Science Interactive LTD Copyright 2005 ⚫The Circulatory System
Science Interactive LTD Copyright 2005 Your blood The human body has about five litres of blood which is continuously p______ around a network of arteries, capillaries and v______. Blood is a moving, liquid tissue that contains many types of cells, each which a unique function. Red blood cells transport oxygen around the body. White blood cells help fight disease. P________ are cell fragments which help scabs to form to prevent bleeding and microbial infection after injury to the skin. The yellow liquid called plasma transports nutrients like glucose and waste products like carbon dioxide and urea. How would you separate the yellow plasma from the red and white blood cells ? Human blood: Transfusions Blood plasma Word bank: pumped veins platelets Blood volume Blood cells Diagram Notes An average human has Blood transfusions are Plasma can also be given One of the specialised five litres or eight pints often performed during during surgery or cells of blood is the red of blood circulating surgery or after a following dehydration. blood cell or erythrocyte. around the body. When major accident. Blood Plasma contains salts, It is highly specialised to you donate blood, is vital for life and water, nutrients like sugar transport oxygen around doctors only take one needs to be replaced and amino acids and the many arteries veins pint or half a litre. quickly if lost. hormones like adrenalin. and capillaries.
Blood is a connective tissue . It provides one of the means of communication between the cells of different parts of the body and the external environment, e.g. it carries: .oxygen from the lungs to the tissues, and carbon .dioxide from the tissues to the lungs for excretion nutrients from the alimentary tract to the tissues, and cell wastes to the excretory organs, principally the .kidneys hormones secreted by endocrine glands to their target . glands and tissues heat produced in active tissues to other less active tissues .protective. substances, e.g. antibodies, to areas of infection .clotting factors that coagulate blood,
Composition of blood
Blood – connective tissue with fluid matrix ◼ A. Fluid = plasma ◼ B. Blood cells = formed elements ❑ 1. Red blood cells (RBC's) = ERYTHROCYTES ◼ a. Flattened, biconcave, anucleated discs ◼ b. Life span - 120 days ◼ c. Function: transport oxygen & carbon dioxide bound pigmented protein = hemoglobin
Blood cont. ◼ 2. White blood cells (WBC's) = LEUKOCYTES ❑ a.granulocytes ◼ i. eosinophils ◼ ii. Basophils ◼ iii. Neutrophils
Blood cont. ◼ 2. White blood cells (WBC's) = LEUKOCYTES ❑ b. Agranulocytes ◼ i. Monocytes ◼ ii. Lymphocytes
Hemopoiesis = Blood Cell formation. Occurs in red bone marrow. ◼ A. Erythropoiesis = RBC formation ◼ B. Leukopoiesis = WBC formation ◼ C. Thrombopoiesis = platelet formation
Blood ❑ Cells ◼ Red blood cells (erythrocytes) ❑ Round cells that carry oxygen ▪ Contain hemoglobin, an iron-containing protein that binds oxygen very strongly in lungs, then releases it in oxygen-poor environment of the capillaries
Physiology of red blood cells
Blood cell formation in red bone marrow
Blood plasma ◼ The constituents of plasma are water (90 to 92%) ◼ dissolved substances, including: . ◼ .plasma proteins . ◼ inorganic salts . ◼ nutrients, principally from digested foods ◼ .waste materials ◼ hormones . ◼ gases.
Oxygen transport ◼ Haemoglobin is a large, complex protein containing a globular protein (globin) and a pigmented iron-containing ◼ complex called haem. ◼ Each haemoglobin molecule contains ◼ four globin chains and four haem units, each with ◼ one atom of iron . ◼ As each atom of iron can combine with an oxygen molecule, this means that a single haemoglobin molecule can carry up to four molecules of oxygen.
• Theassociation of oxygen with haemoglobin is a loose one,so that oxyhaemoglobin releases its oxygen readily, especiallyunder certain conditions. • Low pH. • Low oxygen levels (hypoxia). • Temperature.
Both vitamin B12 and folic acid are required for red blood cell synthesis. They are absorbed in the intestines, although vitamin B12 must be bound to intrinsic factor to allow absorption to take place. Both vitamins are present in dairy products, meat and green vegetables. The liver usually contains substantial stores of vitamin Bl2 several years' worth, but signs of folic acid deficiency appear within a few months.
Destruction of erythrocytes • The life span of erythrocytes is about 120 days and their breakdown, or haemolysis, is carried out by phagocytic reticuloendothelialcells. • These cells are found in many tissues but the main sites of haemolysis are the spleen, • bone marrow and liver. • As erythrocytes age, changes in their cell membranes make them more susceptible to • haemolysis.
• Iron released by haemolysis is retained in • the body and reused in the bone marrow to form new • haemoglobin molecules . Biliverdin is formed • from the haem part of the haemoglobin. It is almost • completely reduced to the yellow pigment bilirubin, • before being bound to plasma globulin and transported • to the liver . In the liver it is changed • from a fat-soluble to a water-soluble form to be excreted as a constituent of bile
Blood groups • The ABO system • About 55% of the population has either A-type antigens • (blood group A), B-type antigens (blood group B) or both • (blood group AB) on their red cell surface. • The remaining 45% have neither A nor B type antigens (blood group 0).
29.16 Blood types must be matched for transfusions ▪ ABO System ▪ Presence or absence of type A and type B antigens on red blood cells determines a person’s blood type ▪ In the ABO system, there are four types of blood: A, B, AB, and O ▪ Type O blood has no antigens on the red blood cells and is sometimes called the universal donor 29-22
29-23
Rh System and Erythroblastosis Fetalis ▪ Rh System ▪ Another important antigen in matching blood types is the Rh factor ▪ 85% of the U.S. population have this particular antigen on red blood cells and are called Rh-positive ▪ Erythroblastosis Fetalis ▪ During pregnancy, if the mother is Rh-negative and the father is Rh-positive, the child may be Rh-positive ▪ Rh-positive red blood cells may begin leaking across the placenta into the mother’s cardiovascular system, since placental tissues normally break down before and at birth ▪ The mother produces anti-Rh antibodies, which may cross the placenta and destroy the child’s red blood cells during a subsequent pregnancy 29-24
Figure 29.16A No agglutination occurs when the donor and recipient have the same type blood 29-25
Figure 29.16B Agglutination occurs because blood type B has anti-A antibodies in the plasma 29-26
The Rhesus system • The red blood cell membrane antigen important here is the Rhesus (Rh) antigen, or Rhesus factor. About 85% of people have this antigen; they are Rhesus positive (Rh +)and do not therefore make anti-Rhesus antibodies. The remaining 15% have no Rhesus antigen (they are Rhesus negative, or Rh-).
Leukocytes (white blood cells) • Thesecells have an important function in defending the • body against microbes and other foreign materials. • Leukocytes are the largest blood cells and they account • for about 1% of the blood volume. They contain nuclei • and some have granules in their cytoplasm. There are two main types : . • granulocytes (polymorphonuclear leukocytes) • - neutrophils, eosinophils and basophils • . agranulocytes • - monocytes and lymphocytes.
Neutrophils • Their main function is to protect against any foreign • material entering the body, mainly microbes, and to • remove waste materials, e.g. cell debris. • They are attracted in large numbers to any area of infection by chemicalsubstances, released by damaged cells, called chemotaxins. • Neutrophils are highly mobile, and squeeze through the • capillary walls in the affected area by diapedesis. • . Thereafter they engulf and kill the microbes by phagocytosis • Their nuclei are characteristically complex, • with up to six lobes, and their granules are lysosomes • containing enzymes to digest engulfed material.
• There is a physiological increase in circulating neutrophils following strenuous exercise and in the later stages of normal pregnancy. Numbers are also increased in: • .microbial infection . • extensive tissue damage, e.g. inflammation, • .myocardial infarction, burns, crush injuries • metabolic disorders, e.g. diabetic ketoacidosis, acute gout • leukaemia
diapedesis Phagocytosis
Eosinophils • Eosinophils, although capable of phagocytosis, are less active in this than neutrophils; their specialised role appears to be in the elimination of parasites, such as worms, which are too big to be phagocytosed. • Allergic conditions
Basophils • Basophils, which are closely associated with allergic reactions, contain cytoplasmic granules packed with heparin (an anticoagulant), histamine (an inflammatory agent) and other substances that promote inflammation. • MAST CELLS - HISTAMINE
Monocytes • These are large mononuclear cells that originate in red bone marrow. • Some circulate in the blood and are actively • motile and phagocytic while others migrate • into the tissues where they develop into macrophages • Produces interleukin -1
interleukin -1 • acts on the hypothalamus, causing the rise in body • temperature associated with microbial infections •. • stimulates the production of some globulins by the • Liver • Enhances the production of activated T-lymphocytes. • Macrophages have important functions in inflammation
The monocyte-macrophage system. (Reticuloendothelial cells) • Collections of fixed macrophages include: • ..histiocytes in connective tissues .synovial cells in joints • Langerhans cells in the skin • . microgliain the brain • . Kupffercellsin the liver • . alveolar macrophages in the lungs • . sinus-lining macrophages (reticular cells) in the spleen, .lymph nodes and thymus gland • mesangialcellsin the glomerulus of nephrons in the kidney . • osteoclastsin bone.
Lymphocytes • Lymphocytes are smaller than monocytes and have large nuclei. • They circulate in the blood and are present in • great numbers in lymphatic tissue such as lymph nodes and the spleen. • Respond to antigens • B-lymphocyte • T - lymphocyte
Platelets (thrombocytes) • These are very small non-nucleated discs, 2 to 4 µm in diameter, derived from the cytoplasm of megakaryocytes in red bone marrow • The normal blood platelet count is between 200000 to 350 000/mm3.
Haemostasis • When a blood vessel is damaged, loss of blood is stopped and healing occurs in a series of overlapping processes, in which platelets playa vital part.
1. Vasoconstriction. When platelets come into contact with a damaged blood vessel, their surface becomes sticky and they adhere to the damaged wall. They then release serotonin (5-hydroxytryptamine), which constricts(narrows) the vessel, reducing blood flow through it. Other chemicals that cause vasoconstriction, e.g. thromboxanes, are released by the damaged vessel itself.
2. Platelet plug formation The adherent platelets clump to each other and release other substances, including adenosine diphosphate (ADP), which attract more platelets to the site. Passing platelets stick to those already at the damaged vessel and they too release their chemicals.
3. Coagulation (blood clotting). This is a complex process that also involves a positive feedback system
STAGES OF BLOOD CLOTTING
4. Fibrinolysis. • After the clot has formed the process • of removing it and healing the damaged blood vessel begins.
Control of coagulation The process of blood clotting relies heavily on several self-perpetuating processes - that is, once started, a Positive feedback mechanism promotes their continuation. For example, thrombin is a powerful stimulator of its own production. The body therefore possesses several mechanisms to control and limit the coagulation cascade; otherwise once started the clotting process would spread throughout the circulatory system, far beyond requirements.
The main controls The perfect smoothness of normal blood vessel lining means that platelets do not adhere to it. The binding of thrombin to a special thrombin receptor on the cells lining blood vessels; once bound, thrombin is inactivated . The presence of natural anticoagulants, e.g. heparin, in the blood, which inactivate clotting factors.
Congenital disorders • The haemophilias • The haemophilias are a group of inherited clotting • disorders, carried by genes present on the X-chromosome • (i.e. inheritance is sex linked • . The faulty genes • code for abnormal clotting factors (Factor VIII and • Christmas factor), and if inherited by a male child always • leads to expression of the disease. • Women inheriting one • copy are carriers, but, provided their second X chromosome • bears a copy of the normal gene, their blood clotting • is normal. It is possible, but unusual, for a woman to • inherit two copies of the abnormal gene and have • haemophilia
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