dr myat lu5

• Circulatory routes


  Systemic, pulmonary and peripheral circulation

  
• Systemic and pulmonary circulation

  • They are in series, 2 sides of heart pumps same amount of blood
  • Systemic circulation has high pressure and resistance, pulmonary circulation has low pressure and resistance
  • Pulmonary vessels have greater distensibility and compressibility

  
• Heart


  • Consists of two pumps: right ventricle pumps blood through the lungs, left ventricle pumps blood through the systemic circulation

  
• Blood circulation


  1. Enters right atrium, passes through to right ventricle, flows out through pulmonary artery to the lungs

  2. From the lungs, blood returns to the heart through pulmonary vein into left atrium, then enters left ventricle, where it is pumped to the body through aorta

  
• Heart valves


  • Bicuspid valve (inlet to the left ventricle)
  • Tricuspid valve (inlet to the right ventricle)
  • Aortic valve (outlet from the left ventricle)
  • Pulmonary valve (outlet from the right ventricle)

  
• Blood flow (BF)


  Velocity of BF is inversely related to cross-sectional area of blood vessels<|>Volume of blood flows through any tissue in a given period of time (mL per minute)<|>Circulation time is approximately 1 minute at rest
• Ohm's Law


  Describes the relationship between volts (V), current (I) and resistance (R) in electrical circuits<|>Can be used to calculate blood flow: BF = ΔP / R
• Blood flow vs. resistance

  • Blood flow through a blood vessel is determined by pressure difference and vascular resistance
  • Peripheral resistance is the most important factor influencing local blood flow

  
• Resistance


  Depends on blood viscosity, total blood vessel length, and blood vessel radius<|>Most resistance is in arterioles, capillaries and venules
• Types of blood flow

  • Laminar (streamline) flow is normal, turbulent flow occurs at or above certain critical velocity or when obstruction is encountered

  
• Blood pressure (BP)


  Pressure exerted by blood on the wall of a blood vessel (mmHg)<|>BP = cardiac output x peripheral resistance<|>Systolic BP (120 mmHg) and diastolic BP (80 mmHg)

  
• Cardiac output


  Amount of blood the heart pumps through the circulatory system in 1 minute<|>Cardiac output = stroke volume x heart rate

  
• Pulse pressure


  Difference between systolic BP and diastolic BP<|>Represents the force that the heart generates each time it contracts<|>A useful predictor of cardiovascular disease

  
• Pulse rate


  Number of times the arteries create a noticeable 'pulse' due to blood pressure (because of heart contraction)<|>Pulse rate is essentially the heart rate
• Mean arterial pressure (MAP)

  diastolic BP + (pulse pressure ÷ 3)

  
• Cardiac output


  Amount of blood the heart pumps through the circulatory system in 1 minute
• Pulse pressure (PP)


  Difference between systolic BP and diastolic BP<|>Represents the force that the heart generates each time it contracts<|>A useful predictor of cardiovascular disease (CVD) esp. in older population. E.g. coronary heart disease (CHD), heart attack, stroke

  
• Normal pulse pressure


  40-60 mmHg
• Pulse pressure


  • Increases, cardiac output decreases = heart failure
  • Increases, risk of CVD, atrial fibrillation (irregular heartbeats) increases
• Pulse rate (Heart rate)

  Ejection of blood from the left ventricle into the aorta produces a pressure wave = pulse<|>Pulse rate = number of times the arteries create a noticeable 'pulse' due to BP (∵ heart contraction)<|>Heart rate = number of times the heart beats in a minute<|>Pulse rate is essentially the heart rate<|>Pressure wave travels rapidly along the arteries<|>Pulse can be felt at locations where large arteries are close to body surface – strongest at arteries closest to heart<|>Radial artery at the wrist is most commonly used to feel pulse<|>Monitoring of pulse is important clinically = heart function

  
• Resting pulse rate (heart rate)

  60-100 beats/minute
• Bradycardia


  Slow heart (< 60 bpm)
• Tachycardia


  Fast heart (> 100 bpm)
• Measurement of blood pressure (1)

  1. Auscultatory Method

  2. BP is usually measured in left brachial artery using a sphygmomanometer and a stethoscope

  3. BP cuff is inflated to high pressure, then the pressure is decreased slowly

  4. BP at which turbulent blood flow is first heard = systolic BP (SBP) = blood is first forced through brachial artery during systole

  5. BP at which sounds disappear = diastolic BP (DBP) = brachial artery remains completely open and non-turbulent blood flow produces no sound

  6. The turbulence produces vibrations in the blood and surrounding tissues that can be heard through stethoscope = Korotkoff sounds

  
• Resting blood pressure for a healthy adult

  Systolic BP = 120 mmHg<|>Diastolic BP = 80 mmHg
• Hypertension


  Systolic BP > 140 mmHg<|>Diastolic BP > 90 mmHg
• Blood pressure is reported as 120 / 80 mmHg
• American College of Cardiology (2017) lowered the definition of high blood pressure to account for complications that can occur at lower numbers and to allow for earlier intervention
• Factors that influence arterial blood pressure

  Cardiac output<|>Peripheral resistance

  
• Cardiovascular regulation


  1. Autoregulation = causes immediate, localized homeostatic adjustments

  2. Neural mechanism = responds quickly to changes at specific sites

  3. Endocrine mechanism = directs long-term changes
• Regulation of blood pressure

  1. Short-term mechanism = regulate blood vessel diameter, heart rate and contractility

  2. Long-term mechanism = regulate blood volume

  
• Neuroendocrine regulation of blood pressure

  • Neural regulation
  • Hormonal regulation
• Hormones that DECREASE arterial blood pressure

  • Atrial natriuretic peptide (ANP)
  • Brain natriuretic peptide (BNP)
  • C type natriuretic peptide
  • Vasoactive intestinal polypeptide (VIP)
  • Acetylcholine
  • Bradykinin
  • Histamine
  • Prostanoids/autocoids (prostaglandin E, thromboxane, prostacyclin)
• Hormones that INCREASE arterial blood pressure

  • Renin-angiotensin-aldosterone system (RAAS)
  • Epinephrine and norepinephrine (NE)
  • Adrenalin or noradrenaline
  • Antidiuretic (ADH) or vasopressin
  • Thyroxine
  • Serotonin
• Microcirculation (Capillary Network)


  An arteriole giving rise to a capillary network<|>The network forms numerous branches<|>Blood flows from capillaries into venules<|>Blood flow through capillaries is regulated by smooth muscle cells (called precapillary sphincters)<|>Precapillary sphincters constrict = blood flow decreases<|>Precapillary sphincters dilate = blood flow increases
• Capillary exchange (1)


  1. Nutrients diffuse across capillary walls into tissue spaces

  2. Waste products diffuse in the opposite direction

  3. A small amount of fluid is forced out of the capillaries into tissue spaces at their arterial ends

  4. Most of the fluid reenters the capillaries at their venous ends

  5. 2 major forces are responsible for fluid movement through the capillary wall: Blood (Hydrostatic) pressure forces fluid out of capillary, Osmotic (Oncotic) pressure moves fluid into the capillary
• Osmotic pressure


  Due to the concentration of blood proteins (albumin, fibrinogen) dissolved in the blood<|>Capillary wall acts as a selectively permeable membrane, which prevents proteins from moving from the blood into the interstitial space (tissue)<|>Follows Starling's Law of the capillaries: Filtration is almost equal to reabsorption
• Capillary exchange (3)


  1. Movement of fluid out of the capillary (resulting from blood pressure) > Movement of fluid into the capillary (resulting from osmosis)

  2. Net movement of fluid out of the capillary into the tissue space

  3. At the Arterial End: Filtration

  4. At the Venous End: Reabsorption
• Capillary exchange (4)


  1. Movement of fluid out of the capillary (resulting from blood pressure) < Movement of fluid into the capillary (resulting from osmosis)

  2. Net movement of fluid from the tissue space into the capillary
• Capillary exchange (5)


  HP = Hydrostatic Pressure (outward) – due to blood pressure<|>OP = Oncotic Pressure (inward) – due to plasma proteins<|>Net filtration – Net absorption = Net outflow