of Blood Vascular System
- There is present an organic transporting system in the
organisms which is called 'Circulatory System'.
- 'Lymph' and 'blood' are the two
liquid media through which circulatory system works.
- The blood continuously flows from the heart to the
other organs and from there back to the heart. This flow is
described as 'circulation'.
- There are two main types of circulatory system namely 'open'
- Closed Circulation: The circulation of
blood in which blood flows through closed blood vessels is
called 'closed circulation'. Here the blood does not come in
direct contact with any open body cavity or space. It is found
in most of annelids like earthworm and in all vertebrates.
- The flow of blood in a closed circulatory system begins
from heart. The heart pumps out the blood into arteries.
Arteries give rise to arterial capillaries which further unite
with each other to form vein capillaries. The vein capillaries
unite to form veins which ultimately carry the blood back to the
- Significance of Closed Circulation:
Open Circulation: In this system,
the blood comes out in the open spaces in body called lacunae
and sinuses. It is found in leeches (annelids), arthropods like
prawns, crabs, insects, spiders. Most of the molluscs except
cephalopods show open circulatory system.
In prawns, the heart pumps out only oxygenated blood
thus the heart is arterial. In cockroach, the heart is
elongated, thick, tubular and 13
- More efficient system which regulates fast flow of
- It maintains proper pressure and unidirectional flow
- It prevents wastage of blood and maintains necessary blood
- It promotes efficient and speedy distribution and
exchange of metabolic products within the body.
and Pumping Action of Human Heart
- Position: Heart is a muscular, thick, reddish
brown organ present in medistinal space present in thoracic
cavity between two pleura. It is conical in shape having a size
of one's closed fist.
- The heart is protected by a sac called pericardium
which is double layered. Pericardial fluid is present between
the two layers which acts as a lubricant and absorbs the shocks
to protect heart.
- Internally, the heart comprises of four chambers,
namely, two auricles and two ventricles. Both auricles are
separated by interauricular septum which prevents mixing
of pure and impure blood.
- Right Auricle: Precaval
(superior vena cava) and Postcaval (inferior vena cava) are
the main veins which bring deoxygenated blood to the right
auricle. Right auricle opens in the right ventricle through
right auriculoventricular aperture which is guarded by tricuspid
It prevents the back flow of blood.
- Chordae tendinae are the whitish, elastic threads which
extend from tricuspid and bicuspid valve to the walls of
respective ventricles. They do not allow the valves to open
upwards when the ventricles contract and thus they prevent the
back flow of the blood.
- Left Auricle: It receives pure
blood from lungs brought by four pulmonary veins. The
left auricle opens in left ventricle by presence of an aperture
guarded by bicuspid valve which is also called mitral
valve. It prevents the back flow of blood with the help of
- Ventricles are thick walled as compared to auricles.
The left ventricle has much thicker wall because it pushes the
pure blood to all the body parts. The ventricles are separated
by interventricular septum.
- Right Ventricle: Pulmonary aorta
carries impure blood from right ventricle to the lungs for
purification. A semilunar valve is present at the base of
pulmonary aorta which prevents the back flow of blood.
- Cardiac Cycle is the period
between end of one heart beat to the
end of next beat. It is formed of three phases, namely, atrial
systole which takes 0.1 second, ventricular systole which
takes about 0.3 seconds and complete cardiac diastole which
takes about 0.4 seconds. Thus, cardiac cycle is completed in 0.8
- The auriculoventricular valves close rapidly to prevent
the back flow of blood from ventricles to auricles. This closing
of valves at the start of ventricular systole produces first
heart sound 'Lub' which is also called systolic sound.
Similarly, the rapid closing of semilunar valves at the
beginning of ventricular diastole produces second heart sound
called 'dup' which is also called diastolic sound.
- Stethoscope is an instrument used to hear the heart
sounds. The receiver of stethoscope is placed on the left side
of chest. Any change in the nature of heart sounds due to
defective valves is called murmur.
- In mammalian heart, the blood passes twice through the
heart to supply once to the body. It involves systemic
circulation and pulmonary circulation.
- In systemic circulation, blood completes its
circulation from left ventricle to right auricle through body
- In pulmonary circulation, blood completes its
circulation from right ventricle to left auricle through the
- The wave of contraction which starts in the aorta travels
down to the wall of the arteries and is called a pulse.
The pulse rate in a normal adult person is 72 per min. It may be
more in children.
- Heart beat is the rhythmic contraction and relaxation
of the heart to pump out and receive blood to and from the body
parts. (Initiation of heart beat is under the control of certain
- S. A. Node: i.e.,
Sinuauricular node is present in the right wall of right auricle
below the opening of superior vena cava. It is called pacemaker
because it is the first to originate the cardiac impulses.
- A. V. Node: i.e.,
Atrioventricular node is present in the right auricle near the
junction of interauricular and interventricular septum.
It produces the cardiac impulses which are conducted to the
muscles of ventricles through bundle of His and Purkinje fibres.
- The pressure exerted by blood on the wall of artery
when the blood flows through it is called 'arterial blood
- The heart is made up of cardiac muscles which carry out
the contraction and relaxation at a regular interval.
- The contraction of the muscle of the heart is called 'systole',
while its relaxation is called 'diastole'.
- During systolic period, the myocardial fibres undergo
maximum tightening and shortening. The blood pressure occurring
during the contraction of the heart is called 'systolic blood
pressure' which rises during excitement and falls during
- Normal systolic blood pressure is 120 mm Hg.
- The blood pressure occurring during relaxation of the
heart is called 'diastolic blood pressure'.
- During diastolic blood pressure, the muscle fibres of
the heart lengthen followed by its dilation and the cavities of
the heart get filled with blood.
- The normal blood pressure during diastole is about 80
- The difference between the systolic and diastolic
pressures is called pulse pressure which is 40 mm Hg.
- There are various factors which affect the arterial
blood pressure such as:
The blood pressure is measured by an instrument called 'Sphygmomanometer'.
Hypertension (High Blood Pressure): An abnormal
increase in blood pressure than the normal blood pressure is
called hypertension or high blood pressure.
Causes of Hypertension:
- Age: Blood pressure increases with the
- Elasticity of Blood Vessels: Blood pressure is
inversely proportional to the elasticity of the blood vessels.
Greater the elasticity of blood vessels, lesser is the blood
- Cardiac Output: The blood pumped
out from heart is called cardiac output. If cardiac output
increases, there is increase in blood pressure.
- Total Peripheral Resistance: The resistance
offered by the walls of blood vessels on blood affects the
blood pressure. Constriction of blood vessels increases the
Ill Effects of Hypertension:
- High consumption of salts.
- Inelasticity of arteries
- Tension, emotional stress
- Deposition of fatty substances on the inner walls of
Hypotension (Low Blood Pressure): An abnormal
decrease in blood pressure than the normal blood pressure is
called hypotension or low blood pressure.
The maximum and minimum blood pressure
of a person suffering from hypotension are less than the
normal values, i.e., 100 / 50 mm Hg.
Causes of Hypotension:
- People having high blood pressure are susceptible to
stroke, heart attacks.
- Kidney malfunctioning.
- Disorders of nervous system.
- Disorders of endocrine system.