Unit 5: Section 2

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3.5.4 Homeostasis is the maintenance of a constant internal environment. Principles

Homeostasis in mammals involves physiological control systems that maintain the

internal environment within restricted limits.

The importance of maintaining a constant core temperature and constant blood pH in relation to enzyme activity.

The importance of maintaining a constant blood glucose concentration in terms of energy transfer and water potential of blood. Temperature control

The contrasting mechanisms of temperature control in an ectothermic reptile and an endothermic mammal.

Mechanisms involved in heat production, conservation and loss.

The role of the hypothalamus and the autonomic nervous system in maintaining a constant body temperature in a mammal. Control of blood glucose concentration

The factors that influence blood glucose concentration.

The role of the liver in glycogenesis and gluconeogenesis.

The role of insulin and glucagon in controlling the uptake of glucose by cells and in activating enzymes involved in the interconversion of glucose and glycogen. The effect of adrenaline on glycogen breakdown and synthesis.

The second messenger model of adrenaline and glucagon action.

Types I and II diabetes and control by insulin and manipulation of the diet.

3.5.5 Negative feedback helps maintain an optimal internal state in the context of a dynamic equilibrium. Positive feedback also occurs. Principles

Negative feedback restores systems to their original level.

The possession of separate mechanisms involving negative feedback controls departures in different directions from the original state, giving a greater degree of control.

Positive feedback results in greater departures from the original levels.

Positive feedback is often associated with a breakdown of control systems, e.g. in temperature control.

Candidates should be able to interpret diagrammatic representations of negative and positive feedback. Control of mammalian oestrus

The mammalian oestrous cycle is controlled by FSH, LH, progesterone and oestrogen.

The secretion of FSH, LH, progesterone and oestrogen is controlled by interacting negative and positive feedback loops.

Candidates should be able to interpret graphs showing the blood concentrations of FSH, LH, progesterone and oestrogen during a given oestrous cycle. Changes in the ovary and uterus lining are not required.

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