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BODY FLUIDS AND CIRCULATION
BODY FLUIDS AND CIRCULATION
Chapter Outline:
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Prerequisites
Learning objectives
Blood
Lymph (Tissue Fluid)
Circulatory Pathways
Double Circulation
Regulation of Cardiac Activity
Disorders of Circulatory System
Summary
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Prerequisites
Transport systems are present in the bodies of all the organisms and they are essential to keep the cells
alive & healthy. Failure of transport system would result in a disease.
Different groups of animals have evolved different methods for this transport. Simple organisms (sponges
& coelenterates) circulate water from their surroundings through their body cavities to facilitate the cells
to exchange these substances.
Complex organisms use special fluids within their bodies to transport such materials.
Blood: Is the most commonly used body fluid by most of the higher organisms. Another body fluid
lymph also helps in transport of certain substances.
Blood is the river of our life. It is the only tissues that flows throughout the body.
Blood is specialized body fluid that delivers necessary substances such as nutrients & CO2 to the cells
and transport metabolic waste product away from those same cells.
Functions of blood:
1. Blood supplies O2 to tissues.
2. Supply of nutrients like glucose, amino acids and fatty acids.
3. Removal of wastes – CO2, urea & lactic acid.
4. Immunological function – circulation of WBC and direction of foreign material by antibodies.
5. Coagulation which is part of body’s self repair mechanism.
6. Messenger function – includes transport of hormones.
7. Regulation of body pH.
8. Regulation of core body temperature
9. This wonderful tissues is easy to transfuse
Learning objectives
1. To know the importance of blood.
2. To understand the different kinds of blood groups.
3. To classify blood component.
4. To gain knowledge about the structure of heart & mechanism blood circulation.
5. To identify the disorder of circulation system.
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Blood
The study of blood is called Haematology. Blood is a fluid tissue having different types of cells. Each
of these cells has different functions. The cells called blood cells or blood corpuscles. The intercellular
fluid (fluid present in between the cells) is called plasma. In blood the volume of intercellular fluid is very
high. In blood, the cells are not attached to each other. These cells freely float in the blood & travel along
with blood to different tissues in the body. Infact blood is called “Fluid tissue of the body”. In an average
adult, there is about 5 litres of blood.
Blood
Blood Corpuscles
Plasma
Plasma
Plasma is a liquid part of the blood. It is straw colored
and clear. It is slightly alkaline in nature. It is the matrix
of the blood and constitutes 60% of the total volume.
About 85% - 90% of plasma is water. The chemical
capillaries
composition of plasma differs in different vertebrates.
These are organic & inorganic compounds in the
plasma.
Plasma
Inorganic components of blood plasma
Several inorganic salts are present in the plasma. These are Cl-, PO4, SO4, and HCO3- of Na+, K+, Ca++,
Mg++ & NH+4. The chlorides and bicarbonates of Na+ are the major salts present in the plasma. Minute
amount of Fe, P & I2 are also present in the plasma. The total salt content in the blood plasma is about
0.85-0.9%. Gases such as O2& CO2 are present in small amounts in the blood plasma. These gases
are in a dissolved state in the plasma.
Organic components of blood plasma
6-8% of plasma is represented by organic components. Sugars (glucose) amino acids, fatty acids, urea,
lipids & proteins are the major organic components of the plasma. Uric acid, vitamins & hormones occur
in minute amounts. Blood also contains a substance called HEPARIN which prevents the blood from
clotting in the blood vessels. There are different types of proteins in the blood plasma. They are
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Albumin
This is one of the major proteins in the blood plasma.
It helps in the transport of some substances and in
maintainance of osmotic pressure of the blood.
Globulins
Are of different types. They participate in transport
of substances, defence reaction of the body and in
Albumin
Globulins
maintainance of osmotic pressure.
Fibrinogen & Prothrombin
These blood proteins help in the clotting of blood, when
the blood vessel is injured. In addition to these proteins,
there are several enzymes in the blood plasma. Plasma
without clotting factors is called serum.
Cellular
components
Fibrinogen
Cellular components of blood
The cells are classified into 3 groups. Erythrocytes, Leucocytes & Platelets which are collectively called
formed elements & they constitute 45% of the blood.
Blood Corpuscles
Red Blood Corpuscles White Blood Corpuscles Blood Platelets
Granulocytes Acidophils
Basophils
Agranulocytes
Neutrophils
Lymphocytes Monocytes
Red blood cells
These are the most numerous cells in the blood. A healthy adult man has, on an average 5millions to
5.5 millions of RBC mm-3 of blood. The number of RBC is more in children than in adults. Each RBC is
circular & biconcave in its shape. Immature RBC has all the organelles. After maturation, organelles like
nucleus, mitochondria, lysosomes, Golgi complex, endoplasmic reticulum and ribosome etc. disappear
in RBC. Therefore mature RBC has only plasma membrane & cytoplasm. In some mammals such as
camel, RBC has a nucleus. In lower chordates like amphibians, RBC is nucleated & is large in size.
In adults RBC are formed only in the marrow of long bones while in embryonic stages they are formed
in the liver and spleen. The production of RBC is called ERYTHROPOIESIS.
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Red Blood Cells
Erythropoiesis
RBC live for 120 days in the blood. The old RBC are destroyed in spleen & to some extent in liver.
Therefore spleen is called “grave yard of RBC”. Every day about 10×1012 RBC are destroyed & the
same number of new blood cells are added to the blood.
RBC has HAEMOGLOBIN in their cytoplasm. The red color of RBC & of the blood is due to
the hemoglobin. This is made up of a protein – Globin, iron – Haem and organic molecule called
PORPHYRIN. Haemoglobin takes part in the transport of O2 and CO2. A healthy individual has 12 – 16
gms of haemoglobin in every 100ml of blood. RBC’s have an average life span of 120 days after which
they are destroyed in the spleen.
Leucocytes
These are also called (WBC) white blood cells or corpuscles. They do not have the pigment hemoglobin
and therefore colorless. They are less numerous than RBC & number average 6000-8000mm-3 of
blood. Their number increases under disease conditions. Leucocytes are short lived. The life span of
WBC is 12-13 days. New WBC is formed in the lymph nodes, spleen & thymus. Old WBC are destroyed
in the blood, liver & lymph.WBC move like amoeba and feed on the foreign germs that enter the body
therefore WBC are also called as phagocytes.
Leucocytes are of 2 major types
Leucocytes
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Granulocytes
These cells have different types of granules in the cytoplasm.
They are therefore called granulocytes (cytos= cell). The
nucleus in these cells is irregular in shape and has many
lobes. There are 3 different types of granulocytes- Acidophils,
Basophils & neutrophils.
Acidophils or eosinophils (2-3%)
Granulocytes
These cells can be stained with acidic dyes therefore they
are called acidophils.The nucleus of these cells has 2 lobes
which are connected by a bridge. The cytoplasm of these
cells has very large size granules. These cells attack the
parasites and also help to reduce the allergic reactions
in the body. The number of eosinophils increases during
allergy conditions. They also engulf the particles formed due
to antigen – antibody interactions and destroy toxins that
enter the body.
eosinophils
Basophils (0.5-1%)
These cells can be stained with basic dyes, therefore they
are called basophils. In these cells the nucleus is elongated
& in the shape of letter “S”. The granules in the cytoplasm
are round, large and are few in number. These cells are
phagocytic in nature and play a part in healing process.
Compared to all the WBC, these are few in number.
Basophils
Neutrophils (60-65%)
These cells can be stained with neutral days. Nucleus in
these cells has 5-6 lobes & cytoplasm has large number
of closely packed granules. These cells search & engulf
bacteria. They kill the bacteria inside the cytoplasm. These
are called microscopic policeman of the body. They are
called the body’s first line of defence against bacterial
infections. Compared to all types of WBC, they are present
in large number.
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Agranulocytes
As the name indicates, these cells do not have any granular
material in their cytoplasm.The nucleus in these cells is
large. There are 2 types of agranulocytes, Lymphocytes &
Monocytes.
Lymphocytes
These are the smallest cells of all the WBC. These cells
have thin layer of cytoplasm & a round large nucleus.
These cells recognize the antigens that enter the blood
and produce antibodies against them. These cells protect
the body against viral & fungal infections and also against a
few bacteria. These cells play a key role in the development
of immunity against a diseases. In the disease AIDS, these
cells are weakened and destroyed by the AIDS virus. As a
result, the resistance to other diseases is lost and a person
with AIDS becomes vulnerable to other infectious diseases.
Agranulocytes
Lymphocytes
Monocytes
They are biggest of all WBC. The nucleus is kidney shaped.
These cells invade the infected areas and kills bacteria.
They also remove dead bacteria, dead cells and other
foreign material present in the ‘injected’ area. They also play
an important role in developing immunity against disease.
Their number increases in leukemia (blood cancer).
Monocytes
Blood platelets: (thrombocytes)
These are oval or round or biconvex in shape. Platelets do
not have nucleus but have cytoplasm. These cells play an
important role in the clotting of blood. When the blood vessel
is injured, the platelets collect at the site of the injury and
form a plug. This reduces the loss of blood to some extent.
They also release several factors into the blood which help in
blood clotting and in the repair and healing of blood vessels.
Blood normally contain 1, 500, 00-3, 500, 00 platelets mm-3.
A reduction in their number can lead to clotting disorders
which will lead to excessive loss of blood from the body.
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Blood platelets
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Number of cells in one ml of blood
90,00,000
Total WBC
Granulocytes
Eosinophils
Neutrophils
Basophils
2,75,000
54,00,000
35,000
Agranulocytes
Lymphocytes
Monocytes
27,50,000
5,40,000
Serum
Is a fluid portion of blood collected after blood is allowed to
clot. It is similar to plasma except some proteins & clotting
factors are absent in serum. Serum is also used for blood
transfusion.
Serum
Blood groups
Two groupings – ABO & Rh, are widely used all over the world.
Blood from one person to another person can be administered if the blood groups of both the people match.
Administering blood of one person to another person through the vein is called BLOOD TRANSFUSION.
Karl Landsteiner (1900) discovered that the blood samples collected from different people are mixed with each
other, only in some cases the RBC present in different blood samples interacted & formed clumps. This clumping
of blood cells is called AGGLUTINATION. If this happens in the blood vessels of a person, these clumps block
and prevent the blood flow leading to the death of a person who is receiving the blood. Based on these reactions,
Landsteiner classified blood into 3 groups. A fourth blood group was discovered later. Agglutination is not seen
if the blood samples of the same blood group are mixed whereas agglutination occurs if the blood samples of
different blood groups are mixed with each other. Agglutination of blood is due to antigen antibody reactions
between RBC and plasma of different blood groups. Antigens for blood groups are present on the membranes of
RBC and the antibodies for blood groups are present in the plasma. An interaction between these two lead to the
agglutination of RBC.
There are 2 types of antigens on the RBC – antigen “A” & antigen “B.” Similarly, there are 2types of antibodies in
the plasma of human beings. They are antibodies for “A” (anti A) and antibody for “B” (anti B).
Blood groups
Four blood groups have been recognised in human beings.
They are:
Blood groups
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BLOOD GROUPS “A”
Persons having this group will have antigen “A” on their
RBC and antibody “B” in their plasma.
Blood groups (A)
BLOOD GROUP “B”
Persons having this blood group will have antigen “B” on
their RBC and antibody “A” in their plasma.
BLOOD GROUP “AB”
Blood groups (B)
Persons having this blood group will have both antigen “A”
and antigen “B” on their blood cells but they do not have
both antibody “A” and antibody “B” in their plasma.
BLOOD GROUP “O”
Blood groups (AB)
Persons having this blood group will not have either antigen
“A” or antigen “B” on their RBC but have both antibody “A”
and antibody “B” in their plasma.
BLOOD GROUP ANTIGEN ON RBC
A
B
A&B
No antigens
A
B
AB
O
Blood groups (O)
ANTIBODY IN PLASMA
B
A
No antibodies
A&B
The patient receiving blood is called RECIPIENT and the person giving blood is called DONOR
E.g: Vijay & Ajay met with an accident & requires blood transfusion. Vijays blood group is “A” & Ajay’s
blood groups is “B”
BLOOD GROUP VIJAY
AJAY
ANTIGEN ON RBC
A
B
A
B
ANTIBODY IN PLASMA
B
A
If AJAY’s blood group is transfused into VIJAY, the anti bodies (anti B) Present in the plasma of Vijay’s blood react
with the antigen “B” present on RBC of Ajay’s blood. This leads to clumping of RBC of Ajay’s blood in the blood
vessels of Vijay which is fatal.
Blood group ‘B’ blood should not be transfused to Persons with blood group ‘A.’ similarly blood group “A” should
not be transfused to person with blood group ‘B.’ However if the required blood group is not available, “O” group
blood is given . The people with blood group “O” do not have antigens on their RBC. Hence there will not be any
clumping of RBC in the recipient.Therefore People with “O” blood group are called “Universal Donors”
People with “AB” blood group have no antibodies in their plasma, so their blood does not react with blood of other
blood groups. People with blood group “AB” can receive blood belonging to blood groups “A”, “B”,& “AB”.
.
. . People with “AB” blood groups are called “Universal Recipients.”
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Recipient blood
group
Donor blood
of group
A
A
Matches
B
Do Not match
AB
Do Not match
O
Matches
B
AB
Do Not match
Matches
Do Not match
Matches
O
Matches
Do Not match
Matches
Do Not match
Matches
Do Not match
Matches
Matches
NO CLOTTING – MATCHES
Clotting – No Match
Matching of blood groups
Donor blood
of group
Recipient
A
Blood Group
B
AB
O
A
B
AB
O
Rh grouping
Rh antigen similar to the one present in Rhesus monkeys
(hence Rh) is observed on the surface of RBC’s of majority
humans (80%) such individuals are called Rh positive (Rh
+ve) & those in whom this antigen is absent are called Rh
negative (Rh–ve).
Rh grouping
An Rh–ve person, if exposed to Rh+ve blood, will form specific antibodies against Rh antigens. Rh group should
also be matched before transfusions. A special case of Rh incompatibility (mismatching) has been observed from
Rh–ve blood of a pregnant mother with Rh+ve blood of the foetus. Rh antigens of the foetus do not get exposed to
Rh–ve blood of the mother in the first pregnancy as the two bloods are well separated by the placenta. However
during the delivery of the first child, there is possibility of exposure of the maternal blood to small amounts of Rh+ve
blood from the foetus. In such cases, the mother starts preparing antibodies against Rh in her blood. In case of
subsequent pregnancies, the Rh antibodies from the mother (Rh–ve) can leak into the blood of the foetus (Rh +ve)
and destroy the foetal RBCs. This could be fatal to the foetus or could cause severe anaemia and jaundice to the
body. This condition is called erythroblastosis foetalis.This can be avoided by administering anti Rh bodies to the
mother immediately after the delivery of the first child.
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When is blood transfusion done
Blood transfusion is recommended by doctors when a person looses large volumes of blood in a very short
period due to bleeding through external injuries that occur in accidents. Blood loss may also occur due to rupture
of internal organs. Severe burning of body, severe anaemia & during or after surgical operations. Loss of large
volumes of blood will affect several functions of the body & the person may die.
Who can donate blood ?
Any healthy person between 16 to 60 years age can donate blood. At the time of blood donation, that the donor
should not have any infectious disease, fever & they should be free from disease, such as hepatitis, leukaemia &
AIDS etc. Same person can donate blood once in 3 – 4 months period. Blood collected from the donor is stored
under sterile conditions in special places called BLOOD BANKS. It is prevented from clotting by adding sodium
citrate or heparin. Blood is stored for 3 weeks & if it not used within 3 weeks after collection it is discarded.
When a blood is taken out of the body immediately its formation is stimulated & within one week most of it is
added back.
Coagulation of blood Immediately after injury, blood flows for sometime & stops
bleeding later. This is due to blood clotting. Clot is observed
as dark reddish brown scum formed at the site of a cut. Clot
is formed as net work of threads called fibrins in which dead
& damaged formed elements of blood are trapped. Fibrins
are formed by the conversion of inactive fibrinogens in the
plasma by the enzyme thrombin. Thrombins are formed
from another inactive substance present in the plasma
called prothrombin. The reaction requires an enzyme
thrombokinase. Calcium ions plays an important role in
clotting.
Prothrombin Thrombokinase Thrombin
Fibrinogen thrombin Fibrin
(Inactive)
Coagulation of blood
Fibrin + RBC → Blood clot
An injury stimulates the platelets in the blood to release certain factors that activate the mechanism of coagulation.
Certain factors released by the tissues at the site of injury also can initiate coagulation.
Lymph (Tissue Fluid)
The word is derived from the name of the Roman deity of fresh water, Lympha.
Lymph is a clear to yellowish watery fluid which is found throughout the body. It circulates through body tissues
picking up fats, bacteria & other unwanted materials, filtering these substances out through lymphatic system. The
circulation of lymph through the body is an important part of immune system. This clear fluid contains WBC, known
as lymphocytes along with small concentration of RBC & Protein. The lymph circulates freely through the body
bathing cells in needed nutrients & O2 while it collects harmful materials for disposal E.g: Lymph acts as a milkman
of the body, dropping off fresh supplies and picking up discarded bottles for processing elsewhere.
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As lymph circulates, it is pulled into lymphatic system, an
extensive network of vessels & capillaries which is linked
to lymph nodes, Small nodes which act as filters to trap
unwanted substances in the lymph. Lymph nodes also
produce more WBC, refreshing the lymph before it is
pumped out of the lymphatic system & back into the blood.
You may have noticed that when you wear tight clothing
or circulation is otherwise impeded fluids build up, causing
Edema, which is painful. Edema happens when lymph
cannot circulate to pull these fluids out.
Lymph
Circulatory Pathways
The circulatory patterns are of 2 types
Open circulatory system
Blood is pumped by the heart passes through large vessels
into open spaces or body cavities called sinuses
e.g: Arthropods & molluscs.
Arthropods
Closed circulatory system
Blood pumped by the heart is always circulated through
closed network of blood vessels.
E.g: Annelids & chordata
All vertebrates have muscular chambered heart.
Molluscs
Fishes
2 Chambered heart with one auricle & one ventricle.
The heart pumps out deoxygenated blood which is oxygenated
by gills & supplied to body parts from where deoxygenated
blood is returned to the heart (single circulation).
Amphibians and reptiles except crocodiles 3chambered hearts.
Annelids
3 chambered hearts – 2 auricles & one ventricle .The left
atrium receives oxygenated blood from gills/ lungs/skin &
right atrium gets deoxygenated blood from other body parts.
However, they get mixed up in single ventricle which pumps
out mixed blood (incomplete double circulation).
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Chordata
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Birds & Mammals 4 Chambered heart – 2 auricles & 2 ventricles. Oxygenated
& Deoxygenated blood received by left & right atria passes
on to the ventricles of the same sides. The ventricles pump
it out without mixing i.e., two separate circulatory pathways,
hence double circulation.
HUMAN CIRCULATORY SYSTEM HEART: Is a hollow organ. It is situated slightly towards
the left side in the middle of the chest cavity, in between the
two lungs. It is made up of cardiac muscle. Heart is conical
in shape with apex facing downwards & the broad base
directed upwards. It is the size of the fist of the person. It is
protected on all sides by rib cage & by vertebral column on
the back side.
Heart of fish
Amphibian heart
Aorta
Vena cava
Pulmonary
Sino Atrial Node
Right Atrium
Left Atria
Atrio Ventricular Node
Bundle of HIS
Left Ventrcle
Inter Ventricular Septum
Apex
Chordae tendinae
Right ventricular
Amphibian Heart
Pericardium: Heart is enclosed in a double layered transparent thin sac called pericardium. The space between
the inner and outer is called pericardial space. It is filled with a fluid called pericardial fluid. Pericardium and
pericardial fluid protect the heart from physical shocks or blows.
The heart is internally divided in to 4 chambers. 2 small upper chambers called atria and 2 larger lower
chambers called ventricles. Internally these 4 chambers are separated by walls or septae. Right and left auricles are
separated by vertical Inter auricular septum. This is thin muscular wall, which prevents the mixing of deoxygenated
blood present in the right auricle with the oxygenated blood present in the left auricle.
Similarly a thick walled inter ventricular septum separates right and left ventricles. This prevents mixing of
deoxygenated blood in the right ventricle with oxygenated blood present in the left ventricle.
The auricles & ventricles of the same sides are also separated by a thick fibrous tissue called Auriculo ventricular
septum. Each of the septa is provided with an opening through which the 2 chambers are connected. The right
auricle opens in to right ventricle through right auriculo ventricular aperture, while left auricle opens in to left
ventricle through left auriculo ventricular aperture.
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Valves: The opening between the right atrium & right ventricle is guarded by a valve formed of 3 muscular flaps
or cusps, the tricuspid valve, where as a bicuspid valve guards the opening between the left atrium and left
ventricle. The openings of the right and left ventricles in to the pulmonary artery & the aorta are provided with semi
lunar valves. The valves in the heart allow the flow of blood only in one direction i.e., from atria → ventricles →
pulmonary artery. These valves prevent the backward flow. The valves are held in position by tough connective
tissue strands. These strands are called chordae tendinae.
The walls of the ventricles are thicker and muscular than those of auricles as the ventricles have to pump the blood
to various parts of the body. Among ventricles, the wall of left ventricle is thicker than the wall of right ventricle, as it
pumps blood to more distant parts of the body (fingers and toes) than the right ventricle. The right ventricle pumps
blood only to lungs which are very close to the heart.
Nodal tissue is a specialized cardiac musculature in the heart. A patch of this tissue present in right upper corner
of right atrium called Sino Atrial Node (SAN). Another mass of tissue is seen on lower left corner of right atrium
close to auriculo ventricular septum called Atrio Ventricular Node (AVN).
A bundle of nodal fibres, atrio ventricular bundle (A V bundle) continues from AVN which passes through atrio
ventricular septa to emerge on the top of inter ventricular septum and divides into right and left bundle. These
branches give rise to minute fibres throughout the ventricular musculature and are called purkinje fibres. These
fibres along with right and left bundles are known as bundle of HIS. The nodal musculature has the ability to
generate action potentials without any external stimuli. The SAN can generate the maximum number of action
potentials i.e. 70-75 min-1 and is responsible for initiating & maintaining the rhythmic contractile activity of the heart
therefore it is called pacemaker. Our heart normally beats 70-75 times in a minute (average =72 beat/min) .
Blood vessels
Large veins that bring blood to the heart are called vena cavae or caval veins. Very large arteries that carry blood
away from the heart are called Aortae (Aorta-sing).
Blood vessels that bring blood to heart
3 large veins bring blood from all parts of the body→ heart .
Superior vena cava – collects deoxygenated blood from upper parts.
Inferior vena cava – brings deoxygenated blood from lower parts.
Pulmonary vein – brings oxygenated blood from lungs → heart.
Veins brings deoxygenated blood from tissues →heart,
except pulmonary vein (oxygenated blood from lungs →heart).
CORONARY VEINS – bring deoxygenated blood from walls of heart → right auricle.
Blood vessels that carry blood away from heart
Heart receives oxygenated blood from lungs & pumps to various organs in the body through large aortae called
systemic aorta – which arises from left ventricle & carries blood to all parts of body except lungs.
Pulmonary Aorta originates in right ventricle. It divides into right & left pulmonary arteries – which carry blood to right & left lungs.
Arteries carry oxygenated blood to the tissue – except pulmonary artery which carries deoxygenated blood to the
lungs.
Coronary arteries
carry oxygenated blood to the heart.
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Cardiac cycle
The heart receives & pumps the blood for the heart to pump the blood. It has to contract and relax. Cardiac
muscles present in the heart is responsible for the contraction & relaxation of the heart. Heart beat represents one
contraction and one relaxation of the heart. The contraction phase is called as systole & the relaxation phase is
called as diastole. Both auricles and ventricles do not contract & relax at the same time.
To begin, all the 4 chambers of heart are in relaxed state i.e., diastole.
Tricuspid and bicuspid valves are open blood from pulmonary veins and vena cava flows into left & right ventricle
through left & right atria. Semilunar valves are closed.
SAN generates an action potential which stimulates both the atria to undergo simultaneous contraction – the
atrial systole. This increases the flow of blood into the ventricles by 30%. The action potential is conducted to the
ventricular side by the AVN & AV bundle from where the bundle of HIS transmits it through the entire ventricular
musculature. This causes the ventricular muscles to contract (ventricular system) & the atria undergoes relaxation
(diastole) coinciding with the ventricular systole. Ventricular systole increases the ventricular pressure causing
closure of tricuspid and bicuspid valves due to attempted back flow of blood into the atria. As the ventricular
pressure increases further, the semi lunar valves guarding the pulmonary artery and aorta are forced open,
allowing the blood in the ventricles to flow through these vessels into the circulatory pathways. The ventricles relax
(ventricular diastole) & the ventricular pressure falls causing the closure of semilunar valves which prevent the
back flow of blood into ventricles. As the ventricular pressure declines further, the tricuspid & bicuspid valves are
pushed open by the pressure in the atria exerted by the blood which was being emptied into them by the veins.
The blood now once again moves freely to the ventricles. The ventricles & atria are now again in a relaxed (joint
diastole) state. soon the SAN generates a new action potential & the events are repeated in the same sequence
& the process continues.
This sequential event in the heart which is cyclically repeated is called cardiac cycle & it consists of systole &
diastole of both the atria & ventricles. Many cardiac cycles are performed per minute. The duration of cardiac
cycle is 0.8 seconds. During cardiac cycle, each ventricle pumps out 70ml of blood which is called stroke
volume. The stroke volume x heart rate =cardiac output.
Therefore, cardiac output can be defined as the volume of blood pumped out by each ventricle per minute and
averages 5000ml or 5L in a healthy individual. The body has the ability to alter the stroke volume, heart rate &
there by the cardiac output. E.g: The cardiac output of an athlete will be much higher than that of an ordinary
man.
During each cardiac cycle 2 sounds are produced which can be heard by stethoscope. The first heart sound
(lub) is associated with closure of tricuspid & bicuspid valves where as the second heart sound (dub) is
associated with closure of semi lunar valves. These sounds are of clinical diagnostic significance.
Electrocardiograph: (ECG)
ECG is a graphical representation of the electrical activity of
the heart during cardiac cycle.
A patient is connected to the machine with electrical 3 leads
(one to each wrist & to the left ankle) that continuously
monitor the heart activity. For detailed evaluation of the hearts
function. Multiple leads are attached to the chest region.
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Electrocardiograph (1)
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Each peak in the ECG is identified with letter from P to T that
corresponds to a specific electrical activity of the heart.
P – Wave represents electrical excitation of the atria which
leads to the contraction of both the atria.
QRS – represents the depolarization of the ventricles
which initiates ventricular contraction .The contraction starts
shortly after Q and marks the beginning of the systole.
T – Wave represents the return of the ventricles from excited
to normal state. The end of T-wave marks the end of systole.
By counting the number of QRS- complex that occur in a
given time period, One can determine the heart beat rate
of in individual. ECG obtained from different individuals has
the same shape, any deviation from different individuals has
the same shape, any deviation from this shape indicates the
possible abnormality or disease. Hence it is of great clinical
significance.
Electrocardiograph (2)
Pulmonary Circuit
Double Circulation
Lung
Pulmonary
artery
The path in which the blood flows is called a circuit
There are 2 circuits for flow of blood.
1. Pulmonary circuit – between heart & lungs.
2 Systemic circuit – between heart & organs of body.
A heart that pumps blood into 2 circuits is called Double
circuit heart.
Pulmonary
vein
Left
atrium
Right
atrium
Aorta
Vena
cavae
Right
ventricle
Left
ventricle
Systemic Circuit
Double circulation
Pulmonary circuit or circulation
In this circuit,deoxygenated blood from organs of body is collected into the right auricle and then sent into right
ventricle . From right ventricle, blood is pumped to the lungs. In the lungs, the blood is oxygenated & the oxygenated
blood is returned to the left auricle by pulmonary veins.
Systemic circuit or circulation
In this circuit, oxygenated blood from the left auricle is pumped into the left ventricle. From left ventricle, blood is
pumped into systemic aorta. This aorta supplies blood to various organs in the body. The deoxygenated blood
from various organs is collected into inferior & superior vena cavae & finally into the right auricle.
The systemic circulation provides nutrients,O2 & other essential substances to the tissues & takes CO2 & other
harmful substances away for elimination.
A unique vascular connection exists between digestive tract & liver called Hepatic portal system. The hepatic
portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation.
A special coronary system of blood vessels is present in our body for circulation of blood to & from the cardiac
musculature.
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BODY FLUIDS AND CIRCULATION
Regulation of cardiac activity
Heart is regulated by specialized muscles (nodal tissue) hence the heart is Myogenic.
A special neural centre in the medulla oblongata can moderate the cardiac function through Autonomic Nervous
system. Neural signals through the sympathetic nerves can increase the rate of heart beat, the strength of
ventricular contraction & there by the cardiac output.
Parasympathetic neural signals decrease the rate of heart beat, speed of conduction of action potential & there
by the cardiac output.
Adrenal Medullary hormones also increase the cardiac output.
Disorders of circulatory system
HYPERTENSION (High Blood Pressure)
Hypertension is the term for blood pressure that is higher than normal (120/80). If repeated checks of B.P is
140/90 or higher, it shows hypertension. One of the reasons for this is the blocking of arteries by cholesterol.
If the level of the cholesterol raises in the blood, it gets deposited on the walls of arteries. Then the arteries become
narrow, stiff & loose their elasticity. When this happens, the arteries cannot exert their moderating influence on
B.P. As a result there will be a rise in B.P.The blood flowing in the arteries exerts on the walls of the arteries.
Constant stress & strain for a long time, improper functioning
of kidneys, smoking, and alcohol consumption are also the
reasons for hypertension. This condition, if not treated for a
long time, may also lead to other health problems and may
lead to the death of the person.
Diet control, moderate exercise, avoiding stress & strain,
smoking, alcohol consumption & taking appropriate
medicines will help to control this problem.
Hypertension
Coronary Artery Disease
Is referred to as Atherosclerosis, affects the vessels that
supply blood to the heart muscles. It is caused by deposition
of calcium, fat, cholesterol & fibrous tissues which makes
the lumen of arteries narrower.
Risk factors are smoking, family history, hypertension
obesity, diabetes, high alcohol consumption, lack of exercise
& stress.
Angina (Angina Pectoris) A symptom of acute chest pain appears when no enough
O2 is reaching the heart muscles. Angina can occur in men
& women of any age but it is more common among middle
aged & elderly. It occurs due to conditions that affect the
blood flow. It is not a disease. It is symptom of heart problem
(CAD)
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Coronary Artery Disease
Heart
Normal
artery
Blocked
artery
Plaque
Angina
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BODY FLUIDS AND CIRCULATION
Heart Failure
Heart failure means the state of heart when it is not pumping
blood effectively enough to meet the needs of the body.
It is sometimes called congestive heart failure because
congestion of the lungs is one of the main symptoms of
this disease. Heart failure is not the same as cardiac arrest
(when the heart stops beating) or a heart attack (when the
heart muscle is suddenly damaged by an inadequate blood
supply).
If blood supply to a portion of heart muscle is cut off entirely
or if energy demands of the heart become much greater
than its blood supply, a heart attack (injury to heart muscle)
may occur.
Heart failure
Summary
Blood is a fluid connective tissue which helps in transport of substances .Blood & lymph are the body fluids which
help in transportation. Blood comprises of plasma and corpuscles. Plasma is a liquid part of the blood containing
organic and inorganic components. Blood corpuscles are 3 types - RBC, WBC & Blood Platelets. WBC is of 2
types - Granulocytes & Agranulocytes. There are 3 different types of Granulocytes - Acidophils, Basophils and
Neutrophils. Agranulocytes are lymphocytes & monocytes. Blood of humans are grouped into A, B, AB & O based
on the presence or absence of two surface antigens A, B on RBC’s. Another blood grouping is done based on the
presence or absence of another antigen called Rhesus factor (Rh) on the surface of RBC’s.
All vertebrates & few invertebrates have closed circulatory system. Heart is a muscular pumping organ consisting
of 2 auricles & 2 ventricles. SAN generates action potentials & sets the pace of the activities of the heart, Hence
called pace maker. The action potential causes atria & then ventricles to undergo contraction (systole) followed
by relaxation (diastole). The systole forces blood to move -> atria -> ventricles -> pulmonary artery --> aorta.
The cardiac cycle is formed sequential events in the heart which is repeated cyclically. Healthy person shows 72
cycles/minute. ECG is a graphical representation of the electrical activity of the heart during cardiac cycle.
2 circulatory pathways - pulmonary & systemic are present hence double circulation.
Disorders of circulatory system are B.P, CAD, Angina and heart failure etc.
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