Immune System

Part 1: Erythrocytes and Leukocytes~

Erythrocyte

Neutrophil

Basophil

Leukocytes & Their Functions

Basophils-.5% Rare

Theses histamine-containing granular leukocytes help initiate the inflammatory response of the body. When tissues are injured, basophils secrete histamine, causing adjacent blood vessels to leak plasma, bringing nutrients, cells and chemicals necessary for repair to the damaged area.

Eosinophils-2%-4%

These granular leukocytes defend against large parasites, such as hookworms and tapeworms(ewwwww!)by bombarding them with digestive enzymes.They also release chemicals that moderate allergic reactions.

Lymphocytes-30%

These agranular leukocytes are found in the spleen, tonsils, lymph nodes, and thymus gland, in addition to the blood stream. B lymphocytes create plasma cells that produce antibodies, and T lymphocytes target specific threats such as cancer, bacteria and viruses.

Monocytes-5%

The largest of the WBCs, these agranular leukocytes make their way out of the bloodstream and live in various tissues. Depending on where they end up, they become various macrophages that engulf nonself cells and cell debris. They increase with the presence of chronic infections.

Neutrophils-60% Most Common

Neutrophils are the first on the scene of an infection, and their numbers increase drastically during acute bacterial infections. These granular leukocytes surround and engulf the bad guys, especially bacteria and a few fungi.

 

Part 2: Lymphatic System

 

Tonsil

 

The lymphatic system is a sister system to the cardiovascular system. Interstitial fluid is gathered up in lymph vessels which are processed through leukocyte-containing lymph nodes. Once the lymph is "cleansed", it continues along into the right lymphatic duct or the thoracic duct, where it meets up with the subclavian veins and is returned to the bloodstream. The flow of lymph is very similar to the flow of returning blood through the veins, with muscular contraction helping the process along. In addition, the spleen removes old and dead red blood cells from the circulatory system, and stores the cleanse blood so that the body can call on it in times of need. The lymphatic system also carries the fats and fat-soluble vitamins absorbed from the digestive tract into the circulatory system for distribution to cells. 

 

Part 3: Nonspecific Body Defenses

Skin-The Integumentary System defends the body from invasion by forming a tough outer barrier that is difficult for microorganisms to breach. The dead, outer-most cells of skin are formed of keratin, and is a difficult membrane to breach. Our skin is constantly being sloughed off, which also sloughs off any pathogens that have been living on the skin. Our skin also maintains an acidic pH which is difficult for pathogens to exist in.

Cilia- Cilia arise from epithilial tissue and exist in our airways where their constant upward motion helps to sweep mucus (and therefore trapped pathogens) into the throat where we expel it, or it is swallowed and eliminated through the digestive system.  

Phagocytosis

 1) Phagocyte captures bacterium.

2) Phagocyte surrounds bacterium with plasma membrane.

3) Bacterium is closed off inside a vesicle.

4) Lysosomes, containing powerful enzymes, fuse with bacterium's vesicle.

5) Lysosome enzymes digest and destroy bacterium.

6) The waste products are expelled from the phagocyte.

Phagocytic Cells-Neutrophil & Macrophage

Inflammatory Response

All tissue injuries trigger inflammation, characterized by redness, warmth, swelling, and pain. Damaged cells release chemicals that stimulate mast cells (connective tissue cells) to release histamine (basophils secrete histamine as well). Histamine causes nearby capillaries to dilate, giving enough space to allow phagocytes to get through to attack foreign cells and destroy damaged cells. Some phagocytes return to the lymph system and stimulate lymphocytes, beginning the specific defense system response. Complement proteins also leak into the area and help by marking pathogens for destruction or destroying them personally (see below). Vasodilation allows blood to seep into the area, which makes it red and also warm-these warmer temperatures heighten phagocyte activity. Swelling is caused by fluids leaking through capillaries, which dilute pathogens and toxins and brings in clotting proteins that create a fibrin mesh that walls off the damaged tissue. It also carries extra oxygen and nutrients for healing, and washes away dead cells, pathogens and debris.Swelling presses on nerve endings. This combined with sensitizing chemicals from inflammation, creates pain, and slows us down to heal.

 

Complement Proteins Killing Bacterium

 There are at least twenty plasma proteins that assist in defense of the body. When they are activated, they seep through the capillaries and create a cascade effect, activating more and more proteins. Some join together to form large protein complexes that pierce holes in the cell walls of bacteria. This allows water and salts to seep in, exploding the cell.

 

Part 4:Specific Body Defenses

The major histocompatibility complex is a set of proteins that are on the surface of our cells. Our MHC proteins are unique to us, and are used as a kind of fingerprint whereby our immune cells can recognize "self" cells.

Antibody Structure

 

 There are five classes of antibodies-IgG, IgM, IgA, IgD, IgE.

Clonal Expansion

 When an antigen-presenting cell activates a T cell, the T cell clones itself with the identical receptors. Some of these clones become memory cells for the next time around. The rest continue to clone and then attack the target cell.

Interferon is secreted by virally infected cells and diffuses to healthy cells. It binds to their cell membranes and causes them to produce proteins that interfere with viral protein synthesis, making it harder for the virus to infect the healthy cells.

 

Cell mediated and antibody mediated immune responses are brought about by lymphocytes. B cells are in charge of antibody-mediated immunity. They produce antibodies that bind with specific antigens and neutralize them. This works best against viruses, bacteria, and foreign molecules that are blood and lymph soluble, as that is where antibodies circulate. T cells are in charge of cell-mediated immunity, where T cells directly attack foreign cells or help with other immune responses by releasing proteins that coordinate T cells, B cells, and macrophages. This works best with parasites, fungi, bacteria, cancer, and foreign cells. 

 

Active and Passive Immunization are both ways medical science helps us to stay well. Active immunization is done with vaccines created from dead, weakened, or synthesized pathogens. They create a primary immune response in the body, which confers long-term immunity through the creation of memory cells. It must be done before the disease is actually contracted. An example is the diphtheria vaccine. Passive immunization can be used once an infection has already occurred and it uses antibodies from a human or animal that already has immunity. it confers short-term immunity as no primary immune response occurs in the body. It can also occur naturally through the placenta or breastfeeding. An example is the tetanus shot.