Heart Circulation & Physiology Ch. 18

Blood Pathway Pulmonary circulation – to and from lungs (right side of heart) Systemic circulation – to and from body (left side) Renal – to and from kidneys Hepatic portal – to and from liver Coronary – to and from heart muscle

Heart Valves Direct blood flow in one direction AV (atrio-ventricular) valves – supported by chordae tendonae; open when atria contract Right AV – “tricuspid” valve Left AV – “bicuspid” or “mitral” valve

Semi-lunar valves – open when ventricles contract Aortic valve – between left ventricle and aorta Pulmonary valve – between right ventricle and pulmonary trunk

Problems when valves “prolapse” or suffer from “stenosis” (scarring); can happen due to genetic defects, strep infections, or heart disease

Coronary arteries supply blood to heart muscle. Coronary Circulation Myocadium too thick for diffusion of blood from heart chambers to be effective Coronary arteries supply blood to heart muscle.

Arteries branch from base of aorta and form a “crown” around the heart Cardiac veins collect and return blood to circulation

Problems happen when blockages occur Angina pectoris – “chest pain” Myocardial infarction – “cardiac muscle death”, “coronary”, “heart attack”

Heart Physiology Nodal System – intrinsic system SA Node – sinus rhythm AV Node – nodal rhythm (.04 secs)

Circuit Starts with SA node ----AV node ------ AV Bundle (Bundle of His) Bundle branches (Purkinje fibers)

Contraction from apex upwards Entire process takes .22 secs Rate controlled by sympathetic and parasympathetic

Problems Arrythmias – irregular rhythm Fibrillation – ineffective ventricular contraction Ectopic focus – development of new pacemaker which interferes with normal pacemaker

Extrasystole – premature contraction Heart block – no AV node; requires artificial pacemaker (2 kinds: fixed rate and on-demand)

Cardiac Cycle All events associated with blood flow through heart during one heart beat Systole – contraction of ventricles Diastole – relaxation of ventricles At 75 bpm average cycle is 0.8 secs

Heart sounds “lub” – AV valve closes, louder, longer and more resonant “dub” – SL valve snaps shut, short, sharp Left side usually closes before right side, so sounds of individual valves can be distinguished

Murmurs – abnormal or unusual sounds; occurs when normally smooth blood flow strikes obstructions or flows in the wrong direction, flow is turbulent and generates sounds.

Electrocardiogram (EKG) Measurement of electrical output of the heart’s electrical system Consists of 3 types of “deflection waves”: P wave – impulse from SA node

QRS wave – depolarization of ventricles (unequal in size due to size differences of ventricles) T wave – repolarization of ventricles

P-R = beginning of atrial excitation Q-T = beginning of ventricle contraction

Regulation of Rate Nervous Control Sympathetic releases norepinephrine to stimulate SA and AV nodes; stress (emotional or physical) Parasympathetic (via vagus nerves) releases ACh to slow things down

Chemical control Hormones Epinephrine Thyroxine

atrial natriuretic factor (ANF) - causes vasodilation and kidneys to dump water; lowers blood pressure Antidiuretic hormone (ADH) – vasoconstriction and tells kidneys to hold water; alcohol interfers with this

Physical factors Age Gender Exercise Body temperature Fetal rate – 2x adult

Pathology Tachycardia – rapid heart rate Bradycardia – slow heart rate Congestive heart failure – ventricles don’t pump effectively, circulation is inadequate Pulmonary congestion – left side fails Systemic congestion – right side fails

Hypotension Hypertension (silent killer); stresses myocardium which enlarges heart, vessels tear which increases platelet deposition and Ca+ deposits

Any Questions?