Neural-humoral erythropoiesis regulation
It is of less importance than the humoral one. But it is well-known than some hypothalamic nuclei can stimulate or inhibit erythropoiesis. All these influencings performance is realized through vegetative nerves. Sympathetic nervous system excitement is accompanied by erythropoiesis activation. That’s why active life position and positive emotions - are important erythropoiesis activators.
Erythropoiesis inhibitors
· Fluorum is erythropoiesis inhibitor, that’s why anemia may be developed at its excess in environment (water, air, foods).
· Estrogens.
· GATA – its absence inhibits completely erythropoiesis.
· NFE-2 – its deficiency disturbs iron absorbtion in intestine and Hb biosynthesis.
Inhibitors are present in blood, they are produced in kidney and liver. Their
action is in following:
v hemoglobin synthesis inhibiting;
v prolonging term of young Er one forms transition to the others.
HEMOGLOBIN is the colouring matter of red blood cell. It is a chromoprotein forming 95% of dry weight of red blood cell and 30 to 34% of wet weight. The function of hemoglobin is to carry the respiratory gases, oxygen and carbon dioxide. The molecular weight of hemoglobin is 68,000.
Normal values:
· adult men – 130-180 g/l
· adult women – 120-160 g/l
· newborns – up to 220-240 g/l
DERIVATIVES OF HEMOGLOBIN
Hemoglobin readily combines with gas or any other substances to form some products, which are called the derivatives of hemoglobin. The following are the derivatives of hemoglobin.
1. OXYHEMOGLOBIN
This is formed by the combination of hemoglobin with oxygen by the physical process of oxygenation. Oxyhemoglobin is an unstable compound and the combination is reversible, i.e. the oxygen can be released from this compound. The iron remains in ferrous state in this compound.
2. REDUCED HEMOGLOBIN OR FERROHEMOGLOBIN
When oxygen is released from oxyhemoglobin, it is called reduced hemoglobin or ferrohemoglobin.
3. CARBHEMOGLOBIN
It is the derivative of hemoglobin with carbon dioxide. Carbon dioxide can be released easily from this. The affinity of hemoglobin for carbon dioxide is 20 times more than for oxygen.
4. CARBOXYHEMOGLOBIN
The combination of hemoglobin with carbon monoxide produces this. The affinity of hemoglobin for carbon monoxide is 210 times more than its affinity for oxygen. Carbon monoxide is a gas produced by the incomplete combustion of hydrocarbons such as gasoline. It binds to the iron in Hb about 210 times as readily as does oxygen and does not tend to dissociate. As a result, the Hb bound to carbon monoxide no longer transports oxygen. Nausea, headache, unconsciousness, and death are possible consequences of prolonged exposure to carbon monoxide. Cigarette smoke produces carbon monoxide. If a nonsmoker smoked a pack of cigarettes a day for a few weeks than carbon monoxide binds to the iron of Hb and prevents the transport of oxygen. The decreased oxygen stimulates the release of erythropoietin, which increases erythrocytes production in red bone marrow, causing the number of erythrocytes in the blood to increase.
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5. SULFHEMOGLOBIN
It is formed by the combination of hemoglobin with hydrogen sulfide.
6. NITROUS OXIDE HEMOGLOBIN
It is produced when hemoglobin combines with nitrous oxide.
7. METHEMOGLOBIN OR FERRIHEMOGLOBIN
It is formed when blood is treated with potassium ferricyanide. It is a stable compound. The iron is in ferric form id est its covalence is III. That is why oxygen binding to Fe is disturbed and person has hypoxy state. Immature babies, the adult at intoxications (in part, with methylenic blue, nitrates, nitrites) can have methemoglobin.
STRUCTURE OF HEMOGLOBIN
Hemoglobin is a conjugated protein. It consists of a protein combined with an iron containing pigment. The protein part is globin and the iron containing pigment is heme.
IRON
It is present in ferrous (Fe++) form. It is in unstable or loose form. Under certain conditions, the iron may be present in ferric (Fe+++) state, which is a stable form.
GLOBIN
This contains four polypeptide chains. Among the four polypeptide chains, two are alpha chains and two are beta chains.
TYPES OF HEMOGLOBIN
Hemoglobin is of two types namely:
1. Adult hemoglobin-HbA
2. Fetal hemoglobin-HbF
There are some structural differences between these two types of hemoglobin. In adult hemoglobin, the globin contains two alpha chains and two beta chains. In fetal hemoglobin, there are two alpha chains and two gamma chains instead of beta chains.
ABNORMAL HEMOGLOBIN
Abnormal hemoglobin is produced because of genetic mutation, which leads to structural variation in the polypeptide chains. There are two categories of abnormal hemoglobin namely, hemoglobinopathies and hemoglobin in thalassemia and related disorders.
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In hemoglobinopathy, there is structural abnormal in the polypeptide chains. Some of the hemoglobinopaties are :
1. Hemoglobin S: This is found in sickle cell anemia. The alpha chains are normal and beta chains are abnormal.
2. Hemoglobin C: This occurs in hemoglobin C disease. Here, the beta chains are abnormal.
3. Hemoglobin E: This occurs in hemoglobin E disease. Here also the beta chains are abnormal.
In thalassemia, the polypeptide chains are decreased absent or abnormal. In alpha- thalassemia, the alpha chains are decreased, absent or abnormal and in beta- thalassemia the beta chains are decreased, absent or abnormal.
DESTRUCTION OF HEMOGLOBIN
After the lifespan of 120 days, the red blood cell is destroyed in the reticuloendothelial system particularly in spleen and the hemoglobin is released into plasma. Soon, the hemoglobin is degraded in the reticuloendothelial cells and split into globin, iron and porphyrin.
IRON
Iron is stored in the body as ferritin and hemosiderin, which are reutilized for synthesize of new hemoglobin.
GLOBIN
It is utilized for the resynthesis of hemoglobin.
PORPHYRIN –(Hb pigment part consisting of 4 pyrole rings)
It is converted into a green pigment called biliverdin. In human being, most of the biliverdin is converted into a yellow pigment called bilirubin. Bilirubin and biliverdin are together called the bile pigments.
IRON METABOLISM
IMPORTANCE OF IRON
Iron is important for the formation of hemoglobin, myoglobin and other substances like cytochrome, cytochrome oxidase, peroxidase and catalase.
NORMAL VALUE AND DISTRIBUTION OF IRON IN THE BODY
The total quantity of iron in the body is about 4 grams. The approximate distribution of iron in the body is as follows:
65 to 68% : In the hemoglobin.
4% : In the muscle as myoglobin.
1% : In the form of various heme compounds, which take part in the intracellular oxidation.
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0.1% : In the plasma as transferrin.
25to 30% : Stored in the reticuloendothelial system and liver in the form of ferritin.
DIETARY IRON
Dietary iron is available in two forms called heme and nonheme. Heme iron is present in fish, meat and chicken.
Nonheme iron is available in vegetables, grains, and cereals.
ABSORPTION OF IRON
Iron is mainly absorbed from the small intestine. Bile is essential for the absorption of iron. Iron is absorbed through the intestinal cells by pinocytosis and transported into the plasma.
TRANSPORT AND STORAGE OF IRON
Immediately, after absorption into the blood, iron combines with a beta globulin called apotransferrin to form transferrin and is transported in this form in the plasma. Iron combines loosely with the globin and can be released easily at any region of the body.
Iron is stored in large quantities in the reticuloendothelial cells and liver hepatocytes. In other cells also, it is stored in small quantities. In the cytoplasm of the cell, iron combines with a protein and forms apoferritin, which is converted into ferritin and is stored in this form in large amount. Small quantity of iron is also stored as hemosiderin, which is highly insoluble.
DAILY LOSS OF IRON
In males, about 1 mg of iron is excreted everyday through feces. In females, the amount of iron lost from the body is very much high. This is because of the menstruation.
1 g of hemoglobin contains 3.34 mg of iron. Normally, 100 ml of blood contains 15 g of hemoglobin and about 50 mg of iron (3.34 x 15). So, if 100 ml of blood is lost from the body, there is a loss of about 50 mg of iron. In females, during every menstrual cycle, about 50 ml of blood is lost by which 25 mg of iron is lost. That is why the iron content of blood is always less in females than in males.
Iron is lost during hemorrhage also. If 450 ml of blood is donated, about 225 mg of iron is lost.
REGULATION OF TOTAL BODY IRON
Absorption and excretion of iron are maintained almost equally under normal physiological conditions. When the iron storage is saturated in the body, it automatically reduces the further absorption of iron from the gastrointestinal tract by feedback mechanism. The factors, which reduce absorption of iron, are:
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1. Stoppage of apotransferrin formation in the liver, so that, the iron could not be absorbed from the intestine and
2. Reduction in the release of iron from the transferrin so that, transferrin is completely saturated with iron and further absorption is prevented. This type of regulation is known as feedback mechanism.
HEMOLYSIS AND FRAGILITY OF RED BLOOD CELLS
HEMOLYSIS : 1) the destruction of formed elements;
2) the process which involves the breakdown of red blood cell and liberation of hemoglobin.
FRAGILITY – the susceptibility (to be affected) of RBC to hemolysis or tendency to easy breakability of RBC (fragile=easily broken). 2 types:
a) osmotic – occurs due to exposure to hypotonic saline;
b) mechanic – due to mechanic trauma (during wound or injury).
HEMOLYSIS PROCESS
Plasma and RBC are in osmotic equilibrium. The fluids inside and outside the cell are separated by cell membrane. When the osmotic equilibrium is disturbed, the cells are affected. For example, when the RBC are immersed in hypotonic solution there is endosmosis, id est water enters the cell. The cells swell up and are damaged by bursting. And the Hb is released from the ruptured Er.
HEMOLYSIS TYPES:
1) intracellular – due to macrophages action;
2) intravascular:
· osmotic – in hypotonic solution (minimal when the least stable RBC are destructed – at 0,42-0,48% NaCl, maximal or complete when the most stable cells are destroyed –at 0,30-0,34% NaCl) – at anemias minimal and maximal boarders are replaced to the side of hypotonic saline concentration rising;
· chemical;
· biological – at snakes venom action;
· mechanic – at ampule (with blood) shaking; in patients with heart and vessels valves; at durable walking because of Er traumatizing in feet capillaries (Hb and its derivatives appeared in urine leading to marsh hemoglobinury);
· thermal – if one frozens Er and then heals them;
· immune – at incompatible blood transfusion and at autoantibodies presence.
CONDITIONS WITH HEMOLYSIS
- hemolytic jaundice;
- antigen-antibody reactions;
- poisoning by chemicals or toxins;
- while using artificial kidney for hemodialysis;
- while using heart-lung machine during cardiac surgery.
HEMOLYSINS OR HEMOLYTIC AGENTS – the substances which cause destruction of erythrocytes. There are 2 types:
1) chemical substances:
a) alcohol, benzene, chloroform and ether;
b) acids (acetic et al.), alkalis (like ammonia), bile salts and saponin;
c) chemical poisons like arsenial preparations, carbonic acid, nitrobenzene and resin;
2) substances of bacterial origin or substances found in body:
a) toxic substances or toxins from bacteria like Streptococcus, Staphylococcus, Bacillus tetani etc.;
b) venom of poisonous snakes like cobra.
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