Fundamentals of Anatomy & Physiology Chapter 22: The Lymphatic System and Immunity
Antibody-Mediated Immunity
- A chain of events that destroys the target compound or organism
Lymph Node Function
- A filter that purifies lymph before return to venous circulation - Removes debris, pathogens, and 99% of antigens - Swell in response to inflammation
Lymph
- A fluid similar to plasma but does not have plasma proteins
Fever
- A maintained high body temperature above 37 degrees C or 99 degrees F - Increases body metabolism - Accelerates defenses - Inhibits some viruses and bacteria - AKA pyrogen, which means origin of fever/heat/fire
Protectin
- A protein released by NK cells that will protect itself from being perforated by its own perforins
Movement & Phagocytosis
- All macrophages move through capillary walls (emigration) and are attracted or repelled by chemicals in surrounding fluids (chemotaxis) - Chemotaxic agents can attract cells to leave where they are and they come to them, using amoeboid movement - Phagocytosis begins when phagocyte attaches to target (adhesion) and surrounds it with a vesicle
Fixed Macrophages
- Also called histiocytes - Stay in specific tissues or organs such as dermis or bone marrow
Free Macrophages
- Also called wandering macrophages - Travel through body - Alveolar macrophages: special free macrophages
Natural Killer (NK) Cells
- Also referred to as surveillance cells or large granular lymphocytes - 5-10% of circulating lymphocytes - Attack foreign cells, virus-infected cells, and cancer cells
Innate (Nonspecific) Defenses
- Always work the same way - Against any type of invading agent - Nonspecific resistance
Immunoglobins
- Antibodies - The binding of a specific antibody to its specific target antigen initiates antibody-mediated immunity
Naturally Acquired Passive Immunity
- Antibodies acquired from the mother - Example: Transferred through breastfeeding or the placenta
Pyrogens
- Any material that causes the hypothalamus to raise body temperature - Such as pathogens, toxins, or antibody complexes
Cancer Cells with Tumor-Specific Antigens
- Are identified as abnormal by NK cells - Some cancer cells avoid NK cells (immunological escape)
Lymphatic Vessel
- Are vessels that carry lymph - Exist alongside veins and arteries - Appear a goldish color - Lymphatic system begins with smallest vessels *Lymphatic capillaries (terminal lymphatics)
Lymphoid Nodules
- Areolar tissue with densely packed lymphocytes - Germinal center contains dividing lymphocytes
Phagocytes
- Attack and remove dangerous microorganisms - 2 classes: microphages and macrophages - Literally means "eating cell"
Helper T Cells
- Attacked by HIV - Stimulate function of T and B cells - Do not want to lose these - Discovered because of HIV
Benefits of Interferon
- Attract NK cells to sites of infection and they make cells more resistant to a virus, slowing the spread of a virus by making the cell impermeable to the virus, which is often used for the treatment of cancer - If you can make the cell more resistant to being attacked by a virus then it could make the cell prone to becoming cancerous
Nonspecific Defenses
- Block or attack any potential infectious organism - Cannot distinguish one attack from another - Examples: Skin, nails, hair, etc. - Nonspecific WBCs such as neutrophils, eosinophils, basophils, monocytes
Lymphedema
- Blockage of lymph drainage from a limb - Causes severe swelling - Very dangerous as it interferes with immune system function
Body Defenses in the Lymphatic System
- Body defenses provide resistance to fight infection, illness, and disease 1 Innate (nonspecific) defenses 2 Adaptive (specific) defenses
Drainage of the Left Thoracic Duct
- Bottom and top left portion of the body
Trabecular Arteries
- Branch and radiate toward capsule - Finer branches surrounded by white pulp - Capillaries discharge red blood cells into red pulp
Trabeculae
- Bundles of collagen fibers - Extend from capsule into interior of lymph node
Artificially Induced Passive Immunity
- By an injection of antibodies - Example: Anti-venom in response to a snake bite
Afferent Lymphatics
- Carry lymph from peripheral tissues to lymph node - Afferent = toward
Lymphatic Vessels (Lymphatics)
- Carry lymph from peripheral tissues to the venous system
Opsonization
- Cells become really sticky, with bacteria it makes it easier for a neutrophil or killer T to surround and engulf it
Viral Infections
- Cells infected with viruses - Present abnormal proteins on plasma membranes - Allow NK cells to identify and destroy them
Cytokines
- Chemical messengers released by tissue cells to coordinate local activities and to act as hormones to affect whole body
Interferons
- Chemical messengers that trigger production of antiviral proteins in normal cells - Proteins (cytokines) released by activated lymphocytes and macrophages - Antiviral proteins do not kill viruses but block replication in cell
Lymphadenopathy
- Chronic or excessive enlargement of lymph nodes may indicate infections, endocrine disorders, or cancer
Complement Activation
- Complement work together in cascades - Two pathways activate the complement system 1 Classical pathway 2 Alternative pathway - Both pathways end with conversion of inactive complement protein C3 to activate form C3b
Lymphoid Tissues
- Connective tissues dominated by lymphocytes
Spleen
- Considered a blood reservoir - Involved in lymphatic and circulatory system
Immunological Surveillance
- Constantly monitors normal tissues with natural killer (NK) cells - Is carried out by NK cells - Activated NK cells: 1 Identify and attach to abnormal cell (nonselective) 2 Golgi apparatus in NK cell forms perforin vesicles 3 Vesicles release proteins called perforins (exocytosis) 4 Perforins lyse abnormal plasma membrane and also attack cancer cells and cells infected with viruses
Thymic Lobule
- Contains a dense outer cortex and a pale central medulla
Red Pulp
- Contains many red blood cells & elements of circulating blood plus fixed and free macrophages - Many lymphocytes
Lymphatic Capillaries
- Differ from blood capillaries in four ways 1 Start as pockets rather than tubes 2 Have larger diameters 3 Have thinner walls, which allow things outside to get inside 4 Flat or irregular outline in sectional view - Lymphatic capillaries start and end blindly - Endothelial cells loosely bound together with overlap, which allows things to get in but doesn't let it back out
The Classical Pathway
- Fast method C1 binds to antibody molecule attached to antigen (bacterium) - Bound protein acts as enzyme which catalyzes chain reaction - Antibodies attracted to specific antigens and attracts complement
Antigen Presentation
- First step in immune response - Extracted antigens are "presented" to lymphocytes or attached to dendritic cells to stimulate lymphocytes
2 Types of Macrophages
- Fixed macrophages - Free macrophages
Reticular Epithelial Cells in the Medulla
- Form concentric layers known as thymus (Hassall's) corpuscles - The medulla has no blood-thymus barrier so T cells can enter or leave bloodstream
Elephantiasis
- Form of lymphedema which is caused by Wucheria Bancroft, a type of nematode, that is transmitted by a mosquito - Treatable, but most common in areas of the world where medicine is scarce
The Circulation of Fluids
- From blood plasma to lymph and back to the venous system - Transports hormones, nutrients, and waste products
Lymphocyte Circulation
- From blood to interstitial fluid through capillaries - Returns to venous blood through lymphatic vessels
Hemocytoblasts
- In bone marrow, divides into two types of lymphoid stem cells
Forms of Immunity
- Innate, present at birth - Adaptive, after birth - Active, antibodies develop after exposure to antigen - Passive, antibodies are transferred from another source
Physical Barriers
- Keep hazardous material outside the body - Examples: Skin, hair, secretions that flush away materials or kill/inhibit microorganisms
Macrophages
- Large phagocytic cells derived from monocytes - Distributed throughout body - Make up monocyte-macrophage system (reticuloendothelial system) - Can be fixed or wandering - Can surround and engulf antigens
Efferent Lymphatics
- Leave lymph node at hilum - Carry lymph to venous circulation - Efferent = away
Inflammatory Response
- Localized, tissue-level response that tends to limit spread of injury or infection - Inflammation - Triggered by any stimulus that kills cells or injures tissue
Thymus
- Located in mediastinum - Atrophies after puberty which diminishes effectiveness of immune system - Where T cells mature - Two thymus lobes and septa divides lobes into smaller lobules
Lymphopoiesis
- Lymphocyte production - Involves bone marrow, thymus, and peripheral lymphoid tissues
Lymphocyte Production & Distribution
- Lymphocytes are produced in lymphoid tissues (e.g., tonsils), lymphoid organs (e.g., spleen, thymus) and in red bone marrow -Lymphocyte distribution detects problems and travels into site of injury or infection
Location of Lymph Nodes
- Majority are located at points of attachment to the trunk, such as shoulders, neck, hips, breasts, etc.
B Cells
- Mature in bone marrow - 10-15% of circulating lymphocytes - Change into plasma cells, which produce and secrete antibodies (immunoglobin proteins) - Provide antibody-mediated immunity - Defend against antigens and pathogens in body fluids - Responsible for antibody-mediated immunity - Attack antigens by producing specific antibodies - Millions of populations, each with different antibody molecules - Can form plasma cells that form platelets
T Cells
- Mature in the thymus - 80% of circulating lymphocytes - Main types: * Cytotoxic T cells * Memory T cells * Helper T cells * Suppressor T cells - Provide cell-mediated immunity - Defend against abnormal cells and pathogens inside cells - Responsible for cell-mediated immunity
Special Histiocytes
- Microglia: found in central nervous system - Kupffer cells: found in liver sinusoids
Pathogens
- Microscopic organisms that cause disease - Organisms such as viruses, bacteria, fungi, or parasites - "Patho-" = disease - "-gen/genesis" =origin of
Group 2 Lymphoid Stem Cells
- Migrates to thymus, but one they mature they may return back to bone marrow - Produces T cells in environment isolated by blood-thymus barrier
Products of Inflammation
- Necrosis, local tissue destruction in area of injury - Pus, a mixture of debris and necrotic tissue - Abscess, pus accumulated in an enclosed space
Microphages
- Neutrophils and eosinophils - Leave the blood stream - Enter peripheral tissues to fight infections
Cytotoxic T Cells
- Often called killer Ts - Surround and engulf cells infected by viruses - Attack cells infected by viruses - Responsible for cell-mediated immunity - Seek out and immediately destroy target cells 1 Releasee perforin to destroy antigenic plasma membrane 2 Secrete poisonous lymphotoxin to destroy target cell 3 Activate genes in target cell that cause cell to die
Spleen Function
- Phagocytes and other lymphocytes in spleen identify and attack damaged and infected cells in circulating blood
Effects of Complement Activation
- Pore formation - Destruction of target plasma membranes, five complement proteins join to form membrane attack complex (MAC) - Enhancement of phagocytosis by opsonization, complements working together with antibodies (opsonins) - Histamine release increases the degree of local inflammation and blood flow
Adaptive (Specific) Defenses
- Protect against specific pathogens - Depend on activities of lymphocytes - Specific resistance (immunity) develops after exposure to environmental hazards - Responds to specific antigens with coordinated action of T cells and B cells
Lymphatic System
- Protects us against disease - Responds to environmental pathogens, toxins, and abnormal body cells such as cancers
Suppressor T Cells
- Provide sensibility or homeostasis - Inhibit function of T and B cells - Tolerance, will prevent others from attacking themselves - Secrete suppression factors - Act after initial immune response - Limit immune reaction to single stimulus
Interleukins
- Released by netrophils or macrophages, raise body temperature and within reason it can increase metabolism to fight infection
Group 1 Lymphoid Stem Cells
- Remains in bone marrow and develop with help of stromal cells - Produces B cells and NK cells
Memory T Cells
- Remember infections because of antigens - Immunity - Clone more of themselves in response to "remembered" antigen - Produced with cytotoxic T cells - Stay in circulation - Immediately form cytotoxic T cells if same antigen appears again
White Pulp
- Resembles lymphoid nodules - Lots of macrophages and dendritic cells
Activated Macrophages
- Respond to pathogens in several ways 1 Engulf pathogen and destroy it with lysosomal enzymes 2 Bind to pathogen so other cells can destroy it 3 Destroy pathogen by releasing toxic chemicals into interstitial fluid
Lymphoid Organs
- Separated from surrounding tissues by a fibrous connective tissue capsule - Lymph nodes - Thymus - Spleen
Hilum
- Shallow indentation where blood vessels and nerves reach the lymph node
The Alternative Pathway
- Slow method exposed to antigen - Factor P (properdin), factor B, and factor D interact in plasma
Lymphocytes
- Specific defense - Part of the immune response - Identify, attack, and develop immunity to a specific pathogen - Most are stored and not circulating - Make up 20-30% of circulating leukocytes - Divide in the cortex - T cells migrate into medulla - Mature T cells leave thymus by medullary blood vessels
Reticular Epithelial Cells in the Cortex
- Surround lymphocytes in cortex - Maintain blood - thymus barrier - Secrete thymic hormones that stimulate stem cell divisions and T cell differentiation
Cardinal Signs & Symptoms
- Swelling (tumor) at site of infection due to plasma leaking - Redness (rubor) due to blood vessels dilating and blood at surface of skin - Heat (calor) due to the blood vessels releasing heat with dilation - Pain (dolor)
Complement
- System of circulating proteins - Assists antibodies in destruction of pathogens - Plasma contains 11 special complement (C) proteins that form complement system and complement antibody action
Antigens
- Targets that identify any pathogen or foreign compound - Literally means "against the origin" - Can produce antibodies
Immunity
- The ability to resist infection and disease - All body cells and tissues are involved in production of immunity, not just lymphatic system
Naturally Acquired Active Immunity
- Through environmental exposure to pathogens - Example: Exposure to smallpox and surviving
Artificially Induced Active Immunity
- Through vaccines containing pathogens - Example: Receiving small pox vaccine
Thymus Hormones
- Thymosin - an extract from the thymus that promotes development of lymphocytes
Function of the Lymphatic System
- To produce, maintain, and distribute lymphocytes
Drainage of Right Lymphatic Duct
- Top right portion of the body
Dendritic Cells
- Very significant - Can cause swollen lymph nodes
HIV /AIDS
- Virus - Depletion of helper T cells - Opportunistic infections such as Kaposi's sarcoma & pneumocystic pneumonia
Perforins
- When released, they will cause a perforation and will cause the cell to lyse
Antigen presenting cells
- Will present a portion of an antigen which will cause the rest of the lymphatic system to come to them
B Cells Differentiate
- With exposure to hormone called cytokine (interleukin-7)
T Cells Differentiate
- With exposure to several thymic hormones
Process of Inflammation
1 Histamines released by mast cells and/or basophils 2 Vasodilation creates pores 3 Chemotaxis 4 Macrophages, neutrophils move out of blood vessel by diapedesis 5 Move by amoeboid movement 6 Surrounding area turns red, gets hot, swelling occurs, pain 7 Complement can squeeze through pores 8 Phagocytosis by WBCs, respiratory burst occurs 9 Pus formation 10 Fibroblasts move into area to repair damage
Organization of the Lymphatic System
1 Lymph 2 Lymphatic vessels (lymphatics) 3 Lymphoid tissues and lymphoid organs 4 Lymphocytes, phagocytes, and other immune system cells
Seven Major Categories of Innate (Nonspecific) Defenses
1 Physical barriers 2 Phagocytes 3 Immunological surveillance 4 Interferons 5 Complement 6 Inflammatory response 7 Fever
Three Functions of the Spleen
1 Removal of abnormal blood cells and other blood components by phagocytosis 2 Storage of iron recycled from red blood cells 3 Initiation of immune responses by B cells and T cells in response to antigens in circulating blood
3 Effects of Inflammation
1 Temporary repair and barrier against pathogens 2 Retards spread of pathogens into surrounding areas 3 Mobilization of local and systemic defenses and facilitation of repairs (regeneration)