1. The Cardiovascular System: The Heart: Part A18
The Cardiovascular System: The Heart: Part A

2. The Heart Beats over 100,000 times a day
Normal Resting Heart Rate 60 – 100 beats per minute (too slow bradycardia – too fast tachycardia)
Approximately the size of a fist
Location
In the mediastinum between second rib and fifth intercostal space
On the superior surface of diaphragm
Two-thirds to the left of the midsternal line
Anterior to the vertebral column, posterior to the sternum
Enclosed in pericardium, a double-walled sac

3. Midsternal line 2nd rib Sternum Diaphragm Point of maximal intensity
(PMI)
(a)
PMI generally found at 4th – 5th ICS at midclavicular line
Figure 18.1a

4. Superior Aorta vena cava Parietal pleura (cut) Pulmonary Left lung
trunk
Left lung
Pericardium
(cut)
Apex of
heart
Diaphragm
(c)
Figure 18.1c

5. Superficial fibrous pericardium
Protects, anchors, and prevents overfilling (overdistention)

6. Deep two-layered serous pericardium
Parietal layer lines the internal surface of the fibrous pericardium
Visceral layer (epicardium) on external surface of the heart
Separated by fluid-filled pericardial cavity (decreases friction)

7. Pulmonary Fibrous pericardium trunk Parietal layer of
serous pericardium
Pericardium
Pericardial cavity
Myocardium
Epicardium
(visceral layer
of serous
pericardium)
Heart
wall
Myocardium
Endocardium
Heart chamber
Figure 18.2

8. Layers of the Heart Wall
Epicardium—visceral layer of the serous pericardium

9. Layers of the Heart Wall
Myocardium
Spiral bundles of cardiac muscle cells
Fibrous skeleton of the heart: crisscrossing, interlacing layer of connective tissue
Anchors cardiac muscle fibers
Supports great vessels and valves
Limits spread of action potentials to specific paths

10. Layers of the Heart Wall
Endocardium is continuous with endothelial lining of blood vessels

11. Pulmonary Fibrous pericardium trunk Parietal layer of
serous pericardium
Pericardium
Pericardial cavity
Myocardium
Epicardium
(visceral layer
of serous
pericardium)
Heart
wall
Myocardium
Endocardium
Heart chamber
Figure 18.2

12. Cardiac
muscle
bundles
Figure 18.3

13. Chambers Four chambers Two atria
Separated internally by the interatrial septum
Coronary sulcus (atrioventricular groove) encircles the junction of the atria and ventricles
Auricles increase atrial volume

14. Chambers Two ventricles Separated by the interventricular septum
Anterior and posterior interventricular sulci mark the position of the septum externally

15. Brachiocephalic trunk Left subclavian artery Superior vena cava
Left common carotid
artery
Brachiocephalic trunk
Left subclavian artery
Superior vena cava
Aortic arch
Ligamentum arteriosum
Right pulmonary
artery
Left pulmonary artery
Ascending aorta
Left pulmonary veins
Pulmonary trunk
Right pulmonary
veins
Auricle of
left atrium
Circumflex artery
Right atrium
Left coronary artery
(in coronary sulcus)
Right coronary artery
(in coronary sulcus)
Anterior cardiac vein
Left ventricle
Right ventricle
Great cardiac vein
Right marginal artery
Anterior interventricular
artery (in anterior
interventricular sulcus)
Small cardiac vein
Inferior vena cava
Apex
(b) Anterior view
Figure 18.4b

16. Atria: The Receiving Chambers
Walls are ridged by pectinate muscles
Vessels entering right atrium
Superior vena cava
Inferior vena cava
Coronary sinus
Vessels entering left atrium
Right and left pulmonary veins

17. Ventricles: The Discharging Chambers
Walls are ridged by trabeculae carneae
Papillary muscles project into the ventricular cavities
Vessel leaving the right ventricle
Pulmonary trunk
Vessel leaving the left ventricle
Aorta

18. Aorta Left pulmonary artery Superior vena cava Right pulmonary artery
Left atrium
Left pulmonary
veins
Pulmonary trunk
Right atrium
Mitral (bicuspid)
valve
Right pulmonary
veins
Fossa ovalis
Aortic valve
Pectinate muscles
Pulmonary valve
Tricuspid valve
Left ventricle
Right ventricle
Papillary muscle
Chordae tendineae
Interventricular
septum
Trabeculae carneae
Epicardium
Inferior vena cava
Myocardium
Endocardium
(e) Frontal section
Figure 18.4e

19. Pathway of Blood Through the Heart
The heart is two side-by-side pumps
Right side is the pump for the pulmonary circuit
Vessels that carry blood to and from the lungs
Left side is the pump for the systemic circuit
Vessels that carry the blood to and from all body tissues

20. Capillary beds of lungs where gas exchange occurs Pulmonary Circuit
Pulmonary veins
Pulmonary arteries
Aorta and branches
Venae cavae
Left atrium
Left ventricle
Right atrium
Heart
Right ventricle
Systemic
Circuit
Oxygen-rich,
CO2-poor blood
Capillary beds of all
body tissues where
gas exchange occurs
Oxygen-poor,
CO2-rich blood
Figure 18.5

21. Pathway of Blood Through the Heart
Right atrium  tricuspid valve  right ventricle
Right ventricle  pulmonary semilunar valve  pulmonary trunk  pulmonary arteries  lungs
PLAY
Animation: Rotatable heart (sectioned)

22. Pathway of Blood Through the Heart
Lungs  pulmonary veins  left atrium
Left atrium  bicuspid valve  left ventricle
Left ventricle  aortic semilunar valve  aorta
Aorta  systemic circulation
PLAY
Animation: Rotatable heart (sectioned)

23. Pathway of Blood Through the Heart
Equal volumes of blood are pumped to the pulmonary and systemic circuits
Pulmonary circuit is a short, low-pressure circulation
Systemic circuit blood encounters much resistance in the long pathways
Anatomy of the ventricles reflects these differences

24. Left
ventricle
Right
ventricle
Interventricular
septum
Figure 18.6

25. Coronary Circulation
The functional blood supply to the heart muscle itself
Arterial supply varies considerably and contains many anastomoses (junctions) among branches
Collateral routes provide additional routes for blood delivery

26. Coronary Circulation Arteries Veins
Right and left coronary (in atrioventricular groove), marginal, circumflex, and anterior interventricular arteries
Veins
Small cardiac, anterior cardiac, and great cardiac veins

27. (a) The major coronary arteries
Aorta
Pulmonary
trunk
Superior
vena cava
Left atrium
Anastomosis
(junction of
vessels)
Left
coronary
artery
Right
atrium
Circumflex
artery
Right
coronary
artery
Left
ventricle
Right
ventricle
Anterior
interventricular
artery
Right
marginal
artery
Posterior
interventricular
artery
(a) The major coronary arteries
Figure 18.7a

28. (b) The major cardiac veins
Superior
vena cava
Great
cardiac
vein
Anterior
cardiac
veins
Coronary
sinus
Small cardiac vein
Middle cardiac vein
(b) The major cardiac veins
Figure 18.7b

29. Right pulmonary artery
Aorta
Superior vena cava
Left pulmonary
artery
Right pulmonary artery
Right pulmonary veins
Left pulmonary
veins
Auricle of left
atrium
Right atrium
Left atrium
Inferior vena cava
Great cardiac
vein
Coronary sinus
Right coronary artery
(in coronary sulcus)
Posterior vein
of left ventricle
Posterior
interventricular
artery (in posterior
interventricular sulcus)
Left ventricle
Apex
Middle cardiac vein
Right ventricle
(d) Posterior surface view
Figure 18.4d

30. Homeostatic Imbalances
Angina pectoris
Thoracic pain caused by a fleeting deficiency in blood delivery to the myocardium
Cells are weakened
Myocardial infarction (heart attack)
Prolonged coronary blockage
Areas of cell death are repaired with noncontractile scar tissue

31. Heart Valves Ensure unidirectional blood flow through the heart
Atrioventricular (AV) valves
Prevent backflow into the atria when ventricles contract
Tricuspid valve (right)
Mitral valve (left)
Chordae tendineae anchor AV valve cusps to papillary muscles

32. Heart Valves Semilunar (SL) valves
Prevent backflow into the ventricles when ventricles relax
Aortic semilunar valve
Pulmonary semilunar valve

33. (right atrioventricular) valve Area of cutaway
Myocardium
Pulmonary valve
Aortic valve
Tricuspid
(right atrioventricular)
valve
Area of cutaway
Mitral valve
Tricuspid valve
Mitral
(left atrioventricular)
valve
Myocardium
Tricuspid
(right atrioventricular)
valve
Aortic
valve
Mitral
(left atrioventricular)
valve
Pulmonary
valve
Aortic valve
Pulmonary valve
Aortic valve
Pulmonary
valve
Area of cutaway
(b)
Fibrous
skeleton
Mitral valve
Tricuspid valve
(a)
Anterior
Figure 18.8a

34. (right atrioventricular) valve
Myocardium
Tricuspid
(right atrioventricular)
valve
Mitral
(left atrioventricular)
valve
Aortic
valve
Pulmonary
valve
Pulmonary valve
Aortic valve
Area of cutaway
(b)
Mitral valve
Tricuspid valve
Figure 18.8b

35. attached to tricuspid valve flap Papillary muscle
Pulmonary
valve
Aortic
valve
Area of
cutaway
Mitral
valve
Tricuspid
valve
Chordae tendineae
attached to tricuspid valve flap
Papillary
muscle
(c)
Figure 18.8c

36. Opening of inferior vena cava Mitral valve Chordae tendineae
Tricuspid valve
Myocardium
of right
ventricle
Myocardium
of left ventricle
Pulmonary
valve
Aortic valve
Area of
cutaway
Papillary
muscles
Mitral valve
Interventricular
septum
Tricuspid
valve
(d)
Figure 18.8d

37. heart fills atria, putting pressure against atrioventricular valves;
Blood returning to the
heart fills atria, putting
pressure against
atrioventricular valves;
atrioventricular valves are
forced open. 1
Direction of
blood flow
Atrium
Cusp of
atrioventricular
valve (open)
As ventricles fill,
atrioventricular valve flaps
hang limply into ventricles. 2
Chordae
tendineae
Atria contract, forcing
additional blood into ventricles. 3
Papillary
muscle
Ventricle
(a) AV valves open; atrial pressure greater than ventricular pressure
Atrium
Ventricles contract, forcing
blood against atrioventricular
valve cusps. 1
Cusps of
atrioventricular
valve (closed)
Atrioventricular valves
close. 2
Blood in
ventricle
Papillary muscles
contract and chordae
tendineae tighten,
preventing valve flaps
from everting into atria. 3
(b) AV valves closed; atrial pressure less than ventricular pressure
Figure 18.9

38. (a) Semilunar valves open
Aorta
Pulmonary
trunk
As ventricles
contract and
intraventricular
pressure rises,
blood is pushed up
against semilunar
valves, forcing them
open.
(a) Semilunar valves open
As ventricles relax
and intraventricular
pressure falls, blood
flows back from
arteries, filling the
cusps of semilunar
valves and forcing
them to close.
(b) Semilunar valves closed
Figure 18.10

39. Histology and Physiology of Cardiac Muscle

40. Requirements of Cardiac Muscle
Have considerable endurance – the heart beats over 100,000 beats per day (75 beats per minute x 1440 minutes in a day)
Both atria must contract as one unit and both ventricles must contract as one unit – even though they are made of separate individual small cells (cells can only get so big due to the surface to volume relationship problem)

41. Endurance
The cardiac muscle cells are smaller than skeletal muscle cells giving good surface to volume relationship- thus allowing more oxygen and nutrients to enter and waste to leave
More myoglobin – red substance akin to hemoglobin that holds reserve oxygen in the cell (more myoglobin than dark – endurance skeletal muscle)
Slow ATPase – the faster ATP is broken down the more energy that is loss as heat instead being put to good use. Thus the slower ATP is broken down to ADP – more useful energy that is harnessed.
Heart muscle uses almost exclusively aerobic metabolism (cannot tolerate too much ischemia)– but can burn lactic acid released by skeletal muscle
Lots of mitochondria

42. Cardiac Muscle must have better endurance than long endurance skeletal muscle

43. Cardiac Metabolism
The heart is so tuned to aerobic metabolism that it is unable to pump sufficiently in ischemic conditions. At basal metabolic rates, about 1% of energy is derived from anaerobic metabolism. This can increase to 10% under moderately hypoxic conditions, but, under more severe hypoxic conditions, not enough energy can be liberated by lactate production to sustain ventricular contractions.
Under basal aerobic conditions, 60% of energy comes from fat (free fatty acids and triglycerides), 35% from carbohydrates, and 5% from amino acids and ketone bodies. However, these proportions vary widely according to nutritional state. For example, during starvation, lactate can be recycled by the heart.

44. Atria and Ventricles Must act as single Units
It is essential that both atria must contract at the same time in order to adequately squeeze the blood into the two ventricles.
Likewise it is important for both ventricles to contract at the same time in order to adequately squeeze the both into their respective outflow pipes (pulmonary artery from right ventricle and aorta from left ventricle)
The problem is that the atria and ventricles must be comprised of several small cells and not one big cell for the atria and one for the ventricles – thus the individual cells must physiologically lock together to form a physiologic unit – syncytium.

45. Cardiac muscle cell mechanisms to form a syncytium
Cardiac muscle cells are branched – the anatomical feature allows the action potential signals to travel along several branches at the same time going to several cardiac muscle cells at the same time and those cells in turn branch doing the same thing.
Hook the cells together by gap junctions – the intercellular connection allows faster travel of impulses between the cells.

46. Microscopic Anatomy of Cardiac Muscle
Cardiac muscle cells are striated, short, fat, branched, and interconnected
Connective tissue matrix (endomysium) connects to the fibrous skeleton
T tubules are wide but less numerous; SR is simpler than in skeletal muscle (more dependence on extracellular calcium)
Numerous large mitochondria (25–35% of cell volume)

47. Table 9.3.1

48. Cardiac Muscle Cell Intercellular Connections
Intercalated discs: junctions between cells anchor cardiac cells
Desmosomes prevent cells from separating during contraction
Gap junctions allow ions to pass; electrically couple adjacent cells
Heart muscle behaves as a functional syncytium

49. Light microscope see intercalated discs In Electron Microscope
Nucleus
Intercalated discs
Cardiac muscle cell
Light microscope
see intercalated
discs
In Electron
Microscope
can resolute
Intercalated
Discs into
Gap junctions
And Desmosomes
Gap junctions
Desmosomes
(a)
Figure 18.11a

50. Cardiac muscle cell Mitochondrion Intercalated disc Nucleus T tubule
Sarcoplasmic
reticulum
Z disc
Nucleus
Sarcolemma
I band
I band
A band
(b)
Figure 18.11b