Week 2.0 - Lymphatics Flashcards
What is the ultimate aim of the lymphatic system?
-Continuous removal of excess tissue fluid and macromolecules such as proteins from the extracellular space back to the venous circulation
Describe the formation of tissue fluid
- Hyrdrostatic pressure at the arterial end of the capillary is greater than at the venous end -> more fluid leaves
- Oncotic pressure at the venous end is greater than at the arterial end -> more fluid returns
- Net difference between filtration and resorption = tissue fluid
- Also some small proteins leak into the interstitium due to the high pressure. These small proteins cannot get back into the capillaries as the pressure is not high enough to drive them back into the capillary
- This causes a small amount of fluid to also remain in the interstitium = tissue fluid
Why is it important to have lymph vessels?
-Tissue fluid would accumulate leading to oedema
Why is it possible for tissue fluid to be removed by lymphatic vessels but not capillaries?
-Lymphatic vessel walls are more porous than capillaries allowing absorption of tissue fluid and proteins into vessel
NB. Once the tissue fluid in the lymphatic vessel it is lymphatic fluid
Are the contents of lymph the same throughout the body?
- No it depends on site of drainage eg in the gut there is a high content of chyylomicrons
- Other contents are cell debris, damaged cells, bacteria, cancer cells etc
How much lymph is produced per day?
-3/4L
What is once major clinical disadvantage of lymphatic vessels?
-Route for spread of infection and malignant disease
State the order of lymphatic flow
-Tissue fluid -> Lymhatic capillary -> Afferent lymphatic vessel -> Lymph node -> Efferent lymphatic vessel -> Lymphatic trunk -> lymphatic duct
How are lymphatic vessels arranged relative to lymph nodes?
-Several afferent lymphatic vessels enter but only one efferent lymphatic vessel leaves
How is lymphatic fluid moved along vessels?
- No central pump
- Valves to ensure unidirectional flow
- Passive constriction by other structures which squash lymphatic vessels
- Intrinsic constriction by smooth muscle cells
In lymphoedema the pressure in the lymphatics reaches a very high level, why does the lymphatic fluid not leave the lymphatic capillaries?
-The endothelia of the lyphatic capillary are oraginsed in such a way that they can only be force open in one direction to allow tissue fluid in, once in the lymphatic capillary it cannot leave
Describe the regional drainage of the body relative to the lymphatic ducts
- Right lymphatic duct drains tissue fluid from right upper limb, right side of head and neck, right side of trunk upto belly button into right subclavian
- The left thoracic duct drains rest of the body into left subclavian
What is lymphoedema?
-Fluid retention and tissue swelling due to comprimised lymphatic system
State some causes of lymphoedema
- Removal/enlargement of lymph nodes
- Infections
- Damage to lymphatic system eg cancer treatment
- Lack of limb movement
- Congenital
What is a lymph node? Briefly describe its structure
- Connective tissue structure which contains large number of lymphocytes and macrophages, playing a key role in immune defence
- tought fibrous outer capsule with reticular connective tissue inside
