Ch 7Body Fluids and Circulation — Class 11 Zoology, concept-first.

Every living cell needs a steady supply of nutrients, oxygen and other substances, and needs its carbon dioxide and other wastes carried away just as steadily.

A body fluid is simply water with dissolved substances in it, and every animal cell lives bathed in, or filled with, one of these fluids.

Plasma is a straw-coloured liquid that is mostly water - typically 80-92% by volume - with everything else dissolved or suspended in it.

Once plasma is removed, what is left of blood is its cellular fraction, collectively called the formed elements: red blood cells (erythrocytes), white blood cells (leucocytes) and platelets.

Red blood cells are the single most abundant cell type in blood: a healthy man carries roughly 5-5.5 million RBCs per cubic millimetre, and a healthy woman slightly fewer, at 4.5-5.0 million per cubic…

White blood cells (leucocytes) are colourless, nucleated, amoeboid cells that lack haemoglobin, and there are far fewer of them than red cells - roughly 6000 to 8000 per cubic millimetre in a healthy…

Platelets, also called thrombocytes, are the third and smallest formed element of blood, normally present at 1,50,000 to 3,50,000 per cubic millimetre.

Two blood-typing systems are used almost everywhere in the world: ABO and Rh. In the ABO system, every person's red cells carry one of four antigen (agglutinogen) patterns on their surface, giving blo…

Blood clotting (coagulation) is the body's emergency repair mechanism, stopping blood loss from an injured vessel within minutes.

Roughly 90% of the fluid that leaks out of capillary walls diffuses straight back into the blood, but the remaining 10% takes a different route: it is picked up by a separate network of thin-walled tu…

All blood vessels are hollow tubes, but the three types - arteries, veins and capillaries - are built very differently because they each face a different job.

The heart muscle itself needs a private blood supply to bring it nutrients and oxygen and remove its waste, and that supply is delivered by the coronary arteries and drained by the coronary veins.

Two fundamentally different circulatory designs exist among animals. In an open circulatory system, seen in arthropods and most molluscs, the heart pumps a fluid called haemolymph into vessels that em…

The human heart, first accurately described by Raymond de Vieussens in 1706, is built from a unique muscle type - cardiac muscle - found nowhere else in the body.

The human heart is myogenic, meaning the cardiac muscle cells themselves can spontaneously and rhythmically depolarise to trigger a heartbeat, with no need for an external nerve signal to start each c…

The cardiac cycle is the complete sequence of events from the start of one heartbeat to the start of the next, and it repeats roughly every 0.8 seconds. It is conventionally broken into five phases.

Cardiac output (CO) is the volume of blood each ventricle pumps out per minute, and it is simply the product of how fast the heart beats and how much blood it ejects with each beat: CO = HR x SV.

An electrocardiogram (ECG) is a recording of the heart's electrical activity over time, picked up through electrodes placed on the skin of the arms, legs and chest, and it plots how electrical potenti…

Double circulation is the arrangement, first described by William Harvey in 1628, in which blood passes through the heart twice for every complete circuit of the body - once through the right side and…

Even though the human heartbeat is myogenic and self-generated, its rate and strength are constantly adjusted by three cooperating control systems: the nervous system, the endocrine system, and local…

Hypertension - persistently high blood pressure, defined here as systolic pressure above 150 mm Hg or diastolic pressure above 90 mm Hg, against a normal reading of about 120/80 mm Hg - is the most co…

A range of diagnostic and treatment options exist for circulatory disease, running from simple imaging through to full organ replacement.

This closing Evaluation exercise gathers questions across the whole chapter - the composition and roles of plasma, blood cells and platelets; ABO and Rh blood grouping; clotting; lymph; the structure…

Sample papers and previous-year board questions for this subject.