1. Unit 7 The Cardiovascular System The Heart
Chapter 18, Cardiovascular System

2. Microscopic Anatomy of Heart Muscle
Cells of interest: Cardiac muscle cells
Cardiac muscle is striated, short, fat, branched, and interconnected
Intercalated discs anchor cardiac cells together and allow cardiac muscle to contract as a unit
Chapter 18, Cardiovascular System

3. Microscopic Anatomy of Heart Muscle

4. Macroscopic Heart Anatomy
Your heart is approximately the size of your fist
Location
Superior surface of diaphragm (above the diaphragm)
Left of the midline
Anterior to the vertebral column (in front of the spine), posterior to the sternum (behind the breastbone)

6. Coverings of the Heart
Pericardium – a fluid-filled double-walled sac around the heart
The Function of the Pericardium:
Protects and anchors the heart
Prevents overfilling of the heart with blood
Allows for the heart to work in a relatively friction-free environment

7. Heart Wall Epicardium Myocardium Endocardium surface/outer layer
muscle layer forming the bulk of the heart
middle layer
Endocardium
endothelial layer
innermost layer

8. Major Vessels of the Heart
Vessels returning blood to the heart include:
Superior and inferior venae cavae
Right and left pulmonary veins

9. Vessels conveying blood away from the heart include:
Pulmonary trunk
splits into right and left pulmonary arteries
Ascending aorta
three branches

10. Anterior View

11. External Heart: Posterior View

12. Gross Anatomy of Heart: Frontal Section

13. Atria of the Heart Atria are the receiving chambers of the heart
The atria receive blood from the venae cavae and pulmonary veins
Right Atrium pumps blood into the Right Ventricle
Left Atrium pumps blood into the Left Ventricle

14. Ventricles of the Heart
Ventricles are the discharging chambers of the heart
Right ventricle pumps blood into the pulmonary trunk
Left ventricle pumps blood into the aorta

15. Myocardial Thickness and Function
Thickness of myocardium varies according to the function of the chamber
Atria are thin walled and only deliver blood to adjacent ventricles
Ventricle walls are much thicker and stronger
right ventricle supplies blood to the lungs (little flow resistance)
left ventricle wall is the thickest to supply systemic circulation (pumps blood to the whole body)

16. Thickness of Cardiac Walls
Myocardium of left ventricle is much thicker than the right.

17. Pathway of Blood Right atrium  tricuspid valve  right ventricle
Right ventricle  pulmonary semilunar valve  pulmonary arteries  lungs
Lungs  pulmonary veins  left atrium
Left atrium  bicuspid valve  left ventricle
Left ventricle  aortic semilunar valve  aorta
Aorta  systemic circulation (body)

18. Pathway of Blood

19. Heart Valves
Heart valves ensure unidirectional blood flow through the heart
Atrioventricular (AV) valves lie between the atria and the ventricles
AV valves prevent backflow into the atria when ventricles contract
Chordae tendineae anchor AV valves to papillary muscles
Semilunar valves prevent backflow of blood into the ventricles

20. Heart Valves

21. Heart Valves

22. Atrioventricular Valve Function

23. Semilunar Valve Function

24. Heart Sounds
Heart sounds (lub-dub) are associated with closing of heart valves
First sound occurs as AV valves close and signifies beginning of systole (contraction)
Second sound occurs when SL valves close at the beginning of diastole (relaxation)

25. Cardiac Muscle Contraction
Heart muscle:
Is stimulated by nerves
Contracts as a unit
Cardiac muscle contraction is similar to skeletal muscle contraction

26. Heart Physiology
Sinoatrial (SA) node generates impulses about 75 times/minute
Atrioventricular (AV) node delays the impulse approximately 0.1 second

27. Heart Physiology
Impulse passes from atria to ventricles via the Bundle of His
Bundle branches carry the impulse toward the apex of the heart
Purkinje fibers carry the impulse to the heart apex and ventricular walls

28. Heart Physiology: Sequence of Excitation

29. Heart Excitation Related to ECG

30. Electrocardiography

31. Extrinsic Innervation of the Heart
Heart is stimulated by the sympathetic nervous system
Heart is inhibited by the parasympathetic nervous system

32. Cardiac Cycle
Cardiac cycle refers to all events associated with blood flow through the heart
Systole – contraction of heart muscle
Diastole – relaxation of heart muscle

33. Cardiac Output (CO)
Cardiac Output is the amount of blood pumped by each ventricle in one minute
CO is the product of heart rate (HR) and stroke volume (SV)
HR is the number of heart beats per minute
SV is the amount of blood pumped out by a ventricle with each beat

34. Cardiac Output: Example
CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)
CO = 5250 ml/min (5.25 L/min)

35. Frank-Starling Law of the Heart
Slow heartbeat and exercise increase venous return to the heart, increasing Stroke Volume
Blood loss and extremely rapid heartbeat decrease Stroke Volume

36. Regulation of Heart Rate
Sympathetic nervous system (SNS) stimulation is activated by stress, anxiety, excitement, or exercise
SNS speeds up heart rate
Parasympathetic nervous system (PNS) stimulation is mediated by acetylcholine and opposes the SNS
PNS slows heart rate

37. Regulation of Heart Rate
Chronotropic factors are those that change heart rate
Positive chronotropic factors increase heart rate
Example: Caffeine
Negative chronotropic factors decrease heart rate
Example: Sedatives