Blood Physiology Lecture 1 PDF

Blood Physiology (Lecture 1) By Dr. Eman Elbassuoni Professor of Physiology Faculty of Medicine  Blood Blood is the vital fluid tissue that circulates inside blood vessels. It represents 8% of body weight (5.6 L). Functions of blood: ▪...

Blood Physiology (Lecture 1) By Dr. Eman Elbassuoni Professor of Physiology Faculty of Medicine  Blood Blood is the vital fluid tissue that circulates inside blood vessels. It represents 8% of body weight (5.6 L). Functions of blood: ▪ Transport function (O2, CO2, nutrients, waste products, hormones). ▪ Defensive function (WBs & antibodies). ▪ Hemostasis (stoppage of bleeding). ▪ Homeostasis: keeping internal environment (extracellular fluid) of the body constant for optimum function of the cell (PH, osmotic pressure, volume, gases, minerals, temperature, nutrients). Composition of Blood 1- Blood Tissue (45% of the blood) 2- Blood Plasma (55% of the blood) Plasma is a yellow clear fluid consisting of: 91 % water. 7 % Proteins: - Albumin - Globulin - Fibrinogen - Prothrombin 2 % other substances: - Ions (Na+, Ca++, Cl– and other ) - Nutrients - Waste products - Gases - Regulatory substances (hormones & vitamins )  Plasma Proteins (7gm/100ml) Type Concentration Function Site of formation Albumin 4 gm/100 ml plasma - Colloidal osmotic Liver. (Highest Concentration) pressure due to its highest concentration. - Transport of some substances. Globulins 2.5 gm/100 ml plasma - Defensive function (γ (α, β, γ): in the liver. (α, β, γ) globulins). (γ): in the liver as well - Transport of some the plasma cells (Reticuloendothelial substances. system (R.E.S)) Fibrinogen 0.4 gm/100 ml plasma - Blood clotting. Liver. (Highest MW) - Plasma viscosity due to its highest MW. Prothrombin 10 mg/100 ml plasma - Blood clotting. Liver.  The Albumin/Globulin (A/G) Ratio: This is the ratio between albumin and globulin concentration in blood = 1.2 – 1.7 Albumin = 1.2 – 1.7 Globulin Significances of A/G ratio: Decreases in: Liver disease due to decreased formation of albumin. ↓↓↓ Albumin ↓ Globulin Kidney disease due to loss of albumin in urine. ↓↓↓ Albumin ↓ Globulin Infection due to increase globulin concentration. Albumin ↑↑↑Globulin  Red Blood Corpuscles (Erythrocytes) These are non-nucleated circular biconcave discs containing the red respiratory pigment (hemoglobin) and have an average life span of 120 days.. The concentration of hemoglobin in R.B.Cs is 34%. The chief ion inside R.B.Cs is potassium (K+) also it contains carbonic anhydrase enzyme and glucose-6- phosphate dehydrogenase (G-6-PD). Normal HB content: In adult male: 14-17 gm/100 ml blood (average 15 gm/100ml) In adult female: 12-15.5 gm/100 ml blood (average 13.5 gm/100ml) In newborn: 20 gm/100 ml blood  R.B.Cs Count: In adult males 5-6 million per cubic mm (due to androgen hormone that stimulate its formation & increase male musculature which need more oxygen). In adult females 4-5 million per cubic mm (due to menstruation). In newly born: 7 million per cubic mm (due to intra-uterine oxygen lack & to increase the iron coming from the damaged RBCs that can be used for recycling and reformation of new RBCs due to poor iron in the milk).  Functions of R.B.Cs: 1. Hemoglobin carry O2 to and take CO2 from tissues. 2. Hemoglobin has buffering action (85% of blood buffering action). 3. R.B.Cs contain carbonic anhydrase enzyme which is important for CO2 carriage. 4. The biconcave shape of R.B.Cs increases the surface area and helps the exchange of gases between R.B.Cs and tissues. 5- R.B.Cs membrane keeps hemoglobin inside them that prevents: a- the increase in the load on the heart which can lead to heart failure; since free hemoglobin increase blood viscosity, and increase in blood volume due to increase plasma colloidal osmotic pressure. b- obstruction of the renal tubules by the free hemoglobin which can lead to renal failure. 6- R.B.Cs membrane contains the specific agglutinogens that determine blood group. 7- The plastic nature of R.B.Cs membrane giving it a high degree of flexibility that allows RBCs to compress passing in the narrow capillaries and then resume their normal shape on leaving these capillaries without rupture.  Formation of R.B.Cs (Erythropoiesis) ❑ Sites of R.B.Cs formation; In the fetus, they are formed in liver and spleen. In the last three months of fetal life and after birth, they are formed in bone marrow of all bone until adolescent. By the age of 20, they are formed by the bone marrow of upper parts of humerus and femur and of membranous bones. After the age of 20 years, they are formed in bone marrow of membranous bone as skull, vertebra, sternum and ribs. Rate of erythropoiesis must be equal to the rate of RBCs destruction to maintain normal RBCs count. After 120 days (life span) due to loss of flexibility, RBCs are engulfed and hemolysed by reticulo-endothelial cells mainly spleen. ❑ Factors affecting erythropoiesis: 1. Oxygen supply to tissues: Hypoxia occurs in hemorrhage (due to RBCs loss), high altitude (due to decrease O2 tension around) and heart failure (blood don’t reach tissue properly). O2 lack (hypoxia) → releases erythropoietin hormone from the kidney mainly → stimulates bone marrow → increase production of R.B.Cs (↑ erythropoiesis rate). 2. Diet: Erythropoiesis requires: ▪ Protein; of high biological value containing essential amino acids that essential for formation of globin of hemoglobin. ▪ Iron; Average daily intake of iron is 20 mg. Most of the diet iron is in ferric state. However ferric iron poorly absorbed & ferrous iron is better absorbed than it.  So, ferric iron is reduced to ferrous in the stomach by HCl and vitamin C. Ferric iron (Fe 3+) HCl & Vitamin C→ Ferrous iron (Fe 2+) The intestinal epithelial cells contain Apoferritin protein that combines with the ferrous iron to form ferritin. Iron is absorbed in this form from the upper part of small intestine (duodenum). Ferrous iron(Fe2+) + Apoferritin → Ferritin (the form in which the iron absorbed) The blood containing transferrin protein which carries iron to bone marrow to form a part of R.B.Cs hemoglobin or to the liver to be stored. Excessive oxalates, phytic acids and phosphates in diet precipitate iron and decrease its absorption. ▪ Vitamins; Vitamin B12: - It is called extrinsic factor and is important for RBC nuclear maturation and cell division. In addition, it is responsible for myelination of the nerves and integrity of digestive system mucosa. - It unites with intrinsic factor, secreted by mucous membrane of the stomach forming intrinsic factor-Vit B12 complex. (intrinsic factor + Vit B 12 → intrinsic factor-Vit B12 complex ) - Intrinsic factor protects vitamin B12 from digestion by gastric enzymes and facilitates its absorption in lower part of ileum. - Vitamin B12 is stored in large amount in liver and released slowly from liver as needed by bone marrow for formation of new red cells.  Folic acid: the same importance as vitamin B12, important for RBC nuclear maturation and cell division.. Vitamin C: stimulates tissue growth and metabolism in general including the bone marrow. ▪ Trace elements: copper and cobalt act as cofactors for hemoglobin formation. 3. Hormones: Specific: Erythropoietin hormone. Non-specific: thyroid hormones (↑ metabolism in general) male sex hormones (Androgen), increase erythropoietin hormone and hence stimulate erythropoiesis. 4. Healthy organs:. Bone marrow: A healthy bone marrow is essential for normal erythropoiesis (site for formation).  Liver: is important for erythropoiesis as: - Formation of globin of hemoglobin. - Secretes 15% of erythropoietin hormone - Site of storage of Iron & Vit B12 Kidney: It secretes 85% of erythropoietin hormone in response to hypoxia, anemia and androgen hormone. N.B. Patients with renal diseases or failure develop severe anemia because erythropoietin production by liver cannot compensate for the inability of the kidney to produce the hormone. Stomach: - Gastric HCl is needed to convert ferric iron to ferrous. - Intrinsic factor secreted by gastric mucosa is essential for vitamin B12 absorption. Small intestine: It is the site of iron and vitamin B12 absorption.  Anaemia It means decreased RBCs number or their hemoglobin content or both. Types and causes of anaemia: I. Normochromic Normocytic Anaemia: including; A- Haemolytic anaemia; due to excessive haemolysis of RBCs. e.g., 1. Incompatible blood transfusion. 2. Snake venoms. 3. Sensitivity to drugs. 4. Infections as some types of malaria. 5. Antibodies against red blood cells. 6. Increased fragility of RBCs as in spherocytosis, sickle cell anaemia and thalassemia. B- Aplastic anaemia; due to bone marrow depression. e.g.; 1. Exposure to radiation such as X-rays. 2. Chemotherapy. 3. Drugs as antibiotics as chloramphenicol. 4. Destruction of bone marrow by malignant tumours. C- Haemorrhagic anaemia; due to acute blood loss (haemorrhage).  II. Microcytic Hypochromic Anaemia: Iron deficiency anaemia, either due to: 1- Deficiency in the diet (commonest cause). 2- Failure of iron absorption due to : Absence or removal of acid producing part of the stomach, e.g. congenital achlorohydra or partial gastrectomy Excess oxalates, phytic acids and phosphates in diet. 3- Diseases of small intestine (upper part) as duodenal ulcers. 4- Liver disease (site of storage of iron) 5- Chronic blood loss, e.g., bleeding piles and menstruation in females. Treatment: Oral iron or injection (in case of gastric or small intestinal causes)  III. Macrocytic (Megaloblastic) Anaemia: It occurs due to deficiency of vitamin B12 or folic acid. 1- Vitamin B12 deficiency (Pernicious anaemia) due to: a- Absence of intrinsic factor from the stomach. b- Malabsorption due to small intestine diseases (lower part). c- Liver disease (site of storage). d- Rarely due to lack of vitamin in diet. Treatment: Vitamin B12 injection for life. 2- Folic acid deficiency due to: Deficiency of folic acid in diet especially during pregnancy. Failure of absorption due to small intestine diseases.  Polycythaemia Polycythaemia means increased number of RBCs. It may reach up to 6-8 million/mm3.