COMPOSITION OF HU-
MAN BLOOD.
Normal structure and function of vari-
ous blood components.
1] ERYTHROCYTES.
Red blood cells are also called erythrocytes. Erythrocytes develop from a type of
cell called the Reticulocytes. The erythrocytes consist of a biconcave shape, they
are very tiny cells being almost 7-8 micrometres in diameter and 2.5 micrometres in
thickness. They do not contain a nucleus, because of their small size there is a large
surface area to volume ratio providing more space for the exchange of substances
like carbon dioxide, oxygen, and other substances. Their cell membranes contain
specialized proteins called Spectrin and this makes the cell membrane flexible,
which helps it move through narrow blood vessels and other narrow spaces within
the body. They also do not contain any endoplasmic reticulum or mitochondria. The
main function of the red blood cells is the exchange and transportation of gases,
they transport oxygen from the heart to various other cells of our body and take up
the carbon dioxide from those cells and bring it back into the lungs through circula-
tion.
The red blood cells or erythrocytes contain haemoglobin which is a molecule made
up of four protein molecules called globin and these globin’s are alpha 1 and 2 and
Beta 1 and 2. Each globin has a heme molecule bound to it and the heme molecules
contain one ion of iron. And each iron molecule can hold on to one oxygen molecule
therefore one whole erythrocyte contains around 270 million haemoglobin mo-
lecules and so can carry around a billion oxygen molecules. When oxygen binds to
the haemoglobin we will now have oxyhaemoglobin and when it reaches cells that
require oxygen the affinity of haemoglobin will decrease which will then release the
bonded oxygen from the haemoglobin and so provide oxygen to the cells that need
it. The carbon dioxide from the other cells can bind with haemoglobin to form car-
baminohaemoglobin or get converted into bicarbonate or gets dissolved in the blood
and this will then take the carbon dioxide to the lungs where it is released for hav-
ing it removed from the body. The red blood cells have a life span of 120 days.
Red blood cells contain certain antigen structures which determine the bold type
for the specific individual. Normal Erythrocyte count for men is from 4.7 -6.1 million
,cells per microlitre, for women, it is from 4.2 – 5.4 million cells per microlitre while
in children it would range from 4.0 – 5.5 million cells per microlitre.
2] LEUKOCYTES.
Leukocytes are also known as White Blood Cells play a major role in the body’s de-
fence mechanisms, the immune system. Leukocytes, unlike erythrocytes, require
mitochondria for energy, they contain a nucleus, endoplasmic reticulum and other
organelles. The leukocytes do not have a long lifespan they usually last around a
few hours and sometimes even less than an hour and this would depend on the in-
fection they are trying to get rid of. The Leukocytes can use diapedesis which helps
them to squeeze between very small spaces between cells to get to the site of the
infection quickly. Leukocytes can be divided into two categories granular and
agranular leukocytes and these granules are vesicles. The granular leukocytes are
the Neutrophils, Eosinophils and Basophils. While the agranular are the Lympho-
cytes and Monocytes. These leukocytes are produced in the bone marrow. The leuk-
ocytes contain lobed nuclei. The Neutrophils make up 50-70% of the leukocytes and
they are the primary line of defence against invading microbes, they will often re-
lease cytokines and they undergo phagocytosis when they encounter a microbe. The
granules in the leukocytes contain lysozyme which will help break down the bac-
terial cell walls, the leukocytes also contain hydrogen peroxide defensins in the
granules and all this help break down the foreign invaders. Eosinophils make up
about 2-4% of the leukocyte population, their nuclei contain 2 to 3 lobes, and their
granules contain substances that deal with allergic reactions, chronic inflammation,
parasitic worm infection and a few autoimmune diseases. Basophils are less than
1% of the total leukocyte population, basophils are important for the local inflam-
matory response, intensifying the response. They contain histamines which would
contribute to the inflammatory response. The lymphocytes consist of three main
types the Natural Killer cells or NK cells and the B and T cells when cells display
fragments of a virus on their surfaces and these abnormal structures will be detec-
ted by the Natural Killer Cells which will then respond to killing the cell that con-
tains the virus inside it, it acts in the same way for cancer cells and other cells that
contain abnormal surface proteins, the B and T cells are specific immune cells and
the B cells will produce antibodies specific to the disease whereas the T cells per-
form specific immunity at a cellular level, this can also give rise to memory cells
which will remember the defence mechanism against the pathogen on the first in-
fection and help in producing a response quicker on reinfection. The Monocytes ac-
count for 2-8% of the leukocytes and when they enter tissues from circulation, they
will become macrophages where it will undergo phagocytosis of bacteria and other
antigenic material, they also help in recruiting other cells to the site of infection.
3] THROMBOCYTES.
Thrombocytes are also known as platelets, and they are involved in wound healing
and clotting. The stopping of blood flow when an open wound has occurred is called
Haemostasis. We have primary and secondary haemostasis, primary Haemostasis is
caused by the platelets whereas secondary is caused by the beta globulins, the nor-
, mal platelet count is 150 thousand to 400 thousand per microlitre. The platelets are
synthesised from the Megakaryocytes which are made in the bone marrow and will
then leave the marrow and try to squeeze through the capillaries because of this
they break down into many fragments and each of these fragments is the platelet.
Therefore, they are not cells but just fragments and they contain the membrane and
cytoplasm from the megakaryocytes. In structure they are biconvex. They do not
contain a nucleus. They are covered by a glycoprotein coat containing receptors.
They are made of lipids, like phospholipids which will produce arachidonic acid
which is pro-inflammatory. It has a Calcium Canalicular system which helps in con-
tracting and release. The cytoplasm will contain actin and myosin for contraction
and release, they contain residuals of Golgi and RER which helps in protein syn-
thesis, mitochondria for ATP and ADP, and also contains Fibrin stabilising factor
and Platelet-derived growth factor which helps repair vessels after thrombus. Plate-
lets contain granules the alpha [proteins] and dense granules [non-proteins].
4] PLASMA AND SERUM.
Blood consists of cells and plasma, Plasma contains water, salts and proteins like
Albumin, Immunoglobulins and Fibrinogen. After the clotting of blood, the liquid
that remains is called the Serum and the serum does not have clotting factors, un-
like blood plasma which does contain clotting factors. The serum and plasma both
contain hormones, glucose, electrolytes and immunoglobulins. Plasma is the liquid
seen remaining to prevent clotting when an anticoagulant is added. When serum
and plasma are separated from the blood the plasma still retains the fibrinogen
while the serum remains after this fibrinogen is removed. Water is mostly what con-
stitutes the blood serum being a source of electrolytes. Serum separates when
blood coagulates, serum is amber in colour while plasma is straw-coloured. Plasma
takes up 55% of total blood volume while serum takes up less volume than that
plasma.
PRACTICAL INVESTIGATION OF DIAGNOSTIC BLOOD TESTS.
Blood smear preparation and staining [microscopic finding].
Equipment needed:
- 2 different blood samples.
- Glass slides
- Leishman’s stain or Wright’s blood stain or Giemsa stain.
- Distilled water
- Droppers
- Petri dish
- Compound light microscope
- Cotton
- Immersion oil
- Rubbing alcohol
Procedure:
