SEMESTER-II
HP-103C
Paper-3 (Theory)
Total Mark = 100 (IA = 40 + ESE = 60) Credit = 04
UNIT I (CARDIOVASCULAR SYSTEM-I)
General anatomy of Heart
❖ LOCATION:
• In the Thoracic cavity.
• Between Lungs.
• Slightly left of the sternum (Breast
bone).
• Rests on Diaphragm.
• Enclosed within Pericardium (Double-
walled sac).
• Approximately from 4th to 9th
Thoracic vertebrae.
❖ ORIENTATION:
• Its triangular superior border, tilted
towards the right and backwards
(Base).
• And it lower narrower portion, tilted towards the left and forwards (Apex).
❖ SHAPE: Pinecone (Broad at the superior surface or base and tapering to the apex).
1|Page
,❖ DIMENTION (SIZE):
• Length: 12 cm
• Width: 8 cm
• Thickness: 6 cm
• In general size of fist.
❖ SURFACES OF HEART: 5 surfaces in all, viz. :
• Base- Posterior Surface; Formed by LEFT ATRIUM.
• Diaphragmatic surface- Inferior Surface; Formed by RIGHT VENTRICLE.
• Sternocostal surface- Anterior Surface; Formed by RIGHT VENTRICLE.
• Left Pulmonary surface- Lateral Left Surface; Formed by LEFT VENTRICLE.
• Right Pulmonary surface- Lateral Right Surface; Formed by RIGHT VENTRICLE.
❖ WALL OF HEART: Wall of heart is made up of 3 layers.
• Epicardium (Outermost) = Simple Squamous epithelium.
• Myocardium (Middle) = Striated but involuntary Cardiac muscles (Thickest layer).
• Endocardium (Innermost) = Simple Squamous epithelium.
❖ COVERING OF HEART: The pericardium, also known as the pericardial sac, is a double-
layered connective tissue membrane that surrounds the heart and the great vessels and
protects the same.
i) Fibrous pericardium: The outermost layer, made of thick connective tissue.
ii) Serous pericardium: The inner layer, that is further divided into two layers:
• Parietal pericardium: The outer layer of the serous pericardium that’s
fused to fibrous pericardium. It is thin and semi-transparent.
• Visceral pericardium/Epicardium: The innermost layer of the pericardium
that directly covers the heart and great vessels.
➢ The space between the two layers of the serous pericardium is
called the pericardial cavity, which contains a small amount of
serous fluid or pericardial fluid. This oily fluid helps to reduce
friction between the layers and thus protects the heart.
2|Page
,1. What are the various properties of Cardiac muscles?
Ans: The various properties of cardiac muscles may be listed as below:
a) Electrical properties:
i) Auto-rhythmicity: Auto-rhythmicity is the ability of a tissue, to produce its
own impulse regularly. It is present in all the tissues of heart. The heart
continues to beat for quite some time, even if it is cut into pieces.
ii) Conductivity: Human heart, has a specialized conductive system, through which,
the repetitive electrical impulses from the natural pace-maker, the SA node, are
transmitted to all other parts of heart.
iii) Excitability: It is defined as the ability of a living tissue, to give respond to a
stimulus. In all the tissues, initial response, to any stimulus, is electrical activity,
in form of action potential.
b) Mechanical properties:
i) Contractility: The contractility is the ability of a tissue, to shorten in length,
after receiving a stimulus. Various factors affect this property of contraction in
cardiac muscle, that includes:
A. All or none law: According to all or none law, when a stimulus is applied-
whatever maybe the strength-the whole cardiac muscle, will either give
maximum response on it, or it will not give any response at all. This
property of cardiac muscle is called as the all or none law.
B. Stair-case Phenomenon: The Bowditch effect, or staircase
phenomenon is the intrinsic property of the heart, to increase the
force of contraction in response to an increment in pacing rate.
C. Refractory period: The refractory period is the time, when a cardiac
muscle can’t respond to a second stimulus. The cardiac muscle has a
longer refractory period than skeletal muscle. This allows the cell to
fully contract before another electrical event can occur.
2. What are the Junctional tissues of the heart? Describe the origin and spread of impulse
through the heart with diagram.
Ans: The junctional tissues of the heart are specialized tissues, that play a crucial role in the
electrical conduction system of the heart. These tissues include, the sinoatrial (SA) node, the
internodal fibres, the atrioventricular (AV) node, the bundle of His, and the Purkinje fibres.
The pathway of transmission of impulse through the heart, can be summarized as below:
i) Origin at the Sinoatrial (SA) Node: The electrical impulse originates in the SA node,
that is located in the right upper corner of the Right Atrium of heart, just below the
Superior Venacava.
3|Page
, ii) Atrial Activation: The impulse spreads across the right and left atria, like concentric
waves and thus the P wave is recorded in ECG. It is to be noted, that the spread of
electrical impulse, through the SA node is very slow (0.05 m/s).
iii) Transmission to the Atrioventricular (AV) Node: The impulse then, can either travel to
the AV node, with a speed of around 1 m/s, or can directly reach the AV node through
internodal fibres.
iv) Delay at the AV Node: After the impulse reaches the AV node, there is a considerable
delay of 0.07 seconds to 0.1 seconds in transmission of impulse. The delay at the AV node,
ensures that the atria have ejected all the blood into the ventricles, before the ventricles
begin to contract.
v) Conduction through the Bundle of His: After the AV node, the impulse travels down the
Bundle of His, and then gets transmitted along the right and left branches of the bundle
of His, at a higher velocity of around 4-5 m/s. Passage of impulse through the bundle of
His and its branches is not recorded in the ECG.
vi) Purkinje Fibers Activation: Finally, the impulse reaches the Purkinje fibres, and also its
multiple ramifications, within the sub-endocardial surfaces of both ventricles.
vii) Conduction through Ventricular muscle: In human beings, the mid-portion of the
interventricular septum is activated normally in a left to right direction. The Purkinje
fibres arise more proximally, from the left bundle branch, than from the right bundle
branch and activates the left side of the septum initially. So, the contraction of the
ventricular muscle, begins at the left side of the interventricular septum. After mid-septal
activation from the left to the right direction, the impulse comes down the septum to the
apex of the heart, and the next portion of myocardium that is activated, is the antero-
septal region of the ventricular myocardium. The impulse then proceeds along the right and
left ventricular walls to the atrioventricular groove. Finally, the impulse travels from
endocardium to the epicardium perpendicularly, and thus the whole of the right and left
ventricular walls contract, producing the QRS complex in ECG.
Fig: Sinoatrial node and conductive system of the heart
4|Page
HP-103C
Paper-3 (Theory)
Total Mark = 100 (IA = 40 + ESE = 60) Credit = 04
UNIT I (CARDIOVASCULAR SYSTEM-I)
General anatomy of Heart
❖ LOCATION:
• In the Thoracic cavity.
• Between Lungs.
• Slightly left of the sternum (Breast
bone).
• Rests on Diaphragm.
• Enclosed within Pericardium (Double-
walled sac).
• Approximately from 4th to 9th
Thoracic vertebrae.
❖ ORIENTATION:
• Its triangular superior border, tilted
towards the right and backwards
(Base).
• And it lower narrower portion, tilted towards the left and forwards (Apex).
❖ SHAPE: Pinecone (Broad at the superior surface or base and tapering to the apex).
1|Page
,❖ DIMENTION (SIZE):
• Length: 12 cm
• Width: 8 cm
• Thickness: 6 cm
• In general size of fist.
❖ SURFACES OF HEART: 5 surfaces in all, viz. :
• Base- Posterior Surface; Formed by LEFT ATRIUM.
• Diaphragmatic surface- Inferior Surface; Formed by RIGHT VENTRICLE.
• Sternocostal surface- Anterior Surface; Formed by RIGHT VENTRICLE.
• Left Pulmonary surface- Lateral Left Surface; Formed by LEFT VENTRICLE.
• Right Pulmonary surface- Lateral Right Surface; Formed by RIGHT VENTRICLE.
❖ WALL OF HEART: Wall of heart is made up of 3 layers.
• Epicardium (Outermost) = Simple Squamous epithelium.
• Myocardium (Middle) = Striated but involuntary Cardiac muscles (Thickest layer).
• Endocardium (Innermost) = Simple Squamous epithelium.
❖ COVERING OF HEART: The pericardium, also known as the pericardial sac, is a double-
layered connective tissue membrane that surrounds the heart and the great vessels and
protects the same.
i) Fibrous pericardium: The outermost layer, made of thick connective tissue.
ii) Serous pericardium: The inner layer, that is further divided into two layers:
• Parietal pericardium: The outer layer of the serous pericardium that’s
fused to fibrous pericardium. It is thin and semi-transparent.
• Visceral pericardium/Epicardium: The innermost layer of the pericardium
that directly covers the heart and great vessels.
➢ The space between the two layers of the serous pericardium is
called the pericardial cavity, which contains a small amount of
serous fluid or pericardial fluid. This oily fluid helps to reduce
friction between the layers and thus protects the heart.
2|Page
,1. What are the various properties of Cardiac muscles?
Ans: The various properties of cardiac muscles may be listed as below:
a) Electrical properties:
i) Auto-rhythmicity: Auto-rhythmicity is the ability of a tissue, to produce its
own impulse regularly. It is present in all the tissues of heart. The heart
continues to beat for quite some time, even if it is cut into pieces.
ii) Conductivity: Human heart, has a specialized conductive system, through which,
the repetitive electrical impulses from the natural pace-maker, the SA node, are
transmitted to all other parts of heart.
iii) Excitability: It is defined as the ability of a living tissue, to give respond to a
stimulus. In all the tissues, initial response, to any stimulus, is electrical activity,
in form of action potential.
b) Mechanical properties:
i) Contractility: The contractility is the ability of a tissue, to shorten in length,
after receiving a stimulus. Various factors affect this property of contraction in
cardiac muscle, that includes:
A. All or none law: According to all or none law, when a stimulus is applied-
whatever maybe the strength-the whole cardiac muscle, will either give
maximum response on it, or it will not give any response at all. This
property of cardiac muscle is called as the all or none law.
B. Stair-case Phenomenon: The Bowditch effect, or staircase
phenomenon is the intrinsic property of the heart, to increase the
force of contraction in response to an increment in pacing rate.
C. Refractory period: The refractory period is the time, when a cardiac
muscle can’t respond to a second stimulus. The cardiac muscle has a
longer refractory period than skeletal muscle. This allows the cell to
fully contract before another electrical event can occur.
2. What are the Junctional tissues of the heart? Describe the origin and spread of impulse
through the heart with diagram.
Ans: The junctional tissues of the heart are specialized tissues, that play a crucial role in the
electrical conduction system of the heart. These tissues include, the sinoatrial (SA) node, the
internodal fibres, the atrioventricular (AV) node, the bundle of His, and the Purkinje fibres.
The pathway of transmission of impulse through the heart, can be summarized as below:
i) Origin at the Sinoatrial (SA) Node: The electrical impulse originates in the SA node,
that is located in the right upper corner of the Right Atrium of heart, just below the
Superior Venacava.
3|Page
, ii) Atrial Activation: The impulse spreads across the right and left atria, like concentric
waves and thus the P wave is recorded in ECG. It is to be noted, that the spread of
electrical impulse, through the SA node is very slow (0.05 m/s).
iii) Transmission to the Atrioventricular (AV) Node: The impulse then, can either travel to
the AV node, with a speed of around 1 m/s, or can directly reach the AV node through
internodal fibres.
iv) Delay at the AV Node: After the impulse reaches the AV node, there is a considerable
delay of 0.07 seconds to 0.1 seconds in transmission of impulse. The delay at the AV node,
ensures that the atria have ejected all the blood into the ventricles, before the ventricles
begin to contract.
v) Conduction through the Bundle of His: After the AV node, the impulse travels down the
Bundle of His, and then gets transmitted along the right and left branches of the bundle
of His, at a higher velocity of around 4-5 m/s. Passage of impulse through the bundle of
His and its branches is not recorded in the ECG.
vi) Purkinje Fibers Activation: Finally, the impulse reaches the Purkinje fibres, and also its
multiple ramifications, within the sub-endocardial surfaces of both ventricles.
vii) Conduction through Ventricular muscle: In human beings, the mid-portion of the
interventricular septum is activated normally in a left to right direction. The Purkinje
fibres arise more proximally, from the left bundle branch, than from the right bundle
branch and activates the left side of the septum initially. So, the contraction of the
ventricular muscle, begins at the left side of the interventricular septum. After mid-septal
activation from the left to the right direction, the impulse comes down the septum to the
apex of the heart, and the next portion of myocardium that is activated, is the antero-
septal region of the ventricular myocardium. The impulse then proceeds along the right and
left ventricular walls to the atrioventricular groove. Finally, the impulse travels from
endocardium to the epicardium perpendicularly, and thus the whole of the right and left
ventricular walls contract, producing the QRS complex in ECG.
Fig: Sinoatrial node and conductive system of the heart
4|Page
