Blood Components - Tracy Unified School District Components of Blood This slide shows the composition of blood in a healthy adult. Notice that most of the formed elements are red blood

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Cardiovascular SystemCardiovascular System

Blood ComponentsBlood Components

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Components of BloodComponents of Blood

Formed elements: Formed elements: erythrocytes, erythrocytes, leukocytes, plateletsleukocytes, platelets

Plasma: water,Plasma: water,proteins, otherproteins, othersolutessolutes

The components of blood can be divided into two broad categories. Formed elements include all the cell (or ex-cell) components of the blood: erythrocytes (red blood cells), leukocytes (white blood cells) and plateletes. Plasma includes the liquid and dissolved blood components. It’s mostly water with proteins, hormones, glucose, oxygen, carbon dioxide, ions, and other products dissolved in it. In this picture, the cell on the left is an erythrocyte (notice the biconcave shape). The small cell in the center is a platelet. The cell on the right is a leukocyte.

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Each of the formed elements can be seen in a blood smear like this one. Most of the cells are red blood cells. The larger pink cells are leukocytes. The small dark spots that look like dust are platelets.

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This slide shows the composition of blood in a healthy adult. Notice that most of the formed elements are red blood cells, with relatively few white blood cells and platelets. The plasma is mostly water with some dissolved proteins and other solutes.

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PlasmaPlasma

Plasma proteins:Plasma proteins:–– AlbuminsAlbumins–– GlobulinsGlobulins–– FibrinogensFibrinogens

The picture on this slide shows the result of “spinning” a blood sample in a centrifuge. When spinning a suspension like blood, the heavier elements settle to the bottom of the test tube while the lighter components are pushed to the top. Erythrocytes collect at the bottom and the yellowish liquid at the top is plasma. The very thin white line between the erythrocytes and plasma is the white blood cells and platelets.The three primary proteins found dissolved in the blood plasma include albumins, globulins and fibrinogens. Albumins hold a lot of water and keep too much water from leaving the blood and entering tissues in the capillaries. Globulins are a category of proteins that bind to other substances. Sometimes, globulins can act as transport proteins to help substances (like glucose) pass across capillary walls. Other globulins (antibodies) can attach to pathogens to “mark” them for destruction. Fibrinogens bind together when vessel walls tear and help prevent blood loss.

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Erythrocytes (Erythrocytes (RBCsRBCs))

No nuclei. Lots of No nuclei. Lots of hemoglobinhemoglobin

Erythrocytes are the most numerous of the formed elements by far. They have a unique biconcave shape, which increases their surface area, allowing more efficient transfer of oxygen. The main function of erythrocytes is to transport oxygen. Mature erythrocytes do not have nuclei, mitochondria or most other organelles. Instead, most of their internal space is dedicated to holding hemoglobin, which binds to oxygen. Erythrocytes cannot divide. Instead, like all of blood’s formed elements, they arise from hemopoietic stem cells in the red bone marrow. Since erythrocytes don’t have mitochondria, all of their metabolism is anaerobic – this ensures that the erythrocytes don’t use any of the oxygen they transport.

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HemoglobinHemoglobin

Each erythrocyte can carry about 250,000,000 hemoglobin molecules. A hemoglobin molecule is a polypeptide chain composed of four protein chains. Each of these globin protein chains has a binding site called a heme where oxygen can bind. Oxygen can only bind if iron is present, though. An iron deficiency can cause inefficient oxygen transport because oxygen will not be able to bind the hemoglobin molecules. Oxygen isn’t the only thing that will bind to the heme site. Carbon monoxide will, too, which can lead to suffocation since it prevents oxygen from binding (carbon monoxide poisoning).

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RegulationRegulation–– Low blood oxygenLow blood oxygen–– ErythropoietinErythropoietin

The production of erythrocytes is governed by the kidneys. When blood oxygen levels drop, the kidneys respond by increasing production of a hormone called erythropoietin. The target tissues of this hormone are the hemopoietic stem cells in the red bone marrow. Increasing levels of erythropoietin causes an increase in erythrocyte production. This indirectly results in an increase in blood oxygen levels.

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Sickle cell disease is a genetic mutation that affects the hemoglobin gene. It results in abnormally-shaped erythrocytes which are very delicate and rupture easily when the body needs a lot of oxygen. The tangled cluster of dead and weak erythrocytes can sometimes get trapped in capillaries, causing a lot of pain. Sickle cells are advantageous, though, in parts of the world where malaria is a problem because they are resistant to malaria.

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Leukocytes (Leukocytes (WBCsWBCs))

Amoeboid movementAmoeboid movement FunctionsFunctions

Unlike erythrocytes, leukocytes can leave the blood and enter the body tissues. Good thing, because any pathogens we pick up aren’t necessarily in our blood stream. The method of transport through tissues is called amoeboid movement –the cell extends a cell membrane process, then the cytoplasm streams into the process, moving the whole cell. White blood cells function in immunity (identifying and destroying pathogens), tissue repair (by destroying dead or damaged cells to make way for new ones) and tumor management (by engulfing and destroying the tumor cells).

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TypesTypes

–– Never let monkeys eat bananas!!Never let monkeys eat bananas!!

This is a mnemonic to help you remember the five types of leukocytes.

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TypesTypes–– NeutrophilsNeutrophils (g)(g)–– MonocytesMonocytes (a)(a)–– Lymphocytes Lymphocytes (a)(a)–– EosinophilsEosinophils (g)(g)–– BasophilsBasophils (g)(g)

Granulocytes vs. Granulocytes vs. agranulocytesagranulocytes

Neutrophils are the body’s first responders and are associated with the inflammatory response. When tissue becomes damaged, it secretes a chemical called histamine, which attracts neutrophils. The neutrophils engulf and destroy cells in the area of the tissue damage very quickly, but they die in the process. A collection of dead neutrophils results in pus. Monocytes grow to form macrophages, which usually target specific invading pathogens or dead or damaged cells. They phagocytize these cells as needed. Lymphocytes are involved in specific immunity, for example by forming a “memory” of previously-encounter pathogens and activating the immune response the next time the same pathogen tries to invade. Eosinophils and basophils work together to stimulate and mediate the inflammatory response.Visually, white blood cells can be categorized as granulocytes or agranulocytes. Granulocytes have lobed nuclei and visible granules in the cytoplasm. Agranulocytes have oval or kidney-shaped nuclei and no visible granules.

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The different types of WBC’s can be identified visually under the microscope. Counting the different types of WBC’s gives us a differential WBC count.Neutrophils have tiny granules – usually individual granules can’t be identified under the microscope, but a “cloudy” nucleus can. The main identifying characteristic of neutrophils is a nucleus with 3-5 lobes.Monocytes are agruanulocytes (no granules) with large oval or kidney-shaped nuclei. While the nucleus is large, a significant amount of cytoplasm is still visible.Lymphocytes are agranulocytes that look similar to monocytes, but the nucleus is usually round and is very large. The nucleus may fill the entire cell, leaving no visible cytoplasm.Eosinophils are granulocytes with nuclei that usually have exactly two lobes.Basophils are granulocytes with a small number very large granules – they are usually visible inside the cytoplasm. The nucleus is lobed, usually with 2 lobes.

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This slide, and the next several will give you some practice identifying different types of white blood cells. Note the very large, round nucleus in the lymphocyte. Become familiar with the cloudy (granule-filled) cytoplasm and the multi-lobed nuclei of the neutrophils.

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Can you identify each cell type?Cell type “a” are erythrocytes. (Notice the lack of a nucleus)“b” is a neutrophil. It has a multi-lobed nucleus and cloudy cytoplasm (granules)“c” is an eosinophil. It has a bi-lobed nucleus and granules.“d” is a lymphocyte. The nucleus is so huge it fills up almost the entire cell.

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How about these cells?In the left picture, the large WBC on the left with the bilobed nucleus is an eosinophil. The dark-staned one with the giant nucleus is a lymphocyte and the one near the right with the multi-lobed nucleus is a neutrophil.In the right picture, the leftmost WBC is a monocyte, the middle cell with the giant nucleus is a lymphocyte, and the large cell with the multilobed nucleus is a neutrophil.

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In the left picture, you can see a number of monocytes and neutrophils. In the picture on the right, you can see at least two lymphocytes and two neutrophils.

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PlateletsPlatelets

MegakaryocytesMegakaryocytes HemostasisHemostasis

Platelets are not full-fledged cells. Rather, they are fragments of immature blood cells called megakaryocytes. They function to prevent blood loss. For a small tear (such as happens all the time in our vessels), a platelet plug forms to stop blood loss. For larger damage, a blood clot forms.

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Blood Components - Tracy Unified School District Components of Blood This slide shows the composition of blood in a healthy adult. Notice that most of the formed elements are red blood