Biology

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Circulation

Open: e.g arthropods and most mollusks. In some, the cells are directly bathed in the haemolymph (there is no distinction between blood and interstitial fluid). In others, a heart like organ pumps haemolymph when alary muscles contract. This is peristalsis.

Closed:e.g mammals, annelids and cephalopods. Blood contained entirely in vessels. Pros=allows for complexity in systems(e.g ultrafiltration), delivers glucose and oxygen faster to cells and also removes waste (blood is at higher pressure), better control of fluids (e.g during injury), allows for shunting (directed to certain tissues), allows for vasoconstiction/dilaion.

Single: e.g fish-blood passes though the heart only once with each complete circuit of the body.-not as efficient at delivery because blood in capillaries at low pressure. heart to veins to gills to tissues to heart.

Double: e.g mammals and birds-blood passes through the heart twice with each complete circuit of the body. pros=no mixing of blood (maximizes gas exchange) & the pressure is replaced when blood returns from pulmonary capillaries to heart.

The carriage of oxygen

Haemoglobin- consists of four polypeptide chains with four central haem groups. Each haem group has an Fe2+ ion which has an affinity for oxygen. Each Hb molecule binds four oxygen molecules. Around 280 million in each erythrocyte!!

Oxygen-haemoglobin dissociation curve: sigmoid curve reflects the properties of Hb molecule. The affinity of Hb for oxygen increases as successive O2 molecules bind (due to conformational changes). Pressure above 60mmHg, curve is quite flat (reflects how small amount of O2 binds even at large p(O2).

Cardiac Cycle

Atrial diastole-both the ventricles and the atria are relaxed, with the AV valves open. blood from vena cava and pulmonary vein flow into the atria and much of it is allowed t fall passively into the ventricles before atrial systole. During systole, the sino-atrial node transmits a wave of electrical excitation which spreads across both atria, initiating contraction. This forces the remaining blood from the atria into the ventricles. Before ventricular systole, there is a 0.1 second delay. This allows the atria to finish contracting, therefore the ventricles will have the maximum amount of blood as is possible. Next, the sino-atrial node sends a wave of electrical excitation to the AV node, which sends it down the bundle of His (in the inter-ventricular septum). This then spreads out across the base of the two ventricles to the Purkyne tissue, initiating contracting. Contraction occurs from the apex of the heart so that blood is forced out from the base upwards. Otherwise, not all the blood in the ventricle would reach the arteries.

TRANSPORT IN ANIMALS

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