Components of Whole Blood
Whole blood is a living substance that circulates through the heart, arteries, veins, and capillaries carrying nourishment, electrolytes, hormones, vitamins, antibodies, heat, and oxygen to the body's tissues. Whole blood composed of red blood cells, white blood cells, and platelets suspended in a fluid called plasma.
Physical Characteristics and Volume:
- Blood is a tenacious, opaque fluid with a metallic taste- Color varies from scarlet to dark red
- The pH of blood is 7.35–7.45
- Temperature is 38°C
- Blood accounts for around 8% of body weight
- Usual volume: 5–6 L for males, and 4–5 L for females
Blood Plasma
Blood plasma is the straw-colored liquid component of blood, in which the blood cells are suspended.It forms about 55% of the total blood volume.
It is composed of mostly water (90% by volume) and contains dissolved proteins, glucose, clotting factors, mineral ions, hormones, and carbon dioxide (plasma being the main medium for excretory product transportation).
Blood plasma is prepared by rotating a tube of fresh blood in a centrifuge until the blood cells fall to the bottom of the tube.
The blood plasma is then spewed or drawn off. Blood serum is blood plasma free of fibrinogen or the other clotting factors.
Blood plasma contains over 100 solutes, including:
● Proteins – albumin, globulins, clotting proteins, and others● Lactic acid, urea, creatinine
● Organic nutrients – glucose, carbohydrates, amino acids
● Electrolytes – sodium, potassium, calcium, chloride, bicarbonate
● Respiratory gases – oxygen and carbon dioxide
Plasma carry materials needed by cells and materials that must be removed from cells:
• various ions (Na+, Ca2+, HCO3)• glucose and traces of other sugars
• amino acids
• other organic acids
• cholesterol and other lipids
• hormones
• urea and other wastes
Formed Elements
- Erythrocytes, leukocytes, and platelets are formed the formed elements.- Most formed elements live in the bloodstream for only a few days.
- Most blood cells do not divide but are renewed by cells in bone marrow
Erythrocyte
- Usually biconcave and circular outline, devoid of a nucleus and essentially no organelles.- The number in man varies between 5 and 5.5 million per cubic mm of blood.
- Contain hemoglobin (Hb), a protein that functions in gas transport.
- Hold the plasma membrane protein spectrin and other proteins that:
● Give erythrocytes their flexibility
● Allow them to change shape as necessary
- Erythrocytes are an example of the harmonizing of structure and function.
- Structural characteristics to come up with its gas transport function.
● The biconcave shape has a huge surface area relative to volume.
● Erythrocytes are more than 97% hemoglobin
● ATP has generated anaerobically, so the erythrocytes do not consume the oxygen they transport
Erythrocyte Function:
• RBCs are dedicated to respiratory gas transport.• Hb reversibly binds with oxygen and most oxygen in the blood is bound to Hb.
• Hb is constituted of the protein globin, made up of two alpha and two beta chains, each bound to a heme group
• Every Hb molecule can transport four molecules of oxygen.
White blood cells:
Leukocytes can be further subdivided into granular leukocytes, i.e. neutrophils, basophils and eosinophils, and non-granular leukocytes, i.e. monocytes and lymphocytes.In healthy persons, the relative numbers of circulating leukocyte types are fully stable.
A differential leukocyte count generally produce the following cell frequencies:
• ~ 60% neutrophils (50% - 70%)
• ~ 3% eosinophils (>0% - 5%)
• ~ 0.5% basophils (>0% - 2%)
• ~ 5% monocytes (1% - 9%)
• ~ 30% lymphocytes (20% - 40%).
- Leukocytes, the only blood elements that are complete cells.
- Are less numerous than RBCs
- Makeup 1% of the total blood volume
- Can leave capillaries via diapedesis
- Move through tissue spaces
Granulocytes
· Granulocytes – neutrophils, eosinophils, and basophils.· Have cytoplasmic granules that stain specifically (acidic, basic, or both) with Wright’s stain.
· Are larger and usually shorter-lived than RBCs.
· Have lobed nuclei.
· Are all phagocytic cells.
· Granular leukocytes are all roughly the same size - about 12-15 μm in diameter.
· Their nuclei form lobes, and nucleoli cannot be seen. The number of nuclear lobes varies according to cell type. All granulocytes are motile.
· The term granulocytes refers to the presence of granules in the cytoplasm of these cells.
· The granules correspond to secretory vesicles and lysosomes.
· Specific granules are the granules that are only found in one particular type of granulocytes.
Neutrophils:
● Neutrophils have two types of granules:
- Take up both acidic and basic dyes.
- Give the cytoplasm a lilac color.
- Have peroxidases, hydrolytic enzymes, and defensins (antibiotic-like proteins).
● Neutrophils are our body’s bacteria, slayers
● have a very characteristic nucleus.
- It is divided into 3-5 lobes which are connected by thin strands of chromatin.
- The number of lobes rises with cell age.
- Up to 7 lobes can be present in very old neutrophils (hypersegmented cells).
● Neutrophils (like all other granulocytes, monocytes, and lymphocytes) contain all the organelles that make up a typical cell.
● In addition to the usual complement of organelles, they also contain two types of granules.
- Primary granules (or A granules) contain lysosomal enzymes and are likely to be primary lysosomes, although they are larger (0.4 μm) than the "ordinary" primary lysosome.
- Secondary granules (or B granules), the specific granules of the neutrophils, contain enzymes with strong bactericidal actions.
• The specific granules of neutrophils stain weakly if they are at all visible - they are "neutral", hence the term neutrophil.
Functions
• Neutrophils play a central role in inflammatory processes.
• Large numbers invade sites of infection in response to factors (e.g. cytokines) released by cells that reside at an infection site.
• Neutrophils are the first wave of cells invading infection sites.
• Receptors in their plasma membrane allow them to recognize foreign bodies, e.g. bacteria, and tissue debris, which they begin to phagocytose and destroy.
• The phagocytotic activity of neutrophils is further stimulated if invading microorganisms are "tagged" with antibodies (or opsonized).
• Neutrophils cannot replenish their store of granules.
• The cells die once their supply of granules has been finished.
• Dead neutrophils and tissue debris are the major components of pus.
• Their lifespan is only about one week.
• Lost neutrophils are soon replenished from a secure population in the bone marrow.
Eosinophils
• Eosinophils account for 1–4% of WBCs.
• Have red staining, bilobed nuclei connected via broadband of nuclear material
• Have red (acidophilic) large, coarse, lysosome-like granules.
• Lead the body’s counterattack against parasitic worms.
• Decrease the severity of allergies by phagocytizing immune complexes.
• Almost all the cytoplasm appears filled with the specific granules of the eosinophils.
• "eosinophil" means, these granules are not neutral but stain red or pink when eosin or a similar dye is used in the staining process.
Functions
• The presence of antibody-antigen complexes stimulates the immune system.
• Eosinophils phagocytose these complexes and this may prevent the immune system from "overreacting".
• Their granules also contain the enzyme's histaminase and arylsulfatase.
• These enzymes break histamine and leukotrienes, which again may lessen the effects of their release by basophils or mast cells.
Basophils
• Account for 0.5% of WBCs.
• Have U- or S-shaped nuclei with two or three visible constrictions.
• Are functionally like mast cells.
• contain large, purplish-black (basophilic) granules that contain histamine.
• Histamine – an inflammatory chemical that acts as a vasodilator and attracts other WBCs (antihistamines counter this effect)
• Basophilic granulocytes have a 2 or 3 lobed nucleus.
• The lobes are not as well defined as in neutrophilic granulocytes and the nucleus may appear S-shaped.
• The specific granules of basophils are stained deeply bluish or reddish-violet.
• The granules are not as many as those in eosinophils.
• They contain heparin, histamine lysosomal enzymes, and leukotrienes.
Functions
• Heparin and histamine are vasoactive substances.
• They dilate the blood vessels, make vessel walls more permeable, and prevent blood coagulation.
• Consequently, they facilitate the access of other lymphocytes and plasma-borne substances of importance for the immune response
(e.g. antibodies) to e.g. a site of infection.
• The release of the contents of the granules of basophils is receptor-mediated.
• Antibodies produced by plasma cells (activated B-lymphocytes) bind to Fc-receptors on the plasma membrane of basophils.
• If these antibodies meet their antigens, they induce the release of the contents of the basophil granules.
Non-granular leukocytes Agranulocytes
Agranulocytes – lymphocytes, and monocytes:• Lack visible cytoplasmic granules
• Are close structurally but are functionally distinct and unrelated cell types
• Have spherical (lymphocytes) or kidney-shaped (monocytes) nuclei
Monocytes
• Monocytes account for 4–8% of leukocytes.
• They are the largest leukocytes
• They have abundant pale-blue cytoplasm with vacuolation.
• They have purple-staining, U- or kidney-shaped nuclei
• They go out of the circulation, enter tissue, and differentiate into macrophages
• These cells can be slightly larger than granulocytes (about 12-18 μm in diameter).
• Their cytoplasm stains commonly somewhat stronger than that of granulocytes, but it does not contain any structures which would be visible in the light microscope using most traditional stains (A little very fine bluish gains may be visible in some monocytes).
• The "textbook" monocyte has a C-shaped nucleus.
Functions
• Once monocytes enter the connective tissue they differentiate into macrophages.
• At the place of infection macrophages are the dominant cell type after the death of the invading neutrophils.
• The phagocytose microorganisms, tissue debris, and the dead neutrophils.
Lymphocytes
• Account for 25% or more of WBCs.
• contain large, dark-purple, circular nuclei with a thin rim of blue cytoplasm.
• Mostly found trapped in lymphoid tissue (some circulate in the blood)
• There are two types of lymphocytes:
- T cells function in the immune response.
- B cells give plasma cells, which produce antibodies.
• These cells are very variable in size.
• The small lymphocyte is smaller than erythrocytes (down to ~5 μm in diameter) while the largest may reach the size of large granulocytes (up to
15 μm in diameter).
• How much cytoplasm is discernible depends very much on the size of the lymphocyte.
• In small ones, which are most lymphocytes in the blood, the nucleus may appear to fill the entire cell. Large lymphocytes have a wider rim of cytoplasm which surrounds the nucleus.
• Both the nucleus and the cytoplasm stain Dark blue.
• The typical lymphocyte only contains the usual complement of cellular organelles.
• The appearance of lymphocytes may change drastically when they are activated.
Functions
• Most lymphocytes in the bloodstream belong to either the group of B-lymphocytes (~5%) or the group of T-lymphocytes (~90%).
• The two groups difficult to distinguish by using routine light or electron microscopy. Except they become activated.
• Upon exposure to antigens by antigen-presenting cells (e.g. macrophages) and T-helper cells (one special group of T-lymphocytes) B-lymphocytes differentiate into antibody-producing plasma cells.
• T-lymphocytes represent the "cellular arm" of the immune response (cytotoxic T cells) and may attack foreign cells, cancer cells, and cells infected by e.g. a virus.
T-lymphocytes and B-lymphocytes form most lymphocytes in the blood flow, but they do not add up to 100%, small lymphocytes are predominant.
The much less common medium-sized or large lymphocytes may represent e.g.
• natural killer (NK) cells that belong to the group of large granular lymphocytes, or
• hemopoietic stem cells of which a few will be circulating in the bloodstream.
Blood Platelets (or thrombocytes):
• Platelets are small cytoplasmic bodies obtained from cells.• They circulate in the blood and are required in hemostasis leading to the formation of blood clots.
• Like red blood cells, platelets don’t contain a nucleus.
• If the number of platelets decreases, excessive bleeding can occur; however, if the number of platelets is too high, blood clots can form (thrombosis). which block blood vessels and may lead to a stroke and/or a heart attack.
• An abnormality or disease of the platelets is called thrombocytopathy which could be either a low number (thrombocytopenia), a decrease in
function (thrombasthenia), or an increase in number (thrombocytosis).
• Platelets are produced by thrombopoiesis in bone marrow, by budding off from megakaryocytes.
• The physiological range for platelets is 150-400 x 109 per liter.
• Around 1 x 1011 platelets are produced per day by an average adult.
• The lifespan of circulating platelets is 7-10 days.
• This process is regulated by thrombopoietin, a hormone usually produced by the liver and kidney.
• Each megakaryocyte produces between 5,000 and 10,000 platelets.
• Old platelets are break by the spleen and by Kupffer cells in the liver.
• Platelets are around 3 μm long but appear smaller in the microscope.
• This is due to their cytoplasm is divided into two zones: an outer hyalomere, which hardly stains, and an inner granulomere, which have bluish staining granules.
• These granules are normally not individually visible with the highest magnification on your microscope, and the granulomere appears more or less homogeneously blue.
Functions
• Platelets assist in hemostasis, the arrest of bleeding.• Serotonin is a potent vasoconstrictor.
• The secretion of serotonin from thrombocytes, which adhere to the walls of damaged vessels, is sufficient to close even small arteries.
• Platelets, which come into contact with collagenous fibers in the walls of the vessel (which are not usually exposed to the bloodstream), swell, become "sticky" and activate other platelets to undergo the same transformation.
• This cascade of events results in the formation of a platelet plug (or platelet thrombus). Finally, activating substances are released from the damaged vessel walls and the platelets.
• These substances mediate the conversion of the plasma protein prothrombin into thrombin.
• Thrombin catalyzes the conversion of fibrinogen into fibrin, which polymerizes into fibrils and forms a fibrous net in the arising blood clot.
• Platelets captured in the fibrin net contract leading to clot retraction, which further assists in hemostasis.
• Blood coagulation is a complex process, which required a large number of other proteins and messenger substances.
• Deficiencies in any one of them, either inherited or acquired, will lead to an impairment of hemostasis.
Comments
Post a Comment