and then to the complete body in this way the blood circulation takes place.

The blood circulation between the lungs and the heart is called pulmonary circulation.

The circulation between heart and body tissue is called as the systemic circulation both these circulation make the total blood circulation which as the blood circulation in the body.

blood circulation in the body.

The conducting system is made up of this special myocardium which is responsible for initiation and conduction of cardiac impulse it contain following parts.

  1. S.A node: Sino auricular node this is called as pace makes of heart. It generated impulses and initiates the heartbeat. The impulse is 70/min the size of SA node is 10-20mm in length at is supplied by Vagus nerve.
  2. A.V Node: Arterio-ventricular node it is present just above the coronary sinus this is also called as the triangle of Koch. It generates the impulse 60/min. This is smaller than SA node length is about 8mm. The nerve supply is by fibers of Vagus nerve.
  3. A-V bundle/bundle of his: This is the only muscular connection between the auricle and ventricle muscle and divides the right and left part of the bundle.
  4. Purkinje fibers: These structures are pace yellow thread like structure and contain the double nuclei. The path of conducting system starts from SA node then passes through AV node and passes to bundle of his and divided into right and left Purkinje fibers in the muscle of ventricles.

Properties of cardiac muscle:

  1. Contractility: By the contraction of cardiac muscle the heart pumps out the blood from chamber.
  2. Conductivity: The impulses from cardiac contractions are conveyed by the special conducting system.
  3. Rhythmicity: Cardiac muscle contract is a regular way in two auricles and two ventricles contract alternate.
  4. Refectory: During diastole the heart doesn’t respond to any other stimuli however strong it may be this is called refectory period.
  5. ECG- electro cardio graph: This is an recording of the electric activity of the heart. The electro cardio graph is the instrument or machine used to record the electrical current produced in the heart with this instrument the electric current produced in the heart is recorded by machines. The current of the heart can be recorded by connecting two parts of body main this instrument to connect is called leads.

Lead I– Right arm and Left arm

Lead II- Right arm and left leg

Lead III- Left arm and left leg



The connections over the chart with different electrodes are also used. The EGC recordings are designed by P, Q, R, S, and T. The wave P is due to the connection of the auricle. The waves Q, R, S are produced by the contraction of the ventricles. The wave T is produced by relaxation of the ventricles.

Pulse: The pulse may be defined as the wave of distention and elongation felt in an artery wall due to contraction of a left artery ventricle forcing about 60-80ml of blood into the already full aorta. The normal pulse at rest is about 60-80 per min.

Factors affecting the pulse rate:

  1. Position: The pulse rate is more in the standing position.
  2. Age: The pulse rate is more rapid in children than adults.
  3. Gender: The pulse rate is more rapid in females than males.
  4. Exercise: Walking, running, playing games increase the pulse rate.

Blood Vessels:

Blood vessels: The blood vessels are the pathway or roots by which the blood travels or flows.

The blood vessels are of two types:

  1. Arteries
  2. Veins

Difference between arteries or veins:

  1. The arteries contain the thick walls
  2. The arteries contain the OBlood
  3. The walls of the arteries are elastic
  4. The arteries do not contain the valves
  5. The arteries are present in deep
  6. The space in the artery is less
  7. The arteries are dark reddish in color
  1. The veins contain the thin walls
  2. The veins contain the COblood
  3. The walls of veins die non-elastic
  4. The veins contain the valves
  5. The veins are clearly visible
  6. The space in the veins is more
  7. The veins are bluish green in color

Transverse section of arteries and veins

Flow of the blood in the veins

When the blood flow is in the forward direction due to the forward pressure of the blood the valves of the vein opens and the blood flows in the forward direction when the blood tries to come back the valves does and no back flow of the blood is possible.

Blood Supply in upper limb:

Blood Supply in upper limb: The sub-clavian artery arises from the aorta and passes over the first rib than near the clavicle. It enters the axilla where becomes the axillary artery.

At the lower boundary of the axilla it becomes the brachial artery which divided into radial and ulnar arteries. The radial artery passes down the radial side and the ulnar artery to the ulnar side.

Passing over the front of the wrist termination of these arteries from the deep and superficial palmar arch

Arteries of right upper limb

The superficial veins of upper arms begin as a network of small veins in the hands.

The blood collection is by these small veins into the median vein.

From the median vein they from the basilica vein, median cuboidal vein and cephalic veins.

The basilica vein continues as the axillary vein.

The cephalic vein runs up to the make a connection with the axillary vein.

Nerve Supply: The upper limbs are supplied by the different branches of brachial plexus which are axillary, ulnar, median, and radial dorsal scapular etc.

Superficial veins of right arm

Blood supply by the common carotid artery:

Blood supply by the common carotid artery: This is the main artery supply the blood to the head and neck. There are two common carotid arteries the right and left.

The right common carotid artery originates from the branch cephalic trunk behind the sterno-clavicle joint in the neck.

The left common carotid artery arises in the thorax directly from the arch of aorta.

Each common caroled artery terminates between Cand C(cervical) vertebra.

It gives the only two terminal branches.

  1. External carotid artery
  2. Internal carotid artery


Carotid artery Image

Axillary artery: This is the continuation of sub clavier artery and it extends from outer boarder of the first rib to lower body of the terse muscles then it continuous as brachial artery. It enters the axilla it is accompanied (along) with the axillary veins and brachial plexus in the axilla.

It is divided into three parts by pectorals major muscle:


  1. Superior thoracic artery
  2. Thoracic acromial artery
  3. Lateral thoracic artery
  4. Ulnar artery

Blood supply in the upper part of body:

  1. Left common artery: This is the wider and larger than the right coronary artery. It arises from the left posterior aortic sinus of ascending aorta. It is present between the pulmonary artery and the left article.

Branches of left common artery:

  1. anterior inter ventricular artery


  1. Anterior ventricular rami b) Septal rami
  2. Circumflex artery: Braches
  3. Anterior Rami: Supply the blood to left auricle
  4. Ventricular Rami: Supply the blood to the left ventricle
  5. Left marginal:
  6. SA-nodal artery: 35% in the individuals
  7. Posterior inter ventricular artery: In 10% individuals

Circle of Willis: This is the polygonal shaped anterior circle that is present in relation to the base of the brain at the level of inter peduncular fossa.

Formation: The circle is formed by branches of two internal carotid arteries and the two vertebral arteries.


  1. It helps to make the balance of the blood flow in the normal condition to different parts of the brain.
  2. Normally there is no intermixing of blood between the internal carotid and vertebral arterial system.

Blood supply to lower limb:

Blood supply to lower limb: The right and the left common iliac artery supply the blood to the lower region. The internal iliac artery supplies the blood to the organs within the pelvic cavity in the females one of the largest braches is the uterine artery.

External iliac artery: It supplies the blood to the thigh to form the femoral artery.

Popliteal artery: It supplies the blood behind the knee.

Femoral artery: The upper part of the popliteal artery is called femoral artery.

Anterior tibial artery: It is present in the form of the leg and angle joint.

Dorsal pedic artery: it supplies the blood to the foot.

Plantar artery: It supplies the blood to sole.

Venous route from lower limb:

There are some deep and some superficial vein in the lower limb. The backward flow of the blood is presented by valves. The superficial veins get less support from the surrounding tissue then the deep veins.

The deep veins are as following:

  1. Digital veins
  2. Plantar venous arch
  3. Posterior tibial vein
  4. Anterior tibial vein
  5. Popliteal vein
  6. Femoral vein
  7. External iliac vein
  8. Internal iliac vein
  9. Common iliac vein
  10. Superficial vein

Superficial veins are of two types:

  1. Small saphenous veins: These are many veins of the foot joint.
  2. Great saphenous veins: Longest vein in the body it starts from the medial half of dorsum of the foot up to the inner side of thigh. It forms an arch the saphenous arch to join the femoral vein in the region of femoral triangle at the saphenous femoral junction.

Portal vein: Any vein of the body collects the blood from the different part of body and breakup in any other organ before reaching the heart is known as portal vein. For example: The hepatic portal vein- it collects the blood from the different parts like small intestine, Spleen and put the blood in the liver before reaching the heart this is called as the hepatic portal vein.

Arterial supply to foot: The foot is supplied by the planter arteries which are the branches of posterior tibias artery.

  1. The medial plants artery is smaller branches of posterior tibia artery and contains the following branches.

Branches of medial plantar artery

  • Anastomosing branch to first meta tarsal
  • Muscular branches to abductor and flexor muscles
  • Cutaneous to skin
  • Articular branches
  • Three superficial digital branches
  1. Lateral plantar artery: This is the larger branch of posterior tibial artery. It terminates at the 5th Meta tarsal.
  2. Planter arterial arch: It is formed by the deep branch of lateral planter artery and the planter branch of dorsalis pedis artery. It is situated acres the base of the 5th, 4th 3rd and 2nd Meta tarsals.

Venus drainage of foot: It is by the medial marginal vein, dorsal veins arch and lateral marginal veins.

Clinical and applied aspects:

Thrombosis: This is the intra vascular blood clot causing the thrombosis may be complete or in complete blocked of artery or vein.

Ascites and effusion: The ascites is the name given to the collection of excess of fluid in the peritoneal cavity. The most common cause are:

  1. Liver disease
  2. Obstruction of lymph vessels in the abdominal cavity.
  3. Acute inflammation

Cardiac failure: When the cardiac output is unable to maintain the blood circulation to meet with the sufficient need of the body. E.g. In exercise heart failure may involve either side of heartFailure of one side results due to failure of other side.

Acute cardiac failure: A sudden reduced in output of blood from both ventricles causes the acute reduction in oxygen supply to all tissue. The death may occur due to anoxia of vital centers in the brain.


  1. Damage to cardiac muscles or coronary artery.
  2. Pulmonary embolism.
  3. Acute toxic myocarditis.
  4. Severe cardiac arrhythmia.
  5. Rupture of a heart chamber or valve disorder.
  6. Severe hypertension.

Shock: The shock occurs when the metabolic need have the cells are not met with because of the poor bleed supply. So there is the reduction or blood circulation in Blood pressure and cardiac output this causes the tissue hypoxia poor nutrition supply and collection of waste products.

Myocardial infarction: Infract means the death of the tissue due to the lack of the poor oxygen supply. In this condition the coronary artery is affected.

Angina pectoris: The increased cardiac output or the poor blood supply causes the angina pectoris.