1. Review of Cardiac Structure and Function

2. Location Heart lies in the mediastinum behind the sternum
1/3 of bulk of the heart lies to the right of the midline; 2/3 lies to the left
Apex lies between the 4th & 5th ribs when lying down and between the 5th and 6th ribs when sitting or standing

4. Pericardium The heart lies within the pericardium
Outer layer of the pericardium is fibrous connective tissue – fibrous pericardium
Anchors the pericardium to the great vessels, the sternum and diaphragm

5. Two inner layers of serous membranes- parietal pericardium and visceral pericardium (epicardium)
Between the serous membranes is the pericardial space, filled with ml of fluid to reduce friction
Fibrous pericardium and parietal pericardium are called the pericardial sac
Visceral pericardium is the epicardium

7. Heart Wall Epicardium Myocardium – muscular layer Thickest layer
Attached to fibrous skeleton of the heart
Bands of muscle arranged longitudinally
Fibers from one side enter other side
Better integration of contractions
Pathology of one ventricle can affect the other

9. Endocardium
Internal lining of squamous epithelium
Continuous throughout cardiovascular system

11. Four chambers (two pumps)
Right heart acts as a volume pump – through low-resistance vessels of the pulmonary system
Left heart acts as a pressure pump – through high-resistance vessels of the systemic circulation

13. Atria
Two upper, thin walled chambers that collect blood returning to the heart
Their contraction aids in filling the ventricles
Right atrium receives blood from superior and inferior vena cavae and coronary sinus
Left atrium receives blood from pulmonary veins

16. Ventricles Thick walled pumping chambers of the heart
Make up about 60 % of the mass of the heart and receive most of coronary blood flow
Blood from right ventricle enters the pulmonary trunk
Blood from left ventricle enters the aorta

17. Path of Blood Flow Pulmonary trunk→ Lungs→ Pulmonary veins→ LA→ LV→
Vena cavae → RA→ RV→
Pulmonary trunk→ Lungs→
Pulmonary veins→ LA→ LV→
Aorta → Systemic circulation→
Vena cavae

19. Valves Made of connective tissue covered by endothelium
Prevent back flow of blood
Open and close passively in response to ventricular contraction
Anchored to the annuli fibrosi cordis to prevent dilation during contraction of the heart

21. Atrioventricular valves
Lie between the atria and ventricles
Tricuspid valve on the right
Bicuspid or mitral valve on left
Anchored against high pressure by the chordae tendineae and papillary muscles

23. Semilunar Valves Lie between ventricles and great vessels
Pulmonary on right side
Aortic on left side

27. Cardiac Cycle
Sequence of events that compose the repeating pumping action of the heart
Typically, systole refers to ventricular contraction and diastole refers to ventricular relaxation
If referring to atria, specify atrial systole, etc.

28. Review
Coronary arteries and cardiac veins – note that it is the right coronary artery that supplies blood to the SA and AV nodes

31. Review
Pressures in chambers: look over the next figure - note especially the pressures in the right atrium – central venous pressure, and the pressures in the aorta – systemic blood pressure

33. Cardiac muscle - Myocytes
Contractile fibers
Fibers are branched
Intercalated discs - contain desmosomes and gap junctions
Gap junctions connect cytoplasm of adjoining cells so that the action potentials pass from one cell to the next
Cells contract as if one cell - syncytium

36. Muscle contraction Striated muscle – contains actin and myosin
Action potential stimulates release of Ca++
Ca++ binds to troponin
Troponin moves the tropomyosin exposing myosin binding sites on the actin
Myosin pulls on the actin, filaments slide past each other and muscle shortens

42. Remember, that unlike skeletal muscle, much of the Ca++ used in cardiac muscle contraction comes from the extracellular fluid.

43. Conduction System
Conduction system cells are specialized myocardial fibers
Heart has autorhythmicity- beats spontaneously at about 100 beats/min
Impulse begins at sinoatrial (SA) node or pacemaker – sinus rhythm
Spreads through atria via conducting myofibers to atrioventricular (AV) node in fibrous skeleton of heart

44. Signal pauses briefly, for ventricular filling by atrial contraction.
Signal continues into ventricle through conduction pathways:
AV bundle ( bundle of His) →right and left bundle branches→ Purkinje fibers→ ventricular contraction (bottom up)

46. Regulation of Heart Rate
Sympathetic N.S. increases heart rate and force of contraction – secrete norepinephrine –accelerator nerves
Parasympathetic N.S. decrease heart rate and force of contraction through the vagus nerve. Sends continuous impulses. Secretes acetylcholine

48. Electrocardiogram ECG
Measures electrical activity of the heart
P wave – represents atrial contraction (depolarization)
QRS complex – represents ventricular contraction (depolarization)
T wave – represents ventricular relaxation (repolarization)

54. Cardiac Output Cardiac Output:
SV (ml/beat) X HR (beats/min) = CO(ml/min.)
70 ml X = 5600 ml /min. or liters L/min

55. Factors affecting cardiac performance
Preload: pressure generated at the end of diastole; depends on both heart and vascular system –the amount of filling of the ventricle during relaxation
Afterload: resistance to ejection during systole; depends on both heart and vascular system - the force that opposes ejection of blood from the heart; for the LV, this is the aortic systolic pressure

56. Heart rate: a intrinsic characteristic of the heart tissue that is influenced by nervous and endocrine systems
Myocardial contractility: the ability of the heart muscle to contract, the force of contraction - another cardiac tissue characteristic that is influenced by nervous and endocrine systems

57. (Frank-) Starling Law
Within limits, the greater the stretching of the muscle fibers (preload), the greater the force of contraction.
The extra force of contraction is necessary to pump the increased volume of blood from the ventricle.
Cardiac output increases

58. Neural reflexes
Bainbridge reflex – increased heart rate due to increased right atrial pressure
Increased pressure in arteries stimulates a baroreceptor reflex that decreases heart rate.