PS120: Adrenergic receptors Flashcards
Alpha adrenergic receptors:
- alpha 1
a) contraction of dilator pupillae ms.
b) contraction of pilo-erector ms.
c) vasocontriction
d) contraction of GIT sphincters & urinary bladder sphincters - alpha 2 (ONLY IN GIT)
inhibitory, causing relaxation of wall.
Mechanism of action for alpha receptors
- alpha 1 receptors increase intracellular calcium
- alpha 2 receptors inhibits adenyl cyclase (drop in cAMP)
sensivity of alpha receptors
more sensitive to noradrenaline than adrenaline
Beta adrenergic receptors:
- beta 1 ONLY IN HEART
causes increase in heart rate & contraction - beta 2
inhibitory causing:
a) vasodilation
b) uterine relaxation
c) intestinal relaxation
d) bladder relaxation
e) bronchodilation
f) glycogenolysis & lipolysis
Mechanism of action for beta receptors
Beta 1 & 2 stimulate adenyl cyclase enzyme (increase cAMP)
Relative sensitivity of beta receptors:
Equally sensitive to noradrenaline & adrenaline
What are adrenergic receptors found in the organ of supply called?
Postsynaptic adrenergic R
What are adrenergic receptors found in the the postganglionic nerve ending membrane called?
Presynaptic adrenergic receptors
What are the functions of presynaptic adrenergic receptors?
- control noradrenaline release as feedback control
- decrease cAMP (like alpha 2 postsynaptic receptors)
How do presynaptic adrenergic receptors control noradrenaline?
the release of noradrenaline stimulates presynaptic adrenergic receptors which in turn inhibit noradrenaline release.
What is Horner’s Syndrome?
group of manifestations that result from interruption of sympathetic supply to head & neck.
What is the cause of Horner’s Syndrome?
lesion in sympathetic supply to head & neck.
Where can the lesion that causes Horner’s Syndrome be?
- Origin: at 1st or 2nd thoracic segments or their ventral roots.
- Ganglia of relay: superior cervical ganglion
- Postganglionic fibres
Manifestations of Horner’s Syndrome:
- Ptosis
- Miosis
- Enophthalmos
- Anhydrosis
- Warm red skin (flushed skin)
What is ptosis?
drop of upper eyeliid due to paralysis of levator palpebrae superioris ms.
What is miosis?
consitriction of the pupil due to paralysis of dilator pupillae ms.
What is enophthalmos?
sinking of eye ball into orbit due to paralysis of Muller’s muscle
What is anhydrosis?
dryness of skin due to loss of sweat secretion
What causes the warm red skin/ flushed skin of Horner’s Syndrome?
the loss of sympathetic vasoconstrictor tone leading to vasodilation
Where do the Horner’s Syndrome’s manifestations appear?
ipsilateral; on the same side of the lesion:
- 3 in the eye
- 2 in the skin.
