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Let us make an in-depth study of the blood in relation to microbiology and infection. The below given article will help you to learn about the following things: 1. Blood Composition 2. Blood Circulation and 3. Application to Nursing.
It is well-established that the blood supplies food to the various cells and tissues of the human body and removes all waste products from them. It also destroys the invading bacteria and their toxin and disposes off with the help of living cells and certain substances contained in it. The blood also plays a great role in the production, transmission, prevention, diagnosis and cure of the disease.
Blood Composition:
Plasma:
The fluid portion of the fresh un-coagulated blood is known as plasma which makes up 55 per cent of whole blood. It is yellowish and transparent. It contains proteins, food for the body tissues and waste products from the tissues. It consists of 91 per cent water, 1 per cent minerals (salts of Na, K, Ca, Mg, P); 1 per cent various substances (uric acid, urea, amino acids, glucose, carbon dioxide, oxygen, lipids and hormones).
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It carries the red blood cells, white cells and platelets which constitute remaining 45 per cent. Plasma contains fibrinogen which is involved in the clotting of the blood, which occurs when the soluble fibrinogen is converted into insoluble fibrin. Other proteins (albumins and various globulins) maintain the water balance of the body.
Gamma globulin is of the globulin fraction or component. Blood is a rich source of antibodies. These antibodies can be used for treatment and prophylaxis of certain diseases and play an important role in the antibody mediated or humoral immunity.
Red Blood Corpuscles:
Human erythrocytes (Greek, erythros, red; kytos, cell) are non-nucleated, biconcave disks. They have a life span of 130 days and are constantly replaced. In adult male, they number about 5 millions per cubic millimetre and in women, it is about 4.5 million per cubic millimeter.
Red blood cells are manufactured in the bone marrow and released into the plasma of the blood. Hemoglobin (respiratory pigment) forms a loose chemical bond with oxygen when exposed to air in the lung, carries oxygen to the tissues of the body and releases it to them.
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Hemoglobin is released into the surrounding when the red blood cells rupture. The process is known as haemolysis (Greek, haima, blood, lysis, to disrupt or dissolve). In vivo and in vitro, red blood cells can be lysed by certain bacterial toxins.
White Blood Corpuscles:
They are also known as leucocytes [Gr. leukos, white).They are larger and less in number than the red blood cells. They are about 7,000 per cubic milli-metre of the blood. They act as scavengers or policemen in the blood. They engulf any foreign particle (dead tissues or bacteria) entering the blood stream, they ingest these particles directly, they move with the help of pseudopodia and enter between the tissue cells of the body.
lf the bacteria enter into the leucocytes through their thin cell membrane, they may be killed and digested by digestive enzymes of the leucocytes. This process is known as phagocytosis. Leucocytes can move out of the blood vessels by their amoeboid movement between the cells lining the blood vessels.
Leucocytes can be attracted by the chemo taxis to the area of the inflammation caused by foreign particles (bacteria). In the infected spot or boil the white, creamy material consists of dead leucocytes (pus cells), dead bacteria, tissue debris, fluid from blood and tissues and is known as “Pus”
Platelets:
They are irregular and disk shaped particles of varying sizes and smaller than erythrocytes. They are about 3,00,000 per cubic millimetre of blood and look like fragments of cells. Their origin is yet unclear and they are also responsible for coagulation of blood. Blood with low platelets may not clot quickly and may cause surgical hazard.
Plasma:
1. Yellowish fluid portion of whole blood.
2. It contains fibrinogen; in blood clotting, soluble fibrinogen is converted into insoluble fibrin, the jelly like substance of the clot.
3. It contains antibodies and bacterial toxins.
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4. In microbiology it is used to diagnose some diseases as it may contain antibodies against some infection.
5. It plays a great role in humoral immunity.
Serum:
1. Straw coloured fluid remaining after clotting of blood.
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2. It contain no fibrinogen.
3. It contain antibodies and bacterial toxins.
4. It is used in the diagnosis of diseases as it contains antibodies against the diseases.
5. It plays an important role in humoral immunity.
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Blood Circulation:
Left ventricle of the heart pushes the blood continuously through the arterial system to the remotest branches – microscopic arterioles, venules or capillary vessels. The wall of the capillary vessels are of one cell thickness. Nutrients and other substances (hormones, oxygen etc.) filter through these thin membranous walls diffuse into the fluid (lymph) which is constantly bathing the tissue cells.
The nutrients are brought from the gastrointestinal tract and liver by the blood. Waste metabolic products (acids, carbon dioxide etc.) diffuse from the tissue cells into the lymph; then from the lymph into the blood stream of capillary venules and venous system which is in continuity with arterioles. These waste products in the venous (impure) blood are carried to the right auricle of the heart and are pumped to the right ventricle through the lungs when the red blood cells and plasma take up oxygen from the air and give off carbon dioxide.
This purified blood returns to the left auricle and then to the left ventricle which pushes again the purified blood to the tissues. In this way, the blood circulates in the body for the benefits of the body (nutrition, metabolism, growth; protection against diseases etc.).
Blood and Disease:
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When blood passes through the tissues infected with toxin producing pathogenic microorganisms (e.g., diphtheria, tetanus) carries with it toxin (toxemia) and if bacteria (Salmonella) enter the blood stream (bacteremia).
The toxin and bacteria are carried along with the blood and are distributed to various parts of the body where they set up the infections, e.g., brain abscess, osteomyelitis (inflammation of bone), otitis media (middle ear infection). Blood borne diseases (malaria, filariasis, yellow fever etc.) can be transmitted by arthropods (mosquitoes) from person to person. The blood carries drugs and antibiotics injected or swallowed to abate the infection.
Blood and Immunity:
Cell and antibody mediated immunities against the infection are performed through the circulating blood, leucocytes in the circulating blood are responsible for cellular immunity, whereas the antibodies for the humoral immunity. Antibodies (Gamma globulins) are soluble protein molecules secreted into the blood by lymphoid cells which are stimulated by the foreign proteins.
Infection:
The term infection is used to designate an entry and the presence of organisms, whereas the disease to designate the response of the host to the infection. Host parasite relationship is a part of science ecology, where the organisms live together and help mutually. A host parasite relationship develops during the evolution of many species of living organisms to their with each other.
Symbiosis or mutualism is a host parasite relationship; when the organisms are mutually antagonistic they are antibiosis. Parasitism or predation, when some organisms live at the expense of the others. The infectious disease is an example of parasitism relationship.
Commensalism is a also an example of host relationship where the organisms thrive side by side peacefully after some struggle for their existence. During the process of infection, immunity and allergy, many hostparasite relationship and adaptation are established.
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Infection is a condition where the microorganisms enter into the human body tissues, grow in or on them, may damage them and the host may react to this damage by manifesting the symptoms like fever, chills, nausea and headache. Infection may be fatal or serious. A pimple is a simple reaction to the infection of the skin; whereas Typhoid is serious if untreated by antibiotics.
Factors of Infection:
(a) Dose of infecting microorganisms.
(b) Virulence of microorganisms:
(i) aggressiveness and
(ii) toxigenicity.
(a) Dose of infecting microorganisms .There is possibility of infection, if the number of microorganisms entering the body is very large; a million of organisms may set up the infection, if the tissue resistance is lowered by fatigue, disease or alcoholism; or after entry into the body, by overcoming the host defence mechanism; whereas a single bacterium (coccus or bacillus) may not be able to establish in the healthy body.
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(b) Virulence of organisms is the ability of organisms to enter, establish, infect, damage the tissues and produce the disease.
The virulence depends upon two factors:
(i) aggressiveness, and
(ii) Toxigenicity.
(i) Aggressiveness:
Skin inhabiting bacteria are not very aggressive as they are unable to penetrate the skin barrier of the body. If they get entry into the skin, they will become aggressive in the favourable environment for their growth. Heavily capsulated organisms (Pneumococci, anthrax bacilli, klebsiella) are highly aggressive and dangerous as they cannot be engulfed by leucocytes.
(ii) Toxigenicity:
Toxigenicity is the ability of organisms to elaborate the toxin. Bacteria producing toxin may not be aggressive (i.e., invasive), but they damage the body tissues by their toxin. For example, toxigenic strains of diphtheria bacilli lodging on the tonsils or in the throat will produce the toxin which is absorbed in the blood (toxemia) carried to various parts of the body and ultimately can cause the death. Tetanus bacilli are also toxigenic as diphtheria bacilli.
Toxins:
Toxigenic strains of organisms produce two types of toxins which are proteins in nature. Toxin may damage the tissues of the body after combining with nerves, heart muscle, liver.
1. Endotoxins (Greek, endon, inside):
They are found in the cytoplasm enclosed by the cytoplasmic membrane. These intracellular toxins, known as endotoxins, are released after the death and lysis of bacterial cells (e.g., Gram-negative bacteria, gonococci, typhoid bacilli) produce endotoxin.
2. Exotoxins (Greek, exo, outside):
Toxin producing bacteria liberate toxins, through their cytoplasmic membrane, which are known as exotoxins. Co-rynebacterium diphtheriae, Clostridium tetani produce exotoxins. Few bacteria produce both endotoxin and exotoxin.
Specificity of Toxin:
Toxins of organisms are specific in their action. Tetanus toxin has an affinity for nerve cells, causing spasm of jaw muscles, i.e., lockjaw. Diphtheria toxin has affinity for heart muscle, death in the severe infections is usually due to acute myocarditis and heart failure.
This toxin may lead to such sequelae as postdiphtheric paralysis. In staphylococcal food poisoning, enterotoxin of Staphylococcus aureus produces vomiting and diarrhea. This enterotoxin is also known as preformed toxin, as this toxin is preformed in the food contaminated by Staphylococcus aureus and consumed later.
Application to Nursing:
A nurse should know that plasma and serum contain antibodies (Gamma globulins) which play a major role by protecting from diseases. She should also be aware of the fact that the patient with low platelet count may be affected by surgical hazard, as his blood may not clot immediately. A knowledge of blood clotting mechanism is necessary, the soluble fibrinogen is changed into insoluble fibrin which causes clotting. Antibiotics and drugs injected or swallowed are carried by the blood to combat the infection. A sound knowledge of toxin is essential, as the toxins are responsible for many diseases.
