1. The Heart

2. Heart

3. The Heart

4. Heart Slightly larger than the size of a fist Hollow, muscular organ
Contains 4 chambers
found in chest between lungs
surrounded by membrane called Pericardium
Pericardial space is fluid-filled to nourish and protect the heart.

5. Serous membrane
Continuous with
blood vessels

6. The Heart Wall Pericardium –outer layer surrounding heart
3 layers of the heart wall are:
Pericardium –outer layer surrounding heart
Myocardium – Middle layer
Endocardium – Inner layer
Between Pericardium and Myocardium
Pericardial cavity made up of 2 layers of serous membrane
Parietal layer
Visceral layer
Pericardial space is fluid-filled to
nourish and protect the heart.

7. Myocardial tissue Structure
Under the microscope, cardiac muscle is seen to consist of interlacing bundles of cardiac myocytes (muscle cells). Like skeletal muscle it is striated with narrow dark and light bands, due to the parallel arrangement of actin and myosin filaments that extend from end to end of each myocyte. However, cardiac myocytes are narrower and much shorter than skeletal muscle cells, being about 0.02 mm wide and 0.1 mm long, and are more rectangular than smooth muscle cells, which are normally spindle-shaped. They are often branched, and contain one nucleus but many mitochondria, which provide the energy required for contraction. A prominent and unique feature of cardiac muscle is the presence of irregularly-spaced dark bands between myocytes. These are known as intercalated discs, and are due to areas where the membranes of adjacent myocytes come very close together. The intercalated discs have two important functions: one is to ‘glue’ the myocytes together so that they do not pull apart when the heart contracts; the other is to allow an electrical connection between the cells, which, as we will see, is vital to the function of the heart as a whole. The electrical connection is made via special junctions (gap junctions) between adjoining myocytes, containing pores through which small ions and therefore electrical current can pass. As the myocytes are electrically connected, cardiac muscle is often referred to as a functional syncytium (continuous cellular material).

8. Cardiac Muscle
Cardiac muscle is seen to consist of interlacing bundles of cardiac myocytes (muscle cells).
It is striated due to the parallel arrangement of actin and myosin filaments that extend from end to end of each myocyte.
They contain one nucleus but many mitochondria, which provide the energy required for contraction.
Structure
Under the microscope, cardiac muscle is seen to consist of interlacing bundles of cardiac myocytes (muscle cells). Like skeletal muscle it is striated with narrow dark and light bands, due to the parallel arrangement of actin and myosin filaments that extend from end to end of each myocyte. However, cardiac myocytes are narrower and much shorter than skeletal muscle cells, being about 0.02 mm wide and 0.1 mm long, and are more rectangular than smooth muscle cells, which are normally spindle-shaped. They are often branched, and contain one nucleus but many mitochondria, which provide the energy required for contraction. A prominent and unique feature of cardiac muscle is the presence of irregularly-spaced dark bands between myocytes. These are known as intercalated discs, and are due to areas where the membranes of adjacent myocytes come very close together. The intercalated discs have two important functions: one is to ‘glue’ the myocytes together so that they do not pull apart when the heart contracts; the other is to allow an electrical connection between the cells, which, as we will see, is vital to the function of the heart as a whole. The electrical connection is made via special junctions (gap junctions) between adjoining myocytes, containing pores through which small ions and therefore electrical current can pass. As the myocytes are electrically connected, cardiac muscle is often referred to as a functional syncytium (continuous cellular material).

9. Myocardial Cells Interconnected by Gap Junctions

10. Cardiac Muscle Cell
The intercalated discs have two important functions to:
glue’ the myocytes together so that they do not pull apart when the heart contracts
allow an electrical connection between the cells, a vital to the function of the heart as a whole.
The electrical connection is made via special gap junctions between adjoining myocytes.
These are pores through which small ions and therefore electrical current can pass.
As the myocytes are electrically connected, cardiac muscle is often referred to as a functional syncytium.

11. Cardiac Muscle Cell
A unique feature of cardiac muscle is the presence of intercalated discs. The intercalated discs have two important functions to:
‘glue’ the myocytes together so that they do not pull apart when the heart contracts
allow an electrical connection between the cells, a vital to the function of the heart as a whole.
The electrical connection is made via special gap junctions between adjoining myocytes.
These are pores through which small ions and therefore electrical current can pass.
As the myocytes are electrically connected, cardiac muscle is often referred to as a functional syncytium.
Structure
Under the microscope, cardiac muscle is seen to consist of interlacing bundles of cardiac myocytes (muscle cells). Like skeletal muscle it is striated with narrow dark and light bands, due to the parallel arrangement of actin and myosin filaments that extend from end to end of each myocyte. However, cardiac myocytes are narrower and much shorter than skeletal muscle cells, being about 0.02 mm wide and 0.1 mm long, and are more rectangular than smooth muscle cells, which are normally spindle-shaped. They are often branched, and contain one nucleus but many mitochondria, which provide the energy required for contraction. A prominent and unique feature of cardiac muscle is the presence of irregularly-spaced dark bands between myocytes. These are known as intercalated discs, and are due to areas where the membranes of adjacent myocytes come very close together. The intercalated discs have two important functions: one is to ‘glue’ the myocytes together so that they do not pull apart when the heart contracts; the other is to allow an electrical connection between the cells, which, as we will see, is vital to the function of the heart as a whole. The electrical connection is made via special junctions (gap junctions) between adjoining myocytes, containing pores through which small ions and therefore electrical current can pass. As the myocytes are electrically connected, cardiac muscle is often referred to as a functional syncytium (continuous cellular material).

12. The Heart

13. Valves The Heart contains four valves
The Tricuspid valve opens from the R atrium into the R ventricle
The Pulmonary (semilunar) valve opens from the R ventricle into the pulmonary artery
The Mitral valve opens from the L atrium into the L ventricle
The Aortic (semilunar) valve opens from the L ventricle into the Aorta

14. The Heart: Valves Function of the valves
Situated at the entrance and exit of the ventricles
Ensure that blood moves only in one direction…Forward
Blood flows though the valves as a result of pressure changes

16. The Cardiac Cycle
Refers to the repeated pattern of contraction and relaxation of the heart
Phase of contraction is called systole,
Phase of relaxation is called diastole
The heart has a two step pumping action: the atria contract simultaneously, followed approx seconds later by the ventricles.

17. Cardiac Cycle Systole Contractile phase of heart
Electrical and mechanical changes
E.g. blood pressure changes
E.g. blood volume changes
Diastole
Relaxation phase of heart
Takes twice as long as systole
E.g. resting HR = 60
Systole = 0.3 s
Diastole = 0.6 s

18. The heart beat begins when the heart muscles relax and blood
Cardiac cycle
STEP ONE
blood from the body
blood from the lungs
The heart beat begins when the
heart muscles relax and blood
flows into the atria.

19. the valves open to allow blood into the ventricles.
Cardiac cycle
STEP TWO
The atria then contract and
the valves open to allow blood
into the ventricles.

20. The cycle then repeats itself.
Cardiac cycle
STEP THREE
The valves close to stop blood
flowing backwards.
The ventricles contract forcing
the blood to leave the heart.
At the same time, the atria are
relaxing and once again filling with
blood.
The cycle then repeats itself.

22. 5. Ventricles contract, about two thirds of the volume they contain is ejected, leaving one third called the end systolic volume
cycle
1. Atria fill with blood
4. Atria contract
Contributing approx 20%
To end diastolic volume
2.AV valve opens when
pressure in atria exceeds ventricle
3. Blood flows from atria
to ventricles through
open AV valve. This
contributes approx 80% of
end diastolic volume
The Cardiac cycle

23. Heart conduction

24. Electrical Activity of the Heart
Contraction of heart depends on electrical stimulation of myocardium
Impulse is initiated on right atrium and spreads throughout the heart
May be recorded on an ECG

25. Electrical Conduction System
Myocardial Cells
Characteristics
automaticity: cells can depolarize without any impulse from outside source (self-excitation)
excitability: cells can respond to an electrical stimulus
conductivity: cells can propagate the electrical impulse from cell to another
contractility: the specialized ability of the cardiac muscle cells to contract

26. The Hearts conduction pathway

27. Depolarization and Impulse Conduction
Heart is autorhythmic
Depolarization begins in sinoatrial (SA) node
Spread through atrial myocardium
Delay in atrioventricular (AV) node
24 Sept. 2008
EKG-Lab.ppt

28. Depolarization and Impulse Conduction
Spread from atrioventricular (AV) node
AV bundle
Bundle branches
Purkinje fibers
24 Sept. 2008
EKG-Lab.ppt

29. Electrocardiogram Records electrical activity of the heart P wave
Atrial depolarization
QRS complex
Ventricular depolarization
T wave
Ventricular repolarization

30. Electrical conduction
P Wave represents atrial depolarisation
QRS Wave represents ventricular depolarisation
T Wave represents Ventricular repolarisation

31. Cardiac blood flow
Cardiac blood flow is different from blood flow in other organs.
Blood flows around coronary vessels during diastole.
Myoglobin in myocardial cells stores oxygen.
This ensures that the heart muscle has a constant supply.

33. Cardiac output = stroke volume x heart rate
Refers to the amount of blood ejected from the left ventricle of the heart per minute
Determined by stroke volume and heart Rate
Cardiac output = stroke volume x heart rate  

34. Factors which influence blood pressure
Cardiac output (CO)
Total Peripheral Resistance (TPR) Or
BP =CO x TPR

35. Cardiac Output Range of normal at rest is 4 – 6 L.min
During aerobic activity the increase in cardiac output is roughly proportional to intensity.
Max. Q is in range of 20 – 40 L.min, depending on size, heredity, and conditioning.

36. Heart Rate Range of normal at rest is 50 – 100 b.m
Increases in proportion to exercise intensity
Max. HR is 220 – age
Medications or upper body exercise may change normal response

37. Factors affecting Heart Rate
Gender
Autonomic nerve activity
Age
Circulating hormones e.g adrenaline, thyroxine
Activity and exercise
Temperature
The baroreceptor reflex
Emotional states
Waugh and Grant (2006)

38. Stroke Volume Range of normal at rest is 60 – 100 ml.b
During exercise, SV increases quickly, reaching max. around 40% of VO2 max.
Max. SV is 120 – 200 ml.b, depending on size, heredity, and conditioning.
Increased SV during rhythmic aerobic exercise is due to complete filling of ventricles during diastole and/or complete emptying of ventricles during systole.

39. Cardiac blood supply
The heart receives its blood supply via the coronary arteries.
These arteries supply a huge network of capillaries
Ensures that myocardial cells are close to their blood supply
Diffusion of gases between the myocardial cells and capillaries occurs very quickly

40. Sympathetic parasympathetic
The heart is influenced by autonomic nerves originating in the cardiovascular centre in the medulla oblongata
Consisting of sympathetic and parasympathetic nerves with antagonistic
autonomic nerves
Sympathetic parasympathetic
Cardiac control center in medulla oblongata
maintains balance between the two

41. Parasympathetic: from medulla oblongata (vagus nerve)
Nerve branches to S-A and A-V nodes, and slows rate
Parasympathetic activity :
Can increase to slow heart rate
Can decrease to increase heart rate
Sympathetic nervous system (celiac plexus)
SA node,
AV node and the
myocardium of the atria and ventricles.
Sympathetic activity :
increases HR
force of contraction

42. Summary
The heart is a four chambered pump, which is effectively two pumps working together
The heart contains valves which function to ensure no backflow of blood
The wall of the heart is made up of the following layers: pericardium, myocardium, endocardium
The heart has ‘autorhythmicity’ it will beat without outside nervous input
The heart has a specialist conduction pathway- ensuring a smooth coordinated contraction,
Cardiac muscle contains large numbers of mitochondria, and the heart has an excellent blood supply