Blood pressure

• Blood Pressure

  Refers to Arterial Pressure, usually reported in millimeters of mercury (mmHg)
• To Keep Blood Moving

  1. The heart must generate sufficient pressure to overcome the resistance to blood flow in the pulmonary and systemic circuits

  2. F = ΔP/R

  3. F- blood flow

  4. ΔP- difference in pressure between to points

  5. R – resistance

  6. Flow is directly proportional to the pressure and inversely proportional to resistance
• Pressure Gradient

  • The largest pressure gradient is found between the base of the aorta and the proximal ends of the peripheral capillary beds
  • Cardiovascular control centers can alter this pressure gradient, and change the rate of capillary blood flow, by adjusting cardiac output and peripheral resistance

  
• Three Values of Cardiovascular Pressure

  • Blood Pressure
  • Capillary Hydrostatic Pressure/Capillary Pressure
  • Venous Pressure
• Blood Pressure


  • Average systemic arterial pressures range from 100 mmHg at the entrance of the aorta to 35 mmHg at the start of the capillary bed
  • Arterial Pressure is not constant; it rises during ventricular systole and falls during ventricular diastole
  • Systolic Pressure - peak blood pressure during ventricular systole
  • Diastolic Pressure - minimum blood pressure at the end of ventricular diastole
  • Recorded as systolic/diastolic (120/80)
  • Pulse Pressure - difference between systolic and diastolic pressures
  • Mean Arterial Pressure = diastolic pressure + 1/3 pulse pressure
• Capillary Hydrostatic Pressure/Capillary Pressure

  Pressures decline from 35 mmHg to 18mmHg along a typical capillary
• Venous Pressure

  Pressure within the venous system, quite low, pressure gradient from the venules to the right atrium is only 18 mmHg
• Total Peripheral Resistance

  • The resistance of the entire cardiovascular system that the circulatory pressure must be sufficient to overcome
  • The arterioles contribute the most to peripheral resistance
• Total Peripheral Resistance

  • Reflects a combination of factors: Vascular Resistance, Blood Viscosity, Turbulence
• Vascular Resistance

  • The resistance of blood vessels is the largest component to Total Peripheral Resistance
  • The most important factor in vascular resistance is friction between blood and vessel walls
  • Depends on vessel length and vessel diameter

  
• Total Blood Vessel Length

  • The longer the vessel the greater the resistance
  • Fairly constant in healthy individuals
• Blood Vessel Diameter


  • The smaller the blood vessel diameter the greater the resistance – BP must increase to maintain flow
  • Small arterioles that can change their diameter under neural or chemical controls are the major determinants of peripheral resistance
  • Fatty plaques on blood vessel walls also affect resistance

  
• Plaque Formation in Blood Vessels
• Blood Viscosity

  • Internal resistance to flow in fluids due to interactions among molecules and suspended material
  • Related to the thickness of the fluid
  • The greater the viscosity the greater the resistance
  • Therefore, more force is required to keep the fluid moving – BP must increase
  • Blood viscosity is fairly constant in healthy individuals
• Venous Return


  • The movement of deoxygenated blood from the tissues to the heart (right atrium)
  • Blood pressure in the venous system is significantly lower than in the arterial system
  • BP at the aorta is 100mmHg and at the capillaries is 35mmHg
  • BP in venules is 18mmHg and at the venae cavae is 2mmHg
  • Although venous pressures are low veins offer little resistance
  • As blood flows toward the heart veins become larger, resistance declines and the velocity of blood flow increases
• Venous Return


  1. When you stand, blood flowing from areas below the heart must overcome gravity as it ascends within the inferior vena cava

  2. Two main factors aid low venous pressures in propelling blood toward the heart: Muscular Compression/Skeletal Muscle Pump, Respiratory Pump
• Venous Return

  • Smooth Muscles in walls of veins constrict under sympathetic stimulation increasing venous return
  • Cardiac Output – maintains blood flow throughout the vascular system because it is a closed system
  • Gravity – increases venous return from areas above the heart

  
• Blood flows from the right side to the lungs where it picks up oxygen.
• Oxygenated blood then returns to the left side of the heart through pulmonary veins.
• Oxygen-rich blood then returns to the left side of the heart via pulmonary veins.
• From there, it travels through the aortic valve into the aorta and out to the rest of the body.
• From there, it pumps out into the rest of the body via the aorta.
• Deoxygenated blood returning from the body enters the superior and inferior vena cavae on the right side of the heart.
• Deoxygenated blood returning from the body enters the right side of the heart through the superior and inferior vena cava.
• The cycle repeats itself with deoxygenated blood returning to the right atrium and starting over again.
• From there, it travels out to the rest of the body through the aorta.
• The right atrium receives deoxygenated blood from the superior and inferior vena cavae.
• The atria contract simultaneously, pushing blood through the tricuspid and bicuspid (mitral) valves into their respective ventricles.
• Capillaries allow for the exchange of nutrients, waste products, and gases between the bloodstream and cells.
• Arteries carry blood away from the heart while veins bring blood back towards the heart.
• Arteries carry oxygenated blood away from the heart towards the organs and tissues of the body.
• The heart has four chambers - two atria (right & left) and two ventricles (right & left).
• The ventricles contract together, forcing blood out of the heart through the semilunar valves.
• Systole is when the ventricles are pumping blood out of the heart.
• Blood is pumped by the right ventricle into the pulmonary artery which carries it to the lungs.
• Blood is pumped by the ventricles (lower chambers) of the heart.
• Blood is pumped by the left ventricle into the arteries that carry oxygen-rich blood throughout the body.
• Atrial systole occurs when both atria contract simultaneously, pushing blood into the ventricles.
• Oxygen-poor blood returns to the right atrium of the heart through the veins.
• Ventricular diastole follows as the ventricles relax and fill up with blood.