6.5 Blood pressure regulation

Blood pressure regulation is crucial for maintaining proper blood flow to organs. The body uses multiple systems to keep pressure in check, including the baroreceptor reflex for quick adjustments and the renin-angiotensin-aldosterone system for long-term control.

Understanding these mechanisms is key to grasping how the body maintains homeostasis in the cardiovascular system. Factors like cardiac output, vessel diameter, and blood volume all play a role in regulating blood pressure and ensuring adequate organ perfusion.

Factors Affecting Blood Pressure

Determinants of Blood Pressure

Top images from around the web for Determinants of Blood Pressure

• 

  Blood Flow, Blood Pressure, and Resistance · Anatomy and Physiology View original

  Is this image relevant?

• 

  Blood Flow, Blood Pressure, and Resistance | Anatomy and Physiology View original

  Is this image relevant?

• 

  Cardiac Physiology · Anatomy and Physiology View original

  Is this image relevant?

• 

  Blood Flow, Blood Pressure, and Resistance · Anatomy and Physiology View original

  Is this image relevant?

• 

  Blood Flow, Blood Pressure, and Resistance | Anatomy and Physiology View original

  Is this image relevant?

1 of 3

Top images from around the web for Determinants of Blood Pressure

• 

  Blood Flow, Blood Pressure, and Resistance · Anatomy and Physiology View original

  Is this image relevant?

• 

  Blood Flow, Blood Pressure, and Resistance | Anatomy and Physiology View original

  Is this image relevant?

• 

  Cardiac Physiology · Anatomy and Physiology View original

  Is this image relevant?

• 

  Blood Flow, Blood Pressure, and Resistance · Anatomy and Physiology View original

  Is this image relevant?

• 

  Blood Flow, Blood Pressure, and Resistance | Anatomy and Physiology View original

  Is this image relevant?

1 of 3

• Blood pressure is determined by cardiac output and total peripheral resistance
• Cardiac output is the product of heart rate and stroke volume
• Stroke volume is influenced by preload (end-diastolic volume), contractility of the heart muscle, and afterload (the pressure the heart must overcome to eject blood during systole)
• Total peripheral resistance is determined by the diameter of the blood vessels, primarily the arterioles
  • Vasoconstriction increases resistance while vasodilation decreases resistance

Factors Influencing Vessel Diameter and Blood Viscosity

• Vessel diameter is influenced by neural and hormonal factors
  • Sympathetic nervous system causes vasoconstriction
  • Local factors like nitric oxide cause vasodilation
• Blood viscosity also affects peripheral resistance
  • Higher viscosity, as seen in polycythemia (increased red blood cell count), increases resistance to blood flow

Baroreceptor Reflex for Blood Pressure Regulation

Baroreceptor Function and Location

• Baroreceptors are stretch receptors that detect changes in blood pressure
  • Located in the walls of the carotid sinuses and aortic arch
• When blood pressure rises, the baroreceptors are stretched, sending increased action potentials to the cardiovascular center in the medulla oblongata

Cardiovascular Center Response to Baroreceptor Input

• The cardiovascular center responds to increased baroreceptor input by:
  • Increasing parasympathetic activity
  • Decreasing sympathetic activity
• This leads to a decrease in heart rate, contractility, and peripheral resistance
• Conversely, when blood pressure falls, the baroreceptors are stretched less, decreasing the firing rate of action potentials to the cardiovascular center
  • The cardiovascular center responds by decreasing parasympathetic activity and increasing sympathetic activity
  • This causes an increase in heart rate, contractility, and peripheral resistance
• The baroreceptor reflex is a negative feedback mechanism that operates on a moment-to-moment basis to maintain blood pressure within a normal range

Renin-Angiotensin-Aldosterone System and Blood Pressure

Renin-Angiotensin-Aldosterone System (RAAS) Overview

• The RAAS is a hormone system that regulates blood pressure and fluid balance
• When blood pressure or blood volume decreases, the juxtaglomerular cells in the kidneys secrete renin into the bloodstream
• Renin catalyzes the conversion of angiotensinogen, produced by the liver, into angiotensin I
• Angiotensin-converting enzyme (ACE), primarily found in the lungs, converts angiotensin I into angiotensin II

Effects of Angiotensin II and Aldosterone

• Angiotensin II is a potent vasoconstrictor that increases peripheral resistance and raises blood pressure
  • Also stimulates the release of aldosterone from the adrenal cortex
• Aldosterone promotes sodium and water retention by the kidneys, increasing blood volume and blood pressure
• Angiotensin II also stimulates the release of antidiuretic hormone (ADH) from the posterior pituitary gland
  • ADH increases water reabsorption in the collecting ducts of the kidneys
• The RAAS is a slower-acting mechanism compared to the baroreceptor reflex, but it plays a crucial role in long-term blood pressure regulation and fluid balance

Consequences of Hypertension vs Hypotension

Hypertension

• Hypertension, or high blood pressure, is a persistent elevation of blood pressure above 130/80 mmHg
• Chronic hypertension can lead to damage to the blood vessels, heart, brain, kidneys, and eyes
  • Increases the risk of atherosclerosis (hardening of the arteries), heart attack, stroke, heart failure, and kidney failure
• Hypertension is often asymptomatic, which is why it is called the "silent killer"
  • Regular blood pressure monitoring is essential for early detection and management

Hypotension

• Hypotension, or low blood pressure, is a persistent blood pressure below 90/60 mmHg
• Acute hypotension can cause dizziness, fainting, and shock due to inadequate perfusion of vital organs (brain, heart, kidneys)
• Chronic hypotension is less common than hypertension and may be caused by conditions such as dehydration, blood loss, heart failure, or endocrine disorders (hypothyroidism, adrenal insufficiency)
• Treatment of hypertension and hypotension depends on the underlying cause and may include lifestyle modifications (diet, exercise), medications (antihypertensives, vasopressors), or addressing any underlying medical conditions