Overview: Cardiovascular System and the Heart Circulatory System = heart, BVs, and blood Cardiovascular System = passageways for blood = heart, arteries veins, etc. Two Hearts: Pulmonary Circuit (right side) - takes blood to lungs for gas exchange Systemic circuit (left side)- takes oxygen rich blood to the organs and oxygen poor blood back to the heart

Right side of heart gets O2 poor blood Pulmonary artery takes it away from heart to lungs Pulmonary veins bring it back O2 rich Left side of heart serves systemic system Aorta takes O2 rich blood out to organs Superior vena cava brings it back from head, neck, upper limbs Inferior vena cava brings it back from organs below diaphragm.

Pericardium Double walled sac enclosing heart In the pericardial cavity is pericardial fluid that allows the heart to beat without friction Pericarditis is the pain caused by friction when the membranes are dry

Heart wall Epicardium outer layer fatty Myocardium thickest layer cardiac muscle that pulls against a fibrous skeleton of fibers focuses the movement of electricity Endocardium Smooth inner lining

Chambers Right and left atria receive returning blood have an easier workload Right and left ventricles eject blood

Heart Valves Ensure one way flow Made of flaps called cusps Open & close as a result of pressure changes When ventricles relax, valves are open Full ventricles contract pressure pushes valves shut AV valves = between atria + ventricles Right AV – tricuspid valve Left AV – bicuspid valve (aka, mitral valve) Semilunar valves = bet. ventricles + the great arteries

Coronary Circulation Getting blood to your heart ~3 billion beats over an 80 year life span Heart needs 5% of body’s O2 delivered by coronary arteries Myocardial Infarction: fat deposits blocking arteries leading to necrosis of tissue Anastomoses: our body’s defense Two arteries covering the same area If the damage is extensive, the heart beat becomes inefficient - coronary bypass may be necesssary

Cardiac Muscle and The Cardiac Conduction System Cardiocytes: short, thick branched cells -mononucleated, striated -myogenic –will beat rythmically w/o CNS stimulation -inherent contractile activity controlled by the ANS • Intercalated discs join cells end to end Gap junctions allow ions to flow between cells, keep electrical current flowing from one cell to the next The action potential travels thru all cells connected together forming a functional syncytium

Cardiac conduction system Our brain can modify the heartbeat, but not create it. Disembodied hearts can beat for hours. Sinoatrial (SA) node = the pacemaker -initiates heart beat and determines heart rate -damage to SA node results in slower heart rate – implant an artificial pacemaker Atrioventricular node = sends signals to the ventricles Purkinje fibers arise from bundle branches near the apex and then spread throughout the myocardium.

Control of Heart Rate Without nervous system control, the heart would beat about 100 times per minute Both sympathetic and parasympathetic nerves innervate the SA node When you are relaxed, your parasympathetic nervous system (via the vagus nerve) sets a resting heart beat rate at about 70 beats/min When exercising or anxious, the sympathetic nervous system ↑ heart beat via hormones like adrenaline – this ↑ flow of O2 blood to muscles Average maximum heart rate is 220 minus your age

Electrical & Contractile Activity Contraction = systole Relaxation = diastole These can apply to parts (e.g., atrial systole), or just to the ventricles Sinus rhythm = normal beat triggered by SA node Can have ectopic focus (alternate source of beat, instead of SA node) called nodal rhythm Arrhythmia = abnormal rhythm

Physiology of the SA node The nerves of the SA node are always slowly moving toward an action potential As soon as the heart beats it’s already starting toward another beat Avg. ~75 beats per minute Cardiac muscle has a sustained contraction, and a longer refractory period This prevents tetanus: continual contraction Membrane potential starts around -60mV. Pacemaker potential is a gradual drift upward (slow inflow of Na+ w/o outflow of K+). Fast calcium channels – inflow of Ca+.

Electrocardiogram (ECG/EKG) Composite reading of many action potentials P wave: atria contract QRS complex: AV node fires, ventricles start to contract T wave: ventricles repolarizing U wave: not always seen – repolarization of papillary muscles or Perkinje fibers

Electrocardiogram

Cardiac cycle “Lub-dub” sounds are made when the heart valves that separate the chambers of the heart open and close in sequence.

Now, you can… Identify the chambers and valves of the heart Trace the flow of blood through the heart chambers Contrast cardiac vs. skeletal muscle Describe the physiological properties of cardiac muscle Describe the heart’s electrical conduction system Describe the physiological mechanism of control of rate of heart beat