How tissue fluid leaves and returns

Science · The Human Body · ages 17-18

Name ______________________ Date ____________

Which of these stays inside the blood at the capillary?
- Glucose
- Plasma proteins
- Water
Which force pushes fluid out of the capillary?
- Hydrostatic pressure of the blood
- Osmotic pull of tissue proteins
- Suction from the lymph vessels
At which end of the capillary does fluid filter out?
- The venule end, where the pull is weakest
- The middle, where the forces exactly balance
- The arteriole end, where the push is strongest
Blood protein falls after illness. Why do the ankles swell?
- The outward push vanishes completely
- The inward pull weakens so fluid strands in tissues
- Lymph vessels start absorbing extra protein
Why is most fluid reabsorbed at the venule end?
- The pull wins because the push has faded
- The wall becomes fully waterproof there
- Lymph vessels pump it back directly
Blood pressure rises sharply. What happens to tissue fluid?
- More fluid is forced out, which can cause oedema
- All filtration stops at the arteriole end
- Water potential reverses and pushes fluid out
About 20 litres filter out daily and about 17 return directly. How many litres travel in the lymph?
Answer: ______________
A student says hydrostatic pressure rises toward the venule end, driving reabsorption. What is wrong?
- Pressure falls along the capillary, and the pull drives reabsorption
- No fluid is ever reabsorbed at the venule end
- Hydrostatic pressure pulls fluid inward everywhere

Answer key

For grown-ups. Fold this page away before handing over the rest.

Plasma proteins · Plasma proteins are too big to cross, while small cargo slips through.
Hydrostatic pressure of the blood · Hydrostatic pressure is the outward push. The water potential gradient pulls inward.
The arteriole end, where the push is strongest · At the arteriole end the push beats the pull, so fluid leaves there.
The inward pull weakens so fluid strands in tissues · Less protein means a weaker inward pull, so more fluid stays out.
The pull wins because the push has faded · Hydrostatic pressure falls along the capillary while the inward pull stays steady.
More fluid is forced out, which can cause oedema · Higher pressure means a stronger push out than the system can reclaim.
3 · The lymph carries the remainder: 20 minus 17 is 3 litres.
Pressure falls along the capillary, and the pull drives reabsorption · The push fades along the capillary. Reabsorption happens because the pull wins there.