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Unformatted text preview: February 3, 2009 The Circulatory System- The Circulatory system includes the blood vascular system (with the heart and all of the major blood vessels) and the lymphatic system (drainage vessel network and associated lymphoid organs and system The Blood Vascular System- Blood leaves the heart by entering vessels known as arteries and radiates outwards to peripheral parts of the body and then returns back to the heart cyclically lifelong- Observation that blood moves in circular fashion by a British physiologist known as William Harvey in 1628 o Could not pinpoint the area where blood starting moving away from the heart and where blood started moving toward- In 1661 (4 years after Harvey’s death), Marrcello Malphighi , an Italian research, was able to pinpoint this location, in a structure known as a capillary o This is because Harvey did not have a microscope available to observe the phenomenon- To view capillaries, o Underside of the tongue of the frog- 10-12 capillaries will make up the diameter of a single strand of hair- RBC must move through the capillaries in single file Types of Blood Vessels in the Human Body Arterial Vessels (Arteries)- Start route of blood moving away from the heart- Arterial vessels can be highly variable in diameter - The aorta is the largest artery in the human body- The distal end of an artery is known as arterioles , the are less than 0.5 mm in diameter and represent the link from the arteries in the body to the capillaries- The walls of arteries are comprised of three different layers o Tunica intima is the innermost layer A single layer of endothelial cells supported by a basement membrane with a small amount of connective tissue which secures the layer to the basement layer This is a thin, single-celled layer o The middle layer in the Tunica media A much thicker layer that is well developed Consists largely of smooth muscle fibres that are oriented circularly and interspersed amongst the smooth muscle fibres are loads of elastic fibres Involved in creating pressure to blood vascular system o The outer layer is the Tunica externa (adventitia) A thinner layer but very tough layer Comprised of many longitudinally located collagenous fibres • Collagenous fibres are very tough, they limit the amount of dilation that the artery can undergo and will prevent the artery from over expanding- Distinguishing feature of arteries is that they have a well developed tunica media, they have lots of elastic fibres which allows them to stretch and accommodate an increase in blood volume during ventricular contraction- Some of the largest blood vessels in the body (i.e. the aorta) have a greater deal of elasticity, they accommodate a large amount of blood during contraction....
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This note was uploaded on 10/23/2011 for the course BIOL 2125 taught by Professor Dr.park during the Winter '02 term at A.T. Still University.
- Winter '02