Blood is a
specialized body fluid that delivers necessary substances such as nutrients and
oxygen to the cells and transports metabolic waste products away from those
same cells. Approximately 3% of an adult body weight is made up of blood;
females have about 4-5 liters of blood while male have about 5-6 liters. Blood
has pH of 7.33-7.45 making it slightly basic (less than 7 is considered acidic)
while blood is about 4.5 to 5.5 time as vicious of water, indicating that it is
more resistance to flow than water.
This viscosity is vital to the function of
blood because if blood flows too easily or with too much resistance it can
strain the heart and cause cardio vascular problems. Blood in the arteries is
brighter than blood in the veins because of the higher level of oxygen found in
the arteries, but its color is straw yellow.
Blood is composed of blood
cells suspended in a liquid called blood plasma; blood plasma which constitutes
55% of body 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 of red cells themselves). Albumin
is the main protein in the plasma and it functions to regulate colloidal osmotic
pressure of blood. The blood cells are mainly red blood cells (erythrocytes)
and white blood cells (leucocytes). (Wikipedia, 2009).
The medical term for blood
is hemo - or hemato- (also spelt haemat and haemo form the Greek word (haima)
for blood. In terms of anatomy and histology, blood is considered a specialized
form of connective tissue, given its origin in the bone and the presence of
potential molecular fibers in the form of fibrinogen, (Wikipedia).
COMPOSITIONS OF BLOOD
Blood is classified as a connective tissue and consists of
two main components, plasma, which is clear extracellular fluid and formed
element, which are made up of the blood cells and platelets.
Blood plasma: This is a mixture of
proteins, enzymes, nutrients wastes hormones and gases. This specific
composition and functions of its component are as follows.
a-Proteins: They are
the most abundant substance in the plasma and plan a part in a variety of roles
including clothing, defence, and transportation.
Collectively
they play several functions which are as follows.
- a-They are important reserve supply of amino acids for cell nutrition;
these amino acids are used by other cells to synthesis new products.
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b- Plasma proteins also serve as a carrier for other molecules. Many types
of small molecules bind to plasma proteins and are transported from the organs
that absorbs these proteins to other tissues for utilization.
-
c- Proteins also helps to keep the blood slightly basic at a stable pH, they
do these by functioning as weak bases themselves to bind excess H+ ions. By doing so they remove excess H+
from the blood which keeps it slightly basic.
-
d- Plasma proteins interact in specific ways to cause the blood to coagulate
which is part of the body’s responds to injury to the blood vessels (also known
as vascular injury), and help protect against the loss of blood and invasion by
foreign microorganisms and viruses.
-
e- Plasma proteins govern the distribution of water between the blood and
body fluid by producing what is known as
colloidal osmotic pressure.
There are
three main categories of plasma proteins and each individual type of protein
has its own specific properties and function in addition to their overall
collective role.
1. Albumins:They are the smallest and most abundant plasma protein in the blood. Reduction in plasma albumin content can result in a loss of fluid in interstitial space (space within the tissue) which may occur in nutritional kidney and liver disease. Albumin also helps much substances dissolve in the plasma by binding to them hence playing an important role in plasma transport of substances such as drugs and fatty acids.
2. Globulins: It can be
subdivided into three classes from smallest to largest in molecular weight into
Alpha, Beta and Gamma globulins. The globulin includes high density
lipoproteins (HDL) and alpha -1 globulin and low density lipoproteins (LDL), a
beta 1 globulin. HDL function in lipid transport carrying fats cell for use in
energy metabolism; membrane construction and hormone function. HDL also appears
to prevent cholesterol from invading and settling in the walls of the arteries.
LDL carries cholesterol and fat to tissue for uses in manufacturing steroid
hormone and building cells membrane, but it also favors the deposition of
cholesterol in arterial walls and thus appears to play a role in disease of the
blood vessels and heart. HDL and LDL therefore play important role in the
regulation of cholesterol and hence have a large impact on cardiovascular
disease.
3. Fibrinogen: This is a
soluble precursor of a sticky protein called FIBRIN, which forms the framework
of blood clot. Fibrin plays a role in coagulation of blood.
a-Amino acid: These are
formed from the breakdown of tissue proteins or from the digestion of proteins.
b-Nitrogenous waste: Nitrogenous waste is toxic, it is obtained from the breakdown of
substances in the body. These are usually cleared from the blood stream and are
excreted by the kidney at a rate that balances their production.
c-Nutrients: Nutrients
absorbed by digestive tracts are transported by the plasma and these include
glucose, amino acids, fats, cholesterol, phospholipids, vitamins and minerals.
d-Gases: Some
oxygen and carbon dioxide are transported by plasma. Plasma also contains a substantial
amount of dissolved nitrogen.
e-The most
abundant of the electrolyte in the blood is sodium ions which account for more
of the blood’s osmolarity than any other solute.
b.The formed elements:
These are so named because they are enclosed in a plasma membrane and have a
definite structure and shape. All formed elements are cells except platelets
which are tiny fragments of bone marrow cells (Wikipedia).
The formed elements include the following:
a.Erythrocyte (red
blood cells): These are minute biconcave
disc shaped cells that lacks nucleus at maturity (anucleate). They range from
7-8cm in diameter and have a large surface area.
Erythrocytes
have a life span of 120days (4months) after which they are destroyed in the
spleen or the liver. Red blood cell contains the ion pigment (hemoglobin) which
gives blood its red color. One cubic liter of blood contain ½ million RBCs
(erythrocytes). Erythrocytes functions to pick up oxygen from the lungs and
deliver it to tissues elsewhere and pickup carbon dioxide from other tissues
and upload it to the lungs.The plasma
membrane of matured erythrocytes (RBCs) has glycoprotein and glycolipids that
determine a person’s blood type (Wikipedia).
b. Leukocytes (white
blood cells)- These are colorless nucleated cells found in the blood. They
are larger than the erythrocyte and are capable of amoeboid movement; white
blood cells are produced in the bone marrow and are part of the body immune
system. White blood cells ingest bacteria, viruses and dead cells and prevent
diseases. They move through blood vessels to the site of injury and form clot,
thereby preventing further loss of blood and entry of foreign pathogens.
White blood
cells can be divided into granulocytes and agranulocytes, the former
have cytoplasm that contains organelles that appears as colored granules
through light microscope, hence their name. Granulocytes consist of Eosinophil
and Basophils, Neutrophil, in contrast, agranulocyte do not contain
granules and consist of Monocytes and Lymphocytes.
1. Neutrophils:
Neutrophils, contains fine cytoplasmic granules. They play a role in the
destructions of bacteria and release of chemicals that inhibit or kill the
growth of bacterial infection, if the number is significantly high, it
indicates early bacterial infection but a gross decrease indicates long lasting
bacterial infection. The normal range of neutrophil is 40-75%.
2. Basophils:
Basophils secrete histamine which increases blood flow via dilating the blood
vessels and also secrete heparin which is an anticoagulant that promotes
motility of other WBCs by preventing clothing. Their nucleus is pale and
usually hidden by granules.
3. Eosinophil: It has a
large granule and a prominent nucleus that is divided into lobes. It functions
in the destruction of allergens and inflammatory chemicals and release enzymes
that disable parasites.
The granulocytes includes
the following
a- Lymphocytes: - these are usually
classifies as small, medium or large. Medium and large Lymphocytes are
generally seen in fibrous connective tissue and only occasionally in
circulating blood stream.
It
functions in destroying cancer cell and cells infected with by viruses and
foreign invading cells, they present antigens to activate other cells of the
immune cells, secrete antibodies and serve in immune memory.
b- Monocyte:These are
the largest of the pre-formed element; they have abundant cytoplasm which is
easily seen. Monocyte functions in differentiating into microphages which are
large phagocytic cells.
C- Thrombocytes
(platelets:- These are tiny fragments of cells responsible for blood
(coagulation). Thrombocytes convert fibrinogen into insoluble fibrin which
creates a mesh unto which red blood cells are trapped and clothed, which then
stops more blood loss and also prevent bacteria from entering the body.
There are
about 250,000 platelets per mm3 of the blood: there diameters range
from 2-4µm, they survive for about two to five days before being
destroyed in the spleen of the liver.
Platelets secrete vasoconstriction which constricts
blood vessels causing vascular spam in broken blood vessels thereby forming
platelet plug to stop bleeding. They also digest and destroy bacteria and
secrete chemical that attracts neutrophils and monocytes to site of
inflammation and also secrete growth factors to maintain the lining of blood
vessels (Jelin 2012).
FUNCTIONS OF BLOOD
The functions of blood are as follows;
a- Transport media:- It
transports the following sub stances
·Nutrients: Are transported from digestive tracts and storage sites to all cells
where they are assimilated.
·Hormone: The blood acts as a vehicle that transports Hormone and enzymes from
glands and site of origin to target site.
·Heat: It distributes heat produce in the muscles to all parts of the
body thereby regulating temperature.
·Waste (Excretory products): The blood transports all waste
products from cells to the liver and kidney where they are detoxified and
eliminated, e.g Urea.
b-Defense: The blood defends the body
from microorganisms and their toxins due to phagocytic action of neutrophils
which destroys invading microorganisms. (Jelin 2012).
c-PH regulation: it
regulates the ph of the body within narrow range of 7.35-7.35, making it
slightly alkaline; blood with a PH of 7.35 is too acidic whereas, PH above 7.45
is too alkaline. Blood PH partial
pressure of oxygen (PO2) Partial pressure of Carbon dioxide (CO2)
and partial pressure of HCO3
are carefully regulated by a number of hemostatic mechanisms which exert their
influences particularly through the respiratory and urinary systems in other to
control the acid base balance and respiration (Wikipedia).
d- The blood also regulates water balance and
blood pressure.
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Thank toe the lecture.
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