physiology of blood - suli pharma · physiology of blood dr. hiwa s. namiq 6-11-2019 23 november...
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Physiology of Blood
Dr. Hiwa S. Namiq 6-11-2019
23 November 2019
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Introduction
Red blood cells (erythrocytes)
• The major function of RBC is to transport Hb which in turn carries oxygen from lungs to the tissues.
• On the other hand, water of blood is able to transport enormous amount of CO2 (in the form of bicarbonate-HCO3_) from tissues to the lungs with the aid of carbonic anhydrase (an enzyme found on RBC) that catalyzes the reversible reaction between CO2 and H2O to form carbonic acid (H2CO3).
• The hemoglobin in the RBCs is an excellent acid-base buffer, so the RBCs are responsible for most of the acid-base buffering power of whole blood
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Shape and size • RBCs are biconcave discs having a mean diameter
of about 7.8 micrometers and a thickness of 2.5 micrometers at the thickest point.
• The shape changes remarkably and can be deformed into any shape.
• In normal men, the average number of red blood cells per cubic millimeter is 5,200,000 (±300,000); in normal women, it is 4,700,000 (±300,000).
• The whole blood contains an average of 15 gm Hb for men and 14 gm for women per each dl of blood .
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Areas of the body that produce RBC
Period of Gestation/ or at birth Area that produce RBC
Early weeks Yolk sac
Middle trimester Liver, spleen and lymph nodes
Last month of gestation and after birth
Exclusively in the bone marrow
Age 5 BM of all bones
Age 20 BM of long bones (except tibiae and humeri)
Beyond 20 Membranous bones
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23 November 2019 Function of the erythropoietin mechanism to increase production of
red blood cells when tissue oxygenation decreases
Tissue Oxygenation Is the Most Essential
Regulator of Red Blood Cell Production.
Conditions that decrease the quantity of oxygen
transported to the tissues ordinarily increase the
rate of RBC production:
Anemia
High altitude
Low blood volume
Chronic cardiac failure and lung disease
Erythropoietin Regulates Red Blood Cell Production
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Regulation of Red Blood Cell Production
• The blood cells are formed in the bone marrow from a single type of cell called the pluripotential hematopoietic stem cell ( from which all the cells of the circulating blood are derived).
• The principal stimulus for red blood cell production in low oxygen states is a circulating hormone called erythropoietin.
• In the absence of erythropoietin, hypoxia has little or no effect in stimulating red blood cell production. 23 November 2019
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• About 90 per cent of all erythropoietin is formed in the kidneys (especially renal tubular epithelial cells); the remainder is formed mainly in the liver.
• Erythropoietin stimulate proerythroblast production by the bone marrow and within about 5 days new red cells appear in the circulation.
• Patients with renal diseases that destroy the kidneys easily develop anemia.
• Vitamin B12 and folic acid (maturation factors) are especially important for final maturation of the red blood cells which are essential for the synthesis of DNA
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Regulation of Red
Blood Cell
Production—Role
of Erythropoietin 90%
10%
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• Maturation failure occurs when there is
deficiency of either vitamin B12 or folic acid (Megaloblastic anemia) .
• In pernicious anemia (atrophic gastric mucosa), the parietal cells of gastric mucosa fail to produce intrinsic factor (a glycoprotein) which is essential for V B12 absorption.
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Total iron quantity 4 – 5 grams
HB 65 %
RES (mononuclear
phagocyte system-in LN
and spleen) and liver
(stored)
15-30%
Myoglobin 4%
Various heme compound 1%
Transferrin (bound) 0.1% 23 November 2019
Iron Metabolism
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The Pathway of Iron Absorption, Transport, and Storage
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ferric
ferrous
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Iron transport and metabolism
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The Life and Death of Erythrocytes
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Anemias
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Anemia means deficiency of
hemoglobin in the blood, which
can be caused by either too few
red blood cells or too little
hemoglobin in the cells.
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Types of Anemia
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• Inadequate nutrition (Iron-deficiency anemia)
• Blood loss anemia (acute or chronic blood loss). The
body replaces the fluid in 1 to 3 days, but the RBC
concentration returns to normal within 3 to 6 weeks. .
• Aplastic anemia (lack of functioning bone marrow due
to high-dose radiation (X ray) radiation, chemicals,
drugs and autoimmunity) .
• Megaloblastic anemia (pernicious anemia, total
gastrectomy and intestinal sprue).
• Hemolytic anemia (hereditary spherocytosis, sickle cell
anemia (HB S), erythroblastosis fetalis Rh –ve mother
born to Rh +ve baby).
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Effects of anemia • Decrease blood viscosity. The resistance to blood flow in
the peripheral blood vessels decrease, so greater than normal quantities of blood flow through the tissues and return to the heart and greatly increasing cardiac output.
• Hypoxia resulting from diminished transport of oxygen by the blood causes the peripheral tissue blood vessels to dilate, followed by increased blood flow to the tissues
• Thus the main effect of anemia is greatly increased cardiac output and increased pumping workload on the heart.
• During exercise, which greatly increases tissue demand for oxygen, extreme tissue hypoxia results and acute cardiac failure may ensue 23 November 2019
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Polycythemia • It means increase in the total number of RBCs.
• Types of polycythemia:
1. Secondary polycythemia (High altitudes (14,000 to 17,000 feet) and cardiac failure. The red cell count rises to 6 – 7 million cells/mm3.
2. Polycythemia vera (erythremia) red blood cell count may reach 7 to 8 million/mm3. It is caused by genetic abnormality. The viscosity of the blood sometimes increases from the normal of 3 times the viscosity of water to 10 times that of water.
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Effects of Polycythemia
• Increase in blood viscosity.
• Blood flow become sluggish.
• Venous return not change.
• Blood pressure is elevated in one third of patients.
• Skin color later becomes bluish (cyanotic) because the amount of deoxygenated blood is increased.
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Leukocytes And
Resistance of the body to infection
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The living body has three lines of defense against pathogens:
• 1.External barriers (skin and mucous membranes) which are impenetrable to most of the pathogens that daily assault us (Innate immunity).
• 2.Antimicrobial proteins (inflammation, fever)(innate immunity). These mechanisms are
Present from birth
Effective against a wide range of pathogens
Work even against pathogens to which the body has never been exposed.
• 3. The specific immune system (Acquired immunity), which not only defeats a pathogen but leaves the body with a “memory” of it.
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Leukocytes (White Blood Cells)
• The leukocytes, also called white blood cells, are the mobile units of the body’s protective system. They are formed and matured partially in the
– Bone marrow (granulocytes and monocytes and a few lymphocytes)
– And partially in the lymph tissue (lymphocytes and plasma cells).
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Neutrophil Basophil Eosinophil
Monocyte Lymphocyte
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LIFE SPAN OF WHITE BLOOD CELLS • After being released from the bone marrow, the
granulocytes normally remain 4 to 8 hours in circulation and 4 to 5 days in tissues.
• At times of tissue infection, their life span is often shortened to only a few hours because they are destroyed in the infected area.
• The monocytes remain 10 to 20 hours in blood and then pass into the tissues. Once in the tissues, they swell to much larger sizes to become tissue macrophages, and they can live for months unless destroyed while performing phagocytic functions
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• Lymphocytes enter the circulatory system continually, along with drainage of lymph from the lymph nodes and other lymphoid tissue. After a few hours, they pass out of the blood back into the tissues by diapedesis. Then they re-enter the lymph and return to the blood again and again
• The platelets in the blood are replaced about once every 10 days
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Leukopenia and leukemia
• Leukopenia is a clinical condition in which the bone marrow produces very few WBCs. This condition leaves the body unprotected against many bacteria and other invaders
• leukemia is uncontrolled production of WBCs caused by cancerous mutation of a myelogenous or lymphogenous cell. It is usually characterized by greatly increased numbers of abnormal WBCs in the circulating blood.
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Resistance of the body to infection
Immunity It is the ability of body to resist almost all types of
organisms or toxins that tend to damage the tissues
and organs.
Types of immunity:
1. Innate immunity (non-specific immunity)
2. Acquired immunity (specific immunity) • Much of immunity is acquired immunity that does not develop until after
the body is first attacked by a bacterium, virus, or toxin; often weeks or
months are required for the immunity to develop.
• While innate immunit results from general processes, rather than from
processes directed at specific disease organisms
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Acquired immunity (specific)
• The body develops this immunity after being first attacked by a bacterium, virus, or toxin, and often requiring weeks or months to develop.
• Acquired immunity is caused by a special immune system that forms antibodies and/or activated lymphocytes that attack and destroy the specific invading organism or toxin.
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Types of acquired immunity
• Humoral immunity or B-cell immunity. In
which the B-lymphocytes produce circulating antibodies.
• Cell-mediated immunity or T-cell immunity. In which the T-lymphocytes produce activated or sensitized T-cells.
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Both types of acquired immunity are initiated by
antigens and they are the product of body's
lymphocytes.
Location of lymphocytes: 1. Lymph nodes (most extensively)
2. Lymphoid tissues (spleen, submucosal areas of
the gastrointestinal tract, thymus, and bone
marrow).
Both of them need to be preprocessed.
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• The T-lymphocytes first migrate to and are
preprocessed in the thymus gland, and thus
they are called “T” lymphocytes
• While B-lymphocytes are preprocessed in the
liver during mid-fetal life and in the bone marrow in late fetal life and after birth. They are first discovered in birds (Bursa of Fabricius).
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Formation of antibodies and sensitized T-lymphocytes by a lymph node in response
to antigen.
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• Formation of memory cells by B and T cells • Subsequent exposure to the same antigen will cause a much
more rapid and much more potent response in the second time.
• This is due to formation of memory cells by both T and B lymphocytes.
Time course of antibody response to a
primary injection of antigen and to a
secondary injection several weeks later
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Nature of the antibodies
• The antibodies are gamma globulins called immunoglobulins (Ig).
• All the immunoglobulins are composed of combinations of light and heavy polypeptide chains.
• Each chain has a variable and a constant portion.
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Structure of immunoglobulin
.
Specific for Ab. Binds
to a particular type of
Ag
Determines:
1.Diffusivity
2.Adherance within tissues
3.Attachment to complement sys
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IgG
• A bivalent antibody. 75 per cent of all antibodies. important when the body is subsequently (secondary response) exposed to the same antigen.
IgE
• Small percentage of the antibodies, especially involved in allergy.
IgM
• Large share of the antibodies during the primary response, have 10 binding sites (exceedingly effective in protection), there are not many IgM antibodies.
IgA • Found in secretions of digestive, respiratory, genitourinary systems
as well as in milk and tear.
IgD
• Present on the surface of many B lymphocytes and the surface of basophil and mast (activates them to secrete antimicrobial proteins during respiratory immune response)
General classes of antibodies
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Direct action
•Agglutination, in which multiple large particles with
antigens on their surfaces, such as bacteria or red cells,
are bound together into a clump.
•Precipitation, in which the antibody forms a complex
with the antigen (such as tetanus toxin) and makes it
insoluble and precipitates.
•Neutralization, in which the antibodies cover the toxic
sites of the antigenic agent.
•Lysis, in which potent antibodies are directly attacking
membranes of cellular agents causing their rupture.
Mechanisms of action of antibodies
Direct action and indirect (activation of complement
system)
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T-Lymphocytes and
Hemostasis
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T-lymphocytes
Three major groups of T-lymphocytes:
• Helper T cells
• Cytotoxic T cells
• Suppressor T cells.
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Produce lymphokines
AIDS
Helper T-cells
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Direct-attack cells
Killer cells
Hole-forming protein
perforins
Fluid flow
Swollen, dissolve
Cytotoxic T cells
Suppressor T cells
Suppresses Cytotoxic cells from causing excessive
immune reactions that might be damaging to the
body’s own tissues
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Injecting toxins
• Toxic nature has been destroyed with chemicals
• Tetanus and botulism
Injecting dead
organisms
• No longer capable of causing disease
• Typhoid fever, whooping cough and diphtheria.
Infecting with live-
attenuated organisms
• Poliomyelitis, yellow fever, measles and smallpox.
Immunization
(Active)
Achieving acquired immunity
against specific diseases
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PASSIVE IMMUNITY • Temporary immunity can be achieved in a person
without injecting any antigen. It can be achieved by infusing antibodies, activated T cells, or both obtained from the blood of someone else or from some other animal that has been actively immunized against the antigen.
• Antibodies last in the body of the recipient for 2 to 3 weeks, and during that time, the person is protected against the invading disease. Activated T cells last for a few weeks if transfused from another person but only for a few hours to a few days if transfused from an animal.
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Hemostasis and
Blood coagulation
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Hemostasis means prevention of blood loss. If a vessel is ruptured several mechanisms operate to achieve hemostasis:
• Vascular constriction.
• Formation of a platelet plug.
• Formation of a blood clot as a result of blood coagulation.
• Growth of fibrous tissue into the blood clot to close the hole in the vessel permanently.
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Platelets • Platelets (thrombocytes) are minute discs 1 to 4
micrometers in diameter, formed in the bone marrow from megakaryocytes.
• The normal concentration of platelets in the blood is between 150,000 and 300,000 per microliter. It has a half-life in the blood of 8 to 12 days
• Platelets have many functional characteristics of whole cells, even though they do not have nuclei and cannot reproduce.
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The cytoplasm contains:
1. Actin and myosin molecules (contractile proteins).
2. Endoplasmic reticulum and the Golgi apparatus residuals (store calcium ions).
3. Mitochondria (forming adenosine triphosphate (ATP) and adenosine diphosphate (ADP).
4. Prostaglandins (vascular and tissue reaction)
5. Fibrin-stabilizing factor
6. Growth factor (causes endothelium, vascular smooth muscle, and fibroblasts to multiply and grow.
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Platelet plug formation
Contact of platelets with exposed collagen
Contractile proteins cause release of granules (contain active factors)
Stick to VWF, secret ADP and TX-A2, activating nearby platelets
Platelet plug formation + fibrin threads
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Clotting in a traumatized blood vessel
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Blood clotting Mechanism of blood coagulation
1. In response to rupture of the vessel or damage to the blood itself, a complex cascade of chemical reactions occurs in the blood involving more than a dozen blood coagulation factors. The net result is formation of a complex called prothrombin activator.
2. The prothrombin activator catalyzes conversion of prothrombin into thrombin.
3. The thrombin acts as an enzyme to convert fibrinogen into fibrin fibers that enmesh platelets, blood cells, and plasma to form the clot.
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• Prothrombin is formed continually by the liver.
• Vitamin K is required by the liver for normal formation of prothrombin. Therefore, either lack of vitamin K or the presence of liver disease can decrease the prothrombin level so low that a bleeding tendency results.
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Conversion of prothrombin to thrombin
and polymerization of fibrinogen to form
fibrin fibers
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Prevention of intravascular clotting
Factors that prevent intravascular clotting
• Endothelial surface factors which are:
1. Smoothness of the endothelial cell surface.
2. Presence of a layer of glycocalyx on the endothelium which repels clotting factors and platelets.
3. Presence of thrombomodulin which binds thrombin.
• Antithrombin action of fibrin and antithrombin III
• Heparin (anticoagulant) (a polysaccharide produced by mast cells and basophils, specially found in the pericapillary tissues surrounding the lungs and the liver).
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• When a clot is formed, a large amount of plasminogen is trapped in the clot along with other plasma proteins.
• In addition to promote clotting, factor XII catalyzes the formation of a plasma enzyme called kallikrein.
• Kallikrein, in turn, converts the inactive protein plasminogen into plasmin, a fibrin-dissolving enzyme that breaks up the clot.
• In fact, many small blood vessels in which blood flow has been blocked by clots are reopened by this mechanism.
Lysis of Clots (Fibrinolysis)
Activation of plasminogen to form plasmin -
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Mechanism for dissolving blood clots (clot lysis)