Topic 31 - Central factors of cardiovascular regulation

Question 1

Words to include

Answer 1

• Central factors
• Short term
• Long term
• Coordinating redistribution

Extrinsic (neural / hormonal) regulation

• Sympathetic effects
  
  • Sympathetic tone
  • Vasocontrictive effect
  • NO production
  • Vasodialation
  • Diameter of vessel
  • CNS
    
    • Vasomotor center
      
      • Medulla
  • Sypathetic activation
    
    • Thoracolumar segments of the spinal cord
    • Cardiovascular regulatory nuclei
      
      • Respiratory center of the reticular formation
    • Anterolateral portion (pressor area)
    • Cardiovascular center
    • Chronotrop effect +
    • Dromotrop effect +
    • Peripheral resistance
  • Caudomedial portion (depressor area)
    
    • Chronotropic effect ÷
    • Dromotropic effect ÷
    • Heart
    • N. vagus
    • Peripheral resistance ↓
  • Ihibitory interneurons
  • Depressed sympathetic activity
• Parasypathetic effect
  
  • Direct parasympathetic stimulation
    
    • Corpus cavernosus (in penis)
    • Uterus
    • Pancreas
  • Indirect cholinergic vasodilation
    
    • Salivary glands
  • Brandykinin
    
    • Paracrine action
    • Vasodilation
  • ACh stimulation
  • Muscarinic choline receptor
  • Acini
• Humoral factors
  
  • Endorcrine system
  • Adrenal medulla
    
    • Epinephrine / adrenalin
      
      • β-adrenergic vasodilation
        
        • Skeletal muscle
      • α- adrenergic vasoconstriction
        
        • Skin
        • Sphlanchinic areas
      • General α- adrenergic vasoconstriction
    • Norepinephrine / noradrenaline
      
      • α- adrenergic vasoconstriction
      • Pressor center
      • Depressor center
• Reflex mechanisms
  
  • Baroreceptor mechanism
    
    • CNS depressor response
    • Circulatory bed
    • Blood pressure
    • 40-170 mmHg
    • Mean arterial blood pressure
    • Sympathetic influence
    • Parasympathetic discharge
  • Volume receptors
    
    • Lung
    • Capacitance system of vessels
    • Medulla
      
      • Cardiovascular center
    • Atrial Natriuretic Factor (ANF)
    • Antidiuretic hormone (ADH)
      
      • Atrial stretch reflex
      • Neurohypophyses
  • Brainbridge reflex
    
    • CNS pressor response
  • pO₂ & pCO₂
    
    • Peripheral receptors
      
      • Glomerus caroticum
      • Glomerus aorticum
    • Peripheral afferentation
    • Central afferentation
    • Efferentation
      
      • Sympathetic activation

Extrinsic long term regulation

• CNS
• Emotional effects
• Climate change (adaption)
• Long run change
• Oxygen supply
• Circulating blood volume
• Redistribution

Question 2

What is the most important task of the extrinsic (neural /humoral) regulation?

Answer 2

Compensation of differences in organ perusion through redistribution

Question 3

What are vessels under the balanced infuence of?

Answer 3

• Small intensity sympathetic-vasoconstrictor tone
• Vasodilating tone
  
  • ​Maintained by NO
• End result:
  
  • Vasoconstriction at rest

Question 4

Neural regulation

Answer 4

• Cardio-vasomotor centers are located in the medulla oblongata (formatio reticularis)
  
  1. Pressor area
     
     • ​Craniolateral part
     • Spontaneous activity
       
       • ​On the heart:
         
         • Chronotropic effect +
         • Dromotropic effect +
       • General sympathetic vasoconstriction
     • Mediated by thoracolumbal sympathetic pregangionic neurons
     • Blood pressure ↑
       
       • ​Cardiac output ↑
       • Peripheral resistance ↑
  2. Depressor area
     
     • ​Caudomedial part
     • Ø spontaneous activity
       
       • ​Vagal fibers effect ÷
       • ​On the heart:
         
         • Chronotropic effect ÷
         • Dromotropic effect ÷
       • Blood pressure ↓
     • The area inhibits the activity of the heart via vagal stimulation and supresses the pressor area
       
       • ​Heart rate ↓
       • Contractility ↓
     • Under resting conditions, it is the n. vagus that determines the work of the heart
  • Cardioaccelerator area
    
    • ​Middle

Question 5

What can central factors be divided into?

Answer 5

• Short term
• Long term
• Coordinating redistribution

Question 6

Extrinsic (neural / hormonal) regulation of circulation

Give the extrinsic short-term regulation

Answer 6

1. Sympathetic effects
2. Parasympathetic effects
3. Redistribution
4. Vasomotor effects
5. Humoral factors
6. Reflex mechanisms (vessel related reflexes)

Question 7

Extrinsic (neural / hormonal) regulation of circulation

Sympathetic effect

Answer 7

• Arteries and veins are under the influence of the sympathetic tone, which exerts vasoconstrictive effects and at the same time under the influence of the continuous local NO production that continuously dilates the vessels. The balance of these two effects results in an actual diameter of the vessel
  
  • Under resting circumstances this diameter is much less than the maximal possible diameter of that vessel
  • The CNS controls the diameter of the vessels via the vasomotor center in the medulla
  • The sympathetic activation is mediated by the thoracolumbar segments of the spinal cord
• Vasodilation is normally the consequence of the depressed sympathetic activity, and not the direct result of the parasympathetic stimulation

Question 8

Extrinsic (neural / hormonal) regulation of circulation

Parasympatheic effect

Answer 8

• Most vessels get parasympathetic neural supply (ø skin and skeletal resistance vessels)
• Direct parasympathetic stimulation location (active parasympathetic vasodilation):
  
  • Corpus cavernosus in penis
  • Uterus
  • Pancreas
• Indirect cholinergic vasodilation location:
  
  • Salivary glands
• Indirect parasympathetic vasodilation:
  
  • ​Mediated by the release of brandykinin as a response to ACh stimulation of the muscarinic choline receptors of the acini
    
    • The released bradykinin acts on paracrine ways and causes vasodilation

Question 9

Extrinsic (neural / hormonal) regulation of circulation

Redistribution

Answer 9

• Resistance vessels (areries) are under the influence of sympathetic postganglionic fibers
  
  • ​Transmitter: norepinephrine
• The response is also determined by the number and quality of the catecholamine receptors in the vessel
• Dilation: (β-receptor)
  
  • Arterioles
  • Metarteriolse
  • Skeletal muscles
• Vasoconstriction: (α-receptor)
  
  • Splanchnic (visceral) area
• High number of α-receptors in veins results in contraction as a response to sympathetic stimulation
  
  • Result: blood is forwarded from the capitance system into the resistance system
  • Therefore the is redistribution of the circulating blood volume

Question 10

Extrinsic (neural / hormonal) regulation of circulation

Vasomotor effects

Answer 10

1. Stress mobilizes the adrenal medulla and secretes epinephrine.
2. Epinephrine dilates the vessels of the skeletal muscle causing increased perfusion in this organ
3. The general dilation in the skeletal muscle does not depress the blood pressure however, since the epinephrine increases the performance of the heart, leading to increased cardiac output

Question 11

Extrinsic (neural / hormonal) regulation of circulation

Humoral factors

Answer 11

• Endocrine system also oversees the regulation of the distribution of blood among organs (besides neural control)
• Hormones of the adrenal medulla play a role in the regulation of circulation under increased activity only (e.g. stress)
• Epinephrine / adrenalin
  
  • ​Small dose:
    
    • β-adrenergic vasodilation in the skeletal muscle
    • α- adrenergic vasoconstriction in skin and sphlanchnic areas
  • High dose:
    
    • General α-adrenergic vasoconstriction
• Norepinephrine / noradrenaline
  
  • ​α-adrenergic vasoconstriction
• Other hormonal influences act via the modulation of the pressor / depressor centers

Question 12

Extrinsic (neural / hormonal) regulation of circulation

Blood vessel related reflex mechanisms

Answer 12

1. Baroreceptors
   
   • ​Function: fast adjustment of blood pressure to the needs of the body
     
     • Ø long term effects
   • Location:
     
     • Sinus caroticus
       
       • ​Afferentation: through n. glossopharyngeus (IX)
     • Arcus aortae
       
       • ​Afferent neurons in n. vagus
   • ​​Functions between 40-170 mmHg of mean arterial blood pressure
   • ↑ blood pressure:
     
     • ↑ Parasympathetic discharge
     • ↓ sympathetic influence on the heart
2. Volumereceptors
   
   • ​​Location:
     
     • Lung
     • Capacitance system of vessels
   • Centripetal fibers from these sensors lead to the cardiovascular center in the medulla
     
     • Atrial natriuretic factor (ANF): produced in the atria as a response to increased EC volume
     • Antidiuretic hormone (ADH): Atrial stretch reflex elicits the inhibition of the neurohypophyses let down of this hormone
3. Bainbridge-reflex
   
   • Increase of the heart rate occurs upon stretching the atrium only if the heart rate low previously correcting it back to normal​
4. Effect of pO₂ & pCO₂
   
   • _​Peripheral receptors, location:
     
     • Glomerus caroticum
     • Glomerus aorticum
   • Peripheral afferentation
     
     • ​Sufficient stimulus is the pO₂ ↓
   • Central affernetation
     
     • ​Sufficient stimuli is the pCO₂ ↑
   • Efferentation through sympathetic activation

Question 13

Extrinsic long term regulation

Answer 13

• ↑/↓ the amount of circulating blood, or the perfusion of the individual organs in case of:
  
  • CNS: changes in the vasoconstrictor tone
  • Extended emotional effects
  • Adaptation to climate changes
  • Long run change in the oxygen supply
  • Adjustment of the circulating blood volume, redistribution of the blood etc