Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 124

Neural control of blood pressure is particularly important for changes in posture or when engaging in strenuous physical activities. The baroreceptor responses highlighted below are classic examples of homeostatic negative feedback (Chapter 2) where deviations from normal systolic and diastolic BP are resisted and BP is normalised.

Many things can cause a drop in BP but a common cause is suddenly standing up (Figure 3.11).

Figure 3.11 Neural responses to decreased BP

In the situation in Figure 3.11, gravity will pull arterial blood downwards (arteries have no valves), leading to a significant drop in BP. If BP is not restored rapidly, there is a risk of reducing cerebral blood flow, potentially leading to dizziness and fainting (syncope). This phenomenon is termed postural hypotension or orthostatic intolerance and becomes more common with age. An understanding of postural hypotension is essential for nurses, so to develop your understanding further read through Janet’s case study before attempting Activity 3.4.