Blood • Blood is not an epithelial tissue, and it’s not loose or dense connective tissue; it’s classified as a “special connective tissue”. • You have about 5 liters of blood, but that is only half of the body fluid. • The other half includes fluid around each cell, and joint fluids, etc.
Blood PLASMA EXTRACELLULAR FLUID ↑ ↓ SYNOVIAL FLUIDS, ETC
Blood consists of the following: • Plasma • Red blood cells • White blood cells • Platelets
FUN FACTS • In one day, your blood travels nearly 12,000 miles. • Your heart beats around 35 million times per year. Your heart pumps a million barrels of blood during the average lifetime -- enough to fill three supertankers. If an artery is cut, blood will shoot out 30 feet.
Plasma • Plasma is what the blood cells float around in. If you spin a blood sample in a test tube, the red blood cells sink to the bottom, and you’ll see the yellow plasma on top. • Some people who need blood just need the packed RBCs, some need the platelets, others need the plasma, and some need whole blood, which is both plasma and RBCs. • The plasma also carries around the platelets and some white blood cells.
Overview: Composition of Blood Figure 17.1
PLASMA CONTENTS • Water (90%) • Dissolved substances (10%) • Proteins • Albumin (egg white). Most common protein in blood (homeostasis) • Antibodies • Clotting factors called fibrinogen and fibrin. • Lipoproteins (move fats through blood: HDL, LDL) • Nutrients • Glucose (main energy source) • Amino Acids (builds proteins) • Wastes (urea) • Gases (O2, CO2, Nitrogen) • Electrolytes = ions (Na+, K+, Cl-, Ca++)
ERYTHROCYTES (Red blood cells) • 5 million • Like a doughnut with the hole not fully cut out. • These are among the smallest cells in the body • They have no nucleus • Biconcave to increase surface area • Filled with hemoglobin (Hgb), which carries O2 throughout the body. Oxygenated Hgb is bright red, deoxyHgb is deeper red, almost a bluish-purple.
ERYTHROCYTES: • Average life span is 120 days. Old ones are destroyed in the spleen and liver, and Hgb is recycled. • In one day, 100 billion of these cells are destroyed, and 100 billion are made: where? • Red marrow.
Microbiology • To understand the function of white blood cells, you will need to learn some general concepts and terminology from Microbiology: • Pathogen • General size of bacteria and viruses • Antigen
Pathogen“Path” = disease “ogen” = generating • A pathogen is something that causes disease. • A biological pathogen is a bacterium, virus, fungi, yeast, protozoa, worms, etc. • A non-biological pathogen can be a toxic chemical, asbestos, etc. • Usually, the term “pathogen” refers to a biological pathogen.
Sizes of Pathogens • Bacteria are so small that hundreds of them can fit inside one white blood cell. • However, bacteria usually do not invade body cells. They live between the cells of the body, using up nutrients in the area, and they cause harm by secreting toxins. • Viruses are so small that thousands of them can fit inside the NUCLEUS of one white blood cell. • They always try to invade body cells because they need a piece of our DNA or RNA in order to replicate. • When a body cell has been invaded by a virus, the entire cell must be killed by a white blood cell.
Antigen • An antigen is anything that causes an immune response, which isn't necessarily a biological pathogen (disease-causing organism). • A non-biological antigen can be pollen, dust, grass, or anything that a person is allergic to. • Pollen can be an antigen to a person with allergies, but it is not an antigen to a person without allergies, because no immune response was launched.
LEUKOCYTES (White blood cells)all fight infection • BASOPHILS • MAST CELL • EOSINOPHILS • NEUTROPHILS • MONOCYTES • MACROPHAGES • LYMPHOCYTES • B CELLS • T CELLS
BASOPHILS • Basophils – only about 0.5% of all leukocytes • Granules secrete histamines (vasodilation; more WBCs can get to the infection site) • Antihistamines interfere with the function of basophils. • Mast Cell: a basophil that leaves the blood vessel and enters the tissues.
Eosinophils • Eosinophils – compose 1-4% of all WBCs • Play roles in: • Ending allergic reactions, parasitic infections • During these conditions they increase in numbers
Neutrophils • Neutrophils – most numerous WBC • First to respond to infection • Phagocytize and destroy bacteria • Also destroy bacterial toxins in body fluids • Nucleus – has two to six lobes
Neutrophils • Neutrophils are the white blood cells that contribute to immunity mainly by engulfing BACTERIA and foreign bodies (thorns, dirt, etc) in a process called phagocytosis. • They release the contents of their lysosomes onto the invader, dissolving it. • When a bacterium has a capsule, it makes it hard to phagocytize, so the neutrophil requires opsonization by antibodies.
Opsonization • Some bacteria have evolved a slippery capsule around them as a defense against phagocytosis. The neutrophil cannot engulf this type of bacteria. Neither can a macrophage. • When an antibody attaches to this type of bacteria, the neutrophil can now grab onto the antibody like a handle, enabling it to phagocytize the bacteria. • This process of facilitation of phagocytosis is called opsonization.
When an invading bacteria has the antibody attached to its cell membrane, the entire structure is now called an antigen-antibody complex. • If a bacterium does not have a capsule, the neutrophil can destroy it without opsonization. The antibody can also destroy the bacterium by itself by popping the cell membrane. • But when a capsule is present, the neutrophil and antibody work best together. • Neutrophils are also the ones that primarily destroy the dissolved toxins that bacteria secrete into body fluids.
Monocytes • Comprise about 5% of all WBC’s. • Like neutrophils, they phagocytize (eat) bacteria, old cells, and foreign bodies. They have more types of lysosome enzymes than neutrophils so they are better at killing difficult pathogens. • They also use antibodies for opsonization. • When they leave the bloodstream and enter the tissues, they are calledMACROPHAGES.
What’s the Difference between Neutrophils and Monocytes/Macrophages? • There are 10x more neutrophils in the bloodstream than monocytes/Macrophages. Consider neutrophils to be the most numerous white blood cell. • However, there are more macrophages in the tissues of the body. They are everywhere! • Neutrophils live only a few days. Monocytes/Macrophages live a few months. Lymphocytes live for years. • Monocytes/Macrophages are larger and slower than neutrophils, but they can phagocytize larger organisms and more of them. • Neutrophils usually just phagocytize bacteria until they die. Macrophages phagocytize and then take pieces of the dead bacteria and present them to lymphocytes so a larger immune response can occur.
Differences in Function • There are two types of phagocytes: Neutrophils and macrophages. • Neutrophils and macrophages both mainly function by phagocytizing bacteria (not viruses). • Lymphocytes are mostly needed to kill off body cells infected by viruses.
Differences in Function • Neutrophils just phagocytize bacteria and secrete chemicals to recruit more white blood cells to the site. • Unlike neutrophils, macrophages have surface receptors; these "recognize" the surface of the pathogen’s cell membrane. • Macrophages phagocytize the bacteria, pop their lysosomes onto it, and dissolve it, except for some pieces of the bacteria’s cell membrane. • The macrophage places these pieces of bacteria on its own cell membrane, and finds a lymphocyte to present it to.
Differences in Function • Macrophages present these pieces to T cell lymphocytes and to B cells lymphocytes. • The lymphocyte feels the shape of the bacteria pieces on top of the macrophage, (this is called “antigen presentation”) and the lymphocyte can then launch an attack on the rest of the bacteria still alive in the body. • In this way, the macrophage recruits even more lymphocytes to join the war. • So, what is a lymphocyte?
Lymphocytes • 20–45% of WBCs • The most important cells of the immune system • There are two types of lymphocytes; one type is effective in fighting infectious organisms like body cells infected with viruses • Both types of lymphocytes act against a specific foreign molecule (antigen)
Lymphocytes • Two main classes of lymphocyte • B cells – Originate in the bone marrow, mature into plasma cells. A mature plasma cell fights infection by producing antibodies • T cells – Originate in the thymus gland. They attack foreign cells directly (including organ transplants!). They can also kill viruses.
B cells – mature into plasma cells Plasma cells secrete antibodies; the plasma cell’s antibodies are what kills the attacking cell. Antibodies attack in two ways: They attach to bacteria and pop the cell membrane They attach to encapsulated bacteria to help neutrophils and macrophages to phagocytize them. Lymphocytes
Mononucleosis: Epstein Barr virus attacks B lymphocytes. It is characterized by inflammation of lymph vessels (lymphangitis). Lymphangitis: lymph vessel inflammation; usually from infection. Infected lymphocytes have a characteristic scalloped edge where they touch RBC’s Disorder of B-cell Lymphocytes
Function of a B Lymphocyte Figure 17.6b
T cells – coordinate the immune response by recruiting other white blood cells. They can directly destroy bacteria by popping their cell membrane. T cells can also directly destroy foreign cells by popping the cell membrane. They do not need to phagocytize the invading cell. They do not need the assistance of antibodies. T-cells can therefore kill a body cell that has become infected with viruses. T-cell Lymphocytes
T cells are the cells that attack organ transplants! Immunosuppression drugs are designed to inhibit the action of T cells. T cells are attacked by the HIV (AIDS) virus. The thymus gland secrets certain hormones which can cause T cells to become immunocompetent (makes the cells mature and start to work) T-cell Lymphocytes
T Cells There are several types of T cells. The main types are • Cytotoxic (Killer) T cells • Go out and directly kill bacteria or infected host cells • Helper T cells • Release chemicals called “cytokines” to call in more white blood cells of all types to join in the war. They also present the macrophage’s antigen to a plasma cell, which causes the plasma cell to produce antibodies against that particular bacteria. • Suppressor T cells • Stop the immune process when it is over, and also "tell" some plasma cells to "remember" how to destroy that specific pathogen. Those plasma B-cells are then called Memory B-Cells. They can react to the same pathogen faster, the next time it invades because Memory B-cells already have the proper antibodies stored up for that pathogen.
Function of a T- Lymphocyte Figure 17.6a
Summary • A pathogen somehow gets past the body's physical and chemical barriers and the inflammation response. • The pathogen is engulfed by a macrophage (or neutrophil). • The macrophage releases the contents of its lysosomes onto the bacterium and dissolves most of it. There are still some pieces of the bacterium’s cell membrane left. The macrophage then forces the surface proteins of the bacterium (antigens) to it's own cell surface. • Helper T-Cells touch these surface antigens, make a copy of their shape, and present them to B-cells to make antibodies against them.
Summary • These Helper T-Cells begin to multiply and have two main roles. • The first is to activate B-Cells and "tell" them how to neutralize the pathogen by presenting the pieces of the bacterium cell membrane so the B-cells can turn into plasma cells which make the antibodies. • The B-Cells (now called Plasma cells because they have been activated) begin to multiply and produce the antibodies to neutralize this specific pathogen. • The second role of Helper T-Cells is to activate the Killer T-Cells by secreting cytokines. • Killer T-Cells can either destroy the pathogen itself (bacteria), or destroy the entire body cell which is infected (viruses). • When the immune response is over, Suppressor T-Cells stop the process and also "tell" some B-Cells (plasma cells) to "remember" how to destroy that specific pathogen. • Those B-cells (plasma cells) now become Memory B-Cells.