BIO 202 - Ch. 5 Lymphatic & Immune System

lymph

contains water, dissolved substances, damaged cells, cellular debris, and microorganisms present in tissues.

flows toward venous system and passes through lymph node checkpoints

lymph nodes

small, strategically located filters to slow lymph

removes pathogens, provides site for T & B cell activation

~450 in an adult

lymph enters through multiple afferent vessels, exits through 1-3 efferent vessels

capsule: dense irregular collagenous CT (DICCT)

lymphocytes

specialized cells that primarily make up the immune system and prevent spread of infections and cancers

primary functions of the lymphatic system

1. transport excess interstitial fluid back to the heart

2. activating immune system and support immune defense by filtering harmful agents

3. aid in fat absorption with gastrointestinal system

pathway of lymph flow

1. fluid loss from blood capillaries

   1. filtration pushes water out of blood into interstitial fluid

   2. ~1.5 mL per minute lost from circulation

   3. w/out return, entire plasma vol. would be lost in a day

2. lymph capillaries

   1. small, blind ended vessels around blood capillary beds

   2. highly permeable walls allow entry of large substances & fluid

   3. fluid inside is lymph

3. lymph collecting vessels

   1. contains valves to ensure 1 way flow

   2. carry lymph to larger trunks

4. lymph trunks (9 total) — drains major body regions

   1. jugular trunks (p) - head & neck

   2. subclavian trunks (p) - upper limbs

   3. bronchomediastinal trunks (p) - thorax

   4. intestinal trunk (unpaired) - abdomen

   5. lumber trunks (p) - pelvis & lower limbs

   6. JS-BIL

5. lymph ducts

   1. right lymphatic duct - drains right upper limb, right side of head, neck, thorax

   2. thoracic duct - drains remainder of the body

6. venous return @ junction of major veins

   1. right lymphatic duct - enters bloodstream at the junction of the right subclavian vein and right internal jugular vein

   2. thoracic duct - enters bloodstream at the junction of the left subclavian vein and left internal jugular vein

summary of lymph flow pathway

fluid leaves blood capillaries

enters lymph capillaries

moves through collecting vessels to JS BIL trunks

into right lymphatic or thoracic duct

and returns to blood at the subclavian–jugular junction

lacteal

delivers fats to lymph collecting vessels, then to intestinal trunks. then fatty lymph moves into large lymphatic vessel, the cisterna chyli

cisterna chyli

posterior to abdominal aorta & anterior to vertebral column

5-7 cm (2-3 inches) long, dilated, sac-like

serves as lymphatic reservoir, collecting lymph from intestinal trunk (carrying fatty lymph from lacteals) and from the R & L lumber trunks (carrying lymph from pelvis and lower limbs)

fatty lymph receives after a meal is milky, called chyle

from cisterna chyli, lymph ascends into thoracic duct, which passes through aortic hiatus of diaphragm to enter thoracic cavity

master pathway and comparison of lymph flow and dietary fat absorption

1. interstitial fluid collection

   1. fluid leaves blood capillaries during filtration and enters lymph capillaries (small, blind ended, highly permeable)

   2. in the small intestine, fats enter specialized lymph capillaries called lacteals instead of blood capillaries

2. initial transport

   1. from tissues: lymph moves into lymph collecting vessels (contain valves for one way flow)

   2. from small intestine: lacteals deliver fatty lymph to lymph collecting vessels

3. regional drainage into lymph trunks

   1. both general lymph and fatty lymph drain into lymph trunks (9 total — JS BIL)

      1. dietary fats specifically enter through intestinal trunks

4. cisterna chyli (dietary fat pathway)

   1. fatty lymph from intestinal trunks collects in cisterna chyli

5. final vessels - lymph ducts

   1. right lymphatic duct - drains R upper limb, R head, neck, thorax (general lymph only)

   2. thoracic duct - drains remainder of body & receives fatty lymph from cisterna chyli

6. venous return

   1. right lymphatic duct - enters bloodstream @ junction of R subclavian vein & R internal jugular vein

   2. thoracic duct - enters bloodstream @ junction of L subclavian vein & L internal jugular veins

      1. technically fatty lymph eventually drains here in venous return #2

lymphatic cells - immune soldiers

natural killer cells, t lymphocytes (t cells), b lymphocytes (b cells), macrophages, dendritic cells, reticular cells

natural killer (NK) cells

lymphatic cells - immune soldiers

large lymphocytes that attack and destroy bacteria, transplanted tissues, & infected host cells by virus or cancer

recognize & eliminate threats without warning

t lymphocytes (t cells)

lymphatic cells - immune soldiers

mature in thymus and later rely on thymic hormones

multiple specialized classes w/ different immune functions

command & coordinate other immune cells

b lymphocytes

lymphatic cells - immune soldiers

differentiate into plasma cells that secrete antibodies

produce targeted ammo (antibodies) to mark enemies

macrophages

lymphatic cells - immune soldiers

very large, active phagocytes that develop from monocytes

cleanup crew & heavy equipment operators, engulfing & digesting large amount of debris

dendritic cells

lymphatic cells - immune soldiers

branched, mobile cells that alert immune system to pathogens that have breached body surfaces

engulf foreign matter by endocytosis rather than phagocytosis

scouts and messengers, detects danger and reports back to HQ

reticular cells

lymphatic cells - immune soldiers

stationary cells that form CT framework of lymphoid organs

architects who build the “barracks” that house immune cells

mucosa associated lymphatic tissue (MALT)

the outposts, positioned where pathogens are most likely to enter

found in mucous membranes of gastrointestinal, urinary, reproductive, & respiratory tracts

most MALT is loosely organized & lacks CT capsule

watches for invading forces before they reach major cities

specialized MALT

partially encapsulated or non-capsulated

tonsils

specialized malt

guards against ingested and inhaled pathogens

each tonsil covered by stratified squamous epithelium

contains deep pits called tonsillar crypts lined with lymphoid follicles

pharyngeal tonsil

posterior nasopharynx

palatine tonsils

paired, posterior oropharynx, largest and often infected

lingual tonsils

numerous, base of tongue

tubal tonsils

small, opening of pharyngotympanic tubes; may be absent in some people

peyer’s patches

clusters of MALT in terminal ileum of small intestine

monitor intestinal bacteria

contain villi, which are lined with simple columnar epithelium (enterocytes)

flow of lymph through lymph node

afferent lymphatic vessels > cortex > medulla > efferent lymphatic vessels (1-3 per node)

security checkpoint where every vehicle (lymph) is slowed, inspected, & cleared before entering city

thymus

training academy

anterior mediastinum

produces thymosin and thymopoietin for t cell maturation

most active in childhood, replaced with adipose t. in adulthood

spleen

central inspection & recycling center

largest lymphatic organ, upper left quadrant of abdominopelvic cavity

red pulp: macrophages surrounding trabecular veins; removes old / damaged RBCs

white pulp: contains phagocytes and T & B lymphocytes for immune defense, macrophages, & dendritic cells surrounding central arteries

blood flow through spleen

splenic artery > trabecular arteries > central arteries (in white pulp) > arterioles > sinusoids (in red pulp) > trabecular veins > splenic veins (to hepatic portal vein)

immune system chain of command

immune cells > MALT > lymph nodes > thymus > spleen > coordinated immune response

lymphoid follicle

cluster of immune cells (mainly b lymphocytes, with framework of reticular fibers)

found in cortex of lymphatic tissues and organs

germinal center

lighter staining central region w/in lymphoid follicle

boundary

densely packed B lymphocytes surrounding lighter germinal center

resistance

nonspecific - general defenses that act against many pathogens without targeting one specifically, 1st & 2nd line of defense

specific resistance - defenses that target and remember a specific pathogen, 3rd line of defense

innate and adaptive/acquired immunity

specialized resistance

body recognizes, targets, & remembers particular pathogen; allowing faster & stronger response upon re-exposure

provided by specific (adaptive) immune system

lines of defense — body’s layered protection strategy

1. 1st line — physical & chemical barriers (nonspecific)

2. 2nd line — internal nonspecific defenses like inflammation, fever, phagocytosis, & antimicrobial proteins

3. 3rd line — specific (adaptive) immunity with T cells, B cells, & antibodies

first line of defense

physical barriers

• skin — tough shield in keratinized dead cells in epidermis

• mucous membranes — trap microbes in cavities open to exterior

• hairs in nose — filter large particle from inhaled air

• cilia in respiratory tract - sweep mucus & debris toward throat (mucociliary escalator)

• epidermal shedding — removes attached microbes

chemical barriers

• lysozyme — enzyme in tears, sweat, saliva that break down bacterial cell walls

• gastric juice — highly acidic (pH 2-3), kills ingested pathogens

• saliva — washes microbes away and has antimicrobial enzymes

• sebum — lowers skin pH & inhibits bacterial growth

• sweat — flushes microbes from skin and has antimicrobial peptides

• earwax (cerumen) traps debris and microbes

• urine flow — flushes microbes from urinary tract

• vaginal secretions -= maintain acidic pH to inhibit pathogens

components of 2nd line of defense

1. inflammatory mediators: inflammation & fever

2. phagocytic cells

3. antimicrobial proteins - complement system

4. natural killer (NK) cells

inflammatory mediators - 2nd line of defense

histamine, prostaglandins, leukotrienes, bradykinin, cytokines

effects:

• vasodilation: histamine & prostaglandins, increase blood flow to area; redness & warmth

• increased capillary permeability: histamine & leukotrienes, allows plasma & immune cells to enter tissues & swell

• increased pain sensitivity: bradykinin & prostaglandins, stim sensory nerve endings to heighten pain awareness

• chemotaxis: cytokines like interleukin 8 & complement fragments C3a and C5a attract large #s of neutrophils and other immune cells to site

• pyrogens: like interleukin 1 and TNF alpha act on hypothalamus to raise body’s temperature set point, leads to fever

phagocytic cells - 2nd line of defense

triggered by

• chemotaxis from cytokines, chemokines, C3a and C5a

• pathogen-associated molecular patterns (PAMPs) like bacterial cell wall

• opsonized pathogens (pathogens marked for destruction by antibodies or complement proteins)

granulocytes

• neutrophils ingest pathogens once, then die

• eosinophils & basophiles primarily secrete inflammatory mediators like histamine

macrophages can ingest multiple pathogens before dying

pus forms when many neutrophils die after extensive tissue damage

antimicrobial proteins complement system - 2nd line of defense

over 20 proteins produced by the liver, always present in blood and tissues in inactive form, circulating plasma

20+ proteins made by complement system are called complement proteins or complement factors

activated by:

• recognition of pathogens through surface molecules

• antigen antibody complexes from adaptive immune response

• signals from damaged or infected cells

defense:

• lyse foreign cells by forming pores in membranes

• enhance phagocytosis through opsonization (marking pathogens for ingestion)

• amplify/enhance inflammation by attract immune cells and increasing vessel permeability

when 1 protein is activated, triggers next in sequence

natural killer (NK) cells - 2nd line of defense

constantly patrol blood, lymph, and tissues in standby mode

activated by:

• cytokines like interferons released in infections / cancer

• stress signals from abnormal cells

• cells with missing / abnormal markers on their surface

offense actions:

• release perforin to punch holes in target cell membrane

• release granzymes that enter cell and trigger apoptosis (programmed cell death)

• secrete cytokines that recruit and activate macrophages and other immune cells

third line of defense - specific resistance (adaptive immunity)

• b & t lymphocytes that target specific antigens (foreign molecules, often proteins, that trigger an immune response)