let's take a closer look at the formed elements urethra sites or red blood cells often abbreviated rbcs are the most common type of blood cell their primary function is to transport oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs mature red blood cells have a biconcave shape and lack a nucleus in mitochondria think of the Bon a shape like a donut that has a thin piece of dough where the hole normally would be this shape provides a huge surface area relative to volume making it much easier for gases to diffuse into or out of the cell the lack of a nucleus and mitochondria maximizes the space that the red blood cell has for hemoglobin the protein that binds to oxygen in addition the lack of a nucleus increases the deformability of the cell this makes it easier for red blood cells to squeeze through those tight little capillaries red blood cells also play a central role in bicarbonate buffering their cytoplasm contains a large quantity of Carbonic and hydrat an enzyme that catalyzes the reversible reaction between carbon dioxide and water to form carbonic acid carbonic acid is then broken down into bicarbonate and hydrogen ions this allows the blood to transport enormous amounts of CO2 in the form of bicarbonate we'll learn more about the role red blood cells play in the bicarbonate buffering system in a later lecture lucaites or white blood cells abbreviated wbcs are immune cells that protect the body against bacteria viruses parasites toxins and tumors unlike the red blood cells white blood cells retain their nuclei and organel lucaites are far less numerous than red blood cells and there are several different types present in the body we'll learn more about the different types of lucaites and the roles they play in the body when we get to the immune in lymphatic lecture platelets are cytoplasmic fragments that form blood clots and help to stop bleeding when a blood vessel is damaged platelets form a temporary plug that helps seal the opening platelets also contain platelet derived growth factor or pdgf a substance that plays a significant role in blood fesal formation and repair you may see some sources refer to platelets as thrombocytes anytime you see the word thrombus you should immediately think blood clot platelets are produced by bone marrow cells called Mega parasytes the body is constantly producing new red blood cells white blood cells and platelets to maintain homeostasis and Keep Us Alive but where do these different blood cells come from hematopoesis is the process of forming new blood cells and platelets the term hematopoesis is derived from two Greek words hea which means blood and po which means to produce something this process begins early in embryonic development and continues throughout a person's life hematopoesis takes place in the red bone marrow found in the epifisis of long bones for example the humorous and femur the flat bones such as the ribs and cranial Bones the vertebrae and the pelvis hematopoetic stem cells or hsc's are undifferentiated cells found in the red bone marrow the term undifferentiated means that these cells haven't developed into a particular cell type yet you can think of undifferentiated cells as kind of like free agents they haven't committed to any one cell team yet we use the term differentiate when a stem cell develops into a more specialized cell type this this typically involves the cell going through several structural and functional changes hematop potic stem cells differentiate to produce two blood cell lines the myoid cell line develops into red blood cells the cells that produce platelets the megaros sites and several different types of white blood cells neutrophils eosinophils basophils monocytes and mass cells the lymphoid cell line develops into to a group of white blood cells called lymphocytes this includes natural killer cells B lymphocytes or B cells and t-lymphocytes or te- cells the process of hematopoesis is controlled by cyto kindes signaling molecules that are released from one cell to affect the growth or development of another cell some of the best known cyto kindes in hematopoesis are Colony stimulating factors and in lucans these cyto kindes stimulate the production and activity of different populations of white blood cells another important cyto kind is thrombo potin a glycoprotein that regulates the growth and maturation of the platelet producing megaros sites this slide gives a simplified overview of hematopoesis notice how the hematopoetic stem cell at the top gives rise to myoid stem cells and and lymphoid stem cells the myoid cell line develops into red blood cells the platelet producing megga caros sites neutrophils eosinophils basophils and monocytes the lymphoid cell line develops into the lymphocytes natural killer cells B lymphocytes and T lymphocytes I should note that this image is a simplified view of hematopoesis for example the pro urethro blast that we see under the myo stem cell line goes through several different stages before it becomes a reticulite for example it goes through being a basophilic urethr blast a polychromatic urethr blast an orthochromatic urethr blast and then has to go through nuclear Extrusion to become the reticul site I don't expect you to memorize all these stages but it is something that you will encounter if you plan on going to medical school urethr poesis is the process used to create new red blood cells so think of it kind of like a subsection of homat poesis this one is specifically focused on red blood cells red blood cells arise from the myoid stem cell line that we just mentioned on the previous slide over the course of About a Week the cell goes through several stages of development as ribosomes proliferate and hemog hobin is synthesized the nucleus is ejected towards the end of this process to produce the depression in the center of the cell young urethr sites then pass into the bloodstream and develop into mature urethr sites after another one to2 days urethr poesis is controlled by urethr potin abbreviated EPO urethr potin is a cyto kind produced mostly by the kidneys in response to hypoxia low oxygen in the blood any condition that causes a drop in oxygen levels can trigger the release of urethro potin this includes reduced numbers of red blood cells due to Hemorrhage which is just a fancy way to say bleeding or excessive red blood cell destruction insufficient hemoglobin for example if you have iron deficiency or the reduced availability of oxygen that occurs if you're at really high altitude UD or have a respiratory condition like say COPD one to two days after urethro potin levels rise in the blood the number of new red blood cells entering circulation begins to increase if the oxygen levels return to normal the secretion of urethr potin decreases and we don't produce as many red blood cells normal red blood cell production requires adequate amounts of iron IR vitamin B9 which is also called folate or folic acid in its synthetic form and vitamin B12 iron is essential for hemoglobin synthesis the liver spleen and bone marrow store very large amounts of iron so that way we don't run out because if you have a deficiency in iron this can reduce hemoglobin levels and cause anemia vitamin B9 and b12 are essential for the synthesis of DNA a lack of either of these vitamins will cause abnormal and diminished DNA synthesis and a failure of cell division since we're constantly dividing to produce red blood cells this means a lack of B9 or B12 can also result in anemia because oxygen has a low solubility in liquids only a very small amount is able to dissolve into the blood plasma directly this accounts for approximately 1 to 1 and a half% of blood oxygen content the remaining 98 to 99% of oxygen is transported by binding to hemoglobin hemoglobin is an iron containing protein found inside the red blood cells each hemoglobin molecule consists of four protein chains called globins there are several ISO forms of globin an isopor by the way is a functionally similar protein that has a slightly different amino acid sequence the most common isoforms are designated Alpha Beta gamma and Delta most adult hemoglobin has two alpha chains and two beta chains however about 2 and a half% of adults have hemoglobin that's formed by two alpha chains and two Delta chains each globin contains a heem group a ring structure with an iron ion at its very center we can see the chemical structure of a heem group in the bottom right each iron ion can bind to one molecule of oxygen since each hemoglobin has four heem groups and each heem group can bind to one oxygen this means that each hemoglobin is capable of binding to four molecules of oxygen interestingly when the first molecule of oxygen binds hemoglobin undergos a confirmational change this makes it easier for additional oxygen molecules to bind to the remaining three heem groups we'll learn more about this in our cardiovascular physiology lecture but this property of hemoglobin is why it has a very high saturation rate in arterial blood Ty typically between 95 to 100% saturation