Cardiovascular System Chapter 20 Cardiovascular System The Heart

The Heart The Heart is two pumps. Pulmonary circulation Carries blood to lungs Returns to the left side of heart Systemic circulation Delivers oxygen and nutrients to the body Returns to the right side of the heart

Functions of the Heart Generating blood pressure Routing blood Heart separates pulmonary and systemic circulations Ensures oxygenation of blood flowing to tissues. Ensuring one-way blood flow Heart valves ensure one-way flow Regulating blood supply Changes in contraction rate and force match blood delivery to changing metabolic needs

Size, Shape, Location of the Heart Size of a closed fist Shape Apex: rounded tip of heart Base: Flat part at opposite of end of cone Located in thoracic cavity within the mediastinum

Heart Cross Section

Pericardium

Heart Wall Three layers of tissue Epicardium: This serous membrane of smooth outer surface of heart Myocardium: Middle layer composed of cardiac muscle cell and responsibility for heart contracting Endocardium: Smooth inner surface of heart chambers

Heart Wall

External Anatomy Four chambers Auricles Major veins Major arteries 2 atria 2 ventricles Auricles Major veins Superior vena cava Inferior vena cava Pulmonary veins Major arteries Aorta Pulmonary trunk

External Anatomy

Coronary Circulation

Heart Valves Atrioventricular Semilunar Tricuspid Bicuspid or mitral Semilunar Aortic Pulmonary Prevent blood from flowing back

Heart Valves

Function of the Heart Valves

Blood Flow Through Heart

Systemic and Pulmonary Circulation

Heart Skeleton Consists of plate of fibrous connective tissue between atria and ventricles Fibrous rings around valves to support Serves as electrical insulation between atria and ventricles Provides site for muscle attachment

Cardiac Muscle Elongated, branching cells containing 1-2 centrally located nuclei Contains actin and myosin myofilaments Intercalated disks: Specialized cell-cell contacts Desmosomes hold cells together and gap junctions allow action potentials Electrically, cardiac muscle behaves as single unit

Conducting System of Heart

Electrical Properties Resting membrane potential (RMP) present Depends on low permiability to Na+ and Ca++ and high permiability to K+. Action potential Depolarization (Fast voltage gated Na+ channels) Early partial repolarization (Voltage gated Na+ channels close and a small number of K+ channels open.) Plateau phase - Prolonged period of slow repolarization (Slow Ca++ channels are open) Rapid final repolarization phase (Voltage gated Ca++ channels close and more K+ channels open)

Action Potentials in Skeletal and Cardiac Muscle

SA Node Action Potential Permiability changes in the pacemaker cells (Autorhythmicity): Prepotential Small number of Na+ channels open Voltage-gated K+ channels are closing Voltage-gated Ca++ channels begin to open Depolarization Phase Voltage-gated Ca++ channels are open Voltage-gated K+ channels are closed. Repolarization phase Voltage-gated Ca++ channels close. Voltage-gated K+ channels open. Note: Ca++ channel blockers like verapamil are used to treat tachycardia and arrhythmias.

Refractory Period Absolute: Cardiac muscle cell completely insensitive to further stimulation Relative: Cell exhibits reduced sensitivity to additional stimulation Long refractory period prevents tetanic contractions

Electrocardiogram Action potentials through myocardium during cardiac cycle produces electric currents than can be measured Pattern P wave Atria depolarization QRS complex Ventricle depolarization Atria repolarization T wave: Ventricle repolarization

Cardiac Arrhythmias Tachycardia: Heart rate in excess of 100bpm Bradycardia: Heart rate less than 60 bpm Sinus arrhythmia: Heart rate varies 5% during respiratory cycle and up to 30% during deep respiration Premature atrial contractions: Occasional shortened intervals between one contraction and succeeding, frequently occurs in healthy people

Alterations in Electrocardiogram

Cardiac Cycle Heart is two pumps that work together, right and left half Repetitive contraction (systole) and relaxation (diastole) of heart chambers Blood moves through circulatory system from areas of higher to lower pressure. Contraction of heart produces the pressure

Cardiac Cycle

Cardiac Cycle

Heart Sounds First heart sound or “lubb” Second heart sound or “dupp” Atrioventricular valves and surrounding fluid vibrations as valves close at beginning of ventricular systole Second heart sound or “dupp” Results from closure of aortic and pulmonary semilunar valves at beginning of ventricular diastole, lasts longer Third heart sound (occasional) Caused by turbulent blood flow into ventricles and detected near end of first one-third of diastole Clinical considerations: Murmurs: abnormal heart sounds Incompetent valve - leaks excessively (gurguling,swishing) Stenosis: abnormally small valve openings (rushing sound before valve closes. Causes: genetic or due to rhematic fever scaring or myocardial infarction affecting the papillary muscles.

Location of Heart Valves

Mean Arterial Blood Pressure Stroke volume Volume of blood pumped during each cardiac cycle at rest ~70 ml can increase to ~200 ml during exercise Heart Rate ~72 BPM and can increase to over 120 BPM during exercise. Cardiac Output =stroke volume X heart rate Resting: 72 beats/min X 70 ml/beat = 5040 ml / min Exercise: 120 beats/min X 200 ml/beat = 24,000 ml/min. Cardiac reserve max cardiac output - resting cardiac output = 24,000-5040ml /min = 18960 ml C.O. is the major factor in determining blood pressure. Blood pressure Blood pressure reflects pressure changes in the aorta not the ventricle Normal BP 120 systolic / 80 diastolic

Factors Affecting MAP

Regulation of the Heart Intrinsic regulation: Results from normal functional characteristics, not on neural or hormonal regulation Starling’s law of the heart Stretching of the SA node. Extrinsic regulation: Involves neural and hormonal control Parasympathetic stimulation Supplied by vagus nerve, decreases heart rate, acetylcholine secreted Sympathetic stimulation Supplied by cardiac nerves, increases heart rate and force of contraction, epinephrine and norepinephrine released

Heart Homeostasis Effect of blood pressure Baroreceptors monitor blood pressure Effect of pH, carbon dioxide, oxygen Chemoreceptors monitor Effect of extracellular ion concentration Increase or decrease in extracellular K+ decreases heart rate Effect of body temperature Heart rate increases when body temperature increases, heart rate decreases when body temperature decreases

Baroreceptor and Chemoreceptor Reflexes

Baroreceptor Reflex

Chemoreceptor Reflex-pH

Effects of Aging on the Heart Gradual changes in heart function, minor under resting condition, more significant during exercise Hypertrophy of left ventricle Maximum heart rate decreases Increased tendency for valves to function abnormally and arrhythmias to occur Increased oxygen consumption required to pump same amount of blood