Describe the balance of hydrostatic and oncotic pressure at the arteriole end of the capillary bed?
Hydrostatic pressure is much higher than oncotic pressure
What is the result of the hydrostatic pressure being much higher than the oncotic pressure at the arteriole end of the capillary bed?
Get movement of fluid from arteriole end of capillary into interstitial space
What is the function of the movement of fluid from arteriole end of capillary to interstitial space?
Bathes cells, delivering glucose etc. that the cells need
What macromolecules leak through the capillary wall into interstitial space?
- Smaller proteins
- Cell debris
What happens to the balance between hydrostatic pressure and oncotic pressure as you pass across the capillary bed?
- Hydrostatic pressure has dropped due to the loss of fluid
- Oncotic pressure remains almost the same
What is the result of the decrease in hydrostatic pressure across the capillary bed?
There is a higher pull into the capillary than push out, so at the venule end you get fluid going back into the capillary
Is the net filtration of fluid the same as the net reabsorption of fluid at the capillary bed?
No, about 9/10 of what is filtered is reabsorbed
What happens to the 1/10 of fluid that is not reabsorbed at the venule end of the capillary bed?
It remains in interstitial space along with proteins, bits of cellular debris, and bacteria, and is drained by lymph
Why do proteins, bits of cellular debris, and bacteria remain in the interstitial space?
They can't get back through the capillary pores
What would happen if we didn't have a lymphatic system?
Would get lots of fluid pooling in the interstital space, and so become very oedematous
When is fluid called lymph?
As soon as tissue fluid and the things it contains pass into the lymphatic capillaries
What does lymph consist of?
- Tissue fluid
- Small proteins
- Lipids (chylomicrons from gut lymphatics)
- Damaged cells
- Cancer cells
How much lymphatic fluid is produced each day?
What does the lymphatic system do?
Continuously removes remaining tissue fluid (and macromolecules such as proteins) from extracellular space back to blood circulation
What is the clinical relevance of the lymphatic system?
Provides route for spread of infection and malignant disease
What are the features of lymphatic flow?
- One directional
- Low pressure system
- No central pump
What allows the one directional flow in the lymphatic system?
- Endothelial cells in the lymphatic capillary act as one way valves to the entry of lymph
- Valves prevent backflow
- Passive and intrinsic constriction
What is passive constriction of lymphatic vessels?
Something from outside helping to squeeze the tubes of lymph vessels
What outside forces contribute to passive contriction?
- External constriction of the muscle that the lymphatic vessel is running through
- Pulsation of an artery running next to lymph vessel
What vessels can perform intrinsic compression?
Larger lymphatic vessels
What happens in intrisinic compression of lymph vessels?
As lymphatic vessels stretch, they contract due to smooth muscle in their walls, therefore as they start to fill with fluid, autonominously contract
Describe the pathway of lymph fluid
- Lymphatic capillary (small to large)
- Afferent lymphatic vessel
- Lymph node
- Efferent lymphatic vessel
- Lymphatic ducts
- Venous circulation
What is the result of their being multiple points of entry from a single lymphatic duct, but only one exit?
Slows down flow
What is the advantage of slowed flow in lymph nodes?
So that whatever is in the lymph node can start to do its roles and functions
What does the lymphatic system drain into?
Where does the lymphatic system drain into the venous circulation on the left?
The junction between left internal jugular and left subclavian
Where does the lymphatic system drain into the venous circulation on the right?
Between right internal jugular vein and right subclavian vein
Where does the right lymphatic duct drain?
- Right side of face
- Right arm
- Right hemithorax
Everything else drained by left
Why is lymph not returned to the artery?
Because the pressure difference is too great