Week 28- The cardiovascular system II

• Blood pressure is not static, pulses due to waves of ventricular contraction from the heart
• Veins are more numerous than arteries, have larger diameter, hold more blood, and lie closer to the body surface
• The pressure wave travels 10x faster than the blood itself
• Systemic circulation

  Blood leaving LHS to Arterial system to Aorta to arteries to arterioles to branch - capillaries
• Cardiac Output = Total Blood Flow
• Blood flows from capillaries into small vessels-venules with thin exchange epithelium and little connective tissue
• Arterioles


  Direct distribution of blood flow to individual tissues by selectively constricting and dilating
• Capillaries have leaky epithelium allowing exchange of materials
• Pressure falls in the aorta during ventricular diastole
• Veins

  Act as a volume reservoir
• Blood vessel composition: Inner lining = thin layer of endothelial cells that secrete paracrine signals
• Arterioles


  The site of variable resistance
• If blood pressure falls too low

  Blood can be sent to the arterial side
• If flow out exceeds flow in, volume decreases and mean arterial pressure falls
• The volume of blood in the arteries is determined by input (cardiac input) and flow out (altered by changing resistance)
• Arterial blood pressure cycles, therefore a single value is used to represent the driving pressure from the heart
• Capillaries


  At the distal end, blood flows into the venous side of the circulation
• Pulmonary circulation

  Right ventricle to lungs to left ventricle
• Systemic circulation

  LHS heart to tissues to RHS heart
• Systemic circulation

  From capillaries to Venus system to small vessels to venules to veins to Vena cava to RHS
• Most blood vessel smooth muscle cells maintain a partial state of contraction influenced by signal molecules, hormones, neurotransmitters
• Highest pressure is in the aorta at ventricular systole
• Rapid pressure increase when the left ventricle pushes blood into the aorta can be felt as a pulse
• Veins have thinner walls than arteries, with less elastic tissue and expand easily
• Mean Arterial Pressure (MAP) = diastolic pressure + 1/3(systolic pressure - diastolic pressure)
• Some veins have internal one-way valves to prevent backflow of blood
• Pulse pressure is a measure of the strength of the pressure wave
• If flow in exceeds flow out, arteries volume increases and arterial pressure increases
• Variable diameter of arterioles represented by adjustable screws
• Traditionally “average” blood pressure value is 120/80 (varying within & between people)
• Arterial pressure (∆P)


  Cardiac output (Q) x Peripheral resistance (R)
• If flow out exceeds flow in

  Volume decreases & mean arterial pressure falls
• Control of blood pressure: CNS CVCC

  CNS co-ordinates control of blood pressure and distribution of blood to tissues
• Peripheral Resistance

  Resistance to blood flow from arterial blood vessels, primarily from arterioles (Determines blood flow leaving the arterial system)
• Cholesterol is carried in blood attached to protein carriers-apolipoproteins
• Cardiovascular disease (CVD)

  • Atherosclerosis
  • Ischaemic Heart Disease (Coronary Heart disease)
  • Angina Pectoris (Angina)
  • Myocardial Infarction (Heart Attack)
  • Cerebrovascular Accident (Stroke)
  • Hypertension
  • Congestive Heart Failure
  • Congenital Heart Disease
  • Mitral Valve Stenosis
  • Septal Defects
  • Ductus Arteriosus
• In a 2003 report, the NIH recommended that individuals maintain blood pressure below 120/80; systolic in the range of 120-139 or diastolic 80-89 are now considered prehypertensive
• High levels of HDL-cholesterol are associated with a lower risk of heart attacks
• Measuring Blood Pressure

  1. Korotkoff sounds first heard = highest pressure in the artery, recorded as systolic pressure

  2. Korotkoff sounds disappear = lowest pressure in the artery, recorded as diastolic pressure

  3. Written as systolic pressure over diastolic (systolic/diastolic)
• Systolic consistently over 140 mm Hg or diastolic over 90 mm Hg is considered hypertension (high blood pressure)