Physiology Of The Lymphatic System Flashcards
What is lymph fluid composed of?
Water
Protein
Cells (lymphocytes, bacteria, viruses and debris)
Fatty acids
Coagulation factors
Electrolytes
What is the difference between blood and lymph?
- Blood is red vs. lymph which looks like plasma
- Blood clots more easily than lymph
- Blood contains RBC, WBC and platelets whereas lymph contains WBC’s
- Blood carries oxygen and more digested food vs. lymph which carries waste products and larger proteins
- Blood is filtered by the kidneys vs lymph which is filtered by lymph nodes
- Blood is pumped by the heart. Lymph system has no pump
- Blood capillaries connect arteries and veins vs lymph capillaries are blind ended
How does fluid get from the blood to the lymphatic system?
- Hydrostatic pressure
- Osmotic pressure
- Filtration
- Reabsorption
In a steady state, fluid flows continuously from one compartment to another to the next. How many litres per day does the the lymph system turnover?
8litres
What is the main process of fluid exchange and what is it affected by?
Filtration is the main process of fluid exchange. It is affected by hydrostatic pressure and osmotic absorption
Filtration is a type of?
Hydrostatic pressure that forces fluid out of the capillaries.
What is filtration (blood capillary pressure) influenced by and where is the pressure greatest?
It is influenced by interstitial pressure and is greatest on the arterial side and less on the venous side
Filtration (interstitial fluid pressure) is a type of……….and is exerted by the……..on the blood capillary surface. It’s tends to be ………..and therefore draws fluid ………..in to the ………
Filtration (interstitial fluid pressure) is a type of HYDROSTATIC PRESSURE and is exerted by the INTERSTITIUM on the blood capillary surface. It’s tends to be NEGATIVE and therefore draws fluid OUTWARDS in to the INTERSTITIUM.
What is osmosis?
Water movement due to proteins
Reabsorption by blood capillaries occurs ……. in most tissue and …….in a steady state.
Reabsorption by blood capillaries occurs rarely in most tissue and not in a steady state.
What is active hyperemia?
Increased capillary permeability. Eg. Heat, exercise and inflammation.
Dilation of precappilary sphincter ➡️blood flow increases ➡️blood capillary pressure increases➡️filtration increases ➡️lymphatic load increases
What is passive hyperaemia?
Increased capillary hydrostatic pressure e.g DVT, congestive heart failure, CVI (causes venous oedema).
Obstruction of venous return ➡️blood backs up in the capillaries ➡️blood capillary pressure increases ➡️filtration increases➡️lymphatic load increases
What does lymphatic load refer to?
To the amount of substances and fluid that have to be removed from the interstitium by the lymphatic system
What is lymph time volume?
The amount of lymph transport in a unit of time. The LTV of the thoracic duct is 1-4L per day
What is transport capacity of the lymphatic system equal to?
The maximum lymph time volume. Our lymph system usually works at 10% of its capacity
Lymphatic drainage is determined by:
The functional integrity of the lymphatic circulation and the extrinsic muscle pump during exercise
What are the 5 main types of oedema?
- Lymphoedema
- Dependency related oedema
- Traumatic oedema
- Venous oedema
- Systemic causes (cardiac malnourishment, kidney failure)
What is lymphatic fluid?
Refers to fluid once it is inside the lymphatic vessels eg. When it enters the lymph capillaries
What are types of oedema/insufficiency?
High output failure
Low output failure
Combined insufficiency
Haemodynamic insufficiency
Explain high output failure
Normal transport capacity with increased lymphatic load. It occurs due to overload of filtration into tissue e.g infection
Increased venous pressure ➡️ increased load ➡️ lymph transport increases ➡️lymph system attempts to return fluid back to venous system where the pressure is higher ➡️Patient eventually develops lymphoedema
Explain low output failure
Decreased transport capacity and normal lymph node
Describe the process of lymphoedema
Lymphoedema is caused by an accumulation of protein rich fluid in the interstitium.
The interstitial fluid stagnates with the accumulation of protein, macromolecules, hyaluronic acid, fat, water and cell debris.
Hypertension develops in the lymphatics that are still functioning causing further damage.
Secondary degenerative changes in the tissue and chronic inflammation develop due to the impaired lymph transport of immune cells
What is the revised Starling principle?
It was originally thought that there was an equilibrium between filtration and reabsorption
HOWEVER
Filtration is the main process that controls fluid exchange and prevails in a steady state. Reabsorption occurs rarely in s steady state.
This means the lymphatic system has a greater role to play in fluid movement than previously believed
Name the four mechanism that fluid, electrolytes, gases and modules transverse the capillary epithelium
- Diffusion
- Bulk flow (through pores and clefts) - small water soluble substances
- Vesicular transport (cell wall encases proteins and pushes it to the other side)
- Active transport
