UNIT HL CARDIOVASCULAR AND LYMPHATIC SYSTEMS Components of Blood and functions Blood is a fluid connective tissue. It circulates continually around the body, allowing constant communication between tissues distant from each other, It transports: * 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, minimising bleeding from ruptured blood vessels. Blood is composed of a clear, straw-coloured, watery fluid called plasma in which several different types of blood cell are suspended. Plasma normally constitutes 55% of the volume of blood. The remaining 45% is accounted for by the cellular fraction of blood. The two fractions of blood, blood cells and plasma, can be separated by centrifugation (spinning) or by gravity when blood is allowed to stand. Because the cells are heavier than plasma, they sink to the bottom of any sample. Blood in the blood vessels is always in motion because of the pumping action of the heart. The continual flow maintains a fairly constant environment for body cells. Blood volume and the concentration of its many constituents are kept within narrow limits by homeostatic mechanisms. Plasma: The constituents of plasma are water (90 to 92%) and dissolved and suspended substances, including: + plasma proteins * inorganic salts © nutrients, principally from digested foods © waste materials * hormones © Gases. Plasma proteins Plasma proteins, which make up about 7% of plasma, are normally retained within the blood, because they are too big to escape through the capillary pores into the tissues.They are largely responsible for creating the osmotic pressure of blood, which keeps plasma fluid within the circulation. If plasma protein levels fall, because of either reduced production or loss from the blood vessels, osmotic pressure is also reduced, and fluid moves into the tissues (oedema) and body cavities. Plasma viscosity (thickness) is due to plasma proteins, mainly albumin and fibrinogen. Plasma proteins, with the exception of immuneglobulins, are formed in the liver ‘There are three types of blood cell. Erythrocytes (Red Blood Cells) * Platelets (Thrombocytes) Leukocytes (White Blood Cells). Erythrocytes (Red Blood Cells (RBC) Red blood cells are Bieoncave dst; they have no] << nucleus, and their diameter is about 7 micrometres. Their] ( foe main function is in gas transport, mainly of oxygen, but they eae also carry some carbon dioxide. Their characteristic shape is suited to their purpose; the biconcavity increases their surface area for gas exchange, and the thinness of the central portion allows fast entry and exit of gases. The cells are flexible so they can squeeze through narrow capillaries, and contain no intracellular organelles, leaving more room for haemoglobin, the large pigmented protein responsible for gas transport. Measurements of red cell numbers, volume and haemoglobin content are routine and useful assessments made in clinical practice. The process of development of red blood cells from stem cells takes about 7 days and is called erythropoiesis. Haemoglobin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. ‘An average red blood cell carries about 280 million haemoglobin molecules, giving each cell a theoretical oxygen-carrying capacity of over a billion oxygen molecules. Oxygen transport When all four oxygen-binding sites on a haemoglobin molecule are full, it is described as saturated. Haemoglobin binds reversibly to oxygen to form oxyhaemoglobin, according to the equation: As the oxygen content of blood increases, its colour changes too. Blood rich in oxygen is bright red because of the high levels of oxyhaemoglobin it contains, compared with blood with lower oxygen levels, which is dark bluish in colour because it is not saturated. The association of oxygen with haemoglobin is a loose one, so that oxyhacmoglobin releases its oxygen readily, especially under certain conditions.Erythrocytes red kane, anudeate &-émilion Di about 15 days ——Tarsportongen blood els, RBCS) disc salmon-colred: 15:100-120.deys and exrbon donde dsmeter 7-8 ym Leukocytes ite Spherical mudeated 4800-10380 Blood et, Ws) els Granulocyes * Neutrophil Mutlobed nuceus, 3000-7000 Diabout 14days_—_Phagooyte bacerta inconspicuous {S:Ghourstoatew (toptesmie granules dap ‘tometer 10-12 um + Eosinophil lobed mucous red 100-400 Deabout 14 days ill parastte worms; «ytoptasmic granules LSiaboutsdas ——conpiexrolein ‘ameter 10212 ym allergy and asthma + Baophil lobed mucous, 20-50 Ot-7daps Release histamine large purlishbiack Is:afewhoustoa — andother mediators ‘gtonlasmic granules fev days ofinfiammation: ‘ameter 10212 ym contain heparin, an arilcoagulant ‘Aayanulocjtes = Lymphocyte Spherical ocindented 1500-3000 Di daystoweeks mount immune @ uous pale bive Isshoursto yeas response by rect (oplasm, diameter call atack or via 7 ym antbodies = Monocne U-oridneysheped 109-700 0.23 days Phagocsoss, rucousgraybiue Issmontns develop inca Gfoplesm diameter macrophages nthe 1-24 wm tues Mates 7 Diced gfopasmic — TSNGOI-AIO MIO ——_DaS days Seal smaieas fragment containing {s:S-10days in blood vessels @@ aruies stain doop instrumental in @ purple; dlameter Blood ecting a’ Pam 2? Leukocytes (white blood cells) These cells have an important function in defence and immunity. Leukocytes are the largest blood cells but they account for only about 1% of the blood volume. They contain nuclei and some have granules in their cytoplasm. ‘There are two main types: Granulocytes — neutrophils, eosinophils and basophils Agranulocytes — monocytes and lymphocytes. Granulocytes. All granulocytes have multi-lobed nuclei in their cytoplasm.Their names represent the dyes they take up when stained in the laboratory. Eosinophils take up the red acid dye, eosin; basophils take up alkaline methylene blue; and neutrophils are purple because they take up both dyes. Neutrophils These small, fast and active scavengers protect the body against bacterial invasion, and remove dead cells and debris from damaged tissues. They are attracted in large numbers to any area of infection by chemical substances called chemotaxins, which are released by damaged cells. Neutrophils are highly mobile, and squeeze through the capillary walls in the affected area by diapedesis. Their numbers rise very quickly in an area of damaged or infected tissue. Once there, they engulf and kill bacteria by phagocyt Their nuclei are characteristically complex, with up to six lobes, and their granules are /ysosomes containing enzymes to digest engulfed material. Neutrophils live on average 6-9 hours in the bloodstream. Pus that may form in an infected area consists of dead tissue cells, dead and live microbes, and phagocytes killed by microbes. (@) Neutrophit: Muttlobod nucious, pale red and blue oytoplasmic granules 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. They are equipped with certain toxic chemicals, stored in their granules, which they release when the cosinophil binds to an infecting organism. Eosinophils are often found at sites of allergic inflammation, such as the asthmatic airway and skin allergies. There, they promote tissue inflammation by releasing their array of toxic chemicals, but they may also dampen down the inflammatory process through the release of other chemicals, such as an enzyme that breaks down histamine. (b) Eosinophil: Bilobed nucleus, red cytoplasmic granules Basophils: