BLOOD VESSELS By: Ms. Reis

Arterial System Arteries – vessels that carry blood away from the heart to arterioles. The aorta is the largest artery in the body carrying blood from the heart to the tissues. Arteries have elastic walls that allow it to first expand as blood passes through then snap back again. This movement keeps blood flowing in the right direction, and provides an additional pumping motion to help force the blood through the blood vessels.

Aneurysm An aneurysm occurs when the inner wall of the artery begins to bulge. When a rupture or blockage occurs in the arterial wall, parts of the brain don't get the blood and oxygen they need which may lead to stroke. Blood from the arteries passes into smaller arteries called arterioles.

Arterioles Blood from the arteries passes into smaller arteries called arterioles. Vasoconstriction occurs when the arterioles contract decreasing blood flow to the tissues. Ex: turning pale when in a state of fear Vasodilation occurs when the arterioles dilate increasing blood flow to the tissues. Ex: blushing when in a state of nervousness

Capillaries Arterioles carry blood to capillaries. Capillaries – smaller blood vessels that carry blood to larger venules. Because of their small diameter red blood cells must travel through capillaries in single file. Nearly every tissue within the body is within 0.1 mm of a capillary.

Capillaries : the Site of Gas and Fluid Exchange Capillaries are the site of fluid and gas exchange between the blood and cells. Capillaries are composed of a single layer of cells. This allows capillaries to provide cells with oxygen, glucose, and amino acids via diffusion through the thin capillary walls. Endocytosis and exocytosis result in the exchange of protein.

Capillaries Oxygenated blood, which appears red in colour, takes on a purple-blue colour as it leaves the capillary. The deoxygenated blood collects in small veins called venules.

Venous System Venules – merge into veins with an even greater diameter. Veins – vessels larger than venules that return blood back to the heart. Once blood reaches the veins after passing the fine network of capillaries it is travelling very slowly. Unlike arteries veins are unable to contract and thus another mechanism must be used to move blood back to the heart.

Blood Vessels How then does blood flow get back to the heart? 1) Veins have valves that open in only 1 direction helping push the blood toward the heart and overcoming the force of gravity. 2) Muscles surrounding the veins exert pressure on the veins which also helps push blood toward the heart.

Blood Vessels: A Comparison Arteries have strong walls capable of withstanding great pressure. Veins are not able to withstand great pressure. Veins have thinner walls but a larger inner circumference. As a result veins lack the elasticity of the artery, but have a greater capacity to carry blood. The venous system contains twice as much blood as the arterial system.

ARTERY CAPILLARY VEIN Wall is composed of 3 layers of cells Wall is one cell thick Thinner wall than artery High elasticity No elasticity Little elasticity but has valves Smaller diameter than veins very narrow diameter Larger diameter than arteries Carries blood away from the heart Site of gas exchange with tissue cells Carries blood toward the heart

Varicose Veins If valves do not function properly gravity carries blood to the feet and blood pooling occurs. This results in veins distending/expanding. Both genetics and lifestyle are factors.