Circulatory

System
Topic 1 Body Fluids and Its Basics
All living organisuns, ineuding uman beings have some kinds of fluids circulating in
their bodies. 'These luids have the ability to pick up substances and distribute them
to various parts of the body. This flow of fluid inside the body is known as
circulation.

Types of Fluids
There are three main types of body fluids found in human beings such as blood, tissue
fluid and lymph. These are described as follows
1. Blood
It is a fluid connective tissue which is found circulating inside the body. The blood
is bright red in colour with a pH of about 7.3-7.5, i.e. slightly alkaline in nature.
The blood is composed of following two main components:

Plasma
It is the liquid portion of the blood, slightly yellow in colour. It constitutes about
of
50-60% the total blood. Plasma mainly consists of water, proteins, inorganic salts
and other substances such as glucose, urea, hormones, etc.
Serum is the fluid that is left out liquid part when the fibrinogen protein are removed
fromm plasina.
Blood Corpuscles
The blood corpuscles are the cellular elements of the blood constituting about
45% of the blood. These includes erythrocytes (RBCs), leucocytes (WBCs) and
thrombocytes (platelcts).
(i) Erythrocytes (RBCs) They are the most abundant type of cells found in the
blood. RBCs are biconcave disc-like structures. They are extremely small in size
of about 7un, due to which they move easily through the capillaries in the body.
Mature RBCs are enucleated, i.e. they lack nucleus and endoplasmic reticulum
which makes them more flexible thus, increasing their surface area to volume
ratio for carrying more oxygen.
Circulatory System 59

They lack mitochondria which means that red cells cannot use oxygen Dy
themselves instead all the oxygen absorbed from the lungs is transported to a

other tissues.
RBCs are red in colour due to the presence of a red coloured pigment called
haemoglobin which acts as an oxygen carrier molecule. It has an iron
has
containing part called haem and a protein called globin. Haemoglobin
ability to combine readily with oxygen to form oxyhaemoglobin, an unstable
compound which readily gives up oxygen to the body tissues.
The average life span of a mature RBC is only 120 days after which it get
destroyed in the spleen (known as graveyard of RBCs).
Function Its major function is to carry and transport respiratory gases to the

tissues.
of
(i) Leucocytes (WBCs) These are the most active and motile constituents
blood. They differ from RBCs as they are nucleated (have nucleus) and lack
the coloured pigment (haemoglobin). WBCs are irregular in shape and are

generally short lived, i.e. only 12-14 days.

they have
Leucocytes also show the property of diapedesis, i. e. oozing out as

the ability to move out of capillaries into the tissues.

AWBC oozing out the blood vessel (diapedesis)

They are of following two major types:

called
(a) Granulocytes They have regularly lobed nucleus and are
granulated as. they contains numerous granules in their cytoplasmn.
on the
They are further divided. as neutrophil, basophil and eosinophil
basis of the dyes with which they are stained.
not granulated and are divided into
(b) Agranulocytes They are

lymphocytes and monocytes.

Different types of white blood cells (leucocytes) after staining

Two major
Cell type Distinguishing features Functions
categories
of WBCs
Nucleus with 3-4 lobes. Engulf bacteria.
Granular Neutrophils (62%)
Granules stain with neutral (phagocytosis)
dyes
Nucleus with 2 lobes. Engulf bacteria.
Eosinophils (2.3%)
(count increases Granules stain dark red with Secrete antitoxins, is
eosin (acid dye). associated with allergy.
during allergic
reactions
Nucleus large indistinctly Release chemicals
Basophils (0.4%)
lobed. Granules stain with (such as histamine) for
basic dyes, i.e. methylene blue. inflammation which
dilate blood vessels
Smallest type of WBC. Produce antibodies.
Agranular Lymphocytes (30%)
It has single large nucleus.

Monocytes (5.3%) Large kidney-shaped nucleus. Ingest germs.

Transform into macrophages
at the site of infection.
 Functions The major function of leucocytes is that they act as a defense
mechanism for body. They have the ability of phagocytosis (e.g. neutrophils
engulf the foreign particle mainly bacteria).
Some type of WBCs help in reducing inflammation caused by injury or trauma
(e.g. monocytes, neutrophils). WBCs also produce antibodies that help in
killing foreign particles or germs, e.g. lymphocytes.
(i) Thrombocytes (Blood platelets) They are minute oval or round, enucleated
structures found floating in the blood. Their life span is about 3-5 days and get
destroyed in the spleen alongwith RBCs.
Function Their main function is to help in clotting or coagulation of blood.
Blood Clotting
It is a mechanism of formation of a clot when an injury or trauma occurs. It has been
seen that when a blood vessel is cut during an injury, blood does not continue to flow
for a longer time, instead it stops flowing after sometime. If somebody fails to exhibit
this property of clotting, that person will continue to bleed when gets injured as
he/she may lack one or the other factor that normally control clotting of blood. This
can even lead to the death of that person. Blood clotting is a complex process which
involves a series of steps to get completed. These are as follows:
Injured tissue cells and plateltes releases thromboplastin (factor X)

Thromboplastin with the help of Ca2 (present in the plasma) converts

prothrombin (Ginactive) into thrombin (active)

Thrombin acts as an enzyme and along with Ca2 reacts with soluble fibrinogen
and convert it into fibrin (insoluble form), a solid substance that forms threads

These threads traps RBCs and finally form a clot

Blood Groups
There are two main types of blood grouping systems, i.e. ABO and Rh system. These
are described below:
(i) ABO System This is the most common system found in human beings
described by Karl Landsteiner.
According to this system, blood is classified into four main types, i.e. A, B, AB
and O blood groups. This grouping is mainly based on the type of antigens and
antibodies present on the surface of red blood corpuscles.
The representation of different antigens and antibodies are depicted in the
table given below:
Blood group Antigen present Antibody present
A A

B B C
ee.wu

AB and B

a and b
Blood Transfusion
It is a mechanism of injecting blood into the
body of the patients (undergoing
operation or any other injury) from a healthy person. The person who gives blood is
known as donor, while a person receiving blood from a healthy person is known as
recipient. A person with blood group "0' is known as universal donor (as it lacks
antigen) and can donate blood to the persons with any blood groups, i.e. A, B, AB
and O, while a person with blood group 'AB' is known as universal recipient (as it
has all known antigens) and can receive blood from every other blood groups, i.e. A,
B, AB and O.
But before transmitting blood from one
person to another, it is necessary to maten
the type of blood groups between the two, in order to avoid clumping of
blood or
it important to match the compatibility (matching) and
destruction ofRBCs. Thus, is
incompatability (mis-matching)
in AB0 blood system.
This can be easily understood by the table given below:

Summaryof ABO Blood Group Matching (Compatability)

Blood group of recipient
Blood group of donor B AB
A X

B
AB
O
(Universal donor) Universal recipient
(i) Rh System It is another type of blood group system found in human beings.
The blood of most people contain a unique factor known as Rh-factor (it was
named after it was first discovered in Rhesus monkey).
Rh-factor is based on the presence of an antigen on the surface of RBCs.
Thus, the person having Rh-antigen on their RBCs are called Rh-positive
(Rh +ve), while person who does not have Rh-antigen on their RBCs are called
Rh-negative (Rh-ve).
It is also necessary to test Rh-factor before transfusing blood as if a Rh +ve
blood is transfused into Rh -ve person, the recipient will develop an antibody
response for Rh-antigen. Due to which during second transfusion, the antibody
produced by first transfusion will cause a reaction with the transfused blood,
which may even cause death of that individual.

2. Tissue Fluid (Extracellular fluid)

During blood flow through the capillaries, plasma and leucocytes from the blood
gets leaked out through their walls and accumulates in the intercellular spaces.
This fluid is known as tissue fluid. Far off cells of the body which are not in contact
with capillaries, use or absorb Oq and other substances from this fluid and inturn
give off CO, and other wastes back to it. Net complete amount of tissue fluid enters
into the lymphatic vessels.

3. Lymph
Tissue fluid after entering the lymph vessels in known as lymph. It only flows in
lymphatic vessels and lymph organs.
Function Its major function is to supply O2, absorption of fats from intestine and
also acts as a defense mechanism.

Examination of a Blood Smear

A blood smear or a blood film can be easily prepared RBCs
Plasma. erythrocytes)
in the laboratory by following the common
procedure. After preparing the film, it is viewed
under the microscope
Blood WBCs
(leucocytes)
Note The slide must be dried before examining. Different platelets
Smear of human blood
components of blood, ie. RBCs, WBCs, blood
platelets, plasma, etc. all can be
observed in the slide.