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Pharmacology > Drugs and the sympathetic nervous system > Flashcards

Drugs and the sympathetic nervous system Flashcards

1
Q

What is the purpose of the autonomic nervous system?

A

Regulate organ function and homeostasis, not subject to voluntary control

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2
Q

Describe efferent autonomic nerves

A

Transmit impulses from CNS to periphery organs

Control heart, blood vessels, gut, bladder eyes, endocrine and exocrine glands

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3
Q

Describe afferent autonomic nerves

A

Periphery to CNS
Baroreceptors and chemoreceptors sensors in organs
Vagus, splanchnic and pelvic nerves

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4
Q

Contrast sympathetic preganglionic and postganglionic fibres

A 
Pre= myelinated, cell bodies in lateral horns of the spinal segments T1-L2 (thoracic lumbar outflow), paravertebral ganglionic chains run from cervical to sacral region, synapse in ganglia
Post= unmyelinated, longer, run all the way to effector organ
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5
Q

What are the exceptions to preganglionic fibres?

A

Do not synapse in sympathetic chains- terminate in separate cervical or abdominal ganglia/ travel in the greater splanchnic nerve and directly synapse with chromaffin cells in adrenal medulla

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6
Q

What is the adrenal medulla?

A

Adrenal glands located on superior aspect of each kidney, synthesises and stores catecholamines (similar to postganglionic nerve endings), additional enzyme converts noradrenaline into adrenaline, transforms neural impulses into hormone secretion

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7
Q

What is the role of the sympathetic nervous system?

A

Enables body to be prepared for flight or flight response

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8
Q

What is the affect of the SNS on the heart?

A
  • Inc heart rate by actions on pacemaker cells in SAN and AVN, inc conduction rate of electrical impulses
  • Inc contractility of ventricle myocardial muscle
  • Inc stroke volume
  • Inc cardiac output
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9
Q

What is the affect of the SNS on blood vessels?

A
  • Vasoconstriction= smooth muscle contractions in most arterial circulations increases resistance to flow thereby reducing local blood flow, inc peripheral vascular resistance and bp
  • Vasodilation= smooth muscle relaxation in large arteries and arterioles supplying skeletal muscle, inc muscle blood flow
  • Venoconstriction= smooth muscle contraction in veins, mobilises blood from venal reservoir into circulation, inc venous return to heart
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10
Q

What is the affect of the SNS on the kidney?

A
  • renal blood vessels= constricts renal arterioles reducing blood flow and urine production
  • Renin secretion= stimulates release of enzyme from juxtaglomerular apparatus, catalyses the conversion of angiotensinogen into angiotensin 1 which is converted into angiotensin 2, potent vasoconstrictor and stimulates release of aldosterone (sodium retaining hormone)
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11
Q

What is the affect of the SNS on the lungs?

A

Bronchodilation= relaxation of smooth muscle surrounding bronchi and bronchioles, increases diameter, reduces resistance to airflow so improved ventilation, more effective transfer of oxygen and CO2

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12
Q

What is the affect of the SNS on the GI tract?

A
  • Salivary glands= stimulates more viscous secretions
  • Bowel wall= relaxes smooth muscle of gut to reduce peristalsis to conserve energy
  • Sphincters= constricts smooth muscle so reduces onward transit of food and bowel contents
  • Liver= stimulates glycogenolysis and gluconeogenesis
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13
Q

What is the affect of the SNS in adipose tissue?

A

Adipocytes= stimulates lipolysis, breaking down triglyceride stores to release free fatty acids as energy source for muscles

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14
Q

What is the affect of the SNS on the bladder?

A
  • Bladder wall= relaxes smooth muscle to reduce possibility of voiding
  • Sphincters= constricts smooth muscle to reduce possibility of voiding
  • Male prostate= constricts smooth muscle so more difficult to urinate
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15
Q

What is the affect of the SNS on the genital tract?

A
  • Male= ejaculation

- Female= contraction of myometrium of pregnant uterus during labour (alpha)/ relaxation of myometrium (Beta2)

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16
Q

What are the other sympathetic effects?

A
  • Pupillary dilation in eyes
  • Muscle tremor
  • Platelet aggregation
  • Skin sweating
17
Q

What are the main endogenous mediators involved in regulation of SNS?

A 
Pre= ACh, nicotinic receptor, adrenal medulla releases adrenaline and noradrenaline
Post= noradrenaline,  sweat glands ACh at muscarinic receptors
18
Q

What are catecholamines?

A

Adrenaline and noradrenaline neurotransmitters
Synthesised from amino acid phenylalanine
Terminal branches of post fibres have swellings/ varicosities- form synaptic contact with effector organ, site of synthesis and storage of noradrenaline.
Released from granules

19
Q

What is the action of noradrenaline terminated by?

A
  • Diffusion from the site of action
  • Reuptake back into the presynaptic nerve ending, inactivated by enzyme monoamine oxidase (MAO) in mitochondria
  • Metabolism locally by enzyme catechol-O-methyl-transferase (COMT)
20
Q

What are the subgroups of adrenoreceptors?

A

Alpha 1= vasoconstriction of blood vessels
Alpha 2= presynaptic membrane, negative feedback, feedback inhibition of NA on own release (self-regulation)
Beta 1= Inc rate and force of contraction in heart
Beta 2= vasodilation in blood vessels, bronchial relaxation in lung

21
Q

What drugs are used at each receptor?

A

Alpha agonists= adrenaline (a1), noradrenaline (a1), phenylephrine (a1), clonidine (a2), ephedrine (a1)
Alpha antagonists= prazosin (a1)
Beta agonists= adrenaline (b1,2), isoprenaline (b1,2), salbutamol (b2), dobutamine (b1)
Beta antagonists= propranolol (b1,2), atenolol (b1)

22
Q

What are the clinical uses of alpha agonists?

A 
Rarely used
Cardiovascular collapse (urgent intensive treatment of shocked patients- a1), nasal congestion (a1), hypertension (a2)
Adverse effects- a1= hypertension, tachycardia, angina
23
Q

What are the clinical uses of alpha antagonists?

A

Alpha-blockers, zosin suffix, prazosin, doxazosin, Tamsulosin
Hypertension, benign prostatic hypertrophy
Adverse; hypotension, dizziness, nasal congestion

24
Q

What are the clinical uses of beta agonists?

A

Non-selective and selective (b1 dobutamine, b2 salbutamol)
Asthma (b2 salbutamol inhaled), premature labour (b2 salbutamol IV), severe heart failure (b1 dobutamine), anaphylaxis and cardiac arrest (non selective adrenaline)
Adverse; b1= tachycardia and palpitations
b2= tremor, hypokalemia

25
Q

What are the clinical uses of beta antagonists?

A

Beta- blockers, olol, non-selective propranolol, selective b1 atenolol (cardio selective)
b1= hypertension, angina pectoris, heart failure
b2= tremor
Adverse= b1- bradycardia and heart failure
b2= bronchospasm, cold peripheries, lethargy

Pharmacology (12 decks)

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