1. Biology 212 Anatomy & Physiology I
The Heart

3. Heart:
Mass: g
Located in center of
thorax (mediastinum)
Anterior to vertebrae
Posterior to sternum &
2nd through 6th rib
Superior to diaphragm
Surrounded by lungs
All vessels, nerves, etc. enter or leave superior end ("base")

4. Layers of Heart:
(Outer Surface) Epicardium - Thin, connective tissue
Myocardium - Thick, cardiac muscle
(Inner Surface) Endocardium - Thin, connective tissue
Simple squamous epithelium
lines inner surface, next to blood

5. Myocardium: Cardiac Muscle
Cardiac myocytes have the
same arrangement of thin
myofibrils and thick myofibrils
as skeletal myocytes, forming
sarcomeres.
Although slightly different in arrangement, the transverse tubules and sarcoplasmic reticulum are the same.
Just like skeletal myocytes, contraction occurs when calcium ions are released from the sarcoplasmic reticulum, bind onto the thin myofilaments, and allow them to form cross-bridges with the thick myofilaments.

6. Myocardium: Cardiac Muscle
One significant difference:
Cardiac myocytes attached end-to-end by intercalated discs which contain both desmosomes (keep the cells from pulling apart) and gap junctions (allow ions to flow directly from one cell to the next).
We will return to that structure when we discuss contraction of cardiac myocytes

8. Heart surrounded by double-layered pericardium
Visceral Layer
Parietal Layer
Serous Pericardium
Visceral Layer
Parietal Layer
Heart
Pericardial
Cavity

9. Heart surrounded by double-layered pericardium
Fibrous Pericardium
Serous Pericardium
Visceral Layer
Parietal Layer
Heart
Pericardial
Cavity

10. Anterior View
Left Atrium
Right Atrium
Left Ventricle
Right Ventricle

12. Anterior View Aorta Superior Vena Cava Pulmonary Trunk
Inferior Vena Cava

13. Anterior View Left Atrioventricular Sulcus
Right Atrioventricular Sulcus
Anterior Interventricular Sulcus

14. Posterior View
Right Atrium
Left Atrium
Right Ventricle
Left Ventricle

15. Posterior View Left Atrioventricular Sulcus
Right Atrioventricular Sulcus
Posterior Interventricular Suclus

16. Posterior View Superior Vena Cava Aorta Pulmonary Arteries
Inferior Vena Cava
Pulmonary Veins

18. Left Coronary Artery
Circumflex Coronary Artery
Right Coronary Artery
Anterior Interventricular Coronary Artery
Marginal Coronary Artery

19. Circumflex Coronary Artery
Right Coronary Artery
Posterior Interventricular Coronary Artery

21. Anterior Cardiac Veins
Great Cardiac Vein
Small Cardiac Vein

22. Great Cardiac Vein
Small Cardiac Vein
Middle Cardiac Vein
Coronary Sinus

24. Valves of the Heart:
Right Atrioventricular Valve
(Tricuspid valve)
Right Atrium to Right Ventricle

25. Valves of the Heart:
Right Atrioventricular Valve
Pulmonary Valve
(Right semilunar valve)
Right Ventricle to
Pulmonary Trunk

26. Valves of the Heart:
Right Atrioventricular Valve
Pulmonary Valve
Left Atrioventricular Valve (Bicuspid or Mitral valve)
Left Atrium to Left Ventricle

27. Valves of the Heart:
Right Atrioventricular Valve
Pulmonary Valve
Left Atrioventricular Valve
Aortic Valve
(Left semilunar valve)
Left Ventricle to
Ascending Trunk

28. Valves of the Heart:
Right Atrioventricular Valve
Pulmonary Valve
Left Atrioventricular Valve
Aortic Valve
Note: There are no valves controlling movement of blood
a) From superior or inferior vena cavae into right atrium
b) From pulmonary veins into left atrium

30. Sinoatrial Node
Atrioventricular
Node
Atrioventricular
Bundle (of His)
Bundle Branches
Purkinje fibers

31. Just like skeletal myocytes, the contraction of cardiac myocytes is triggered by changes in the electrical charge (depolarization and repolarization) which moves along the plasma membrane (sarcolemma) as an action potential”.
However, the mechanism of that depolarization and repolarization is significantly different.

32. Recall:
Cardiac myocytes attached end-to-end by intercalated discs which contain gap junctions, allowing ions to flow directly from one cell to the next).

33. The starting point is essentially the same: the sarcolemma is polarized because there are many more positive ions (Na+ and Ca++) outside the myocyte than inside the myocyte (K+); and many more negative ions (proteins, chloride, nucleic acids, phosphates, etc) inside the cell.

34. Cardiac myocytes in the sinoatrial node (“pacemaker cells”) spontaneously depolarize:
1. Na+ constantly leaks into the cells followed by Ca++,
decreasing the voltage until threshold voltage is reached.
Ca++ channels then open and Ca++ floods into the cell
and depolarize it.

35. Cardiac myocytes in the sinoatrial node (“pacemaker cells”) spontaneously depolarize:
2. Na+ and Ca++ channels close as K+ channels open
and K+ floods out of the cell, repolarizing the membrane.
Pumps then return all of the ions to their original
positions.

36. Cardiac myocytes in the sinoatrial node (“pacemaker cells”) spontaneously depolarize:
3. Na+ leakage continues and starts another cycle.

37. Remember that cardiac myocytes are connected by intercalated discs which contain gap junctions allowing ions to flow directly from cell to cell.
Thus, when the myocytes of the sinoatrial node depolarize, they can pass that electrical signal directly to all of the cells with which they have intercalated discs, which can pass it on to other cells, which can pass it on to other cells …...

38. In these non-pacemaker cells, large amounts of Na+ flood into the cell as their channels open, followed by slower movement of Ca++, causing
rapid depolarization (”phase 0”).
Just after K+ channels open
to begin repolarization (phase 1),
additional Ca++ channels
open and dramatically slow
It down (phase 2).
Eventually, those Ca++ channels close. Large amounts of K+ leave the cell as their channels open, repolarizing the myocyte (phase 3).
All of these ion channels close and pumps turn on to return all of the ions to their original locations, so the membrane remains polarized (phase 4).

39. Contraction of the heart (or any one of its chambers) is Systole
Relaxation of the heart (or any one of its chambers) is Diastole
One systole followed by one diastole is one Cardiac Cycle

43. Flow of blood through the heart is controlled entirely by changes in pressure.
Blood always flows along its pressure gradient, from the area of higher pressure to an area of lower pressure.
The open or closed position of a valve depends entirely on the difference in pressure from one side to the other:
The higher pressure pushes the valve open or closed,

45. Assume the chambers of the heart and vessels have the following pressures:
Left ventricle = 115 mm Hg
Right ventricle = 5 mm Hg
Pulmonary trunk = 22 mm Hg
Superior vena cava = 2 mm Hg
Inferior vena cava = 2 mm Hg
Left atrium = 20 mm Hg
Right atrium = 10 mm Hg
Aorta = 125 mm Hg
Which valves of the heart will be open?
Which valves of the heart will be closed?

46. Terms to know:
Heart rate: The number of cardiac cycles per minute
End diastolic volume: Volume of blood in a ventricle at the
end of diastole, just before it begins systole.
End systolic volume: Volume of blood in a ventricle at the
end of systole, just before it begins diastole.
Stroke volume: Volume of blood ejected from a ventricle
during a single systole ( = ESV – EDV)
Cardiac Output: Volume of blood pumped by a ventricle
in one minute (= Heart rate) x (Stroke volume)
Cardiac Index: Volume of blood pumped by a ventricle per
minute per square meter of body surface

47. Given the following information:
a) Dr. Thompson's total blood volume is 5.8 liters
b) His heart ejects 75 ml of blood per contraction
c) His kidneys produce 320 ml of urine per hour
d) All of his wisdom teeth have been removed
e) His heart contracts 70 times per minute
f) His systolic blood pressure is 130 mmHg
g) His diastolic blood pressure is 80 mmHg
h) The pressure in his left ventricle changes between
1 mmHg and 133 mmHg during each cardiac cycle
Calculate his Heart Rate
Stroke Volume
Cardiac Output

48. Therefore: You can regulate your cardiac output, and
therefore your cardiac index, by:
a) Increasing or decreasing your heart rate
b) Increasing or decreasing your stroke volume
In fact: Your ventricles modify both heart rate and stroke
volume on a beat-by-beat basis.
This depends on how much the cardiac muscle cells are stretched during the preceding diastole, which itself depends on the volume of blood in the chamber
= Frank-Starling Law of Cardiac Contraction

49. Sympathetic stimulation increases heart
rate by increasing the frequency with which your sinoatrial node depolarizes.
Parasympathetic stimulation decreases heart rate by decreasing the frequency
with which your sinoatrial node depolarizes.
Increasing the end-diastolic volume and/or decreasing the end-systolic volume will increase stroke volume.
Decreasing the end-diastolic volume and/or increasing the end-systolic volume will decrease stroke volume.