Blood Physiology PDF

# Blood ## Definition It is a complex reddish fluid that circulates continuously inside the cardiovascular system. ## Volume About 5.6 Liters in a 70 kg man. ## Functions of the blood 1. **Major transport medium in the body:** It transports: - O2 - CO2 - End products of metabolism as...

# Blood ## Definition It is a complex reddish fluid that circulates continuously inside the cardiovascular system. ## Volume About 5.6 Liters in a 70 kg man. ## Functions of the blood 1. **Major transport medium in the body:** It transports: - O2 - CO2 - End products of metabolism as urea. - Glucose - Hormones 2. **Haemostatic function:** Stoppage of bleeding from injured blood vessel by clotting. 3. **Homeostatic function:** Keep the composition of the internal environment constant. 4. **Defensive function:** White blood cells provide defense against microorganisms by phagocytosis & antibody formation. ## Composition of blood 1. **Blood Cells:** Represent about 45% of the total blood volume. - They include: - Red blood corpuscles (RBCs) - White blood cells (WBCs) - Platelets 2. **Plasma:** Represents about 55% of the total blood volume. # Plasma - It is a clear fluid in which blood cells are suspended. ## Composition: 1. Water 90% 2. Solids: - **Organic substance:** 9% - Plasma proteins (7%) - Other organic substance 2% (metabolic products urea creatinine), nutritive substance (e.g. glucose, amino acids, enzymes, hormones, vitamins). - **Inorganic substance:** 1% e.g. Na, K, Ca, Cl ## Plasma Proteins **Types and concentrations of plasma proteins:** The total plasma protein concentration is about 6-8 gm/dL. | | Albumin | Globulin | Fibrinogen | Prothrombin | | --------------- | -------- | -------- | ----------- | ------------ | | Concentration | 3.5-5 | 2.4-2.7 | 0.4 | 0.01-0.16 | | (gm/dL) | | | | | | Molecular weight | 69.000 | 90.000 - | 340.000 | 68.700 | | (Dalton) | | 156.000 | | | | Subdivisions | | α1, α2, β1, | | | | | | β2, γ | | | <start_of_image> Table 1. Plasma Protein Concentration ## Site of Formation | Protein | Site of Formation | | -------- | --------------------- | | Albumin | Liver | | Globulin | Liver except γ globulin | | | in plasma cells | | | in lymphatic tissues | | Fibrinogen | Liver | | Prothrombin | Liver | | **γ globulin** | **Plasma cells formed** | | ** ** | **in lymphoid tissue ** | ## Functions of plasma proteins 1. **Osmotic pressure of plasma proteins (mainly albumin):** Which maintains body fluids? 2. **Carrier functions:** - Pl. prot transport important substances as hormones, vitamins, minerals from the site of synthesis or absorption to the site of action or storage. - **Examples:** | Pl. prot | Carries | | ---------- | -------- | | Albumin | Hormones (thyroxine and steroids), amino acids, vitamins, fatty acids | | Globulins | Iron, Copper, Steroid hormones | - **Importance:** - Prevent rapid loss of substances in urine. - Reservoir of the substance used when needed. 3. **Defense action:** Antibodies are gamma globulins 4. **Blood coagulation:** By fibrinogen & prothrombin. 5. **Blood viscosity:** - Blood viscosity 3 times more than water - 1.5 times formed by plasma proteins mainly by fibrinogen - 1.5 times formed by RBCs - Viscosity maintains diastolic blood pressure. 6. **Buffering action:** Maintains body PH. 7. **Carriage of CO2.** # Red Blood Corpuscles (R.B.Cs) ## R.B.C's count RBCs count is 5.0-5.5 million/mm³ in ♂ and 4.5-5.0 million/mm³ in ♀. ## Shape and Size 1. **Shape:** RBCs are circular, non-nucleated, biconcave discs. 2. **Size:** - Its diameter → 7.5 um. - Its thickness → At the thickest point is about 2.5 um. - Its average volume → 90 to 95 u3. ## Structure of R.B.C's - RBCs are not true cells, because they have no nuclei, so called Corpuscles. 1. **The cell membrane:** They are surrounded with plastic semipermeable membrane. 2. **Its contents:** They contain: - **Hb:** It is the main constituent of RBCs (34% of their weight). - **Ions:** K is the chief intracellular cation. - **Enzymes:** Carbonic anhydrase enzyme, which is important for CO2 transport. - **Mitochondria:** There are no mitochondria in the RBCs, so they obtain their energy from anaerobic glycolysis. ## Functions of RBCs: 1. **Functions of cell membrane:** - **a) It has a large surface area than the actual cell volume:** - It gives RBCs its biconcave shape. - It allows easy diffusion of gases through the cell membrane. - **b) It is plastic:** Enhances cell flexibility → allow RBCs to be squeezed in small capillaries without rupture of it. - **c) It keeps Hb inside RBCs:** Prevent its loss in urine. 2. **Functions of Hb:** - It transports CO2 and O2 between lungs and tissues. - It is an excellent acid-base buffer. 3. **Functions of carbonic anhydrase enzyme:** It helps in the transport of CO2. 4. **Blood viscosity:** RBCs are responsible for the production of blood viscosity, which maintains arterial blood pressure. # Erythropoiesis ## Definition It is the process of new RBCs production. ## Sites of Erythropoiesis 1. **The red bone marrow:** - **i) In infants:** Red bone marrow is present in all bones. - **ii) In adults (after the age of 20 years):** Red bone marrow is present only in the membranous bones such as the vertebrae, sternum, and ribs. ## Factors affecting Erythropoiesis 1. **Tissue oxygenation:** - Hypoxia (↓ of O2 supply to the tissues) → Increase the rate of RBCs formation. ## Causes of hypoxia 1. High altitudes. 2. ↑ed demand for O2 as in athletes. 3. Loss of RBCs as in hemorrhage. ## Mechanism Hypoxia stimulates erythropoietin hormone secretion from the kidney (90%) and liver (10%), which in turn stimulates RBCs production in bone marrow. ## Healthy Bone Marrow - A healthy bone marrow is essential for the production of RBCs. - Destruction of bone marrow by irradiation, or drugs will lead to deficiency of all blood cells → aplastic anemia. ## Healthy Liver Healthy liver is essential for normal RBCs formation as it is the site of: - Formation of globin portion of Hb. - Formation of 10% of erythropoietin. - Storage of iron and vitamin B 12. ## Hormones - Thyroid hormones → Stimulate metabolism of bone marrow cells. - Glucocorticoids → Stimulate metabolism of bone marrow cells. - Androgens → ↑ erythropoietin hormone. ## Nutritional Factors 1. **Proteins:** Of high biological value proteins are essential for erythropoiesis. 2. **Minerals:** - **i) Iron:** It is important for the formation of Hb - **ii) Copper:** It acts as a cofactor in Hb synthesis. - **iii) Cobalt:** It acts as a cofactor in Hb synthesis. 3. **Vitamins:** - All vitamins are needed for erythropoiesis, especially vitamin B12 and folic acid. - They are important for final maturation of the RBCs → So, lack of them causes failure of maturation of blood cells → Megaloblastic anemia. # White Blood Cells (WBCS) ## Total Count of WBCs Ranges from 4000-11000/mm³. ## Types Depending on the presence of granules in the cytoplasm, leukocytes are divided into. ### Granular leukocytes: | Leukocyte | Percentage of Total Leukocytes | | ----------- | ------------------------------ | | Neutrophils | 60-70% | | Esinophils | 1-5% | | Basophils | 0.5- 1% | ### A granular leukocytes | Leukocyte | Percentage of Total Leukocytes | | ---------- | ------------------------------ | | Lymphocytes | 20-30% | | Monocytes | 3-8% | ## Functions of leukocytes ### Granular leukocytes **Neutrophils:** - **Constitute the first defensive line:** Against invading microorganisms. - **Main function:** Phagocytosis and destruction of invading bacteria. **Esinophils:** 1. Weak phagocytosis. 2. Defense against parasitic infections e.g. schistosomiasis. 3. Decrease allergy. **Basophils:** 1. Liberation of heparin into blood (prevent blood coagulation). 2. Play a role in allergy. ### Non-Granular leukocytes **Lymphocytes:** T lymphocytes for cell-mediated immunity and B lymphocytes secrete antibodies **Monocytes:** - They phagocytes and kill bacteria but more powerful than neutrophils. ## Platelets **Counts:** 150000-400000/mm³. **Life span:** 8- 12 days ## Function of platelets - Has a role in haemostasis: - a. Release of serotonin which produces vasoconstriction. - b. Formation of platelet plug. - c. Release some clotting factors which help clot formation. # Hemostasis ## Definition It means arrest of bleeding from injured blood vessels. ## Steps It occurs in the following steps: 1. Vascular spasm 2. Formation of a platelet plug. 3. Formation of a blood clot. 4. Fibrosis of the blood clot closes the hole in the vessel permanently. ## Formation of the Blood Clot - The clot begins to develop in 15 to 20 sec if the trauma to the vascular wall is severe and in 1 to 2 min if the trauma is minor. - **Mechanism of blood clot formation (blood coagulation):** - The clotting takes place in 4 steps: 1. Formation of a complex substance called prothrombin activators by 2 pathways extrinsic pathway and intrinsic pathway. 2. The prothrombin activator catalyzes the conversion of prothrombin into thrombin. 3. The thrombin acts as an enzyme to convert fibrinogen into fibrin threads. 4. Stabilization of clot. # Blood Groups - The blood of humans is classified into many groups according to certain antigens present on the surface of RBCs. They include ABO and Rh systems. ## Types of blood groups: ### ABO system 1. This system includes 2 related antigens (or agglutinogens) A and B. 2. According to the presence or absence of these 2 antigens, the human blood is normally classified into 4 major groups: | Blood group | Agglutinogen in RBC | Agglutinin in plasma | % frequency | | ----------- | ---------------------- | ------------------------ | ------------- | | A | A | Anti B | 41% | | B | B | Anti A | 9% | | AB | A, B | - | 3% | | O | - | Anti A and Anti B | 47% | ### Rh system (Rh factor) 1. There are six common types of Rh antigens named C, D, E, c, d, and e. 2. The type D-antigen is considerably the most antigenic than the others, so: - **Presence of D-antigen:** Rh+ve (85% of people). - **Absence of D-antigen:** Rh-ve (15% of people). ## Importance of blood groups 1. **Blood transfusion**: The transfused blood must be compatible with that of the recipient as regards ABO & Rh systems to avoid transfusion reactions. 2. **Pregnancy:** Rh system must be tested during pregnancy to avoid erythroblastosis foetalis. It occurs when Rh-ve mother gets pregnant in Rh +ve baby. 3. **Medicolegal importance:** - i) **Establish parentage:** Blood groups can prove that a man cannot be the father, although it cannot prove that he is the father. - ii) **Identify criminals:** Blood groups help in identifications of criminals in many accidents like rape. # Blood Transfusion ## Indications of blood transfusion 1. To restore the whole blood as in hemorrhage. 2. To restore one element of the blood when it is deficient, e.g. RBCs as in cases of anemia, WBCs as in leucopenia, platelets as in purpura, and clotting factors as in hemophilia. ## Precautions before blood transfusion The transfused blood must be: 1. Compatible with that of the recipient as regards ABO & Rh systems. 2. Its Hb content is not less than 90%. 3. Free from diseases e.g. infective hepatitis, AIDS & malaria. 4. Fresh and not frozen (stored at 4°C for a period not exceeding 21 days). 5. Cross matching test should be done to it with recipient blood. ## Dangers of blood transfusion 1. **Incompatibility:** - It is due to mismatched blood groups. - This is manifested by: - a) **Circulatory shock:** → Drop of ABP. - b) **Hyperkalemia:** Cardiac arrhythmia. - c) **Jaundice:** ↑ Serum bilirubin → Yellow coloration of the skin and mucous membranes. - d) **Acute renal failure.** 2. **Allergic reactions:** It is due to the presence of leukocytes and platelets in the transfused blood. 3. **Transmission of diseases** e.g. AIDS, hepatitis, and malaria.