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

Intrinsic Control

Extrinsic Control

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

A Problem...

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.