describe the principles of cell signalling using the example of the control of blood glucose concentration by glucagon, limited to: • binding of hormone to cell surface receptor causing conformational change • activation of G-protein leading to stimulation of adenylyl cyclase • formation of the second messenger, cyclic AMP (cAMP) • activation of protein kinase A by cAMP leading to initiation of an enzyme cascade • amplification of the signal through the enzyme cascade as a result of activation of more and more enzymes by phosphorylation • cellular response in which the final enzyme in the pathway is activated, catalysing the breakdown of glycogen

outline the main stages in the process of cell signalling leading to specific responses: • secretion of specific chemicals (ligands) from cells • transport of ligands to target cells • binding of ligands to cell surface receptors on target cells

state the functions of tissue fluid and describe the formation of tissue fluid in a capillary network