Arteries
Carry blood away from the heart Horse has about 20 million arteries
Arteries have the three layers of typical blood vessels. High compliance – able to stretch easily without becoming damaged. Smooth muscle is innervated by sympathetic fibres of the ANS and typical stimulation causes the smooth muscle to contract, narrowing the lumen called Vasoconstriction . An increase in lumen diameter is called Vasodilation .
Elastic Arteries AKA Conducting Arteries
Largest arteries in the body ranging from plumbing pipe (aorta) to finger-sized branches off the aorta. Largest diameter among arteries but vessel walls are relatively thin (1/10 total diameter). Thick tunica media dominated by elastic fibres called Elastic Lamellae Examples include aorta, pulmonary trunk, brachiocephalic, subclavian, common carotid, common iliac arteries. Major function: propel blood onward during ventricular diastole . As blood is ejected from the heart, the artery walls stretch, and the elastic fibres store mechanical potential energy (pressure reservoir). The elastic fibres recoil and the potential energy is converted to kinetic energy. Thus, blood continues to move through the arteries
Muscular Arteries AKA Distributing Arteries
Medium-sized arteries
More smooth muscle and fewer elastic fibres than elastic arteries Capable of greater vasoconstriction/vasodilation to adjust the rate of blood flow Examples range from garden hose femoral and axillary arteries that enter organs. Branch and ultimately distribute blood to each of the various organs. Do not have the ability to recoil due to less elastic fibres and therefore cannot help to propel blood. Main function is to maintain a state of partial contraction known as Vascular Tone which is important in maintaining vessel pressure and efficient blood flow.
Arterioles
Meaning small arteries
Tunica externa layer contains abundant unmyelinated sympathetic fibres and along with chemical mediators, can alter the diameter of arterioles and thus vary the rate of blood flow and resistance through the vessels. Main function is to regulate blood flow into the capillaries.
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