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• Blood pressure


  The pressure exerted by the blood on the wall of arteries
• The term 'blood pressure' generally refers to arterial blood pressure
• Arterial blood pressure


  Expressed as systolic blood pressure and diastolic blood pressure
• Systolic blood pressure


  The maximum pressure exerted in the arteries during systole of the heart. Normal range is 90-140 mmHg.
• Diastolic blood pressure


  The minimum pressure exerted in the arteries during diastole of the heart. Normal range is 60-90 mmHg.
• Pulse pressure


  The difference between systolic and diastolic pressure
• Mean arterial blood pressure

  Diastolic pressure + 1/3 of pulse pressure
• Arterial blood pressure


  • Directly proportional to cardiac output, heart rate, peripheral resistance, blood volume, venous return, viscosity of blood
  • Inversely proportional to elasticity of blood vessels, diameter of blood vessels

  
• Blood pressure is inversely proportional to the elasticity of blood vessels
• Cardiac output and total peripheral resistance are the most important factors affecting blood pressure
• Blood pressure


  Determined by cardiac output multiplied by peripheral resistance
• Regulatory mechanisms of blood pressure

  • Nervous mechanism (short-term)
  • Renal mechanism (long-term)
  • Hormonal mechanism
  • Local mechanism

  
• Nervous mechanism for regulation of blood pressure


  • Rapid, operates only for a short period, then adapts to new pressure
  • Operates through the vasomotor system
• Components of the vasomotor system

  • Vasomotor center
  • Vasoconstrictor fibers
  • Vasodilator fibers
• Vasomotor center


  Bilaterally situated in the reticular formation of medulla oblongata and lower pons, consists of vasoconstrictor area, vasodilator area, and sensory area
• Vasoconstrictor area


  Also called the pressor area, sends impulses to blood vessels through sympathetic vasoconstrictor fibers, stimulation causes vasoconstriction and rise in blood pressure
• Vasodilator area


  Also called the depressor area, suppresses the vasoconstrictor area and causes vasodilatation, involved with cardio inhibition
• Sensory area


  Receives sensory impulses from baroreceptors via glossopharyngeal and vagal nerves, controls the vasoconstrictor and vasodilator areas
• Vasoconstrictor fibers


  Belong to the sympathetic division of the autonomic nervous system, cause vasoconstriction by releasing noradrenaline which acts on alpha receptors of smooth muscle fibers in blood vessels
• Vasodilator fibers


  • Parasympathetic vasodilator fibers (release acetylcholine)
  • Sympathetic vasodilator/cholinergic fibers (release acetylcholine, important for increasing blood flow to skeletal muscles during exercise)
• Mechanism of action of vasomotor center in regulation of blood pressure

  1. Receives impulses from baroreceptors and chemoreceptors

  2. Inhibits vasoconstrictor area and excites vasodilator area when blood pressure rises

  3. Reduces vasomotor tone, causing vasodilatation and decreased peripheral resistance

  4. Simultaneously decreases heart rate and force of contraction, reducing cardiac output

  5. These factors bring blood pressure back to normal
• Baroreceptor mechanism


  Baroreceptors in carotid sinus and aortic arch are activated by rise in blood pressure, send stimulatory impulses to nucleus of tractus solitarius, which inhibits vasoconstrictor area and excites vasodilator area, leading to decreased peripheral resistance and cardiac output, bringing blood pressure back to normal
• Chemoreceptor mechanism


  Peripheral chemoreceptors in carotid and aortic bodies are sensitive to lack of oxygen, excess carbon dioxide and hydrogen ions in blood, which occurs when blood pressure decreases, they excite the vasoconstrictor center, increasing blood pressure