3. Lymph and Immune Outline

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I. Lymphatic Vessels
An elaborate network of drainage vessels that collect the excess protein-containing
interstitial fluid and return it to the bloodstream. Called lymph once it enters the lymphatic
A. Lymphatic Capillaries
Structure: simple sq. epithelium, cells overlay like roof shingles, creating
minivalves that prevent backflow of lymph
Function: hydrostatis pressure drives fluid into capillaries
Lacteals: special set of lymphatic capillaries that transport fat absorbed in the
small intestine to the blood
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B. Flow of Lymph
Collecting Vessels – like veins with thinner walls and more anastomoses
Lymphatic Trunks – formed
a) Paired lumbar
b) Paired bronchomediastinal
c) Paired subclavian
d) Paired jugular trunks
e) Single intestinal trunk
Lymphatic Ducts – empty lymph into venous circulation at junction of internal
jugular and subclavian veins
a) Right lymphatic duct – drains right upper arm and right side of head and
b) Thoracic duct arises as cisterna chyli, drains rest of body
Cisterna Chyli
Transport – lymph propelled by:
a) Milking action of skeletal muscle
b) Pressure changes in thorax during breathing
c) Valves that prevent backflow
d) Pulsations of nearby arteries
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e) Contractions of smooth muscle in walls of lymphatics
C. Lymphoid Cells
T Cells – fight intracellular pathogens – longer training
B Cells – produce plasma cells which secrete antibodies (mark antigens for
destruction), fight extracellular pathogens
Macrophages – phagocytize foreign substances; help activate T cells, act as
APCs, mobile
Dendritic Cells – capture antigens and deliver to lymph nodes; activate T cells,
can act as APCs, not mobile
Reticular Cells – produce reticular fiber stroma that support other cells in
lymphoid organ
D. Lymphoid Tissue – largely reticular CT, surveillance vantage point for
lymphocytes and macrophages, home/proliferation site of lymphocytes
Diffuse – large collections found in MALT
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Follicles – germinal centers of proliferating B cells, isolated aggregations of
Peyer’s patches and in appendix
II. Primary Lymphatic Organs
A. Red Bone Marrow
Produces B & T lymphocytes, maturation site of B cells
B. Thymus
T cell training and maturation site – happens mostly early in life; does not
directly fight antigens; no follicles (lacks B cells)
Endocrine connection: the thymus is a huge player in the endocrine system,
and it secretes thymosin, which stimulates development of the T cells
III. Secondary Lymphatic Organs
– Where lymphocytes encounter antigens, become activated
A. Lymph Nodes
Location: segmentally located in inguinal, axillary, cervical, popliteal areas, in
connective tissues, in clusters along lymphatic vessels
a) Filter lymph
b) Immune system activation – lymphocytes activated and mount attack
against antigens
Lymph circulation: a) Enters convex side via afferent lymphatic vessels, travels
through subcapsular sinus and small sinuses to medullary sinuses, exits
concave side at hilum via efferent vessels
Endocrine connection: the filtering of lymph makes changes to the blood
volume and solute/solvent concentration, which is under endocrine control as
discussed in the cardiovascular section.
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B. Spleen – largest lymphoid organ, site of lymphocyte proliferation and immune
surveillance/response; cleanses blood of old RBCs, platelets, and debris
White pulp – around central arteries, mostly lymphocytes on reticular fibers,
involved in immune functions
Red pulp - in venous sinuses and splenic cords, rich in RBCs and macrophages
for disposal of old RBCs and bloodborne pathogens
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C. MALT – Mucosa-associated lymphoid tissue
Tonsils – form ring of lymphatic tissue around pharynx, gather and remove
pathogens from air, trap bacteria/particulates, allow immune cells to build
memory for pathogens
a) Palatine tonsils – at posterior end of oral cavity
b) Lingual tonsil – at base of tongue
c) Pharyngeal tonsil – posterior wall of nasopharynx
d) Tubal tonsils – surrounds openings of auditory tubes in pharynx
Peyer’s Patches – destroy bacteria, preventing them from breaching intestinal
wall, generate memory lymphocytes, in wall of distal portion of small intestine
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Appendix – behave like Peyer’s patches, vestigial organ
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I. Innate Immune System
Defense you are born with, protects from a wide variety of pathogens, nonspecific
A. First Line of Defense: Surface Barriers
Skin – physical barrier ,acid mantle (antimicrobial), dendritic cells in epidermis,
mast cells and phagocytes provide local immunity
Mucous Membranes – wet membrane lining cavities, traps debris, cilia beats it
back and moves it to the pharynx (goes to stomach and is destroyed by HCl);
mucin traps microorganisms in the digestive/respiratory pathway; defensins –
antimicrobial proteins for bacteria and fungi
B. Second Line of Defense: Innate Internal Cells & Chemicals
Phagocytes – engulf/digest foreign particles
a) Neutrophils – eat bacteria and die
b) Macrophages – primary phagocytes – wandering
c) Dendritic cells – resident phagocytes
Natural Killer Cells (NKC) – only non-specific lymphocyte, anti-cancer: find cells
doing unregulated DNA replication to induce apoptosis, can fight some viruses
Inflammatory response
a) Benefits – prevents injurious agents from spreading to adjacent tissues,
disposes of pathogens and dead tissue cells, and promotes tissue repair
b) Cardinal signs
(1) Heat – from increased blood flow and tissue activity
(2) Redness – from increased blood flow
(3) Swelling – from increased blood flow, increase in exudate (high ECF,
washes area, drains into lymphatic capillaries)
(4) Pain – Nociceptors compressed from swelling
c) Stages
(1) Inflammatory chemical release – local mast cells release histamine and
heparin (anticoagulant and increase tissue permeability, allows adequate
blood flow); damaged cells release chemotactic factors
(2) Vascular changes – increase size of intercellular clefts; capillaries become
leaky, CAMs exposed by endothelium, slow traveling WBCs
(3) Leukocyte mobilization – neutrophils first, then macrophages and
(a) Margination – WBCs roll along and stick to CAMs
(b) Diapedesis – WBCs squeeze through clefts
(c) Chemotaxis – WBCs follow chemotactic factors to side of damage, ECF
builds up (exudate) goes to lymph nodes if need be
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Antimicrobial Proteins
a) Interferons – proteins released by virus-infected cells and certain
lymphocytes; act as chemical messengers to protect uninfected cells from
viral takeover; mobilize immune system
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b) Activation of Complement – bloodborne proteins that upon activation, lyse
microorganisms, enhance phagocytosis by opsonization, and intensify
inflammatory/other immune responses
Fever – systemic response initiated by pyrogens, high temperature inhibits
microbes from multiplying and enhances body’s repair process
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II. Adaptive Immune System Overview
Trained defense with exposure to antigens; specific, has memory, and can vary in strength
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A. MHC and Antigens
B. B and T Lymphocytes and Antigen-presenting cells
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C. Humoral Immunity
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D. Cellular Immunity
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III. Active vs. Passive Immunity
IV.Endocrine Connection
A. Chemical messengers of the immune system stimulate the release of cortisol
and ACTH; lymph provides a route for the transport of hormones
B. Lymphocytes programmed by thymic hormones seed the lymph nodes;
glucocorticoids depress the immune response to inflammation
C. Lymphatic vessels pick up leaked fluids and proteins; lymph helps distribute