Overview: Cardiovascular System and the Heart

1. 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

2. 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.

3. 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

4. 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

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

6. 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

7. 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

8. 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

9. 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.

10. 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

11. 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

12. 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+.

13. 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

14. Electrocardiogram

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

16. 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