Chapter 21 Lymphatic and Immune System

at least 10 times

how many more bacterial cells than human cells in the body?

immune system

this is not an organ system, but instead a cell population that inhabits all organs and defends the body from agents of disease; it is especially concentrated in the lymphatic system

lymphatic system

network of organs and vein-like vessels that recover fluid; inspect fluid for disease agents; activates immune responses; returns fluid to the bloodstream

fluid recovery

function of the lymphatic system in which fluid continually filters from the blood capillaries into the tissue spaces; blood capillaries reabsorb 85% of fluid that leaks out; 15% of the water and about half of the plasma proteins enter the lymphatic system and then are returned to the blood

immunity

function of the lymphatic system in which excess filtered fluid picks up foreign cells and chemicals from the tissues; fluid passes through lymph nodes where immune cells stand guard against foreign matter and a protective immune response is activated

lipid absorption

function of lymphatic system in which lacteals in the small intestine absorb dietary lipids that are not absorbed by the blood capillaries

lacteal

site of lipid absorption

lymph

the recovered fluid in the lymphatic system

lymphatic vessels

transports the lymph; they branch all throughout the body but are concentrated in the groin, neck, and armpit

lymphatic tissues

composed of aggregates of lymphocytes and macrophages that populate many organs in the body; example is the priors patches in the large intestine

lymphatic organs

defense cells are especially concentrated in these organs; they are separated from surrounding organs by connective tissue capsules; they work together for the purpose of moving lymphatic fluid (lymph)

clear, colorless fluid, similar to plasma, but with much less protein; it originates as extracellular fluid drawn into lymphatic capillaries; the chemical composition varies in different places (ex: in small intestines, lymph has higher concentration of lipids)

characteristics of lymph

cartilage, cornea, bone, and bone marrow

lymphatic capillaries penetrate nearly every tissue of the body but are absent from what?

capillary wall is endothelial cells overlapping each other like roof shingles; they are closed at one end; the cells are tethered to surrounding tissue by protein filaments, but the gaps between the cells are large enough to allow bacteria and cells to enter the lymphatic capillary; the endothelium creates valve-like flaps that open when interstitial fluid pressure is high, and close when it is low

characteristics of lymphatic capillaries

tunica interna (endothelium, valves); tunica media (elastic fibers, smooth muscle); tunica externa (thin outer layer)

what three layers compose larger lymphatic vessels?

skeletal muscle pump

what is the biggest source of pressure for lymphatic vessels?

they converge into larger and larger vessels; collecting vessels course through many lymph nodes; there are six lymphatic trunks that drain major portions of the body which merge to form bigger tubes called ducts; there are two collecting ducts (right lymphatic duct and thoracic duct)

characteristics of lymphatic vessels

right lymphatic duct

receives lymph from right arm, right side of head and thorax; empties into right subclavian vein

thoracic duct

larger and longer that the right lymphatic duct; begins as a prominent sac in abdomen called the cisterna chyli, receives lymph from below the diaphragm, left arm, left side of head, neck, and thorax; empties into left subclavian vein

it flows under forces similar to those that govern venous return, except there is no pump (heart); the lymph also flows at a lower pressure and a slower speed than venous blood

how does flow of lymph compare to venous blood

rhythmic contractions of lymphatic vessels (the stretching of vessels stimulates contraction); arterial pulsation rhythmically squeezes lymphatic vessels; flow is also aided by the skeletal muscle pump; thoracic pump aids flow from abdominal to thoracic cavity; valves prevent backward flow; rapidly flowing blood in subclavian veins draws lymph into it

what moves lymph along?

exercise

what significantly increases lymphatic return?

natural killer cells

large lymphocytes that attack and destroy bacteria, transplanted tissue, and host cells that are infected with viruses or that have turned cancerous; they don’t go through phagocytosis; these are able to make the determination by themselves of whether a cell should live or die

T lymphocytes

these mature in the thymus; they are cells that destroy other human cells; these can not work by themselves but instead need to be trained to recognize a particular antigen

B lymphocytes

activation causes proliferation and these differentiate into plasma cells that produce antibodies

macrophages

large, avidly phagocytic cells of connective tissue that develop from monocytes; they phagocytize tissue debris, dead neutrophils, bacteria, and other foreign matter; they process the foreign matter and display antigenic fragments to certain T cells which alerts the immune system to the presence of the enemy (therefore they are antigen-presenting cells)

dendritic cells

branched, mobile antigen-presenting cells found in the epidermis, mucous membranes, and lymphatic organs; they alert the immune system to pathogens that have breached the body surface

reticular cells

branched stationary cells that contribute to the stroma of a lymphatic organ; these are only present within the lymph nodes and they are antigen-presenting cells

macrophages, dendritic cells, reticular cells

what are 3 antigen-presenting cells?

lymphatic tissue

aggregations of lymphocytes in the connective tissues of mucous membranes and various organs

diffuse lymphatic tissue

this is the simplest form of lymphatic tissue; its lymphocytes are scattered (not clustered); it is prevalent in body passages open to the exterior (including respiratory, digestive, urinary, and reproductive tracts); ex: mucosa-associated lymphatic tissue

lymphatic nodules (follicles)

dense masses of lymphocytes and macrophages that congregate in response to pathogens; they are a constant feature of the lymph nodes, tonsils, and appendix

aggregated lymphoid nodules

dense clusters in the ileum, the distal portion of the small intestine

they have a connective tissue capsule that separates lymphatic tissue from neighboring tissues

what makes lymphatic organs anatomically well-defined?

red bone marrow and thymus; these are sites where T and B cells become immunocompetent (able to recognize and respond to antigens)

what are the primary lymphatic organs?

lymph nodes, tonsils, and spleen; immunocompetent cells populate these tissues

what are the secondary lymphatic organs?

red bone marrow

what 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 bloodstream

characteristics of red bone marrow

thymus

what is a member of the endocrine, lymphatic, and immune system?

houses developed lymphocytes (T lymphocytes populate the cortex and medulla); secretes hormones regulating the activity of the lymphocytes/produce signaling molecules

functions of the thymus

bilobed organ that is located in the superior mediastinum between the sternum and the aortic arch; it degenerates/involutes with age; has fibrous capsule that gives off trabeculae that divide the gland into several lobes (the lobes have a cortex and medulla populated by T lymphocytes); it has epithelial cells that seal off the cortex from the medulla forming a blood-thymus barrier

characteristics/structure of the thymus

lymph nodes (about 450 in typical young adult)

what is the most numerous lymphatic organ?

cleanse the lymph and act as a site of T and B cell activation

what are the two functions of the lymph nodes?

elongated, bean-shaped structure with hilum; enclosed with fibrous capsule that has trabeculae that divides the interior into compartments; it has a stroma of reticular fibers and reticular cells; it has more lymphatic vesicles entering than exiting which creates a pressure gradient helping to move lymphatic fluid; the interior is divided into a cortex and medulla (the germinal centers are where B cells multiply and differentiate into plasma cells)

structure of lymph nodes

there are several afferent lymphatic vessels that lead into the lymph node along its convex surface; lymph leaves the lymph node through one to three efferent lymphatic vessels that leave the hilum

explain the afferent and efferent lymphatic vessels in the lymph nodes

metastasis

cancerous cells that break free from the original tumor, travel to other sites in the body, and establish new tumors; these cells easily enter lymphatic vessels and tend to lodge in the first lymph node they encounter where they multiply and destroy the node; after they tend to spread to the next node downstream

lumpectomy, mastectomy, along with the removal of nearby axillary nodes

what is the treatment for breast cancer?

tonsils

patches of lymphatic tissue located at the entrance to the pharynx

guard against ingested or inhaled pathogens; not necessary to stay alive

function of tonsils

covered with epithelium; have deep pits - tonsillar crypts lined with lymphatic nodules (potential pathogens work their way down these to be exposed to the immune system and phagocytized)

structure/characteristics of tonsils

palatine (pair at posterior margin of oral cavity that is most often infected); lingual (pair at root of tongue); pharyngeal (single tonsil on wall of nasopharynx) - one most frequently removed because they most impair breathing

what are the three main sets of tonsils

spleen

what is the body’s largest lymphatic organ?

red pulp (sinuses filled with erythrocytes) and white pulp (lymphocytes and macrophages surrounding small branches of the splenic artery; has individual arterial in each section of the white pulp)

what are the two types of tissue in the spleen?

highly vascular and vulnerable to trauma and infection; ruptured spleen requires splenectomy but leaves the person susceptible to future infections and premature death

characteristics of spleen

healthy RBCs come and go; the spleen is an erythrocyte graveyard for old, fragile, RBCs; for fetuses and very anemic adults, blood cell production occurs; white pulp monitors blood for foreign antigens and keeps an army of monocytes for release when needed; it stabilizes blood volume through plasma transfers to the lymphatic system (because the spleen is also part of the circulatory system)

functions of the spleen

pathogens

agents capable of producing disease that include viruses, bacteria, and fungi

skin and mucous membranes

first line of defense against pathogens?

includes several innate defense mechanisms: leukocytes and macrophages, antimicrobial proteins, natural killer cells, inflammation, and fever; this is nonspecific (for any and all bacteria that don’t belong system wide)

seconds line of defense against pathogens?

adaptive immunity; defeats a pathogen and leaves the body with a “memory” of it so it can defeat it faster in the future; this is targeted and effective but takes a while to upregulate

third line of defense against pathogens?

in an infection pathogen goes through reproduction but with a disease there is enough of the pathogen to break homeostasis

what is the difference between infection and disease?

first and third line of defense

which lines of defense do we rely on most?

innate defenses

guard equally against a broad range of pathogens; they lack the capacity to remember pathogens; local, nonspecific, and lacks memory; includes the first and second lines of defense

protective proteins, protective cells, and protective processes

what are the three kinds of innate defenses?

adaptive immunity

body must develop separate immunity to each pathogen; the body adapts to a pathogen and wards it off more easily upon future exposure; antibodies

makes it mechanically difficult for microorganisms to enter the body; has tough keratin; it is too dry and nutrient-poor for microbial growth; has dermicidin, defensins, and cathelicidins that are peptides in the skin that kill microbes; has the acid mantle

what makes skin an effective barrier?

acid mantle

thin film of lactic and fatty acids from sweat and sebum that inhibits bacterial growth; salt dehydrates and acid makes pH too acidic and denatures proteins

mucous membrane

an external barrier present in the digestive, respiratory, urinary, and reproductive tracts which are open to the exterior; the mucus physically traps microbes

lysozyme

enzyme that destroys bacterial cell walls; it is present in mucous and saliva

phagocytes

cells that engulf foreign matter

neutrophils, eosinophils, basophils, monocytes, lymphocytes

five types of leukocytes

wander in connective tissue killing bacteria; can kill using phagocytosis and digestion; can kill by producing a cloud of bactericidal chemicals: lysosomes degranulate so enzymes are discharged into tissue fluid causing a respiratory burst; and it creates a killing zone around the neutrophil, destroying several bacteria

functions of neutrophils

found especially in mucous membranes; guard against parasites, allergens, and other pathogens; kills tapeworms and roundworms by producing superoxide, hydrogen peroxide, and toxic proteins; promotes action of basophils and mast cells; phagocytize antigen-antibody complexes; limit action of histamine and other inflammatory chemicals

functions of eosinophils

secrete chemicals that aid mobility and action of other leukocytes; secretes leukotrienes, histamine, heparin (mast cells also secrete these substances - they are another type of connective tissue cell similar to basophils)

function of basophils

leukotrienes

chemical that activates and attracts neutrophils and eosinophils

histamine

this is a vasodilator, which increases blood flow; it speeds the delivery of leukocytes to the area

heparin

inhibits clot formation; clots would impede leukocyte mobility

T, B, and NK cells

what are the 3 basic categories of lymphocytes?

80% T, 15% B, 5% NK

percentage of lymphocytes in circulating blood

NK cells are part of innate immunity; T and B cells are part of adaptive immunity; helper T cells function in both

the diverse functions of lymphocytes

continually patrol body looking for pathogens and diseased host cells; attack and destroy bacteria, transplanted cells, cells infected with viruses, and cancer cells; they are concentrated in the connective tissues

function of natural killer cells

they recognize an enemy cell and bind to it; then they release proteins called perforins which polymerizes a ring and creates a hole in its plasma membrane; it then secretes a group of protein-degrading enzymes (granzymes) that enter through the pore and degrade cellular enzymes and induce apoptosis

how do NK cells attack the threats?

monocytes

these emigrate from the blood into connective tissues and transform into macrophages

macrophage system

all of the body’s avidly phagocytic cells, except leukocytes; includes wandering and fixed macrophages

wandering macrophages

actively seek pathogens and are widely distributed in loose connective tissue

fixed macrophages

phagocytize only pathogens that come to them; they are organ specific (microglia are in CNS, alveolar macrophages are in the lungs, and hepatic macrophages are in the liver)

antimicrobial proteins

proteins that inhibit microbial reproduction and provide short-term, innate immunity to pathogenic bacteria and viruses

interferons and complement system

what are the two families of antimicrobial proteins?

interferons

what are secreted by certain cells infected by viruses

alert neighboring cells and protect them from being infected; they bind to surface receptors on neighboring cells and activate second-messenger systems within; there is no benefit to the cell that secretes them

function of interferons

the alerted cell synthesizes various proteins that defend it from infection (breaks down viral genes or prevents replication); it also activates NK cells and macrophages which destroy the infected cell before they can liberate a swarm of newly replicated viruses; the activated NK cells destroy malignant cells

what happens after interferons are secreted and alert neighboring cells?

complement system

a group of 30 or more globular proteins that make powerful contributions to both innate immunity and adaptive immunity; they are synthesized mainly by the liver and circulate in the blood in an inactive form; they become activated in the presence of a pathogen

inflammation, immune clearance, phagocytosis, cytolysis

the activated complement system brings about what 4 methods of pathogen destruction?

classical pathway, alternative pathway, lectin pathway

what are the three routes of complement activation?

protein stimulates mast cells and basophils to secrete histamine (vasodilator) and other inflammatory chemicals which activates and attracts neutrophils and macrophages; pathogen destruction is spread up

explain inflammation as a mechanism of action of complement proteins

protein binds with antigen-antibody complexes to RBCs which circulate through the liver and spleen; macrophages of those organs strip off and destroy the complexes leaving the RBCs unharmed; this is the principal means of clearing foreign antigens from the bloodstream

explain immune clearance as a mechanism of action of complement proteins

neutrophils and macrophages can’t phagocytize “naked” bacteria, viruses, or other pathogens so a protein assists them by opsonization; the protein coats microbial cells and serves as binding sites for phagocyte attachment ultimately making the foreign cell more appetizing

explain phagocytosis as a mechanism of action of complement proteins

protein splits other complement protein which binds to enemy cell; this attracts more complement proteins and a membrane attack complex forms; a hole forms in the target cell so electrolytes leak out, water flows in rapidly, and the cell ruptures

explain cytolysis as a mechanism of action of complement proteins

fever

abnormal elevation of body temp; also called pyrexia and febrile pertains to it; can result from trauma, infections, drug reactions, brain tumors, and other causes

it is an adaptive defense mechanism that, in moderation, does more good than harm; it promotes interferon activity, elevates metabolic rate and accelerates tissue repair, and inhibits reproduction of bacteria and viruses (pathogens are at optimal temp when not in fever state)

what is the function of fever?

antipyretics

fever-reducing medications; include aspirin/ibuprofen that inhibit prostaglandin E2 synthesis