ANATOMY OF THE HUMAN ANATOMY OF THE HUMAN CIRCULATORY SYSTEMCIRCULATORY SYSTEM

Blood VesselsBlood Vessels

There are three There are three types of blood types of blood vessels in vessels in mammalian mammalian circulation: arteries, circulation: arteries, veins and capillaries.veins and capillaries.

Together they form a Together they form a network of blood network of blood vessels throughout vessels throughout the organism that the organism that transport blood.transport blood.

ArteriesArteries Arteries are blood Arteries are blood

vessels that carry vessels that carry oxygen rich blood oxygen rich blood away from the heart. away from the heart.

The walls of arteries The walls of arteries are very thick layers are very thick layers of connective tissue of connective tissue and muscle fibres.and muscle fibres.

The walls are also The walls are also elastic to allow for elastic to allow for increased blood flow.increased blood flow.

ArteriesArteries

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

The diameter The diameter changes in response changes in response to the heartbeat.to the heartbeat.

AneurysmAneurysm An aneurysm is s fluid-An aneurysm is s fluid-

filled bulge found in filled bulge found in the weakened wall of the weakened wall of an artery as a result of an artery as a result of a birth defect or injury.a birth defect or injury.

Complications arise Complications arise when the wall ruptures when the wall ruptures and the decrease and the decrease blood flow results in blood flow results in cell death.cell death.

A weakened artery in A weakened artery in the brain can lead to a the brain can lead to a stroke.stroke.

ArteriesArteries Arteries decrease in Arteries decrease in

size to become size to become arterioles which are arterioles which are composed of composed of smooth muscle and smooth muscle and elastic fibre.elastic fibre.

The nervous system The nervous system controls the controls the diameter of the diameter of the arterioles in order arterioles in order to control blood to control blood flow.flow.

Vasoconstriction and Vasoconstriction and VasodilationVasodilation

The smooth muscles The smooth muscles on the arterioles relax on the arterioles relax and contract to either and contract to either increase or decrease increase or decrease blood flow.blood flow.

Vasoconstriction Vasoconstriction decreases blood flow decreases blood flow while vasodilation while vasodilation increases blood flow.increases blood flow.

ArteriolesArterioles Blood flows through Blood flows through

sphincter muscles that sphincter muscles that control the movement control the movement of blood from the of blood from the arterioles into the arterioles into the capillaries.capillaries.

The muscle opens The muscle opens only when cells in that only when cells in that area require blood or area require blood or we would need about we would need about 200 litres of blood if 200 litres of blood if all the arterioles were all the arterioles were open at once.open at once.