Blood vessels

• The types of blood vessels include: arteries, arterioles, capillaries, venules, veins
• The wall of an artery has three layers: tunica interna, tunica media, and tunica externa.
• The functional properties of arteries are elasticity and contractility
• Elasticity, due to the elastic tissue in the tunica interna and media, allows arteries to accept blood under great pressure from the contraction of the ventricles
• Contractility, due to the smooth muscle in the tunica media, allows arteries to increase or decrease lumen size, and to limit bleeding from wounds.
• Through vasoconstriction (a decrease in the size of the lumen of a blood vessel) and vasodilation (an increase in the size of the lumen of a blood vessel)
• arterioles assume a key role in the regulation of blood flow from the arteries into the capillaries, and in the alternation of arterial blood pressure.
• Capillaries, known as exchange vessels, are microscopic vessels that usually connect arterioles and venules.
• The flow of blood through the capillaries is called microcirculation
• Capillary walls are composed of only a single layer of cells (endothelium) and a basement membrane
• Capillaries branch to form an extensive capillary network throughout the tissue. This networking increases their surface area, which allows a rapid exchange of large quantities of materials.
• Precapillary sphincters, rings of smooth muscle fibres (cells) on arterioles and metarterioles, regulate blood flow through the capillaries.