In human transport of materials takes place through two systems.

  • Lymphatic system: A complex network of vessels, tissues and organs that maintains the fluid balance in the body is called Lymphatic system. From the bloodstream plasma leaks. This plasma is accumulated by the lymphatic system and transported back to the bloodstream.
  • Circulatory system: organ system that conveys blood through vessels to and from all parts of the body, carrying nutrients and oxygen to tissues and removing carbon dioxide and other wastes is called circulatory system.

Types of circulatory system

There are two types of circulatory system: –

Open Circulatory System: –

  • In this type blood is pumped through heart in open spaces called sinuses.
  • The blood is in direct contact with tissues and after exchange of materials it

returns back to heart.

Closed Circulatory System: –

  • In this type muscular heart is present with its incoming (veins) and out going

(arteries) vessels. The blood remains confined to the blood vessels during


  • It is elaborated, complicated and efficient system.

Question) What are the basic components of blood circulatory system?

Answer: Components of the human blood circulatory system:

The main components of the human blood circulatory system are blood, heart and blood vessels.


Question) List the functions of the components of blood?

Answer: BLOOD: Blood is a specialized body fluid (a connective tissue) that is composed of a liquid called blood plasma and blood cells. A reddish fluid in animals that contain water, cell bodies and other substances and is used for transport of materials is called blood. The weight of blood in our body is about 1/12th of our body. The average adult body has about 5 liters of blood.

In a healthy person, plasma constitutes about 55% by volume of blood, and cells or cell-like bodies are about 45% by volume of the blood.


Functions of blood:

  1. i) It helps to transport materials in all the body.
  2. ii) It transports oxygen from lungs to all body cells.

iii) It bring back CO2 from all body cells to lungs.

  1. iv) It brings all wastes from body to kidney for their removal.
  2. v) Blood carries hormones from glands to all body parts.



Plasma is primarily water in which proteins, salts, metabolites and wastes are dissolved. Water constitutes about 90-92% of plasma and 8-10% are dissolved substances. Salts make up 0.9 % of plasma, by weight.

Sodium chloride (the table salt) and salts of bicarbonate are present in considerable amounts. Ca, Mg, Cu, K and Zn are found in trace amounts. Changes in the concentration of any salt can change the pH of blood(normal is 7.4). Proteins make 7-9 % by weight of plasma.

The important proteins present in plasma are antibodies, fibrinogen (blood clotting protein), albumin (maintains the water balance of blood) etc. Plasma also contains the digested food (absorbed from digestive system), nitrogenous wastes and hormones. Respiratory gases i.e. CO2and O2 are present in the plasma.


How is plasma separated from blood?

Blood is taken from an artery and an anticoagulant (chemical that inhibits blood clotting) is mixed in it. After about 5 minutes, plasma separates from blood cells, which settle down.



BLOOD CELLS and cell-like bodies:

These include red blood cells (erythrocytes), white blood cells (leukocytes) and platelets (thrombocytes).


Red Blood Cells (Erythrocytes “erythro means red and cyte means cell”)

  • These are the most numerous of blood cells. A cubic millimeter of blood contains 5 to 5.5 million of RBCs in males, and 4 to 4.5 million in females.
  • When RBCs are formed, they have nucleus. In mammals, when a red blood cell matures, its nucleus is lost. After the loss of nucleus, RBC enters blood.
  • About 95% of the cytoplasm of RBCs is filled with hemoglobin, which transports O2 and small amounts of CO2.
  • The remaining 5% consists of enzymes, salts and other proteins.
  • RBCs are biconcave and have an elastic cell membrane. In the embryonic and foetal life, they are formed in liver and spleen. In adults, they are formed in the red bone marrow of short and flat bones, such as sternum, ribs and vertebrae.
  • Average life span of RBC is about four months (120 days) after which it breaks down in liver and spleen by phagocytosis.

For your information: In a normal person about 2-10 million red blood cells are formed and destroyed every second.


White Blood Cells (Leukocytes)

  • These are colourless, because they do not contain pigments.
  • They are irregular in shape.
  • They have nucleus.
  • They are not confined to blood vessels and also migrate out into tissue fluid.
  • One cubic millimeter of blood contains 7000 to 8000 WBCs.
  • Their life span ranges from months to even years, depending on body’s needs. WBCs function as the main agents in body’s defence system.
  • They are produced in bone marrow, thymus gland and lymph nodes.

Types of WBC: There two main types of WBCs.

Granulocytes: Granulocytes have granular cytoplasm. These include neutrophils (destroy small particles by phagocytosis), eosinophils (break inflammatory substances and kill parasites) and basophils (prevent blood clotting).

Agranulocytes: Agranulocytes have clear cytoplasm and include monocytes(produce macrophages which engulf germs) and B and T lymphocytes (produce antibodies and kill germs).


Platelets (Thrombocytes)

  • They are not cells, but are fragments of large cells of bone marrow, called megakaryocytes.
  • They do not have any nucleus and any pigment. Plateletes of vertebrates except mammals are complete cells.
  • One cubic millimeter of blood contains 250,000 platelets.
  • The average life span of a blood platelet is about 7 to 8 days.
  • Platelets help in blood clotting. The clot serves as a temporary seal at the damaged area.


For your information: WBCs die in the process of killing the germs. These dead cells accumulate and make the white substance called pus, seen at infection sites.


For your information: In dengue fever , there is a sharp decrease in the number of platelets in blood. Because of this, patients bleed from the nose, gums and under the skin.



Composition of blood
Plasma Description Amount in %age Functions
Liquid portion of blood 55% by volume Carries blood cells and important blood proteins, hormones, salts etc.
Cell Types Description Average



Red Blood Cells


Like a biconcave disc; without nucleus; contain haemoglobin 5,000,000 per mm3 Transport Oxygen and a small amount of CO2
White Blood Cells


Granular and agranular; contain nucleus Larger in size than


7500 per mm3 Play role in body’s defense by different ways like: Engulf small particles Release anticoagulants Produce antibodies


Fragments of bone marrow cells


250,000 per mm3 Involved in blood clotting


Analyzing and Interpreting:

Identify red blood cells, white blood cells and platelets in specimens of prepared slides or diagrams.


Question) State the signs and symptoms, causes and treatments of leukemia and thallassemia?


Following are important blood disorders.


Leukaemia (blood cancer)

Definition: Leukaemia is the production of great number of immature and abnormal white blood cells.

Causes: This is caused by a cancerous mutation (change in gene) in bone marrow or lymph tissue cells. The mutation results in uncontrolled production of defective white blood cells (leukocytes).

Treatment: It is a very serious disorder and patient needs to change blood regularly with normal blood, got from donors. It can be cured by bone marrow transplant. It is effective in most cases , but very expensive treatment.



Thalassaemia (g. thalassa = sea; haem = blood) :Thalassemia (Greek: “sea blood”) is so called because it was first discovered among peoples around the Mediterranean Sea, among whom its incidence is high.

It is also called Cooley’s anaemia on the name of Thomas B. Cooley, an American physician (1945A.D). It is a genetic problem due to mutations in the gene of haemoglobin.

The mutation results in the production of defective haemoglobin and the patient cannot transport oxygen properly.

The blood of these patients is to be replaced regularly, with normal blood. It can be cured by bone marrow transplant but it does not give 100% cure rate.


For your information: The world celebrates the International Thalassaemia Day on 8th of May. This day is dedicated to raise public awareness about thalassaemia and to highlight the importance of the care for thalassaemia patients.


For your information: There are about 60-80 million people in the world who carry thalassaemia. India, Pakistan and Iran are seeing a large increase of thalassaemia patients. Pakistan alone has 250,000 such patients. The patients require blood transfusions for lifetime. (Source: The Thalassaemia International Foundation).


For your information: A total of 29 human blood group systems are now recognized by the International Society of Blood Transfusion (ISBT).



Question) How do we classify blood groups in terms of the ABO and the Rh blood group systems?

Answer: Blood group systems:

Blood group systems are a classification of blood based on the presence or absence of antigens on the surface of red blood cells. An antigen is a molecule that can stimulate an immune response (antibody production etc.).

ABO Blood Group System

It is the most important blood group system in humans.

Discoverer: It was discovered by the Austrian scientist Karl Landsteiner, who found four different blood groups (blood types) in 1900. He was awarded the Nobel Prize in Medicine for his work.

Different blood groups according to ABO blood group systems: In this system, there are four different blood groups which are distinct from each other on the basis of specific antigens (antigen A and B) present on the surface of RBCs.

  • A person having antigen A has blood group A. People with blood group A have antibody B.
  • A person having antigen B has blood group B. People with blood group B have antibody A.
  • A person having both antigens has blood group AB. People with blood group AB have no antibody.
  • A person having none of the A and B antigens has blood group O. People with blood group O have both antibody A and B.

Presence and absence of antigens and antibodies in ABO blood group system.


For your information: A number of infectious diseases (such as AIDS, hepatitis B and hepatitis C etc.) can pass from the affected blood donor to recipient. Before blood transfusion, the blood of donor is checked for the presence of germs etc.

Blood transfusions in ABO blood group system

1)Persons with blood group O are called universal donors . They do not

have any antigens A or B so they can donate their blood to a person with

any type of blood group.

  • Persons with blood group AB are called universal recipient. They can receive each type of blood because they have no antibody and have both antigens.
  • Persons with blood group A can donate blood only to A group peoples.
  • Persons with blood group B can donate blood only to B group peoples.

Rh Blood Group System (+ ve & – ve blood group system)

In 1930’s, Karl Landsteiner discovered the Rh-blood group system. In this system, there are two blood groups i.e. Rh-positive and Rh-negative. These blood groups are distinct from each other on the basis of antigens called Rh factors (first discovered in Rhesus monkey), present on the surface of RBCs.

A person having Rh factors has blood group Rh-positive while a person not having Rh factors has blood group Rh-negative. Unlike the naturally occurring anti-A & anti-B antibodies of the ABO-system, an Rh-negative person does not produce anti-Rh antibodies unless Rh-factor enters in his / her blood.

Blood transfusions in Rh blood group system

Rh-positive blood group can be transfused to Rh-positive recipient because recipient’s blood already has Rh-antigens and it will not produce anti-Rh antibody. Rh-negative blood group can be transfused to Rh-negative because donor’s blood does not have Rh-antigen and so recipient’s blood will not produce anti-Rh antibody.

If an Rh-negative person receives Rh-positive blood, he / she will produce anti-Rh antibodies against Rh-factors. Rh-negative blood can be transfused to Rh-positive recipient, only if donor’s blood (Rh-negative) has never been exposed to Rh-antigens and does not contain any anti-Rh antibody.


Recalling: Cardiac muscles are involuntary in action and are composed of branched striated cells,each with a single nucleus.

Useful intresting information: The heart is usually felt to be on the left side because the left chamber of the heart i.e. (left ventricle) is stronger (it pumps blood to all body parts).


Useful intresting information: The walls of left ventricle are the thickest one. These are about a halfinch thick. They have enough force to push blood into the body. This gives an evidence that the structures of the parts of heart are adaptive to their functions.


Question) What four chambers make the human heart and how blood flows through these chambers?


Structure of Heart: –

  • Human heart is muscular contractile organ responsible for pumping blood through blood vessels by repeated contractions.
  • Location: Human heart is located in between the two lungs, in the middle of chest cavity beneath the breast bone.
  • Heart is protected by ribs.
  • Moreover heart is enclosed in tough, fibrous and extensible membrane called pericardium. There is a fluid between heart walls and pericardium called pericardial fluid. Its functions are as under:
  1. It acts as shock absorber.
  2. It protects the heart from friction(pericardial fluid).
  3. It prevents the over flow of blood.
  4. It keeps the heart moist.
  • Heart muscles are called cardiac muscles.
  • Heart consists of four chambers.
  1. Two upper atria (Single Atrium).
  2. Two lower ventricles.

Function of Heart: –

  1. i) Atria are thin walled independent chambers. They receive blood.
  2. ii) Right atrium receives deoxygenated blood from all parts of the body and left atrium receives oxygenated blood from lungs.

iii) Ventricles are thick walled chambers. They pump blood.

  1. iv) Right ventricle pump deoxygenated blood to lungs and left ventricle pump

blood to all parts of body through aorta.

  1. v) Valves are present between atria and ventricles which prevents the

backward flow of blood.

  1. vi) The right atrio-ventricular valve consists of three tissues and called tricuspid


vii) The left atrio-ventricular valve consists of two tissues and called bicuspid


viii) The alternating contraction and relaxation of the heart chambers is called the

cardiac cycle.

  1. ix) The period of ventricular contraction is called systole and their relaxation is called



Blood from all parts of the body is collected in right atrium. At same time left atrium receive oxygenated blood from lungs through pulmonary veins. This is diastolic phase of atria. After this both atria contract and blood is pumped to the respective ventricles through bicuspid and tricuspid valves. This is systolic phase of atria.

After this both ventricles contract and blood is pumped to lungs from right ventrical and to all parts of the body from left ventrical. This is ventricular systole.


Pulmonary and systemic circulation

The pathway on which deoxygenated blood is carried from heart to lungs and in return oxygenated blood is carried from lungs to heart is called pulmonary circulation or pulmonary circuit. Similarly, the pathway on which oxygenated blood is carried from heart to body tissues and in return deoxygenated blood is carried from body tissues to heart is called systemic circulation or systemic circuit.


Question) Write a note on Heart beat?

Answer: Heartbeat:

The relaxation of heart chambers fills heart with blood and contraction of chambers propels blood out of heart. The alternating relaxations and contractions make up the cardiac cycle and one complete cardiac cycle makes one heartbeat.

Complete cardiac cycle consists of the following steps. Atria and ventricles relax and blood is filled in atria. This period is called cardiac diastole. Immediately after their filling, both atria contract and pump blood towards ventricles. This period in cardiac cycle is called atrial systole. Now, both ventricles contract and pump blood towards body and lungs.


The period of ventricular contraction is called ventricular systole. In one heartbeat, diastole lasts about 0.4 seconds, atrial systole takes about 0.1 seconds, and ventricular systole lasts about 0.3 seconds (Figure 9.17). When ventricles contract, tricuspid and bicuspid valves close and “lubb” sound is produced. Similarly when ventricles relax, the semilunar valves close and “dubb” sound is produced. “Lubb-dubb” can be heard with the help of a stethoscope.


Question) What do you know about heart rate?

Answer: Heart rate and Pulse rate

Heart rate is the number of times the heart beats per minute. At rest or during normal activities, the normal heart rate is 70 times per minute in men and 75 times per minute in women. The heart rate fluctuates a lot depending on factors such as activity level and stress level.

Heart rate can be measured by feeling the pulse. Pulse is the rhythmic expansion and contraction of an artery as blood is forced through it by the regular contractions of heart. Pulse can be felt at areas where artery is close to skin for example at wrist, neck, groin or top of foot. Most commonly, people measure their pulse in their wrist.


Question) Compare the structure and function of an artery, a vein and a capillary?


2-Blood Vessels: –

Blood vessels consists of Arteries, Capillaries and Veins.


  1. i) The vessels that carry blood from heart to all parts of the body are

called arteries.

  1. ii) They are made up of three layers.
  2. Innermost layer is called endothelium.
  3. Middle layer is made up of smooth muscles and elastic tissues.
  4. Outer layer is made up of collagen fibers and other supporting


iii) Because of elastic walls, the arteries stretched when blood enters and

then recoil slowly. It is called pulse. They withstand the high blood pressure and maintain the flow of blood.

  1. iv) All the arteries carries oxygenated blood with the exception of pulmonary arteries that carry deoxygenated blood from heart to lungs.

Capillaries: –

  1. i) Arteries on reaching to different body parts divides into very small vessels

called capillaries.

  1. ii) They are very thin walled. They consist of single celled layer.

iii) They are so narrow that only one RBC can move in line.

  1. iv) Gases, hormones, and other wastes are exchanged by simple diffusion.
  2. v) They join to form veins.

Veins: –

  1. i) The vessels that bring blood back from all parts of body to heart are called
  2. ii) They are less elastic.

iii) Valves are present in veins which prevent the backflow of blood.

  1. iv) All veins carry deoxygenated blood with the exception of pulmonary vein that carry oxygenated blood to heart from lungs.


General Plan of Human Blood Circulatory System

Many scientists worked for discovering the facts about the circulation of blood in human body. Two important scientists who revealed much knowledge of blood circulatory system were Ibn-e-Nafees and William Harvey.

Ibn-e-Nafees (1210-1286 AD) was a physician and he is honoured as the first scientist who described the pathway of blood circulation. William Harvey (1578-1657 AD) discovered the pumping action of heart and the pathway of blood in major arteries and veins.


Question) Draw diagrams which can illustrate the origins, locations and target areas of the main arteries in human blood circulatory system?


Answer: Arterial System:

  • Large pulmonary trunk emerges from right ventricle and divides into right and left pulmonary arteries, which carry the deoxygenated blood to right and left lungs.
  • The oxygenated blood leaving the left ventricle of heart is carried in a large artery i.e. aorta. It ascends and forms an aortic arch. The arch curves left and descends inferiorly into body. From the upper surface of aortic arch, three arteries emerge, which supply blood to head, shoulders and arms. As aorta passes down through thorax, it becomes dorsal aorta.
  • It gives off many branches and the important ones are listed here. Several intercostal arteries supply blood to ribs. Coeliac artery and superior mesenteric artery supply blood to digestive tract while hepatic artery supplies blood to liver. Inferior to these, there are a pair of renal arteries that supply blood to kidneys.
  • Gonadal arteries supply blood to gonads. Just below the gonadal arteries, is inferior mesenteric artery, which supplies blood to a part of the large intestine and rectum. Then aorta divides into two common iliac arteries, each of which divides into an internal iliac artery and an external iliac artery. Each external iliac becomes femoral artery in upper thigh. It gives branches to thigh, knee, shank, ankle and foot.


Question) Draw diagrams which can illustrate the areas and locations of the main veins in human blood circulatory system?

Answer: Venous System:

Veins from lungs, called pulmonary veins return the oxygenated blood to the left atrium of heart.

Two major veins i.e. superior vena cava and inferior vena cava carry the deoxygenated blood from rest of the body and empty into right atrium.

Superior vena cava forms when different veins from head, shoulders and arms join together. From legs, the deoxygenated blood is returned to heart by many veins which empty into inferior vena cava.

Veins carrying blood from calf, foot and knee join together to form femoral vein. It empties into external iliac vein which joins with the internal iliac and both empty into common iliac vein. Right and left common iliac veins join to form inferior vena cava. Many short veins empty into inferior vena cava. Among these are hepatic vein, renal veins, and gonadal veins.

All veins coming from stomach, spleen, pancreas and intestine drain into hepatic portal vein, which carries blood to liver. From liver, a hepatic vein carries blood and empties into inferior vena cava. Two renal veins carry blood from kidneys while two gonadal veins carry blood from gonads to inferior vena cava. In thoracic cavity, inferior vena cava also receives veins from thoracic walls and ribs.


For your information: Vascular surgery is a field in surgery in which diseases of arteries and veins (like thrombosis etc.) are managed by surgical methods. A vascular surgeon treats the diseases of all parts of blood circulatory system except that of heart and brain.


For your information: Even though the heart chambers are continually bathed with blood, this does not nourish heart muscles. The blood supply to heart muscles is provided by coronary arteries, which emerge from the base of aorta. Heart muscles are drained by coronary veins, which empty into right atrium. Coronary arteries and veins are collectively called coronary circulation and it is a part of systemic circulation.


Question) What do you mean by Cardiovascular disorders?


The diseases that involve the heart or blood vessels are collectively called cardiovascular disorders. These diseases have similar causes, mechanisms, and treatments.

The risk factors that lead to cardiovascular disorders include advanced age, diabetes, high blood concentration of low density lipids (e.g. cholesterol) and triglycerides, tobacco smoking, high blood pressure (hypertension), obesity, and sedentary lifestyle.

Question) Define Arteriosclerosis and Atherosclerosis? How would you differentiate between atherosclerosis and arteriosclerosis?


Atherosclerosis and arteriosclerosis are the diseases of arteries. These diseases also lead to heart diseases.


Atherosclerosis : Atherosclerosis is commonly referred to as a “narrowing” of arteries. It is a chronic disease in which there is accumulation of fatty materials, cholesterol, or fibrin in arteries. When this condition is severe, arteries can no longer expand and contract properly, and blood moves through them with difficulty.

Accumulation of cholesterol is the prime contributor to atherosclerosis. It results in the formation of multiple deposits called plaques within arteries. Plaques can form blood clots called thrombus within arteries. If a thrombus dislodges and becomes free floating, it is called an embolus.

Arteriosclerosis is a general term describing any hardening of arteries. It occurs when calcium is deposited in the walls of arteries. It can happen when atherosclerosis is severe.

Difference between Arteriosclerosis and atherosclerosis: Arteriosclerosis is a defect in the artery artery walls. In this problem hardening of the flexible walls of blood arteries takes place and thus arteries loss elasticity. In young age the arteries are flexible due to the presence of a protein called elastin.

As age advances , there is loss of these elastin proteins cause thickening of arterial walls. In atherosclerosis fat plaques and cholesterols are deposited on the arteries and thus causing narrowing of the arteries.

Question) State the causes, treatments and prevention of myocardial infarction?


The term myocardial infarction is derived from myocardium (the heart muscle) and infarction (tissue death). It is more commonly known as a heart attack. It occurs when blood supply to a part of heart is interrupted and leads the death of heart muscles. It is a medical emergency, and the leading cause of death for both men and women all over the world.

Causes: Heart attack may be caused by blood clot in coronary arteries.

Symptoms: Severe chest pain is the most common symptom of myocardial infarction and may be in the form of sensation of tightness, pressure, or squeezing. Pain radiates most often to left arm, but may also radiate to lower jaw, neck, right arm and back. Loss of consciousness and even sudden death can occur in myocardial infarction.

Prevention and Treatment: Immediate treatment for suspected acute myocardial infarction includes oxygen supply, aspirin, and sublingual tablet of glyceryl trinitrate.

Most cases of myocardial infarction are treated with angioplasty (mechanical widening of a narrowed or totally obstructed blood vessel) or bypass surgery (surgery in which arteries or veins from elsewhere in the patient’s body are grafted to the coronary arteries to improve blood supply to heart muscles). Use of less fatty food materials and exercises is the major preventive methods.


For your information: Approximately one fourth of all myocardial infarctions are silent i.e. without chest pain or other symptoms. A silent heart attack is more common in the elderly, in patients with diabetes mellitus and after heart transplantation,……..


For your information: Angina pectoris means “chest pain”. It is not as severe as heart attack. The pain may occur in heart and often in left arm and shoulder. It is a warning sign that blood supply to heart muscles is not sufficient but shortage is not enough to cause tissue death.


For your information: World Heart Day is held on 28th September every year throughout the world. Its objective is to help people better understand their personal risks of cardiovascular disorders.


For your information: Cardiovascular disorders are the cause of 12% of adult deaths in Pakistan (Source: Federal Bureau of Statistics of Pakistan). Hypertension (blood pressure higher than normal) is the most common cause of cardiovascular disorders in Pakistan.

  • There are over 12 million hypertension patients in Pakistan.
  • About 10% of our population is diabetic.
  • According to the World Health Organization, in Pakistan 1 in 7 urban adults is obese.


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