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Vitamins - Overview

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Weight Loss: Physiology And Psychology

The circulation medium is the transport system of the body and carries food, oxygen, water, waste and other essentials for cell maintenance. It is divided into three parts. The blood is the fluid in which all materials are carried to tissues. The heart is the driving force to the propel blood and the vessels are the routes by which blood travels from and back to the heart.

Blood is a thick red fluid when oxygenated but turns purplish red when deoxygenated. It is slightly alkaline with little tolerance, but is fairly stable. This ensures cell survival (see lactic acid/exhaustion rather than cell death). The volume is roughly three to four litres. This fluid is plasma (clear) in which there are solid particles. The small round bodies are blood corpuscles or cells. Solid part is about 45% liquid and 55% plasma. It is a straw coloured watery fluid. Mostly water (90%) and contains mineral salts (chlorides: mostly Na and some K), phosphates and carbonates (Na, K and Ca).

Proteins make blood viscous and include albumin which is thought to be formed in the liver. If this is constantly lost as in kidney disease then osmotic pressure drops and liquid escapes through capillary walls into tissues. This results in oedema. The viscosity also assists the maintenance of the blood pressure. Globulin is derived from white blood cells (lymphocytes). Fibrinogen and prothrombin are both produced in liver and are involved in blood clotting. Plasma without fibrinogen is serum and is a clear yellow liquid - often seen seeping from wounds when clotting has occured.

Heparin is formed in the liver and stops blood clotting in vessels. Simple foodstuffs are glucose, amino acids fatty acids and glycerol and vitamins. These all come from digestion and combustion of the foodstuffs to provide energy. Gases in solution are oxygen, carbon dioxide and nitrogen. Wastes are uric acid, urea and creatinine. These are made in liver to be excreted by kidney. Antibodies and antitoxins are complex proteins which protect against bacterial infection. Hormones arrive from ductless glands. Enzymes are protein catalysts for biochemical processes to occur.

• The fresh water (46 litres) to cells is supplied from plasma and both bathes the cells (extracellular, 17/46 litres approx) and includes water in blood vessels (3 of 17 litres). The other 14 litres of the extracellular water is known as the interstitial fluid and renews that within the cell (intracellular, 29/46 litres approx).

Blood cells are of three types:

• Erythrocytes (red)
• Leucocytes (white)
• Platelets (thrombocytes)

Red cell formation occurs in the bone marrow: mature products released into the blood. Marrow is found at the extremity of long bones and in flat and irregular bones. In childhood the red bone marrow extends throughout the shaft of the long bones (more need for red cells). Eight different cells are formed all from a single type - the pluripotent stem cell.

Stem Cells

This gives five lines of cell. The myeloblast which gives rise to three types of granulocyte cell (eosinophil, neurophils and basophils). The monoblast and lymphoblast lines give rise to the agranulocyte cell (monocyte and T-lymphocyte/B-lymphocyte respectively). The red cells (erythrocyte) derived from proerythroblast cell line and platelets (thrombocytes) from the megakaryoblast through megakaryocyte cell lines. Red cells contain no nucleus but have protein haemoglobin. They are yellow in colour, but the massed effect is red. They contains an atom of iron. Haemoglobin has a great affinity for oxygen. It passes through the lungs and takes up oxygen becoming the bright red oxyhaemoglobin. It gives up oxygen to the tissues and turns a dull purplish-red as a result. The function is thus to carry oxygen to and take carbon dioxide away from tissues. Either insufficient haemoglobin or a low red cell count leads to anaemia.

Red cells pass through various stages of development in the bone marrow. The size reduces, but the amount of haemoglobin steadily increases until the nucleus eventually disintegrates. As red cells are broken down the iron content is stored and reused. Between 10-15mg iron daily should be ingested for normal health. The lifespan of a red blood cell is about 120 days after which it is ingested by the monocyte/macrophage system in the spleen and lymph nodes.

The cells in this system have the ability to move about and combined with phagocytic powers makes this one of the most important defences of the body against micro-orgnisms. They are also concerned with the production of antibodies. Cells of this system occur in connective tissue (histiocytes), blood (monocytes), lining blood vessels of bone marrow, spleen and liver and parts of the suprarenal gland and the anterior lobe of the hypophysis. In the lymph nodes, lymph follicles of the small intestines and the tonsils. In the meninges where they are called meningiocytes. Red cell production and destruction occurs at roughly the same rate so levels remain constant.

Cyanocobalamin (vitamin B12) is necessary for the maturation of red cells and usually comes from the diet. It is an extrinsic factor which can only be absorbed from the small intestine when it is combined with the intrinsic factor (from the stomach). This mixture is known as the anti-anaemic (or haemopoietic) factor and is stored in the liver to be passed to the bone marrow as required. Other factors include vitamin C, folic acid (from B-complex), the hormone thyroxine along with trace levels of copper and manganese.

White cells (leucocytes) are larger than red cells (10 micrometres v 7.2 micrometres), but less numerous. This number increases (leucocytosis) considerably upon infection.:

• Polymorphonuclear leucocyte (granulocytes)

• about 75% white cell count (survival around 21 days). About 70% of this comprises neutrophils (phagocytes) which are capable of ingesting small particles (bacteria or cell debris). Process known as phagocytosis. This can accumulate where there is infection by passing out of blood stream through capillary walls (amoeboid movement). Eosinophils (4%) levels increase during allergic states (asthma). Basophils (1% or less) contain heparin and histamine.
  

• Lymphocytes (20% white cell count)

• made in lymph nodes and lymphatic tissue of spleen, liver and other organs. Show amoeboid movement but are not actively phagocytic. Concerned with the production of antibodies.

• Monocytes (5% total)

• largest and have horse-shoe shape nucleus. They have amoeboid movement and are phagocytic.

• Platelets (thrombocytes)

• smaller than red cells but made in bone marrow. They are necessary for clotting blood. Blood loss following a cut is prevented by haemostasis and is in three parts. Vascular spasm - narrowing of lumen to slow down loss (muscular contraction). This is followed by a platelet plug formation. Finally, formation of insoluble fibrin (from soluble fibrinogen). The process is stimulated by the formation of thrombin which is itself stimulated by formation of prothrombin activator.This all acts to form a plug around cut and leads to the retraction of fibrin (seal the cut and pull the edges together). The extrinsic system is stimulated by the cut itself (damaged tissue) and quickly forms a very small amount of fibrin to form the clot. The intrinsic system takes a few minutes to work but leads to formation of larger amount of fibrin to complete the formation of the clot (unless damage too great). The enzyme plasmin then goes to work to remove the clot and so begins the wound healing process.
  

A non-specific inflammatory response brings white blood cells to the site of injury and removes the bacteria which may lead to infection. The next stage is the migratory phase when epithelial cells migrate beneath the clot. This forms the scab. Fibroblast cells, which produce collagen, also migrate to the wound. Damaged blood vessels repair and grow in the granulation phase. The proliferation phase is characterized by continued growth of epithelium beneath the scab. Vessel repair is by production of collagen fibres (from fibroblasts) to give strength to the healing wound. In the maturation phase (maybe months) collagen fibres become more organized and pull edges of wound together. The number of fibroblsts decreases and normal blood supply is restored.

The non-specific inflammatory response is initiated by chemicals released from the damaged tissues. Redness, pain, heat, swelling and sometimes loss of function are cardinal signs of inflammation. Swelling of the blood vessel (vasodilation) is a result of this inflammatory response increasing their permeability. Macrophagocyte cells (monocytes and neutrophils) migrate to the injury site. Basophil cells (mast cells in the skin) release histamine causing the inflammation. A collection of white cells (pus) is of dead cells and fluid. Body temperature may rise and this results in fever and is the body response to dealing with invasion of foreign matter. Although uncomfortable and sometimes dangerous if too prolonged, it is a normal body response. Cells of the non-specific defences along with T-lymphocytes play a role in immune system as antigen presenting cells (APC). By ingesting foreign bodies these APCs subsequently display parts of these antigens (foreign body) on their surface at the outside of the plasma membrane. This is all part of the process which triggers the immune system.

Two types of immunity are cell-mediated (T-lymphocyte) and antibody-mediated (B-lymphocyte). In response to an antigen the lymphocytes produce T-cells which can attach to and ingest foreign bodies. B-cells are also produced which are specific antibody proteins and can also attach to antigens. This attachment inactivates the antigens and the immune complex is later ingested by the eosinophils. Three types of T-lymphocyte are produced:

• T-killer cells (ingest foreign body)
• T-helper cell (helps activate production of antibodies)
• T-memory cell which is responsible for specific recognition of invasion by the antigen.
  

Together with B-memory cell this forms the basis of immunity. An antigen is a foreign body (may be micro-organism or drug), animal and vegetable protein (pollens) and tissues (transplants). The substance produced in response to the antigen is the antibody. This is the antigen-antibody reaction and in response to micro-organisms is immunity. Useful against infection. A specific antibody is produced in recognition of a particular micro-organism. This destroys that antigen and no other. The first contact with invader produces the antibody which enables subsequent defense.

Active immunity is when the antibody is made by cells of the body. This may be achieved in several ways. Passive immunity is when the antibody is produced by cells of another person. Active natural immunity is gained by having the disease after which the antibody remains in the blood ready to prevent another attack by the same disease. This type of immunity is also developed by what are called sub-clinical infections. Body is exposed to small number of micro-organisms insufficient to give rise to any definite symptoms, but which are sufficient to stimulate antibody production. Active artificial immunity is achieved by giving an injection of killed micro-orgnisms (or live ones rendered harmless). This produces the antibodies and immunty is built up. Harmless toxins are similarly used to build up the immunity.

Toxins are chemical poisins produced by micro-orgnisms and when rendered harmless act as antigens (foreign bodies). Harmless micro-organisms are called vaccines and harmless toxins are toxoids. Many diseases can be prevented by active artificial immunity (tuberculosis, smallpox, diphtheria, measles). Passive natural immunity is gained by a baby before birth - antibodies passed to foetus by mother. Passive artificial immunity is useful in prevention of disease or in its treatment. Antibodies are produced in another human or animal and injected into person at risk. Passive immunity is always short-lived as the antibodies are destroyed after a short time. Antigen-antibody reactions normally occur in the blood stream and the debris is carried away by the monocyte/macrophage system. When the immune reaction occurs in the tissues themselves the cells are damaged or destroyed by its side effects and this is known as allergy.

Allergic reactions are often due to protein-like substances called allergens. The allergic reaction releases histamine which causes redness and swelling in the skin. as urticaria, and the outpouring of fluid as in hayfever. There may be constriction of smooth muscle in the respiratory tract causing asthma. Autoimmunity describes when body makes antibodies against some of its own cells. Many diseases are thought to be autoimmune in origin - rheumatoid arthritis and rheumatic fever for example.