Heart

1. Size – 250 t0 350 grams; fist size

2. Location – mediastinum; 2/3^rds left of the midsternal line

3. Apex – points inferiorly

4. Base – superior surface; associated blood vessels

Pericardium

1. Pericardium – double walled sac which encloses the heart

2. Fibrous pericardium – lose fitting superficial; dense tough connective tissue

3. Serous pericardium thin slippery serous membrane; two layers

-a. Parietal layer – lines the internal surface of fibrous pericardium

-b. Visceral layer – parietal layer turns inferiorly at large vessels

-c. Pericardial cavity – contains a film of serous fluid; reduce friction

Heart Layers

1. Epicardium – visceral layer of the serous pericardium

2. Myocardium – mostly cardiac muscle; forms bulk of heart

3. Endocardium – simple squamous epithelium; continuous with endothelium

Chambers and vessels

1. Right atrium – superior right

-a. Vena cava – from below diaphragm (inferior) and above it (superior)

2. Right ventricle – inferior right

-a. Pulmonary trunk – oxygen poor blood to lungs

3. Left atrium – superior left

-a. Pulmonary veins – oxygen rich blood from lungs

4. Left ventricle – inferior left

-a. Aorta – delivers oxygen rich blood to body

5. Septum – internal portion that divides the heart longitudinally

Grooves

1. Atrioventricular groove (coronary sulcus) – separates atria and ventricles

2. Interventricular sulci – separates right and left ventricles

Atria

1. Atria – superior receiving chambers

2. Auricles – small wrinkled protruding appendages

3. Pectinate muscles – muscle bundles; ridge anterior internal surface

4. Fossa ovalis – shallow depression; interatrial septum; foramen ovale

Ventricles

1. Ventricles – inferior discharging chambers; most of heart mass

2. Trabeculae carneae – irregular muscle ridges; line ventricular chamber

3. Papillary muscles – cone like muscle fibers; valve function

4. Cordae tendinae – heart strings; collagen; papillary muscles; secure valve cusps

Pathway of blood

1. Pathway– a double pump; two circuits

2. Pulmonary circuit

-a. Right atrium – oxygen poor carbon dioxide rich; superior and inferior vena cava

-b. Right ventricle – blood from right atrium; pumps out the pulmonary trunk

-c. Pulmonary trunk (arteries) – caries oxygen poor blood to lungs

-d. Pulmonary veins – caries oxygen rich blood from lungs back to left atrium

3. Systemic circuit

-a. Left atrium – oxygen rich blood from four pulmonary veins

-b. Left ventricle – blood from left atrium; pumps blood out aorta

-c. Aorta – branches much; oxygen blood to body

-d. Capillary beds – where gas exchange takes place

Arterial supply (coronary circulation)

1. Left coronary artery – from aorta; left in coronary sulcus

2. Right coronary artery – from aorta; right in coronary sulcus

3. Anterior interventricular artery – from left coronary artery; location

4. Circumflex artery – from left coronary artery; left atrium and ventricle

5. Posterior interventricular artery – from right coronary artery;

6. Marginal artery – from right coronary; lateral part of right heart

Venous drainage (coronary circulation)

1. Coronary sinus – large; posterior atrioventricular groove; into right atrium

2. Great cardiac vein – anterior interventricular sulcus

3. Middle cardiac vein – posterior interventricular sulcus

4. Small cardiac vein – right inferior margin

Pathology in coronary circulation

1. Angina pectoris - pain; fleeting deficiencies in oxygen; weakened but not dead

2. Myocardial infarction – heart attack; prolonged blockage; cell death; scar tissue

Atrioventricular valves

1. Function – prevent backflow into atria; made up of cusps

2. Tricuspid valve – right AV valve; three cusps

3. Bicuspid (Mitral) valve – left AV valve; two cusps

Semilunar valves

1. Function – each made up of three pocket-like cusps

2. Aortic semilunar valve– stops aorta left ventricle backflow

3. Pulmonary semilunar valve – stops pulmonary trunk right ventricle backflow

Valve pathology

1. Incompetent valve – heart pumps same blood over and over; works harder

2. Valvular stenosis – narrowing; valve flap becomes stiff with scar tissue

3. Valve replacement – artificial or pig valve

Cardiac muscle cells

1. Striated – reflect similarity in arrangement of myofilaments

2. Shape – short, fat and branching

3. Nucleus – one (or two) centrally located

4. Intercalating disc – junction between cardiac cells

5. Gap junctions – connection between cells; transmission of depolarizing current

6. Desmosomes – rivet like junctions; stop cells from tearing apart

7. T tubules – enter at Z disc, not A band I band junction

8. Sarcoplasmic reticulum – no terminal cisternae; less elaborate; no triads

9. Mitochondria – much more numerous than in skeletal muscle

Energy requirements

1. Aerobic respiration – almost exclusively

2. Mitochondria – many; reflect aerobic respiration

3. Fuels – wide variety; glucose, fatty acids

Myocardium Depolarization

1. Rising phase

-a. Stimulation – by autorhythmic cells; opens voltage regulated sodium channels

-b. Sodium channels – open; leading to threshold and opening of more Na channels

-c. Peak – sodium channels close; at about +30 mV

-d. Slow calcium channels – also opened by depolarization; delayed; Ca into cell

-e. Sarcoplasmic reticulum – releases calcium due to influx of both Ca and Na

2. Plateau

- a. Slow calcium channels – remain opened; prolong depolarization

- b. Potassium channels – closed; prevent Potassium movement out of cell

3. Repolarization

- a. Calcium channels – close; calcium is excluded from nonstimulated cardiocytes

- b. Potassium channels – open; potassium leaves; resting membrane potential

Myocardial Contraction

1. Calcium – binds to troponin; excitation-contraction coupling

2. Contraction duration – much longer; Over 200 vs. 14 -100 ms; plateau

3. Absolute refactory period – close to contraction duration; prevents summation

-a. Skeletal – action potential 1-5; contraction 15-100 ms

-b. Cardiac – action potential 200; contraction 200 ms (or less)

4. Summation – with complete tetanus is prevented

Autorhythmic cell depolarization

1. Pacemaker potential – no stable resting potential; constantly drift to threshold

2. Fast calcium channels – influx of calcium cause rising phase

3. Repolarization – calcium permeability decreases; potassium increases

Sequence of autorhythmic cell excitation

1. Sinoatrial (SA) node – 75 tpm; pacemaker; inferior to superior vena cava

2. Atrioventricular (AV) node – inferior portion of the interatrial septum

3. Atrioventricular (AV) bundle (of His) – connection between atria and ventricles

4. Bundle branches – right and left; down interventricular septum to apex

5. Purkinje fibers – turn superiorly into the ventricular walls

Heart rhythm pathologies

1. Arrhythmias – irregular heart rhythm

2. Fibrillation – rapid irregular contractions; defibrillation

Electrocardiogram

1. P wave – atrial depolarization

2. QRS wave – ventricular depolarization

3. T wave – ventricular repolarization

4. P-Q interval – atrial contraction occurs

5. Q-T interval – ventricular contraction occurs

Cardiac Cycle

1. Ventricular filling – mid to late diastole

-a. Quiescent period – no contraction; blood passive from atria to ventricle; 0.4 ms

-b. Atrial systole – atrial contraction; remaining blood forced into ventricle; 0.1 ms

2. Ventricular systole – ventricular contraction; 0.3 ms

-a. Isovolumetric contraction – volume same; all valves close; pressure building

-b. Ventricular ejection – pressure reaches a point to open semilunar valves

3. Isovolumetric relaxation – low pressure, ventricle; all valves close; early diastole

Cardiac volume changes

1. End systolic volume – after systole about 50 ml of blood remains

2. End diastolic volume – after filling there is about 120 ml of blood in the ventricle

3. Stroke volume – about 70 ml; the amount that is ejected into the aorta

Heart sounds

1. Heart sounds – sounds made when valves close; blood turbulent; ventricle stretch

2. AV valves – closing causes first, louder sound

3. Semilunar valves – closing causes second, quieter sound

Heart rate

1. Newborns – 120 bpm (beats per minute)

2. Adults – about 70 bpm

3. Tachycardia – above 100 bpm; drugs, high temperature; heart disease

4. Bradycardia – below 60 bpm; low temperature; drugs

Cardiac output

1. Cardiac output – blood pumped per minute; stroke volume times heart rate

2. Stroke volume – 70 ml; amount of blood ejected from ventricle

3. Heart rate – the number of beats per minute

4. Cardiac reserve – difference between resting and maximum CO

-a. Non athletes – 4 to 5 times as great

-b. Athletes – about 7 times greater

Stroke volume regulation

1. Preload – degree of stretch of heart muscle; greater stretch, greater contraction

2. Contractility – increased contractility not due to stretch; calcium increase

3. Afterload – back pressure exerted by arterial blood

Influences on heart rate

1. Sympathetic – increases heart rate

-a. Cardioacceleratory center – medulla; sympathetic chain ganglion

2. Parasympathetic – decreases heart rate

-a. Cardioinhibitory center – medulla; branches of vagus nerve

-b. Vagal tone – normally parasympathetic dominates at rest; keeps heart rate lower

4. Baroreceptors – monitors pressure; ANS responds

5. Hormones –epinephrine and thyroxin

6. Electrolytes imbalances – especially sodium, calcium, and potassium

Congestive Heart Failure

1. Congestive heart failure– pumping efficiency inadequate to meet tissue demands

2. Pulmonary edema – left ventricle failure; blood pools in lungs

3. Peripheral edema – right ventricle failure; blood pools in tissue spaces