0-1 Chapter 21 Lymphatic and immune system Flashcards
immune system
not an organ system, but a population of cells that inhabit all of our organs and defend the body from agents of disease
lymphatic system
- network of organs and vein-like vessels that recover fluid
- inspect it for disease agents
- activate immune responses
- return the fluid to the bloodstream
Lymphatic and Immune Systems
functions
maintain fluid balance
•protect body from infection and disease
Functions of Lymphatic System
fluid recovery
immunity
lipid absorption
fluid recovery
–fluid continually filters from the blood capillaries into the tissue spaces
•blood capillaries reabsorb 85%
•15% (2 –4 L/day) of the water and about half of the plasma proteins enters lymphatic system and then returned to the blood
immunity
excess filtered fluid picks up foreign cells and chemicals from the tissues
•passes through lymph nodes where immune cells stand guard against foreign matter
•activate a protective immune response
lipid absorption
lacteals in small intestine absorb dietary lipids that are not absorbed by the blood capillaries
Components of the Lymphatic System
lymph
lymphatic vessels
lymphatic tissues
lymphatic organs
lymph
–the recovered fluid
lymphatic vessels
–transport the lymph
lymphatic tissues
composed of aggregates of lymphocytes and macrophages that populate many organs in the body
lymphatic organs
–defense cells are especially concentrated in these organs
–separated from surrounding organs by connective tissue capsules
lymph
–clear, colorless fluid, similar to plasma, but much less protein
–extracellular fluid drawn into lymphatic capillaries
lymphatic capillaries
(terminal lymphatics)
–sacs of thin endothelial cells that loosely overlap each other
–closed at one end
–cells tethered to surrounding tissue by protein filaments
–endothelium creates valve-like flaps that open when interstitial fluid pressure is high, and close when it is low
Lymphatic Vessels
larger ones composed of three layers
–tunica interna:
–tunica media:
–tunica externa:
•converge into larger and larger vessels
tunica interna
endothelium and valves
tunica media
elastic fibers, smooth muscle
tunica externa
thin outer layer
Route of Lymph Flow
- lymphatic capillaries
- collecting vessels
- six lymphatic trunks:
- two collecting ducts:
- subclavian veins
two collecting ducts:
right lymphatic duct
thoracic duct
right lymphatic duct
receives lymph from right arm, right side of head and thorax; empties into right subclavian vein
thoracic duct
larger and longer, begins as a prominent sac in abdomen called the cisterna chyli; receives lymph from below diaphragm, left arm, left side of head, neck, and thorax; empties into left subclavian vein
Mechanisms of Lymph Flow
- lymph flows under forces similar to those that govern venous return, except no pump (heart)
- lymph flows at low pressure and slower speed than venous blood
- moved along by rhythmic contractions of lymphatic vessels
- flow aided by skeletal muscle pump
- arterial pulsation rhythmically squeeze lymphatic vessels
- thoracic pump aids flow from abdominal to thoracic cavity
- valves prevent backward flow
- rapidly flowing blood in subclavian veins, draws lymph into it
- exercise significantly increases lymphatic return
natural killer (NK) cells
–large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or have turned cancerous
–responsible for immune surveillance
T lymphocytes (T cells)
–mature in thymus
B lymphocytes (B cells)
–activation causes proliferation and differentiation into plasma cells that produce antibodies
macrophages
–very large, avidly phagocytic cells of the connective tissue
–develop from monocytes
–phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter
–process foreign matter and display antigenic fragments to certain T cells alerting the immune system to the presence of the enemy
–antigen presenting cells (APCs)
dendritic cells
–branched, mobile APCs found in epidermis, mucous membranes, and lymphatic organs
–alert immune system to pathogens that have breached their surface
reticular cells
–branched stationary cells that contribute to the stroma of a lymphatic organ
–act as APCs in the thymus
lymphatic (lymphoid) tissue
aggregations of lymphocytes in the connective tissues of mucous membranes and various organs
diffuse lymphatic tissue
simplest form
–lymphocytes are scattered, rather than densely clustered
–prevalent in body passages open to the exterior
•respiratory, digestive, urinary, and reproductive tracts
MALT
mucosa-associated lymphatic tissue (MALT)
lymphatic nodules (follicles)
dense masses of lymphocytes and macrophages that congregate in response to pathogens
–constant feature of the lymph nodes, tonsils, and appendix
Peyer patches
dense clusters in the ileum, the distal portion of the small intestine
Lymphatic Organs
•lymphatic organs have well-defined anatomical sites
–have connective tissue capsule that separates the lymphatic tissue from neighboring tissues
primary lymphatic organs
–red bone marrow and thymus
–site where T and B cells become immunocompetent–able to recognize and respond to antigens
secondary lymphatic organs
–lymph nodes, tonsils, and spleen
–immunocompetent cells populate these tissues
Red Bone Marrow
red bone marrow is involved in hemopoiesis(blood formation) and immunity
–soft, loosely organized, highly vascular material
–separated from osseous tissue by endosteum of bone
–as blood cells mature, they push their way through the reticular and endothelial cells to enter the sinus and flow away in the blood stream
thymus
member of the endocrine, lymphatic, and immune systems
–houses developing lymphocytes
–secretes hormones regulating their activity
–bilobed organ located in superior mediastinum between the sternum and aortic arch
reticular epithelial cells
seal off cortex from medulla forming blood-thymus barrier
produce signaling molecules
thymosin, thymopoietin, thymulin, interleukins, and interferon
lymph nodes
the most numerous lymphatic organs –about 450 in typical young adult –serve two functions: •cleanse the lymph •act as a site of T and B cell activation
parenchyma divided into
cortex and medulla
–germinal centers where B cells multiply and differentiate into plasma cells
Lymph Node Locations
cervical lymph nodes axillary lymph nodes thoracic lymph nodes abdominal lymph nodes intestinal and mesenteric lymph nodes inguinal lymph nodes popliteal lymph nodes
cervical lymph nodes
–deep and superficial group in the neck
–monitor lymph coming from head and neck
axillary lymph nodes
–concentrated in armpit
–receive lymph from upper limb and female breast
thoracic lymph nodes
–in thoracic cavity especially embedded in mediastinum
–receive lymph from mediastinum, lungs, and airway
abdominal lymph nodes
–occur in posterior abdominopelvic wall
–monitor lymph from the urinary and reproductive systems
intestinal and mesenteric lymph nodes
–found in the mesenteries, adjacent to the appendix and intestines
–monitor lymph from the digestive tract
inguinal lymph nodes
–in the groin and receive lymph from the entire lower limb
popliteal lymph nodes
–occur on the back of the knee
–receive lymph from the leg proper
lymphadenopathy
collective term for all lymph node diseases
lymphadenitis
swollen, painful node responding to foreign antigen
lymph nodes are common sites for
metastatic cancer
–swollen, firm and usually painless
metastasis
phenomenon in which cancerous cells break free from the original, primary tumor, travel to other sites in the body, and establish new tumors.
tonsils
patches of lymphatic tissue located at the entrance to the pharynx
–guard against ingested or inhaled pathogens
–each covered with epithelium
tonsillar crypts
have deep pits –tonsillar crypts lined with lymphatic nodules –tonsillitis and tonsillectomy
three main sets of tonsils
palatine tonsils
lingual tonsils
pharyngeal tonsil (adenoid)
palatine tonsils
- pair at posterior margin of oral cavity
* most often infected
lingual tonsils
•pair at root of tongue
pharyngeal tonsil (adenoid)
- single tonsil on wall of nasopharynx
- covered by epithelium
- pathogens get into tonsillar crypts and encounter lymphocytes
spleen
the body‟s largest lymphatic organ
spleen highly vascular and vulnerable to trauma and infection
parenchyma exhibits two types of tissue:
red pulp
white pulp
red pulp
sinuses filled with erythrocytes
white pulp
lymphocytes, macrophages surrounding small branches of splenic artery
functions
–blood production in fetus
–blood reservoir
–„erythrocyte graveyard‟ -RBC disposal
–white pulp monitors blood for foreign antigens
splenectomy
ruptured spleen
pathogens
environmental agents capable of producing disease
–infectious organisms, toxic chemicals, and radiation
three lines of defenses against pathogens
first line of defense
external barriers, skin and mucous membranes
second line of defense
several nonspecific defense mechanisms
•leukocytes and macrophages, antimicrobial proteins, immune surveillance, inflammation, and fever
•effective against a broad range of pathogens
third line of defense
the immune system
•defeats a pathogen, and leaves the body of a „memory‟ of it so it can defeat it faster in the future
nonspecific resistance
guards equally against a broad range of pathogens
–their effectiveness does not depend on prior exposure
–skin and mucous membranes
–leukocytes and macrophages, antimicrobial proteins, immune surveillance, inflammation, and fever
immunity
specific defense because it results from prior exposure to a pathogen
–usually provides future protection only against that particular one
External Barriers
skin
mucous membranes
skin
–makes it mechanically difficult for microorganisms to enter the body
–toughness of keratin
–too dry and nutrient-poor to support microbial growth
defensins
peptides that kill microbes by creating holes in their membranes
acid mantle
thin film of lactic acid from sweat which inhibits bacterial growth
mucous membranes
–digestive, respiratory, urinary, and reproductive tracts are open to the exterior and protected by mucous membranes
–mucus physically traps microbes
lysozyme
enzyme destroys bacterial cell walls
phagocytes
phagocytic cells with a voracious appetite for foreign matter
five types of leukocytes
–neutrophils –eosinophils –basophils –monocytes –lymphocytes
Neutrophils
wander in connective tissue killing bacteria
–phagocytosis and digestion
–produces a cloud of bactericidal chemicals
killing zone
–degranulation
•lysosomes discharge into tissue fluid
–respiratory burst –neutrophils rapidly absorb oxygen
•toxic chemicals are created (O2.-, H2O2, HClO)
–kill more bacteria with toxic chemicals than phagocytosis
Eosinophils
- found especially in the mucous membranes
- stand guard against parasites, allergens(allergy causing agents), and other pathogens
- kill tapeworms and roundworms by producing superoxide, hydrogen peroxide, and toxic proteins
Basophils
secrete chemicals that aid mobility and action of WBC other leukocytes
histamine
a vasodilator which increases blood flow
•speeds delivery of leukocytes to the area
heparin
inhibits the formation of clots
•would impede leukocyte mobility
mast cells
also secrete these substances
–type of connective tissue cell very similar to basophils
Lymphocytes
•three basic categories •circulating blood contains –80% T cells –15% B cells –5% NK cells •many diverse functions
monocytes
emigrate from the blood into the connective tissue and transform into macrophages
macrophage system
all the body‟s avidly phagocytic cells, except leukocytes
wandering macrophages
actively seeking pathogens
•widely distributed in loose connective tissue
fixed macrophages
phagocytize only pathogens that come to them
microglia
in central nervous system
alveolar macrophages
in lungs
hepatic macrophages
in liver
Antimicrobial Proteins
proteins that inhibit microbial reproduction and provide short-term, nonspecific resistance to pathogenic bacteria and viruses
two families of antimicrobial proteins:
–interferons
–complement system
interferons
secreted by certain cells infected by viruses
–of no benefit to the cell that secretes them
–alert neighboring cells and protect them from becoming infected
–bind to surface receptors on neighboring cells
–alerted cell synthesizes various proteins that defend it from infection
–also activates NK cells and macrophages
–activated NK cells destroy malignant cells
complement system
a group of 30 or more globular proteins that make powerful contributions to both nonspecific resistance and specific immunity
–synthesized mainly by the liver
–circulate in the blood in inactive form
–activated by presence of the pathogen
activated complement brings about four methods of pathogen destruction
- inflammation
- immune clearance
- phagocytosis
- cytolysis
three routes of complement activation
- classical pathway
- alternative pathway
- lectin pathway
classical pathway
–requires antibody molecule to get started
–thus part of specific immunity
–antibody binds to antigen on surface of the pathogenic organism
•forms antigen-antibody (Ag-Ab) complex
–changes the antibody‟s shape
•exposing a pair of complement-binding sites
•binding of the first complement (C1) sets off a reaction cascade called complement fixation
–results in a chain of complement proteins attaching to the antibody
alternative pathway
–nonspecific, does not require antibody
–C3 breaks down in the blood to C3a and C3b
•C3b binds directly to targets such as human tumor cells, viruses, bacteria, and yeasts
•triggers cascade reaction with autocatalytic effect where more C3 is formed
lectin pathway
Exists
mechanisms of action of complement proteins
- inflammation
- immune clearance
- phagocytosis
- cytolysis
inflammation
- C3a stimulates mast cells and basophils to secrete histamine and other inflammatory chemicals
- activates and attracts neutrophils and macrophages
- speed pathogen destruction in inflammation
immune clearance
- C3b binds with antigen-antibody complexes to red blood cells
- these RBCs circulate through the liver and spleen
- macrophages of those organs strip off and destroy the Ag-Ab complexes leaving RBCs unharmed
- principal means of clearing foreign antigens from the bloodstream
phagocytosis
•neutrophils and macrophages cannot phagocytize “naked” bacteria, viruses, or other pathogens
•C3b assist them by opsonization
–coats microbial cells and serves as binding sites for phagocyte attachment
–makes the foreign cell more appetizing