Introduction of Blood

Department of Biotechnology, V.N.S.G.U., Surat

Milan R. Patel
Assistant Professor, DBT VNSGU, Surat
UGC-CSIR-NET
• What is Blood?

• Blood can be regarded as both a tissue and a fluid. It is a tissue

because it contains a group of different cells which have specific
functions despite being a liquid.
• Its is look like pinkish red in artery and dark red in our vein. But due
to the skin covering its look like blueish in color.
• The fact that blood is constantly flowing through the circulatory
system means it is primed to adapt to changing conditions.
Components of blood
• Blood has four main components:
1. Red blood cells
2. White blood cells
3. Platelets
4. Plasma

• Plasma makes up 45-55% of the blood, red blood cells about 45%
(higher in men) and white blood cells and platelets a comparably small
proportion of 1%.
Haematopoiesis
• Hematopoiesis is a process that occurs in the bone marrow where new
blood cells form from pluripotent hematopoietic stem cells.

• Throughout life, there is rapid turnover of blood cells , so

hematopoiesis plays a crucial role in maintaining oxygen delivery and
maintenance of the immune system.

• There are two broad progenitor lineages: myeloid and lymphoid.

Red blood cells
• Erythrocytes (alternatively referred to as red blood cells) are cells
whose primary function is to deliver oxygen to tissues. Erythrocytes
are able to do this as they possess hemoglobin, which binds to oxygen
to form oxyhemoglobin.
• Erythrocytes are specialized for this function as they lose their nucleus
and other organelles to make room for as much hemoglobin as
possible.
• Hemoglobin undergoes conformational changes depending on its
environment and oxygenated states, which alters how it binds to and
releases oxygen. If hemoglobin is deficient or mutated then tissue
oxygenation is negatively affected.
 It is small and biconcave in shape, giving it a higher
surface area to volume ratio that facilitates rapid gas
exchange. This shape also allows for increased flexibility,
allowing erythrocytes to pass through narrow capillaries.

This shape is dependent on membrane proteins. Hence,

defects in membrane proteins can change the shape of the
red blood cell and affect its functionality.
Erythrocytes survive on average for 120 days in the circulation. After this time, they are
consumed by macrophages in the reticuloendothelial system in the spleen or bone
marrow.

Hemoglobin is metabolized into haem and globin, the former of which is further broken
down to bilirubin. Hence in diseases that lead to increased breakdown of red blood cells,
bilirubin levels increase overall.
White blood cells
• White blood cells, also known as leukocytes, have a main function of
fighting infection. They generally remain in the circulation but may be
upregulated in infective and inflammatory states, or abnormally high
due to malignancy.

• On the other hand, certain bone marrow disease states can lead to
lower levels than normal. There are two broad categories of white
blood cells: myeloid and lymphoid.
Myeloid cells
• There are three broad groups of myeloid cells: granulocytes, monocytes and
mast cells. They are all produced in a process called myelopoiesis in the
bone marrow.
• Granulocytes make up the largest proportion of white blood cells in the
circulation. They are called as such due to the presence of granules in their
cytoplasm. Granulocytes include:

• Neutrophils: the first type of white blood cell to arrive at a site of

inflammation through the mechanism of chemotaxis. They are involved in
the phagocytosis of extracellular pathogens. They contain granules that
enable them to kill these pathogens with proteolytic enzymes and
myeloperoxidase. On blood films they have multi-lobulated nuclei.
• Eosinophil: present at a much lower level than neutrophils. They are
elevated in hypersensitivity reactions and in response to parasitic infection.
On a blood film they have pink-staining granules in the cytoplasm and have
a kidney shaped nucleus. The granules contain histamine, leukotrienes and
other molecules that help with phagocytosis.
• Basophils: represent the smallest proportion of white cells. They are
elevated in inflammatory and allergic reactions. The granules contain
histamine and heparin which induce vasodilation and increased vessel
permeability. They are more blue on staining and tend to obscure the
nucleus.
• Monocytes do not remain in the circulation for very long and differentiate
into macrophages when they migrate into the tissues. If they are found in
the peripheral blood, they are large leukocytes with a horseshoe shaped
nucleus. Macrophages differentiate further upon reaching their target
tissues, such as Kupffer cells in the liver and microglial cells in the nervous
system. Macrophages’ main role is phagocytosing pathogens, debris and
dead cells and presenting antigens from the debris to lymphocytes, which
will commence the adaptive response.

• Mast cells are found in tissue (e.g. interstitial connective tissue and
submucosa) rather than blood and have similarities to basophils in that they
contain basophilic granules and receptors for IgE antibodies. They are
involved in mediating the type I hypersensitivity reaction.
Lymphoid cells
• Lymphoid cells include T cells, B cells and natural killer (NK) cells. T
cells mature in the thymus (hence ‘T’) and B cells mature in the bone
marrow.
• These cell types undergo several mechanisms during development,
including somatic recombination and tolerance, which allow them to
recognize multiple different epitopes whilst at the same time ignoring
self-antigens.
• NK cells are part of the innate immune system and therefore do not
require these processes.
Platelets
• Platelets, also known as thrombocytes, are fragments
of megakaryocytes which are involved in clotting of
the blood. As they do not contain a nucleus, they are
not considered true cells.
• They exist in the circulation for 5-7 days.
• Their main function is hemostasis and thrombosis.
Platelets contain granules which initiate the clotting
cascade, particularly von Willebrand factor,
fibrinogen, and platelet factor 4.
• They have several surface proteins which allow
them to aggregate and bind to blood vessel walls.
Plasma
• Plasma contains a variety of different substances, such as albumin,
immunoglobulins, coagulants and electrolytes. It is the liquid
component of blood. Without it, blood could not perform many of its
functions, such as coagulation, immune function and nutrition.
• Albumin is the main protein in the plasma and has a primary role in
maintaining oncotic pressure and transporting substances.
• Plasma can be separated from the cellular components of blood and
stored as fresh frozen plasma, which is given in major hemorrhage.
Blood cell maturation
• The production of blood cells is continuous throughout one’s life, and
therefore varying the rate of production makes the system much more
adaptable to environmental pressures. One way the hematological
system is regulated is with hematopoietic growth factors.

• Erythropoiesis is initiated by erythropoietin from the kidneys. This

growth factor promotes differentiation of stem cells to the erythroid
cell line. The stage before a mature erythrocyte is a reticulocyte and
these may be present in the circulation in certain pathological
conditions.
• Thrombopoiesis, the production of platelets, is initiated by
thrombopoietin, which triggers development of megakaryoblasts.
• Granulopoiesis, which leads to the production of granulocytes, begins
with Granulocyte macrophage colony stimulating factor (GM-CSF);
this promotes differentiation of the common myeloid precursor to the
myeloblast.
• Monopoiesis is promoted by monocyte colony stimulating factor
(M-CSF).
• Lymphocytes all originate in the bone marrow but have secondary
sites of maturation which reflect their different functions in the
adaptive immune system.
Functions of blood
• Transportation of oxygen to tissues
• Removal of carbon dioxide, urea and other waste products from
tissues
• Delivery of nutrition for cell growth and development: glucose,
protein, fats, vitamins, minerals. Certain substance such as glucose and
electrolytes are more tightly regulated than others.
• Initiating the immune response
• Thermoregulation by adjusting the rate of heat loss
• Haemostasis and coagulation cascade
• Red blood cell- Oxygen and CO2 transportation take O2 from lungs to
the tissues and take CO2 from the tissue to the lings that exhale Co2 to
the environment

• White blood cell- army of the body protection from any forein partical
like viruses and microorganisms

• Platelets- coagulation of blood flow

• Plasma- conations 90%water, salt, enzyme, antibody etc.

Bone marrow
• Bone marrow fills the cavity within bone and has a very different
consistency, being a more jelly-like substance. There are two key
types of bone marrow:

1. Red marrow: highly vascular and haematopoietically active. Red

marrow is present in all skeletal structures until the 5th year of life.
From then onwards it becomes restricted in the central flat bones and
proximal ends of long bones. Supporting cells are required in the red
marrow, such as reticular cells and macrophages. Reticular cells
produce reticulin that support the hematopoietic cells in the marrow.
Macrophages clear cellular debris to enable efficient hematopoiesis.
• Yellow marrow: less haematopoietically centered and contains more
adipocytes. Yellow marrow takes up a bigger proportion of the bone
marrow with age. Reticular cells take up lipid and this begins the
conversion to yellow marrow. The number of adipocytes increase as
well as reduction in hematopoietic centers.

• In many hematological conditions the bone marrow may be assessed

to get a fuller picture of what is going on with the patient. It allows us
to assess if the bone marrow is healthy or dysfunctional, and for what
reason that may be, be it infiltrative disease, depletion of progenitor
cells and/or nutrient deficiencies.
Condition of blood
• In the blood RBC level is decrease that’s call anaemia
• In the blood RBC level is Increase that’s call Polycythaemia.

• In the blood WBC level is decrease that’s call leukopenia

• In the blood WBC level is Increase that’s call Leucocytosis.

• In the blood platelet level is decrease that’s call thrombocytopenia

• In the blood platelet level is Increase that’s call Thrombocytosis.