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Blood and Circulation By the end of this class you should understand: • The components of blood by volume and their functions • The most vital materials circulated by blood • The purpose and process of hemostasis • The process of producing and removing red blood cells • The nature of blood types and the risks of improper transfusions Blood! • Blood is the liquid inside us all that keeps us alive • Essentially functions as a common liquid that all cells have equal access to – Think of roads in a city – How cells send molecules to other cells Blood Flow • Blood flows through the entire body thanks to the heart • Heart failure results in blood stagnation • All cells in the body depend on a steady flow of blood to live and will die once blood flow stops Nutrient Delivery • Blood is responsible for delivering all nutrients and removing all waste products – Glucose – Oxygen – Vitamins, amino acids, & fats – CO2 – Waste such as urea, creatinine, and lactic acid Blood Plasma • Almost all materials in blood dissolve directly into the liquid, called plasma • Plasma is also filled with plasma proteins such as antibodies (for the immune system) and clotting proteins • Only one nutrient does not dissolve in the blood plasma – Which one? Oxygen • Oxygen must be delivered to all cells of the body that use aerobic respiration (mitochondria) – Essentially all living cells of the body • Oxygen does not mix with water and so must be transported in molecules called hemoglobin Hemoglobin • Hemoglobin is a protein that contains a pigment called heme (contains iron) – Same way rhodopsin containing retinal • Each heme can bind to one O2 molecule, so a hemoglobin can carry 4 O2 molecules • These hemoglobin molecules are not allowed to float freely in blood – This can cause severe kidney damage Red Blood Cells • Red blood cells, or erythrocytes, are essentially cell membranes packed with hemoglobin – Virtually no organelles remain in a mature erythrocyte, not even a nucleus – This is to improve the amount of oxygen a RBC can carry – This also means the cell cannot regenerate and is no longer technically alive Red Blood Cell Lifespan • Red blood cells are produced in the red marrow of bone • They circulate through the blood for around 3-4 months • Because they have no organelles, they cannot repair wear and tear and so are broken down in the liver and spleen Red Bone Marrow • Red bone marrow is filled with stem cells called hemocytoblasts – Literally means “blood cell creators” • These stem cells constantly reproduce to replace the ones that differentiate into blood cells – Hemocytoblasts produce all the blood cells of the body Erythrocyte Formation • A hemocytoblast that has been signaled to become a RBC produces hemoglobin in large quantities using its organelles (nucleus and mitochondria) • The cell then degrades its organelles once it has about 300 million hemoglobin molecules – It is now a mature erythrocyte! Erythrocyte Signal? • There is a hormone in the blood called erythropoietin (EPO) • The kidneys monitor oxygen delivery in the body and the lower oxygen delivery is, the more EPO they release • This is also why people at high altitudes have more red blood cells Hematocrit • The percent by volume of red blood cells in the blood is called the hematocrit – Most visible when the blood is spun in a centrifuge • Hematocrit is influenced by EPO levels and also reflects health and athleticism • Low hematocrit: anemia • High hematocrit: polycythemia Blood Cells • The hematocrit is usually 4045% of blood volume – Most of the rest is plasma • The buffy coat between the two is all of the other cells of the blood – Platelets (hemostasis) – White blood cells (immune system) • Will be covered in chapter 9 Platelets and Hemostasis • Platelets, like RBCs, are incomplete cells – Lack any organelles except for granules (vesicles) filled with clotting agents • Platelets assist with blood clotting (hemostasis) – Physically stick to the damaged blood vessels – Release chemicals that stimulate coagulation Coagulation • As blood is exposed to damaged blood vessels, an enzyme called thrombin is formed from factors in the blood and in platelets • Thrombin catalyzes other proteins in the blood to form a fiber called fibrin – Fibrin is sticky and makes the blood viscous Hemophilia • The blood proteins for coagulation are produced by the liver • A problem with the gene for these proteins can cause a condition called hemophilia, where the blood cannot clot when injured – Absence of platelets can also cause bleeding disorders but is much rarer – Now treatable with injections of the missing proteins Blood Loss • When a person has lost a lot of blood, the remaining RBCs have difficulty delivering oxygen • One treatment is to inject blood from a donor into the patient • A serious problem with this approach is that the body has an immune system (the white blood cells) that may attack foreign markers ABO Blood Type • The most common and well-known difficulty with blood transfusion is the gene for a particular marker on red blood cells • This gene has three major versions: A, B and O – Since everyone has two of each chromosome (one from each parent) everyone has two of these genes • The O marker is small and the immune system will not recognize it as an antigen (trigger) Blood Antigens • A and B are antigens only if the body does not already have these markers – The immune system is trained when the person is a fetus, so blood injections into a fetus will train its immune system not to attack those markers • A blood type A person will accept type A blood but reject type B and type AB blood • A type AB person will accept all four blood types • A type O person will reject all other blood types ABO Blood Types Blood Rejection • Antibodies produced by the immune system cause antigens to stick together • In the case of transfused blood, this means blood will agglutinate (clot) inside blood vessels – This can potentially be very harmful to any organs they get stuck in What About the + or -? • A+ and A- are the same ABO blood type – The second symbol refers to another blood type antigen, the Rh factor • The immune system, for reasons unknown, is already sensitized to ABO antigens in most adults, but rarely to the Rh marker • Sensitization can occur from a blood transfusion (A+ into A- person) or by giving birth to a baby with Rh+ blood Rh Factor Sensitization See you Thursday! • Prepare to learn the secrets of your heart!