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UT BIO 311D - Circulation and Gas Exchange (Part II)
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Lecture 15 BIO 311D 1st EditionOutline of Last Lecture I. Circulatory SystemII. Gastrovascular CavitiesIII. Evolutionary Variation in Circulatory SystemsIV. Open and Closed Circulatory SystemsV. Organization of Vertebrae Circulatory SystemsVI. The HeartOutline of Current Lecture I. Fluid Return by the Lymphatic SystemII. Blood ComponentsIII. PlasmaIV. ErythrocytesV. LeukocytesVI. Stem CellsCurrent LectureFluid Return by the Lymphatic System• The lymphatic system returns fluid that leaks out from the capillary beds• Fluid, called lymph, reenters the circulation directly at the venous end of the capillary bed and indirectly through the lymphatic system• The lymphatic system drains into veins in the neck• Valves in lymph vessels prevent the backflow of fluid• Lymph nodes are organs that filter lymph and play an important role in the body’s defense• Edema is swelling caused by disruptions in the flow of lymphBlood components contribute to exchange, transport, and defense• With open circulation, the fluid that is pumped comes into direct contact with all cells• The closed circulatory systems of vertebrates contain blood, a specialized connective tissue• Blood consists of several kinds of cells suspended in a liquid matrix called plasma• The cellular elements occupy about 45% of the volume of bloodPlasma• Blood plasma is about 90% water• Among its solutes are inorganic salts in the form of dissolved ions, sometimes called electrolytes• Another important class of solutes is the plasma proteins, which influence blood pH, osmotic pressure, and viscosity• Various plasma proteins function in lipid transport, immunity, and blood clottingCellular Elements• Suspended in blood plasma are two types of cells– Red blood cells (erythrocytes) transport oxygen O2– White blood cells (leukocytes) function in defense• Platelets, a third cellular element, are fragments of cells that are involved in clottingErythrocytes• Red blood cells, or erythrocytes, are by far the most numerous blood cells• They contain hemoglobin, the iron-containing protein that transports O2• Each molecule of hemoglobin binds up to four molecules of O2• In mammals, mature erythrocytes lack nuclei and mitochondria• Sickle-cell disease is caused by abnormal hemoglobin proteins that form aggregates• The aggregates can deform an erythrocyte into a sickle shape• Sickled cells can rupture or block blood vesselsLeukocytes• There are five major types of white blood cells, or leukocytes: monocytes, neutrophils, basophils, eosinophils, and lymphocytes• They function in defense by phagocytizing bacteria and debris or by producing antibodies• They are found both in and outside of the circulatory systemPlatelets/Blood Clotting:• Platelets are fragments of cells and function in blood clotting• Coagulation is the formation of a solid clot from liquid blood• A cascade of complex reactions converts inactive fibrinogen to fibrin, forming a clot• A blood clot formed within a blood vessel is called a thrombus and can block blood flowWhich of the following is a type of leukocyte?A. BasophilB. EosinophilC. MonocyteD. All of the aboveE. None of the aboveStem Cells and the Replacement of Cellular Elements• The cellular elements of blood wear out and are being replaced constantly• Erythrocytes, leukocytes, and platelets all develop from a common source of stem cells in the red marrow of bones, especially ribs, vertebrae, sternum, and pelvis• The hormone erythropoietin (EPO) stimulates erythrocyte production when O2 delivery is


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UT BIO 311D - Circulation and Gas Exchange (Part II)

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