The Fluid of Life
What is Blood?
The average adult has about five liters of blood coursing through their vessels. It delivers essential elements,
and removing harmful wastes from each and every cell in the body. What most medical and allied health students
don't realize until it is mentioned either by their instructor or they read about it in their anatomy text book is
that blood falls under the category of connective tissues!
REMEMBER: BLOOD IS A LIQUID CONNECTIVE TISSUE THAT MEASURES ABOUT 5 LITERS
IN THE ADULT HUMAN AND ACCOUNTS FOR 8 PERCENT OF THE BODY WEIGHT. ITS NORMAL pH RANGE IS
Our bodies consist of metabolically active cells that need a continuous supply
of nutrients and oxygen. Metabolic waste products need to be removed from the cells to maintain a stable
cellular environment. Blood is the primary transport medium that is responsible for meeting these cellular
demands. Materials transported by the blood include nutrients, waste products, gases, and hormones. The blood
helps to regulate the fluid and electrolyte balance, acid base balance, and the body temperature. Protection
against pathogens is provided by white blood cells, and the clotting mechanism prevents excessive loss of
blood after injuries.
Functions of Blood
BLOOD FUNCTIONS AS A TRANSPORT MEDIUM. IT ALSO HAS ROLES IN TEMPERATURE REGULATION, FLUID AND ELECTROLYTE
BALANCE, pH REGULATION, PREVENTION OF FLUID LOSS, NOURISHMENT AND DISEASE PREVENTION. The general functions of
blood include transportation, regulation, and protection. These categories overlap and interact as the blood
carries out its role in providing suitable conditions for cellular function.
- The following activities are under the
- Carries O2 and nutrients to the cells
- Transports CO2 and wastes from the tissues to the lungs and the kidneys where wastes can be removed
from the body
- Carries hormones to the endocrine glands to the target tissue
- The following activities are under the
- Helps to regulate body temperature by removing heat from active areas, such as skeletal muscles and
transporting it to other areas of the skin so the heat can be dissipate
- Plays a significant role in fluid and electrolyte balance because salt and plasma proteins
contribute to the osmotic pressure by providing weight and bulk to our blood
- Functions in pH regulation through the action of buffers in the blood
- Functions of the blood that are in the
- Clotting mechanisms prevent fluid loss through hemorrhage when blood vessels become damaged
- Certain cells in the blood, phagocytic white blood cells help to protect the body against diseases
by engulfing and destroying the agent
- Antibodies in the plasma help protect against disease by their reactions with offending agents
Characteristics of Blood
Blood has distinctive physical characteristics:
Amount—a person has 4-6 liters of blood, depending on the body size. Of the total blood
volume in the human body, 38% to 48% is composed of the various blood cells also called “formed elements”.
The remaining 52% to 62% of the blood volume is the plasma or the liquid portion of the blood.
Color—yeah… of course we all know it is red. Arterial blood is bright red because
it contains high levels of oxygen. Venous blood has given up much of its oxygen in tissues and has a
darker, dull red color. This may be important in the assessment of the source of bleeding.
PH—the normal pH range of blood is 7.35-7.45, which is slightly alkaline.
Viscosity—this means the thickness or the resistance to flow. Blood is about 3 to 5 times thicker than
water. Viscosity is increased by the presence of blood cells and the plasma proteins, and this thickness
contributes to normal blood pressure.
Composition of Blood
When a sample of blood is spun in a centrifuge, the cells and cell fragments are
separated from the liquid. Because the formed elements are heavier than the liquid matrix, they are packed in the
bottom of the tube by the centrifugal force. The straw colored liquid on the top is the plasma.
A GIVEN VOLUME OF BLOOD IS 55 PERCENT PLASMA AND 45 PERCENT FORMED CELLS.
Plasma is the liquid portion of blood. It is about 90%
water. The remaining portion consists of more than 100 different organic and inorganic solutes that are dissolved
in water. Because plasma is a transport medium, it's solutes are continuously changing as substances are added or
removed by the cells.
Plasma proteins are the most abundant solutes in the plasma.
These proteins remain in the blood and interstitial fluid and are not used for energy. The three major classes of
plasma proteins are: albumins, globulins, and fibrinogen. Many of the plasma proteins are synthesized in the liver,
and each one has a different function.
Albumins are the most abundant plasma proteins. It is synthesized by the liver. Because they are
so abundant, they contribute to the osmotic pressure of the blood and play an important role in maintaining fluid
balance between blood and interstitial fluid. If the osmotic pressure of the blood decreases, fluid moves from the
blood into the interstitial spaces, which results in edema. This also decreases blood volume and, in severe cases,
may reduce blood pressure. When blood osmotic pressure increases, fluid moves from the interstitial spaces into the
blood and increases the blood volume. This increases blood pressure and decreases the amount of water available to
Globulins—there are three types of globulins; alpha, beta, and
gamma. Alpha and beta globulins are produced in the liver and function in transporting lipids and fat soluble
vitamins in the blood. Gamma globulins are the antibodies that function in immunity.
Fibrinogen makes up the smallest fraction of plasma proteins. It
is produced in the liver and functions in blood clotting. These types of plasma proteins are the largest of the
Solutes transported in blood plasma are nutrients, oxygen, and
Production of Blood
The production of these formed elements or blood cells is called hemopoeisis! The
formed elements are cells and cell fragments that are suspended in the plasma. The three classes of formed elements
- Erythrocytes or red blood cells
- Leukocytes or white blood cells
- Thrombocytes or platelets
When the body sustains a minor wound, the platelets cause the blood to clot and
with that the bleeding usually stops. The body can easily replace the lost blood from specialized cells, mostly
within the red bone marrow. However, if the human body loses a great volume of blood it is possible that this blood
has to be replaced through a blood transfusion from blood that was previously donated by someone else.
However, it is important to remember that everybody's blood is not the same. Blood
transfusions must be carefully matched. There are four different blood types. Also there are Rh factors which make
every person's blood type even more unique. Therefore, blood from a donor must match exactly that of the
Patients who are scheduled to have major surgery sometimes are offered a choice to
make autologous blood donations (donations of their own blood) so that they have a perfect match.