Location and Structures The Heart Location and Structures

Structure cross section

location Within the thoracic cavity Between the lungs In Mediastinal cavity (mediastinum) The base of the Heart is posterior to the sternum Cone shape; approximately the size of your fist Apex of the Heart is superior to the diaphragm, just left of the midline

Pericardial membrane encloses the heart 3 layers Fibrous outer layer, is a sac that encloses the heart. Called the fibrous pericardium. (fibrous connective tissue) Serous membrane with 2 layers that line the fibrous pericardium Parietal pericardium Visceral pericardium (epicardium) between these membranes is a serous fluid that prevents rub/friction as the heart beats.

Cardiac muscle (smooth muscle action with striated appearance) All 4 chambers of the heart are made of myocardium All 4 chambers are lined with endocardium (squamous epithelium, including the valves and the inside of the vessels entering and leaving the heart.

Important to note that this is very smooth muscle and it is designed to prevent any aggregation of blood that might initiate clotting. Any rough surface inside the heart or vessels is considered abnormal; and contributes to or is secondary to disease of the heart and vessels. (CAD)

4 heart chambers Two upper chambers Two lower chambers Left and right atria (plural) atrium (singular) Separated by the interatrial septum Two lower chambers Left and right ventricles Thicker wall separated by the interventricular septum

Valves: 4 valves function inside the heart: location and function is stated below 1. Tricuspid valve: located between the rt. atrium and the rt. ventricle; it opens to allow blood to flow from the rt. atrium into the rt. Ventricle and closes to prevent backflow of blood when the ventricle contract. 2. Pulmonary (semilunar) valve: located at the junction of the rt. Ventricle and the entrance to the rt. pulmonary artery

Valves continues 3. Mitral valve: between the left atrium and the left ventricle, allows blood to flow into the left ventricle and prevents backflow of blood when the lft ventricle contracts. 4. Aortic (semilunar) valve: at the junction of the left atrium and the lft ventricle, prevents backflow when the left ventricle contracts.

Two Atria Right Atrium Receives blood returning from the upper and lower body via the superior and inferior vena cava (largest veins in the body) The blood returning is deoxygenated blood. During atrial contraction this blood is pumped through the R. atrioventricular valve aka The tricuspid valve (having 3 flaps or cusps). The purpose of valves is to prevent backflow of blood. **leaking valves are a pathological condition contributing to disease processes.

Right Ventricle Blood enters the R. ventricle from the R. atrium, passing through the tricuspid valve (R. AV valve) From here the blood still w/o oxygen is pumped into the pulmonary artery to the lungs ** the pulmonary artery is the only artery that carries deoxygenated blood. When the R. ventricle contracts the tricuspid valve closes. With contraction the blood goes through the pulmonary valve. Some time called the semilunar valve. It closes when the ventricle relaxes and prevents backflow. Now the blood is in the lungs picking up oxygen.

Blood returning from the lungs From the 4 Pulmonary veins *** only vein in the body to carry oxygenated blood The blood returns into the Left atrium and then flows through the Left atrioventricular valve aka MITRAL VALVE, OR BICUSPID VALVE Into the Left Ventricle. This ventricle has a much thicker myocardial wall. Major pump of the heart and it functions to push all blood out to the body, leaving through the aortic semilunar valve First to the AORTA –largest artery, and immediately the first oxygenated blood branches off to……TBA…………… ** as the pressure of contraction opens the aortic valve the mitral valve closes

FYI All valves within the heart are attached to the heart wall with tendons called chordae tendineae and muscles known as papillary muscles. The heart is actually 2 pumps that contract simultaneously: the atria contract together and then the ventricles contract together

PART II LABELING OF STRUCTURES

Electrical system of the Heart EKG/ECG Normal sinus rhythm Lub dub (cardiac sound) = 1 heart beat. Auscultation; listening with a stethoscope. Normal resting heart beat 60-80 per minute. Lower in athletes, higher due to age/medication/anxiety/pathology. Bradycardia: under 60 beats/minute Tachycardia: over 80 beats/minute Heard on auscultation at the apex of the heart. Called the Apical pulse.

Systole: to contract; period during the cardiac cycle when the heart is contracting and blood is ejected through the aorta and out to the pulmonary artery As related to BP, this is the pressure exerted against artery walls when the heart contracts Diastole: to expand, period during the cardiac cycle when the blood flows into the chambers and the myocardium is relaxed. As related to BP, this is the relaxation phase when no pressure is exerted against artery walls.

Pg. 281 of your text

Cardiac Conduction Electrical stimulus necessary to cause the heart muscle to pump blood by the continual contraction and relaxation of the myocardium. aka: systole and diastole.

Sequence of action SA node which sits the upper tissue of the Right Atrium fires off an impulse to the... (sinoatrial node) also called the pacemaker of the heart, AV (atrioventricular node), where the impulse is held for just a nano second, and is send by impulse to the bundle of His, located just slightly lateral to the interatrial septum;

Then from the bundle of His the impulse flows down the interventricular septum, and out to the Purkinje fibers located in the walls of the myocardium. ** mid paragraph page 282. Refer to box 12-3 and 12-4 Pg. 282 of text

Terms Ectopic focus Arrhythmias Flutter Fribrillation Cardiac output: amount of blood pumped by a ventricle in 1 minute Stroke volume a term for the amount of blood pumped per beat, approx 60-80 ml/beat Starling’s law of the heart: increase in stroke volume when the heart muscle fibers are stretched during exercise and more blood is pumped with more force, and a formula to calculate an individual’s cardiac output during exercise. This can be as much as 4 x that of a resting level.

More: The difference between cardiac output during exercise and during normal resting output = cardiac reserve. Important because this is what the heart can do when needed. (flight or fright) Cardiologist to stress testing to check cardiac output and measure the percent of blood in a ventricle during contraction (systole) and this % is called the ejection fraction, which when normal is 60-70% of the blood inside of the ventricle. Lower % rates indicate that the ventricle is weakening.

Assignment: Answer the end of the Chapter 12 review questions due Monday, word processed only. Late review questions will receive no points and will not be able to be used during the test. Monday: lecture on the Vascular System. Thursday Chapter Test covering Chapter 12. Read Chapter 13.