Human Physiology Cardiovascular System

Heart Anatomy Approximately the size of a fist Location ▫In the mediastinum between second rib and fifth intercostal space ▫On the superior surface of diaphragm ▫Two-thirds to the left of the midsternal line Enclosed in pericardium, a double-walled sac

Layers of the Heart Wall 1.Epicardium—visceral layer of the serous pericardium 2.Myocardium ▫Spiral bundles of cardiac muscle cells ▫Layer that contracts ▫Fibrous skeleton of the heart: crisscrossing, interlacing layer of connective tissue  Anchors cardiac muscle fibers  Supports great vessels and valves  Limits spread of action potentials to specific paths 3.Endocardium lines the heart chambers and covers the skeleton of the valves

Chambers Four chambers ▫Two atria  Separated internally by the interatrial septum  Coronary sulcus (atrioventricular groove) at the junction of atria  Auricles increase atrial volume Two ventricles ▫Separated by the interventricular septum ▫Anterior and posterior interventricular sulci mark the position of the septum externally

Atria: The Receiving Chambers Walls are ridged by pectinate muscles Vessels entering right atrium ▫Superior vena cava ▫Inferior vena cava ▫Coronary sinus Vessels entering left atrium ▫Right and left pulmonary veins (2 branches each, total of 4)

Ventricles: The Discharging Chambers Walls are ridged by trabeculae carneae Papillary muscles project into the ventricular cavities Vessel leaving the right ventricle ▫Pulmonary artery Vessel leaving the left ventricle ▫Aorta

Pathway of Blood Through the Heart The heart is two side-by-side pumps ▫Right side is the pump for the pulmonary circuit  Vessels that carry blood to and from the lungs ▫Left side is the pump for the systemic circuit  Vessels that carry the blood to and from all body tissues

Pathway of Blood Through the Heart Right atrium  tricuspid valve  right ventricle Right ventricle  pulmonary semilunar valve  pulmonary trunk  pulmonary arteries  lungs

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

Heart Valves Ensure unidirectional blood flow through the heart Atrioventricular (AV) valves ▫Prevent backflow into the atria when ventricles contract ▫Tricuspid valve (right) ▫Mitral valve (left) Chordae tendineae anchor AV valve cusps to papillary muscles Semilunar (SL) valves ▫Prevent backflow into the ventricles when ventricles relax ▫Aortic semilunar valve ▫Pulmonary semilunar valve

Heart Physiology: Sequence of Excitation 1.Sinoatrial (SA) node (pacemaker) ▫Generates impulses about 75 times/minute (sinus rhythm) ▫Depolarizes faster than any other part of the myocardium 2.Atrioventricular (AV) node ▫Smaller diameter fibers; fewer gap junctions ▫Delays impulses approximately 0.1 second ▫Depolarizes 50 times per minute in absence of SA node input

Heart Physiology: Sequence of Excitation 3.Atrioventricular (AV) bundle (Bundle of His) ▫Only electrical connection between the atria and ventricles 4.Right and left bundle branches ▫Two pathways in the interventricular septum that carry the impulses toward the apex of the heart 5.Purkinje fibers ▫Complete the pathway into the apex and ventricular walls ▫AV bundle and Purkinje fibers depolarize only 30 times per minute in absence of AV node input

Electrocardiography Electrocardiogram (ECG or EKG): a composite of all the action potentials generated by nodal and contractile cells at a given time Three waves 1.P wave: depolarization of SA node (atrial contraction) 2.QRS complex (0.12 s): ventricular depolarization (ventricular contraction) 3.T wave: ventricular repolarization (ventricular recovery)

Figure Sinoatrial node Atrioventricular node Atrial depolarization QRS complex Ventricular depolarization Ventricular repolarization P-Q Interval S-T Segment Q-T Interval

Mechanical Events: The Cardiac Cycle Cardiac cycle: all events associated with blood flow through the heart during one complete heartbeat ▫Systole—contraction ▫Diastole—relaxation

Blood Vessels Three major blood vessels ▫Arteries: carry blood away from the heart; oxygenated except for pulmonary circulation and umbilical vessels of a fetus ▫Capillaries: contact tissue cells and directly serve cellular needs ▫Veins: carry blood toward the heart

Structure of Blood Vessel Walls Arteries and veins ▫Tunica intima, tunica media, and tunica externa Lumen ▫Central blood- containing space

Physiology of Circulation: Definition of Terms Blood flow ▫Volume of blood flowing through a vessel, an organ, or the entire circulation in a given period  Measured as ml/min  Equivalent to cardiac output (CO) for entire vascular system  Relatively constant when at rest  Varies widely through individual organs, based on needs

Physiology of Circulation: Definition of Terms Blood pressure (BP) ▫Force per unit area exerted on the wall of a blood vessel by the blood  Expressed in mm Hg  Measured as systemic arterial BP in large arteries near the heart ▫The pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas

Physiology of Circulation: Definition of Terms Resistance (peripheral resistance) ▫Opposition to flow ▫Measure of the amount of friction blood encounters ▫Generally encountered in the peripheral systemic circulation Three important sources of resistance ▫Blood viscosity ▫Total blood vessel length ▫Blood vessel diameter

Relationship Between Blood Flow, Blood Pressure, and Resistance Blood flow (F) is directly proportional to the blood pressure gradient (  P) ▫If  P increases, blood flow speeds up Blood flow is inversely proportional to peripheral resistance (R) ▫If R increases, blood flow decreases: F =  P/R R is more important in influencing local blood flow because it is easily changed by altering blood vessel diameter

Physiology of Circulation: Definition of Terms Blood flow ▫Volume of blood flowing through a vessel, an organ, or the entire circulation in a given period  Measured as ml/min  Equivalent to cardiac output (CO) for entire vascular system  Relatively constant when at rest  Varies widely through individual organs, based on needs

Physiology of Circulation: Definition of Terms Blood pressure (BP) ▫Force per unit area exerted on the wall of a blood vessel by the blood  Expressed in mm Hg  Measured as systemic arterial BP in large arteries near the heart ▫The pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas

Physiology of Circulation: Definition of Terms Resistance (peripheral resistance) ▫Opposition to flow ▫Measure of the amount of friction blood encounters ▫Generally encountered in the peripheral systemic circulation Three important sources of resistance ▫Blood viscosity ▫Total blood vessel length ▫Blood vessel diameter

Relationship Between Blood Flow, Blood Pressure, and Resistance Blood flow (F) is directly proportional to the blood pressure gradient (  P) ▫If  P increases, blood flow speeds up Blood flow is inversely proportional to peripheral resistance (R) ▫If R increases, blood flow decreases: F =  P/R R is more important in influencing local blood flow because it is easily changed by altering blood vessel diameter

Long-Term Mechanisms: Renal Regulation Long-term mechanisms step in to control BP by altering blood volume Kidneys act directly and indirectly to regulate arterial blood pressure 1.Direct renal mechanism 2.Indirect renal (renin-angiotensin) mechanism