Functions of Blood
• Blood performs a number of
functions:
– Substance distribution
– Regulation of blood levels of
particular substances
– Body protection
Blood Functions: Distribution
• Blood transports:
– Oxygen from the lungs and nutrients from the
digestive tract
– Metabolic wastes from cells to the lungs and
kidneys for elimination
– Hormones from endocrine glands to target
organs
Blood Functions: Regulation
• Blood maintains:
– Appropriate body temperature by absorbing and
distributing heat to other parts of the body
– Normal pH in body tissues
– Adequate fluid volume in the circulatory
system
Blood Functions: Protection
• Blood prevents blood loss by:
– Activating plasma proteins and platelets
– Initiating clot formation when a vessel is broken
• Blood prevents infection by:
– Synthesizing and utilizing antibodies
– Activating complement proteins & WBCs to defend the
body against foreign invaders
Physical Characteristics of Blood
• Average volume:
– 5–6 L for males; 4–5 L for females
• The pH is 7.35–7.45
• Accounts for approximately 8% of body weight
Composition of Blood
• Blood is the body’s only fluid tissue (a
connective tissue)
• 2 major components
– Liquid = plasma (55%)
– Formed elements (45%)
• Erythrocytes, or red blood cells (RBCs)
• Leukocytes, or white blood cells (WBCs)
• Platelets – cell fragments
Components of Whole Blood
Plasma
(55% of whole blood)
Buffy coat:
leukocyctes and
platelets
(<1% of whole blood)
1 Withdraw blood
and place in tube
2 Centrifuge
Erythrocytes
(45% of whole blood)
Formed
elements
Blood Plasma
• Blood plasma components:
– Water = 90-92%
– Proteins = 6-8%
• Albumins-maintain osmotic pressure of the blood
• Globulins-used for transport purposes
• Fibrinogen-a clotting protein
– Organic nutrients – glucose, carbohydrates, amino acids
– Electrolytes – sodium, potassium, calcium, chloride,
bicarbonate
– Non-protein nitrogenous substances – lactic acid, urea,
creatine
– Respiratory gases – oxygen and carbon dioxide
Formed Elements
– Only WBCs are complete cells
– RBCs have no nuclei or organelles, and
platelets are just cell fragments
• Most F.E. survive in the bloodstream for
only a few days
• Most do not divide but are renewed by cells
in bone marrow
Erythrocytes (RBCs)
• Biconcave disc
– Folding increases surface area (30% more surface area)
• Anucleate, no centrioles, no organelles
– No cell division
– No mitochondria means they generate ATP anaerobically
• This prevents consumption of O2 being transported
• Filled with hemoglobin (Hb) - 97% of cell contents
– Hb functions in gas transport
• Most numerous of the formed elements
Erythrocyte Function
• Erythrocytes are dedicated to respiratory gas
transport
• Hb reversibly binds with oxygen and most oxygen
in the blood is bound to Hb
• Composition of Hb
– A protein called globin
– A heme molecule (a metal complex with iron as the
central metal atom, that can bind or release molecular
oxygen.) Heme groups are embedded in the
hemoglobin protein,
Production of Erythrocytes
• Hematopoiesis – blood cell formation
– Occurs in the red bone marrow
• Axial skeleton and girdles
• Epiphyses of the humerus and femur
Erythrocyte Disorders
• Anemia – blood has abnormally low oxygencarrying capacity
• There are many forms of anemia, each with its
own cause.
• Anemia can be temporary or long term, and it
can range from mild to severe.
– Blood oxygen levels cannot support normal
metabolism
– Signs/symptoms include fatigue, paleness,
shortness of breath, and chills
Leukocytes (WBCs)
– Protect the body from infectious
microorganisms
– Can leave capillaries
– Move through tissue spaces
– Many are phagocytic- that engulfs and absorbs waste
material, harmful microorganisms, or other foreign
bodies in the bloodstream and tissues.
• Two major types of leukocytes
– Granulocytes: Neutrophils, Eosinophils, Basophils
– Agranulocytes: Monocytes, Lymphyocytes
• Leukemia - a cancer of WBC
Granulocytes
– Contain cytoplasmic granules that stain
specifically with Wright’s stain
– Are larger and usually shorter-lived than
RBCs
– Have lobed nuclei
– Are all phagocytic cells
Granulocytes: Neutrophils
• Account for 65-75% of total WBC’s
• Neutrophils have two types of granules that:
– Contain peroxidases, hydrolytic enzymes, and
defensins (antibiotic-like proteins)
• Neutrophils are our body’s bacteria slayers
Granulocytes: Eosinophils
• Eosinophils account for 1–4% of WBCs
– Function:
• Lead the body’s counterattack against parasitic
infections
• Lessen the severity of allergies by phagocytizing
immune complexes (ending allergic reactions)
Granulocytes: Basophils
• Account for 0.5-1% of all WBCs
– Have large, purplish-black granules that contain
histamine
• Histamine – inflammatory chemical that acts as a
vasodilator and attracts other WBCs
(antihistamines counter this effect)
Agranulocytes: Lymphocytes
• Account for 20-25% or more of WBCs and:
– Found mostly in lymphoid tissue (some circulate in the
blood)
• Most important cells of the immune system
• Involved in graph rejection, fighting tumors
and viruses
• There are two types of lymphocytes: T cells and
B cells
– T cells - attack foreign cells directly
– B cells give rise to plasma cells, which produce
antibodies
Monocytes
• Account for 3–7% of leukocytes
– They are the largest leukocytes
– They have purple-staining, U- or kidney-shaped
nuclei
– They leave the circulation, enter tissue, and
differentiate into macrophages
– Increase in # during chronic infections.
Platelets
• Platelets are fragments of megakaryocytes
• Platelets function in the clotting mechanism
by forming a temporary plug that helps seal
breaks in blood vessels.
Platelet
Human Blood Groups
• RBC membranes have glycoprotein antigens on
their external surfaces
• These antigens are:
– Unique to the individual
– Recognized as foreign if transfused into another
individual
– Promoters of agglutination and are referred to as
agglutinogens
• Presence or absence of these antigens is used to
classify blood groups
ABO Blood Groups
• The ABO blood groups consists of:
– Two antigens (A and B) on the surface of the RBCs
– Two antibodies in the plasma (anti-A and anti-B)
• An individual with ABO blood may have various
types of antigens and spontaneously preformed
antibodies
• Agglutinogens (antigens) and their corresponding
antibodies cannot be mixed without serious
reactions
Group A – has only the A antigen on red cells (and B antibody
in the plasma)
Group B – has only the B antigen on red cells (and A antibody
in the plasma)
Group AB – has both A and B antigens on red cells (but neither
A nor B antibody in the plasma)
Group O – has neither A nor B antigens on red cells (but both A
and B antibody are in the plasma)
• The universal red cell donor has Type O negative
blood type.
• The universal plasma donor has Type AB
positive blood type.
Transfusion Reactions
• Transfusion reactions occur when mismatched
blood is infused
• Donor’s cells are attacked by the recipient’s
plasma agglutinins causing:
– Diminished oxygen-carrying capacity
– Clumped cells that impede blood flow
– Ruptured RBCs that release free hemoglobin into the
bloodstream
• Circulating hemoglobin precipitates in the kidneys
and causes renal failure