Adrenergic receptors

 

Adrenergic receptors are two

  • α

  • β receptors

Noerphinephine excites mainly α receptors but also β receptors to a lesser extent as well. Epinephrine excites α and β receptors equally

Isopropyl norepinephine a synthetic hormone chemically similar to epinephrine and norepinephrine with strong action on β receptors but none on α.

There are two adrenergic receptors and they include

  • Classical α1 adrenoceptors which cause vasoconstriction

  • α2 adrenoceptors are present in presynaptic and postsynaptic endings. Presynaptic receptors are also called autoreceptors.

Alpha receptors

Beta receptor

Vasoconstrictor

Vasodilation (β2)

Iris dilation

Cardioacceleration (β1)

Intestinal relaxation

Increased myocardial strength (β1)

Intestinal sphincter contraction

Intestinal relaxation (β1)

Pilomotor contraction

Uterus relaxation (β2)

Bladder sphincter contraction

Bronchodilation (β2)_

 

Calorigenesis (β2)

 

Lipolysis (β1)

 

Bladder wall relaxation (β2)

Adrenergic receptors and functions*

Organ

Effect of sympathetic stimulation

Effect of parsympathetic stimulation

Eye

 

 

   Pupil

Dilated

Constricted

   Ciliary muscle

Slight relaxation (far vision)

Constricted (near vision)

Glands

Vasoconstriction and slight secretion

Stimulation of copious secretion (containing many enzymes for enzyme-secreting glands)

   Nasal

 

 

   Lacrimal

 

 

   Parotid

 

 

   Submandibular

 

 

   Gastric

 

 

   Pancratic

 

 

   Sweat glands

Copious sweating (cholinergic)

Sweating on palms of hands

   Aprocine glands

Thick, odoriferous secretion

None

Blood vessels

Most often constricted

Most often little or no effect

Heart

 

 

   Muscle

Increased rate

Slowed rate

   Coronaries

Increased rate of contraction

Decreased force of contraction (especially of atria)

Lungs

 

 

   Bronchi

Dilated

Constricted

Blood vessels

Mildly constricted

?Dilated

Gut

 

 

   Lumen

Decreased peristalsis and tone

Increased peristalsis and tone

   Sphincter

Increased tone (most times)

Relaxed (most times)

Liver

Glucose released

Slight glycogen synthesis

Gallbladder and bile ducts

Relaxed

Contracted

Kidney

Decreased output and rennin secretion

None

Bladder

 

 

   Detrusor

Relaxed (slight)

Contracted

   Trigone

Contracted

Relaxed

Penis

Ejaculation

Erection

Systemic arterioles

 

 

Abodminal visera

Constricted

None

Muscle

Constricted (adrenergic alpha)

None

 

Dilated (Adrenergic B2)

 

 

Dilated (cholinergic)

 

Skin

Constricted

None

Blood

 

 

Coagulation

Increased

None

Glucose

Increased

None

Lipids

Increased

None

Basal metabolism

Increased up to 100%

None

Adrenal medullary secretion

Imcreased

None

Mental activity

Increased

None

Piloerector muscles

Contracted

None

Skeletal muscle

Increased glycogenolysis

None

 

Increased strength

 

Fat cells

Lipolysis

None

 

 

 

cAMP

Adenylate cyclase system

Intracellular receptors

Calcium messenger system

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Brainstem Medulla Pons Midbrain Thalamus Epithalamus
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* Guyton A.C.  and Hull, A.C. (2006). Textbook of Medical Physiology: Saunders.
 

 

 

 

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