Chapter 18 Circulatory System

Heart (general) Size of a fist Size of a fist Almost one pound in weight Almost one pound in weight Middle of chest points to left Middle of chest points to left Just superior to zyphoid process Just superior to zyphoid process

Layers of Heart Epicardium (pericardial sack) Epicardium (pericardial sack) –Protects heart –Anchors it to surrounding tissue –Prevents overfilling of heart with blood –Pericarditis – hinders production of serous fluid sometimes under severe friction inflammatory fluid rushes in and can lead to cardiac tamponade (heart plug)

Myocardium (heart muscle) Fibers embedded in layer form skeleton to support and prevent over dilation or expansion. Fibers embedded in layer form skeleton to support and prevent over dilation or expansion. More prevalent around valves and major vessels off of heart. More prevalent around valves and major vessels off of heart.

Endocardium Thin tissue layer which lines the inside of the heart. Thin tissue layer which lines the inside of the heart.

Chambers of the Heart (Atria) Atria – located on the top of heart Atria – located on the top of heart Very thin relative to ventricles. Very thin relative to ventricles. Only have to pump to ventricles. Only have to pump to ventricles. Fossa ovalis – opening in the fetal heart (seen as shallow depression in atrial septum. Fossa ovalis – opening in the fetal heart (seen as shallow depression in atrial septum.

Right Atrium Right atrium – receives oxygen poor blood. Right atrium – receives oxygen poor blood. – superior vena cava – diaphragm and above – inferior vena cava – below –Coronary sinus – vein from heart –Veins are any large vessel moving blood toward heart.

Left Atrium Receives oxygen rich blood from lungs (pulmonary veins) Receives oxygen rich blood from lungs (pulmonary veins)

Ventricles Located on the bottom Located on the bottom Right ventricle lies toward the front Right ventricle lies toward the front Left ventricle lies towards the back (largest and most muscular chamber) Left ventricle lies towards the back (largest and most muscular chamber) Septum – portion that divides the left from the right chambers Septum – portion that divides the left from the right chambers Sulcus – groove formed between atria and ventricles Sulcus – groove formed between atria and ventricles

Circulatory Circuit Pulmonary circuit – right side Pulmonary circuit – right side Systemic circuit – left side Systemic circuit – left side Coronary circuit – feeds the heart to thick for diffusion – blockages or narrowing of these vessels can be fatal if not corrected (bi – pass) Coronary circuit – feeds the heart to thick for diffusion – blockages or narrowing of these vessels can be fatal if not corrected (bi – pass)

Valves Atioventricular valves Atioventricular valves –Tricuspid valve – 3 flaps of tissue – right side –Bicuspid valve (mitral valve) 2 flaps of tissue – left side –Chordae tendinae – connective tissue that attaches to valves and inferior muscle surface located in ventricles. –Blood flows into ventricles - ventricles contract shoving flaps upward – but the flaps can only go so far up because of the chords attached.

Semi – lunar valves Valves that prevent backflow into ventricles from major arteries. Valves that prevent backflow into ventricles from major arteries. Valves have pockets distal to heart – these fill with blood and act as sails slamming shut to prevent additional backflow. Valves have pockets distal to heart – these fill with blood and act as sails slamming shut to prevent additional backflow.

Contraction As with skeletal muscle – a wave of depolarization Na+ in elicits an action potential. This causes the sarcolemma to dump Ca ++ ions out which binds to troponin sliding tropomyosin out of the way sot that myosin can interact with actin. (sliding filament) As with skeletal muscle – a wave of depolarization Na+ in elicits an action potential. This causes the sarcolemma to dump Ca ++ ions out which binds to troponin sliding tropomyosin out of the way sot that myosin can interact with actin. (sliding filament) Cells are connected via gap junctions so if one cell is stimulated to fire all cells are stimulated. Cells are connected via gap junctions so if one cell is stimulated to fire all cells are stimulated. Rhythmic Control – nervous system – see notes on generating an action potential (nervous system) Rhythmic Control – nervous system – see notes on generating an action potential (nervous system)

Excitable Fibers SA node – SA node – –Located right atrial wall just below superior vena cava –Fires about 100 times per minute fastest stimulated tissue so it sets the pace (pace maker)

Other excitable tissues Located in septum receives message from SA node and transmits down septum stimulating ventricle to contract Located in septum receives message from SA node and transmits down septum stimulating ventricle to contract Bundle of His – branches out from AV node Bundle of His – branches out from AV node Purkinje fivers – runs along the bottom of ventricles and toward the lateral portions causing stimulation. Purkinje fivers – runs along the bottom of ventricles and toward the lateral portions causing stimulation. If SA node is damaged than AV becomes pacemaker but it is slower in its rate of contraction (and so on) If SA node is damaged than AV becomes pacemaker but it is slower in its rate of contraction (and so on)

EKG / ECG electrocardiogram P wave – atrial depolarization P wave – atrial depolarization QRS complex – ventricle depolarization QRS complex – ventricle depolarization T wave – ventricle repolarization T wave – ventricle repolarization