Heart Anatomical PositionThe heart:Sits near the anterior chest wall, directly posterior to the sternumLies slightly to the left of the midline Sits at an angle to the longitudinal axis of the bodyIs rotated towards the left sideSurrounded by the pericardium in the anterior of the mediastinumMediastinum separates the 2 pleural cavities and also contains the esophagus, trachea, and thymus.

PericardiumSerous membrane lining the pericardial cavityAnalogous to a fist in a balloonSubdivided into visceral and parietal pericardiumVisceral layer (brown arrow) is the outer layer of the heart itself a.k.a. the epicardiumParietal layer (red arrow) lines the inner portion of the pericardial sac and is deep to a meshwork of collagen fibers that stabilize the position of the heart

PericardiumSpace btwn the visceral & parietal layers is the pericardial cavity.Normally contains 10-20mL of pericardial fluid secreted by the membranesA variety of pathogens may infect the pericardium, causing pericarditis.Pericardial irritation and inflammation results in an in pericardial fluid production which limits the movement of the heart. Known as cardiac tamponade.

The Heart Wall3 distinct layers:EpicardiumVisceral pericardiumConsists of an exposed mesothelium underlain by a layer of loose connective tissue MyocardiumMuscular wall of the heartContains cardiac muscle tissue, blood vessels, and nervesEndocardium Simple squamous epithelium that lines the internal spaces of the heart and covers the valves.Continuous with the endothelium of blood vessels

General Heart AnatomyBlood vessels can be divided into a pulmonary circuit (between the heart and the gas exchange surfaces of the lungs) and a systemic circuit (between the heart and the rest of the body)Heart contains 4 muscular chambers, 2 associated with each circuitRight atrium receives deO2 blood from the systemic circuit and passes it to the right ventricle which discharges it into the pulmonary circuit.Left atrium receives O2 blood from the pulmonary circuit and passes it to the left ventricle which discharges it into the systemic circuit

The 2 atria are superior to the ventricles and mostly posterior Each atrium has a small earlike extension called an auricle which slightly its volumeThe ventricles are inferior to the atria. The RV constitutes most of the anterior aspect of the heart, while the LV forms the apex and inferoposterior aspect.

Atria have thin flaccid walls corresponding to their light workload. Why is it light?Right and left atria are separated by the interatrial septum.RA and both auricles exhibit internal ridges of myocardium called pectinate muscles.The thick interventricular septum separates the LV and RV. LV is 2-4x as thick as the RV because of its large workload.Both ventricles exhibit internal muscular ridges known as trabeculae carneaeLVRVSEPTUM

ValvesNecessary to ensure one-way flow.Found btwn each atria and each ventricle and btwn each ventricle and its great artery

Each consists of 2-3 flaps of connective tissue covered by endotheliumAtrioventricular ValvesTricuspid Valve Btwn RA and RVBicuspid Valve Btwn LA and LV. A.k.a. mitral valveStringlike chordae tendineae connect the valve flaps to conical papillary muscles found on the ventricular floor. These function to prevent the valves from bulging (prolapsing) into the atria.

Here, the mitral valve is open as blood flows from the left atrium into the left ventricle. Notice how the chordae tendineae and papillary muscles are relaxed.

Now, the mitral valve is closed as blood flows from the left ventricle into the aorta. What are the chordae tendineae and papillary muscles doing now?

ValvesSemilunar Valves:Pulmonary Semilunar ValvePrevents backflow of blood from pulmonary artery into RVAortic semilunar valvePrevents backflow of blood from aorta into LV

Blood Flow back to the HeartBlood high in CO2 and low in O2 arrives at the RA from 3 vessels:Superior Vena CavaDrains head, upper torso, and armsInferior Vena Cava Drains abdomen, pelvis, and legsCoronary Sinus Drains coronary circulation

Blood Flow back to the HeartBlood high in O2 and low in CO2 arrives at the LA from 4 blood vesselsRight superior and right inferior pulmonary veinsLeft superior and left inferior pulmonary veins

Basic Pathway of Blood FlowSVCIVCCSRight AtriumTricuspid ValveRight VentriclePulmonary Semilunar ValvePulmonary TrunkPulmonary ArteriesPulmonary CapillariesPulmonary VeinsLeft AtriumBicuspid ValveLeft VentricleAortaAortic Semilunar ValveSystemic Capillaries

Coronary CirculationWhy does the heart require a prodigious amt of O2 and nutrients?Cardiac muscle is not nourished to any extent by the blood flowing thru its chambers, so it has its own network of arteries, capillaries, and veins the coronary circulation5% of circulating blood is delivered to the heartAfter the aorta emerges from the LV it gives off 2 branches, the left & right coronary arteriesThe coronary circulation has many anastomoses where 2 arteries come together and combine their blood flow.What is the advantage to this?Blockage of coronary arteries causes ischemia a loss of blood flow. Temporary and reversible ischemia produces a sense of pain known as angina pectoris. Prolonged coronary blockage can lead to myocardial cell death - a myocardial infarction (a.k.a., heart attack or coronary)

After blood passes thru the coronary capillaries, it enters coronary veins which combine to form the coronary sinus which empties into the RA

Cardiac Conduction SystemAutorhythmic cardiac myocytes have the ability to spontaneously depolarize to threshold and fire action potentials.Locations:Sinoatrial Node Adjacent to the SVC opening in the RAAtrioventricular Node Near the right AV valve at the bottom of the interatrial septumAtrioventricular Bundle Inferior interatrial septumRight & Left Bundle Branches Interventricular septumPurkinje Fibers Distributed throughout the LV and RV

Intrinsic Control of the Heart RateWithout input from any other cell, the heartbeat originates at the SA node. For this reason, it is known as the hearts pacemaker and its rhythm (sinus rhythm) determines heart rate.The depolarization begun in SA node cells spreads via gap junctions throughout the atria and via the internodal pathway to the AV node.How will the atrial contractile cells respond to depolarization?

Intrinsic Control of the Heart RateAt the AV node, the impulse is delayed momentarily to allow the atria to complete their contraction before the ventricles contractFrom the AV node, the impulse travels to the AV bundle. The AV bundle is the ONLY electrical connection btwn the atria and the ventricles. Why is this important?The impulse travels on to the L&R bundle branches and onward to the Purkinje fibers which begin at the heart apex and extend upward thru the ventriclesHow do the ventricles respond to depolarization?What is significant about the fact that the Purkinje fibers begin at the apex and course upwards?

Conduction PathologiesArrhythmia Irregular heart rhythmFibrillation Condition of rapid and out-of-phase contractions. Why are fibrillating ventricles useless as pumps?Ectopic Focus An abnormal pacemaker. A region of the heart becomes hyperexcitable and generates impulses faster than the SA node. Can also lead to premature contractions or extrasystole (e.g., premature ventricular contraction (PVC)) before the SA node initiates the next contractionHeart Block Any damage to the AV node. Interferes with the transmission of impulses to the ventricles. Can very in severity.

Cardiac CyclePeriod btwn the start of one heartbeat and the beginning of the nextFor any one chamber in the heart, the cardiac cycle can be divided into 2 phases:Systole contractionDiastole relaxationA basic principle that governs the movement of blood thru the heart is that blood will flow from one chamber to the next only if the pressure in the 1st chamber exceeds the pressure in the 2nd

Valve PathologyMurmur Abnormal heart sound due to a malfunctioning heart valveValvular Stenosis Valve cusps become stiffened and the opening is constricted by scar tissue. How would this effect the workload of the heart?Mitral Valve Prolapse insufficiency in which one or both mitral valve flaps bulge into the atrium during ventricular systole

Cardiac OutputVolume of blood ejected by each ventricle in 1 minuteCardiac Output = Heart Rate (beats/minute) x Stroke Volume (mL/beat)CO=(HR)(SV)Suppose Tims heart rate was 60bpm, his ESV was 50mL and his EDV was 140mL. What is Tims CO?Cardiac output varies with the bodys state of activity.What do you suppose happens to CO during exercise?

Heart RateTachycardia is a persistent resting HR >100bpmBradycardia is a persistent resting HR

Baroreceptor ReflexBaroreceptors are pressure sensitive neurons in the aortic arch and carotid sinus.Why are they found in these 2 locations?They respond to decreased BP by decreasing cardioinhibitory activity and by increasing both cardioacceleratory activity and the vasoconstrictor center (all in the medulla oblongata)How would they respond to increased BP?What type of control is demonstrated by this reflex?

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