Formation of Tissue Fluid

Question 1

Blood:

Answer 1

The fluid held in out blood vessels, consists of plasma containing blood cells (erythrocytes, leucocytes
[white]), dissolved O2, CO2, minerals, glucose, amino acids, hormones and plasma proteins and platelets.

Question 2

Tissue fluid:

Answer 2

The fluid surrounding cells and tissues, similar to blood plasma. Doesn’t contain most blood cells or plasma proteins as they are too large to be pushed out of the capillary walls.
It is formed by plasma leaking from the capillaries, it contains dissolved substances from the blood and supplies cells with these. This movement is mass flow, not diffusion.

Question 3

Lymph:

Answer 3

The fluid held in the lymphatic system, which is a system of tubes that returns excess tissue fluid back into the blood system. It is similar in composition to tissue fluid, however, contains more lymphocytes, as these are produced in lymph nodes.
Lymph nodes are swellings found at regular intervals along the lymphatic system. When a tissue is infected the capillaries become more leaky and more fluid (containing bacteria) is directed into the lymph system to the lymph nodes, where the lymphocytes kill them.

Question 4

Hydrostatic Pressure:

Answer 4

The fluid pressure. Water osmoses to where hydrostatic pressure is lower.
Oncotic Pressure: The pressure created by the osmotic effects of solutes (plasma proteins in capillaries). Water osmoses to where there is high oncotic pressure. It is negative, 0 means no solutes (i.e. pure water), the more solutes dissolved in the water the more negative the oncotic pressure – higher oncotic pressure.

Question 5

Tabel

Answer 5

Draw it.

Question 6

Formation of tissue fluid – Pressure filtration:

Answer 6

• When arteries reach tissues they branch into arterioles, and then
capillaries. So, blood flowing into organs/tissues is contained in
the capillaries.
• At the arterial end of the capillary the blood is at relatively high
hydrostatic pressure (higher than surrounding tissue fluid). This pressure pushes blood fluid out of the capillaries through the tiny gaps between cells in the capillary wall.
• The fluid that leaves the capillaries consists of dissolved nutrients and O2. All red blood cells, platelets and most white blood cells remain in the blood, as do plasma proteins – these are too large to fit through the gaps between cells in the capillary wall.
• The tissue fluid surrounds body cells, so exchange of gases and nutrients can occur across plasma membranes. The exchange occurs by diffusion, facilitated diffusion and active uptake.

Question 7

Returning into the blood:

Answer 7

• As the fluid leaves the capillaries the hydrostatic pressure decreases, so it is much lower at the end
closest to the venules.
• Oncotic pressure is generated by plasma proteins in the capillaries, it allows tissue fluid to re-enter
the capillary (due to hydrostatic pressure decreasing). At the venule end of the capillary bed, the water potential in the capillaries is lower than surrounding tissue fluid. There is a net inflow due to the difference in oncotic pressure being greater than the difference in hydrostatic pressure. This means some tissue fluid to returns to the capillary, carrying CO2 and other waste products of metabolism into the blood.
• Not all tissue fluid re-enters the blood – some is directed into the lymphatic system, where once inside a lymph vessel the tissue fluid is called lymph. This drains the excess tissue fluid out of the tissues and returns it to the blood system later.

Question 8

Oncotic pressure always opposes hydrostatic pressure:

Answer 8

• The hydrostatic pressure of the blood pushes fluid out of tissues, and the hydrostatic pressure of
  tissue fluid pushes fluid back into capillaries. Hydrostatic pressure is higher in the capillary then in the tissue fluid, so the net effect is fluid leaving the capillary. However, hydrostatic pressure is lower at the venule end than the arteriole end, due to fluid loss from blood to the tissue fluid (but still higher than in the tissue fluid).
• The oncotic pressure of the blood pulls water back into the blood, and the oncotic pressure of the tissue fluid pulls water into the tissue fluid. The oncotic pressure is usually constant in the blood fluid and in the tissue fluid.
  The net result of these forces creates a pressure that pushes fluid out of the capillary at the arteriole end (as the difference in hydrostatic pressure is greater than oncotic pressure), and into the capillary at the venule end (as hydrostatic pressure decreases, difference in oncotic pressure is greater than difference in hydrostatic pressure).