Body Fluids & Circulation

Body Fluids and Circulation

EXERCISE

Q1. Name the components of the formed elements in the blood and mention one major function of each of them.

Q2. What is the importance of plasma proteins?

Q3. Match Column I with Column II :

Column I....................... Column II

(a) Eosinophils............. (i) Coagulation

(b) RBC .........................(ii) Universal Recipient

(d) Platelets ..................(iv) Contraction of Heart

(e) Systole...................... (v) Gas transport

Q4. Why do we consider blood as a connective tissue?

Q5. What is the difference between lymph and blood?

Q6. What is meant by double circulation? What is its significance?

Q7. Write the differences between :

(a) Blood and Lymph

(b) Open and Closed system of circulation

(d) P-wave and T-wave

Q8. Describe the evolutionary change in the pattern of heart among the vertebrates.

Q9. Why do we call our heart myogenic?

Q10. Sino-atrial node is called the pacemaker of our heart. Why?

Q11. What is the significance of atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?

Q12. Define a cardiac cycle and the cardiac output.

Q13. Explain heart sounds.

Q14. Draw a standard ECG and explain the different segments in it.

SUMMARY

Vertebrates circulate blood, a fluid connective tissue, in their body, to transport essential substances to the cells and to carry waste substances from there. Another fluid, lymph (tissue fluid) is also used for the transport of certain substances.

Blood comprises of a fluid matrix, plasma and formed elements. Red blood cells (RBCs, erythrocytes), white blood cells (WBCs, leucocytes) and platelets (thrombocytes) constitute the formed elements.

Blood of humans are grouped into A, B, AB and O systems based on the presence or absence of two surface antigens, A, B on the RBCs.

Another blood grouping is also done based on the presence or absence of another antigen called Rhesus factor (Rh) on the surface of RBCs.

The spaces between cells in the tissues contain a fluid derived from blood called tissue fluid. This fluid called lymph is almost similar to blood except for the protein content and the formed elements.

All vertebrates and a few invertebrates have a closed circulatory system. Our circulatory system consists of a muscular pumping organ, heart, a network of vessels and a fluid, blood.

Heart has two atria and two ventricles. Cardiac musculature is auto-excitable.

Sino-atrial node (SAN) generates the maximum number of action protentials per minute (70-75/min) and therefore, it sets the pace of the activities of the heart. Hence it is called the Pacemaker. The action potential causes the atria and then the ventricles to undergo contraction (systole) followed by their relaxation (diastole).

The systole forces the blood to move from the atria to the ventricles and to the pulmonary artery and the aorta. The cardiac cycle is formed by sequential events in the heart which is cyclically repeated and is called the cardiac cycle. A healthy person shows 72 such cycles per minute.

About 70 mL of blood is pumped out by each ventricle during a cardiac cycle and it is called the stroke or beat volume.

Volume of blood pumped out by each ventricle of heart per minute is called the cardiac output and it is equal to the product of stroke volume and heart rate (approx 5 litres). The electrical activity of the heart can be recorded from the body surface by using electrocardiograph and the recording is called electrocardiogram (ECG) which is of clinical importance.

We have a complete double circulation, i.e., two circulatory pathways, namely, pulmonary and systemic are present. The pulmonary circulation starts by the pumping of deoxygenated blood by the right ventricle which is carried to the lungs where it is oxygenated and returned to the left atrium.

The systemic circulation starts with the pumping of oxygenated blood by the left ventricle to the aorta which is carried to all the body tissues and the deoxygenated blood from there is collected by the veins and returned to the right atrium.

Though the heart is autoexcitable, its functions can be moderated by neural and hormonal mechanisms.

Q1 Name the components of the formed elements in the blood and mention one major function of each of them.

Ans. The component elements in the blood are:

a. Erythrocytes:

They are the most abundant cells and contain the red pigment called haemoglobin. They carry oxygen to all parts of the body. Red blood cells are produced continuously in some parts of the body such as the marrow of long bones, ribs etc. There are about 4-6 million RBCs per cubic millimeter of blood.

b. Leukocytes:

Leucocytes are colourless cells. These cells do not contain haemoglobin. They are the largest cells of the body and are divided into two main categories: (i) Granulocytes ; (ii) Agranulocytes;

........(i) Granulocytes: These leucocytes have granules in their cytoplasm and include neutrophils, eosinophils, and basophils. Neutrophils are phagocytic cells that protect the body against various infecting agents. Eosinophils are associated with allergic reactions, while basophils are involved in inflammatory responses.

.......(ii) Agranulocytes: Lymphocytes and monocytes are agranulocytes. Lymphocytes generate immune responses against infecting agents, while monocytes and phagocytic in nature.

c. Platelets:

Platelets are small irregular bodies present in blood. They contain essential chemicals that help in clotting. The main function of platelets is to promote clotting.

Q2 What is the importance of plasma proteins?

Ans. Plasma is the colourless fluid of blood which helps in the transport of food, CO2, waste products and salts. It constitutes about 55% of blood. About 6.8% of the plasma is constituted by proteins such as fibrinogens, globulins, and albumins. Fibrinogen is a plasma glycoprotein synthesised by the liver. It plays a role in the clotting of blood.

Globulin is a major protein of the plasma. It protects the body against infecting agents. Albumin is a major protein of the plasma. It helps in maintaining the fluid volume within the vascular space.

Q3. Match Column I with Column II :

Column I....................... Column II

(a) Eosinophils............. (i) Coagulation

(b) RBC .........................(ii) Universal Recipient

(d) Platelets ..................(iv) Contraction of Heart

(e) Systole...................... (v) Gas transport

Ans.

(a) Eosinophils = Resist infections

(b) RBC = Gas transport

(d) Platelets = Coagulation

(e) Systole = Contraction of heart

Q4 Why do we consider blood as a connective tissue?

Ans. Connective tissues have cells scattered throughout an extra-cellular matrix/ They connect different body systems. Blood is considered as a type of connective tissue because of the two reasons

a. Like the other connective tissues, blood is mesodermal in origin

b. It connects the body systems, transport oxygen and nutrients to all the parts of the body, and removes the waste products. Blood has an extra-cellular matrix called plasma, with red blood cells, white blood cells, and platelets floating in it.

Q5 What is the difference between lymph and blood?

Q6. What is meant by double circulation? What is its significance?

Ans. Double circulation is a process during in which blood passes twice through the heart during once complete cycle. This type of circulation is found in amphibians, reptiles, birds and mammals. However, it is more prominent in birds and mammals as in them the heart is completely divided into four chambers - the right atrium, the right ventricle, the left atrium and the left ventricle.

The movement of blood in an organism is divided into two parts:

a. Systemic circulation

b. Pulmonary circulation

Systemic circulation: It involves the movement of oxygenated blood from the left ventricle of the heart to the aorta. It is then carried by blood through a network of arteries, arterioles, and capillaries to the tissues. From the tissues, the deoxygenated blood is collected by the venules, veins, and vena cava, and is emptied into the left auricle.

Pulmonary circulation: It involves the movement of deoxygenated blood from the right ventricle to the pulmonary artery, which then carries blood to the lungs for oxygenation. From the lungs, the oxygenated blood is carried by the pulmonary veins into the left atrium.

Hence, in double circulation, blood has to pass alternatively through the lungs and the tissues.

Significance of double circulation:

The separation of oxygenated and deoxygenated blood allows a more efficient supply of oxygen to the body cells. Blood is circulated to the body tissues through systemic circulation and to the lungs through pulmonary circulation.

Q7. 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

Q8. Describe the evolutionary change in the pattern of heart among the vertebrates.

Ans. All vertebrates possess a heart - a hollow muscular organ composed of cardiac muscle fibres. The function of the heart is to pump oxygen to all parts of the body. The evolution of the heart is based on the separation of oxygenated blood from deoxygenated blood for efficient oxygen transport. In fishes, the heart was like a hollow tube. This evolved into the four - chambered heart in mammals.

Piscean heart: Fish has only two chambers in its heart - one auricle and one ventricle. Since both the auricle and the ventricle remain undivided, only deoxygenated blood passes through it. The deoxygenated blood enters the gills for oxygenation from the ventricle. It has additional chambers such as sinus venosus and conus arteriosus.

Amphibian heart: Amphibians, such as frogs have three chambered hearts, with two auricle and one ventricle. The auricle is divided into a right and a left chamber by an inter-auricular septum, while the ventricle remains undivided. Additional chambers such as sinus venosus and conus arteriosus are also present. The oxygenated blood from the lungs enters the left auricle and simultaneously, the deoxygenated blood from the body enters the right auricle. Both these auricles empty into the ventricle, wherein the oxygenated and deoxygenated blood get mixed to some extent

Reptilian heart: Reptiles have incomplete four-chambered hearts, except for crocodiles, alligators and gharials. They have only one accessory chamber called sinus venosus. The reptilian heart also shows mixed blood circulation.

Avian & mammalian hearts: They have two pairs of chambers for separating oxygenated and deoxygenated bloods. The heart is divided into four chambers. The upper two chambers are called atria and the lower two chambers are called ventricles. The chambers are separated by a muscular wall that prevents the mixing of the blood rich in oxygen with the blood rich in CO2.

Q9 Why do we call our heart myogenic?

Ans. In the human heart, contraction is initiated by a special modified heart muscle known as sinoatrial node. It is located in the right atrium. The SA node has the inherent power of generating a wave of contraction and controlling the heartbeat. Hence, it is known as the pacemaker. Since the heart beat is initiated by the SA node and the impulse of contraction originates in the heart itself, the human heart is termed myogenic. The hearts of vertebrates and molluscs are also called myogenic.

Q10 Sino-atrial node is called the pacemaker of our heart. Why?

Ans. The sino-atrial (SA) node is a specialised bundle of neurons located in the upper part of the right atrium of the heart. The cardiac impulse originating from the SA node triggers a sequence of electrical events in the heart, thereby controlling the sequence of muscle contraction that pumps blood out of the heart. Since the SA node initiates and maintains the rhythmicity of the heart, it is known as the natural pacemakers of the human body.

Q11 What is the significance of the atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?

Ans. The atrioventricular (AV) node is present in the right atrium, near the base of the inter-auricular septum that separates the right auricle from the ventricle. It gives rise to the bundle of his that conducts the cardiac impulses from the auricles to the ventricles. As the bundle of His passes the ventricle along the inter-ventricular septum, it divides into two branches - the right ventricle and the left ventricle. The end branches of this conducting system then forms a network of Purkinje fibres that into the myocardium. Hence, the atrio-ventricular node and the atrioventricular bundle play a role in the contraction of ventricles.

Q11 What is the significance of the atrio-ventricular node and atrio-ventricular bundle in the functioning of heart?

Q12 Define a cardiac cycle and the cardiac output.

Ans. Cardiac cycle is defined as the complete cycle of events in the heart from the beginning of one heart beat to the beginning of the next. It comprises three stages - atrial systole, ventricular systole, and complete cardiac diastole.

Cardiac output is defined as the amount of blood pumped out by the ventricles in a minute.

Q13 Explain heart sounds.

Ans. Heart sounds are noises generated by the closing and opening of the heart valves. In a healthy individual, there are two normal heart sounds called lub and dub.

Lub is the first heart sound. It is associated with the closure of the tricuspid and bicuspid valves at the beginning of systole.

The second heart sound dub is associated with the closure of the semilunar valves at the beginning of diastole.

These sounds provide important information about the condition and working of the heart.

Q14 Draw a standard ECG and explain the different segments in it.

Ans. Electrocardiogram is a graphical representation of the cardiac cycle produced by an electrograph. The diagrammatic representation of a standard ECG is shown below.

A typical human electrocardiogarm has five waves - P, Q, R, S and T.

The P, R and T waves are above the base line and are known as positive waves. The Q and S waves are below the base line and are known as negative waves. The P -wave is of atrial origin, while the Q, R, S and T - waves are of the ventricular origin.

a. The P-wave indicates atrial depolarisation. During this wave, the impulse of contraction is generated by the SA node. The PQ-wave represents atrial contraction.

b. The QR wave is preceded by ventricular contraction. It represents the spread of the impulse of contraction from the AV node to the wall of the ventricle. It leads to ventricular depolarisation.

c. The RS wave represents ventricular contraction of about 0.3 sec.

d. The ST wave represents ventricular relaxation of about 0.4 sec. During this phase, the ventricles relax and return to their normal state.

e. The T-wave represents ventricular relaxation.