Coronary Artery Disease Essay

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Science Case Study: Coronary Artery Disease (CAD)

Introduction:
CAD is defined as the impairment of the flow of blood to the myocardium and is a vascular disease but directly impacts cardiac function by reducing oxygenation of cardiac tissue (Porth, 2005). Mrs. X has been experiencing episodes of chest pain for the last 18 months and has been diagnosed with stable angina resulting from CAD. She has been admitted to the ward prior to undergoing an off pump coronary artery bypass graft (CABG) of her right coronary artery and her anterior descending artery to help improve coronary blood flow and alleviate the angina.

Anatomy and Physiology:
Blood vessels work to direct and transport blood flowing from the heart to the body and from the body to the heart. They carry blood full of nutrients and oxygen that allows tissue to function normally. Blood vessels also help to remove waste from tissue that result as a product of metabolism. There are three types of blood vessels, arteries, veins and capillaries. Both arteries and veins are comprised of three main layers, the tunica intima, the tunica media and the tunica externa. The capillaries however, are only comprised of one layer of endothelial tissue, one cell thick (Marieb, 2007).

The layers of blood vessels

Tunica Externa:
This is the outer most layer of blood vessels. It helps provide structure for the vessel as a whole, being made of large collagen fibres, and helps to keep blood vessels in place by anchoring them to surrounding organs and tissue. It is also where nerves and lymphatic vessels (in the venous system) connect to the vascular system (Marieb, 2007).

Tunica Media:
The middle layer of blood vessels is constructed primarily from smooth muscle and sheets of elastin. This gives blood vessels their ability to stretch and contract. Vasoconstriction is when the smooth muscle of the tunica media contracts making the lumen of the vessel smaller. Vasodilatation is a relaxing of the smooth muscle allowing the lumen of the vessel to dilate (Marieb, 2007).

Tunica Intima:
This is the innermost layer of blood vessels. The intima is made up of the endothelium and, in larger blood vessels, the subendothelial layer. The endothelium is constructed of a simple squamous epithelium. It is this thin, tightly packed layer of cells that provide a slick surface for the blood that travels within and minimises friction between blood cell and vessel wall (Marieb, 2007).

Blood vessels

Arteries:
These blood vessels carry blood away from the heart and move from the largest diameter vessel, the aorta, to the smallest diameter vessels, arterioles, before becoming part of the capillary network. Arteries have a smaller lumen and larger smooth muscle layer, the tunica media, when compared with veins (see diagram 1). This allows them to maintain a high-pressure environment, which is essential to facilitate the movement of oxygen, wastes and nutrients between tissue and the blood. It also allows blood to move rapidly (Martini, 2004).

Veins:
These blood vessels, as apposed to arteries, carry blood towards the heart and move from the smallest diameter vessels, venules that begin at the capillary bed, to the largest vein, the vena cava, which ends at the right atrium of the heart. Veins have a wide lumen meaning they can accommodate a larger volume of blood then arteries. At any given time in an average adult, the veins hold up to 65% of the total blood volume (Marieb, 2007). Because veins hold a large volume of blood but are only under a fraction of the pressure of arteries they rely on gravity and the movement of muscles external to the veins themselves to propel blood. Small valves located at regular intervals on the tunica intima help prevent back flow of blood (Martini, 2004).

Capillaries:
Capillaries connect the arterial and venous systems. The capillary bed is a system of inter woven capillaries that start as arteriole and gradually fade in...
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