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Cardiovascular System

Structure and locationCardiac tissue & ECGCoronary blood flow

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Associated Terms• Systemic circulation• Pulmonary circulation• Arteries• Arterioles• Capillary beds

• Venules• Veins• Electorcardiography

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Location of the Heart• Lies in the mediastinum of the thoracic cavity – 2/3 of the heart mass lies to the left of the body’s midline

• Rests on the diaphragm

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Dimensions of the Heart• Hollow, cone shaped organ• About the size of a person’s closed fist• Weighs 300g• 12 cm long• 9 cm wide at broadest part• 6 cm thick• Inferior point of (L) ventricle - Apex

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Pericardium• Triple-layered sac

– Fibrous pericardium– Serous pericardium

• Parietal layer• Visceral layer

• Surrounds the heart• Provides protection and confines the heart to its position in the mediastinum

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Pericarditis & Cardiac Tamponade

• Pericarditis – inflammation of the pericardium

• Cardiac tamponade – build up of fluid/blood within the pericardial space.– Life threatening

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Structure of the Heart Wall • Three layers:

– Epicardium (external layer – visceral layer of the serous pericardium)– Myocardium (middle layer – muscle layer)– Endocardium (internal layer – thin layer of endothelial tissue) Endocardium covers the valves and is continuous with the endothelial lining of the large blood vessels.

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Cardiac Muscle Tissue• Involuntary striated muscle• Muscle fibres are:

– Shorter, fatter and squarish in shape compared to other striated muscle– Exhibits branching – Y shape

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Cardiac Muscle Tissue• Sarcoplasm is more abundant in cardiac muscle tissue• Mitochondria are larger and more numerous• Has limited reserves of Ca++ (Ca++ enters the muscle fibres from extracellular fluid during contraction)

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Cardiac Muscle Tissue• Intercalated discs connect each fibre with its neighbour• Gap junctions allow muscle action potentials to spread from one muscle fibre to another• This connection allows connected units to function as one

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Physiology of Cardiac Muscle

• Under normal resting conditions, muscle fibres contract and relax about 75 times per minute• Cardiac muscle is greatly dependant on a constant supply of oxygen• Reliant on aerobic system to generate ATP

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Physiology of Cardiac Muscle

• Cells are capable of autorhythmicity • Contraction is maintained for 10-15 times longer than that of skeletal muscle due to prolonged Ca++ delivery• Refractory periods of several 1/10ths of a second allows time for the chambers to fill between contractions

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Action Potential of Cardiac Muscle

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Heart Chambers• Four chambers

– 2 - Atria– 2 – Ventricles

• Anterior wall of the atrium is rough due to internal muscular ridges called pectinate muscles. Posterior wall is smooth• Atria have an appendage called an auricle

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Ventricles• Located below the atria• Grooves known as coronary sulci separate atria from ventricles and separate ventricles• Sulci provide a cradle for the coronary vessels and hold a variable amount of fat

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Heart Sulci

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Chamber Divisions• Interatrial septum divides the atria• Fossa ovalis – an oval depression is the remnant of the foramen ovale• Interventricular septum separates the ventricles• Irregular ridges on the internal surfaces of the ventricles are called the trabeculae carneae

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Wall Thickness• Wall thickness depends on the function of the area• Atrial walls are thin• Left ventricular wall is two to four times thicker than right

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Valves of the HeartFive valves • Atrioventricular valves

– Tricuspid valve– Bicuspid valve (Mitral valve)

• Semilunar valves– Pulmonary valves (2)– Aortic valve

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Papillary Muscles and Chordae Tendineae

• Chordae tendineae – tendon like cords connect the pointed ends and under surfaces of the cuspid valves to the papillary muscles.• Papillary muscles lie on the inner surface of the ventricles

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Tricuspid Valve

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Blood Flow through the Heart

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(R) Atria to (R) Ventricle

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(R) Ventricle to Pulmonary Artery

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Lungs to (L) Atrium

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(L) Atrium to (L) Ventricle

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(L) Ventricle to Aorta

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Coronary Blood Flow• The walls of the heart have their own blood supply – coronary vessels• The arteries of the coronary circulation encircle the heart like a crown• Little blood flows through these vessels during contraction• Coronary circulation takes place during diastole

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Coronary Blood Flow• The entrance of the coronary arteries is located directly behind the leaves of the aortic valve• During systole, the arteries are occluded by the open valve• When valve closes, blood flows into the coronary arteries

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Coronary Circulation

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(L) Coronary Artery Angiogram

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(R) coronary Artery Angiogram

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Coronary Veins

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Conduction System

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ECG

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ECG Lead Placement

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Wave forms

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12 Lead ECG

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Angina• Reduced O2 / blood supply to an area of myocardium

– Discomfort in the chest (often but not always)– Heavy, pressing, squeezing, “couldn’t get my breath”, “not really a pain”– Cold sweat– Onset with exercise (or not)– Offset with rest +/- medication

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Myocardial Infarction• Lack of blood supply to an area of myocardium

– Symptoms similar to angina but more severe– Ongoing, not relieved by rest +/- nitrate medications– Cold sweat, pallor– Change to conscious state– Life threatening

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Thrombosis• Stationary clot

– May occur in any vessel where blood flow is impeded (arterial or venous)– Symptoms depend on location

• Deep Vein Thrombosis (leg)– Pain on walking or standing– Heat or swelling of the limb– Pain reduced when leg elevated

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Clot Embolus• Pulmonary

– Sudden– Breathless, hypoxic, disorientated– Death

• Cerebral – Sudden– Slurring speech, weakness on one side, change in conscious state, coma, death

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Peripheral Vascular Disease• Narrowing of the arteries in the arms and legs

– Mild – no symptoms– Progressive – claudication, rest pain or vascular ulceration– Cold limb– Painful when elevated– Commonly associated with diabetic patient

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Vascular Ulcer

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References• Tortora, GJ & Grabowski, SR (1996) Principles of Anatomy and Physiology (8th ed). New York. HarperCollins Publishers Inc. (580-589)• www.firearmstactical.com/images/Wound%20Profiles/Cardiovascular%20Structures.jpg• www.abe.msstate.edu/…/03/cva_struc_funct.html• www.info.med.yale.edu/intmed/cardio/imaging/findings/normal_heart/graphics/rad1.gif• www.bami.us/CardiacAnatomy.html• www1.shimadzu.com/…/angio/app_data.html• www.womensfitness.net/reena_img/coronaryartery.gif• connection.lww.com/Products/porth7e/Ch26.asp

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References• www.numed.co.uk/electrodepl.jpg• www.merck.com/media/mmhe2/figures/fg021_1.gif• www.fammed.wisc.edu/pcc/ecg/axis.html• www.gonzaga.k12.nf.ca/…/biology/biology.html• http://www.diabetes.usyd.edu.au/foot/Pvdx1.html