13.arteries and arterioles

1. ARTERIES AND ARTERIOLES NAME: BETTY ANDY-NWEYE CLASS: PRE MED FOUR COURSE: PHYSIOLOGY

2. INTRODUCTION Arteries are blood vessels that carry blood away from the heart. The blood is normally oxygenated except the case of the pulmonary and umbilical arteries. Arterioles are small diameter blood vessels in the microcirculation that extends and branches out from an artery and leads to capillaries. NOTE: pulmonary arteries carry deoxygenated blood that has just returned from the body to the heart and takes it to the lungs where carbon dioxide is exchanged for oxygen.

3. Artery The main functions of arteries is to carry blood away from the heart to other organs in the body The systemic arteries are subdivided into two types according to their relative compositions of elastic and muscle tissue as well as their size and makeup. They are: Elastic (large conducting) arteries Muscular (medium size distributing) arteries

4. Elastic arteries These arteries are important for helping to propel blood onward while the ventricles are relaxing Their walls stretch to accommodate the surge of blood from the left ventricles during systole. Examples of elastic arteries are; Aorta- root systemic artery Brachiocephalic artery- an artery of the mediastinum that supplies blood to the right arm, head and neck Right and left common carotid arteries Right and left subclavian arteries Right and left vertebral arteries Right and left common iliac arteries

5. Arteries continued… The elastic fibers of the above mentioned arteries function as pressure reservoir. Pressure reservoir: stretched elastic arteries momentarily store some of this energy and therefore function as pressure reservoirs. During systole, the elastic fibers recoil, converting their stored energy into kinetic energy thereby pushing blood forward in the vascular system in a more or less continuous fashion.

6. Muscular arteries These are arteries that branch out into various regions of the body These arteries branch from larger, more elastic arteries and perform the function of distributing blood to various parts and regions of the body They have more smooth muscle than elastin in their tunica media and are therefore, capable of vasoconstriction and vasodilation than are elastic arteries.

7. Muscular arteries are: Brachial artery- arm Radial artery- forearm

8. Structure of an artery Arteries consist of three layers or coats surrounding a hollow center called the lumen . Three layers of an artery are: Tunica interna/intima Tunica media Tunica adventitia

9. Tunica interna This is the proximal and innermost coat of all blood vessels It is in direct contact with the flow of blood It consists of a simple squamous endothelium lying on its basement membrane and a thin connective tissue component called the internal elastic lamina This layer is made up of mainly endothelial cells The hollow internal cavity which the blood flows is lumen

10. Tunica media This is the middle layer that is made up of smooth muscle cells and elastic tissue Thick layer It consists of elastic fibers and smooth muscle which are arranged circularly about the artery like a ring Due to their elastic fibers, walls can stretch easily or expand in response to increase in pressure

11. Tunica adventitia/externa The outermost layer Consists of two components: elastin fibers and collagen fibers which form a connective tissue wrap for the vessel

12. Arterioles These are the smallest of the true arteries Branches from the medium size arteries and begin to loose wall thickness Helps to regulate blood pressure by the variable contraction of the smooth muscle of their walls They deliver blood to the capillaries

13. Arterioles and blood pressure Arterioles have the greatest influence on both local blood flow and on overall blood pressure. They are the primary “adjustable nozzles” in the blood system, across which the greatest pressure drop occurs. The combination of heart output and systemic vascular resistance, which refers to the collective resistance of all of the body’s arterioles, are the principal determinants of arterial blood pressure at any given moment.