Cardiovascular System

 Cardiovascular system HAP 1 (B pharma)

v  Cardiovascular system includes heart and blood vessels.

v   Heart pumps blood into the blood vessels. Blood vessels circulate the blood throughout the body.

v   Blood transports nutrients and oxygen to the tissues and removes carbon dioxide and waste products from the tissues.

HEART

Ø  Heart is a muscular organ that pumps blood throughout the circulatory system.

Ø   It is situated in between two lungs in the mediastinum.

Ø   It is made up of four chambers, two atria and two ventricles.

Ø   The musculature of ventricles is thicker than that of atria. Force of contraction of heart depends upon the muscles.

HEART ANATOMY:

Heart is made up of three layers of tissues:

1. Outer pericardium

2. Middle myocardium

3. Inner endocardium.

v   PERICARDIUM

It is the outer covering of the heart, made up of two layers:

i. Outer parietal pericardium

ii. Inner visceral pericardium.

The space between the two layers is called pericardial cavity or pericardial space and it contains a thin film of fluid.

i. Outer Parietal Pericardium

Parietal pericardium forms a strong protective sac for the heart. It helps also to anchor the heart within the mediastinum.

ii. Inner Visceral Pericardium

Inner visceral pericardium lines the surface of myocardium. It is made up of flattened epithelial cells. This layer is also known as epicardium.

v  MYOCARDIUM

Myocardium is the middle layer of wall of the heart and it is formed by cardiac muscle fibers or cardiac myocytes. Myocardium forms the bulk of the heart and it is responsible for pumping action of the heart. Unlike skeletal muscle fibers, the cardiac muscle fibers are involuntary in nature.

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v  ENDOCARDIUM

Endocardium is the inner most layer of heart wall. It is a thin, smooth and glistening membrane. It is formed by a single layer of endothelial cells, lining the inner surface of the heart. Endocardium continues as endothelium of the blood vessels.

 

v  VALVES OF THE HEART

There are four valves in human heart. Two valves are in between atria and the ventricles called atrioventricular valves. Other two are the semilunar valves, placed at the opening of blood vessels arising from ventricles, namely systemic aorta and pulmonary artery.

Valves of the heart permit the flow of blood through heart in only

one direction.

Atrioventricular Valves

Left atrioventricular valve is otherwise known as mitral valve or bicuspid valve. It is formed by two valvular cusps or flaps.

Right atrioventricular valve is known as tricuspid valve and it is formed by three cusps.

Atrioventricular valves is attached to atrioventricular ring, which is the fibrous connection between the atria and ventricles. Cusps of the valves are attached to papillary muscles by means of chordae tendineae.

Papillary muscles arise from inner surface of the ventricles. Papillary muscles play an important role in closure of the cusps and in preventing the back flow of blood from ventricle to atria during ventricular contraction. Atrioventricular valves open only towards ventricles and prevent the backflow of blood into atria.

 

Semilunar Valves

Semilunar valves are present at the openings of systemic aorta and pulmonary artery and are known as aortic valve and pulmonary valve respectively.

Because of the half moon shape, these two valves are called semilunar valves. Semilunar valves are made up of three flaps.

Semilular valves open only towards the aorta and pulmonary artery and prevent the backflow of blood into the ventricles.

 

Ø  Right side of the heart has two chambers, right atrium and right ventricle.

Ø   Right atrium is a thin walled and low pressure chamber. It has got the pacemaker known as sinoatrial (SA) node that produces cardiac impulses and atrioventricular (AV) node that conducts the impulses to the ventricles.

Ø   Right atrium receives venous (deoxygenated) blood via two large veins:

1.       Superior vena cava that returns venous blood from the head, neck and upper limbs.

2.        Inferior vena cava that returns venous blood from lower parts of the body.

Ø  Right atrium communicates with right ventricle through tricuspid valve.

Ø  Wall of right ventricle is thick. Venous blood from the right atrium enters the right ventricle through this valve.

Ø  From the right ventricle, pulmonary artery arises. It carries the venous blood from right ventricle to lungs.

Ø  In the lungs, the deoxygenated blood is oxygenated.

Ø  Left side of the heart has two chambers, left atrium and left ventricle.

Ø   Left atrium is a thin walled and low pressure chamber.

Ø   It receives oxygenated blood from the lungs through pulmonary veins.. This is the only exception in the body, where an artery carries venous blood and vein carries the arterial blood.

Ø   Blood from left atrium enters the left ventricle through mitral valve (bicuspid valve). Wall of the left ventricle is very thick.

Ø   Left ventricle pumps the arterial blood to different parts of the body through systemic aorta.

Regulation of Heart Action

All the actions of heart are continuously regulated. It is essential for the heart to cope up with the needs of the body. All the actions are altered by stimulation of nerves supplying the heart or some hormones or hormonal substances secreted in the body.

Blood circulation:

Blood flows through two divisions of circulatory system:

1. Systemic circulation

       2. Pulmonary circulation.

 

SYSTEMIC CIRCULATION

Systemic circulation is otherwise known as greater circulation. Blood pumped from left ventricle passes through a series of blood vessels, arterial system and reaches the tissues.

Exchange of various substances between blood and the tissues occurs at the capillaries.

After exchange of materials, blood enters the venous system and returns to right atrium of the heart. From right atrium, blood enters the right ventricle.

Thus, through systemic circulation, oxygenated blood is supplied from heart to the tissues and venous blood returns to the heart from tissues.

 

PULMONARY CIRCULATION

Pulmonary circulation is otherwise called lesser circulation.

Blood is pumped from right ventricle to lungs through pulmonary artery.

Exchange of gases occurs between blood and alveoli of the lungs at pulmonary capillaries.

Oxygenated blood returns to left atrium through the pulmonary veins.

Thus, left side of the heart contains oxygenated or arterial blood and the right side of the heart contains deoxygenated or venous blood.

Hemodynamics

v  The circulatory system consists of the heart and an extensive branched system of vessels containing blood, whose primary function is the transport of oxygen, nutrients and other substances and heat throughout the body.

v   In medical contexts, the term “hemodynamics” often refers to basic measures of cardiovascular function, such as arterial pressure or cardiac output. Hemodynamics is concerned with the distribution of pressures and flows in the circulatory system.

v   In this context, “pressure” refers to hydrostatic pressure, equivalently can be considered as internal mechanical energy per unit volume. By pressurizing blood, the pumping heart provides it with this internal energy that is available to drive its motion through the circulation. 

Cardiac Cycle

Cardiac cycle is defined as the sequence of coordinated events taking place in the heart during each beat. Each heartbeat consists of two major periods called systole and diastole.

During systole, heart contracts and pumps the blood through arteries. During diastole, heart relaxes and blood is filled in the heart. All these changes are repeated during every heartbeat, in a cyclic manner.

Events of cardiac cycle are classified into two:

1. Atrial events

2. Ventricular events.

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When the heart beats at a normal rate of 72 beats/minute, duration of each cardiac cycle is about 0.8 second.

Cardiac Output

Cardiac output is a term used in cardiac physiology that describes the volume of blood being pumped by the heart, by the left and right ventricle, per unit time.

Heart rate (HR) or pulse rate is the number of heart beats per minute (bpm)

Stroke volume (SV) is the volume of blood pumped from the ventricle per beat

Cardiac output (CO) is the product of the heart rate (HR) and the stroke volume (SV), thus, CO = HR × SV.

Values for cardiac output are usually denoted as L/min. For a healthy person weighing 70 kg, the cardiac output at rest averages about 5 L/min; assuming a heart rate of 70 beats/min, the stroke volume would be approximately 70 ml.

Heart Sounds:

Heart sounds are the sounds produced by mechanical activities of heart during each cardiac cycle. Heart sounds are produced by:

1. Flow of blood through cardiac chambers

2. Contraction of cardiac muscle

3. Closure of valves of the heart.

Four heart sounds are produced during each cardiac cycle:

1. First heart sound

2. Second heart sound

3. Third heart sound

4. Fourth heart sound.

First and second heart sounds are called classical heart sounds and are heard by using the stethoscope. These two sounds are more prominent and resemble the spoken words ‘LUB, (or LUBB) and ‘DUBB’ (or DUP), respectively.

Blood Pressure:

Arteries carry blood from heart to other parts of the body. Each time heart beats, it pumps blood into the arteries. Blood pressure is the pressure of blood pushing against the walls of the arteries. A normal blood pressure level is less than 120/80 mmHg.

Systolic blood pressure (the first number) – indicates how much pressure blood is exerting against the artery walls when the heart beats.

Diastolic blood pressure (the second number) – indicates how much pressure blood is exerting against the artery walls while the heart is resting between beats.

Normal Cardiac Rhythm & Electrophysiology of Heart

Rhythmicity is the ability of a tissue to produce its own impulses regularly. It is also called autorhythmicity or self-excitation. heart has a specialized excitatory structure, from which the discharge of impulses is rapid. This specialized structure is called pacemaker. From here, the impulses spread to other parts through the specialized conductive system.

Pacemaker is the structure of heart from which the impulses for heartbeat are produced. It is formed by the pacemaker cells called P cells. In mammalian heart, the pacemaker is sinoatrial node (SA node). Mammalian heart has got a specialized conductive system, by which the impulses from SA node spreads to other parts of the heart.

Electrical Conduction in Heart

CONDUCTIVITY

Human heart has a specialized conductive system, through which impulses from SA node are transmitted to all other parts of the heart.

CONDUCTIVE SYSTEM IN HUMAN HEART

Conductive system of the heart is formed by the modified cardiac muscle fibers. These fibers are the specialized cells, which conduct the impulses rapidly from SA node to the ventricles. Conductive tissues of the heart are also called the junctional tissues.

Electrocardiography

Electrocardiography is the technique by which electrical activities of the heart are studied. The spread of excitation through myocardium produces local electrical potential. This low-intensity current flows through the body, which acts as a volume conductor. This current can be picked up from surface of the body by using suitable electrodes and recorded in the form of electrocardiogram. This technique was discovered by Dutch physiologist, Einthoven Willem, who is considered the father of electrocardiogram (ECG).

Electrocardiograph

Electrocardiograph is the instrument (machine) by which electrical activities of the heart are recorded.

Electrocardiogram

Electrocardiogram (ECG or EKG from electrokardiogram in Dutch) is the record or graphical registration of electrical activities of the heart, which occur prior to the onset of mechanical activities. It is the summed electrical activity of all cardiac muscle fibers recorded from surface of the body.

WAVES OF NORMAL ECG

Normal ECG consists of waves, complexes, intervals and segments. Waves of ECG recorded are considered as the typical waves. Normal electrocardiogram has the following waves, namely P, Q, R, S and T.

Major Complexes in ECG

1. ‘P’ wave, the atrial complex

2. ‘QRS’ complex, the initial ventricular complex

3. ‘T’ wave, the final ventricular complex

4. ‘QRST’, the ventricular complex.

 

Electrocardiogram is useful in determining and diagnosing the following:

1. Heart rate

2. Heart rhythm

3. Abnormal electrical conduction

4. Poor blood flow to heart muscle (ischemia)

5. Heart attack

6. Coronary artery disease

7. Hypertrophy of heart chambers.

 

DEFINITION OF PULSE:

A pulse represents the tactile arterial palpation of the cardiac cycle by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the neck, wrist, at the groin, behind the knee, near the ankle joint, and on foot.