Chapter 22 - Lymphatic System & Immunity

Created by jcaigne 

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Pathogen

a disease producing microbe.

Lymphatic System

Consist of a fluid called lymph, lymphatic vessels, structures and organs containing lymphatic tissue, and red bone marrow. Contributes to homeostasis by draining interstitial fluid and providing defense against disease / pathogens. Is a housing for the immune system and also returns fluids back into the blood.

Lymph

Interstitial fluid that enters a lymphatic vessel.

Lymphatic Tissue

Reticular connective tissue containing large numbers of lymphocytes.

Lymphatic System Functions (3)

1) Drains excess interstitial fluid - lymphatic vessels return 3 Liters of fluid back to the blood stream per day.

2) Transports dietary lipids - lipids have a difficult time going through the blood stream so they're transported through the lymphatic system. The presence of these lipids give lymph tissue a white color (milky).

3) Carries out immune responses - fight against pathogens and abnormal cells / cancer cells.

Lymphatic Vessels and Circulation

The vessels begin in the capillary network and are located in the spaces between tissue cells. Lymphatic capillaries have a unique one-way structure that allows interstitial fluid in but not out. When interstitial fluid pressure is greater than lymph pressure, lymph will enter the vessel. It will stay in the vessel until it gets to our subclavian veins. Lymph nodes are located along lymph vessels containing B and T cells.

Lymph Trunks and Ducts

Lumbar, Interstitial, Bronchomediastinal, Subclavian and Jugular trunks. Lumbar trunks drain lymph from the lower limbs and pelvis. Interstitial trunks drain lymph from stomach, intestines and liver. Bronchomediastinal trunk drains lymph from lungs and heart. Subclavian drains from upper arms. Jugular trunks drains from head and neck.

Thoracic Duct

The main duct for return of lymph to the blood. It returns the fluid at the junction of the left internal jugular and left subclavian vein.

Right Lymphatic Duct

Returns lymph from the right arm, head and ... into junction of right jugular vein and right subclavian vein.

Formation and Flow of Lymph

Most blood plasma that filters into the interstitial fluid returns in our veins. The remaining 3 Liters of plasma, not returned in our veins, are returned by the lymphatic system. Plasma proteins (albumin, fibrinogen, globulin) once they leave the blood stream can't get back in due to their size - they must be returned back to the blood stream via the lymphatic system. The respiratory pump and skeletal muscle pump also moves lymph back to the heart.

Primary Lymphatic Organs

Sites where stem cells divide and are capable of causing an immune response. Red bone marrow and thymus glands are the two primary organs. Pluipotent stem cells in the bone marrow make B cells and T cells. Thymus gland matures T cells from the bone marrow, once matured, they will be released back into the blood. The thymus reduces in size with age.

Secondary Lymphatic Organs

Sites where most of our immune responses occur, e.g. lymph nodes, spleen and lymph nodules.

Thymus

Located above the heart and contains large numbers of T cells. It functions to mature T cells. The mature T cells are sent out of the thymus to populate our lymph nodes and spleen.

Lymph Nodes

About 600 in the body, large numbers in axilla, groin and breasts. It's a house for mature T cells and the site of memory B cell formation. They're located along the vessels. It functions as a type of filter, traps and destroys foreign material.

Spleen

Largest of secondary lymphatic tissues, it has 2 types of tissues, white pulp (lymphatic tissue consisting of lymphocytes and macrophages), and red pulp (filled with blood and consists of RBCs, macrophages and lymphocytes).

Red Pulp (3 Functions)

1) F1 - removal of worn out RBC's and platelets
2) F2 - storage of platelets
3) F3 - production of our blood cells during fetal life

Lymphatic Nodules

Does not contain a capsule like a node. They're found scattered throughout mucous membranes of GI tract, respiratory tract, reproductive tract and urinary tract. Tonsils are lymphatic nodules and malt (mucosa associated lymphatic tissue) found throughout GI tract.

Innate Immunity

Protective barriers to disease that one is born with, this includes the external physical and chemical barriers provided by the skin and mucous membrane. These prevent antigens from entering the body.

First Line of Innate Immunity

First line of defense against pathogens, includes skin and mucus membranes.

Skin - multiple layers of stratified squamous epithelium keep foreign objects from entering the blood stream and other underlying tissues.
Mucous membranes - lines our bodies cavities and secretes mucus which traps foreign objects and is then removed by the body.
Nose Hairs - help prevent particles from entering
Cilia - along respiratory tract that pushes mucus out
Digestive tract - gastric acid in the stomach provides a harsh environment that many microbes can't withstand

Second Line of Innate Immunity (4)

These are internal defenses of the body after the pathogen penetrates the skin and mucus membrane. There are 4 antimicrobial substances that help prevent further replication of the infection:

1) Interferons - proteins released by virus infected cells that induce neighboring cells to produce anti-viral proteins. These prevent the virus from replicating.
2) Complement system - proteins in blood plasma that enhance immune reactions by causing cytolysis. They bind to the foreign cells and cause it to burst.
3) Iron-binding system - proteins that bind to iron so that bacteria can't bind to iron; bacteria need iron to function and replicate.
4) Antimicrobial proteins - AMP's, have a wide range of antimicrobial activity. These AMP's are substance that microbes can't become resistant to.

Natural Killer Cells

Type of lymphocyte that releases toxic granules in target cells causing the cell to be destroyed, it can kill a wide variety of body cells. They can also destroy cancerous cells.

Phagocytes (2 types)

Cells that ingest microbes, cellular debris and affected cells. Two types:
1) Neutrophils
2) Macrophages

Inflammation

A defense response to damaged tissue, which can be caused by: physical injury, chemical irritation or a pathogen. Signs / symptoms include: redness, pain, swelling and heat. It swells to isolate the affected area and keep lymphocytes in the site of injury / infection.

Fever

Abnormally high body temperature. Works to:
1) Intensify the effects of interferon
2) Speed up body reactions of metabolism

Adaptive Immunity

The ability of the body to defend itself against bacteria, viruses and foreign tissue. It's a process where each new infection creates a new memory cell that is specific to that infection to recognize that same infection in the future.

Antigen

A substance (e.g. virus, bacteria, foreign tissues, etc.) that is recognized as foreign and provokes an immune response. Adaptive immunity can differentiate between self and none-self. It also has memory, the second encounter with the antigen will prompt a quicker more vigorous response.

Immune System

Any cell and tissue that carries out an immune response.

T-Cells

Made in the red bone marrow but mature in the thymus gland. Most T-Cells are already made and given to the thymus by puberty. Once matured, they get stored in secondary tissues.

B-Cells

Made in the red bone marrow and mature in the bone marrow. These are produced all throughout life. Also get stored in secondary tissues.

Immunocompetence

The ability to carry out an immune response. B and T cells develop proteins in their plasma membrane that function to recognize specific antigens. These are developed over time through exposures to specific antigens.

Types of Adaptive Immunity (2)

1) Cell mediated immunity - involves cytotoxic T cells directly attacking the invading antigen.

2) Antibody mediated immunity - involves B cells transforming into plasma cells and making protein antibodies. Helper T cells aid in both cell mediated immunity and antibody mediated immunity. Works with extracellular pathogens in the body fluids outside the body cells (lymph or blood).
· Effective against intracellular pathogens, they're inside the cells
· Effective against cancer cells
· Effective against foreign tissue transplants

Clonal Selection

The process in which copies of cells are made. Lymphocytes can differentiate and divide.

Effector Cells

Cells that die once the infection is destroyed, they do the actual destruction.

Memory Cells

Cloned cells that initiate a swifter reaction than the first encounter.

Antigens / Antigen Receptors

Antibody generators (what an antigen is). When the body destroys an antigen for the first time, it takes a fragment of it and places it in its plasma membrane so it can recognize any secondary infections.

Immunogenicity

The ability to provoke an immune response by stimulating the production of antibodies and T-cells.

Reactivity

The ability of the antigen to react with the antibody or cells it provokes.

Epitopes

The fragments that are in the plasma membrane that's used to recognize the foreign invaders - the parts of an antigen that trigger an immune response. Most antigens have multiple epitopes. The human immune system can recognize a billion different epitopes.

Major Histocompatibility Complex

"Self" antigens that functions to help T cells recognize an antigen as foreign and not "self" via Antigen Presenting Cells (APC).

Cell Mediated Immunity

The response begins by the activation of T cells by the antigen. Once the T cell is activated it under goes clonal selection. The cloned cells carry out the immune response and eliminate the intruder.

T-Cell Receptors

Recognize and bind to the foreign antigen

Helper T-Cells

Stimulate the immune response by stimulating memory T cells and cytotoxic T cells.

Cytotoxic T-Cells

Cells that destroy the invading antigen (an effector cell)

Memory T-Cells

Cells that memorize the antigen for the next encounter

Elimination of Invaders (2 mechanisms)

1) T cell binding to the infected cell that has the anitgen present. It releases granzymes (protein digesting enzymes) that trigger apoptosis. Macrophages then eat the particles of the now dead cell, including the infective agents.

2) T cell binding to the infected cell and releases perforin which creates holes in the infected cell causing it to burst. Granulysin is also released and enters the microbe and destroys the microbe itself.

Antibody mediated Immunity

Involves B cells. In the presence of a foreign antigen, B cells in lymph nodes, spleen or tonsils become activated. Activiated B cells differentiate into plama cells. Plasma cells secrete antibodies. Antibodies leave the secondary lymphatic tissue and travel to the site of the antigen, can be in the blood. Memory B cells memorize that specific antigen. B cells secrete one antibody for one antigen. (B cells don't leave the lymph tissue)

Antibodies

IgM is high and is the first response to the antigen. IgG, if high, means it's present in higher amounts during the second time you're exposed. If IgM is high you know it's the first time you've been exposed to this particular antigen.

Actions of Antibodies (4)

1) Neutralization - antibodies can neutralize an antigen by binding to the active regions of the pathogen masking them and essentially disarming them

2) Complement Fixation - antibodies IgM and IgG bind to an antigen changing their shape and exposing their complement binding sites. This initiates inflammation, phagocytosis, immune clearance and cytolysis - this is the primary mechanism of defense against foreign cells

3) Agglutination - multiple antibodies can bind to an antigen and cause them to stick together. This immobilizes microbes / antigen molecules preventing them from spreading throughout the tissues

4) Precipitation - similar to agglutination but instead binds only to antigen molecules causing them to stick together which when large enough pulls them out of solution and allows the immune system to clear them out

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