Leading Causes of Death (2010)
National Vital Statistics Reports, Vol. 62, Number 6
National Vital Statistics Reports, Vol. 62, Number 6
Heart Development
Anatomy Review
Anatomy Review
• Chambers
• Atria
• Ventricles
• Atrioventricular (AV) valves
• Tricuspid valve
• Bicuspid valve (mitral valve)
• Semilunar valves
• Pulmonary semilunar valve
• Aortic semilunar valve
Cardiac Cycle
• Cardiac cycle = contraction, relaxation cycle of the heart
• Systole = contraction
• Diastole = relaxation
• Stroke volume = volume of blood ejected by ventricles as they contract
Phases of the Cardiac Cycle
• 1. Atrial and Ventricular Diastole
• Atria fill, AV valves open, ventricles filling
• 2. Early Ventricular Systole
• Ventricles begin to contract, AV valves close
• Isovolumic ventricular contraction
Phases of the Cardiac Cycle
• 3. Ventricular Systole and Blood Ejection
• Semilunar valves open, blood enters the arteries
• 4. Ventricular Diastole
• Ventricles relax, pressure decreases
• Semilunar valves close
• AV valves remain closed
Heart Sounds
• Lub = closing of AV valves during isovolumetric contraction of ventricles (systole)
• Dub = closing of semilunar valves (heard when ventricles relax at the beginning of diastole)
!
• Heart Murmurs
Cardiac Muscle Cells
• Myocardial muscle cells are branched
• Single nucleus / cell
• 1/3 of the cell volume is mitochondria
• Desmosomes and gap junctions connect neighbors
Control of Heart Rate
• Cardiac muscle cells contract without innervation (like all ANS targets)
• 1% of myocardial cells are autorhythmic
• Pacemakers (located in the SA node) make the heart myogenic
Ectopic pacemaker
Contraction Events in Cardiac Muscle
AP opens voltage-gated Ca++ channels and Ca++ enters the cell
Ca++-induced Ca++ release through RyR channel
Ca++ spark
Summed Ca++ sparks create a Ca ++ signal
Ca++ binds to troponin... etc.
Ca++ removal:
Ca++ ATPase (in the SR membrane)
Na+/Ca++ secondary active transport (cell membrane)
Contraction Events in Cardiac Muscle
Graded Contractions
• Force generated proportional to number of crossbridges formed; the myocardial calcium concentration is variable
• amount of Ca ++ that enters the cell through voltage-gated channels
• amount of Ca ++ stored by SR
• Catecholamine control this!
• epi and norepi bind to ß1receptors, stimulating cAMP which:
• increases the time Ca++ channels remain open
• increase Ca++/ATPase activity in SR
Graded Contractions
Electrocardiogram (ECG or EKG)
• An ECG is a recording of the electrical activity of the heart (summed together)
• P wave = atrial depolarization
• QRS wave = depolarization of ventricles (and repolarization of atria).
• T wave = repolarization of ventricles
Arteriosclerosis and Cardiac Arrhythmia
• Plaques can clog the arteries, causing restricted blood flow
• Smoking, hypertension, and a diet high in cholesterol and fats contribute
• High ratio of HDL to LDL is desirable
• Myocardial ischemia
• Myocardial infarction = heart attack.
Cardiac Arrhythmias
• Arrhythmias
• Bradycardia = heart rate less than 60 beats/ min
• Tachycardia = heart rate more than 100 / min
• Flutter = rapid, controlled contractions of atria or ventricles
• Fibrillation = rapid, uncontrolled contractions
• Electrical defibrillation can sometimes re-regulate the myocardial cells to become synchronous again.