Blood Circulation in Human

BiologyBody Fluids and CirculationFor NEET aspirants

Blood circulation in human is a complete double circulation: the pulmonary and the systemic pathways carry blood separately, so oxygenated and deoxygenated blood never mix. This page covers the three layers of blood vessels, both pathways, the hepatic portal and coronary systems, the neural and hormonal regulation of the heart, and disorders such as hypertension, coronary artery disease, angina and heart failure, as given in the NCERT Class 11 chapter Body Fluids and Circulation. For blood circulation in human, NEET often asks the route of blood and blood pressure values.

On this page1Blood vessels2Double circulation3Portal and coronary systems4Regulation5Disorders6Exam essentials7Quick revision8Solved examples9Practice

Key Points at a Glance

★ Must learn Arteries and veins have three layers: tunica intima (squamous endothelium), tunica media (smooth muscle, elastic fibres), tunica externa (fibrous connective tissue with collagen fibres).
The tunica media is comparatively thin in veins.
★ Must learn Pulmonary circulation: right ventricle, pulmonary artery (deoxygenated), lungs, pulmonary veins (oxygenated), left atrium.
★ Must learn Systemic circulation: left ventricle, aorta, arteries, arterioles, capillaries, tissues, venules, veins, vena cava, right atrium.
Hepatic portal vein: carries blood from the intestine to the liver before it enters the systemic circulation.
Coronary system: blood vessels that circulate blood to and from the cardiac musculature only.
★ Must learn The heart is myogenic (nodal tissue); a neural centre in the medulla oblongata moderates it through the ANS.
Sympathetic signals and adrenal medullary hormones increase cardiac output; parasympathetic signals decrease it.
★ Must learn Normal blood pressure 120/80 mm Hg; repeated readings of 140/90 or higher mean hypertension.
CAD (atherosclerosis): deposits of calcium, fat, cholesterol and fibrous tissue narrow the arteries supplying the heart.
Angina pectoris: acute chest pain when too little oxygen reaches the heart muscle; heart failure is not cardiac arrest or heart attack.

1. Blood Vessels

Blood flows strictly by a fixed route through the blood vessels: the arteries and veins.
Basically, each artery and vein has three layers.

Layer	Position	Made of
Tunica intima	Inner lining	Squamous endothelium
Tunica media	Middle layer	Smooth muscle and elastic fibres
Tunica externa	External layer	Fibrous connective tissue with collagen fibres

★ Exam imp The tunica media is comparatively thin in the veins.

Memory Trick

The names give the order from the lumen outwards: Intima = inside, Media = middle, Externa = external.

Artery

Carries blood away from the heart towards the tissues (aorta, arteries, arterioles)
Thicker tunica media (smooth muscle)

Vein

Carries blood from the tissues back to the heart (venules, veins, vena cava)
Tunica media comparatively thin

Key idea

Every artery and vein has the same three layers; the middle smooth-muscle layer is thinner in veins.

2. Double Circulation

The right ventricle pumps blood into the pulmonary artery; the left ventricle pumps blood into the aorta.

2.1 Pulmonary circulation

The right ventricle pumps deoxygenated blood into the pulmonary artery.
The pulmonary artery carries it to the lungs, where it is oxygenated.
The pulmonary veins carry the oxygenated blood into the left atrium.

2.2 Systemic circulation

The left ventricle pumps oxygenated blood into the aorta.
A network of arteries, arterioles and capillaries carries it to the tissues.
From the tissues, the deoxygenated blood is collected by a system of venules, veins and vena cava.
The vena cava empties it into the right atrium.

★ Exam imp The systemic circulation provides nutrients, $O_{2}$ and other essential substances to the tissues.
It also takes $C O_{2}$ and other harmful substances away from the tissues for elimination.

Test yourself: hide labels

Figure 1: Schematic plan of blood circulation in human. Pulmonary circulation (right ventricle to lungs to left atrium) and systemic circulation (left ventricle to body parts to right atrium) form two separate pathways, so oxygenated (red) and deoxygenated (blue) blood never mix.

★ Very important Humans have a complete double circulation: two separate circulatory pathways, the pulmonary (right ventricle to lungs to left atrium) and the systemic (left ventricle to body tissues to right atrium).

Feature	Pulmonary circulation	Systemic circulation
Starts in	Right ventricle	Left ventricle
Vessel leaving the heart	Pulmonary artery	Aorta
Blood leaving the heart	Deoxygenated	Oxygenated
Goes to	Lungs	Body tissues
Returns through	Pulmonary veins (oxygenated blood)	Venules, veins and vena cava (deoxygenated blood)
Ends in	Left atrium	Right atrium

Memory Trick

Right pumps to the lungs, left pumps to the rest. Each pathway then ends on the opposite side: lungs to the left atrium, body to the right atrium.

NEET Focus

The pulmonary artery carries deoxygenated blood and the pulmonary veins carry oxygenated blood: the reverse of the systemic arteries and veins.
Order in systemic circulation: aorta, arteries, arterioles, capillaries, venules, veins, vena cava.
Pulmonary circulation starts in the right ventricle, not the right atrium; systemic circulation starts in the left ventricle.

Extra Depth: Blood vessels are named by the direction of flow: arteries carry blood away from the heart and veins carry it towards the heart, whatever its oxygen content. This is why the pulmonary artery carries deoxygenated blood.

Key idea

Two separate pathways keep the blood apart: the right side sends deoxygenated blood to the lungs, and the left side sends oxygenated blood to the body.

3. Hepatic Portal and Coronary Systems

Hepatic portal system: a unique vascular connection between the digestive tract and the liver.
★ Exam imp The hepatic portal vein carries blood from the intestine to the liver before it is delivered to the systemic circulation.
Coronary system: a special system of blood vessels present exclusively for the circulation of blood to and from the cardiac musculature.

Hepatic portal system

Connects the digestive tract and the liver
Hepatic portal vein: intestine to liver
Blood reaches the liver before entering the systemic circulation

Coronary system

Serves the heart muscle only
Carries blood to and from the cardiac musculature
Coronary artery disease affects these vessels

Key idea

Two special circuits: the hepatic portal vein takes intestinal blood to the liver first, and the coronary vessels feed the heart muscle itself.

Quick Recall: tap to check

Which vessel carries deoxygenated blood out of the right ventricle?

The pulmonary artery.

In which chamber does the systemic circulation end?

The right atrium, into which the vena cava empties.

Which layer of the vessel wall is comparatively thin in veins?

The tunica media.

Which vein carries blood from the intestine to the liver?

The hepatic portal vein.

4. Regulation of Cardiac Activity

Normal activities of the heart are regulated intrinsically, that is, auto regulated by specialised muscles, the nodal tissue.
★ Exam imp A special neural centre in the medulla oblongata can moderate cardiac function through the autonomic nervous system (ANS).

★ Very important The human heart is myogenic: its normal activity is started and regulated by its own specialised muscle, the nodal tissue.

Signal	Effect on the heart
Sympathetic nerves (part of the ANS)	Increase the rate of heart beat and the strength of ventricular contraction, and so the cardiac output
Parasympathetic neural signals (another part of the ANS)	Decrease the rate of heart beat and the speed of conduction of the action potential, and so the cardiac output
Adrenal medullary hormones	Increase the cardiac output

Memory Trick

Sympathetic speeds up, parasympathetic slows down. The adrenal medulla sides with the sympathetic: it also raises cardiac output.

NEET Focus

The heart beat starts in the nodal tissue; nerves and hormones only moderate it.
The cardiac centre lies in the medulla oblongata.
Sympathetic: more strength of ventricular contraction. Parasympathetic: less speed of conduction of the action potential.

Key idea

The heart beats on its own, while the medulla oblongata, through sympathetic and parasympathetic signals, and the adrenal medullary hormones speed it up or slow it down.

5. Disorders of Circulatory System

5.1 High blood pressure (hypertension)

Hypertension: blood pressure that is higher than normal (120/80).
In this reading, 120 mm Hg (millimetres of mercury pressure) is the systolic, or pumping, pressure.
80 mm Hg is the diastolic, or resting, pressure.
★ Exam imp If repeated checks of a person's blood pressure read 140/90 (140 over 90) or higher, it shows hypertension.
High blood pressure leads to heart diseases and also affects vital organs such as the brain and kidney.

★ Very important Normal blood pressure is 120/80 mm Hg (systolic/diastolic); repeated readings of 140/90 or higher indicate hypertension.

Memory Trick

The top number is the pumping (systolic) pressure, the bottom one the resting (diastolic) pressure. Normal: 120 over 80. Hypertension: 140 over 90 or more, on repeated checks.

5.2 Coronary artery disease (CAD)

Coronary artery disease (CAD) is often referred to as atherosclerosis.
It affects the vessels that supply blood to the heart muscle.
★ Exam imp It is caused by deposits of calcium, fat, cholesterol and fibrous tissues, which make the lumen of the arteries narrower.

Memory Trick

The four CAD deposits are two Cs and two Fs: calcium, cholesterol, fat and fibrous tissue.

5.3 Angina

Angina, also called angina pectoris: a symptom of acute chest pain that appears when not enough oxygen reaches the heart muscle.
It can occur in men and women of any age, but it is more common among the middle-aged and elderly.
It occurs due to conditions that affect the blood flow.

5.4 Heart failure

Heart failure: the state of the heart when it is not pumping blood effectively enough to meet the needs of the body.
It is sometimes called congestive heart failure, because congestion of the lungs is one of its main symptoms.

Condition	What happens
Heart failure	The heart does not pump blood effectively enough to meet the body's needs
Cardiac arrest	The heart stops beating
Heart attack	The heart muscle is suddenly damaged by an inadequate blood supply

Tips and Tricks

Tell the three apart by one word each: heart failure = weak pumping, cardiac arrest = stopped beating, heart attack = sudden damage to heart muscle. An option that calls heart failure the same as cardiac arrest is wrong.

Key idea

Know the numbers 120/80 and 140/90, the four deposits in CAD, angina as chest pain from too little oxygen, and heart failure as weak pumping.

Quick Recall: tap to check

Which pressure does the 80 in 120/80 represent?

The diastolic, or resting, pressure (80 mm Hg).

Which disorder is often referred to as atherosclerosis?

Coronary artery disease (CAD).

Why is heart failure also called congestive heart failure?

Because congestion of the lungs is one of its main symptoms.

Where is the neural centre that moderates cardiac function?

In the medulla oblongata.

6. Exam Essentials

Pairs to Match

List I	List II
Tunica intima	Squamous endothelium
Tunica media	Smooth muscle and elastic fibres
Tunica externa	Fibrous connective tissue with collagen fibres
Pulmonary artery	Deoxygenated blood from the right ventricle to the lungs
Pulmonary veins	Oxygenated blood from the lungs to the left atrium
Vena cava	Empties deoxygenated blood into the right atrium
Hepatic portal vein	Blood from the intestine to the liver
Coronary system	Blood to and from the cardiac musculature
Medulla oblongata	Neural centre that moderates cardiac function
Sympathetic nerves	Increase heart rate and strength of ventricular contraction
Parasympathetic signals	Decrease heart rate and speed of conduction
Adrenal medullary hormones	Increase cardiac output
Atherosclerosis	Coronary artery disease
Angina pectoris	Acute chest pain from too little oxygen to the heart muscle
Congestion of the lungs	One of the main symptoms of heart failure

Exceptions

The pulmonary artery carries deoxygenated blood, and the pulmonary veins carry oxygenated blood.
The tunica media is thinner in veins than in arteries.
The hepatic portal vein takes blood to the liver first, not straight into the systemic circulation.
Of the three regulators, only parasympathetic signals decrease cardiac output.
Heart failure is not the same as cardiac arrest or a heart attack.
Angina can occur at any age in men and women, though it is more common in the middle-aged and elderly.

Numbers to Remember

Blood vessel wall: 3 layers (intima, media, externa).
Normal blood pressure: 120/80 mm Hg; systolic 120, diastolic 80.
Hypertension: repeated readings of 140/90 or higher.
CAD deposits: 4 kinds (calcium, fat, cholesterol, fibrous tissue).

7. Quick Revision

Blood flows by a fixed route through arteries and veins.
Three layers: tunica intima (squamous endothelium), tunica media (smooth muscle, elastic fibres), tunica externa (collagen-rich connective tissue).
Tunica media is comparatively thin in veins.
Right ventricle to pulmonary artery; left ventricle to aorta.
Pulmonary circulation: deoxygenated blood to the lungs, oxygenated blood back to the left atrium by pulmonary veins.
Systemic circulation: aorta, arteries, arterioles, capillaries, tissues, venules, veins, vena cava, right atrium.
Systemic circulation supplies nutrients and oxygen and removes carbon dioxide and harmful substances.
Humans have complete double circulation: two separate pathways with no mixing of blood.
Hepatic portal vein: intestine to liver before the systemic circulation. Coronary system: heart muscle only.
Heart is myogenic; the medulla oblongata moderates it through the ANS.
Sympathetic and adrenal medullary hormones raise cardiac output; parasympathetic lowers heart rate, conduction speed and output.
Normal blood pressure 120/80 mm Hg; hypertension at repeated readings of 140/90 or higher; harms heart, brain and kidney.
CAD (atherosclerosis): calcium, fat, cholesterol and fibrous tissue narrow the coronary arteries.
Angina pectoris: acute chest pain from low oxygen to heart muscle. Heart failure: weak pumping, lung congestion.

8. Solved Examples

Solved Example 1

Match List I with List II.
List I: A. Tunica intima, B. Tunica media, C. Tunica externa, D. Hepatic portal vein
List II: I. Smooth muscle and elastic fibres, II. Carries blood from the intestine to the liver, III. Squamous endothelium, IV. Fibrous connective tissue with collagen fibres
Choose the correct answer:
(A) A-I, B-III, C-IV, D-II
(B) A-III, B-I, C-IV, D-II
(C) A-III, B-IV, C-I, D-II
(D) A-IV, B-I, C-III, D-II

Solution:

Answer: (B). Intima is squamous endothelium (III), media is smooth muscle with elastic fibres (I), externa is collagen-rich connective tissue (IV), and the hepatic portal vein links the intestine to the liver (II).

Solved Example 2

Read the statements about regulation of the heart.
A. The human heart is myogenic.
B. The neural centre that moderates cardiac function lies in the cerebellum.
C. Sympathetic signals increase the strength of ventricular contraction.
D. Parasympathetic signals decrease the speed of conduction of the action potential.
E. Adrenal medullary hormones decrease the cardiac output.
Choose the correct answer:
(A) A, B and C only
(B) A, C and D only
(C) B, D and E only
(D) A, C, D and E only

Solution:

Answer: (B). B is wrong: the centre lies in the medulla oblongata. E is wrong: adrenal medullary hormones increase cardiac output. A, C and D are correct.

Solved Example 3

Starting from the left ventricle, arrange the vessels in the order in which blood passes through them in systemic circulation.
A. Arterioles
B. Aorta
C. Venules
D. Capillaries
E. Vena cava
Choose the correct answer:
(A) B, A, C, D, E
(B) B, D, A, C, E
(C) B, A, D, C, E
(D) A, B, D, C, E

Solution:

Answer: (C). Aorta, arterioles, capillaries, venules and finally the vena cava, which opens into the right atrium.

Solved Example 4

Which repeated blood pressure reading shows hypertension?
(A) 120/80 mm Hg
(B) 110/70 mm Hg
(C) 140/90 mm Hg or higher
(D) 100/60 mm Hg

Solution:

Answer: (C). Normal blood pressure is 120/80 mm Hg; repeated readings of 140/90 or higher indicate hypertension.

Solved Example 5

Which statement about coronary artery disease is NOT correct?
(A) It is often referred to as atherosclerosis
(B) It affects the vessels that supply blood to the heart muscle
(C) It is caused by deposits of calcium, fat, cholesterol and fibrous tissue
(D) It widens the lumen of the coronary arteries

Solution:

Answer: (D). The deposits make the lumen of the arteries narrower, not wider.

Solved Example 6

Statement I: Heart failure is sometimes called congestive heart failure.
Statement II: Heart failure is the same as cardiac arrest.
(A) Both Statement I and Statement II are correct
(B) Statement I is correct but Statement II is incorrect
(C) Statement I is incorrect but Statement II is correct
(D) Both Statement I and Statement II are incorrect

Solution:

Answer: (B). Congestion of the lungs is a main symptom of heart failure, hence the name. In cardiac arrest the heart stops beating, which is a different state.

9. Practice Questions

Practice Questions

Match List I with List II.
List I: A. Hypertension, B. Angina, C. Heart failure, D. Coronary artery disease
List II: I. Acute chest pain when too little oxygen reaches the heart muscle, II. Heart does not pump effectively enough for the body's needs, III. Narrowing of the arteries that supply the heart muscle, IV. Repeated readings of 140/90 or higher
(A) A-IV, B-I, C-II, D-III
(B) A-I, B-IV, C-II, D-III
(C) A-IV, B-II, C-I, D-III
(D) A-IV, B-I, C-III, D-IIAnswer: (A). Each disorder matches its defining feature.
Read the statements.
A. The right ventricle pumps blood into the aorta.
B. Pulmonary veins carry oxygenated blood to the left atrium.
C. Systemic circulation removes $C O_{2}$ from the tissues.
D. The vena cava empties into the right atrium.
E. Pulmonary circulation starts in the left ventricle.
(A) A, B and C only
(B) B, C and D only
(C) C, D and E only
(D) B, D and E onlyAnswer: (B). The right ventricle pumps into the pulmonary artery, and pulmonary circulation starts in the right ventricle.
Arrange the parts in the order of pulmonary circulation.
A. Lungs
B. Right ventricle
C. Left atrium
D. Pulmonary artery
E. Pulmonary veins
(A) B, D, A, E, C
(B) B, E, A, D, C
(C) D, B, A, E, C
(D) B, D, E, A, CAnswer: (A). Right ventricle, pulmonary artery, lungs, pulmonary veins, left atrium.
Statement I: The tunica media is comparatively thin in the veins.
Statement II: The tunica intima is made of smooth muscle and elastic fibres.
(A) Both Statement I and Statement II are correct
(B) Statement I is correct but Statement II is incorrect
(C) Statement I is incorrect but Statement II is correct
(D) Both Statement I and Statement II are incorrectAnswer: (B). The tunica intima is squamous endothelium; smooth muscle and elastic fibres form the tunica media.
The coronary system of blood vessels serves:
(A) The liver
(B) The lungs
(C) The cardiac musculature
(D) The intestineAnswer: (C). The coronary system circulates blood exclusively to and from the cardiac musculature.
Which of the following does NOT increase cardiac output?
(A) Sympathetic neural signals
(B) Adrenal medullary hormones
(C) Parasympathetic neural signals
(D) A higher stroke volumeAnswer: (C). Parasympathetic signals decrease the heart rate, the speed of conduction and so the cardiac output.
Angina pectoris is best described as:
(A) Stopping of the heart beat
(B) Acute chest pain when not enough oxygen reaches the heart muscle
(C) Blood pressure of 140/90 or higher
(D) Congestion of the lungsAnswer: (B). Angina is a symptom of acute chest pain due to poor oxygen supply to the heart muscle.
What is meant by double circulation? What is its significance?Answer: Double circulation means blood flows in two separate pathways: pulmonary (right ventricle to lungs to left atrium) and systemic (left ventricle to body tissues to right atrium). Oxygenated and deoxygenated blood never mix, so the tissues receive fully oxygenated blood with nutrients, while carbon dioxide and wastes are carried away efficiently.
Why do we call our heart myogenic?Answer: The normal activities of the heart are started and regulated by its own specialised cardiac muscle, the nodal tissue, which is autoexcitable. Nerves and hormones only moderate this activity, so the heart is called myogenic.

Common Mistakes to Avoid

Watch out

Writing that pulmonary veins carry deoxygenated blood. They carry oxygenated blood from the lungs to the left atrium.
Writing that the tunica media is thicker in veins. It is comparatively thin in veins.
Reversing the hepatic portal vein. It carries blood from the intestine to the liver.
Placing the cardiac centre in the cerebellum. It lies in the medulla oblongata.
Saying parasympathetic signals increase heart rate. They decrease it; sympathetic signals increase it.
Calling 120 the diastolic pressure. 120 mm Hg is systolic (pumping); 80 mm Hg is diastolic (resting).
Treating heart failure as cardiac arrest. In heart failure the heart pumps weakly; in cardiac arrest it stops beating.
Writing that CAD deposits widen the coronary arteries. They make the lumen narrower.

Frequently Asked Questions

What is double circulation and why is it significant?

Double circulation means blood flows through two separate pathways. In pulmonary circulation the right ventricle sends deoxygenated blood to the lungs, and it returns to the left atrium. In systemic circulation the left ventricle sends oxygenated blood to the body, and it returns to the right atrium. The two kinds of blood never mix.

What are the three layers of a blood vessel?

Each artery and vein has an inner tunica intima of squamous endothelium, a middle tunica media of smooth muscle and elastic fibres, and an outer tunica externa of fibrous connective tissue with collagen fibres. The tunica media is comparatively thin in veins, which is a common exam point.

What is the hepatic portal system?

The hepatic portal system is a unique vascular connection between the digestive tract and the liver. Its hepatic portal vein carries blood from the intestine to the liver before the blood is delivered to the systemic circulation. It is different from the coronary system, which serves only the heart muscle.

Why is the human heart called myogenic?

The human heart is called myogenic because its normal activity is started and regulated by its own specialised muscle, the nodal tissue. The nodal tissue is autoexcitable and the SAN sets the pace. Nerves from the medulla oblongata and adrenal medullary hormones only moderate this built-in activity.

How do sympathetic and parasympathetic nerves affect the heart?

Sympathetic signals increase the rate of heart beat and the strength of ventricular contraction, so cardiac output rises. Parasympathetic signals decrease the heart rate and the speed of conduction of the action potential, so cardiac output falls. Adrenal medullary hormones also increase cardiac output.

What blood pressure reading indicates hypertension?

Normal blood pressure is 120/80 mm Hg, where 120 is the systolic or pumping pressure and 80 is the diastolic or resting pressure. If repeated checks show 140/90 or higher, the person has hypertension. It can lead to heart diseases and harm vital organs such as the brain and kidney.

How is heart failure different from cardiac arrest and heart attack?

In heart failure the heart still beats but does not pump blood effectively enough for the body's needs; lung congestion is a main symptom. In cardiac arrest the heart stops beating. In a heart attack the heart muscle is suddenly damaged because its blood supply is inadequate.

What causes coronary artery disease and angina?

Coronary artery disease, often called atherosclerosis, is caused by deposits of calcium, fat, cholesterol and fibrous tissue that narrow the arteries supplying the heart muscle. Angina pectoris is acute chest pain that appears when not enough oxygen reaches the heart muscle, due to conditions that affect blood flow.

Previous year questions on Blood Circulation in Human

8 questions from past papers, each with a step-by-step solution.

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