ANATOMY OF THE HUMAN CIRCULATORY SYSTEM

Blood Vessels There are three types of blood vessels in mammalian circulation: arteries, veins and capillaries. Together they form a network of blood vessels throughout the organism that transport blood.

Arteries Arteries are blood vessels that carry oxygen rich blood away from the heart. The walls of arteries are very thick layers of connective tissue and muscle fibres. The walls are also elastic to allow for increased blood flow.

Arteries The pulse you feel near your wrist or at other locations on the body is created by the increase in diameter of the artery at that location. The diameter changes in response to the heartbeat.

Aneurysm An aneurysm is s fluid-filled bulge found in the weakened wall of an artery as a result of a birth defect or injury. Complications arise when the wall ruptures and the decrease blood flow results in cell death. A weakened artery in the brain can lead to a stroke.

Arteries Arteries decrease in size to become arterioles which are composed of smooth muscle and elastic fibre. The nervous system controls the diameter of the arterioles in order to control blood flow.

Vasoconstriction and Vasodilation The smooth muscles on the arterioles relax and contract to either increase or decrease blood flow. Vasoconstriction decreases blood flow while vasodilation increases blood flow.

Arterioles Blood flows through sphincter muscles that control the movement of blood from the arterioles into the capillaries. The muscle opens only when cells in that area require blood or we would need about 200 litres of blood if all the arterioles were open at once.