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CVS > 9. Regulation of the Cardiovascular System > Flashcards

9. Regulation of the Cardiovascular System Flashcards

1
Q

What is central venous pressure?

A
  • Mean pressure in the right atrium
  • Determines the amount of blood flowing back to the heart
  • If high, less blood comes back to the right atrium
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2
Q

What are 3 ways of regulating flow?

A
  • Local mechanisms
  • Hormonal
  • Autonomic nervous system
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3
Q

Describe the local mechanisms to regulate blood flow

A
  • Autoregulation = intrinsic capacity to compensate for changes in perfusion pressure by changing vascular resistance
  • e.g. if BP drops, autoregulation causes a gradual decrease in resistance and increase in flow
  • Injury to the vessel can change autoregulation - platelets aggregate and release serotonin (vasoconstrictor)
  • Release of NO, prostacyclin, thromboxane A2 and endothelins from the endothelium
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4
Q

What are the 2 theories for autoregulation?

A

• Myogenic theory
- smooth muscle fibres contract and pressure rises to keep flow constant
- due to stretch sensitive channels being involved
• Metabolic theory
- vessels supplying a particular vascular bed cotnracts
- flow decreases so vascular bed produces more metabolites
- metabolites feed back on the vessel causing vasodilation
- increased flow - metabolites washed away

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5
Q

Describe the systemic regulation of blood flow by (3 types of) hormones

A
  • Kinins - e.g. bradykinin, interact with the Renin-Angiotensin System, tend to relax VSMCs
  • ANP (Atrial Natriuretic Peptide) - circulating peptides, as the cardiac atria stretch, they secrete more ANP => vasodilation
  • Circulating Vasoconstrictors - Vasopressin (ADH) secreted from posterior pituitary, Angiotensin II formed by increased renin secretion from kidney, Noradrenaline released from adrenal medulla
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6
Q

Describe the design of the Autonomic Nervous System, comparing the Parasympathetic and Sympathetic nerves

A

• Regions going down the CNS - cranial, thoracic, lumbar + sacral

Parasympathetic 
• cranial + sacral
• long pre-ganglionic fibre and short post-ganglionic fibre
• ganglion beside the SA node
• ACh transmitter throughout
• Nicotinic synapse at ganglion
• Muscarinic synapse at effector
• important in regulating heart rate

Sympathetic
• thoracic + lumbar
• short pre-ganglionic fibre and long post-ganglionic fibre
• pre-ganglionic fibre secretes ACh at ganglion
• post-ganglionic fibres secrete NA at effector
• important in controlling flow

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7
Q

Which vessels do sympathetic nerve fibres innervate?

A

All vessels except capillaries

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8
Q

Why is the distribution of sympathetic nerve fibres uneven?

A
  • More innervate vessels supplying the kidney, gut, spleen and skin
  • Fewer innervate the skeletal muscle and brain
  • More potential to constrict the blood going to these places
  • Blood can therefore be diverted to other more important organs
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9
Q

How does concentration affect the types of receptors adrenaline binds to?

A
  • Normally - Beta 2 adrenoreceptors - vasodilation

* High concentration - Alpha adrenoreceptors - override vasodilatory effects and produce vasoconstriction

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10
Q

Where is the vasomotor centre located and what does it do (including the differences between the lateral and medial portions)?

A
  • Located bilaterally in the reticular substance of the medulla
  • Lower third of the pons
  • Consists of a vasoconstrictor area (pressor), vasodilator area (depressor), Cardioregulatory Inhibitory Area (heart rate)
  • Transmits impulses distally through the spinal cord to almost all blood vessels
  • Higher centres in the brain (e.g. hypothalamus) can exert excitatory and inhibitory effects on the VMC
  • Lateral portions: control heart activity - heart rate and contractility
  • Medial portions: transmit signals via the vagus nerve to the heart - decreases heart rate
  • Anticipatory response to exercise - heart rate and ventilation goes up slightly before exercise because of the higher sensors in the brain
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11
Q

Why do the parasympathetic pathways slow down the heart rate?

A
  • Acetylcholine decreases the gradient of the pacemaker potential
  • Potential takes longer to reach threshold and fire
  • Heart rate slows down
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12
Q

Why do the sympathetic pathways increase the heart rate?

A
  • Adrenaline and noradrenaline increase the gradient of the pacemaker potential
  • Threshold is reached more quickly
  • Heart rate increases
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13
Q

What happens to the heart rate if you cut the sympathetic nerves?

A
  • Lose the ability to increase the heart rate

* Heart rate falls

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14
Q

What is the normal resting heart rate, and what would be the normal rate without innervation?

A
  • Normal - 70bpm

* No innervation - 100 bpm

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15
Q

What 2 factors can increase the force of contraction

A
  • Starling’s Law

* Sympathetic activity

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16
Q

How does noradrenaline lead to the contraction of muscle cells?

A
  • NA binds to Beta 1 adrenoreceptors
  • Increase in cAMP which activates Protein Kinase A
  • PKA phosphorylates the LTCCs and the SR calcium release channel + SERCA
  • More calcium influx and more calcium taken back up into the stores
  • Increased contraction
  • Altered heart rate and strength of contraction
17
Q

What effect does parasympathetic activity have on the strength of contraction?

A

None

18
Q

How do baroreceptors in the aortic arch and carotid bodies feed back to the vasomotor centre?

A
  • Aortic arch - Vagus Nerve (C10)

* Carotid Sinus - Glossopharyngeal Nerve (C9)

19
Q

What do the different baroreceptors respond to?

A
  • Stretch of smooth muscle
  • NOT BP
  • Carotid respond to pressure between 60 and 180 mmHg
  • Most sensitive around 90-100 mmHg (around mean BP)
20
Q

What is reciprocal innervation?

A

Innervation so that the contraction of a muscle is accompanied by the simultaneous inhibition of an antagonistic muscle

21
Q

How does reciprocal innervation work?

A
  • Receptor detects an increase in pressure
  • Nerve activity increases and fires down the afferent nerve directly to the parasympathetic nerve synapse
  • Decrease in sympathetic activity - due to increased activity of the inhibitory interneurone
  • Slows down tonic activity
22
Q

In which direction does the afferent input, parasympathetic nerves and sympathetic nerves go, with reference to reciprocal innervation?

A
  • Afferent input towards the brain
  • Stimulates the parasympathetic nerves to the heart
  • Simultaneously inhibits sympathetic innervation to heart, arterioles and veins
23
Q

How does the vagus nerve have both an afferent and efferent activity?

A
  • Afferent activity from baroreceptor to the VMC

* Efferent activity from VMC to the heart

24
Q

What effect does decreased sympathetic stimulation have on the heart and blood vessles?

A
  • Decreased heart rate and stroke volume

* Vasodilation

25
Q

What can best be used to reflect baroreceptor activity?

A

Parasympathetic activity

CVS (21 decks)

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