9.1, 9.2

• Homeostasis is the maintenance of internal environment in dynamic equilibrium within set limits around an optimum.
• Core temperature stability is important as it maintains a stable rate of enzyme-controlled reactions.
• Blood pH stability is important as it maintains a stable rate of enzyme-controlled reactions and optimum conditions for other proteins.
• Blood water potential stability is important to prevent osmotic lysis or crenation of cells.
• Negative feedback are self-regulatory mechanisms that return the internal environment to optimum when there is a fluctuation.
• Positive feedback are changes that result in an even greater deviation from the normal level when a fluctuation occurs.
• The mode of action of oestrogen involves a steroid hormone diffusing through the cell membrane, forming a hormone-receptor complex with ER 𝛼 receptor in the cytoplasm.
• Negative feedback involves receptors detecting deviation, coordinator, corrective mechanism by effector, and receptors detecting that conditions have returned to normal.
• Separate negative feedback mechanisms control fluctuations in different directions to provide more control, especially in case of 'overcorrection', which would lead to a deviation in the opposite direction from the original one.
• Hormones are proteins secreted by endocrine glands and transported in the bloodstream.
• The mode of action of adrenaline involves a secondary messenger model where hormone-receptor complex forms, conformational change to receptor activates G-protein, activates adenylate cyclase, which converts ATP to cAMP, cAMP activates protein kinase A pathway, and results in glycogenolysis.
• Specific tertiary structure is only complementary to receptors on certain cells.
• There is a time lag between hormone production and response by an effector because it takes time to produce hormone, transport hormone in the blood, and cause required change to the target protein.