Maarg Manthan · Topic 3.10

Transport System: Blood Vascular System and Lymphatic System

Science & Technology › Human Physiology – Organ Systems · Topic 3.10

The transport system of humans has two parts: the blood vascular system, made of the heart, blood and blood vessels, and the lymphatic system, made of lymph, lymph vessels and lymphoid organs. Blood is a fluid connective tissue, with about 55 per cent plasma and 45 per cent cells: red blood cells that carry oxygen using haemoglobin, white blood cells that defend the body, and platelets that help clotting. An adult has about 5 litres of blood. The heart has four chambers, two atria and two ventricles, and circulation is double: the pulmonary circuit takes blood to the lungs and the systemic circuit takes it to the body. The lymphatic system returns tissue fluid to the blood and supports immunity.

5 min read · UPSC Prelims · Science & Technology · Human Physiology – Organ Systems

At a Glance

Blood volume About 5 litres
Heart chambers Four
Pacemaker Sinoatrial node
Normal blood pressure About 120/80 mm Hg
Blood groups ABO (Landsteiner, 1901) and Rh
Exam link UPSC Prelims, Science & Technology: Human Physiology – Organ Systems

Where Does It Fit?

This is the tenth topic of the macro on human physiology and organ systems. It links the lungs and digestive system to every cell through the blood, and also covers lymph. Previous topic: Respiratory System: External and Internal Respiration in Humans, Animals, Plants and Insects. Next topic: Transport System in Plants and in a Single Cell.

What Does Blood Contain?

Component	Features and function
Plasma	About 55 per cent of blood, 90 per cent water with proteins, nutrients, hormones and wastes
Red blood cells	About 5 million per cubic millimetre, with no nucleus, biconcave and full of haemoglobin. They live for about 120 days, are made in the bone marrow and destroyed in the spleen and liver
White blood cells	About 5,000 to 10,000 per cubic millimetre. Neutrophils, lymphocytes, monocytes, eosinophils and basophils defend the body
Platelets	Cell fragments, about 1.5 to 4 lakh per cubic millimetre, which help blood to clot with fibrin and calcium
Blood groups	ABO groups found by Karl Landsteiner in 1901, and the Rh factor found in 1940. Group O negative is the universal donor and AB positive is the universal recipient
Haemoglobin	An iron-containing protein, about 12 to 16 grams per 100 millilitres in adults. Low levels cause anaemia

How Does the Heart and Circulation Work?

Heart structure: the right atrium and right ventricle handle deoxygenated blood, and the left atrium and left ventricle handle oxygenated blood. Valves prevent backflow, and the left ventricle has the thickest wall.
Double circulation: blood passes through the heart twice in one round. The right ventricle pumps blood to the lungs through the pulmonary artery, and the left ventricle pumps it to the body through the aorta.
Pacemaker: the sinoatrial node in the right atrium starts each heartbeat, about 72 times a minute at rest, and the sounds lub and dub come from closing of the valves.
Blood vessels: arteries carry blood away from the heart and have thick elastic walls, veins carry blood to the heart and have valves, and capillaries are thin vessels where exchange takes place.
Blood pressure: measured by a sphygmomanometer. Normal is about 120 over 80 millimetres of mercury, and a persistent higher value is hypertension.
ECG: the electrocardiogram records electrical activity of the heart.

What Is the Lymphatic System and What Else Should You Remember?

Lymph: a colourless fluid similar to plasma but with fewer proteins, formed from tissue fluid that drains into lymph vessels.
Functions: returns fluid and proteins to the blood, absorbs fats from the intestine through lacteals, and defends the body through lymph nodes, as in Immune System and Immunity.
Organs: lymph nodes filter lymph, the spleen filters blood and stores red cells, and the thymus and tonsils are also lymphoid.
Oedema and filariasis: blocked lymph vessels cause swelling, as in elephantiasis caused by filarial worms.
Heart diseases: atherosclerosis is the build-up of fatty deposits in arteries, leading to heart attack and stroke, and cholesterol is a risk factor.
Blood disorders: anaemia from lack of iron or vitamin B12, sickle cell disease and thalassaemia, haemophilia that is X-linked, and leukaemia as a cancer of white cells, as in Genetic Mutations: Types and Causes.
Blood donation: World Blood Donor Day is on 14 June, and one unit of blood is about 350 to 450 millilitres.
Other animals: fishes have a two-chambered heart, amphibians three, crocodiles and birds and mammals four, and insects have open circulation.
Blood vascular system: the blood vascular system is a closed system in humans, in which blood stays inside vessels, unlike the open system of insects and molluscs.

As an analytical point, circulation carries oxygen, nutrients, hormones and defence cells to every tissue. Lifestyle diseases such as hypertension and heart disease are now a leading cause of death in India.

Why Does It Matter for the Exam?

Numbers and names: blood cell counts, blood group facts and the pacemaker.
Concept questions: double circulation, the roles of arteries and veins, and lymph versus blood.
Health link: hypertension, heart attack and anaemia are major public health issues, and programmes such as anaemia control target women and children.
Technology link: artificial hearts, stents, pacemakers and blood substitutes.
Common errors: believing that all arteries carry oxygenated blood or that lymph has red cells.

Why Is This Topic Important?

Facts Blood groups and counts asked
Concept Double circulation
Link Heart disease and anaemia

What Came Next?

The next topic covers transport in plants and in a single cell. Next topic: Transport System in Plants and in a Single Cell.

Key People and Terms

Haemoglobin Oxygen-carrying protein
Plasma Liquid part of blood
Sinoatrial node Natural pacemaker
Artery and vein Away from and to the heart
Lymph Fluid in lymph vessels
Hypertension High blood pressure

Exam Corner

Points to Remember

ABO groups: Landsteiner, 1901.
O negative universal donor; AB positive recipient.
Pacemaker: SA node.
Normal pressure 120/80.
RBCs live about 120 days.

Do Not Confuse With

Artery and vein Away from heart versus towards heart
Blood and lymph With red cells versus without
Pulmonary and systemic circuits Heart to lungs versus heart to body

Memory Hook

Plasma, red, white, platelet four; O negative gives to all, AB positive takes from more; SA node starts the beat before.

Mains Angle

Questions ask about the heart, blood and heart disease. These points add depth.

Blood Components and groups
Heart Double circulation
Disease Hypertension, anaemia

A Question You May Face

An original practice question, not a past paper question.

“Describe the structure of the human heart and the process of double circulation, with a note on the lymphatic system.”

How to Answer

Blood Parts.
Heart Chambers.
Circulation Double.
Lymph Role.

GS Relevance

Prelims: blood components, blood groups, heart structure, blood vessels, lymph functions, disorders. GS Paper 3: science and technology, health.

Frequently Asked Questions

What are the components of blood?

Blood has about 55 per cent plasma, which is mostly water with proteins, nutrients and hormones, and about 45 per cent cells. The cells are red blood cells that carry oxygen using haemoglobin, white blood cells that defend the body, and platelets that help the blood to clot.

What is double circulation?

Double circulation means that blood passes through the heart twice in one complete round of the body. In pulmonary circulation the right side of the heart sends blood to the lungs and back, and in systemic circulation the left side sends oxygenated blood to the body and back, so the two kinds of blood do not mix.

Which blood group is the universal donor?

Blood group O negative is called the universal donor because its red cells have neither A nor B antigens nor the Rh antigen, so most people can receive it in an emergency. AB positive is called the universal recipient because it can receive all blood groups.

What is the function of the lymphatic system?

The lymphatic system returns fluid and proteins that leak from capillaries back to the blood, absorbs fats from the intestine through lacteals, and defends the body, because lymph nodes filter microbes and contain lymphocytes. Blocked lymph vessels cause swelling, as in elephantiasis caused by filarial worms.

What is normal blood pressure?

Normal blood pressure in a healthy adult is about 120 over 80 millimetres of mercury, where the first number is the systolic pressure when the heart contracts and the second is the diastolic pressure when it relaxes. A persistent reading of 140 over 90 or more is called hypertension and raises the risk of heart attack and stroke.

PYQ Practice — Statement Analysis

1 The sinoatrial node acts as the pacemaker of the heart.

True

It starts the heartbeat.

2 Red blood cells in humans have a nucleus.

False

They have none.

3 Karl Landsteiner discovered the ABO blood groups.