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Biology Heart and circulatory system

Biology:

the Heart and Circulatory system

In Mammles, Blood flow is maintained by:

a muscular Hear, which pumps blood throughout arteries and capillaries.

rythmical co-ordination of the muscle in the thick walled arteries , which can be felt as a pulse

contraction of the body muscles during normal movements which help to squeeze blood along the long thin-walled veins

veins have semi-lunar valves to prevent the backwards flow of blood

inhalation creates a negative pressure in the cardiothoracic area, helping to draw blood to the heart.

Blood vessels:

Arteries, capillaries and veins.

Arteries carry blood away from the heart branching to form smaller arterioles, Arterioles than divide into thin walled capillaries

Capillaries allow rapid diffusion off materials between blood and the cells. Capillaries join together to form Venules. the Venules than Join to form larger veins

The walls of Arteries and Veins are made up of three main layers:

a thin inner lining of epithelial cells

middle layer made up of elastic tissue and smooth muscle

and outer layer of collagen fibers and elastic tissue.

the semi-lunar valves work in a vein by the fact the blood has enough pressure to force the valves open as it flows towards the heart.

the backwards flow of the blood due to the large lumen and thin endothelial and collagen fibers forces the semi lunar valve close.

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BIOLOGY HEART AND CIRCULATORY SYSTEM: HEART STRUCTURE AND CARDIAC CYCLE.

The heart structure

- made up of mainly cardiac muscle, the fibers are made of interconnecting muscle cells, each cell is joined to the next by intercalary discs.

there are two chambers on either side of the heart: The Atria and the ventricles

the right atrium receives blood from the Vena Cava.

the left atrium receives blood from the pulmonary veins.

the right ventricle contracts when it pumps blood out into the pulmonary arteries.

the left ventricle pumps blood into the thoracic aorta when it contracts.

the ventricles have thicker walls because they have to gain enough pressure to force the blood further.

the artria have thinner walls because they only have to pump blood a short distance down the ventricles.

two sets of valves keep the blood flowing in the right direction:

the atrio-ventricular valves are found on each side, between the atria and the ventricles. they prevent the backwards flow of blood into the atria when the ventricles contract.

on the right side is the tri-cuspid valve, having three flaps.

on the left side is the bi-cuspid valve having two flaps.

the semi lunar valves - the second type of valve are found at the base of the thoracic aorta and pulmonary artery, to prevent the backwards flow of blood when the ventricles relax.

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Cardiac Cycle

Atrial Systole

the heart is full of blood and the ventricles are relaxed

both the atria contract and blood passes down through the ventricles

the atrio-ventricular valves open due to pressure of the blood against them

70% of the blood flows passibley down to the ventricles so the atria do not have to contract a great amount

Ventricular systole

the atria relax

the thick muscular walls of the ventricles contract forcing blood out of the heart into the pulmonary artery and the aorta.

the pressure of the blood against the atrio-ventricular valves causes them to shut, preventing blood going back into the atria, producing the sound of the heart beating.

the pressure of the blood against the semi lunar valves opens them.

the pulmonary artery carries deoxygenated blood to the lungs, while the aorta carries oxygenated blood round the body.

Diastole

the ventricles relax

the pressure inside the ventricles drops below that of in the arteries.

blood under high pressure in the arteries causes the semi-lunar valves to close, preventing blood going back into the ventricles. this produces the second sound of the heartbeat.

during diastole, all the muscle in the heart relaxes.

blood from the vena cava and pulmonary veins re-enters the atria and the cycle starts again

the cardiac cycle and its beginning is started by a specialized muscle tissue called the sino-atrial node (pacemaker) the contractions of the caridac muscles in the walls of the atria are rhythmic to the impulses sent by the sino-atrial node.