Lymphatic System Flashcards
Organs and tissues
Lymph nodes
Spleen
Thymus
Tonsils
Red bone marrow
Three function of lymphatic system
- Fluid recovery:
• Absorb excess interstitial fluid and return to blood (~2 - 4 L/day)
• Excess fluid = lymphedema which is characterised by swelling - Immunity:
Contains immune cells
• Detects and removes foreign cells and chemicals from tissue - Lipid absorption:
• Lymphatic vessels called ‘lacteals’ absorb lipids not absorbed by capillaries particularly in the lining of small intestine
Components
- Lymph
• The recovered fluid - Lymphatic vessels
• Transport the lymph - Lymphatic tissue
• Composed of aggregates of lymphocytes and macrophages - Lymphatic organs
• Defense cells are especially concentrated
• Separated from surrounding organs by connective tissue capsules
Lymph
- Lymph
• Usually clear, colorless fluid like blood plasma but low in protein ( protein stays in the capillaries)
• Composition varies at different times and places.
+ After a meal, lymph from the small intestine is milky from lipid content
+Lymph leaving nodes is highly concentrated with lymphocytes
+ Can also contain macrophages,
hormones, bacteria, viruses, cell debris and cancer cells
Lymphatic capillaries only have one end
Interstitial fluid can only go into lymphatic capillaries it can’t leave it the same way it came in
Lymphatic vessels
• Lymph flows through lymphatic vessels
• Beginning of vessel network = lymphatic capillaries (terminal lymphatics)
• Penetrate almost every tissue
• Closed at one end
Consist of thin endothelial cells that loosely overlap
• Overlapping edges of the endothelial cells act as valves
• Gaps large enough for bacteria, lymphocytes, particles to pass to lymph fluid
• Formed from veins
• Larger lymphatic vessels:
• Tunica interna with an endothelium and valves
• Tunica media with elastic fibres and smooth muscle
• Thin outer tunica external
Lymphatic vessels pathway to bloodstream
Lymphatic capillaries -> collecting vessels - 11 lymphatic trunks -›
2 collecting ducts -› subclavian veins
• The vessels travel alongside veins and arteries
• Pass through multiple lymph nodes:
• Bacteria phagocytised
• Immune Cells monitor for foreign antigens
Flow of lymph
• Flow pressure is lower and speed of flow is slower than venous return
• Mechanisms:
1. Rhythmic contractions: vessels contract
when fluid stretches them
2. Skeletal muscle squeezing
3. Arterial pulsation
4. Thoracic (respiratory) pump
5. Rapid flowing of the bloodstream
• Flow speed increases with
EXERCISE
Lymphatic tissue
Lymphatic Cells
3. Lymphatic tissue
- Consists of lymphatic cells
- Scattered in mucous membranes of the respiratory, digestive, urinary and reproductive tracts
-Composed of variety of lymphocytes and other cells for defense and immunity:
1. Neutrophils
Aggressive anti-bacterial leukocytes
2. Natural killer (NK) cells
Large lymphocytes
Attack and destroy bacteria, ransplanted tissue, or cells that are infected with viruses or are cancerous Responsible for immune surveillance
3. T lymphocytes (T cells)
Mature in thymus
4. B lymphocytes (B cells)
Mature in bone marrow
Differentiate into plasma cells that produce antibodies
5. Macrophages
Very large, avidly phagocytic cells( engulf and digest a range of substances) of the connective tissue
Develop from monocytes
Phagocytize tissue debris, dead neutrophils, bacteria and other foreign matter
6. Dendritic cells
Alert immune system to pathogens that have breached their surface
Receptor-mediated endocytosis
7. Reticular cells
Act as antigen-presenting cells (APCs)
Contribute to connective tissue framework of the lymphatic organs
Diffuse lymphatic tissue and lymphatic nodules
Lymphatic Tissues
Aggregations of lymphocytes in connective tissues of mucosa membranes & organs
Diffuse lymphatic tissue
• Simplest form
• Lymphocytes scattered
• Located in body passages open to the exterior
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Respiratory, digestive, urinary and reproductive tracts
• ‘Mucosa-associated lymphatic tissue’ (MALT)
• Lymphatic nodules
• Lymphocytes and macrophages congregate in
masses = lymphatic nodules
• Nodules relatively constant in lymph nodes, tonsils, and appendix
Lymphatic organs
- 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
• Functions:
1. Hemopoiesis (blood formation);
2. Immunity - supplies lymphocytes
• Composition:
• Soft, loosely organized, highly vascular material
• Separated from osseous tissue by endosteum of bone
• Spaces between sinusoids occupied by hematopoietic tissue
• Composed of macrophages and blood cells
• Macrophages destroy malformed blood cells and nuclei discarded by developing erythrocytes( marcophages is what eliminates the nuclei)
Thymus
Member of the endocrine, lymphatic, and immune systems
• Houses developing lymphocytes (hormones regulate activity)
•Bilobed organ
• Located - superior mediastinum between the sternum and aortic arch
• Degeneration (involution) with age ( gets smaller with age)
•Cortical cells surround the blood capillaries and form a blood-thymus barrier
•From the cortex, T-cells migrate to the medulla
- Mature T-cells enter blood/ lymph vessels here and leave the thymus
• Epithelial cells secrete several signalling molecules that promote T-cells locally and systemically
Lymph node
• Most numerous lymphatic organs
• 450 - 600 in typical young adult
• Two functions
1. Cleanse the lymph
2. Act as a site of T and B cell activation( help with immune response)
• Secondary lymphatic organs
• Contain lymphocytes and macrophages
• Congregate around blood vessels in clusters
Physical description of lymph nodes
Lymph Nodes
• Bean-shaped structure enclosed in a fibrous capsule
- < 3cm long
- Outer cavity: reticular fibres, macrophages and dendritic cells
- Inner cavity: lymphocytes and antigen-presenting cells
• Cortex
- Encircle 4/5 of the organ
- Composed of ovoid to conical lymphatic nodules
-When fighting pathogens acquire a germinal centre where B cells multiply and differentiate into plasma cells
• Medulla
- Composed of lymphocytes, plasma cells, macrophages, reticular cells and reticular fibers
• Only organ that filters lymph ( unique role)
• Flows through lymph node -> lymph node = slow flow = well cleansed fluid before re-entering the bloodstream
• When challenged may become swollen and painful to touch (lymphadenitis)
• Cancers that metastasize often end up in lymph nodes
Lymph nodes location
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, adiacent 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
