2. THE HEART
The heart is a chambered muscular organ that pumps
blood received from the veins into the arteries, and
maintains flow of blood through the entire circulatory
system.
It has roughly the size of closed fist.
It lies in the mediastinum behind sternum between 4th
and 8th thoracic vertebrae.
The weight of the heart is 225 to 300 gms in adults.
Heart is transverse in shape for children but it has
normal pyramidal shape in adults by 25 years.
6. LOCATION OF HEART
The human heart is located within the thoracic cavity,
medially between the lungs in the space known as the
mediastinum.
Within the mediastinum, the heart lies in its own
space called the pericardial cavity.
The base of the heart is located at the level of the
third costal cartilage.
The inferior tip of the heart, the apex, lies just to the
left of the sternum between the junction of the
fourth and fifth ribs.
7. Cont..
The slight deviation of the apex to the left is reflected
in a depression in the medial surface of the inferior
lobe of the left lung, called the cardiac notch.
8. COVERINGS OF HEART
The heart is surrounded by membrane called
Pericardium.
The pericardium lies within the middle mediastinum.
Its function is to restrict excessive movements of the
heart as a whole and to serve as a lubricated container
in which the different parts of the heart can contract.
11. LAYERS OF HEART WALL
Epicardium: The outer layer of the heart. The
term epicardium means “on the heart”. This is
the visceral layer of the pericardium called as
serous pericardium.
12. Cont..
Myocardium:
a. This is the thick, contractile, middle layer of the
heart.
b. They possess interconnected muscle cell junctions
called syncytium for the electrical
connections to work. It can pass an action
potential from fiber to fiber.
c. The interconnected muscle fibers also helps to hold
the high pressured blood strongly inside the heart.
d. Myocardium is damaged in case of MI and cardiac
arrest.
13. Cont..
Endocardium:
a. It is innermost layer of heart and made of endothelial
tissues.
b. It also cover the beam like projections of myocardial
tissue. These projections are called trabeculae
carneae and it helps to add force to the contraction of
heart.
c. Inward folds or pockets formed by the endocardium
and connective tissues are called valves (AV & SL) which
prevents the return flow of the blood. There are
tricuspid valves and bicuspid valves.
14.
15. CHAMBERS OF HEART
The heart consists of four chambers.
1. Right atrium: Two large veins deliver de-
oxygenated blood to the right atrium. The superior
vena cava carries blood from the upper body. The
inferior vena cava brings blood from the lower body.
Then the right atrium pumps the blood to right
ventricle.
2. Right ventricle: The lower right chamber pumps
the de-oxygenated blood to the lungs through the
pulmonary artery. The lungs reload blood with
oxygen.
16. Cont..
3. Left atrium: After the lungs fill blood with
oxygen, the pulmonary veins carry the blood
to the left atrium. This upper chamber pumps
the blood to left ventricle.
4. Left ventricle: The left ventricle is slightly
larger than the right. It pumps oxygen-rich
blood to the rest of body.
17. THE RIGHT ATRIUM
Right border of the heart.
It receives blood from three veins; superior
vena cava, inferior vena cava and coronary
sinus.
The valve between right atrium and right
ventricle is called tricuspid valve/right
atrioventricular valve. It is made of dense
cusps of connective tissue.
18.
19. THE RIGHT VENTRICLE
Receives blood from the right atrium through the
tricuspid valve .
The edges of the valve cusps are attached to chordae
tendineae which are, in turn, attached below to
papillary muscles.
The wall of the right ventricle is thicker than that of the
atria and contains a mass of muscular bundles known as
trabeculae carneae.
Blood flows through the valve and into the pulmonary
arteries via the pulmonary trunk to be oxygenated in the
lungs.
21. The Left Atrium
Receives oxygenated blood from four
pulmonary veins.
The walls are same thick as right atrium.
The mitral (bicuspid) / left
atrioventricular valve guards the passage
of blood from the left atrium to the left
ventricle.
23. The Left Ventricle
The wall of the left ventricle is thicker than the right
ventricle but the structure is similar. This is the thickest
chamber of the heart.
It forms the apex of the heart.
Like the right ventricle it also contains Trabeculae
carneae and chordae tendineae that anchor the cusps
to papillary muscles.
Blood pass from the aortic valve/semilunar valve into the
ascending aorta.
A branch of the ascending aorta called coronary artery
provides blood supply to the cardiac tissues.
25. The Heart Valves
Atrio-ventricular valves
Right AV (Tricuspid): Separates the right atrium from the
right ventricle. Prevents backflow into atrium.
Left AV (Bicuspid): Separates the left atrium from the left
ventricle. Prevents backflow into atrium.
Semi-lunar valves
Pulmonary valve: Separates the right ventricle from the
pulmonary arteries. Prevents backflow after ventricular
contraction.
Aortic valve: Separates the left ventricle from the aorta.
Prevents backflow after ventricular contraction.
26.
27.
28. Blood flow through the heart
The blood flow starts from right atrium.
Then it flows to right ventricle through atrio-ventricular /
tricuspid valve.
From right ventricle it flows through pulmonary
semilunar valves into the pulmonary artery and then to
pulmonary trunk.
The pulmonary trunk branches to form right and left
pulmonary artery for gas exchange at left and right lungs.
From lungs the oxygenated blood comes to left atrium
through pulmonary veins.
From left atrium blood flows through mitral valve/left
atrio-ventricular/bicuspid valve to left ventricle.
29. Cont..
From left ventricle blood is
pumped to aorta through aortic
valve then the supply goes to
different branches to different
parts of the body.
The venous drainage from
different parts of the body
brings deoxygenated blood back
to right atrium through inferior
vena cava and superior vena
cava.
32. Arterial Supply of the Heart
Myocardial cells receive blood
supply from coronary arteries both
right and left.
The closure of aortic valve during
ventricular relaxation prevents the
backflow of the blood and fills the
coronary artery.
The arterial supply of the heart is
provided by the right and left
coronary arteries, which arise from
the ascending aorta immediately
above the aortic valve.
33. Branches of Coronary Arteries
1. Right Coronary artery: Branches
Right marginal arteries.
Posterior descending artery
2. Left Coronary artery: Branches
Circumflex artery.
Left Marginal artery.
Left anterior descending artery
Diagonal branches
34.
35. Venous Drainage of the Heart
Most venous blood from
the coronary capillaries
drain into the coronary
sinus ,which lies in the
posterior part of the atrio-
ventricular groove .
Some veins do not enter
the sinus rather it drain the
venous blood directly into
right atrium with inferior
vena cava.
37. CARDIAC CONDUCTION SYSTEM
The cardiac conduction
system is a network of
specialized cardiac muscle cells
that initiate and transmit the
electrical impulses responsible
for the coordinated
contractions of each cardiac
cycle.
38. Cont..
Two types of cells control heartbeat:
Conducting cells carry the electric signals.
Muscle cells control heart’s contractions.
39. Components of the Cardiac
Conduction System
1. Sinoatrial node
2. Atrioventricular node
3. Atrioventricular bundle (bundle of His)
4. Purkinje fibres
40.
41. 1. Sinoatrial Node
Sinoatrial node is sometimes called as heart’s
natural pacemaker. It sends the electrical
impulses that start the heartbeat.
The SA node is in the upper part of heart’s
right atrium. It is at the edge of atrium near
superior vena cava.
42. 2. Atrioventricular Node
The atrio-ventricular node delays the SA
node’s electrical signal. It delays the signal by a
consistent amount of time (a fraction of a
second) each time.
The AV node is located in an area known as
the triangle of Koch. This is near the central
area of the heart.
43.
44. 3. Bundle of His
The bundle of His is also called the
atrioventricular bundle. It is a branch of fibers
(nerve cells) that extends from AV node.
This fiber bundle receives the electrical signal
from the AV node and carries it to the Purkinje
fibers.
The bundle of His runs down the length of the
interventricular septum.
45.
46. Cont..
The bundle of His has two branches:
Left bundle branch sends electrical signals
through the Purkinje fibers to left ventricle.
Right bundle branch sends electrical signals
through the Purkinje fibers to right ventricle.
47. 4. Purkinje Fibers
The Purkinje fibers are branches of specialized
nerve cells. They send electrical signals very
quickly to the right and left heart ventricles.
When the Purkinje fibers deliver electrical
signals to the ventricles, the ventricles
contract.
49. Conduction of Impulse in the Heart
Initiation of impulse: Impulse is generated in SA
node at a rate of 70-80/minute. Therefore SA
node is called as pacemaker of heart.
50. Cont..
Spread of impulse:
The wave of impulse spreads to both atria through
muscle tissues simultaneously causing them to
contract.
From SA node impulse passes to ventricles through
AV node.
Upon reaching the atrioventricular (AV) node, the
signal is delayed by 0.13 seconds.
This delay causes ventricles to contract after atrial
contraction is over.
51. Cont..
It is then conducted into the bundle of his, down the
interventricular septum.
The bundle branches and the Purkinje fibres spread
the wave impulses at fastest rate along the ventricles,
causing them to contract.
Impulse generation and transmission is an electrical
event whereas contraction and relaxation of heart
muscle are mechanical events.
Mechanical events always follow electrical events.
