BiologyNCERT Class 11

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Body Fluids and Circulation Notes

Study Notes

6 Topics13 Formulas10 PYQs36 Key Points

Chapter Overview Blood Lymph Human Circulation Cardiac Cycle Double Circulation Circulatory Disorders

Chapter at a Glance

Topics6

Key Points36

Formulas13

Diagrams18

NEET PYQs10

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Topics

Chapter Overview

Overview

This chapter explains how transport of gases, nutrients, hormones, wastes and immune cells occurs in the human body. NCERT focuses mainly on blood, lymph, the human heart, blood vessels, cardiac cycle, double circulation and common circulatory disorders. Blood is a connective tissue made of plasma and formed elements. Lymph returns tissue fluid to blood and helps immunity. The four-chambered human heart pumps blood through pulmonary and systemic circuits. The cardiac cycle explains rhythmic systole and diastole, while ECG records electrical activity of the heart. NEET frequently asks blood groups, coagulation, cardiac output, heart sounds, hypertension, CAD and double circulation.

Key Points5

1Transport systems maintain homeostasis by distributing materials and removing wastes.
2Human circulation is closed, double and complete because blood remains in vessels and passes twice through the heart in one complete circuit.
3NCERT values such as 5 litres blood volume, 55 percent plasma, 45 percent formed elements, 72 beats per minute and 5 litres per minute cardiac output are high-yield.
4Pulmonary circulation oxygenates blood; systemic circulation supplies oxygenated blood to tissues.
5ECG waves represent electrical events: P wave for atrial depolarisation, QRS for ventricular depolarisation and T wave for ventricular repolarisation.

Memory Tricks2

Chapter Order Trick

Remember the chapter flow as B-L-H-C-D-D: Blood, Lymph, Heart, Cardiac cycle, Double circulation, Disorders.

NEET Number Pack

Keep 55-45-72-70-5 together: plasma 55 percent, formed elements 45 percent, heart rate 72/min, stroke volume 70 mL, cardiac output about 5 L/min.

Examples1

Daily Life Connection

When you run, muscles need more oxygen. Heart rate and cardiac output rise so blood can deliver more oxygen and remove carbon dioxide faster.

Reference Tables1

Chapter Map for NEET

Area	Core Idea	High-Yield NEET Focus
Blood	Plasma plus RBCs, WBCs and platelets	ABO/Rh groups, coagulation, cell functions
Lymph	Tissue fluid in lymph vessels	Composition, functions, lymphoid organs
Human Circulation	Heart, vessels and conducting system	Blood flow pathway and valves
Cardiac Cycle	Events in one heartbeat	0.8 s cycle, heart sounds, ECG waves
Double Circulation	Two circuits through heart	Pulmonary vs systemic circulation
Disorders	Abnormal cardiovascular conditions	Hypertension, CAD, angina, heart failure

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Common Mistakes2

Mixing Blood and Lymph

Lymph is not identical to blood. It lacks RBCs and has fewer proteins, but contains lymphocytes and returns tissue fluid to blood.

Single vs Double Circulation

Humans do not have single circulation like fishes. In one complete circulation, blood passes through the heart twice.

Formula Cards2

Cardiac Output

Amount of blood pumped by each ventricle per minute. In a healthy adult, it is approximately 70 mL × 72 min⁻¹ = 5040 mL min⁻¹, about 5 L min⁻¹.

Variables

CO=

Cardiac output in mL per minute or L per minute

SV=

Stroke volume, blood pumped by one ventricle per beat

HR=

Heart rate, number of beats per minute

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Diagrams3

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Blood

Overview

Blood is a specialized fluid connective tissue that transports gases, nutrients, hormones, wastes and immune components. It consists of plasma, the straw-coloured fluid matrix, and formed elements: RBCs, WBCs and platelets. Plasma contains water, proteins, ions, nutrients, hormones and wastes. RBCs are biconcave, enucleated cells rich in haemoglobin and transport oxygen. WBCs are nucleated immune cells classified as granulocytes and agranulocytes. Platelets are cell fragments that help blood coagulation. Blood grouping depends on antigens present on RBCs, mainly ABO and Rh systems. In NEET, blood composition, cell counts, universal donor/recipient and clotting factors are frequently tested.

Key Points6

1Plasma proteins include fibrinogen for clotting, globulins for defence and albumins for osmotic balance.
2Erythrocytes are formed in red bone marrow and have an average lifespan of about 120 days.
3Neutrophils and lymphocytes are the most abundant WBCs and are high-yield for NEET.
4Platelet deficiency can cause clotting disorders and excessive bleeding.
5AB blood group is universal recipient for RBC transfusion; O negative is commonly considered universal donor.
6Rh incompatibility is prevented clinically by anti-Rh antibodies after first delivery.

Memory Tricks3

Plasma Proteins

FAB: Fibrinogen for clotting, Albumin for osmotic balance, Globulin for defence.

ABO Antibody Logic

Your plasma carries antibodies against the antigen you do not have. A has anti-B, B has anti-A, O has both, AB has none.

WBC Types

Never Let Monkeys Eat Bananas: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils.

Examples2

Blood Donation

Before transfusion, ABO and Rh matching is checked to prevent agglutination caused by antigen-antibody reactions.

Clot at a Cut

When skin is cut, platelets stick to the injured site and trigger fibrin formation, preventing excessive blood loss.

Reference Tables3

Blood Cell Comparison

Feature	RBCs	WBCs	Platelets
Also called	Erythrocytes	Leucocytes	Thrombocytes
Nucleus	Absent in mature human RBCs	Present	Absent; cell fragments
Main function	Transport O₂ and some CO₂	Defence and immunity	Blood clotting
Approximate count	5 to 5.5 million mm⁻³	6000 to 8000 mm⁻³	1.5 to 3.5 lakh mm⁻³
Origin	Red bone marrow	Bone marrow and lymphoid tissues	Megakaryocytes in bone marrow

ABO Blood Group Chart

Blood Group	Antigen on RBC	Antibody in Plasma	Can Receive RBC From
A	A	Anti-B	A, O
B	B	Anti-A	B, O
AB	A and B	None	A, B, AB, O
O	None	Anti-A and Anti-B	O

Rh Factor Summary

Condition	Meaning	NEET Point
Rh positive	Rh antigen present on RBCs	Can receive Rh positive or Rh negative if ABO compatible
Rh negative	Rh antigen absent	Should preferably receive Rh negative blood
Rh incompatibility	Rh negative mother with Rh positive fetus	Can cause erythroblastosis foetalis in later pregnancies

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Common Mistakes3

Universal Donor Confusion

For RBC transfusion, O negative is safest universal donor, but plasma transfusion rules are different. NEET usually asks RBC transfusion unless stated otherwise.

RBC Nucleus Error

Mature human RBCs are enucleated. Do not generalize this to all vertebrates.

Platelets as Cells

Platelets are cell fragments derived from megakaryocytes, not complete typical cells.

Formula Cards2

Haematocrit

Percentage of blood volume occupied by RBCs. It approximately corresponds to the formed element fraction, especially RBCs.

Variables

RBC volume=

Packed red blood cell volume after centrifugation

Total blood volume=

Total volume of blood sample

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Diagrams4

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Lymph

Overview

Lymph is a colourless fluid formed when tissue fluid enters lymphatic capillaries. As blood passes through capillaries, some plasma and small molecules filter into intercellular spaces, forming tissue fluid. Most returns directly to blood, while the remaining fluid enters lymph vessels and becomes lymph. Lymph is similar to plasma but has fewer proteins, no RBCs and many lymphocytes. It transports absorbed fats from intestinal lacteals, returns excess tissue fluid to blood and supports immunity. Lymphatic vessels ultimately drain into large veins near the heart. Lymphoid organs such as lymph nodes, spleen, thymus and tonsils help filter pathogens and produce immune responses.

Key Points5

1Lymph acts as a middle link between blood and tissue cells.
2Exchange of nutrients and gases occurs through tissue fluid, not by direct contact of most cells with blood.
3Lymph flow is slow and assisted by skeletal muscle contraction and valves.
4Lymphatic capillaries are blind-ended and highly permeable.
5The immune role of lymph is mainly due to lymphocytes and lymphoid organs.

Memory Tricks2

Lymph Functions

RFI: Return fluid, Fat absorption, Immunity.

Lymph is Like Plasma

Think: lymph is plasma minus many proteins and minus RBCs, plus many lymphocytes.

Examples2

Swollen Lymph Nodes

During throat infection, cervical lymph nodes may swell because lymphocytes multiply and pathogens are filtered there.

Edema Connection

If lymph drainage is blocked, excess tissue fluid accumulates, causing swelling.

Reference Tables2

Blood Plasma vs Lymph

Feature	Blood Plasma	Lymph
Location	Inside blood vessels	Inside lymph vessels and lymph spaces
Protein content	Higher	Lower
RBCs	Absent in plasma but present in whole blood	Absent
Major cells	Blood cells in whole blood	Lymphocytes
Main function	Transport medium of blood	Fluid return, fat transport, immunity

Lymphoid Organs

Organ	Main Role	NEET Focus
Lymph nodes	Filter lymph and trap pathogens	Swelling indicates immune activity
Spleen	Filters blood and stores immune cells	Largest lymphoid organ
Thymus	Maturation of T lymphocytes	Important in early life
Tonsils	Defence at pharynx	First-line lymphoid protection

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Common Mistakes2

Calling Lymph Red

Lymph is colourless because it does not contain RBCs or haemoglobin.

Ignoring Fat Transport

Lymph is not only for immunity. Intestinal lacteals absorb dietary fats into lymph.

Formula Cards1

Tissue Fluid Balance

A conceptual balance showing why lymphatic drainage is necessary to prevent fluid accumulation in tissues.

Variables

Filtered fluid=

Plasma-derived fluid leaving blood capillaries

Returned fluid=

Fluid reabsorbed directly into venous end of capillaries

Lymph=

Excess tissue fluid entering lymphatic vessels

Diagrams3

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Human Circulation

Overview

Human circulation is a closed circulatory system driven by a four-chambered muscular heart. The right atrium receives deoxygenated blood from the venae cavae and sends it to the right ventricle, which pumps it to lungs through the pulmonary artery. The left atrium receives oxygenated blood from pulmonary veins and sends it to the left ventricle, which pumps it through the aorta to the body. Valves prevent backflow. The conducting system includes SA node, AV node, bundle of His and Purkinje fibres, ensuring rhythmic contraction. Arteries carry blood away from the heart, veins carry blood toward the heart and capillaries allow exchange.

Key Points5

1Pulmonary artery is exceptional because it carries deoxygenated blood away from the heart.
2Pulmonary veins are exceptional because they carry oxygenated blood toward the heart.
3The left ventricle has the thickest wall because it pumps blood to the entire body.
4The conducting system coordinates atrial systole followed by ventricular systole.
5Semilunar valves at the base of aorta and pulmonary artery prevent backflow into ventricles.

Memory Tricks2

Valve Positions

Try Before Leaving: Tricuspid on right before lungs; Bicuspid on left before body.

Impulse Path

SABP: SA node → AV node → Bundle of His → Purkinje fibres.

Examples2

Pulse Feeling

The pulse at the wrist is due to pressure waves in arteries produced by ventricular systole.

Varicose Veins

Weak venous valves can allow pooling of blood, producing swollen veins, often in legs.

Reference Tables2

Arteries, Veins and Capillaries

Feature	Arteries	Veins	Capillaries
Direction	Away from heart	Toward heart	Between arterioles and venules
Wall	Thick, elastic, muscular	Thinner, less elastic	One-cell thick endothelium
Pressure	High	Low	Very low
Valves	Usually absent	Present in many veins	Absent
Function	Distribution	Collection and return	Exchange

Conducting System Sequence

Part	Location	Function
SA node	Right upper corner of right atrium	Initiates impulse; pacemaker
AV node	Lower left corner of right atrium near AV septum	Receives and delays impulse
Bundle of His	AV node to interventricular septum	Conducts impulse to ventricles
Purkinje fibres	Ventricular walls	Spread impulse for ventricular contraction

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Common Mistakes3

Artery Means Oxygenated

Artery means away from heart, not always oxygenated. Pulmonary artery carries deoxygenated blood.

Vein Means Deoxygenated

Vein means toward heart. Pulmonary veins carry oxygenated blood.

Pacemaker Confusion

SA node is the natural pacemaker, not AV node.

Formula Cards1

Heart Rate from Cardiac Cycle Duration

If one cardiac cycle takes 0.8 s, heart rate is 60/0.8 = 75 beats per minute, close to the NCERT average of 72 beats per minute.

Variables

Heart Rate=

Number of heartbeats per minute

Duration=

Time taken for one complete heartbeat in seconds

Diagrams4

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Cardiac Cycle

Overview

The cardiac cycle is the sequence of events completed during one heartbeat. At an average heart rate of about 72 beats per minute, one cycle lasts about 0.8 seconds. It includes joint diastole, atrial systole and ventricular systole. During joint diastole, all chambers relax and blood flows passively into ventricles. Atrial systole completes ventricular filling. Ventricular systole closes AV valves, produces the first heart sound, and pumps blood into aorta and pulmonary artery. Ventricular relaxation closes semilunar valves, producing the second heart sound. ECG records electrical activity: P wave, QRS complex and T wave, which correspond to atrial and ventricular electrical events.

Key Points5

1Atrial systole increases ventricular filling but most filling occurs passively during diastole.
2Ventricular systole raises ventricular pressure, forcing semilunar valves to open.
3AV valves prevent backflow into atria during ventricular systole.
4T wave represents ventricular repolarisation, not atrial relaxation.
5ECG is useful for detecting rhythm abnormalities and myocardial problems.

Memory Tricks3

Cardiac Cycle Durations

Remember 4-1-3 in a total of 8 tenths: joint diastole 0.4 s, atrial systole 0.1 s, ventricular systole 0.3 s.

Heart Sounds

LUB closes AV doors before ventricles pump; DUB closes arterial doors after pumping.

ECG Waves

P for Push by atria, QRS for Quick ventricular squeeze, T for Tired ventricles relaxing.

Examples2

Stethoscope Sounds

Doctors hear lub-dub sounds to check valve function and rhythm. Murmurs may indicate abnormal valve flow.

ECG in Emergency

An ECG can quickly detect abnormal rhythms or signs of reduced blood supply to heart muscle.

Reference Tables3

Events of Cardiac Cycle

Phase	Duration	Main Event	Valve Status
Joint diastole	0.4 s	Atria and ventricles relaxed; passive filling	AV valves open, semilunar closed
Atrial systole	0.1 s	Atria contract and complete ventricular filling	AV valves open
Ventricular systole	0.3 s	Ventricles pump blood to arteries	AV valves closed, semilunar open during ejection

ECG Wave Meaning

ECG Part	Represents	Mechanical Result
P wave	Atrial depolarisation	Atrial systole
QRS complex	Ventricular depolarisation	Ventricular systole begins
T wave	Ventricular repolarisation	Ventricular relaxation

Heart Sounds

Sound	Cause	Timing
Lub	Closure of tricuspid and bicuspid valves	Beginning of ventricular systole
Dub	Closure of semilunar valves	Beginning of ventricular diastole

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Common Mistakes3

T Wave Misinterpretation

T wave is ventricular repolarisation, not atrial repolarisation. Atrial repolarisation is hidden by QRS.

Heart Sound Source

Heart sounds are due to valve closure, not valve opening.

Cycle Duration Calculation

Do not confuse 72 beats per minute with exactly 0.8 s. 0.8 s corresponds to 75/min; NCERT uses approximate average values.

Formula Cards2

Duration of Cardiac Cycle

Time for one heartbeat. At 75 beats per minute, duration is 0.8 s.

Variables

Duration=

Time taken for one cardiac cycle in seconds

Heart Rate=

Beats per minute

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Diagrams5

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Double Circulation

Overview

Double circulation means blood passes through the heart twice during one complete circulation: once through the pulmonary circuit and once through the systemic circuit. In pulmonary circulation, deoxygenated blood from the right ventricle goes to the lungs via pulmonary artery and returns oxygenated to the left atrium through pulmonary veins. In systemic circulation, oxygenated blood from the left ventricle goes to body tissues through the aorta and returns deoxygenated to the right atrium through venae cavae. This separation maintains high oxygen efficiency and prevents mixing. Blood pressure measures force exerted by blood on arterial walls, while cardiac output measures blood pumped per minute.

Key Points5

1Pulmonary circuit is low-pressure compared with systemic circuit.
2Systemic circuit requires high pressure because blood must reach the entire body.
3Complete double circulation supports high metabolic rate in mammals.
4Blood pressure is measured using a sphygmomanometer.
5Cardiac output can increase during exercise by increasing heart rate and stroke volume.

Memory Tricks3

Pulmonary Path

R-L-L: Right ventricle sends blood to Lungs, which return it to Left atrium.

Systemic Path

L-B-R: Left ventricle sends blood to Body, which returns it to Right atrium.

Blood Pressure

120 is the Pumping peak, 80 is the Resting base.

Examples2

Exercise Response

During running, cardiac output may increase several times to supply oxygen to muscles.

Blood Pressure Reading

A reading of 120/80 mm Hg means arterial pressure reaches about 120 during systole and falls to about 80 during diastole.

Reference Tables2

Pulmonary vs Systemic Circulation

Feature	Pulmonary Circulation	Systemic Circulation
Starts from	Right ventricle	Left ventricle
Goes to	Lungs	Body tissues
Returns to	Left atrium	Right atrium
Main vessel leaving heart	Pulmonary artery	Aorta
Main purpose	Oxygenation of blood	Supply oxygen and nutrients to tissues
Pressure	Lower	Higher

Blood Pressure Terms

Term	Normal Value	Meaning
Systolic pressure	About 120 mm Hg	Pressure during ventricular systole
Diastolic pressure	About 80 mm Hg	Pressure during ventricular diastole
Hypertension	Persistently above normal	Often defined clinically as 140/90 mm Hg or higher

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Common Mistakes3

Double Circulation Count

Double circulation does not mean two hearts. It means blood crosses the heart twice in one complete round.

Wrong Pressure Assignment

Systolic pressure is the higher value and diastolic pressure is the lower value.

Cardiac Output Unit

Cardiac output is volume per minute, not volume per beat. Volume per beat is stroke volume.

Formula Cards3

Cardiac Output

Amount of blood pumped by each ventricle per minute. Example: 70 mL × 72 min⁻¹ ≈ 5040 mL min⁻¹.

Variables

CO=

Cardiac output

SV=

Stroke volume

HR=

Heart rate

Pulse Pressure

For normal blood pressure 120/80 mm Hg, pulse pressure is 40 mm Hg.

Variables

PP=

Pulse pressure

Systolic BP=

Maximum arterial pressure

Diastolic BP=

Minimum arterial pressure

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Circulatory Disorders

Overview

Circulatory disorders arise when normal heart or blood vessel function is disturbed. Hypertension is persistently elevated blood pressure, commonly above 140/90 mm Hg, and can damage heart, brain and kidneys. Coronary artery disease occurs when coronary arteries supplying the heart become narrowed, often due to atherosclerosis. Atherosclerosis is deposition of calcium, fat, cholesterol and fibrous tissue in arterial walls, reducing lumen size. Angina pectoris is chest pain due to insufficient oxygen supply to heart muscle, usually during exertion or stress. Heart failure means the heart cannot pump enough blood to meet body needs; it is not the same as cardiac arrest or heart attack.

Key Points5

1Atherosclerosis is an underlying cause of many cases of CAD.
2Angina pain can radiate to left arm, shoulder, neck or jaw.
3Hypertension increases workload on heart and damages arteries over time.
4Heart failure does not mean heart has stopped beating.
5Lifestyle factors such as high-fat diet, smoking, obesity, stress and inactivity increase risk.

Memory Tricks2

CAD Chain

Fat Plaque Closes Coronary Artery: Atherosclerosis → CAD → low oxygen → angina or heart attack.

Heart Failure Meaning

Failure means weak pumping, not stopped beating. Cardiac arrest means sudden stopping of effective heart action.

Examples2

Angina During Climbing Stairs

A person with narrowed coronary arteries may feel chest pain while climbing because the heart needs more oxygen than the narrowed vessels can supply.

Silent Hypertension

Many people with high blood pressure feel normal, but long-term pressure can damage kidneys, eyes, brain and heart.

Reference Tables2

Disease Comparison Chart

Disorder	Main Problem	Key Symptom or Effect	NCERT/NEET Point
Hypertension	Persistent high arterial pressure	Often silent; damages organs	Commonly 140/90 mm Hg or higher
Coronary Artery Disease	Narrowing of coronary arteries	Reduced blood supply to myocardium	Often due to atherosclerosis
Angina Pectoris	Temporary oxygen shortage to heart muscle	Acute chest pain	Occurs with exertion or stress
Heart Failure	Heart cannot pump enough blood	Fatigue, breathlessness, congestion	Not equal to cardiac arrest
Atherosclerosis	Plaque deposition in artery wall	Reduced lumen and elasticity	Deposition of fat, cholesterol, calcium and fibrous tissue

Clinical Summary

Condition	Affected Structure	Immediate Concern
CAD	Coronary arteries	Reduced oxygen to heart muscle
Angina	Myocardium	Chest pain due to ischemia
Heart failure	Whole pumping system	Inadequate tissue perfusion
Hypertension	Arteries and organs	Long-term vascular damage

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Common Mistakes3

Heart Failure vs Heart Attack

Heart failure is chronic inability to pump enough blood. Heart attack is death of heart muscle due to blocked blood supply.

Angina vs CAD

CAD is the artery disease; angina is chest pain caused by inadequate oxygen supply, often due to CAD.

Hypertension as Temporary Stress

A single high reading during stress is not enough. Hypertension means persistent elevation.

Formula Cards2

Blood Pressure Expression

Clinical readings are written as two values, such as 120/80 mm Hg. Persistently high values suggest hypertension.

Variables

Systolic Pressure=

Arterial pressure during ventricular contraction

Diastolic Pressure=

Arterial pressure during ventricular relaxation

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Formula Sheet

Cardiac Output

Amount of blood pumped by each ventricle per minute. In a healthy adult, it is approximately 70 mL × 72 min⁻¹ = 5040 mL min⁻¹, about 5 L min⁻¹.

Variables

CO=

Cardiac output in mL per minute or L per minute

SV=

Stroke volume, blood pumped by one ventricle per beat

HR=

Heart rate, number of beats per minute

Pulse Pressure

Difference between maximum arterial pressure during ventricular systole and minimum arterial pressure during ventricular diastole.

Variables

SP=

Systolic pressure, normally about 120 mm Hg

DP=

Diastolic pressure, normally about 80 mm Hg

Haematocrit

Percentage of blood volume occupied by RBCs. It approximately corresponds to the formed element fraction, especially RBCs.

Variables

RBC volume=

Packed red blood cell volume after centrifugation

Total blood volume=

Total volume of blood sample

Blood Composition Ratio

NCERT-highlighted approximate composition of human blood by volume.

Variables

Plasma=

Fluid matrix of blood

Formed elements=

RBCs, WBCs and platelets

Tissue Fluid Balance

A conceptual balance showing why lymphatic drainage is necessary to prevent fluid accumulation in tissues.

Variables

Filtered fluid=

Plasma-derived fluid leaving blood capillaries

Returned fluid=

Fluid reabsorbed directly into venous end of capillaries

Lymph=

Excess tissue fluid entering lymphatic vessels

Heart Rate from Cardiac Cycle Duration

If one cardiac cycle takes 0.8 s, heart rate is 60/0.8 = 75 beats per minute, close to the NCERT average of 72 beats per minute.

Variables

Heart Rate=

Number of heartbeats per minute

Duration=

Time taken for one complete heartbeat in seconds

Duration of Cardiac Cycle

Time for one heartbeat. At 75 beats per minute, duration is 0.8 s.

Variables

Duration=

Time taken for one cardiac cycle in seconds

Heart Rate=

Beats per minute

Cardiac Output from Cycle

The cardiac cycle generates stroke volume; multiplying by heart rate gives cardiac output.

Variables

CO=

Cardiac output

SV=

Stroke volume, about 70 mL

HR=

Heart rate, about 72 beats per minute

Cardiac Output

Amount of blood pumped by each ventricle per minute. Example: 70 mL × 72 min⁻¹ ≈ 5040 mL min⁻¹.

Variables

CO=

Cardiac output

SV=

Stroke volume

HR=

Heart rate

Pulse Pressure

For normal blood pressure 120/80 mm Hg, pulse pressure is 40 mm Hg.

Variables

PP=

Pulse pressure

Systolic BP=

Maximum arterial pressure

Diastolic BP=

Minimum arterial pressure

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Blood is a fluid connective tissue composed of plasma and formed elements.

RBCs transport respiratory gases; WBCs defend the body; platelets help clotting.

Lymph is tissue fluid entering lymph vessels and returning to venous blood.

The heart has four chambers: two atria and two ventricles.

SA node initiates heartbeat and is called the pacemaker.

One cardiac cycle lasts about 0.8 s at 72 beats per minute.

Double circulation keeps oxygenated and deoxygenated blood separate.

Hypertension, CAD, angina, heart failure and atherosclerosis are important disorders.

Transport systems maintain homeostasis by distributing materials and removing wastes.

Human circulation is closed, double and complete because blood remains in vessels and passes twice through the heart in one complete circuit.

Blood volume in adults is about 5 litres.

Plasma forms about 55 percent of blood; formed elements form about 45 percent.

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NEET PYQs — Body Fluids and Circulation

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NEET 2026Set 11MediumQ1

Select the incorrect statement with reference to Rh grouping: A. Erythroblastosis foetalis is a condition observed having foetus with Rh⁻ᵛᵉ blood and mother with Rh⁺ᵛᵉ blood. B. Rh antigen is observed on RBCs in the majority of human beings. C. Before blood transfusion, Rh group should also be matched. D. Rh incompatibility is observed when a pregnant mother is Rh⁻ᵛᵉ and the foetus is Rh⁺ᵛᵉ. E. Erythroblastosis foetalis can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the second child.