Chapter 11 The Cardiovascular System

The Cardiovascular System A closed system of the heart and blood vessels -heart pumps blood -blood vessels - circulate to all parts of body Deliver oxygens & nutrients and to remove carbon dioxide & waste products

The Heart Size of fist In thorax between lungs Pointed apex toward left hip Size of fist

Figure 18.1a Location of the heart in the mediastinum. Midsternal line 2nd rib Sternum Diaphragm Point of maximal intensity (PMI) (a)

Heart Coverings & Wall Layers Pericardium – double serous membrane Visceral - next to heart Parietal - outside layer Serous fluid fills space between the layers Three layers 1.Epicardium- Outside visceral pericardium Connective tissue 2.Myocardium- Middle Mostly cardiac muscle 3.Endocardium - Inner Endothelium

Figure 18.2 The pericardial layers and layers of the heart wall. Pulmonary trunk Fibrous pericardium Parietal layer of serous pericardium Pericardium Pericardial cavity Myocardium Epicardium (visceral layer of serous pericardium) Heart wall Myocardium Endocardium Heart chamber

External Heart Anatomy Figure 11.2a

The Heart: Chambers Right and left act as separate pumps Four chambers 2 Atria - Receiving - Right atrium - Left atrium 2 Ventricles - Discharging - Right ventricle Left ventricle Septum - divides the right from left side of the heart.

Figure 18.6 Anatomical differences between the right and left ventricles. Interventricular septum

The Heart: Associated Great Vessels Aorta - Leaves left ventricle Pulmonary arteries - Leave right ventricle Vena cava - Enters right atrium Pulmonary veins (four) - Enter left atrium

The Heart: Valves Allow blood to flow in only one direction Four valves 2 Atrioventricular valves – between atria & ventricles Bicuspid valve (left) Tricuspid valve (right) 2 Semilunar valves - between ventricle & artery Pulmonary semilunar valve Aortic semilunar valve Held in place by chordae tendineae (“heart strings”)

Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Myocardium Tricuspid (right atrioventricular) valve Mitral (left atrioventricular) valve Aortic valve Pulmonary valve Fibrous skeleton (a) Anterior

Figure 18.8b Heart valves. Myocardium Tricuspid (right atrioventricular) valve Mitral (left atrioventricular) valve Aortic valve Pulmonary valve Pulmonary valve Aortic valve Area of cutaway (b) Mitral valve Tricuspid valve

Figure 18.8c Heart valves. Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve Chordae tendineae attached to tricuspid valve flap Papillary muscle (c)

Opening of inferior vena cava Mitral valve Chordae tendineae Tricuspid valve Myocardium of right ventricle Myocardium of left ventricle Pulmonary valve Aortic valve Area of cutaway Papillary muscles Mitral valve Interventricular septum Tricuspid valve (d)

Operation of Heart Valves

heart fills atria, putting pressure against atrioventricular valves; Blood returning to the heart fills atria, putting pressure against atrioventricular valves; atrioventricular valves are forced open. 1 As ventricles fill, atrioventricular valve flaps hang limply into ventricles. 2 Atria contract, forcing additional blood into ventricles. 3 Direction of blood flow Atrium Cusp of atrioventricular valve (open) Chordae tendineae Papillary muscle Ventricle (a) AV valves open; atrial pressure greater than ventricular pressure

Ventricles contract, forcing blood against atrioventricular valve cusps. 1 Atrioventricular valves close. 2 Atrium Cusps of atrioventricular valve (closed) Blood in ventricle Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria. 3 (b) AV valves closed; atrial pressure less than ventricular pressure

Figure 18.10a The semilunar valves. Aorta Pulmonary trunk As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open. (a) Semilunar valves open

Figure 18.10b The semilunar valves. As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close. (b) Semilunar valves closed

Pathway of Blood Through the Heart Right atrium  tricuspid valve  right ventricle Right ventricle  pulmonary semilunar valve  pulmonary trunk  pulmonary arteries  lungs PLAY Animation: Rotatable heart (sectioned)

Pathway of Blood Through the Heart Lungs  pulmonary veins  left atrium Left atrium  bicuspid valve  left ventricle Left ventricle  aortic semilunar valve  aorta Aorta  systemic circulation PLAY Animation: Rotatable heart (sectioned)

Figure 18.19 Areas of the thoracic surface where the heart sounds can be best detected. Aortic valve sounds heard in 2nd intercostal space at right sternal margin Pulmonary valve sounds heard in 2nd intercostal space at left sternal margin Mitral valve sounds heard over heart apex (in 5th intercostal space) in line with middle of clavicle Tricuspid valve sounds typically heard in right sternal margin of 5th intercostal space

Mitral Regurgitation Aortic Stenosis

Current Event Causes of elevated cholesterol levels in our blood and typical medical methods to reduce high cholesterol.  Then focus on if/how hypercholesterolemia can be controlled without the use of drugs.  Be very specific about how it can be done if it is possible.

Coronary Circulation Blood in heart doesn’t nourish the heart Heart’s nourishing circulatory system Coronary arteries Come off the aorta - Cardiac veins - Blood empties into the right atrium via the coronary sinus

Figure 18.7a Coronary circulation. Aorta Pulmonary trunk Superior vena cava Left atrium Anastomosis (junction of vessels) Left coronary artery Right atrium Circumflex artery Right coronary artery Left ventricle Right ventricle Anterior interventricular artery Right marginal artery Posterior interventricular artery (a) The major coronary arteries

Figure 18.7b Coronary circulation. Superior vena cava Great cardiac vein Anterior cardiac veins Coronary sinus Small cardiac vein Middle cardiac vein (b) The major cardiac veins

Aorta Coronary Arteries Myocardium Coronary Circulation Pattern Aorta Coronary Arteries Myocardium As you must be able to trace the flow of blood through the coronary circulation, indicating the sequential vessels and structures the blood must flow through, we will now go over this. * The pulmonary circulation is a specialized branch of the systemic circulation which circulates blood to and from the heart. As such, it begins with the aorta. * * The first arteries to branch off of the aorta * are the coronary arteries * * which assure an ample supply of highly oxygenated blood, nutrients and hormones to the myocardium. *

Coronary Circulation Pattern Aorta Coronary Arteries Myocardium Cardiac Veins Coronary Sinus From the capillaries in the myocardium * the blood flows into the cardiac veins * * which carry blood * to the coronary sinus. * * After collecting blood low in O2 from the cardiac veins, the coronary sinus * introduces the blood into the right atrium * adjacent to where the inferior vena cava enters the right atrium.* Right Atrium

Collateral Circulation Most organs receive blood from more than one arterial branch. Arterial anastomosis - where arteries supplying the same area join. Collateral circulation refers to the situation where most organs have the potential of receiving blood from more than a single arterial branch. * An anastomis is a junction between blood vessels * through which blood can flow directly from one vessel into the other. * An arterial anastamosis is a junction between arteries. * *

Myocardial Infarction (MI) Coronary bypass surgery Embolism Angina pectoris Myocardial Infarction (MI) Coronary bypass surgery Open Heart Surgery Coronary artery disease (Adam) Atherosclerosis

Heart Dissection (Lab Manual pg 306) Heart Dissection I Heart Dissection II

The Heart: Cardiac Cycle Cardiac cycle – events of one heart beat Terms: Systole = contraction Diastole = relaxation Atria contract simultaneously Atria relax, then ventricles contract

Phases of the Cardiac Cycle Ventricular filling—takes place in mid-to-late diastole AV valves are open 80% of blood passively flows into ventricles Atria contract occurs, delivering the remaining 20%

Phases of the Cardiac Cycle Ventricular systole Atria relax and ventricles begin to contract Rising ventricular pressure results in closing of AV valves In ejection phase, ventricular pressure exceeds pressure in the large arteries, forcing the SL valves open

Phases of the Cardiac Cycle Early diastole Ventricles relax Backflow of blood in aorta and pulmonary trunk closes SL valves.

The Heart: Conduction System Intrinsic conduction system (nodal system) Heart muscle cells contract, without nerve impulses, in a regular, continuous way Sinoatrial node – Pacemaker initiates contraction Sequential stimulation occurs at other autorhythmic cells Atrioventricular node Atrioventricular bundle Bundle branches Purkinje fibers

Heart rate controlled by its own internal control center Heart rate controlled by its own internal control center. The SA Node (known as the pacemaker, 75/min) is located in the wall of the right atrium and sends out signals that cause the atria to contract.

These signals also travel to the AV Node (50/min) located in the septum between the atria, which relays the signals to the ventricles via the bundle of His (30/min) and Purkinje fibers causing them to contract. Animation

Figure 18.14 Cardiac intrinsic conduction system and action potential succession during one heartbeat. Superior vena cava Right atrium The sinoatrial (SA) node (pacemaker) generates impulses. 1 Pacemaker potential Internodal pathway Left atrium SA node The impulses pause (0.1 s) at the atrioventricular (AV) node. 2 Atrial muscle Purkinje fibers The atrioventricular (AV) bundle connects the atria to the ventricles. 3 AV node Pacemaker potential Ventricular muscle 4 The bundle branches conduct the impulses through the interventricular septum. Inter- ventricular septum Plateau The Purkinje fibers depolarize the contractile cells of both ventricles. 5 Milliseconds (a) Anatomy of the intrinsic conduction system showing the sequence of electrical excitation (b) Comparison of action potential shape at various locations

Extrinsic Innervation of the Heart Heartbeat is modified by the ANS Cardiac centers are located in the medulla oblongata Cardioacceleratory center innervates SA and AV nodes, heart muscle, and coronary arteries through sympathetic neurons Cardioinhibitory center inhibits SA and AV nodes through parasympathetic fibers in the vagus nerves

Figure 18.15 Autonomic innervation of the heart. Dorsal motor nucleus of vagus The vagus nerve (parasympathetic) decreases heart rate. Cardioinhibitory center Medulla oblongata Cardio- acceleratory center Sympathetic trunk ganglion Thoracic spinal cord Sympathetic trunk Sympathetic cardiac nerves increase heart rate and force of contraction. AV node SA node Parasympathetic fibers Sympathetic fibers Interneurons

Homeostatic Imbalances Defects in the intrinsic conduction system may result in Arrhythmias: irregular heart rhythms Fibrillation: rapid, irregular contractions; useless for pumping blood

Homeostatic Imbalances Defective SA node may result in Ectopic focus: abnormal pacemaker takes over If AV node takes over, there will be a junctional rhythm (40–60 bpm) Defective AV node may result in Partial or total heart block Few or no impulses from SA node reach the ventricles

Electrocardiogram A graphic record of the hearts electrical activity. 3 characteristic waves called the P wave, QRS complex, and the T wave.

Figure 18.16 An electrocardiogram tracing (lead I). QRS complex Sinoatrial node Ventricular depolarization Ventricular repolarization Atrial depolarization Atrioventricular node S-T Segment P-Q Interval Q-T Interval

Atrial depolarization, initiated by the SA node, causes the P wave. 1 Figure 18.17 The sequence of depolarization and repolarization of the heart related to the deflection waves of an ECG tracing. SA node R Depolarization Repolarization R P T P T Q S Atrial depolarization, initiated by the SA node, causes the P wave. 1 Q S 4 Ventricular depolarization is complete. AV node R R P T P T Q S With atrial depolarization complete, the impulse is delayed at the AV node. 2 Q S Ventricular repolarization begins at apex, causing the T wave. 5 R R P T P T Q S Q Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs. 3 S Ventricular repolarization is complete. 6

Figure 18.18 Normal and abnormal ECG tracings. (a) Normal sinus rhythm. (b) Junctional rhythm. The SA node is nonfunctional, P waves are absent, and heart is paced by the AV node at 40 - 60 beats/min. (c) Second-degree heart block. Some P waves are not conducted through the AV node; hence more P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1. (d) Ventricular fibrillation. These chaotic, grossly irregular ECG deflections are seen in acute heart attack and electrical shock.

Animation

Depolarization describes the electrical activity just before contraction. Repolarization begins just before the relaxation phase.

P wave is depolarization of the atria. QRS complex is depolarization of the ventricles. T wave is repolarization of the vetricles. Repolarization of atria is hidden by the QRS complex.

The Heart: Cardiac Output Cardiac output (CO) Amount of blood pumped by each side of the heart in one minute CO = (heart rate [HR]) x (stroke volume [SV]) Stroke volume [SV] Volume of blood pumped by each ventricle in one contraction

The Heart: Regulation of Heart Rate Stroke volume usually remains relatively constant - Starling’s law of the heart: the more that the cardiac muscle is stretched, the stronger the contraction Changing heart rate is the most common way to change cardiac output

Regulation of Heart Rate Decreased Heart Rate 1. Parasympathetic nervous system 2. High blood pressure or blood volume 3. Decreased venous return Increased Heart Rate 1. Sympathetic nervous system Crisis Low blood pressure 2. Hormones Epinephrine Thyroxine 3. Exercise 4. Decreased blood volume