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)