CIRCULATORY SYSTEM
1. INTRODUCTION
The circulatory system is also known as the cardiovascular system. This system is a double circulatory closed system which transports blood via arteries, veins and capillaries to the lungs through the pulmonary circulation and to the rest of the body tissues in the systemic circulation. Since the blood travels to varying distances around the body, the blood vessels have to be adapted to overcome different pressures. The pressure changes in the four chambers on the heart (two atria’s and two ventricles) allow the blood to continuously flow in one direction. This is also aided by the valves (artioventricular and semi lunar valves). The circulatory system consists of the heart as well. The heart is a complex
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The vessels make up two systems which are closed that begins and ends at the heart. However, based on the structure and function, the vessels are put into categories such as arteries and veins.
ARTERY
These are vessels carrying blood away from the heart. These carry oxygenated blood from the heart to the rest of the blood tissues. However, there is one artery which does not carry oxygenated blood, and that the pulmonary artery. The pulmonary artery carries deoxygenated blood from the heart to the lung, where the blood gets oxygenated. Since, the blood is in high pressure, the artery has some structural modifications that help in overcoming the pressure exerted and not to burst. The artery is composed of tunica externa, tunica media, and tunica intima. It also has a relatively narrow lumen.
The tunica externa is the furthermost, strong outer covering of the artery. It is composed of connective tissues, collagen and elastic fibres. The collagen in the artery helps the wall to be stable and not collapse. The elastic fibre helps the walls to stretch and recoil when necessary.
The tunica media is the middle covering of the artery. It consists of smooth muscle, collagen and elastic
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These receive blood directly from the heart. These are the Aorta and the pulmonary artery. The Aorta transports blood from the heart to the rest of the body tissues, whereas the pulmonary artery transports blood from the right ventricle of the heart to the lungs. The arteries need to be elastic because the diameter is small compared to the actual size of the artery. When the heart contracts and pours blood in these arteries, the walls need to stretch to house the blood. The arterial hydrostatic pressure that results from ventricular contraction is the systolic blood pressure. The period between the heart constrictions, the elastic walls recoil to maintain the blood pressure. The arterial hydrostatic pressure between contractions is the diastolic blood pressure. The walls of these have a lot of elastin .Elastin is a fibre which is made up of proteins. However, these arteries have three main walls. These are the tunica externa, tunica media and tunica