|
Blood Questions Review
1. What are the main functions of the blood?
The blood is a means of substance transportation throughout the body. The blood distributes nutrients, oxygen, hormones, antibodies and cells specialized in defense to the tissues and collects residuals like nitrogen wastes and carbon dioxide from them.
2. What are the constituent elements of the blood?
The blood is made of a liquid and a cellular part. The fluid part is called plasma and in it there are several substances, like proteins, lipids, carbohydrates and mineral salts. The cellular constituents of the blood are also known as blood corpuscles and they comprise the erythrocytes (red blood cells), leukocytes and platelets.
Blood Questions - Image Diversity: red blood cells leukocytes platelets
3. What is hematopoiesis?
Hematopoiesis is the formation of blood cells and other constituent elements of the blood.
4. Where does hematopoiesis occur?
Hematopoiesis occurs in the bone marrow (mainly within flat bones), where erythrocytes, leukocytes and platelets are made, and in the lymphoid tissue, responsible for the maturation of leukocytes and found in the thymus, spleen and lymphnodes.
Blood Questions - Image Diversity: bone marrow
5. In which bones can bone marrow chiefly be found? Is the bone marrow made of osseous tissue?
Bone marrow can mainly be found in the internal cavities of flat bones, like the vertebrae, the ribs, the scapulae, the sternum and the hips.
The bone marrow is not made of osseous tissue, although it is a connective tissue as bone tissue is.
6. What are blood stem cells?
Stem cells are undifferentiated cells able to differentiate into other types of specialized cells.
The stem cells of the bone marrow originate the differentiated blood cells. According to stimulus from specific growth factors the stem cells are turned into red blood cells, leukocytes and megakaryocytes (cells that form platelets). Research shows that stem cells of the bone marrow can also differentiate into muscle, nervous and hepatic cells.
Blood Questions - Image Diversity: blood stem cell
7. What are the other names by which erythrocytes are known? What is the function of these cells?
Erythrocytes are also known as red blood cells (RBCs), or red corpuscles. Red blood cells are responsible for oxygen transport from the lungs to the tissues.
8. What is the name of the molecule that transports oxygen in red blood cells?
The respiratory pigment of the red blood cells is hemoglobin.
9. What is the molecular composition of hemoglobin? Does the functionality of hemoglobin as a protein depend upon its tertiary or upon its quaternary structure?
Hemoglobin is a molecule made of four polypeptide chains, each bound to a iron-containing molecular group called a heme group. So the molecule contains four polypeptide chains and four heme groups.
As a protein composed of association of polypeptide chains, the functionality of hemoglobin depends upon the integrity of its quaternary structure.
Blood Questions - Image Diversity: hemoglobin molecule
10. On average what is the life duration of the red blood cells? Where are they destroyed? What is the destination of the heme groups after the destruction of hemoglobin molecules?
On average red blood cells live around 120 days. The spleen is the main organ where old red blood cells are destroyed.
During the red blood cell destruction the heme groups turn into bilirubin and this substance is then captured by the liver and later excreted in the bowels as part of the bile.
11. What are the functions of the spleen? Why is a total splenectomy (surgical removal of the spleen) compatible with life?
The spleen has many functions: it participates in the destruction of old red blood cells; in it specialized leukocytes are matured; it helps the renewal of the hematopoietic tissue of the bone marrow when necessary; it can act as a spongelike organ to retain or liberate blood from or for the circulation.
Total splenectomy is not incompatible with life as none of the functions of the spleen are vital and at the same time exclusive of this organ.
12. What is anemia? What are the four main types of anemia?
Anemia is low concentration of hemoglobin in the blood.
The four main types of anemia are the nutrient-deficiency anemia, anemia caused by blood loss, hemolytic anemia and aplastic anemia.
Nutrient-deficiency anemia is caused by dietary deficiency of fundamental nutrients for the production or functioning of the red blood cells, like iron (iron deficiency anemia), vitamin B12 and folic acid.
Anemia caused by blood loss occurs in hemorrhagic conditions or in diseases like peptic ulcerations and hookworm disease.
Hemolytic anemia is caused by excessive destruction of red blood cells, for example, in diseases like malaria or in hypervolemic conditions (excessive water in blood that causes lysis of red blood cells).
Aplastic anemia occurs from deficiencies of the hematopoiesis and it happens when the bone marrow is injured by cancers from other tissues (metastasis), by autoimmune diseases and by intoxication from drugs (like sulfas and anticonvulsants) or by chemical substances (like benzene, insecticides, paints, herbicides and solvents in general). Some genetic diseases also affect the bone marrow causing aplastic anemia.
13. What is the difference between white and red blood cells? What are leukocytes?
Red blood cells are erythrocytes and white blood cells are the leukocytes.
Leukocytes are cells specialized in the defense of the body against strange agents and they are part of the immune system.
14. What are the types of leukocytes and how are they classified into granulocytes and agranulocytes?
The types of leukocytes are lymphocytes, monocytes, neutrophils, eosinophils and basophils. Granulocytes are those in whose cytoplasm there are granules (when viewed under electronic microscopy): neutrophils, eosinophils and basophils are granulocytes. Agranulocytes are the other leukocytes: lymphocytes and monocytes.
Blood Questions - Image Diversity: lymphocytes monocytes neutrophils eosinophils basophils
15. What is the generic function of leukocytes? What are leukocytosis and leukopenia?
The generic function of leukocytes is to participate in the defense of the body against strange agents that penetrate it or are made inside the body.
Leukocytosis and leukopenia are clinical conditions in which the count of leukocytes in a blood sample is abnormal. When the leukocyte count in a blood sample is above the normal level for the individual leukocytosis is defined. When the leukocyte count is lower than the expected normal level leukopenia is defined. The multiplication of these defense cells, leukocytosis, generally takes place when the body is suffering infections or in cancers of these cells. The lowering of these defense cells, or leukopenia, occurs when some diseases attack the cells, like in AIDS, or when immunosuppressor drugs are used.
In general the body creates leukocytosis as a defense reaction when it is facing infectious or pathogenic agents. The clinical condition of leukocytosis is thus a sign of infection. Leukopenia occurs when there is a deficiency in the production (for example, in bone marrow diseases) or excessive destruction of leukocytes (for example, in case of HIV infection).
16. What are the mechanisms of hemorrhage contention called?
The physiological mechanisms of hemorrhage contention (one of them is blood clotting) are generically named hemostasis, or hemostatic processes.
17. How are platelets formed? What is the function of platelets? What consequences does the clinical condition known as thrombocytopenia yield?
Platelets, also known as thrombocytes, are fragments of giant cells of the bone marrow called megakaryocytes. With their properties of aggregation and adhesiveness they play a direct role in blood clotting and they also liberate substances that activate other hemostatic processes.
Thrombocytopenia is a clinical condition in which the platelet count of the blood is lower than normal. In this situation the person becomes susceptible to hemorrhages.
18. How does the organism understand that a clotting process must begin?
When there is some tissue wound with injury of blood vessel the platelets and endothelial cells of the wall of the damaged vessel liberate substances (respectively platelet factors and tissue factors) that trigger the clotting process.
19. How can the blood coagulation (clotting) process be described?
Blood clotting encompasses a sequence of chemical reactions whose respective products are enzymes that catalyze the following reactions (that is why the clotting reactions are called cascade reactions). In the plasma thromboplastinogen transforms into thromboplastin, a reaction triggered by tissue and platelet factors liberated after injury of the blood vessel. Thromboplastin then catalyzes along with calcium ions the transformation of prothrombin into thrombin. Thrombin then catalyzes a reaction that produces fibrin from fibrinogen. Fibrin, as an insoluble substance, precipitates to form a network that traps red blood cells and platelets forming the blood clot and containing the hemorrhage.
Blood Questions - Image Diversity: clotting cascade
20. What are clotting factors?
Clotting factors are substances (enzymes, coenzymes, reagents) necessary for the clotting stages to happen. Besides those triggering factors and reagents already described (tissue and platelet factors, thromplastinogen, prothrombin, fibrinogen, calcium ions), other substances participate in the blood clotting process as clotting factors, like factor VIII, whose deficiency causes hemophilia A, or the factor IX, whose deficiency causes hemophilia B.
21. What is the organ where most of the clotting factors are produced? What is the role of vitamin K in the blood coagulation?
Most of the clotting factors are produced in the liver.
Vitamin K participates in the activation of several clotting factors and it is fundamental for the well-functioning of the blood coagulation.
22. What is factor VIII? What is the genetic disease in which this factor is absent?
Factor VIII has the function of activating factor X that in its turn is necessary for the transformation of prothrombin into thrombin in the clotting cascade. Hemophilia A is the X-linked genetic disease in which the individual does not produce factor VIII and so is more susceptible to severe hemorrhages.
23. How is hemophilia treated? Why is hemophilia rare in females?
Hemophilia is medically treated with administration of factor VIII, in case of hemophilia A, or of factor IX, in case of hemophilia B, by means of blood or fresh frozen plasma transfusions.
Hemophilia, A or B, is an X-linked recessive inheritance and for a girl to be hemophilic it is necessary for both of her X chromosomes to be affected while boys, that have only one X chromosome, are more easily affected. A girl with only one affected chromosome does not present the disease since the normal gene of the unaffected other X chromosome produces the clotting factor.
24. What is the epidemiological association between hemophilia and HIV infection?
Since hemophilic patients need frequent transfusions of clotting factors (VIII or IX) they are more susceptible to contamination by infectious agents present in the blood from which the transfused elements come. In the past the blood banks did not usually perform HIV detection tests and many hemophilic patients have become infected with the virus.
25. What are anticoagulants? What are the practical applications of anticoagulants, like heparin, in Medicine?
Anticoagulants are substances that block the clotting reactions and thus stop the coagulation process. Ordinarily there are anticoagulants circulating in the plasma since under normal conditions the blood must be kept fluid.
In Medicine anticoagulants like heparin are used in surgeries in which tissue injuries made by the surgical act could trigger undesirable systemic blood clotting. They are also used to avoid the formation of thrombus inside blood vessels of patients facing increased thrombotic risk.
26. What is dicoumarol? How does this substance act in the clotting process and what are some examples of its toxicity?
Dicoumarol is an anticoagulant drug. Due to its molecular structure dicoumarol competes with vitamin K for the binding to substrates blocking the formation of clotting factors and interrupting the making of prothrombin. Dicoumarol is found in some vegetables undergoing decomposition, and it can cause severe internal hemorrhages when those vegetables are accidentally ingested. Coumarinic anticoagulants cannot be administered during pregnancy since they pass the placental barrier and can cause fetal hemorrhages.
27. Streptokinase is a substance used in the treatment of acute myocardial infarction. How does this substance act?
Substances known as fibrinolytics, like streptokinase and urokinase, can destroy thrombi (clots formed inside blood vessels, capillaries or within the heart chambers) and are used in the treatment of obstructions of the coronary arteries or other blood vessels.
Streptokinase destroys the fibrin network and so it dissolves the thrombotic clot. Its name comes after the bacteria that produce it, the streptococci.
|
