Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 58

Recently Ian has been waking up several times during the night to pass urine; as a result, he has a permanently dry mouth and a raging thirst which he has been able to relieve by drinking from the large bottle of water which he now keeps on his bedside cabinet. These disturbances to his sleep have left Ian permanently exhausted and of late it has been a real struggle to even get out of bed in the morning. While at work Ian has been tired and crotchety and has found it increasingly difficult to concentrate on even the simplest tasks.

During an appointment with his GP a random blood glucose reading of 24.5 mmol/l was recorded and a urine sample revealed the presence of large amounts of glucose. Ian was asked to return the following morning after skipping breakfast to have his fasting blood glucose level recorded, which at 11.2 mmol/l confirmed his GP’s suspicion of diabetes mellitus and Ian was promptly referred to his local diabetes clinic. Further tests confirmed that Ian has type II diabetes mellitus which he is currently managing via a combination of diet, exercise and drugs.

To ensure optimal health, the cells of the human body need to be maintained within a stable environment with minimal fluctuations in temperature, pH and chemical composition, otherwise pathological states may arise. This chapter will explore the mechanisms by which key internal variables of the body are maintained and balanced. We shall begin by defining homeostasis and exploring the nature of the negative feedback mechanisms that allow variables to be held within their normal ranges. We shall then examine the role of the endocrine and nervous system in maintaining homeostasis and highlight problems that may occur when these mechanisms do not function optimally. Finally, we shall introduce the concept of positive feedback and highlight how positive feedback mechanisms differ from those of negative feedback. Throughout the chapter we shall link the often abstract concepts of homeostasis to common clinical scenarios encountered by nurses.