Blood
Objectives
At the end of this
lecture, student will be able to
• Explain the
functions of blood
• Describe the
physical characteristics of blood
• List the
components of blood
• List the major
components of plasma
• Outline blood
cell production, function, and destruction
• Describe the
structure of red blood cells
• Explain the types and functions of WBC
• Describe the haemostatic mechanism
• Explain the role of platelet in haemostasis
Content
Hemopoietic system
• Blood
• Plasma
• Red blood cells
• White blood cells
• Hemostatic mechanism
Formed
Elements in the Blood
RBC
• Biconcave discs
with a diameter of 7–8 micro m
• 4.8 million/microL in females
• 5.4 million/microL in males
• Plasma Membrane
– Strong and flexible
– Allows them to deform without rupturing as they squeeze
through narrow capillaries
– Glycolipids in the plasma membrane antigens
• Mature RBCs lack
– Nucleus and other organelles
– Neither reproduce
nor carry on extensive metabolic activities
• The Cytosol
– Contains hemoglobin molecules (each RBC -280 million Hb
molecules)
RBC
Physiology – Advantages
• No Nucleus
– All their internal space is available for oxygen transport
• Lack Mitochondria
– Generate ATP anaerobically (without oxygen)
• Biconcave disc
shape
– Facilitates its function – greater surface area for the
diffusion of gas molecules
• Hemoglobin
• Helps in oxygen transport (binding to Iron molecule)
• Also transports
about:
• 23% of the total
carbon dioxide (by binding to aminoacid)
• Waste products of
metabolism
• Plays a role in the regulation of blood flow and blood
pressure
Hemoglobin
(Hb)
• Consists of a protein called globin (2 Alpha & @ Beta
chains)
• A ringlike nonprotein pigment called a heme – bound to
each of the four chains
• At the center of each heme ring is an iron ion
• Each Hb is capable of binding four molecules of oxygen
Formation
of Blood Cells
RBC
Physiology – Role of Hb
RBC Life
Cycle
Erythropoiesis
Reticulocytes develop into mature red blood cells within 1
to 2 days after their release from red bone marrow
Negative
Feedback Regulation of Erythropoiesis
• Lower oxygen content of air at high altitudes, anemia, and
circulatory problems may reduce oxygen delivery to body tissues
• Give a negative feedback
White Blood
Cell
• WBCs – Live only a few days
• Lymphocytes – Live for several months or years
• During a period of infection Phagocytic WBCs (Neutrophils
and macrophages) live only a few hours
• Classified into granulocytes and agranulocytes
Types of WBC
• Once pathogens enter the body – combat them by
phagocytosis or immune responses
• Granular leukocytes and monocytes leave the
bloodstream to fight injury or infection
• They never return to it
• Lymphocytes continually recirculate – From blood to
interstitial spaces to lymphatic fluid
• Leukocytosis
– Increase in the number of WBCs above 10,000/L
– Normal, protective response to stress such as invading
microbes, strenuous exercise, anesthesia, and surgery
• Leukopenia
– An abnormally low level of white blood cells (below
5000/L)
– Never ďeŶefiĐial and may be caused by radiation, shock, and
certain chemotherapeutic agents
Emigration
• WBCs leave the bloodstream by a process termed emigration
• Formerly called diapedesis
Chemotaxis
• Microbes and inflaeed tissue Unregistered release different
chemicals – attract phagocytes
Hemostasis
• Hemostasis – Sequence of responses that stops bleeding
• Hemostatic response must be;
– Quick
– Localized to the region of damage
• Three mechanisms reduce blood loss:
– Vascular spasm
– Platelet plug formation
– Blood clotting (coagulation)
Vascular
Spasm
• Arteries or arterioles are damaged
• The circularly arranged smooth muscle contracts
immediately
• Reduces blood loss for several Min to Hrs (Meanwhile other
haemostatic mechanisms go into operation)
The spasm is probably caused by:
• Damage to the smooth muscle
• Substances released from activated platelets
• By reflexes initiated by pain receptors
Platelet
Plug Formation
Platelets store an impressive array of chemicals
• Clotting factors
• Calcium
• Serotonin
• ADP & ATP
• Enzymes that produce TXA2, PG
• FSF – helps to strengthen a blood clot
Membrane Systems
• Take up and store calcium
• Provide channels for release of the granule contents
PDGF
• Cause proliferation of vascular endothelial cells,
vascular smooth ŵusĐle fiďers & fiďroďlasts
• Help repair damaged blood vessel walls
Platelet Adhesion
• Initially, platelets contact and stick to parts of a
damaged blood vessel
• To ĐollageŶ fiďers of the connective tissue underlying the
damaged endothelial cells
Platelet Release
Reaction – Initiation
• Due to adhesion, the platelets become activated
• Extend many projections – enable them to contact and
interact with one another
Platelet Release
Reaction
• Begin to liberate the contents of their vesicles
• Liberated ADP & TXA2 activates nearby platelets
• Serotonin and TXA2 – vasoconstrictors (sustaining
contraction)
Platelet Aggregation
Release of ADP makes other platelets in the area sticky
– This leads to gathering of platelets
– Eventually, the accumulation and attachment of large
numbers of platelets form a mass called a platelet plug
Summary
• Whole blood can be separated as Liquid and cellular
components
• Formed elements – Component buffy coat
• Blood plasma pH – 7.4 the pH level required for normal
cellular functioning
• Erythrocytes carry oxygen and Corban dioxide
• Platelets and blood proteins protect the body against
blood loss by forming blood clots on damaged vessels
• White blood cells are classified into granulocytes and
agranulocytes
• Hemostasis – Sequence of responses that stops bleeding
• Three mechanisms reduce blood loss
– Vascular spasm
– Platelet plug formation
– Blood clotting (coagulation)