Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 62

The normal range for blood glucose is roughly between 4 and 6 mmol/l (Figure 2.1). When blood glucose rises, for example after eating a slice of sweet cake, this is detected by the pancreas and the hormone insulin is released. Insulin stimulates cells throughout the body to take up glucose from the blood; gradually blood glucose levels return back towards the set point. Conversely, if carbohydrates are not consumed for a few hours, e.g. you have just gone to bed and fallen asleep, blood sugar will fall and the hormone glucagon is released from the pancreas, stimulating the liver to release glucose increasing concentrations back towards the set point.

Figure 2.1 Homeostatic control of blood glucose via negative feedback

The regulation of blood glucose described above is a classic example of negative feedback; here two antagonistic hormones are constraining a variable within its normal range by minimising any deviations from the physiological set point.

If a variable remains consistently outside of its normal physiological range then pathological (disease) states usually occur. In the case study at the start of the chapter, Ian’s blood glucose was recorded at 24.5 mmol/l, which is greatly outside its normal range of 4–6 mmol/l. As a patient with type II diabetes, over time Ian had become progressively resistant to the effects of his own insulin. Without an effective insulin response to reduce his blood glucose, Ian arrived at his GP surgery with pronounced hyperglycaemia (see next section).

In some patients with type II diabetes insulin injections are also prescribed to help lower their blood glucose. Occasionally, particularly when the patient has not eaten enough carbohydrate, insulin injections can lead to blood glucose dropping below its normal range; this is referred to as hypoglycaemia. Hypoglycaemia is extremely dangerous and can potentially lead to coma and death unless treated quickly. Fortunately, most patients who use insulin learn to become aware of the early warning signs of hypoglycaemia (e.g. feeling shaky and disorientated) and carry something sweet such as a bar of chocolate or some biscuits to quickly boost their blood glucose.