The main factors that regulate blood pressure include:
- Cardiac output: Determined by heart rate and stroke volume, which are influenced by factors such as sympathetic stimulation, catecholamines (epinephrine, norepinephrine), thyroid hormones, and calcium levels.
- Systemic vascular resistance (or peripheral vascular resistance): Influenced by the anatomy of blood vessels and the degree of vasoconstriction or vasodilation, affected by vascular tone and compliance of the vessel walls.
- Blood volume: Regulated primarily by the kidneys through sodium and water retention or excretion, which affects central venous pressure and preload.
- Neurohumoral mechanisms: Including the baroreceptor reflex, renin-angiotensin-aldosterone system (RAAS), antidiuretic hormone (ADH or vasopressin), and atrial natriuretic peptide (ANP), which modulate heart rate, vascular resistance, and blood volume.
- Blood viscosity and elasticity of vessel walls: Blood viscosity affects resistance to flow, while vessel elasticity affects the ability to accommodate blood volume.
To organize these factors based on their physiological role:
- Factors affecting Cardiac Output
- Heart rate (regulated by autonomic nervous system)
- Stroke volume (inotropy, preload determined by venous return and blood volume)
- Factors affecting Systemic Vascular Resistance
- Vascular tone (vasoconstriction or vasodilation)
- Vessel compliance and elasticity
- Anatomy of vascular network
- Factors affecting Blood Volume and Preload
- Renal regulation of sodium and water (via RAAS and aldosterone)
- ADH-mediated water retention
- Blood volume changes (e.g., shifts due to posture)
- Neurohumoral Regulation
- Baroreceptor reflex (rapid response to pressure changes)
- RAAS (long-term blood pressure regulation)
- ADH (water retention and vasoconstriction)
- ANP (vasodilation and sodium excretion)
This grouping reflects the integrated control of blood pressure by cardiac performance, vascular resistance, and blood volume, modulated by neurohumoral feedback systems.