Cardiovascular system L1 Faisal I. Mohammed, MD, PhD Yanal A. Shafagoj, MD, PhD University of Jordan

Cardiovascular System Anatomy Main Function of heart is to pump blood….Ejection

Anatomy of the heart 3

Anatomy of the heart 4

Cardiac valves

Cardiac Valves Open and Close Passively

Importance of Chordae Tendineae

Importance of Chordae Tendineae

Layers of the Heart Wall Epicardium (external layer) Visceral layer of serous pericardium Smooth, slippery texture to outermost surface Myocardium 95% of heart is cardiac muscle Endocardium (inner layer) Smooth lining for chambers of heart, valves and continuous with lining of large blood vessels University of Jordan

Internal anatomy of the heart and Cardiac valves 12

Heart Valves and Circulation of Blood Atrioventricular valves Tricuspid and bicuspid valves Atria contracts/ ventricle relaxed AV valve opens, cusps project into ventricle In ventricle, papillary muscles are relaxed and chordae tendinae slack Atria relaxed/ ventricle contracts Pressure drives cusps upward until edges meet and close opening Papillary muscles contract tightening chordae tendinae Prevents regurgitation University of Jordan

Movement of blood in the heart 14

Systemic and pulmonary circulation - 2 circuits in series Systemic circuit Left side of heart Receives blood from lungs Ejects blood into aorta Systemic arteries, arterioles Gas and nutrient exchange in systemic capillaries Systemic venules and veins lead back to right atrium Pulmonary circuit Right side of heart Receives blood from systemic circulation Ejects blood into pulmonary trunk then pulmonary arteries Gas exchange in pulmonary capillaries Pulmonary veins takes blood to left atrium University of Jordan

Cardiac Muscle Tissue and the Cardiac Conduction System Histology Shorter and less circular than skeletal muscle fibers Branching gives “stair-step” appearance Usually one centrally located nucleus Ends of fibers connected by intercalated discs Discs contain desmosomes (hold fibers together) and gap junctions (allow action potential conduction from one fiber to the next) Mitochondria are larger and more numerous than skeletal muscle Same arrangement of actin and myosin University of Jordan

Cardiac Muscle Tissue Cardiac muscle, like skeletal muscle, is striated. Unlike skeletal muscle, its fibers are shorter, they branch, and they have only one (usually centrally located) nucleus. Cardiac muscle cells connect to and communicate with neighboring cells through gap junctions in intercalated discs. 18

Action Potentials and Contraction Action potential initiated by SA node spreads out to excite “working” fibers called contractile fibers Depolarization Plateau Repolarization University of Jordan

Action Potentials and Contraction Depolarization – contractile fibers have stable resting membrane potential Voltage-gated fast Na+ channels open – Na+ flows in Then deactivate and Na+ inflow decreases Plateau – period of maintained depolarization Due in part to opening of voltage-gated slow Ca2+ channels – Ca2+ moves from interstitial fluid into cytosol Ultimately triggers contraction Depolarization sustained due to voltage-gated K+ channels balancing Ca2+ inflow with K+ outflow University of Jordan

Action Potentials and Contraction Repolarization – recovery of resting membrane potential Resembles that in other excitable cells Additional voltage-gated K+ channels open Outflow K+ of restores negative resting membrane potential Calcium channels closing Refractory period – time interval during which second contraction cannot be triggered Lasts longer than contraction itself Tetanus (maintained contraction) cannot occur Blood flow would cease University of Jordan

Action Potential in a ventricular contractile fiber Depolarization Repolarization Refractory period Contraction Membrane potential (mV) Repolarization due to closure of Ca2+ channels and K+ outflow when additional voltage-gated K+ channels open Rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open Plateau (maintained depolarization) due to Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open 0.3 sec + 20 –20 –40 – 60 – 80 –100 2 1 3 Depolarization Repolarization Refractory period Contraction Membrane potential (mV) Rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open Plateau (maintained depolarization) due to Ca2+ inflow when voltage-gated slow Ca2+ channels open and K+ outflow when some K+ channels open 0.3 sec + 20 –20 –40 – 60 – 80 –100 2 1 Depolarization Repolarization Refractory period Contraction Membrane potential (mV) Rapid depolarization due to Na+ inflow when voltage-gated fast Na+ channels open 0.3 sec + 20 –20 –40 – 60 – 80 –100 1 University of Jordan

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University of Jordan 24