Chapter 21 - Lymphatic & Immune System Flashcards
Lymphatic System
Structural basis of immune system, houses phagocytes and lymphocytes. Returns fluid that leaked from blood vessels back to blood. Includes: Tonsils, Thymus, Spleen, Aggregated Lymphoid, Appendix
3 Parts of Lymphatic System
- Network of Lymphatic Vessels
- Lymph - fluid in vessels
- Lymph nodes - cleanse lymph, checkpoints
Differences between lymphatic vessels and capillaries
- Permeable (proteins, debris, pathogens)
- Endothelia cells have one way mini valves (flaps)
- Increased extracellular fluid volume opens mini valves
Where are lymphatic vessels absent in body?
Bones, teeth, bone marrow, central nervous system
Lacteals
Specialized lymph capillaries in intestinal mucosa that absorbs digested fat and deliver fatty lymph to the blood.
Lymph delivered into blood stream via 2 large ducts
Thoracic duct - Left subclavian Vein and left internal jugular vein ( Rest of body)
Right Lymphatic Duct - Right Subclavian Vein (Right head and arm)
Lymphatic Collecting vessels are similar to veins except for:
Thinner walls, more intestinal valves, anastomose more frequently, nutrients supplied from vaso vasorum
What is Lymph Propelled By?
Milking action of skeletal muscle Pressure changes in thorax during breathing Valves to prevent backflow Pulsations of nearby arteries Contraction of smooth muscle in walls.
Lymphocytes
Main warrior of immune system that arise in red marrow, mature into 1 of 2 main varieties, T-Cell (thymus) or B-Cell (marrow)
Macrophage
Phagocyte foreign substances, help activate T-cells
Dendritic cells
capture antigens and deliver them to lymph nodes
Reticular cells
produce reticular fiber stroma; supports cells in lymphoid organs
Functions of Lymphoid Tissue
Houses and provides proliferation site for lymphocytes
Survellance vantage point for lymphocyte and macrophage
composed mainly of reticular connective tissue
Where are lymph nodes found
Principal lymphoid organs, embedded in CT, in clusters along lymphatic vessles, nearby surfaces in inguinal, axillary and cervical areas.
Functions of lymph nodes
Filter lymph: macrophages destroy microorganisms and debris
Immune system activation: lymphocytes activated and mount attack on antigens
Circulation of lymph
Lymph enters via afferent lymphatic vessels; to subcapsular sinus and smaller sinuses to medullary sinuses; exits at hilum via efferent vessels
Chyle
Fatty Lymph
Lymphoid follicles
solid, spherical bodies of tightly packed lymphoid cells and reticular fibers
• Germinal centers of proliferating B cells
• Isolated aggregations of Peyer’s patches and in appendix
Spleen
Largest lymphoid organ
Site of lymphocyte proliferation and immune surveillance and response
Cleanses blood of aged cells and platelets, macrophages remove debris
FUNCTIONS:
Stores breakdown products of RBCs
Stores blood platelets and monocytes
May be site of fetal erythrocyte production
Contains lymphocytes, macrophages, and huge numbers of erythrocytes
White pulp
around central arteries**
Mostly lymphocytes on reticular fibers
Red pulp
in venous sinuses and splenic cords
Rich in RBCs and macrophages
Thymus
increases in size, most active during childhood but stops growing during adolescence, then atrophies
-Slowly produces immunocompetent cells
Most thymic cells are lymphocytes
Cortex contains rapidly dividing lymphocytes and macrophages
Medulla contains fewer lymphocytes and thymic corpuscles (regulatory T cell dev.)
Thymus differs from other lymphoid organs:
-Has no follicles because it lacks B cells
-Functions strictly in T cell maturation
Stroma of epithelial cells provide place where T cells become immunocompetent
Mucosa-associated Lymphoid Tissue (MALT):
In mucous membranes
-Protects from pathogens entering body
Tonsils, Peyer’s patches, Appendix
Mucosa of respiratory, genitourinary organs; rest of digestive tract
Tonsils
Simplest lymphoid organs
Ring of lymphatic tissue around pharynx
Gather and remove pathogens in food or air
tonsillar crypts
Epithelium indents
Trap and destroy bacteria,particulate matter
Immune cells build memory for pathogens
Peyer’s patches
Clusters of lymphoid follicles in wall of small intestine
• Destroy bacteria, preventing them from breaching intestinal wall
• Generate “memory” lymphocytes
Innate Defense
Surface Barriers - Mucous Membranes and Skin. Internal defenses • Phagocytes • Natural killer cells • Inflammation • Antimicrobial proteins • Fever
Adaptive Defense
- Specific: recognizes specific antigens
- Systemic: not restricted to initial site
- Memory: stronger attacks to “known” antigens
Two separate, overlapping arms
Humoral (antibody-mediated) immunity
Cellular (cell-mediated) immunity
Humoral Immunity
B-Cells
Cellular Immunity
T-Cells
Skin
Physical barrier to microorganisms
Keratin resistant to weak acids and bases, bacterial enzymes, and toxins
Acidity of skin and secretions – acid mantle – inhibits growth
Enzymes - lysozyme of saliva, respiratory mucus, lacrimal fluid kill microorganisms
Defensins – antimicrobial peptides
Other- lipids (sebum), dermcidin (sweat)
Respiratory system modifications
Mucus-coated hairs in nose
Cilia of upper respiratory tract sweep dust/bacteria-laden mucus toward mouth
Internal Defenses: If deeper tissues invaded
Phagocytes
Natural killer (NK) cells
Interferons and complement proteins
Inflammatory response