Untitled Flashcards Set

# Functions of tissue fluid:

Tissue fluid is the fluid that bathes all cells. The area between vessels and cells is lined with this tissue fluid. Tissue fluid has all the components of plasma, excluding plasma proteins.

Capillaries transport blood through the tissues - blood contains all the materials that a cell required for metabolism.

- The range of substances have to pass from the plasma and red blood cells, into the tissues and then into the cells. They do this by diffusing through the fluid and then into the fluid surrounding the cells (the tissue fluid).

Tissue fluid is a solution of oxygen, fatty acids, amino acids, glucose, hormones and ions. These all pass into the cells from the tissue fluid - Waste products pass out of cells into tissue fluid.

>**The functions of the tissue fluid are to:**

>- Bathe all cells

>- Help maintain a constant environment around cells (homeostasis)

>- Supply oxygen, glucose, hormones and ions to cells.

>- Remove waste from cells.

## Formation of tissue fluid:

Blood enters a capillary bed from an arteriole.

![[Pasted image 20250306131803.png|300]]

Blood in arterioles has a high hydrostatic pressure - Capillaries are a single layer of endothelial cells; these cells have gaps between them called fenestrations which mean the capillaries are leaky.

- The high hydrostatic pressure forces fluid out through the fenestrations. As plasma proteins are too large to leave, they lower the water potential of blood.

- There is an opposing force due to the hydrostatic pressure as the osmotic gradient between tissue fluid and blood means water enters the capillary by osmosis.

At the arterial end of the capillary, the hydrostatic pressure difference exceeds the water potential difference, the net movement is out of the capillary.

As fluid is lost, blood passes through the capillary, the hydrostatic pressure of the blood is reduced. This loss of water means that the water potential is lowered.

- At the venule end of the capillary bed, the osmotic difference exceeds the hydrostatic pressure difference, meaning the water is reabsorbed into the blood by osmosis.

In total, the rate of tissue fluid formation is greater than the rate of reabsorption. Excess tissue fluid diffuses into blind ending lymph vessels.

- Lymph circulates in the lymphatic system and drains into the blood stream by the thoracic duct. ![[Pasted image 20250306132553.png]]

## Factors affecting tissue fluid formation:

Oedema is swelling caused by more tissue fluid being formed than can be reabsorbed or drained by the lymph vessels.

Kwashiorkor is caused by severe protein deficiency. A lack of protein in the blood raises the water potential, meaning that at the venule end of the capillary, the osmotic gradient is lower than normal. Less tissue fluid is reabsorbed, and the accumulation causes oedema.

Blockage of lymph vessels, by parasites or external pressure from tumours, means that less tissue fluid is drained into the lymph vessels, causing oedema.

High blood pressure can also cause oedema by increasing the hydrostatic pressure, forcing more fluid out of the capillaries.