14.1: Blood Pressure
Blood pressure (BP) is the pressure or force of blood exerted on the artery's walls as it circulates through the body. It is essential for maintaining blood flow throughout the body.
The average BP in an adult is typically around 120/80 mmHg (millimeters of mercury). In this measurement, the numerator (120) indicates the systolic pressure, which is the pressure in the arteries during the contraction of the heart's ventricles as blood is expelled. The denominator (80) represents the diastolic pressure in the arteries when the heart is at rest and the ventricles refill with blood.
BP regulation involves several interconnected physiological processes:
Hormonal Control: Hormones significantly influence BP regulation. When BP decreases, the adrenal medullae release adrenaline (epinephrine) and noradrenaline (norepinephrine). These hormones increase cardiac output (the volume of blood the heart pumps per minute) and contractility (the strength of the heart's contraction), thereby raising BP.
Neural Control: The autonomic nervous system, consisting of the sympathetic and parasympathetic systems, modulates BP. The sympathetic nervous system induces vasoconstriction (narrowing of blood vessels), increasing BP, often during stress or physical activity. Conversely, the parasympathetic system promotes vasodilation (widening blood vessels), decreasing BP during rest.
Renal Control: The kidneys also play a crucial role in BP regulation through the renin-angiotensin-aldosterone system (RAAS). When low BP is detected, the kidneys release renin, which converts angiotensinogen, a plasma protein, into angiotensin I. The lung's angiotensin-converting enzyme (ACE) converts angiotensin I to angiotensin II, a potent vasoconstrictor.
Additionally, angiotensin II stimulates aldosterone secretion from the adrenal cortex, promoting sodium and kidneys reabsorbing water and boosting blood volume and blood pressure.
Understanding these mechanisms is vital for clinical practice, especially in managing patients with hypertension or hypotension. Nurses regularly monitor BP and interpret the values to assess cardiovascular health, adjust medications, and provide appropriate care.
