Lymphatics & Immunity Flashcards
What does the lymphatic system consist of?
Lymph
Lymphatic vessels
Lymphatic tissue
Lymph
A liquid type of connective tissue that is clear and colourless.
Found in lymphatic vessels and tissues
In between cells = interstitial fluid
In blood = plasma
Lymphatic tissues
Lymph organs, RBM.
Specialized forms of reticular connective tissue that contain a large number of lymphocytes
Lymphocytes
Agranular white blood cells that participate in adaptive immune response (B and T cells)
(Plus granular nonspecific NK cells)
3 Major functions of the lymphatic system
- Drains excess interstitial fluid
- - returns it to the blood via subclavian veins
- - approximately 3 litres/day
- - also returns lost plasma protein to blood stream - Transports dietary lipids
- - plus lipid soluble vitamins (A, D, E and K) - Carries out immune responses
Lymphatic vessel pathway
Blood capillaries –> interstitial space –> lymphatic capillaries –> lymph vessels –> lymph trunks –> lymph ducts –> veins
Lymphatic capillaries
- Located in the spaces between cells
- Have terminal (closed) ends on one end
- Cells overlap so interstitial fluid flows in by not out
- when pressure greater in interstitial fluid, cells separate; when greater in lymph, cells adhere - Unite to form lymphatic vessels
- HIghly permeable
Anchoring filaments
Contain elastic fibres; attach lymphatic endothelial cells to surrounding tissues.
Also when excess interstitial fluid accumulates and tissues swell, filaments are pulled and openings between cells increase.
Lacteals
Specialized lymphatic capillaries in small intestines that carry dietary lipids into lymphatic vessels
Chyle
Lymph containing dietary lipids drained from small intestine, carried in lacteals. Appear creamy white.
Principle Lymph Trunks
- Lumbar (lower limbs, wall and viscera of pelvis, kidneys, adrenals, abdominal walls)
- Intestinal (stomach, intestines, pancreas, spleen, part of liver)
- Bronchomediastinal (thoracic wall, lung, heart)
- Subclavian (upper limbs)
- Jugular (head and neck)
Lymph Ducts
- Thoracic (Left Lymphatic) Duct
- - begins ate Cisterna Chyli
- - located anterior to L2
- - main duct for return of lymph to blood
- - receives from: R&L lumbar trunks; R&L intestinal trunks; Left jugular trunk; left subclavian trunk; left bronchomediastinal trunk - Right Lymphatic Duct
- - Receives lymph from the: Right jugular, Right subclavian, and Right bronchiomediastinal trunk
Where do the lymph ducts drain?
Thoracic (Left Lymphatic) duct drain into venous blood at the junction of the left internal jugular and left subclavian veins
Right Lymphatic duct drains into venous blood at the junction of the right internal jugular and right subclavian veins
Like veins, lymph flow is affected by
Valves
Skeletal muscle pump
Respiratory pump
Primary lymphatic organs
Where stem cells divide and become immunocompetent
Red bone marrow and thymus
Secondary lymphatic organs
Sites where most immune responses occur
Lymph nodES, spleen, lymph nodULES
Pluripotent cells in the RBM give rise to:
- Mature immunocompetent B Cells
2. Pre-T cells
Thymus
Bilobed
In mediastinum, between sternum and aorta
Two lobes divided by CT capsule
Each lobule contains outer cortex and inner medulla
Mature T cells leave thymus via blood and travel to lymph nodes, spleen, and other lymphatic tissue.
Large in infants; after puberty not so much. Gets replaced by adipose and areolar CT
Trabeculae (thymus)
Extension of the CT capsule which penetrate inward and divide each lobe into lobules
Outer cortex (thymus)
Receive pre-T cells from RBM
Dendritic cells (derived from monocytes) assist T cell maturation
Epithelial cells: produce thymic hormones; educate pre-T cells through Positive Selection
Macrophages: clear out debris
Only 2% of developing T cells survive
Inner medulla (thymus)
Mature T cells
Epithelial cells: created clusters called thyme (Hassall’s) corpuscles. (function unknown)
Dendritic cells
Macrophages.
Lymph nodes
Secondary lymphatic organs
Usually occur in groups
Encapsulated
Important Lymph Nodes
Neck 1. supraclavicular Arms 2. axillary 3. cubital Legs 4. inguinal 5. popliteal Thorax 6. paraspinal 7. parasternal
Trabeculae (lymph)
Capsular extension which:
- divide lymph node into compartments
- provide support
- provide a route for blood vessels
Stroma (lymph)
Structural supportive framework
Composed of :
- capsule
- trabeculae
- reticular fibres
- fibroblasts
Parenchyma (lymph)
Functional part of lymph node Composed of: 1. Superficial cortex a. outer cortex b. inner cortex 2. Deep medulla
Lymphatic sinuses
In lymph nodes
Series of irregular channels that contain branching reticular fibres, lymphocytes and macrophages
Route through lymph node
Afferent lymphatic vessels
Subcapsular –> trabecular –> medullary sinuses
Efferent lymphatic vessels emerging from hilum
Hilum
Fissure of depression through which nerves or blood vessels enter an organ.
Lymphatic nodules (in lymph nodes)
Found in the outer cortex. Mostly secondary lymphatic nodules.
Primary Lymphatic Nodules
composed mostly of B cells
Secondary Lymphatic Nodules
Form in response to anagenetic challenge
Sites of plasma cell and memory B cell formation
Inner lymphatic cortex
In superficial cortex of lymphatic node.
Consists mainly of T cells and dendritic cells (APC/support cells) that enter lymph cell from other tissue
Spleen
Largest single mass of lymphatic tissue
Located in left hypochondriac region between stomach and diaphragm
Splenic artery, vein and efferent lymphatic vessel travel through hilum
Splenic arteries – central arteries – white pulp – B and T cells carry out immune functions
Structure of spleen
Encapsulated by dense CT, covered by visceral peritoneum (serous membrane)
Trabeculae extend inwards from capsule
Splenic stroma
Capsule +
Trabeculae +
Reticular fibres +
Fibroblasts
Splenic parenchyma
White Pulp: lymphatic tissue; lymphocytes and macrophages arranged central arteries of spleen
Red Pulp: blood filled venous sinuses and cords of splenic tissue called splenic (Bilroth’s) cords. Closely associated with veins.
3 Functions of Red Pulp
- Removal by macrophages of ruptured, worn out or defective blood cells or platelets
- Storage of platelets (up to 1/3 supply)
- Fetal hemopoesis
Ruptured Spleen
Most often damaged in abdominal trauma
Can cause significant haemorrhage and shock
After splenectomy, RBM and liver can take over some of the functions
Lymphatic Nodules
Eggs shaped masses of lymphatic tissue
NOT encapsulated
Scattered through lamina propria of mucous membranes lining GI, urinary, reproductive and respiratory tracts = MALT (mucosa associated lymphatic tissue)
Often small and solitary, but can occur in aggregations.
Where lymphatic nodules aggregrate
Tonsils Pharyngeal/adenoid x 1 Palentine x 2 Lingual x 2 Peyer's Patch (ileum of small intestine)
Innate Immunity
Non-specific immunity
Includes external and internal defences
First line of defence (innate immunity)
- skin - epidermis
- physical barrier, plus shedding removes microbes
- mucous membranes
What elements of the muscosa combine to help first line of defence?
Mucus Hairs Cilia Lacrimal apparatus Saliva Lysosomes Effluents (urine, vaginal secretions, barfing) Chemicals -- all acidic to discourage bacterial growth
Second line of defense
- Antimicrobial substances
- - Interferon
- - Complement
- - Iron binding proteins
- - Antimicrobial Proteins - Natural killer cells and phagocytes
Interferon
IFN
Released by virus-infected cells
Interfere with viral replication in neighbouring cells
Complement
Normally inactive proteins in blood plasma and plasma membranes
When infected enhance immune reactions:
–> cytolysis
–> phagocytosis (opsinization)
–> inflammation (histamine release, chemotaxis)
Iron binding proteins
inhibit bacterial growth by reducing amount of available iron (transferrin, lactoferrin, ferreting, hemoglobin)
Antimicrobial proteins
Short peptides that have a broad spectrum of antimicrobial activity
ex. dermicidin, defensin, catherlicidins, thrombocidin
Natural Killer Cells
5-10% lymphocytes in blood. Also in spleen, lymph nodes and RBM
Attack any cell with unusual plasma membrane proteins
Release perforins and granzymes
Perforins
Cytokine released by NK cells that act like spears, poking holes in the membrane of the target cells
Granzymes
Cytokine that causes target cell to undergo apoptosis. Released by NK cells
Phagocytes
Neutrophils and macrophages
5 steps of phagocytosis
- Chemotaxis
- Adherence
- Ingestion
- Digestion
- Killing
Inflammation
Nonspecific response of the body to tissue damage.
Characterized by swelling, heat, altered function, redness and pain.