Anatomy and Physiology 2 Chapter 22 - Lymphatic System

lymphatic system

returns fluids that leaked from blood vessels back to blood; acts as a storm drain

what are 3 parts of the lymphatic system

1. lymphatic vessels (lymphatics): return interstitial fluid and leaked plasma proteins back to blood; one-way system and lymph flows toward heart

2. lymphatic capillaries: similar to blood capillaries, but are very permeable (endothelial cells overlap loosely to form one-way minivalves), pathogens travel throughout body, and absent from bone, teeth, bone marrow, and CNS; want fluid to leak in, but not out

3. major-lymph-collected vessels: similar to veins, but have thinner walls, more internal valves; travel with superficial veins/arteries and empties lymph into venous circulation

   1. thoracic duct: collects lymph from almost all of the body except for the superior right side

   2. right lymphatic duct: collects lymph from right side of the body superior to the diaphragm

lymph

interstitial fluid that enters lymphatic vessels (lymphatics)

lymphedema

obstruction of the lymphatic vessels that causes swelling; toxins and pathogens can accumulate, overwhelming local defenses

5 ways lymph is transported

1. milking action of skeletal muscle

2. pressure changes in thorax during breathing

3. valves to prevent backflow

4. pulsations of nearby arteries

5. contractions of smooth muscle in walls of lymphocytes

*first 2 similar to the venous return mechanisms of muscular and respiratory pump

what are the 4 types of lymphatic cells

1. lymphocytes: main warriors of immune system; arise in bone marrow and mature into B or T cells; B cells = attack invaders outside the cell; T cells = attack infected cells

2. macrophages: phagocytize foreign substances; help activate T cells

3. reticular cells: produce reticular fiber stroma (protein fiber) that supports other lymphoid cells; builds extracellular matrix

4. dendritic cells: capture antigens and deliver them to lymph nodes; activate T cells

lymphoid tissue

houses and provides proliferation site for lymphocytes, surveillance vantage point for lymphocytes and macrophages, and largely reticular connective tissue; have large collections in mucous membranes

3 types of lymphoid tissue

1. MALT: located in mucous membranes throughout the body and protects from pathogen entry; the largest sites are tonsils, Peyer’s patches, and appendix

2. lymphoid nodule: lymphocytes densely packed in an area of areolar tissue such as tonsils

3. tonsils: simplest lymphoid organs; forms a ring of lymphatic tissue around pharynx, gather and remove pathogens from air or food; overlying epithelium invaginates forming tonsillar crypts to trap and destroy bacteria and allow immune cells to build memory

lymphoid follicles

tightly packed lymphoid cells and reticular fibers

1. germinal centers of proliferating B cells

2. may form part of larger lymphoid organs

3. isolated aggregations of Peyer’s patches and in appendix

Peyer’s patches

cluster of lymphoid follicles, in wall of distal protion of small intestine; destroy bacteria, preventing wall breach, and generate memory lymphocytes

4 types of tonsils

1. palatine: at posterior end of oral cavity

2. lingual: grouped at base of tongue

3. pharyngeal: in posterior wall of nasopharynx (nose to pharynx)

4. tubal: surrounding openings of auditory tubes into pharynx

lymph nodes

embedded in connective tissue in clusters along lymphatic vessels and cleans lymph

5 structures of lymph nodes

1. trabeculae: divide node into compartments and are bundles of collagen

2. hilum: composed of blood vessels and nerves

3. afferent lymphatics: bring lymph to the lymph node from peripheral tissue

4. efferent lymphatics: carry lymph away from lymph node toward venous circulation

5. cortex: lymph passes here and contains B cells within germinal centers

2 functions of lymph nodes

1. filter lymph: macrophages destroy microbes and debris

2. immune system activation: lymphocytes activated and mount attack against antigens

thymus

found in inferior neck, extends into mediastinum and partially overlies heart; important functions early in life (when we are more susceptible to infections) and is the site of T lymphocyte maturation (blood thymus barrier)

spleen and its 3 functions

largest lymphoid artery and is served by splenic artery and vein, enter and exit at hilum; contains the red and white pulp; the following functions are:

1. site of lymphocyte proliferation and immune surveillance and response

2. cleanses blood of aged cells and platelets, macrophages remove debris

3. Fe storage from RBC breakdown

red vs. white pulp of the spleen

• red pulp: in venous sinuses and splenic cords; rich in RBCs and macrophages for disposal of worn-out RBCs and bloodborne pathogens

• white pulp: around central arteries; mostly lymphocytes of reticular fibers, involved in immune functions

2 types of immunity

1. innate immunity: non-specific defense mechanisms; generalized against all foreign invaders and has 2 lines of defense

2. adapative immunity: specific defense mechanisms; immune memory, antibodies, etc.; change throughout our lives

4 things involved in our immune system

1. physical barriers: keep hazardous organisms and materials outside the body; includes sweat glands, hair, secretions, and skin

2. phagocytes: engulf pathogens and debris; includes fixed and free macrophages; includes neutrophils, basophils, and eosinophils

3. immune surveillance: abnormal cell destruction by NK cells

4. interferons: chemical messengers that coordinate defense against viral infections

what are 2 mechanisms of the first line of defense

1. physical barriers: prevent microbes from penetrating deeper tissues; includes skin, tears, saliva, mucous, residential microbes, chemical barriers

2. chemical barriers: oil gland secretions (antimicrobials), lysozymes (in saliva, tears, and sweat), and acidic environments (stomach, skin, and vagina)

what are the 6 mechanisms of internal defenses (2nd line of defense)

1. complement system

2. interferons

3. phagocytes

4. immune surveillance of NK cells

5. inflammation

6. fever

complement system

antimicrobial proteins; plasma proteins that poke holes in bacterial membranes and mark cells for phagocytosis

interferons

proteins produced by virally infected cells to “warn” neighboring cells; stimulates macrophages and NK cells; act as paracrines

phagocytes and list the 5

granulocytes and agranulocytes; utilizes toll-like receptors (TLRs)

this includes:

1. neutrophils: engulf and destroy microbes

2. lymphocytes: part of adaptive immune response

3. monocytes: phagocyte and become wandering macrophage in tissue; release chemicals that stimulate neutrophils and other monocytes

4. eosinophils: fight large parasites; involved in allergic response

5. basophils: initiate inflammatory response by histamine

toll-like receptors (TLRs)

pathogens are recognized by this on the surface of WBCs and bind to pathogen components; helps macrophages engulf pathogens and digest them intracellularly

4 steps of immune surveillance of NK cells

1. NK cells recognize via TLRs and adheres to abnormal cell

2. golgi apparatus of NK cells aligns with abnormal cell

3. perforin is secreted into abnormal cell; perforin complexes created to help rupture cell

4. lysis of abnormal cell

*used to help target ghost cells (lost identifying receptor) that can’t be targeted anymore by other WBCs

inflammation

caused by release of inflammatory chemicals from innate immune system

• histamines: cause capillary dilation to increase blood flow; causes swelling, redness, warmth; flushes tissue with fluids allow WBCs to easily move from blood to tissue

• cytokines: call more WBCs; cause fatigue, fever, and increase strength of inflammatory response

fever and 4 benefits of moderate fevers

systemic inflammation triggered by pyrogens (type of cytokine), high fevers can denature enzymes, moderate fevers are beneficial because of the following:

1. inhibits growth of certain microbes

2. enhances effects of interferons

3. speeds up tissue repair

4. enhances phagocytosis and adaptive immunity