Blood Flashcards
Blood
PH maintained between 7.35-7.45. 7% total body weight , 70kg man has 5.6L.
Specialised connective tissue but atypical as has no fibres. Contains variety of cells and fluid ground substance. Blood circulates continuously throughout the body by pumping action of heart. Travels in blood vessels and allows constant communication between body tissues. Responsible for transporting following.
Oxygen - lungs to tissue
Carbon dioxide - tissues to lungs
Nutrients - alimentary tract to tissues
Waste products - tissues to organs of excretion
Hormones - endocrine glands to target tissues
Heat - point of production to less active tissues
Protective factors - point of production to infection
Clotting factors - blood stream to vessel damage.
Plasma
55% blood. Clear, straw coloured liquid.
WATER - 90-92% plasma.
PLASMA PROTEINS- large molecules retained in blood vessels. Made in liver except immunoglobulin made by B lymphocytes. Main ones albumins and globulins. Albumins maintain plasma osmotic pressure and carrier molecules for fatty acids, steroid hormones and some drugs. Globulins have functions as antibodies , transport of hormones( thyroglobulin carries thyroxine) , transport of minerals( transferrin carries iron). Clotting factors responsible for coagulation( fibrinogen and Christmas factor).
ELECTROLYTES- inc calcium , sodium( nerve impulses) and phosphate( acid base balance).
NUTRIENTS - main products of digestion eg glucose , amino acids. Transported in blood for use or storage.
WASTE PRODUCTS - most are from breakdown of protein. Formed in liver and carried to kidneys for excretion eg urea and uric acid.
HORMONES
GASES - oxygen and carbon dioxide dissolved in plasma and in combination with haemoglobin in RB Cs . Most oxygen in RBCS and small amount in solution but most carbon dioxide carried as bicarbonate ions dissolved in plasma and small amount in RBCS. Nitrogen carried but with no function.
Blood cells
3 main types:
Erythrocytes
Thrombocytes
Leukocytes - granulocytes & agranulocytes
Blood cells mainly produced in red bone marrow but lymphocytes produced in lymphoid tissue. Process of blood cell production known as haemopoeisis.
All originate from stem cells.
Erythrocytes
Biconcave discs with no nucleus and intracellular structures. Flexible and can squeeze through smallest capillaries. 99% of blood cells. Main function to transport oxygen and carbon dioxide and packed full of haemoglobin. Vit B12 and folic acid essential for RBC production. Lasts about 120 days in circulation. Breakdown known as haemolysis and and takes place in spleen , bone marrow and liver. Iron released during haemolysis retained in body and reused in bone marrow to make new haemoglobin. Haem part of haemoglobin broken down to biliverdin which is then further broken down to bilirubin ( yellow pigment). Bilirubin then attaches to plasma globulin and carried to liver. There it’s exchanged from fat soluble to water soluble for excretion into bile.
Oxygen transport
When all four binding sites of haemoglobin are full its saturated. It binds reversibly to oxygen. As oxygen content in blood increases its bright red( arterial blood) and blood low in oxygen is dark blue ( venous blood). LOW PH - metabolically active tissues release acid waste products and ph falls. Oxyhemoglobin readily breaks up releasing oxygen for tissue use. LOW OXYGEN ( HYPOXIA) - oxyhemoglobin breaks down releasing oxygen. In tissues which constantly consume oxygen levels are always low. This increases oxygen levels to cells. Oxyhemoglobin formation is favoured in the lungs. TEMPERATURE - actively metabolising tissues are warmer than less active ones. This drives the equation to the left and means more break down.
Blood groups
Antigens on RBC membranes stimulate immune response and these antigens determine blood group. Wrong blood type stimulates transfusion reaction ( antibodies produced to destroy foreign antigens). ABO system - 55% population has A type or B type or both antigens on their surface. Remaining have neither and called group O. A group makes B antigens etc. AB group known as universal recipients and O is universal donors.
Rhesus system - here antigen is Rh. 85% have this antigen. Rh- is capable of making anti rhesus antibodies but stimulated to do so only in certain circumstances eg pregnancy.
Leukocytes
Granulocytes
NEUTROPHILS - complex nuclei. Packed with granules containing lysosomes. 6-9 hours in bloodstream. Attracted to an area of infection or tissue damage by chemotaxis. Actively phagocytic. Small , fast and motile. Remove dead cells.
EOSINOPHILS - capable of phagocytosis but less active than neutrophils. Special role in elimination of parasitises. Toxic chemicals stored in granules which released when binding to infecting organism.
BASOPHILS- closely associated with allergic reactions , contain granules of histamine and heparin promoting inflammation.
Agranulocytes - 25-50%. Large nucleus.
MONOCYTES- largest of Leukocytes. Single large nucleus. Some circulate in blood and actively motile and phagocytic ( histiocytes) and some migrate into tissues and become macrophages. Longer lived than neutrophils and play role in body’s defence.
LYMPHOCYTES - smaller than monocytes. Formed in bone marrow and lymphoid tissue . Present in circulation and in lymphatic tissues. 2 types B and T and both involved in immune response.
Thrombocytes
Non nucleated disc shaped cell fragments 2-4 micro metres in diameter. Cytoplasm packed with granules containing chemicals that promote blood coagulation.
Lifespan 8-11 days .
Emergency store held in the spleen( about 1/3) in case of excessive bleeding.
Haemostasis
vasoconstriction and platelet plug
When blood vessel damaged , loss of blood is stopped( haemostasis) and healing occurs. The more badly damaged the quicker it begins, sometimes in 15 seconds).
- VASOCONSTRICTION- platelets come into contact with the damaged vessel and their surface becomes sticky and they adhere to damaged wall. They then release seratonin and thromboxanes which constrict the blood vessel , reducing or stopping blood flow. Other vasoconstrictors eg endothelins are released by damaged vessel itself .
- PLATELET PLUG FORMATION- sticky platelets clump together and release other substances including ADP which attract more platelets to the site. Passing platelets stick to those already at the damaged vessel and they release their chemicals.positive feedback by which many platelets rapidly gather at site of vascular damage , quickly form temporary seal- platelet plug. Formation usually complete within 6 minutes of injury. The plug however soft and easily disrupted and is pre cursor to far more durable blood clot.
Coagulation
Complex process involving positive feedback. Clotting factors activate each other in specific order eventually resulting in formation of prothrombin activator , first step in final common pathway. Prothrombin activates enzyme thrombin which converts inactive fibrinogen to insoluble threads of fibrin. As clotting proceeds the platelet plug progressively stabilised by increasing amounts of fibrin laid down. Maturing blood clot traps blood cells and plasma proteins inc plasminogen ( which will eventually destroy the clot) much stronger than plug. Final common pathway can be initiated in 2 ways. Extrinsic is activated rapidly(secs). Damaged tissue releases complex of chemicals called thromboplastin ( tissue factor) which initiates coagulation. Intrinsic slower(3-6mins) triggered by blood coming into contact with damaged vessel lining. After time clot shrinks as platelets contract , squeezing out serum consisting of plasma from which clotting factors have been removed. Clot shrinkage pulls the edges of damaged vessels together reducing blood loss.
Final common pathway in blood clotting
Thromboplastin released Platelets adhere
by damaged tissue cells to damaged
enters the blood. blood vessel lining
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Extrinsic pathway. Intrinsic pathway
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Prothrombin activator
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Prothrombin —- thrombin
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Fibrinogen– loose
fibrin
threads
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Stabilised fibrin clot
Thrombolysis
After clot has formed , process of removing it and healing the damaged vessel begins. The breakdown of fibrin ( fibrinolysis) is the first stage. Plasminogen , trapped within the clot as it forms is converted to enzyme plasmin by activators released from the damaged endothelial cells. Plasmin breaks down fibrin, progressively removing the clot to allow tissue repair.
Control of coagulation
Process of blood clotting relies heavily on several self perpetuating processes. Eg thrombin is a powerful stimulator of its own production . Control and braking mechanisms therefore essential to limit clotting to affected area and terminate process at appropriate time.
- perfect smoothness of normal blood vessel liming prevents platelet adhesion
- activated clotting factors rapidly deactivated by anticoagulants such as heparin.
- activated clotting factors quickly cleared from blood by the liver.
