Circulatory system.docx

Plasma is the transport medium for many inorganic and organic substances. Consists of 90% water, Na+, Cl-, waste products, hormones etc. Plasma proteins: Albumins – contribute to colloid osmotic pressure. Globulins – can be alpha, beta (transports water insoluble substances e.g. clotting factors) an...

Plasma is the transport medium for many inorganic and organic substances. Consists of 90% water, Na+, Cl-, waste products, hormones etc. Plasma proteins: Albumins – contribute to colloid osmotic pressure. Globulins – can be alpha, beta (transports water insoluble substances e.g. clotting factors) and gamma (antibodies) Fibrinogen – inactive precursor for clot’s fibrin meshwork. Erythrocytes are specialised for O2 transport. Contains haemoglobin made of globin and haem group. They lack nucleus and organelles. Flat and disc shaped. Has flexible membrane which allows them to squeeze in the capillaries to allow efficient transport. Only contain glycolytic enzyme (needed to fuel the active transport mechanisms) and carbonic anhydrase (enzyme that converts CO2 into HCO3- which is the form CO2 is transported in). Development of Erythrocytes Pluripotent stem cell-- myeloid stem cell--- erythroblast --- reticulocyte---- Erythrocyte. Short life span of 120 days. Old Erythrocytes are removed by the spleen. New red blood cells a made in the bone marrow by the process called Erythropoiesis. Erythropoiesis is controlled by erythropoietin from kidneys. The magnitude of erythropoietin released depends on the degree of O2 insufficiency detected by the kidneys. Reduced O2 delivery to the kidneys stimulate them to secrete erythropoietin into the blood. Erythropoietin stimulates their proliferation and maturation into mature red blood cells. Anaemia can be caused by variety of disorders, Nutritional anaemia- caused by dietary deficiency. Pernicious anaemia- caused by inability to absorb enough indigested vitamin B12 from digestive tract. It is essential for RBC production and maturation. Aplastic anaemia- caused by bone marrow failing to produce enough RBCs. Renal anaemia- result from kidney disease as erythropoietin is primary stimulus for promoting erythropoiesis. Haemorrhagic anaemia- caused by losing a lot of blood. Haemolytic anaemia- caused by rupture of too many RBC in the circulation. Malaria and sickle cell disease- sickle cell disease is when the RBCs become sickled therefore unable to carry oxygen. Polycythaemia An excess of erythrocytes therefore a contrast to anaemia. Can be primary and secondary. Primary= erythropoiesis proceeds to an excessive uncontrolled rate. Secondary= erythropoietin- induced adaptive mechanism to improve the blood’s O2 carrying capacity in response to prolonged reduction in O2 delivery to the tissues. Blood types depends on their antigen on the surface of the RBCs. ABO blood types Type A- contains A antigens. Type B- contains B antigens. Type AB- contains A & B antigens. Type O- contains neither A nor B antigens. Type O can be transfused into people with any blood type. If a person is given wrong type of blood, the antigen-antibody interacts and causes agglutination and ruptures of RBCs. People who have Rh factor are said to be Rh positive and ones who lack it are considered Rh negative. The Rh factor is a protein that can be inherited and found on the surface of RBC. Positive blood cell type contains Rh protein otherwise negative blood type don’t. Leukocytes Body’s immune defence system. 5 types of leukocytes Neutrophils Eosinophils Basophils Monocytes Lymphocytes Neutrophils Phagocytic specialists Go through programmed cell death called NETosis which kills nearby bacteria. During NETosis, neutrophils release neutrophil extracellular traps (NETs). Fibres are made of chromatin studded with antimicrobial proteins. NETs tap and destroy the bacteria. Eosinophils Associated with allergic conditions. Attach to the cell and secrete substances to kill it. Basophils Like mast cells and both synthesise and store histamines and heparin. Monocytes Become professional phagocytes. Emerge from bone marrow. Continues to mature and become macrophages. Lymphocytes B and T lymphocytes. B produce antibodies whilst T directly destroys the target cells. The rate of leukocytes production varies and depends on body’s needs. Abnormalities can also happen such as leukaemia. Platelets/ thrombocytes are cell fragments shed from megakaryocytes. Megakaryocytes derive from same undifferentiated stem cells that differentiate into red and white cells. Platelets are removed from the circulation by macrophages in spleen and liver and replaced by new ones from bone marrow. The hormone thrombopoietin produced by the liver increases number of megakaryocytes in bone marrow and stimulates each megakaryocyte to produce more platelets. Haemostasis- arrest of bleeding from vessels to stop blood flow. A damaged/cut vessel immediately constricts also known as vascular spasm. It slows blood down. Platelets also aggregate to from a plug at the vessel injury. When the endothelial lining of the blood vessel is disrupted, (vWf)- a plasma protein secreted by megakaryocytes, platelets etc adheres to the exposed collagen. Clot formation. Fibrinogen is converted into fibrin catalysed by thrombin. Fibrin molecules adhere to the damaged surface and forms a meshwork that traps RBC’s. the meshwork of fibrin is strengthened and stabilised by cross linkages catalysed by clotting factors known as XIII (fibrin stabilising factors). Thrombin has other roles as well which includes: Converts Fibrinogen to fibrin. Activates XIII to stabilise the fibrin mesh. Positive feedback to form more thrombin. Enhances platelets aggregation. Thrombin exists in plasma in form of inactive precursor called prothrombin. Factor X converts prothrombin into thrombin. After the clot has formed, clot retraction happens where platelets contract and shrink causing the mesh to also shrink. Clot dissolution- clot is dissolved by enzyme called plasmin. Plasmin is produced in the liver and present in the blood as inactive precursor called plasminogen. Plasmin works continuously to prevent inappropriate clots from forming. Thromboembolism Caused due to excessive or inappropriate clotting. A free-floating clot is called emboli. Haemophilia Causes excessive bleeding due to deficiency of one of the clotting factors needed in the clotting cascade. Blood flow through a vessel depends on: Pressure gradient. Vascular resistance (r4). Pressure gradient. Difference in pressure between the beginning and the end of the vessel. Blood flows from area of high pressure to area of low pressure. Resistance As resistance increases, it’s more difficult for blood to pass through the vessel therefore flow rate decrease. Viscosity refers to the friction developed between the molecules of a fluid as they slide over each other. Flow is directly proportional to pressure gradient and inversely proportional to vascular resistance. Low resistance has a larger flow compared to high resistance has no flow.