Formation of Tissue Fluid

As blood passes through the capillaries in tissues, some water along with many small water-soluble substances move out into the spaces between the cells of tissues. This movement is driven by high pressure in the arteries.

  • Retained Components: Larger proteins and most of the formed elements (RBCs, Platelets) remain in the blood vessels.
  • Resulting Fluid: The fluid released out is called the Interstitial Fluid or Tissue Fluid.

The fluid that collects between cells is called:

  • Tissue fluid / Interstitial fluid

Key Point:

  • Tissue fluid = Plasma minus proteins and RBCs

Properties and Importance of Tissue Fluid

Composition

  • Mineral/salt distribution is similar to plasma
  • Has much less protein than plasma
  • No RBCs

Why is tissue fluid important?

All exchange between blood and body cells happens through tissue fluid:

  • Nutrients go: Blood → Tissue fluid → Cells
  • Wastes go: Cells → Tissue fluid → Blood

Key Point:

  • Actual exchange medium = Tissue fluid (not directly blood → cells)

Lymphatic System (Drainage System)

If tissue fluid keeps collecting, tissues will swell. So the body has a special drainage network called the lymphatic system.

An elaborate network of vessels called the lymphatic system collects this fluid and drains it back to the major veins.

What does lymphatic system do?

  • Collects excess tissue fluid from spaces between cells
  • Carries it as lymph through lymph vessels
  • Finally returns it back to major veins (blood circulation)

Lymph = Tissue fluid inside lymph vessels

Characteristics of Lymph

  • Colourless fluid
  • Contains lymphocytes (WBCs)
  • Very few proteins compared to plasma
  • No RBCs

Functions of Lymph

1. Fluid Balance (Drainage)

  • Returns excess interstitial fluid back to blood
  • Prevents swelling (oedema)

2. Fat Absorption (Lacteals)

  • In small intestine villi, special lymph vessels called lacteals absorb fats (lipids)

3. Immunity / Defence

  • Lymph carries lymphocytes (B and T cells)
  • Lymph nodes filter germs and help immune response

4. Transport

  • Carries nutrients, hormones, and some wastes between tissues and blood

Lymph

  • Tissue fluid forms when plasma leaks out of capillaries
  • RBC + platelets stay inside, proteins mostly stay inside
  • Exchange medium = tissue fluid
  • Lymph = tissue fluid in lymph vessels
  • Lacteals absorb fats
  • Lymphocytes = immunity
  • Lymph returns fluid to major veins

💡 Questions and Answers

Q1: How is lymph different from blood?

Answer: Blood is red because it has RBCs and haemoglobin, and it has more proteins. Lymph is colourless, has no RBCs, has very little protein, and is rich in lymphocytes for immunity.

Key Points:

  • Blood: RBC present, more protein, red
  • Lymph: RBC absent, less protein, colourless, lymphocytes present

Q2: What is the main job of lacteals?

Answer: Lacteals are lymph vessels inside intestinal villi that absorb fats from digested food and carry them through lymph.

Key Points:

  • Lacteals = fat absorption
  • Present in intestinal villi

Q3: Where does tissue fluid finally go?

Answer: Extra tissue fluid is collected by lymph vessels and finally drained back into the major veins, so it becomes part of blood again.

Key Points:

  • Lymphatics collect excess fluid
  • Return it to major veins

Q4: Why is lymph important for immunity?

Answer: Lymph contains lymphocytes (B and T cells) and passes through lymph nodes, which help in fighting germs. So it supports the body’s defence system.

Key Points:

  • Lymphocytes = immune defence
  • Lymph nodes filter pathogens