Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 123

Two specialised regions are located within the medulla oblongata (inferior portion of the brain stem) which can rapidly either raise or lower the BP to match the body’s current needs. The cardioregulatory centre or cardiac centre regulates the heart rate and hence the cardiac output (CO). The vasomotor centre regulates vascular tone by controlling the diameter of blood vessels (vasodilation or vasoconstriction). By regulating vascular tone, the vasomotor centre is able to increase or decrease the peripheral resistance (PR).

Both the cardiac and vasomotor centres require a continuous ‘real-time’ measurement of the current BP. This is achieved using specialised stretch receptors called baroreceptors which are located in the walls of the aortic arch and carotid sinuses (bulbous regions of the carotid arteries in the neck). Measuring the degree of stretch gives a good measure of current BP, with more stretch equating to a higher BP and less stretch indicative of a lower BP. In humans the aortic arch baroreceptors relay information to the cardioregulatory and vasomotor centres via the vagus nerve and the carotid sinus baroreceptors via the glossopharyngeal nerve (Figure 3.10).

Figure 3.10 Baroreceptor response