Select your language

Suggested languages for you:
Log In Start studying!
StudySmarter - The all-in-one study app.
4.8 • +11k Ratings
More than 3 Million Downloads
Free
|
|

All-in-one learning app

  • Flashcards
  • NotesNotes
  • ExplanationsExplanations
  • Study Planner
  • Textbook solutions
Start studying

Tissue Fluid

Save Save
Print Print
Edit Edit
Sign up to use all features for free. Sign up now
Tissue Fluid

Tissue fluid is a watery liquid distinct from the blood surrounding body cells. It brings nutrients and oxygen to the cells and removes wastes products.

The functions of tissue fluid

Tissue fluid serves two functions in the body:

  1. Bathes the tissues - tissue fluid can seep into tiny gaps between cells (i.e. enter intercellular spaces) where capillaries cannot reach.

  2. Facilitates exchange of materials (e.g., glucose) between cells and the blood - tissue fluid allows contact between cells and the blood.

How is tissue fluid formed?

Tissue fluid is ‘leaked plasma’ formed from blood plasma leaking out of capillaries via fenestrations in the capillary endothelium.

Fenestrations describes the tiny holes found on the surface of capillaries.

As the body has intrinsic mechanisms to regulate the composition of blood plasma (i.e. homeostasis), tissue fluid has a mostly constant environment. In other words, the composition of tissue fluid is stable without much variation.

Differences between tissue fluid and blood

Although the tissue fluid is formed from the blood plasma, both fluids differ in composition.

Tissue fluid and blood plasma have these in common:

  • Solutes - glucose, amino acids, ions

  • Gases - oxygen

  • Metabolic wastes - water, carbon dioxide

Tissue fluid mainly lacks large plasma proteins (e.g., albumin) and red blood cells present in the blood plasma. These are too large to pass through the small fenestrations of the capillaries. The tissue fluid will still contain white blood cells, as their flexibility lets them squeeze through the fenestrations.

Study tip: Don’t write ‘tissue fluid is lacking in proteins’ in exams as it contains small proteins, such as hormones like insulin. Just state ‘tissue fluid lacks large plasma proteins (e.g., albumin)’ instead.

How are materials transferred between capillaries and tissue fluid?

Do you recall that tissue fluid is formed from plasma that leaks out of the capillary fenestrations? The volume of plasma fluid that leaves the capillary to form tissue fluid results from two opposing pressures - osmotic and hydrostatic pressures. Therefore, the transfer of materials between capillaries and tissue fluid undergoes pressure filtration. This process is when pressure differences push tissue fluid in and out of capillaries.

Oncotic/colloid osmotic pressure: pressure induced by the proteins.

Osmotic versus hydrostatic pressures in pressure filtration

As osmotic and hydrostatic pressures influence the formation of tissue fluid, these are two critical concepts to grasp to understand the process of pressure filtration:

  1. Osmotic (or oncotic) pressure - the tendency of pure water to enter a solution; this pressure causes tissue fluid higher in water potential to move into the capillary.

  2. Hydrostatic pressure - pressure in the capillary caused by the preceding arteriole; this pressure causes blood plasma to move out of the capillary.

Pressure filtration process

The arteriole carries blood at high pressures, whereas the venule carries blood at low pressures. Refer to the article on blood vessels for more information.

The pressure filtration process is divided into two steps:

  1. Plasma is pushed out from the capillaries at the arteriole end.

  • The arteriole end has a high hydrostatic pressure due to the high-pressure blood flow.

  • The osmotic pressure in the capillaries is high as more proteins reduce its water potential.

  • But hydrostatic pressure > osmotic pressure, so overall plasma moves out of the capillary as tissue fluid, losing oxygen and nutrients.

  1. Tissue fluid returns to the capillaries at the venule end.

  • The venule end has a low hydrostatic pressure due to the low-pressure blood flow.

  • As fluid is lost from the capillaries previously, the osmotic pressure in the capillaries is now higher.

  • Osmotic pressure > hydrostatic pressure, so overall tissue fluid moves in, gaining carbon dioxide and metabolic wastes in the process.

Disruption to the pressure filtration process can lead to a condition called oedema. This is when tissue fluid accumulates without returning to the venous end of the capillary. The buildup of fluid in oedema causes swelling, as shown in the diagram below. The most common cause of oedema is heart failure.

Another cause of oedema is a condition called kwashiorkor. Kwashiorkor results from protein deficiency, a lack of plasma proteins disrupts the osmotic pressure needed for tissue fluid to return to the capillaries. The fluid then accumulates in the belly area.

Tissue fluid in the lymphatic system?

Tissue fluid that is not returned to the capillaries is carried back to the lymphatic system via lymph vessels.

The lymphatic system is separate from the circulatory system. Lymph vessels of the lymphatic system begin in the tissues; the region of the lymph vessels near tissues often have dead ends. Dead ends are ends that do not connect with any vessels or tissues. Multiple lymph vessels across different parts of the body then merge into larger vessels that form a network throughout the body.

The fluid enclosed in lymph vessels is known as lymph.

When tissue fluid enters the lymphatic system, it becomes lymph. Therefore, lymph is similar in composition to tissue fluid, just a different name given as it is found in the lymphatic system.

Unlike the transport of blood where the heart is involved in pumping it across the body, the transport of lymph only relies on the contraction of the surrounding skeletal muscles. Hence, lymph flow is very slow. Through the thoracic duct, the largest lymph vessel, lymph travels at about 100 in a resting human. Lymph vessels adapt to the slow lymph flow by having valves to prevent backflow. The action of lymph valves in preventing backflow is similar to that of heart valves, whereby they shut whenever lymph flows in the unintended direction. Lymph contents eventually enter the left and right subclavian veins found in your shoulders, back into the vena cava.

Apart from preventing the backflow of lymph, lymphatic valves are also large enough to allow plasma proteins to enter. The role of lymphatic valves in regulating plasma protein entry, which allows plasma proteins to enter and prevent plasma proteins from leaking out, is crucial for if the rate of protein loss from plasma is not in balance with the lymph, this can also lead to oedema.

The lymphatic system has bean-shaped structures called lymph nodes. These contain specialised immune cells called lymphocytes that are involved in fighting infections.

Tissue Fluid - Key takeaways

  • Tissue fluid is a watery liquid surrounding cells, whose function is to bathe tissues and facilitate substance exchange between the cells and blood.

  • Tissue fluid is formed from ‘leaked plasma’. Unlike plasma, it does not contain large plasma proteins and red blood cells.

  • Materials are transferred between the capillary and tissue fluid via pressure filtration. At the arteriole end, the high hydrostatic pressure pushes the plasma out of the capillary. In contrast, the drop in hydrostatic pressure at the venule end causes the osmotic pressure to overpower, and tissue fluid returns to the capillary.

  • Tissue fluid that does not return to the veins gets drained into lymph vessels. Lymph vessels form the lymphatic system and have distinct properties.

Frequently Asked Questions about Tissue Fluid

Tissue fluid is a watery liquid distinct from blood that surrounds cells.

Tissue fluid is formed from the leakage of blood plasma out of capillaries into cellular spaces.

The transfer of substances between capillaries and tissue fluid follows a process called pressure filtration. Pressure filtration is dependent on both hydrostatic and osmotic pressures. At the arteriole end, the high hydrostatic pressure pushes plasma out of the capillaries. The low hydrostatic pressure at the venule end causes the osmotic pressure to overpower. Instead, venous return occurs as tissue fluid re-enters the capillaries.

Tissue fluid leaves the capillaries through the fenestrations of the capillary endothelium via a pressure-mediated process.

Capillaries act as a filter to stop larger particles in the blood (eg. red blood cells, albumin) from leaking out.

Final Tissue Fluid Quiz

Question

Outline two functions of tissue fluid.

Show answer

Answer

  1. Bathes the tissues - tissue fluid can enter intercellular spaces where capillaries cannot reach.
  2. Facilitates exchange of materials between cells and the blood - tissue fluid allows contact between cells and the blood.

Show question

Question

Tissue fluid is formed from blood plasma leaking out of capillaries via fenestrations in the capillary endothelium. True/ False

Show answer

Answer

True

Show question

Question

Suggest why tissue fluid has a constant environment.


Show answer

Answer

The composition of blood plasma, where tissue fluid is derived from, is controlled by homeostasis.

Show question

Question

Outline with examples, the similarities in the composition of both tissue fluid and blood plasma.


Show answer

Answer

Both tissue fluid and blood plasma contain:

  • Solutes - glucose, amino acids, ions

  • Gases - oxygen

  • Metabolic wastes - water, carbon dioxide

Show question

Question

Explain why tissue fluid lacks red blood cells and large plasma proteins but contains white blood cells.


Show answer

Answer

The fenestrations of the capillary endothelium are too small to allow red blood cells and large plasma proteins (e.g., albumin) to pass through. Even though the white blood cells are large, they are flexible and can squeeze through the fenestrations in the capillaries.

Show question

Question

Name the two opposing pressures that affect the volume of plasma that leaks out of capillaries.


Show answer

Answer

Hydrostatic and osmotic pressures

Show question

Question

Fill in the blanks

Osmotic pressure is the tendency of water to move from a ____to ____water potential. It is also known as _____ pressure. In pressure filtration, this pressure causes tissue fluid to move ____ the capillary.


On the other hand, ________ pressure is the pressure in the capillary caused by the preceding ________. This pressure causes blood plasma to move _____ ____the capillary.

Show answer

Answer

Osmotic pressure is the tendency of water to move from a high to low water potential. It is also known as oncotic pressure. In pressure filtration, this pressure causes tissue fluid to move into the capillary.


On the other hand, hydrostatic pressure is the pressure in the capillary caused by the preceding arteriole. This pressure causes blood plasma to move out of the capillary.

Show question

Question

Suggest why the osmotic pressure is higher in the capillaries than in tissue fluid.


Show answer

Answer

Tissue fluid has fewer proteins as large plasma proteins cannot leak out of the capillaries.

Show question

Question

Describe the pressure changes at the arteriole end during pressure filtration.


Show answer

Answer

As the blood flow in the arteriole is high in pressure, this results in a large hydrostatic pressure at the arterial end of the capillary bed. Plasma is then being pushed out. Though the high osmotic pressure provides resistance to the movement of plasma, overall there is more fluid that moves out than into the capillary. Oxygen and nutrients are lost from the capillary into the tissue spaces.

Show question

Question

Describe the pressure changes at the venule end during pressure filtration.


Show answer

Answer

The low-pressure blood flow in the venule leads to low hydrostatic pressure at the venule end of the capillary bed. The osmotic pressure at that end of the capillary is also higher as fluid is lost from the capillary previously. Consequently, the capillary has a net gain of fluid as the high osmotic pressure overcomes the resistance brought by the hydrostatic pressure. The capillary then gains carbon dioxide and metabolic wastes in the process.

Show question

Question

Outline what happens to tissue fluid that is not returned to the capillaries.


Show answer

Answer

Tissue fluid that is not returned to the capillaries enters the lymph vessels.

Show question

Question

Lymph vessels have dead ends. True/ False


Show answer

Answer

True

Show question

Question

Suggest why lymph is higher in fatty acids relative to blood plasma.


Show answer

Answer

Fatty acids get absorbed into the lacteal of intestinal villi that are connected to the lymphatic system.

Show question

Question

Explain why lymph flow is slow.


Show answer

Answer

Lymph flow is slow because the lymphatic system does not have its own ‘pump’. Lymph is transported through contraction of surrounding muscles, alongside valves in lymph vessels to prevent backflow.

Show question

Question

Lymphatic valves stop plasma proteins from entering as the loss of plasma proteins into the lymph can lead to oedema. True/ False


Show answer

Answer

False - lymphatic valves are large enough to allow plasma proteins to enter for there needs to be a balance of plasma proteins in both blood and lymphatic vessels to prevent oedema from occurring.

Show question

60%

of the users don't pass the Tissue Fluid quiz! Will you pass the quiz?

Start Quiz

Discover the right content for your subjects

No need to cheat if you have everything you need to succeed! Packed into one app!

Study Plan

Be perfectly prepared on time with an individual plan.

Quizzes

Test your knowledge with gamified quizzes.

Flashcards

Create and find flashcards in record time.

Notes

Create beautiful notes faster than ever before.

Study Sets

Have all your study materials in one place.

Documents

Upload unlimited documents and save them online.

Study Analytics

Identify your study strength and weaknesses.

Weekly Goals

Set individual study goals and earn points reaching them.

Smart Reminders

Stop procrastinating with our study reminders.

Rewards

Earn points, unlock badges and level up while studying.

Magic Marker

Create flashcards in notes completely automatically.

Smart Formatting

Create the most beautiful study materials using our templates.

Sign up to highlight and take notes. It’s 100% free.