CVS: Introduction to Lymphatics Flashcards
What is lymph and what does it contain?
- Formed from interstitial (tissue) fluid
- Fluid originates as a plasma filtrate
- Contains:
- Salts
- Proteins
- Fat
- Cells (mainly lymphocytes, but also dendritic cells + macrophages)
Think of it as the fluid that isn’t contained within blood vessels
What are lymph nodes?
Filter stations on drainage pathway for lymph fluid
Describe the function of the components of the lymphatic system
Consists of lymphatic vessels which absorb and direct fluid and immune cells, as lymph, from tissues to lymph nodes (+ other lymphoid organs) which act as filter stations to cleanse and initiate acquired immunity
Lymph glands are connected to lymph vessels. Lymph vessels absorb the microbes responsible for an infection and transport them to lymph glands.
In lymph glands, immune cells become sufficiently developed to produce resources to fight specific infections
What are secondary lymphoid organs?
Organs that acts a filters where foreign invaders e.g. microbes, are capture and lymphocytes, activated
What are 2 examples of mucosa-associated lymphoid tissues?
- Tonsils
- Peyer’s patches (small intestine, jejenum, ileum)
What are the primary lymphoid organs?
- Thymus
- Bone marrow
These generate lymphocytes from immature progenitor cells
What organs are the secondary lymphoid organs?
SLOs are defined structures comprising of lymph nodes, the spleen and mucosa-associated lymphoid tissue (MALT) where lymphocytes are activated
What are tertiary lymphoid organs (TLOs)?
Acquired loose lymph node-like immune cell clusters in tissues
What is the lymphatic system?
Countercurrent system (to heart) that drains waste materials from tissues and recycles surplus fluid, salts, proteins, fat and immune cells back to body
The lymphatic system is a network of drainage tubes connected to lymph glands which act as drainage channels for the body’s tissues
What are the functions of the lymphatic system?
- Fluid homeostasis
- Cellular drainage from tissues
- Immune surveillance
- Regulation of inflammation
- Facilitation of fat transport around body
How does the lymphatic system drain?
- Interstitial fluid drains into blind-ended lymphatic capillaries
- Muscles in walls of collecting vessels contract, push lymph proximally
- Contractions in arteries + skeletal muscles, breathing, BP and volume of lymph in lymphatic system can also influence the rate at which lymph is drained via the lymphatic vessels
- Valves along walls collecting vessels prevent lymph from flowing backwards
The endothelium has specialized cell junctions that allow the cell margins to act as one-way valves, permitting the entry of interstitial fluid into the lymphatic vessel while blocking its escape
What are the 2 types of lymphatic vessels?
- Smaller peripheral, non-contractile initial lymphatics (capillaries)
- Main contractile lymphatic collecting vessels
Describe the anatomy of the lymphatic capillaries
- Blind ended
- No smooth muscle
- Incontinuous basement membrane
Describe the anatomy of the collecting vessels
- Smooth muscle coverage
- Luminal valves
- Basement membranes
What does a tender lymph gland indicate?
Immune response to infection
Describe the functions of the lymphatic system
Provide pathways by which information regarding infection is transported from the affected tissues to sites, namely lymphoid organs, where an appropriate immune response can be generated
A second function is tissue immunosurveillance and prevention of infection
- Cellulitis is a common complication of impaired lymph drainage and is often recurrent. Impaired immune cell trafficking causes a failure to eradicate the infection.
Lymphatic system is also involved in fat transport:
- Impaired lymph drainage causes increased peripheral tissue fat deposition
Describe the role of Starling’s forces in the movement of fluids
Direction fluid movement cross capillary wall determined by predominantly by differences in hydrostatic pressure (capillaries) and osmotic (oncotic) pressure (interstitial fluid) b/w blood/plasma inside capillaries and interstitial fluid outside
What causes pulmonary oedema in heart failure?
Raised pulmonary venous pressure causing increased amounts of interstitial fluid which is not sufficiently cleared by lymph so congesting lung.
This interstitial oedema spills out into the alveoli and interferes with O2 exchange
- Lung generates lymph even though pulmonary capillary pressure lower than plasma COP
- Pulmonary capillaries are in filtration state bcs pulmonary interstitial protein concentration is high (70% of plasma). COP gradient is therefore lower than the hydraulic pressure gradient
- LS Heart failure increases pulmonary capillary pressure, increasing filtration. Unless lymph drainage increases accordingly, oedema occurs in lung parenchyma.
- Overflow of increased interstitial fluid into alveoli and impairment of O2 exchange
Describe tissue fluid homeostasis
Blood vessels supply fluid, lymph drains it away
Tissue fluid formed from plasma escaping through blood vessel wall.
Tissue (interstitial) fluid drains predominantly as lymph and not by venous reabsorption
What governs microvascular filtration?
Starling principle of fluid exchange:
Jv = LpS ((Pc - Pi) - s (pp - pi))
Where
- Lp= hydraulic conductance of capillary wall
- S = surface area for exchange
- P = pressure within capillary (c) or interstitium (i)
- s = osmotic reflection coefficient of capillary wall
- p = osmotic pressure of plasma (p) or interstitial fluid (i)
Outline the significance of cancer and the lymphatic system
- Cancer spreads preferentially by the lymphatic system
- Should part of a primary tumour break off, it can be carried in the lymph vessels, in a vesicle with monounsaturated oleate-containing lipids, into lymph nodes
- From the lymph nodes, the cancer can metastasise
- Sentinel lymph node biopsy is the recommended staging investigation for breast cancer
Name some diseases in which lymphatic disorder is involved
Resp: Asthma, Chronic airways disease
CVS: Hypertension, Plasma volume homeostasis, Atheroslerosis
CNS: Glaucoma, Dementia
Infection: HIV, Cellulitis, TB
Immunity: Organ, rejection, autoimmunity, wound healing
GI: Crohn’s
Cancer: Metastases
Obesity
Describe pitting oedema
- Indicates excess interstitial fluid
- Results from too much fluid filtration from blood vessels overwhelming lymph drainage or too little lymph drainage
Describe venous oedema
- Varicose veins or venous engorgement e.g. heart failure, creates high venous pressure and increased microvascular fluid filtration into tissues
- If lymph drainage is adequate, oedema can be avoided
What is chylothorax?
- Presence of lymphatic fluid (chyle) in pleural space
- Secondary to leakage from thoracic duct or one of its main tributaries
- Traumatic or iatrogenic (0.2-1% after thoracic surgery)
What is lymphoedema?
Swelling of any body site
Develop when lymphatic system cannot drain fluid properly from our tissues
Causes are:
- Cancer treatment
- Obesity
- Varicose veins, immobility
- Inflammatory skin disease
- BP drugs
- Trauma
- Primary lymphoedema
What causes lymphoedema?
- Increase filtration (e.g. venous hypertension)
- Impaired flow of lymph (e.g. abnormal development of lymphatic vessles - primary lymphoedema or interruption of lymphatic pathways - secondary lymphoedema)
Occurs when dominant fault is a failure of lymph drainage with no increase in capillary filtration (normal lymph load) e.g. breast cancer related lymphoedema, elephantitis.
What is primary lymphoedema?
Chronic oedema caused by a development abnormality of the lymphatic system, due to a genetic fault
Phenotypes vary in age of onset, site, inheritance patterns, associated features
What causes primary lymphoedema?
Due to inborn, presume genetic fault in lymph drainage
What is secondary lymphoedema caused by?
- Malignancy (disease/treatment)
- Infection (including filariasis)
- Inflammation (RA, psoriasis, eczema, acne, cutaneous Crohn’s)
- Medications (e.g. CCBs)
- Trauma
- Venous disease
- Immobility/ dependency
- Obesity
How can lymphoedema be managed?
- Treat underlying cause if possible
- ‘Conservative’ therapy (bandages, garments)
- Debulking surgery
- Lympathticovenous anastomosis surgery
- Lymph node transfer procedure
- Liposuction
Describe decongestive treatment for lymphoedema
- Principle to get most out of remaining lymph drainage capacity
- MLD massage
- Compression (intensive vs maintenance)
- Exercise
- Weight management
- Prevention of infection through:
- Skin care
- Antibiotic prophylaxis
