 This video will cover part one of the cardiovascular system, covering blood. As we go, we'll cover the following study objectives. List the functions of blood. Describe the composition of whole blood. Define and describe the process of hematopoiesis. Define and describe the mechanism of hemostasis. So let's start off by listing the functions of blood, transport, regulation, and protection. And so transport is the major function of blood. Blood is moving through the vessels of the cardiovascular system. The heart is pumping the blood and blood is transporting nutrients and waste. The blood is also transporting hormones. And these hormones are important for the related function of regulation. The blood carries hormones from endocrine organs to affector organs, regulating the activity of those affector organs. And blood is also important for the regulation of our body temperature by absorbing and distributing heat. And blood is important for protection, where the white blood cells or leukocytes fight infection and the mechanism of hemostasis is where platelets, also known as thrombocytes, prevent blood loss. They stop bleeding by forming a blood clot. Here we can see the three major types of formed elements or blood cells. On the left we see an erythrocyte or red blood cell that has the primary function of transporting oxygen. In the middle, just on the right of the erythrocyte, we see a platelet or thrombocyte. Technically a platelet is just a cell fragment, not an entire cell, but it's one of the formed elements of blood. And then in the top right corner here, we see a leukocyte or white blood cell. Leukocytes are the cells that are important for defending against infection, and we'll study leukocytes in more detail as we study the lymphatic and immune system. In response to an injury when pathogens invade a tissue, leukocytes are attracted to the injury. Leukocytes can migrate from the blood into the injured tissue. Once leukocytes arrive in the injured tissue, they bind to pathogens. Some types of leukocytes can perform phagocytosis. For example, the macrophage we see here is performing phagocytosis and golfing the pathogen in order to destroy it. Another type of leukocyte called an eosinophil contains cytoplasmic granules filled with cytotoxic chemicals that destroy the pathogen, kill the pathogen in order to defend against infection. Here we see the shape of erythrocytes is a biconcave disc. That is a disc that's dimpled in on both sides in order to increase the amount of surface area in order to facilitate gas exchange because the primary function of erythrocytes is to transport oxygen in the blood. Hemoglobin is a protein inside of erythrocytes that transports oxygen. Each hemoglobin protein is made of four polypeptides, four globin protein subunits, two alpha chains and two beta chains. Within each of these subunits is a cofactor, a chemical called heme. You can see here the chemical structure of heme on the right. I wouldn't expect you to memorize the chemical structure of heme, but I want you to know that there is an iron atom inside of heme and that iron atom is important for binding oxygen within hemoglobin. Nutritional iron deficiency impairs the ability to produce heme and therefore hemoglobin and erythrocytes leading to a condition known as anemia. Iron deficiency anemia impairs the ability to transport oxygen in the blood leading to the feeling of tired weakness. Another form of anemia is known as sickle cell anemia. Sickle cell anemia results from a mutation in the gene for hemoglobin. This mutation causes the hemoglobin protein to have a different shape which causes erythrocytes to have a sickle shape or crescent shape. These sickle shaped erythrocytes clump together and break easily leading to anemia or a decreased number of erythrocytes in the blood decreasing the oxygen transport capacity of the blood. Now we're going to move on to study the composition of blood. In order to study the composition of blood we can take a sample of whole blood and separate it in a machine called a centrifuge. A centrifuge spins a tube at very high velocity and the more dense substances in blood will sink to the bottom whereas the lighter less dense substances float to the top. We can see the plasma is at the top. Plasma is the liquid component of blood. Plasma is mostly water with dissolved solutes. Including proteins, nutrients and hormones. The most abundant protein in plasma is called albumin. Albumin is important for maintaining the osmotic pressure of plasma and also important for transporting nutrients in the blood. Another important protein in plasma is called fibrinogen. Fibrinogen can be activated to form insoluble protein fibers called fibrin. Some of the important nutrients in blood include glucose and amino acids and also minerals. Sodium is the most abundant mineral in plasma. There's also several other minerals like calcium, magnesium and iron that are important in the blood plasma. Underneath the blood plasma we see the formed elements. In the Buffy Coat is a thin layer of white blood cells and platelets and below the Buffy Coat is the hematocrit layer containing the red blood cells or erythrocytes. In a healthy adult female the hematocrit represents about 37 to 47% of the total blood volume whereas in men it's normally a little higher between 40 to 52%. A depressed hematocrit is known as anemia. Anemia is a decreased number of erythrocytes and this can cause us to feel tired and weak. In contrast polycythemia is an elevated hematocrit. Here we see light microscope images of the major types of leukocytes in blood basophils, eosinophils, neutrophils, monocytes and lymphocytes. Basophils, eosinophils and neutrophils are called granular leukocytes or granular sites because they contain cytoplasmic granules. Whereas monocytes and lymphocytes do not contain cytoplasmic granules so they are known as agranular leukocytes or agranulocytes. Basophils are named after the basic dye that stains their cytoplasmic granules a dark blueish color. Basophils are the least common of the leukocytes representing less than 1% of the total number of leukocytes in whole blood and their cytoplasmic granules contain histamine an inflammatory chemical that attracts other leukocytes to defend against infection. Eosinophils represent about 1-4% of the leukocytes in blood and eosinophils have a bright red staining cytoplasmic granule. These cytoplasmic granules are filled with defense proteins that are cytotoxic chemicals that destroy pathogens in order to defend against infection. And the eosinophils have a bilope shaped nucleus that is the nucleus has two large regions, two large lobes. Neutrophils are the most common leukocytes representing approximately 60-70% of leukocytes in whole blood. Neutrophils have a light purple staining cytoplasmic granule and multiple lobes to their nucleus. Neutrophils are also phagocytic cells that can engulf pathogens in order to defend against infection but they can release cytoplasmic granules in order to attract other leukocytes to come help defend against infection. Monocytes do not contain cytoplasmic granules but they have a large nucleus with a curved shape that in this image we can see has the shape of a U although you may see it from a different perspective where the nucleus would be pushed off to one side there would be still one large nucleus and a large region of cytoplasm on the other side of the monocyte. Monocytes can move out of the blood and into a tissue to differentiate into a macrophage that performs phagocytosis in order to defend against infection. Lymphocytes have a large round nucleus with a small ring of cytoplasm surrounding the nucleus. Lymphocytes represent about 25 to 30% of the leukocytes in blood and so they're the second most common of the leukocytes and lymphocytes are important for the specific immune response the adaptive defense against a specific pathogen where our immune system will form a memory against infection in order to mount a more efficient response in the future. Here we can see an illustration of the major types of granulocytes the neutrophils, eosinophils and basophils and this illustration nicely shows the shape of the nucleus in a neutrophil there are multiple lobes whereas an eosinophil has a bilob nucleus and a basophil has a curved shape to the nucleus sometimes it looks like an S shape although it's difficult to see the nucleus in a basophil under the light microscope because the cytoplasmic granules stain with a dark bluish purple color that obscures our view of the nucleus. Here we can see a diagram showing the process of hematopoasis which occurs in red bone marrow where multipotent hematopoetic stem cells divide and differentiate to form all the formed elements of blood. Hemopoetic stem cells are also known as hemocytoblasts that these cells can divide in order to produce more hemopoetic stem cells or differentiate to form two major lineages of stem cells the myeloid stem cells and lymphoid stem cells lymphoid stem cells further differentiate into lymphoblasts that are immature cells that differentiate further to form lymphocytes myeloid stem cells differentiate eventually to form all of the other types of formed elements the thrombocytes, erythrocytes, and all the leukocytes that are not lymphocytes myeloid stem cells differentiate into megakaryoblasts that are immature cells that differentiate further into megakaryocytes and then the megakaryocyte inside of our red bone marrow breaks off small cytoplasmic fragments that exit the bone marrow as platelets platelets or thrombocytes then circulate in the blood and respond to bleeding to carry out the mechanism of hemostasis forming a blood clot to stop bleeding. the pro-erythroblast differentiates into a reticulocyte as it differentiates into a reticulocyte it ejects its nucleus then the reticulocyte migrates out of the bone marrow into the blood and differentiates to form an erythrocyte the mature cell that transports oxygen in our blood myeloblasts are immature cells that can differentiate to form the granular leukocytes, basophils, neutrophils, and eosinophils and monoblasts are immature cells that can differentiate to form monocytes the erythrocyte life cycle starts in red bone marrow where hemopoietic stem cells differentiate into the myeloid stem cells that further differentiate to form erythroblasts then the erythroblast ejects its nucleus becoming a reticulocyte and a reticulocyte then exits the red bone marrow into the blood stream and matures into an erythrocyte then erythrocytes transport oxygen in the blood as they circulate for an average of 120 days worn out erythrocytes are then degraded by phagocytosis where macrophages in the bone marrow liver and spleen engulf erythrocytes and then the erythrocyte is broken down by the lysosome inside of the macrophage proteins inside of the erythrocyte are degraded for example the hemoglobin is digested inside of the lysosome the globin subunit is broken down into its amino acids and those amino acids can then be reused to build new proteins the cofactor heme within the hemoglobin is then released and the heme can be further broken down to recycle the iron to build new hemoglobin and the rest of the heme molecule can be converted into bilirubin and excreted hemostasis is a mechanism that stops bleeding in response to an injured blood vessel when a blood vessel is torn the first step of hemostasis is a vascular spasm where a smooth muscle in the blood vessel wall contracts constricting the blood vessel and reducing blood flow to the injured tissue then platelets will stick to the torn edges of the blood vessel becoming activated to release clotting factors these clotting factors will attract more platelets to stick together forming a platelet plug and clotting factors will also stimulate the mechanism of coagulation where the fibrinogen protein which is soluble in plasma is converted into an insoluble protein called fibrin fibrin forms in a network of protein that traps the formed elements of blood in the blood clot in order to stop bleeding