CRITICAL CARE CLASS

The Heart

Weighs about 300 – 400 grams Function is to pump Has both right and left pumps that work as one 4 chambers : 2 atria and 2 ventricles

Basic Structure Located in the middle, slightly to the left mediastinum Wider at the base smaller at the apex Anteriorly it is protected by the sternum and ribs Rests on the diaphragm Three layers surrounded by the Pericardial Sac Epicardium : outermost layer contains coronary arteries Myocardium : muscle Endocardium : smooth inner layer, smoothness prevents clot formation

The chambers of the heart atria are the top The Atria

The Ventricles The ventricles pump the blood from the heart Right ventricle pumps to the lungs to be oxygenated Left ventricle pumps into the aorta to deliver blood to the body

Coronary vessels Consists of arteries Blood is supplied to the tissues of the heart by the first two branches of the aorta--right and left coronary arteries. Left coronary artery has 2 branches : circumflex and left anterior descending

left anterior descending artery travels to the anterior interventricular sulcus and its branches supply the walls of both ventricles. follows the coronary sulcus between the right and left ventricle. circumflex artery

Coronary Sinus Most of the cardiac veins drain into coronary sinus, which lies in the atrioventricular groove. It is 2-3 cm long and end in the right atrium

Coronary Sinus

Chordae Tendineae

Blood Flow Through the Heart The heart has four chambers. The right and left sides of the heart are separated by a muscular wall (septum). This prevents blood without oxygen from mixing with blood that contains oxygen. The heart also contains valves that separate the chambers and connect to major blood vessels.

Normally blood flows from the body into the right upper heart chamber. The blood on the right side of the heart has been used by the body and contains little oxygen (oxygen-poor). The oxygen-poor blood flows from the right upper heart chamber through the valve to the right lower chamber. From the right lower heart chamber, blood is pumped through the valve into the blood vessel that goes to the lungs (pulmonary artery). This blood then picks up oxygen (oxygenated).

Oxygen-rich blood flows from the lungs through blood vessels (pulmonary veins) back to the heart's upper left chamber. From the upper left heart chamber, blood goes through the valve and into the lower left chamber. The lower left heart chamber pumps blood through the valve to a major blood vessel (aorta) and to the body. The blood delivers oxygen to the body. Blood is then returned to the upper right heart chamber through veins and repeats the cycle.

Blood Flow through the Heart Inferior/ Superior Vena cava → Right Atrium→ Tricuspid Valve → Right Ventricle → Pulmonary Valve→ Pulmonary Artery →Lungs→ Pulmonary Vein→ Left Atrium →Mitral Valve → Left Ventricle →Aorta

What makes the Blood Flow Blood doesn't flow by itself — your heart's chambers work hard to keep blood moving. The chambers relax and expand to let blood flow into them. Then they tighten and pull inward (contract) to help push blood out. When a chamber is relaxed, or expanded, it is in diastole. When a chamber is contracted, or small, it is in systole

Right heart: right atrium and right ventricle Left heart : left atrium and left ventricle Systole : contraction/squeezing/emptying/ work phase Diastole: relaxation/stretching/filling/resting phase These terms apply to all four chambers Valves : Act to retain blood in one chamber until the next chamber or vessel is ready to receive it. Valve function is in response to pressure changes in the chambers Atrial-Ventricular Valves and the Semi-Lunar Valves Heart Sounds are made by vibration. First heart sound: when AV valves close and ventricles are in systole Second heart sound: when semilunar valves close and ventricles are in diastole

Your Heart in Action

Blood supply to the Heart Vessels supply blood to heart muscle under pressure. Vessels encircle the heart, most flow occurring during diastole when ventricular muscles release and relieve pressure on the artery walls, allowing them to fill with blood. The faster the heart rate, the less time there is available for coronary artery filling, since diastolic time is shortened.

Cardiac Output The amount of blood moved out by ventricular contraction per minute It is the product of heart rate X stroke volume Normal CO : approximately 4-8 liters per minute

Regulation of Heart Rate Under influence of autonomic nervous system Both sympathetic and parasympathetic fibers innervate the SA and AV nodes Sympathetic fibers act on myocardial tissue Parasympathetics : affect atrium -> SA node stimulate = decreased HR, conduction, irritability Sympathetics: atrium, ventricle will increase HR< increase conduction, and irritability Reflexes: Aortic and Bainbridge

SYMPATHETIC Affects the atria and the ventricles Increases : heart rate, conduction and irritability PARASYMPATHETIC Affects only the atria Decreases : heart rate, conduction, and irritability

How Cardiac Output is Determined Stroke volume : amount of blood ejected with ventricular systole Preload : How much blood returns to the heart Afterload : The pressure the heart pumps against Contractility : How effectively the heart pumps Frank Starling Mechanism : Affects preload, the more you stretch the harder the contraction Cardiac Output = Stroke Volume X Heart Rate The amount of blood the heart pumps out /min is = to the amount of blood it pumps out per contraction times the number of contractions /min. In order to meet tissue demands, the heart must be able to increase its output several times over.

Peripheral Circulation Significance of the cardiovascular system is tissue perfusion, which supplies cells with oxygen and nutrients and carries away carbon dioxide. Blood flow dependant on MAP, vessel resistance, vessel length, and blood viscosity Blood Pressure = Cardiac Output X peripheral resistance

The electrical system in your heart controls the speed of your heartbeat. The system includes a network of electrical pathways, similar to the electrical wiring in your home. The pathways carry electrical signals through your heart. The movement of the signals is what makes your heart beat. When working properly, your heart's electrical system automatically responds to your body's changing need for oxygen. It speeds up your heart rate as you climb stairs, for example, and slows it down when you sleep. When your heart rate speeds up, it means your heart pumps faster and your body gets more oxygen-rich blood. Your heart's electrical system is also called the cardiac conduction system.

Electrical conduction Sa node → AV Node → Bundle of His → Purkinje Fibers Depolarization initiated by impulse from SA node (atria kick) Impulse spreads through both atria Impulse reaches AV node Impulse transmitted along bundle of His to Purkinje fibers, activating ventricles almost simultaneously