What went wrong when the king rode under the arch?

It was too low and knocked off his crown

How does the chain of blame unfold in the poem?

Each accused person blames another, ending with the king's own changes

Name the formed elements of blood and a function of each.

Erythrocytes transport respiratory gases, leucocytes defend against infection, and platelets help in coagulation of blood.

What is the importance of plasma proteins?

Fibrinogen helps in clotting, globulins are involved in defence, and albumins help maintain osmotic balance.

Why is blood considered a connective tissue?

Because it is of mesodermal origin and consists of a fluid matrix (plasma) with cells (formed elements), linking different parts of the body.

What is the difference between lymph and blood?

Blood contains plasma, red and white cells and platelets, while lymph is a colourless fluid similar to plasma but lacking red cells and most proteins, containing mainly lymphocytes.

What is meant by double circulation and its significance?

It is the presence of two separate circulatory pathways, pulmonary and systemic, so that oxygenated and deoxygenated blood do not mix, allowing efficient supply of oxygen.

Why is the heart called myogenic?

Because the heartbeat is initiated and maintained by specialised cardiac muscle (nodal tissue) rather than by nerves.

Why is the sino-atrial node called the pacemaker?

Because it generates the maximum number of action potentials per minute (70-75) and so sets the pace of the heart's activities.

Define a cardiac cycle and cardiac output.

A cardiac cycle is the sequence of systole and diastole of the atria and ventricles; cardiac output is the volume of blood pumped out by each ventricle per minute, about five litres.

Explain the heart sounds.

The first sound (lub) is associated with closure of the tricuspid and bicuspid valves and the second (dub) with closure of the semilunar valves.

What do the P-wave, QRS complex and T-wave of an ECG represent?

The P-wave represents atrial depolarisation, the QRS complex represents ventricular depolarisation, and the T-wave represents ventricular repolarisation.

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Chapter 15: Body Fluids and Circulation — Class 11 Biology

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Chapter 15: Body Fluids and Circulation

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The straw-coloured fluid matrix of blood is called:

Summary

This chapter describes the body fluids blood and lymph and the human circulatory system. Blood is a fluid connective tissue with plasma (a straw-coloured fluid that is mostly water with proteins such as fibrinogen, globulins and albumins) and formed elements, namely erythrocytes (red blood cells with haemoglobin), leucocytes (granulocytes and agranulocytes) and platelets. Human blood is grouped by the ABO system, based on A and B antigens, and the Rh system; matching is essential before transfusion, and Rh incompatibility can cause erythroblastosis foetalis. Coagulation forms a fibrin clot to prevent blood loss. Lymph is the colourless tissue fluid that drains back to the veins and carries lymphocytes and absorbed fats. Circulation may be open or closed; vertebrate hearts range from two-chambered in fishes to four-chambered in birds and mammals, which have complete double circulation. The human heart, with two atria and two ventricles guarded by valves, is myogenic, with the sino-atrial node acting as the pacemaker. The cardiac cycle of systole and diastole produces heart sounds and an electrocardiogram (ECG), and the cardiac output is the stroke volume times the heart rate. Cardiac activity is regulated by the autonomic nervous system and adrenal hormones. Disorders include hypertension, coronary artery disease, angina and heart failure.

Blood: plasma and formed elementsBlood groups and coagulationLymph or tissue fluidHuman circulatory system and the heartCardiac cycle, ECG and double circulationRegulation and disorders of circulation

Key terms

Plasma

The straw-coloured fluid matrix of blood, mostly water with proteins, minerals and dissolved substances.

Formed elements

The cells of blood: erythrocytes, leucocytes and platelets.

Double circulation

A circulatory pattern with separate pulmonary and systemic pathways, as in birds and mammals.

Pacemaker

The sino-atrial node, which generates the maximum action potentials and sets the rhythm of the heartbeat.

Cardiac cycle

The sequential systole and diastole of the atria and ventricles, repeated about 72 times per minute.

Cardiac output

The volume of blood pumped by each ventricle per minute, equal to stroke volume times heart rate.

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The straw-coloured fluid matrix of blood, mostly water with proteins, minerals and dissolved substances.

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