Body Fluids and Circulation Class 11 Chapter Notes

Key Terms and Definitions

Haemopoiesis

The process of formation of blood corpuscles (RBCs, WBCs, platelets), which occurs in the red bone marrow.

Diapedesis

The process by which white blood cells (especially neutrophils) squeeze through the capillary walls to reach the site of infection.

Stroke Volume (SV)

The volume of blood pumped out by each ventricle per beat. It is approximately 70 mL in a healthy individual.

Cardiac Output (CO)

The volume of blood pumped out by each ventricle per minute. It is calculated as Stroke Volume (SV) × Heart Rate (HR). (CO = 70 mL × 72 beats/min ≈ 5 litres/min).

Systole

The phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries.

Diastole

The phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood.

Hypertension

High blood pressure. A condition where the blood pressure in the arteries is persistently elevated, typically above 140/90 mmHg.

Angina Pectoris

A type of chest pain caused by reduced blood flow to the heart muscles. It's a symptom of coronary artery disease.

Blood: The Fluid Connective Tissue

Blood is a vital fluid connective tissue composed of plasma and formed elements. It's the primary medium for transporting essential substances throughout the body.

1. Plasma:
Plasma constitutes about 55% of the blood. It is a straw-coloured, viscous fluid, of which 90-92% is water. The remaining 6-8% consists of proteins. The major plasma proteins are:

• Fibrinogen: Essential for blood clotting or coagulation.
• Globulins: Primarily involved in the body's defense mechanisms (as antibodies or immunoglobulins).
• Albumins: The most abundant plasma protein, crucial for maintaining blood colloid osmotic pressure.

Plasma also contains small amounts of minerals (Na+, Ca++, Mg++, HCO3-, Cl-), glucose, amino acids, lipids, and waste products like urea. Plasma without the clotting factors (like fibrinogen) is called serum.

2. Formed Elements:
These make up about 45% of the blood and include Erythrocytes (RBCs), Leucocytes (WBCs), and Thrombocytes (Platelets).

• Erythrocytes (RBCs): These are the most abundant cells (5 to 5.5 million per mm³). They are biconcave discs, devoid of a nucleus in mammals, which increases surface area for oxygen transport. They contain haemoglobin, the iron-containing protein that binds to oxygen. A healthy individual has 12-16 g of haemoglobin in every 100 ml of blood. RBCs have a lifespan of about 120 days.
• Leucocytes (WBCs): These are colourless due to the lack of haemoglobin. They are nucleated and fewer in number (6000-8000 per mm³). They are part of the immune system. WBCs are categorized into Granulocytes (Neutrophils, Eosinophils, Basophils) and Agranulocytes (Lymphocytes, Monocytes).
• Thrombocytes (Platelets): These are cell fragments produced from megakaryocytes in the bone marrow. They are essential for initiating blood coagulation.

ABO Blood Grouping

Mechanism of Blood Coagulation

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Must-Remember Facts

• Normal Blood Pressure: 120/80 mmHg. 120 mmHg is the systolic pressure (pumping), and 80 mmHg is the diastolic pressure (resting).
• Pacemaker of the Heart: The Sino-atrial Node (SAN) located in the upper right corner of the right atrium is the heart's natural pacemaker.
• Cardiac Cycle Duration: A complete cardiac cycle lasts for about 0.8 seconds.
• Heart Sounds: The first heart sound 'LUB' is produced by the closure of the tricuspid and bicuspid (mitral) valves. The second sound 'DUB' is from the closure of the semilunar valves.
• Cardiac Output Formula: Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR).
• Universal Donor: Blood group O negative (O-).
• Universal Recipient: Blood group AB positive (AB+).
• ECG Waves: P-wave (atrial depolarisation), QRS complex (ventricular depolarisation), T-wave (ventricular repolarisation).
• Pulmonary Circulation Exception: The pulmonary artery carries deoxygenated blood away from the heart, and the pulmonary vein carries oxygenated blood towards the heart.
• Lymph: A colourless fluid containing specialised lymphocytes responsible for the immune responses of the body. It acts as a 'middleman' for transport between blood and tissues.

Understanding the ECG

Exam Traps and Tips

Examiners often test your understanding of the exceptions in the circulatory system and the precise meaning of ECG waves.

• Arteries vs. Veins: Remember that arteries carry blood away from the heart and veins carry it towards the heart. The exception is the pulmonary artery (carries deoxygenated blood) and pulmonary vein (carries oxygenated blood). Don't just define them by the type of blood they carry.
• ECG Interpretation: Do not confuse depolarisation with contraction. Depolarisation is the electrical event that leads to the mechanical event of contraction. For example, the P-wave is atrial depolarisation, which causes atrial systole (contraction).
• Diagrams are Key: Practice drawing a neat, well-labeled diagram of the human heart and the pathway of double circulation. These are very common questions and fetch full marks if drawn correctly.

Quick Revision Check

• What is the formula for Cardiac Output and what is its average value? Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR). The average value is approximately 5040 mL or ~5 litres per minute.
• Why is a person with blood group AB considered a 'universal recipient'? Because their plasma lacks both Anti-A and Anti-B antibodies, so their body will not produce an immune reaction against A or B antigens present on the donor's RBCs.
• What does the T-wave in a standard ECG represent? The T-wave represents ventricular repolarisation, which is the return of the ventricles from an excited state to a resting state.
• Name the node that acts as the natural pacemaker of the human heart. The Sino-atrial Node (SAN).

Frequently Asked Questions

Frequently Asked Questions