blood pressure regulation

• Blood pressure

  • Force exerted upon vessels walls as blood flows through
  • Needed as a minimum pressure (capillary hydrostatic pressure) is required toexchange substances across capillary networks
  • BP = cardiac output x total peripheral resistance

  ○ TPR = dependant upon arteriolar resistance
• Autoregulation of local flow (low levels of activity)

  *Directs blood to match tissue demand at rest
• Central mechanisms

  • Activated during higher activity and increases CO and TPR
  • Endocrine → vasoconstriction, long term regulation
  • Neural → vasoconstriction, short term regulation
• SHORT TERM REGULATIONIntrinsic control/autoregulation - when BP is low

  *Can be due to physical stress, chemical changes or increased tissue activity (lactate)

  *When we are at rest not every capillary bet is open so:

  1. Inactive tissue: precapillary sphincters are constricted
  2. When active, an increase in vasodilatory metabolites concentrationincrease in tissue bed (NO, K+, H+, CO2 and lactate)
  3. Stimulates sphincters to relax allowing blood in and an increase bloodpressure
• Chemoreceptor reflexes (chemical)

  • Location: medulla and carotid body
  • Medulla (ESF) only detects CO2 as blood can pass through membrane
  • Carotid body senses blood
  • Coordination of cardiovascular and respiratory response
• If still too low

  • Stimulation of endocrine response
  • Long term increase in BP via increasing blood volume and vasoconstriction
  • adrenaline/NA secretion from adrenal glands
• LONG TERM REGULATION

  *Endocrine responses to low BP

  • Antidiuretic hormone (ADH/vasopressin) leads to vasoconstriction, increase in fluid retention thirst and fall in blood volume
  • Erythropoietin (Epo) leads to vasoconstriction, increase in blood volume and a fall in BP or O2
  • Renin-angiotensin-aldosterone system (RAAS) leads to vasoconstriction and increase in Na+ reabsorption fluid retention
  • more Na+ reabsorption in the convoluted tubule = more H2O absorbed = increase in blood volume and CO2
• Special considerations for local flow*Blood flow regulation in different in some organs

  • Pulmonary circulation
  • In lungs arterioles constrict in regions of low O2 to shunt bloodflow to O2-rich areas
  • In other organs vessels dilate when O2 falls
  • Cerebral circulation■ In emergencies there is Vasodilation of cerebral vessels whilethere is vasoconstriction in the periphery
  • Coronary circulation
  • ■ A wide range of molecules regulate myocardial perfusion (pumping)