Histology: Blood & it’s
Components
Blood
A mixture of cellular elements, fluid, proteins and metabolites
Transportation of substances and it plays a role in the defence of bodily tissue
Plasma (fluid component)
A Proteinaceous solution in which cells circulate. It carries nutrients, metabolites,
antibodies, hormones, proteins of the blood clotting system and other molecules
throughout the body
Red blood cells (erythrocytes)
Transportation of oxygen from the lungs to peripheral tissues
White blood cells (leukocytes)
Have a defensive rile in destroying infective organisms (bacteria, viruses) and also
remove dead/damages tissues could become infective
Platelets (thrombocytes)
The first line of defence against damage to blood vessels
Erythrocytes
6.5-8.5 μm in diameter
They are highly deformable (can squeeze through small blood vessels as small as 3-4 μm
in diameter)
Have a biconcave shape to maximise the oxygen carrying capacity
Appear paler at the centre and darker at the periphery
Do not contain a nucleus or organelles gives more space for the cell to carry oxygen
They contain a cell membrane which surrounds an electron-dense cytoplasm that
contains haemoglobin
The cell membrane is braced by an actin/spectrin-containing cytoplasm cytoskeletal
meshwork which is largely responsible for maintaining the distinctive biconcave shape
It derives energy by anaerobic metabolism of glucose
Has a lifespan of 100-120 days
Is disposed of mainly by the spleen but the liver and bone marrow also play a role
Anaemia
Impaired red blood cell formation or excessive red blood cell destruction
The most common: iron deficiency (which is essential for haemoglobin formation).
Red blood cells are released into circulation containing much less haemoglobin
compared to normal
Haemolytic anaemia: red blood cells are structurally abnormal and are removed
prematurely from circulation
Sickle cell anaemia: abnormal haemoglobin that causes the red blood cells to appear
distorted (under a microscope)
Aplastic anaemia: an autoimmune disease where the body stops producing all blood
cells there is less oxygen transport, and the body cannot fight off diseases/infections
Symptoms include weakness, pallor and (sometimes) breathlessness
, Leukocytes (white blood cells)
Use the blood for transport from the bone marrow to the major activity sites
Majority of functions of white blood cells take place when they leave the blood
circulation to enter the tissues
There of 5 types of leukocytes
Neutrophils (40-75%)
Lymphocytes (20-50%)
Eosinophils (5%)
Monocytes (1-5%)
Basophils (0.5%)
Neutrophils, eosinophils and basophils
Also known as granulocytes as the cytoplasm contains prominent granules
Also called myeloid cells as they have similar origins
Lymphocytes and monocytes
Mononuclear lymphocytes
Found mainly in tissues e.g. lymph nodes and the spleen
Monocytes transform into macrophages in the tissue
a) Neutrophils
The most abundant of the circulating white blood cells
They circulate in a resting state but will become activated when required (e.g. bacterial
infection), leave the blood and enter the tissues where they become highly motile
phagocytic cells (engulf and kill microorganisms and ingest cell debris)
Play a central role in the early stages of acute inflammatory response to tissue injury
and are the main constituent of pus
Characteristically have 2-5 lobed nuclei
b) Eosinophils
Have a bi-lobed appearance and contain strongly eosinophilic granules
They are phagocytic with a particular affinity for antigen-antibody complexes but have
less microbial activity than neutrophils a more parasitic response
They are produced in the bone marrow and stored for ±8 days before they are released
into circulation where they remain for 6-12hrs before preferentially migrating to the
skin, lungs and gastrointestinal tract where they reside for 1-2 weeks
They play a role in certain allergic states and in adverse reactions to drugs
They do not usually re-enter circulation after tissue migration
c) Basophils
The least common leukocyte in the blood
Characterised by large, intensely basophilic cytoplasmic granules
Have a bi-lobed nucleus
They play a role in allergic reactions
They are created in the bone marrow and released into the blood as mature cells where
they are then replaced after a few days
Exposure to allergens results in rapid exocytosis of granule hence releasing histamines
and other vasoactive mediators and resulting in an immediate hypersensitivity reaction
e.g. allergic rhinitis (hay fever), some forms of asthma, urticaria and anaphalaxis
Components
Blood
A mixture of cellular elements, fluid, proteins and metabolites
Transportation of substances and it plays a role in the defence of bodily tissue
Plasma (fluid component)
A Proteinaceous solution in which cells circulate. It carries nutrients, metabolites,
antibodies, hormones, proteins of the blood clotting system and other molecules
throughout the body
Red blood cells (erythrocytes)
Transportation of oxygen from the lungs to peripheral tissues
White blood cells (leukocytes)
Have a defensive rile in destroying infective organisms (bacteria, viruses) and also
remove dead/damages tissues could become infective
Platelets (thrombocytes)
The first line of defence against damage to blood vessels
Erythrocytes
6.5-8.5 μm in diameter
They are highly deformable (can squeeze through small blood vessels as small as 3-4 μm
in diameter)
Have a biconcave shape to maximise the oxygen carrying capacity
Appear paler at the centre and darker at the periphery
Do not contain a nucleus or organelles gives more space for the cell to carry oxygen
They contain a cell membrane which surrounds an electron-dense cytoplasm that
contains haemoglobin
The cell membrane is braced by an actin/spectrin-containing cytoplasm cytoskeletal
meshwork which is largely responsible for maintaining the distinctive biconcave shape
It derives energy by anaerobic metabolism of glucose
Has a lifespan of 100-120 days
Is disposed of mainly by the spleen but the liver and bone marrow also play a role
Anaemia
Impaired red blood cell formation or excessive red blood cell destruction
The most common: iron deficiency (which is essential for haemoglobin formation).
Red blood cells are released into circulation containing much less haemoglobin
compared to normal
Haemolytic anaemia: red blood cells are structurally abnormal and are removed
prematurely from circulation
Sickle cell anaemia: abnormal haemoglobin that causes the red blood cells to appear
distorted (under a microscope)
Aplastic anaemia: an autoimmune disease where the body stops producing all blood
cells there is less oxygen transport, and the body cannot fight off diseases/infections
Symptoms include weakness, pallor and (sometimes) breathlessness
, Leukocytes (white blood cells)
Use the blood for transport from the bone marrow to the major activity sites
Majority of functions of white blood cells take place when they leave the blood
circulation to enter the tissues
There of 5 types of leukocytes
Neutrophils (40-75%)
Lymphocytes (20-50%)
Eosinophils (5%)
Monocytes (1-5%)
Basophils (0.5%)
Neutrophils, eosinophils and basophils
Also known as granulocytes as the cytoplasm contains prominent granules
Also called myeloid cells as they have similar origins
Lymphocytes and monocytes
Mononuclear lymphocytes
Found mainly in tissues e.g. lymph nodes and the spleen
Monocytes transform into macrophages in the tissue
a) Neutrophils
The most abundant of the circulating white blood cells
They circulate in a resting state but will become activated when required (e.g. bacterial
infection), leave the blood and enter the tissues where they become highly motile
phagocytic cells (engulf and kill microorganisms and ingest cell debris)
Play a central role in the early stages of acute inflammatory response to tissue injury
and are the main constituent of pus
Characteristically have 2-5 lobed nuclei
b) Eosinophils
Have a bi-lobed appearance and contain strongly eosinophilic granules
They are phagocytic with a particular affinity for antigen-antibody complexes but have
less microbial activity than neutrophils a more parasitic response
They are produced in the bone marrow and stored for ±8 days before they are released
into circulation where they remain for 6-12hrs before preferentially migrating to the
skin, lungs and gastrointestinal tract where they reside for 1-2 weeks
They play a role in certain allergic states and in adverse reactions to drugs
They do not usually re-enter circulation after tissue migration
c) Basophils
The least common leukocyte in the blood
Characterised by large, intensely basophilic cytoplasmic granules
Have a bi-lobed nucleus
They play a role in allergic reactions
They are created in the bone marrow and released into the blood as mature cells where
they are then replaced after a few days
Exposure to allergens results in rapid exocytosis of granule hence releasing histamines
and other vasoactive mediators and resulting in an immediate hypersensitivity reaction
e.g. allergic rhinitis (hay fever), some forms of asthma, urticaria and anaphalaxis
