Blood Vessels

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 & ARTERIOLESTransport Blood away from heartWall are thicker than veinsWalls made up of 3 layersWhen they are cut, they remain opened

because of their thick wall nature.

VEINS & VENULESTransport blood to the heartWall are thinner than arteriesWall made up of same 3 layersWhen they are cut, they remain opened

because of their thick wall nature

STRUCTURE…Composed Of Three Layers (Tunics)

Tunica intima –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.

LumenCentral blood-filled

space of a vessel

Major Types Of Blood Vessels:

Click icon to add picture

• Artery • Vein • Capillary

WALL OF BLOOD VESSELS

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Structure of Blood VesselsComposed 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

LumenCentral 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 ArteriesElastic arteries – the largest arteries

Diameters range from 2.5 cm to 1 cmIncludes the aorta and its major branchesSometimes called conducting arteriesHigh elastin content dampens surge of blood

pressure

Figure 19.2a

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Muscular (distributing) arteriesLie distal to elastic

arteriesDiameters range from 1

cm to 0.3 mmIncludes most named

arteriesTunica media is thickUnique features

Internal and external elastic laminae

Figure 19.2b

Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

CapillariesSmallest 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 VEINSTransport blood away from the heart

Transport 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 lumens Have relatively wide lumens

Have relatively more muscle/elastic tissue

Have relatively less muscle/elastic tissue

Transport blood under higher pressure

Transport 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.