Formation of tissue fluid (WJEC A-level Biology)

This lesson describes how tissue fluid is formed and reabsorbed in order to emphasise its importance as the link between the blood and cells. The PowerPoint and accompanying resources have been designed to cover point (h) in topic 3 of AS unit 2 of the WJEC A-level Biology specification and explains how a combination of the effects of hydrostatic pressure and oncotic pressure results in the formation of tissue fluid in animals.

The lesson begins with an introduction to the arteriole and venule end of a capillary as these will need to be considered as separate entities when describing the formation of tissue fluid. A quick quiz competition introduces a value for the hydrostatic pressure at the arteriole end and students are challenged to first predict some parts of the blood will move out of the capillary as a result of the push from the hydrostatic pressure and this allows oncotic pressure to be initially explored. The main part of the lesson uses a step by step guide to describe how the net movement is outwards at the arteriole end before students will use this guidance to describe what happens at the venule end. In the concluding part of the lesson, students will come to recognise oedema as a condition where tissue fluid accumulates and they again are challenged to explain how this occurs before they finally learn how the fluid is returned to the circulatory system as lymph