Blood is a bodily fluid in animals that delivers necessary substances such as
nutrients and oxygen to the cells and transports metabolic waste products away
from those same cells. In vertebrates, it is composed of blood cells suspended in
Functions of Blood:
- Supply of oxygen to tissues (bound to hemoglobin, which is carried in red cells)
- Supply of nutrients such as glucose, amino acids, and fatty acids (dissolved in
the blood or bound to plasma proteins (e.g., blood lipids))
- Removal of waste such as carbon dioxide, urea, and lactic acid
- Immunological functions, including circulation of white blood cells, and
detection of foreign material by antibodies
- Coagulation, which is one part of the body's self-repair mechanism (blood
clotting after an open wound in order to stop bleeding)
- Messenger functions, including the transport of hormones and the signaling of
- Regulation of body pH
- Regulation of core body temperature
- Hydraulic functions
Plasma, which constitutes 55% of blood fluid, is mostly water (92% by
volume), and contains dissipated proteins, glucose, mineral ions, hormones,
carbon dioxide (plasma being the main medium for excretory product
transportation), and blood cells themselves.
Albumin is the main protein in plasma, and it functions to regulate the colloidal
osmotic pressure of blood. The blood cells are mainly red blood cells (also called
RBCs or erythrocytes) and white blood cells, including leukocytes and platelets.
Plasma also serves as the protein reserve of the human body. It plays a vital role
in intravascular osmotic effect that keeps electrolyte in balance form and
protects the body from infection and other blood disorders Red Blood Cells:
The most abundant cells in vertebrate blood are red blood cells. These contain
hemoglobin, an iron-containing protein, which facilitates transportation of
oxygen by reversibly binding to this respiratory gas and greatly increasing its
solubility in blood. In contrast, carbon dioxide is almost entirely transported
extracellularly dissolved in plasma as bicarbonate ion.
These cells' cytoplasm is rich in haemoglobin, an iron-containing biomolecule
that can bind oxygen and is responsible for the blood's red color. The cell
membrane is composed of proteins and lipids, and this structure provides
properties essential for physiological cell function such as deformability and
stability while traversing the circulatory system and specifically the capillary
In humans, mature red blood cells are flexible and oval biconcave disks. They
lack a cell nucleus and most organelles, in order to accommodate maximum
space for haemoglobin.
Platelets are small, disk shaped clear cell fragments, which are derived from
fragmentation of precursor megakaryocytes. The average lifespan of a platelet is
normally just 5 to 9 days. Platelets are a natural source of growth factors. They
circulate in the blood of mammals and are involved in hemostasis, leading to the
formation of blood clots.
If the number of platelets is too low, excessive bleeding can occur. However, if
the number of platelets is too high, blood clots can form (thrombosis), which
may obstruct blood vessels and result in such events as a stroke, myocardial
infarction, pulmonary embolism or the blockage of blood vessels to other parts
of the body, such as the extremities of the arms or legs.
Neutrophil granulocytes are the most abundant type of white blood cells in
mammals and form an essential part of the innate immune system.
Neutrophils are a type of phagocyte and are normally found in the blood stream.
During the beginning (acute) phase of inflammation, particularly as a result of
bacterial infection, environmental exposure, and some cancers, neutrophils are
one of the first-responders of inflammatory cells to migrate towards the site of
inflammation. They migrate through the blood vessels, then through interstitial
tissue, following chemical signals such as Interleukin-8 (IL-8), C5a, fMLP and
Leukotriene B4 in a process called chemotaxis. They are the predominant cells in
pus, accounting for its whitish/yellowish appearance.
Neutrophils are recruited to the site of injury within minutes following trauma
and are the hallmark of acute inflammation. Being highly motile, neutrophils quickly congregate at a f