NCERT Solutions for Class 11 Biology Chapter 15: Body Fluids and Circulation

The formed elements are the cellular components of blood. They constitute about 45% of the total blood volume. The three main components are:

1. Erythrocytes (Red Blood Cells - RBCs):
   • Major Function: Their primary role is the transport of respiratory gases. The red pigment, haemoglobin, binds with oxygen to transport it from the lungs to the tissues and carries carbon dioxide from the tissues back to the lungs.
2. Leucocytes (White Blood Cells - WBCs):
   • Major Function: WBCs are the soldiers of our body and are a crucial part of the immune system. They protect the body against infections and foreign particles.
3. Thrombocytes (Platelets):
   • Major Function: Platelets are essential for the coagulation or clotting of blood. When a blood vessel is injured, platelets gather at the site and release substances that initiate the clotting cascade, preventing excessive blood loss.

Plasma proteins, which include fibrinogen, globulins, and albumins, are vital for several body functions:

• Fibrinogen: This protein is essential for the clotting or coagulation of blood. It is converted into insoluble fibrin threads that form a mesh to trap blood cells and seal wounds.
• Globulins: These are primarily involved in the defence mechanisms of the body. Gamma globulins, also known as antibodies (immunoglobulins), fight against pathogens like bacteria and viruses.
• Albumins: These are the most abundant plasma proteins. They play a crucial role in maintaining the osmotic balance of the blood, which helps regulate blood volume and pressure by keeping fluid within the blood vessels.

Individuals with blood group ‘O’ are considered universal donors because their Red Blood Cells (RBCs) lack both antigen A and antigen B on their surface.

• During a blood transfusion, the recipient's immune system can attack foreign antigens present on the donor's RBCs.
• Since O-group RBCs have no A or B antigens, the immune systems of recipients with blood groups A, B, AB, or O will not recognize them as foreign.
• This prevents an antigen-antibody reaction (agglutination), making O-group blood safe for transfusion into individuals of any other ABO blood group.

(Note: This is specifically for the ABO system. For complete safety, the Rh factor must also be matched. O-negative is the true universal donor.)

Individuals with blood group ‘AB’ are considered universal recipients because their blood plasma lacks both anti-A and anti-B antibodies.

• Antibodies in the recipient's plasma can attack the antigens on the donor's RBCs, causing a transfusion reaction.
• Since AB-group individuals have no anti-A or anti-B antibodies, they can safely receive blood from donors of any ABO blood group (A, B, AB, and O).
• Their system will not mount an immune attack against either antigen A or antigen B on the donated RBCs.

The hepatic portal system is a unique vascular connection that exists between the digestive tract and the liver. A hepatic portal vein carries blood directly from the intestine to the liver before it is delivered to the systemic circulation.

Significance:

1. Detoxification: The liver acts as a filter. It detoxifies harmful substances and chemicals that may have been absorbed from the food in the intestine before they can enter the general circulation and affect other organs.
2. Metabolic Processing: The nutrient-rich blood from the intestine (containing glucose, amino acids, etc.) is first processed by the liver. The liver can store excess glucose as glycogen, synthesize proteins, and regulate blood nutrient levels. This ensures a stable supply of nutrients to the rest of the body.

For a normal, healthy adult human, the blood pressure is expressed as two values:

• Systolic Pressure: This is the pressure in the arteries when the heart's ventricles contract (systole). The normal value is 120 mm Hg (millimetres of mercury).
• Diastolic Pressure: This is the pressure in the arteries when the heart's ventricles relax (diastole). The normal value is 80 mm Hg.

Therefore, the normal blood pressure is written as 120/80 mm Hg.

Double circulation is a circulatory system in which the blood passes through the heart twice during one complete cycle. This type of circulation is found in birds and mammals, including humans. It consists of two distinct circuits:

1. Pulmonary Circulation: The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery. In the lungs, the blood gets oxygenated. The oxygenated blood is then returned to the left atrium of the heart via the pulmonary vein.
2. Systemic Circulation: The left ventricle pumps this oxygenated blood to the rest of the body (except the lungs) via the aorta. The tissues use the oxygen, and the resulting deoxygenated blood is collected by veins and returned to the right atrium via the vena cava.

Significance of Double Circulation:

• Efficient Oxygen Supply: It prevents the mixing of oxygenated and deoxygenated blood. This ensures that the body tissues receive a highly efficient supply of oxygen.
• Higher Blood Pressure: It allows for a much higher blood pressure to be maintained in the systemic circuit, enabling rapid and efficient transport of blood to all body parts, even those far from the heart.
• Supports High Metabolism: This efficient system is crucial for warm-blooded animals (mammals and birds) as it supports their high metabolic rate and helps maintain a constant body temperature.

(a) Differences between Blood and Lymph

(b) Differences between Open and Closed Circulatory System

(c) Differences between Systole and Diastole

The human heart is a muscular organ, about the size of a clenched fist, located in the thoracic cavity between the lungs. It is protected by a double-walled membranous bag called the pericardium.

Structure of the Human Heart: The human heart has four chambers:

1. Two upper chambers called the atria (singular: atrium), which are relatively small and thin-walled.
2. Two lower chambers called the ventricles, which are larger and have thick, muscular walls.

Key Features:

• Septum: A muscular wall called the interatrial septum separates the right and left atria, while the inter-ventricular septum separates the right and left ventricles. This prevents the mixing of oxygenated and deoxygenated blood.
• Valves: The heart has four valves that ensure unidirectional blood flow:
  • Tricuspid Valve: Located between the right atrium and the right ventricle. It has three muscular flaps.
  • Bicuspid (or Mitral) Valve: Located between the left atrium and the left ventricle. It has two muscular flaps.
  • Pulmonary Valve (Semilunar): At the opening of the pulmonary artery from the right ventricle.
  • Aortic Valve (Semilunar): At the opening of the aorta from the left ventricle.
• Major Blood Vessels:
  • Vena Cava (Superior and Inferior): Brings deoxygenated blood from the body to the right atrium.
  • Pulmonary Artery: Carries deoxygenated blood from the right ventricle to the lungs.
  • Pulmonary Veins: Bring oxygenated blood from the lungs to the left atrium.
  • Aorta: The largest artery, carrying oxygenated blood from the left ventricle to the rest of the body.
• Heart Walls: The wall of the left ventricle is significantly thicker than that of the right ventricle because it needs to pump blood to the entire body, whereas the right ventricle only pumps blood to the lungs.

The cardiac cycle refers to the sequence of events that takes place in the heart during a single heartbeat. It involves the rhythmic contraction (systole) and relaxation (diastole) of the heart muscles. In a healthy human, the heart beats about 72 times per minute, making the duration of one cardiac cycle approximately 0.8 seconds.

Brief Description of the Cardiac Cycle: The cycle can be described in three main phases:

1. Joint Diastole (approx. 0.4 seconds):
   • All four chambers of the heart are in a relaxed state.
   • The tricuspid and bicuspid (AV) valves are open.
   • Blood from the pulmonary veins and vena cava flows passively into the left and right ventricles, respectively. The semilunar valves are closed.
2. Atrial Systole (approx. 0.1 seconds):
   • The Sino-Atrial Node (SAN) generates an action potential, causing both atria to contract simultaneously.
   • This contraction pushes the remaining blood from the atria into the ventricles. The ventricular blood volume increases by about 30%.
3. Ventricular Systole (approx. 0.3 seconds):
   • The electrical impulse travels from the atria to the ventricles, causing them to contract. The atria relax (diastole) during this phase.
   • First phase: As the ventricles contract, ventricular pressure rises, causing the closure of the tricuspid and bicuspid valves. This produces the first heart sound, "LUB".
   • Second phase: Ventricular pressure continues to increase until it exceeds the pressure in the pulmonary artery and aorta. This forces the semilunar valves to open, and blood is ejected from the ventricles into these vessels.

After ventricular systole, the ventricles relax (ventricular diastole), and ventricular pressure falls. The backflow of blood causes the closure of the semilunar valves, producing the second heart sound, "DUB". The cycle then repeats.

An Electrocardiogram (ECG) is a graphical representation of the electrical activity of the heart during a cardiac cycle. An electrocardiograph machine records this activity.

Standard ECG Waves: A standard ECG consists of specific waves:

• P-wave: Represents the electrical excitation (or depolarisation) of the atria. This leads to the contraction of both atria.
• QRS Complex: Represents the depolarisation of the ventricles, which initiates ventricular contraction (systole).
• T-wave: Represents the return of the ventricles from the excited to the normal state (repolarisation). The end of the T-wave marks the end of systole.

Significance of ECG: ECG is a crucial diagnostic tool because:

1. Heart Rate Measurement: By counting the number of QRS complexes in a given time, we can accurately determine the heart rate.
2. Diagnosis of Abnormalities: Any deviation from the normal shape and size of these waves can indicate a possible abnormality or disease.
3. Clinical Importance: ECG is invaluable in diagnosing conditions like arrhythmias (irregular heartbeat), heart attacks (myocardial infarction), coronary artery disease, and other cardiac problems.

Erythroblastosis foetalis is a haemolytic disease of the newborn. It occurs when an Rh-negative (Rh-) mother carries an Rh-positive (Rh+) foetus.

• During the first pregnancy, some Rh+ RBCs from the foetus can enter the mother's bloodstream. The mother's body develops anti-Rh antibodies.
• In subsequent Rh+ pregnancies, these maternal anti-Rh antibodies can cross the placenta and attack the foetal RBCs, causing severe anaemia and jaundice.

Avoidance: The condition can be avoided by administering anti-Rh antibodies (RhoGAM) to the Rh- mother immediately after the delivery of her first Rh+ child. This prevents her from producing her own antibodies.

The nodal tissues are specialised cardiac musculature that can auto-generate action potentials.

1. Sino-atrial Node (SAN): Located in the upper right corner of the right atrium. It is the "pacemaker" of the heart.
2. Atrio-ventricular Node (AVN): Located in the lower-left corner of the right atrium, close to the atrio-ventricular septum.

Cardiac Output (CO) is the volume of blood pumped by each ventricle per minute. It is calculated by multiplying the stroke volume (SV) by the heart rate (HR).

Formula: CO = SV × HR

Calculation:
Given: Stroke Volume (SV) = 70 mL; Heart Rate (HR) = 75 beats/min
CO = 70 mL/beat × 75 beats/min
CO = 5250 mL/min or 5.25 litres/min.
Thus, the cardiac output is 5.25 litres per minute.

The wall of the left ventricle is thicker because it has a larger workload:

• The left ventricle must pump blood to the entire systemic circulation (all over the body), which requires generating very high pressure.
• The right ventricle only pumps blood to the nearby lungs through the low-pressure pulmonary circulation.

Blood coagulation is a cascade of enzyme-catalyzed reactions to prevent blood loss. The steps are:

1. Injury and Platelet Response: An injury exposes collagen fibres, attracting platelets. Platelets and injured tissues release factors like thromboplastin.
2. Formation of Prothrombin Activator: A series of reactions involving clotting factors leads to the formation of an enzyme complex called prothrombin activator (or thrombokinase).
3. Conversion of Prothrombin to Thrombin: The enzyme prothrombin activator converts inactive prothrombin into active thrombin. This requires calcium ions (Ca²⁺).
4. Conversion of Fibrinogen to Fibrin: Active thrombin converts soluble fibrinogen into insoluble threads of fibrin.
5. Formation of the Clot: The insoluble fibrin threads form a mesh that traps RBCs and platelets to form a clot or coagulum, stopping the bleeding.

A standard ECG shows:

• P wave: Represents the depolarisation of the atria, leading to atrial contraction.
• QRS Complex: Represents the depolarisation of the ventricles, leading to ventricular contraction.
• T wave: Represents the repolarisation of the ventricles, as they relax.
• PR Interval: Time for the impulse to travel from atria to ventricles.
• QT Interval: Total time for ventricular depolarisation and repolarisation.

Deviations in these waves help diagnose various cardiac conditions.

1. (a) What is the name of the condition Mr. Sharma is suffering from?
   He is suffering from Hypertension (High Blood Pressure).
2. (b) Which values in his reading are systolic and diastolic? Are they normal?
   Systolic is 150 mm Hg and diastolic is 95 mm Hg. They are not normal (normal is 120/80 mm Hg).
3. (c) What are two potential long-term risks if this condition is left untreated?
   1. Heart diseases (heart attack, failure). 2. Brain stroke and kidney damage.
4. (d) Suggest two lifestyle changes the doctor might have recommended.
   1. Dietary changes (reducing salt). 2. Regular exercise.