Blood vessels are intricate networks of tubes that transport blood throughout the entire body. They carry blood through miles in a never ending stream. If you could take all the blood vessels of a average size child and line them up they could reach about 60,000 miles long. In an adult, the blood vessels could reach 100,000 miles long. Part of the Circulatory System. WHAT ARE BLOOD VESSELS ?

TYPES ARTERIES, ARTERIOLES VEINS, VENULES CAPILLARIES

ARTERIES & ARTERIOLES Transport Blood away from heart Wall are thicker than veins Walls made up of 3 layers When they are cut, they remain opened because of their thick wall nature.

VEINS & VENULES Transport blood to the heart Wall are thinner than arteries Wall made up of same 3 layers When they are cut, they remain opened because of their thick wall nature

STRUCTURE… Composed Of Three Layers (Tunics) Tunica i ntima –is the innermost layer, composed of epithelium Tunica media –made up of smooth muscle cells coated with elastic tissue. Tunica externa (adventitia) – Entirely composed of connective tissue. It also contains nerves that supply the vessel. Lumen Central blood-filled space of a vessel

Major Types Of Blood Vessels : Artery Vein Capillary

WALL OF BLOOD VESSELS

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Blood Vessels Composed of three layers (tunics) Tunica intima – composed of simple squamous epithelium Tunica media – sheets of smooth muscle Contraction – vasoconstriction Relaxation – vasodilation Tunica externa – composed of connective tissue Lumen Central blood-filled space of a vessel

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings % Figure 19.1a

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Types of Arteries Elastic arteries – the largest arteries Diameters range from 2.5 cm to 1 cm Includes the aorta and its major branches Sometimes called conducting arteries High elastin content dampens surge of blood pressure Figure 19.2a

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Muscular (distributing) arteries Lie distal to elastic arteries Diameters range from 1 cm to 0.3 mm Includes most named arteries Tunica media is thick Unique features Internal and external elastic laminae Figure 19.2b

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings Capillaries Smallest blood vessels Diameter from 8–10 µm Red blood cells pass through single file Site-specific functions of capillaries Lungs – oxygen enters blood, carbon dioxide leaves Small intestines – receive digested nutrients Endocrine glands – pick up hormones Kidneys – removal of nitrogenous wastes

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings RBCs in a Capillary Figure 19.3

Superficial veins Superficial veins are those whose course is close to the surface of the body, and have no corresponding arteries. Deep veins Deep veins are deeper in the body and have corresponding arteries. Pulmonary veins The pulmonary veins are a set of veins that deliver oxygenated blood from the lungs to the heart. Systemic veins Systemic veins drain the tissues of the body and deliver deoxygenated blood to the heart. Classification Of Vein

Comparism Btw Arteries and Veins ARTERIES VEINS Transport blood away from the heartTransport blood towards the heart Carry Oxygenated blood ( except the Pulmonary and Umbilical Artery) Carry Deoxygenated Blood (except the Pulmonary and Umbilical artery) Have relatively narrow lumensHave relatively wide lumens Have relatively more muscle/elastic tissue Have relatively less muscle/elastic tissue Transport blood under higher pressureTransport blood under lower pressure than arteries They do not have valves (except for the semi-lunar valves of the pulmonary artery and the aorta) Have valves throughout the main veins of the body. These are to prevent blood flowing in the wrong direction, as this could (in theory) return waste materials to the tissue

ROLE IN DISEASE Main article: Vascular disease Blood vessels play a role in virtually every medical condition. Cancer, for example, cannot progress unless the tumor causes angiogenesis,(formation of new blood vessels) to supply the malignant cells' metabolic demand. Atherosclerosis, the formation of lipid lumps (atheromas) in the blood vessel wall, is the most common cardiovascular disease, the main cause of death in the Western world.

Blood vessel permeability is increased in inflammation. Damage, due to trauma or spontaneously, may lead to haemorrhage due to mechanical damage to the vessel endothelium. In contrast, occlusion of the blood vessel by atherosclerotic plaque, by an embolised blood clot or a foreign body leads to downstream ischemia (insufficient blood supply) and possibly necrosis. Vessel occlusion tends to be a positive feedback system; an occluded vessel creates eddies in the normally laminar flow or plug flow blood currents. These eddies create abnormal fluid velocity gradients which push blood elements such as cholesterol or chylomicron bodies to the endothelium. These deposit onto the arterial walls which are already partially occluded and build upon the blockage. Vasculitis is inflammation of the vessel wall, due to autoimmune disease or infection.