Body Fluids and Circulation Class 11 Biology NCERT Solutions

Step-by-step solution

1. 1The formed elements are the cellular part of blood. Erythrocytes, leucocytes and platelets are collectively called formed elements, and they constitute nearly 45 per cent of the blood, the remaining 55 per cent being plasma.
2. 2Erythrocytes, the red blood cells, are the most abundant of all the cells in blood, a healthy adult man having on an average 5 millions to 5.5 millions of RBCs per mm3. They are formed in the red bone marrow in the adults, are devoid of nucleus in most of the mammals and are biconcave in shape. They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and the name of these cells, and these molecules play a significant role in transport of respiratory gases. A healthy individual has 12 to 16 g of haemoglobin in every 100 ml of blood. The one function asked for here is gas transport, and a healthy individual has 12 to 16 g of haemoglobin in every 100 ml of blood; their average life span is 120 days, after which they are destroyed in the spleen, called the graveyard of RBCs.
3. 3Leucocytes, the white blood cells, are colourless due to the lack of haemoglobin, and they are nucleated and relatively lesser in number, averaging 6000 to 8000 per mm3 of blood. They are generally short lived. Their function is defence: they are the cells that fight infection, and the chapter sorts them into granulocytes, neutrophils, eosinophils and basophils, and agranulocytes, lymphocytes and monocytes. Neutrophils are the most abundant at 60 to 65 per cent of the total WBCs, and both neutrophils and monocytes, the latter at 6 to 8 per cent, are phagocytic cells which destroy foreign organisms entering the body. Basophils, the least numerous at 0.5 to 1 per cent, secrete histamine, serotonin, heparin and similar substances and are involved in inflammatory reactions. Eosinophils, at 2 to 3 per cent, resist infections and are also associated with allergic reactions, and lymphocytes, at 20 to 25 per cent, are of two major types, the B and T forms, and both are responsible for the immune responses of the body.
4. 4Platelets, also called thrombocytes, are cell fragments produced from megakaryocytes, special cells in the bone marrow, and blood normally contains 1,500,00 to 3,500,00 platelets per mm3. Their function is clotting. Platelets can release a variety of substances, most of which are involved in the coagulation or clotting of blood, and a reduction in their number can lead to clotting disorders which will lead to excessive loss of blood from the body.
5. 5Summarise the division of labour: erythrocytes transport respiratory gases, leucocytes defend the body against infection, and platelets bring about clotting. That is the three-fold answer the question asks for.

Step-by-step solution

1. 1First the size of the contribution. Plasma is a straw coloured, viscous fluid constituting nearly 55 per cent of the blood, and 90 to 92 per cent of that plasma is water, with proteins contributing 6 to 8 per cent of it.
2. 2The chapter names the three major proteins, and each has a distinct job. Fibrinogen, globulins and albumins are the major proteins, and the importance of plasma proteins is best shown by giving one function to each.
3. 3Fibrinogen is needed for clotting or coagulation of blood. This is the protein that is converted into the threads of the clot, and without it the blood would not be able to seal a wound.
4. 4Globulins are primarily involved in the defence mechanisms of the body, so they are the plasma's contribution to immunity.
5. 5Albumins help in osmotic balance, which is the protein's role in maintaining the osmotic pressure of the blood and therefore in the distribution of water between the blood and the tissues.
6. 6Two further points belong in the answer. Plasma also contains small amounts of minerals such as Na+, Ca++, Mg++, HCO3- and Cl-, and it carries glucose, amino acids and lipids because these are always in transit in the body.
7. 7Finally the important clinical consequence. Factors for the coagulation or clotting of blood are present in the plasma in an inactive form, and plasma without the clotting factors is called serum, so the whole clotting machinery is already carried in the plasma, ready to be switched on.

Step-by-step solution

1. 1This is a matching question with five pairs, and each item of Column I has to be tied to the one entry of Column II that describes its function or its special character.
2. 2(a) Eosinophils with (iii) Resist Infections. Eosinophils make up 2 to 3 per cent of the total WBCs, and the chapter states directly that they resist infections and are also associated with allergic reactions, so resist infections is the correct match.
3. 3(b) RBC with (v) Gas transport. The red coloured, iron containing complex protein in the erythrocytes is haemoglobin, and these molecules play a significant role in transport of respiratory gases, so gas transport is the correct match.
4. 4(c) AB Group with (ii) Universal Recipient. The AB group carries both antigens A and B and nil antibodies in the plasma, so such persons can accept blood from persons with AB as well as from the other groups of blood, and are therefore called universal recipients.
5. 5(d) Platelets with (i) Coagulation. Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood, and a reduction in their number leads to clotting disorders, so coagulation is the correct match.
6. 6(e) Systole with (iv) Contraction of Heart. Systole is the contraction phase of the cardiac cycle, the atrial systole being the simultaneous contraction of both atria and the ventricular systole the contraction of the ventricular muscles, so contraction of heart is the correct match.
7. 7Note that the option Universal Recipient is the only entry in Column II that is not a function, and the entry Coagulation is used up by the platelets, which is the usual trap in this question.

Step-by-step solution

1. 1The definition comes first. Blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements, so it is a connective tissue by the chapter's own opening sentence.
2. 2Connective tissue is defined by its matrix rather than by its cells. Here the matrix is plasma, a straw coloured, viscous fluid constituting nearly 55 per cent of the blood, with the formed elements suspended in it and making up the remaining nearly 45 per cent, so the cells are scattered in an abundant matrix, which is the hallmark of connective tissue.
3. 3The cells are not packed together as in an epithelial tissue. The erythrocytes, leucocytes and platelets are suspended freely in the fluid matrix, and the erythrocytes are themselves biconcave and devoid of nucleus in most of the mammals, so there is no close cellular arrangement of the sort found in epithelium.
4. 4The function it performs is transport rather than protection or secretion, and transport is a connective-tissue function. Blood carries oxygen, nutrients and hormones to the cells and carries carbon dioxide and other waste away, which is the same kind of long-distance transport that connective tissue performs elsewhere in the body.
5. 5It shares the origin of connective tissue. The heart, which pumps this fluid, is described in the chapter as the mesodermally derived organ, and mesoderm is the germ layer that gives rise to connective tissues, so the tissue and the organ that drives it share a common origin.

Step-by-step solution

1. 1Give the origin of each, since that is where the difference begins. Blood is the fluid circulating in the blood vascular system, the network of closed branching blood vessels, whereas lymph is the tissue fluid collected by the lymphatic system.
2. 2Lymph begins as interstitial fluid. As the blood passes through the capillaries in tissues, some water along with many small water soluble substances move out into the spaces between the cells of the tissues, leaving the larger proteins and most of the formed elements in the blood vessels, and this fluid released out is called the interstitial fluid or tissue fluid.
3. 3The composition difference follows from that filtration. The larger proteins and most of the formed elements are retained in the blood vessels, so lymph is poor in proteins and contains no formed elements such as erythrocytes, leucocytes and platelets, apart from the specialised lymphocytes it does carry, whereas blood is rich in both.
4. 4Lymph then returns to the blood. An elaborate network of vessels called the lymphatic system collects this fluid and drains it back to the major veins, so lymph is a one-way overflow that is returned to the circulation, whereas blood is continuously circulated.
5. 5List the components of lymph. It is a colourless fluid containing specialised lymphocytes which are responsible for the immune responses of the body, and it is also an important carrier for nutrients, hormones and similar substances, while fats are absorbed through lymph in the lacteals present in the intestinal villi.
6. 6The functions differ accordingly. Blood is the general transport medium carrying oxygen, nutrients, hormones and wastes, while lymph serves immune defence, the return of tissue fluid to the veins, and the absorption of fats from the intestine.

Step-by-step solution

1. 1Define it in the chapter's own terms. Double circulation is the condition in which oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides, and the ventricles pump it out without any mixing up, so that two separate circulatory pathways are present.
2. 2The two pathways should be named. The blood pumped by the right ventricle enters the pulmonary artery and is passed on to the lungs, from where the oxygenated blood is carried by the pulmonary veins into the left atrium, and this pathway constitutes the pulmonary circulation. The oxygenated blood entering the aorta is carried by a network of arteries, arterioles and capillaries to the tissues, from where the deoxygenated blood is collected by a system of venules, veins and vena cava and emptied into the right atrium, and this is the systemic circulation.
3. 3The structural basis is the four-chambered heart. Crocodiles, birds and mammals possess a 4-chambered heart with two atria and two ventricles, and because the left and right sides are separated by septa the two bloods never meet, which is what makes two separate pathways possible.
4. 4Contrast it with the arrangements that do not achieve this. In fishes the heart pumps out deoxygenated blood which is oxygenated by the gills and supplied to the body parts, from where deoxygenated blood is returned to the heart, which is single circulation. In amphibians and reptiles the left atrium receives oxygenated blood from the gills, lungs or skin and the right atrium gets the deoxygenated blood from other body parts, but they get mixed up in the single ventricle, which pumps out mixed blood, and this is incomplete double circulation.
5. 5Now the significance, and give the physiological consequence first. Because the oxygenated and deoxygenated blood are kept entirely separate, the tissues receive blood of fully oxygenated content, and the oxygenation of the blood is not compromised by mixing.
6. 6The second consequence is a higher and more precisely controlled rate of flow. Since the two circuits are separate, the flow of blood to the lungs and the flow to the tissues can be regulated independently, and the chapter notes of the closed pattern generally that this is more advantageous as the flow of fluid can be more precisely regulated. In animals of high metabolic demand such as birds and mammals this supports the high rate of oxygen delivery that sustained activity requires.

Step-by-step solution

1. 1Take the four pairs in order, and for each give the defining feature on one side and the consequence on the other.
2. 2For (a), blood and lymph. Blood is the fluid circulated by the heart through the blood vascular system, it is rich in proteins and in the formed elements, and it carries oxygen, nutrients, hormones and wastes. Lymph is the tissue fluid collected by the lymphatic system, it is poor in proteins and lacks formed elements, though it carries specialised lymphocytes, and its roles are immune defence, returning tissue fluid to the major veins, and the absorption of fats in the lacteals of the intestinal villi.
3. 3For (b), open and closed circulation. The open circulatory system is present in arthropods and molluscs, in which blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. The closed system is found in annelids and chordates, in which the blood pumped by the heart is always circulated through a closed network of blood vessels, and this pattern is considered more advantageous as the flow of fluid can be more precisely regulated.
4. 4For (c), systole and diastole. Systole is the contraction phase, the atrial systole being the simultaneous contraction of both atria and the ventricular systole the contraction of the ventricular muscles, whereas diastole is the relaxation phase, the atria undergoing relaxation coinciding with the ventricular systole and the ventricles relaxing in the ventricular diastole. Both systole and diastole of the atria and ventricles together make up the cardiac cycle, so the two terms are the contraction and relaxation halves of one repeating sequence.
5. 5For (d), the P-wave and the T-wave. The P-wave represents the electrical excitation, or depolarisation, of the atria, which leads to the contraction of both the atria, and it therefore stands for atrial activity and marks the start of atrial systole. The T-wave represents the return of the ventricles from the excited to the normal state, that is repolarisation, and the end of the T-wave marks the end of systole, so the T-wave stands for the recovery of the ventricles.
6. 6The single summary difference that separates each pair is that in every case the two terms are opposites or near-opposites of the same process, whether of the fluid, of the circuit, of the muscular phase or of the electrical event.

Step-by-step solution

1. 1Take the trend first, since the question asks for an evolutionary change. All vertebrates possess a muscular chambered heart, and along the vertebrate series that heart becomes progressively more subdivided, from two chambers in fishes to four in the highest groups.
2. 2Start at the bottom with fishes. Fishes have a 2-chambered heart with an atrium and a ventricle, and the heart pumps out deoxygenated blood which is oxygenated by the gills and supplied to the body parts, from where the deoxygenated blood is returned to the heart. Only one circuit is involved, so this is single circulation.
3. 3Then the intermediate stage, amphibians and reptiles. Amphibians and the reptiles, except crocodiles, have a 3-chambered heart with two atria and a single ventricle, and this is the first step towards separation of the two bloods, since the left atrium receives the oxygenated blood from the gills, lungs or skin while the right atrium gets the deoxygenated blood from the other body parts.
4. 4But the separation is incomplete, and this is the point to state clearly. The two bloods get mixed up in the single ventricle, which pumps out mixed blood, so amphibians and reptiles have incomplete double circulation, and the incomplete double circulation is what the extra chamber buys and what it fails to buy.
5. 5Then the final stage, crocodiles, birds and mammals. These possess a 4-chambered heart with two atria and two ventricles, and the oxygenated and deoxygenated blood received by the left and right atria respectively passes on to the ventricles of the same sides and is pumped out without any mixing, so two separate circulatory pathways are present and these animals have double circulation.
6. 6In human terms the structural correlate of the trend is the septation. The heart has four chambers, and a thin muscular wall called the inter-atrial septum separates the right and the left atria, whereas a thick-walled inter-ventricular septum separates the left and the right ventricles, so the four-chambered condition is achieved by dividing both the atrial and the ventricular chambers.
7. 7State the functional meaning of the trend. The change from one to two atria and from one to two ventricles progressively prevents the mixing of oxygenated and deoxygenated blood, so the tissues receive better oxygenated blood and the flow can be regulated more precisely, which suits the rising metabolic demand of the higher vertebrates, with complete separation reached only in crocodiles, birds and mammals.

Step-by-step solution

1. 1Give the definition of the term. A heart that can generate its own stimulus is myogenic, and the chapter states the reason in one sentence: the normal activities of the heart are regulated intrinsically, that is, auto regulated by specialised muscles, the nodal tissue, hence the heart is called myogenic.
2. 2Name the tissue responsible. A specialised cardiac musculature called the nodal tissue is distributed in the heart, and it comprises the sino-atrial node, the atrio-ventricular node, the atrio-ventricular bundle with its right and left branches, and the purkinje fibres.
3. 3The decisive property is autoexcitability. The nodal musculature has the ability to generate action potentials without any external stimuli, that is, it is autoexcitable, and this is precisely what makes the heart self-starting rather than dependent on a nerve.
4. 4Show that the stimulus is rhythmic and ordered. The number of action potentials that could be generated in a minute varies at different parts of the nodal system, and the sino-atrial node can generate the maximum number, 70 to 75 per minute, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart.
5. 5Contrast it with extrinsic control, which the term myogenic is distinguishing itself from. A special neural centre in the medulla oblongata can moderate the cardiac function through the autonomic nervous system, and sympathetic signals can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output, while parasympathetic signals decrease the rate of heart beat, the speed of conduction of action potential and thereby the cardiac output, and adrenal medullary hormones can also increase the cardiac output.
6. 6So the sense to stress is that neural and hormonal influences only adjust a beat that the heart has already initiated by itself, and the heart would go on beating if these extrinsic controls were removed.

Step-by-step solution

1. 1The chapter states the reason directly. The sino-atrial node can generate the maximum number of action potentials, that is 70 to 75 per minute, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart, and this is exactly why it is called the pacemaker.
2. 2Locate it, since position supports the function. A patch of nodal tissue is present in the right upper corner of the right atrium, and the right atrium receives the deoxygenated blood from the body, which is the chamber that fills first in each cycle and so is well placed to trigger the whole sequence.
3. 3The key comparative fact is that the rate is not equal throughout the nodal system. The nodal musculature is autoexcitable, but the number of action potentials that could be generated in a minute vary at different parts of the nodal system, so the fastest node sets the pace for the rest.
4. 4Show what the node actually starts. The sino-atrial node generates an action potential which stimulates both the atria to undergo a simultaneous contraction, the atrial systole, and this increases the flow of blood into the ventricles by about 30 per cent, so the node begins the cycle for the whole heart.
5. 5The cycle then depends on that one impulse, and it is transmitted in order. The action potential is conducted to the ventricular side by the atrio-ventricular node and atrio-ventricular bundle, from where the bundle of His transmits it through the entire ventricular musculature.
6. 6Tie it back to the beat count. Since the heart normally beats 70 to 75 times in a minute, an average of 72 beats per minute, and that many cardiac cycles are performed per minute, the node's intrinsic 70 to 75 impulses per minute is exactly the observed rhythm, which is the numerical proof of the pacemaker claim.

Step-by-step solution

1. 1Locate the two structures, since their geometry is the reason for their function. A mass of nodal tissue called the atrio-ventricular node is seen in the lower left corner of the right atrium close to the atrio-ventricular septum, and a bundle of nodal fibres, the atrio-ventricular bundle, continues from it and passes through the atrio-ventricular septa to emerge on the top of the inter-ventricular septum, where it immediately divides into a right and a left bundle.
2. 2State the significance of the node as a relay and a delay. The action potential generated by the sino-atrial node is conducted to the ventricular side by the atrio-ventricular node and atrio-ventricular bundle, and this relay is indispensable because the only electrical connection between the atria and the ventricles is the atrio-ventricular septum, which is the thick fibrous tissue separating the atrium and the ventricle of the same side, and through which an opening is provided.
3. 3The delay is the physiologically valuable part. Because the impulse must pass through the atrio-ventricular node before reaching the ventricles, the atria complete their contraction and empty blood into the ventricles before the ventricles begin to contract, and the chapter notes that the atrial systole increases the flow of blood into the ventricles by about 30 per cent, so that filling is finished before emptying starts.
4. 4Explain the role of the bundle as the distribution system. The atrio-ventricular bundle passes through the atrio-ventricular septa to emerge on the top of the inter-ventricular septum and immediately divides into a right and a left bundle, and these branches give rise to minute fibres throughout the ventricular musculature of the respective sides, which are called the purkinje fibres.
5. 5State what the distribution achieves. Because the purkinje fibres spread through the whole of the ventricular musculature, the bundle of His transmits the impulse through the entire ventricular musculature, so the ventricular contraction is coordinated and near-simultaneous over both ventricles, which is what makes the ventricular systole an effective pump rather than a local twitch.
6. 6Note the dependency. The whole route is a single conducting system, and the chapter describes the bundle of His transmitting the impulse through the entire ventricular musculature to cause the ventricular muscles to contract, so an interruption anywhere on the atrio-ventricular node or bundle would break the link between the atrial and the ventricular phases of the cardiac cycle.

Step-by-step solution

1. 1Define the cardiac cycle first. This sequential event in the heart which is cyclically repeated is called the cardiac cycle, and it consists of the systole and the diastole of both the atria and the ventricles.
2. 2Give its duration, and derive it. The heart beats 72 times per minute, that is, that many cardiac cycles are performed per minute, and the duration of a cardiac cycle is 0.8 seconds, since 60 divided by 72 gives 0.83, conventionally stated as 0.8 seconds.
3. 3Trace one cycle so the definition is anchored. It begins in joint diastole, with all four chambers relaxed, the tricuspid and bicuspid valves open so that blood from the vena cava and the pulmonary veins flows into the right and the left ventricle respectively through the right and left atria, and the semilunar valves closed.
4. 4Then the atrial systole, when the sino-atrial node generates an action potential which stimulates both the atria to undergo a simultaneous contraction, increasing the flow of blood into the ventricles by about 30 per cent. Then the ventricular systole, the impulse being conducted by the atrio-ventricular node and bundle and the bundle of His, which causes the ventricular muscles to contract while the atria relax, and the rising ventricular pressure closes the tricuspid and bicuspid valves against backflow and then forces the semilunar valves guarding the pulmonary artery and the aorta open, so blood leaves through those vessels.
5. 5Then the ventricular diastole, in which the ventricles relax and the falling ventricular pressure closes the semilunar valves, preventing backflow, and then the tricuspid and bicuspid valves are pushed open by the pressure of the blood being delivered into the atria by the veins, so the heart is back in joint diastole and the sequence repeats.
6. 6Now define the cardiac output, and build it in two steps. During a cardiac cycle each ventricle pumps out approximately 70 mL of blood, which is called the stroke volume, and the stroke volume multiplied by the heart rate, that is the number of beats per minute, gives the cardiac output.
7. 7State the value and the definition. The cardiac output is the volume of blood pumped out by each ventricle per minute and averages 5000 mL, or 5 litres, in a healthy individual, and it can be checked arithmetically, since 70 mL multiplied by 72 beats per minute is 5040 mL per minute. The body has the ability to alter the stroke volume as well as the heart rate and thereby the cardiac output, and the cardiac output of an athlete will be much higher than that of an ordinary man.

Step-by-step solution

1. 1Start with the observation. During each cardiac cycle two prominent sounds are produced, which can be easily heard through a stethoscope, and these sounds are of clinical diagnostic significance.
2. 2Give the first sound and its cause. The first heart sound, lub, is associated with the closure of the tricuspid and bicuspid valves, and it occurs at the start of the ventricular systole, when the ventricular systole increases the ventricular pressure, causing the closure of the tricuspid and bicuspid valves due to attempted backflow of blood into the atria.
3. 3The word to keep is backflow. The closure is a safety action, since the atrio-ventricular valves prevent any backward flow, and the sound is produced by the tension of the valve cusps being checked as the ventricles contract.
4. 4Give the second sound and its cause. The second heart sound, dub, is associated with the closure of the semilunar valves, and it occurs later in the systole, when the ventricles relax in the ventricular diastole, the ventricular pressure falls and this causes the closure of the semilunar valves, which prevents the backflow of blood into the ventricles.
5. 5Note that the two sounds close the two sets of valves in turn, so the sequence of a cycle is: the atrio-ventricular valves close at the start of ventricular systole, giving lub, and the semilunar valves close at the start of ventricular diastole, giving dub, and the interval between the two sounds is the systole itself.
6. 6Close with the clinical point. These sounds are of clinical diagnostic significance, because an abnormal, extra, split or absent heart sound indicates that a valve is not closing properly or that the sequence of the cardiac cycle has been disturbed, and the chapter lists the disorders accordingly, with heart failure meaning the state of the heart when it is not pumping blood effectively enough to meet the needs of the body.

Step-by-step solution

1. 1Define what the tracing is. An electrocardiogram is a graphical representation of the electrical activity of the heart during a cardiac cycle, and it is obtained with an electro-cardiograph. Each peak in the ECG is identified with a letter from P to T that corresponds to a specific electrical activity of the heart.
2. 2Describe how the standard tracing is recorded. To obtain a standard ECG a patient is connected to the machine with three electrical leads, one to each wrist and to the left ankle, which continuously monitor the heart activity, and for a detailed evaluation of the heart's function multiple leads are attached to the chest region.
3. 3The P-wave is atrial depolarisation. The P-wave represents the electrical excitation, or depolarisation, of the atria, which leads to the contraction of both the atria, so it stands for the electrical trigger of the atrial systole that fills the ventricles.
4. 4The QRS complex is ventricular depolarisation. The QRS complex represents the depolarisation of the ventricles, which initiates the ventricular contraction, and the contraction starts shortly after Q and marks the beginning of the systole, so the QRS complex is the electrical event that opens the ventricular systole.
5. 5The T-wave is ventricular repolarisation. The T-wave represents the return of the ventricles from the excited to the normal state, that is repolarisation, and the end of the T-wave marks the end of systole, so the T-wave closes the ventricular phase and the complex is complete.
6. 6
   $$\text{Standard ECG:}\underset{\text{P}}{\underbrace{}}\underset{\text{QRS}}{\underbrace{}}\underset{\text{T}}{\underbrace{}}\text{(P, QRS, T in order; QRS is the tallest)}$$
7. 7Give the two uses of the tracing. By counting the number of QRS complexes that occur in a given time period, one can determine the heart beat rate of an individual, and since the ECGs obtained from different individuals have roughly the same shape for a given lead configuration, any deviation from this shape indicates a possible abnormality or disease, so the ECG is of great clinical significance.