The cardiac cycle consists of alternating periods of systole and diastole. During systole, the atria and ventricles contract to pump blood out of the heart. During diastole, the atria and ventricles relax and refill with blood. The cardiac cycle is regulated by the heart's intrinsic conduction system, which generates electrical impulses that cause coordinated contractions of the atria and ventricles. These electrical impulses can be recorded as an electrocardiogram (ECG), which maps the electrical activity of the heart to the different phases of the cardiac cycle.

1. P R E S E N T E D B Y
A N U S H K A V E R M A
A S S T . P R O F E S S O R , R A M A U N I V E R S I T Y ,
K A N P U R
Cardiovascular system
Functional anatomy of heart
Conducting system of heart
Cardiac cycle
ECG (Electrocardiogram)

2. Functional anatomy of heart
Conducting system of heart
Cardiac cycle
ECG (Electrocardiogram)

3. Circulatory Routes
 Systemic Circulation – blood flow from the L
ventricle to the body & back to the R atrium
 Pulmonary Circulation – blood flow from the R
ventricle to the lungs and back to the L atrium

4. Circulatory Routes

5. Circulatory Routes

6. Superior Vena Cava
Inferior Vena Cava
Right Atrium
Tricuspid Valve
Right Ventricle
Aorta
Pulmonary Artery
Lung Capillaries
Pulmonary Vein
Left Atrium
Mitral Valve
Left Ventricle
HEART
Blood
travels to
all parts of
the body
Aortic
Valve
Pulmonary
Valve
HEART LUNG
Blood enters heart
Pathway of Blood Through the Heart
O2 inhaled
CO2 exhaled
Pulmonary Artery
Note:
Blue represents deoxygenated blood
Red represents oxygenated blood

7. Cardiovascular System = circulatory system
 Cardiovascular System = circulatory system
Consists of:
 The Heart,
 Arteries,
 Veins,
 Capillaries

8. Heart
 Four chamber muscular organ
 Comparable to the size of a closed fist
 Located in the mediastinum
 Behind sternum
 Between 2nd and 6th ribs
 Between T5-T8
 Apex – base of heart
 Located at the 5th intercostal space

9. Heart

10. Coverings of the Heart

11. Coverings of the Heart
 Pericardium – loose fitting sac surrounding the
heart
 Fibrous pericardium – tough, loose-fitting, inelastic
 Serous pericardium
 Parietal layer: lines the inside of the fibrous pericardium
 Visceral layer: adheres to outside of the heart
 Pericardial space: between parietal and visceral layer
 Filled with 10-15mL of pericardial fluid
 Decreases friction

12. Walls of the Heart
 Epicardium – outer layer
 Epicardium = serous pericardium
 Myocardium – thick, contractile layer composed of cardiac
muscle cells
 Intercalated disks contain many gap junctions
 Allow cardiac muscle cells to function as a single unit 
syncytium
 Endocaridium – interior of cardiac wall
 Endothelial tissue
 Covers projections of myocardial tissue called trabeculae

13. Walls of the Heart

14. Cardiac Muscle
 Characteristics
 Striated
 Short branched cells
 Uninucleate
 Intercalated discs
 T-tubules larger and
over z-discs

15. Chambers of the Heart
 Atria – two superior chambers
 “Receiving chambers”
 Blood from veins enters atria
 Ventricles – two inferior chambers
 “pumping chambers”
 Thick muscular walls to increase force of pumping action
 Left > right
 Separated by interventricular septum

16. Valves of the Heart
 Permit blood flow in one direction during circulation
 Atrioventricular valves (AV valves)
 Also cuspid valves
 Between atria and ventricles
 Semilunar (SL valves)
Between R ventricle and
pulmonary arteries and
L ventricle and aorta

17. Atrioventricular Valves
 Tricuspid valve
 Between R atrium and ventricle
 3 flaps of endocardium
 Connected to ventricular
papillary muscle via
chordae tendinae
 Bicuspid valve
 Between L atrium and ventricle
 Also called mitral valve
 Two flaps of endocardium

18. Semilunar Valves
 Pulmonary semilunar valve
 Between R ventricle and pulmonary trunk
 Aorta semilunar valve
 Between L ventricle and aorta

19. Chambers & Valves
Trace the blood flow through the heart

20. Chambers & Valves
Trace the blood flow through the heart

21. Blood Supply to the Heart
 Right and left coronary arteries
 First branches of aorta
 Right coronary artery 
I. right marginal artery
II. posterior interventricular artery
 Left coronary artery 
I. circumflex artery
II. anterior interventricular artery
 Most of the blood goes to the L ventricle
 In 50% -70% of the population, the R coronary artery is
dominant

22. Types of Blood Vessels
 Artery – carries oxygenated blood away from the
heart( Except Pulmonary Artery)
 “distributors”
 Arteriole: small artery
 Pre-capillary sphincters: regulate the blood flow into
capillaries

23. Blood Supply to the Heart
 After traveling through the capillaries of the heart,
blood empties into the R atrium via the coronary
sinus

24. Types of Blood Vessels
 Vein – carries deoxygenated blood towards the heart
 Great ability to stretch (capacitance)
 Function as reservoirs: blood pools in the valves then is pushed
forward from the pumping pressure
 Venules: small vein

25. Types of Blood Vessels
 Capillaries – arterial system switches to venous
system
 “primary exchange vessels”
 Transport materials to and from the cells
 Speed of blood flow decreases to increase contact time
 Microcirculation: blood flow between arterioles, capillaries
and venules

26. Types of Blood Vessels

27. Structure of Blood Vessels
 Tunica adventitia - outermost layer
 Fibrous connective tissue
 Holds vessels open; prevents tearing of vessels walls during
body movements
 Larger in veins than arteries
 Tunica media – middle layer
 Smooth muscle and elastic CT
 Helps vessels constrict and dilate
 Larger in arteries

28. Structure of Blood Vessels
 Tunica intima – innermost layer
 Composed of endothelium
 Semilunar valves present in veins
 One cell thick in capillaries

29. Structure of Blood Vessels

30. Functional anatomy of heart
Conducting system of heart
Cardiac cycle
ECG (Electrocardiogram)

31. Components of the Conduction System
 Sinoatrial Node (Part I):
 located in back wall of the right atrium near the entrance of
vena cava
 initiates impulses 70-80 times per minute without any nerve
stimulation from brain
 establishes basic rhythm of the heartbeat
 called the pacemaker of the heart
 impulses move through atria causing the two atria to contract.
 at the same time, impulses reach the second part of the
conduction system

32. Components of the Conduction System
 Atrioventricular Node (Part II):
 located in the bottom of the right atrium near the septum
 cells in the AV node conduct impulses more slowly, so there is
a delay as impulses travel through the node
 this allows time for atria to finish contraction before ventricles
begin contracting

33. Atrioventricular Bundle
 A.K.A. “Bundle of His”
 From the AV node,
impulses travel through
to the right and left
bundle branches
 These branches extend to
the right and left sides of
the septum and bottom
of the heart.

34. Atrioventricular Bundle Continued….
 These branch a lot to form
the Purkinje fibers that
transmit the impulses to
the myocardium (muscle
tissue)
 The bundle of His, bundle
branches and Purkinje
fibers transmit quickly and
cause both ventricles to
contract at the same time
 Like a “phone tree”

35. Atrioventricular Bundle Continued….
 As the ventricles contract, blood is forced out
through the semilunar valves into the pulmonary
trunk and the aorta.
 After the ventricles complete their contraction phase,
they relax and the SA node initiates another impulse
to start another cardiac cycle.

37. Cardiac Cycle
 Cardiac cycle is the sequence of events as blood
enters the atria, leaves the ventricles and then starts
over.
 This is the Intrinsic Electrical Conduction System
 Influencing the rate (chronotropy & dromotropy) is
done by the sympathetic and parasympathetic
divisions of the ANS

38. Cardiac Cycle
 The electrical system gives rise to electrical changes
(depolarization/repolarization) that is transmitted
through isotonic body fluids and is recordable
 The ECG!
 A recording of electrical activity
 Can be mapped to the cardiac cycle

39. Cardiac Cycle
Phases
 Systole = period of contraction
 Diastole = period of relaxation
 Cardiac Cycle is alternating periods of systole and
diastole
 Phases of the cardiac cycle
1. Rest(late diastole)
 Both atria and ventricles in diastole
 Blood is filling both atria and ventricles due to low pressure conditions
2. Atrial Systole
 Completes ventricular filling
3. Isovolumetric Ventricular Contraction
 Increased pressure in the ventricles causes the AV valves to close…
why?
 Creates the first heart sound (lub)
 Atria go back to diastole
 No blood flow as semilunar valves are closed as well

40. Cardiac Cycle
Phases
4. Ventricular Ejection
 Intraventricular pressure overcomes aortic pressure
 Semilunar valves open
 Blood is ejected
5. Isovolumetric Ventricular Relaxation
 Intraventricular pressure drops below aortic pressure
 Semilunar valves close = second heart sound (dup)
 Pressure still hasn’t dropped enough to open AV valves so
volume remains same (isovolumetric)
Back to Atrial & Ventricular Diastole

41. Cardiac Cycle
Phases

42. Functional anatomy of heart
Conducting system of heart
Cardiac cycle
ECG (Electrocardiogram)

43. Cardiac Cycle(Putting it all together)