Body Fluids and CirculationClass 11 Biology NCERT Solutions
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Q1Exercises
Name the components of the formed elements in the blood and mention one major function of each of them.
Solution
The components of the formed elements in the blood are Erythrocytes (RBCs), Leucocytes (WBCs), and Platelets. They constitute about 45 per cent of the blood.
Their major functions are as follows:
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Erythrocytes (Red Blood Cells or RBCs): These are the most abundant cells in the blood. Their primary function is the transport of respiratory gases, mainly oxygen, from the lungs to the tissues. This is possible due to the presence of the iron-containing protein, haemoglobin.
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Leucocytes (White Blood Cells or WBCs): These cells are part of the body's immune system. Their main function is to provide defense against foreign organisms and infections. For example, neutrophils and monocytes are phagocytic, destroying foreign organisms, while lymphocytes are responsible for immune responses.
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Platelets (Thrombocytes): These are cell fragments that play a crucial role in blood coagulation or clotting. They release substances that initiate the clotting mechanism at the site of an injury, preventing excessive blood loss.
Q2Exercises
What is the importance of plasma proteins?
Solution
Plasma proteins are crucial for several physiological functions in the body. The major proteins found in plasma are fibrinogen, globulins, and albumins. Their importance is as follows:
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Fibrinogen: This protein is essential for the clotting or coagulation of blood. It is converted into fibrin threads to form a clot at the site of an injury, preventing excessive bleeding.
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Globulins: These proteins are primarily involved in the defense mechanisms of the body. They act as antibodies (immunoglobulins) that identify and neutralize foreign agents like bacteria and viruses.
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Albumins: These are the most abundant plasma proteins. Their main function is to maintain the osmotic balance of the blood. They help in retaining fluid within the blood vessels, regulating blood volume and pressure.
Q3Exercises
Match Column I with Column II : Column I (a) Eosinophils (b) RBC (c) AB Group (d) Platelets (e) Systole Column II
(i)
Coagulation
(ii)
Universal Recipient
(iii)
Resist Infections
(iv)
Contraction of Heart
(v)
Gas transport
Solution
The correct matches are as follows:
- (a) Eosinophils matches with (iii) Resist Infections. Eosinophils are a type of white blood cell that resists infections and is also associated with allergic reactions.
- (b) RBC matches with (v) Gas transport. Red blood cells contain haemoglobin, which plays a significant role in the transport of respiratory gases like oxygen.
- (c) AB Group matches with (ii) Universal Recipient. Persons with AB blood group can accept blood from persons with AB as well as other groups of blood because their plasma lacks anti-A and anti-B antibodies.
- (d) Platelets matches with (i) Coagulation. Platelets, or thrombocytes, release substances involved in the coagulation or clotting of blood.
- (e) Systole matches with (iv) Contraction of Heart. Systole is the phase of the cardiac cycle when the heart muscle contracts to pump blood out of the chambers.
Q4Exercises
Why do we consider blood as a connective tissue?
Solution
Blood is considered a special connective tissue for two main reasons that align with the definition of connective tissues:
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Presence of a Matrix: Like other connective tissues, blood consists of cells and cell fragments (the formed elements) suspended in an extensive extracellular matrix. In the case of blood, this matrix is a fluid called plasma.
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Origin: Blood, like all other connective tissues, is mesodermal in origin. It connects different parts of the body by transporting nutrients, gases, hormones, and waste products, thus serving a connecting function.
Therefore, because it has a fluid matrix (plasma) and formed elements, it fits the definition of a connective tissue.
Q5Exercises
What is the difference between lymph and blood?
Solution
The main differences between lymph and blood are:
| Feature | Blood | Lymph (Tissue Fluid) |
|---|---|---|
| Composition | Consists of plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets. | Consists of plasma without larger proteins, and contains specialized lymphocytes. It lacks RBCs and platelets. |
| Colour | Red in colour due to the presence of haemoglobin in RBCs. | Colourless as it lacks RBCs. |
| Protein Content | Has a higher concentration of proteins (6-8 per cent), including fibrinogen and albumin. | Has a lower concentration of proteins as larger proteins cannot pass through capillary walls. |
| Function | Transports respiratory gases (, ), nutrients, hormones, and waste products. It is also involved in clotting and defense. | Primarily involved in the immune response of the body (due to lymphocytes) and acts as a middleman for the exchange of materials between blood and cells. It also carries absorbed fats from the intestine. |
| Circulation | Circulates in a closed system of blood vessels (arteries, veins, capillaries) and is pumped by the heart. | Circulates in the lymphatic system, which is an open system, and flows from tissues back to the major veins. Its flow is slow and not pumped by the heart. |
Q6Exercises
What is meant by double circulation? What is its significance?
Solution
Double Circulation is a system of circulation in which blood flows through the heart twice for each complete circuit of the body. It consists of two separate pathways:
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Pulmonary Circulation: This pathway involves the circulation of blood between the heart and the lungs. The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery. In the lungs, the blood gets oxygenated and returns to the left atrium of the heart through the pulmonary veins.
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Systemic Circulation: This pathway involves the circulation of blood between the heart and the rest of the body. The left ventricle pumps oxygenated blood into the aorta, which carries it to all body tissues. Deoxygenated blood from the tissues is then collected by veins and returned to the right atrium via the vena cava.
Significance of Double Circulation:
The primary significance of double circulation is the complete separation of oxygenated and deoxygenated blood. This prevents the mixing of the two types of blood, ensuring that the body tissues receive a highly efficient supply of oxygen. This efficient oxygen supply is necessary to support the high metabolic rate of warm-blooded animals like birds and mammals, allowing them to maintain a constant body temperature.
Q7Exercises
Write the differences between :
(a)
Blood and Lymph
(b)
Open and Closed system of circulation
(c)
Systole and Diastole
(d)
P -wave and T -wave
Solution
(a) Differences between Blood and Lymph:
| Feature | Blood | Lymph |
|---|---|---|
| Colour | Red due to haemoglobin. | Colourless. |
| Cells | Contains RBCs, WBCs, and platelets. | Lacks RBCs and platelets, contains specialized lymphocytes. |
| Protein | Higher protein concentration. | Lower protein concentration. |
| Function | Transports gases, nutrients, wastes. | Part of the immune system, transports fats. |
(b) Differences between Open and Closed system of circulation:
| Feature | Open Circulatory System | Closed Circulatory System |
|---|---|---|
| Vessels | Blood is pumped into open spaces or cavities called sinuses. Vessels are not extensive. | Blood is always circulated through a closed network of blood vessels (arteries, veins, capillaries). |
| Blood Flow | Blood flow is slow and under low pressure. Flow cannot be precisely regulated. | Blood flow is rapid and under high pressure. Flow can be more precisely regulated. |
| Efficiency | Less efficient in transporting substances to tissues. | More advantageous and efficient as blood reaches tissues directly. |
| Examples | Arthropods and molluscs. | Annelids and chordates (including humans). |
(c) Differences between Systole and Diastole:
| Feature | Systole | Diastole |
|---|---|---|
| Definition | The contraction phase of the heart chambers (atria or ventricles). | The relaxation phase of the heart chambers. |
| Action | Blood is pumped out of the contracting chambers. | Chambers fill with blood. |
| Pressure | Blood pressure in the arteries is at its highest (systolic pressure). | Blood pressure in the arteries is at its lowest (diastolic pressure). |
| In Cardiac Cycle | Atrial systole precedes ventricular systole. | Joint diastole is when all four chambers are relaxed. |
(d) Differences between P-wave and T-wave:
| Feature | P-wave | T-wave |
|---|---|---|
| Representation | Represents the electrical excitation or depolarisation of the atria. | Represents the return of the ventricles from the excited to the normal state (repolarisation). |
| Resulting Action | It leads to the contraction of both atria (atrial systole). | It marks the end of ventricular systole. |
| Position in ECG | It is the first small upward wave in a standard ECG. | It is a broader, dome-shaped upward wave that follows the QRS complex. |
Q8Exercises
Describe the evolutionary change in the pattern of heart among the vertebrates.
Solution
The pattern of the heart among vertebrates shows a clear evolutionary progression from a simple two-chambered heart to a more complex and efficient four-chambered heart.
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Fishes: They possess the simplest heart, which is 2-chambered, consisting of one atrium and one ventricle. The heart pumps out deoxygenated blood to the gills for oxygenation. This oxygenated blood is then supplied directly to the rest of the body. This is known as single circulation, as blood passes through the heart only once in a complete circuit.
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Amphibians and most Reptiles: These animals have a 3-chambered heart, with two atria and a single ventricle. The left atrium receives oxygenated blood from the gills/lungs/skin, while the right atrium receives deoxygenated blood from the body. Both types of blood enter the single ventricle, where some mixing occurs. The ventricle then pumps out this mixed blood. This is called incomplete double circulation.
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Crocodiles, Birds, and Mammals: These vertebrates possess the most advanced, 4-chambered heart, with two atria and two ventricles. The right side of the heart handles deoxygenated blood, and the left side handles oxygenated blood. The inter-ventricular septum completely separates the two ventricles, preventing any mixing of blood. This allows for two distinct circulatory pathways (pulmonary and systemic), known as complete double circulation. This efficient system supports the high metabolic needs of these warm-blooded animals.
Q9Exercises
Why do we call our heart myogenic?
Solution
The human heart is called myogenic because its normal rhythmic contractile activity is initiated and regulated intrinsically by a specialized muscle tissue within the heart itself, known as the nodal tissue. This tissue, particularly the sino-atrial node (SAN), has the ability to generate electrical impulses (action potentials) automatically and rhythmically without any external stimulation from the nervous system. This property is called autoexcitability. While the rate can be moderated by the nervous and endocrine systems, the origin of the heartbeat is within the heart muscle itself, hence it is myogenic (myo = muscle; genic = originating from).
Q10Exercises
Sino-atrial node is called the pacemaker of our heart. Why?
Solution
The sino-atrial node (SAN), a patch of specialized nodal tissue located in the right upper corner of the right atrium, is called the pacemaker of the heart because it initiates the cardiac impulse that determines the heart rate.
The SAN has the unique property of autoexcitability and can generate the maximum number of action potentials per minute, typically . This rate is faster than any other part of the heart's conductive system. Because it has the highest rhythmicity, it sets the pace for the entire heart. It is responsible for initiating and maintaining the rhythmic contractile activity of the heart, ensuring that the atria and ventricles contract in a coordinated manner. Therefore, it acts as the natural pacemaker.
Q11Exercises
What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?
Solution
The atrio-ventricular node (AVN) and the atrio-ventricular bundle (AV bundle or Bundle of His) are crucial components of the heart's conduction system and have the following significance:
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Conduction of Impulse: They act as the electrical relay station between the atria and the ventricles. The action potential generated by the SAN first spreads across the atria, causing them to contract. This impulse is then picked up by the AVN.
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Coordination of Contraction: The AVN slightly delays the impulse before passing it to the AV bundle. This delay is critical because it allows the atria to complete their contraction and empty their blood into the ventricles before the ventricles begin to contract. This ensures efficient, sequential pumping of blood.
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Distribution to Ventricles: From the AVN, the impulse is transmitted through the AV bundle, which divides into right and left branches. These branches further give rise to Purkinje fibres that spread the impulse throughout the ventricular musculature. This coordinated spread ensures that both ventricles contract simultaneously and forcefully, pumping blood into the pulmonary artery and aorta.
In essence, the AVN and AV bundle ensure that the ventricles contract shortly after the atria, in a coordinated and efficient manner.
Q12Exercises
Define a cardiac cycle and the cardiac output.
Solution
Cardiac Cycle:
The cardiac cycle is the sequential event in the heart which is cyclically repeated from the beginning of one heartbeat to the beginning of the next. It consists of the systole (contraction) and diastole (relaxation) of both the atria and the ventricles. In a normal person with a heart rate of 72 beats per minute, the duration of one cardiac cycle is approximately 0.8 seconds.
Cardiac Output:
Cardiac output is defined as the volume of blood pumped out by each ventricle per minute. It is a measure of the heart's efficiency. It can be calculated by multiplying the stroke volume (the volume of blood pumped by a ventricle in one beat, approx. 70 mL) by the heart rate (number of beats per minute).
For a healthy individual, it averages about 5000 mL or 5 litres per minute.
Q13Exercises
Explain heart sounds.
Solution
During each cardiac cycle, two prominent sounds are produced which can be heard using a stethoscope. These sounds are of clinical diagnostic significance.
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First Heart Sound (lub): This is the first sound, 'lub'. It is produced by the closure of the atrioventricular (AV) valves, namely the tricuspid valve (between the right atrium and right ventricle) and the bicuspid or mitral valve (between the left atrium and left ventricle). This sound occurs at the beginning of ventricular systole (contraction) when the ventricular pressure rises above the atrial pressure, causing the valves to snap shut to prevent the backflow of blood into the atria.
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Second Heart Sound (dub): This is the second sound, 'dub'. It is produced by the closure of the semilunar valves at the beginning of ventricular diastole (relaxation). When the ventricles relax, the pressure within them falls below the pressure in the aorta and pulmonary artery. This pressure difference causes the aortic and pulmonary semilunar valves to close, preventing the backflow of blood into the ventricles. The 'dub' sound is shorter and sharper than the 'lub'.
Q14Exercises
Draw a standard ECG and explain the different segments in it.
Solution
A standard electrocardiogram (ECG) is a graphical representation of the electrical activity of the heart during a cardiac cycle. As I cannot draw, I will describe the components with reference to Figure 15.3 in the textbook. A standard ECG has the following waves:
1. P-wave:
- This is the first small, upward wave.
- It represents the electrical excitation, or depolarisation of the atria.
- This electrical activity leads to the contraction of both atria (atrial systole).
2. QRS Complex:
- This complex begins with a small downward deflection (Q), followed by a large, sharp upward peak (R), and ends with a downward wave (S).
- It represents the depolarisation of the ventricles.
- This electrical activity initiates ventricular contraction (ventricular systole), which starts shortly after the Q wave.
3. T-wave:
- This is a broad, dome-shaped upward wave that appears after the QRS complex.
- It represents the return of the ventricles from the excited to the normal state, which is called repolarisation of the ventricles.
- The end of the T-wave marks the end of ventricular systole.
By counting the number of QRS complexes in a given time, the heart beat rate can be determined. Any deviation from the standard shape of these waves can indicate a possible abnormality or disease, making the ECG a tool of great clinical significance.