## Blood Pressure Blood pressure is a critical physiological parameter that reflects the efficiency of the cardiovascular system. It is closely linked to the and the . * **Definition**: The force exerted by the blood against any unit area on the inner walls of a blood vessel. * **Measurement**: * Standard reference: Mercury (Hg) manometer (Sphygmomanometer). * Unit: Millimetres of mercury (mm Hg). * *Explanation*: A reading of 100 mm Hg means the pressure is sufficient to lift a column of mercury 100 mm high. ## Types of Arterial Blood Pressure Arterial blood pressure fluctuates in response to the cardiac cycle. ### Systolic Pressure * **Definition**: The highest arterial blood pressure recorded during the cardiac cycle. * **Occurrence**: Occurs when the ventricles of the heart contract (systole), forcefully pushing blood into the aorta and pulmonary arteries. ### Diastolic Pressure * **Definition**: The lowest arterial blood pressure recorded during the cardiac cycle. * **Occurrence**: Occurs when the ventricles of the heart relax (diastole) and are filling with blood from the atria. ## Factors Affecting Blood Pressure Blood pressure is not static and is regulated by several factors, including peripheral resistance and blood volume. Regulation is often mediated by . * **Peripheral Resistance**: The friction between blood and the walls of the blood vessels. Vasoconstriction increases resistance and BP, while vasodilation decreases it. * **Cardiac Output**: The volume of blood pumped by the heart per minute. * **Blood Volume**: Regulated largely by the kidneys; a decrease in volume (e.g., dehydration) leads to a decrease in BP. ## Clinical Significance Monitoring blood pressure is essential for diagnosing . * **Hypertension**: Persistent high blood pressure (usually above 140/90 mmHg), which can lead to or stroke. * **Hypotension**: Abnormally low blood pressure. * **Kidney Function**: Blood pressure significantly impacts the , specifically the glomerular filtration rate.