Difference Between Alpha and Beta Receptors (With Table)

Alpha Receptors are one of the two types of adrenergic receptors. They are again subdivided into Alpha1 and Alpha2 receptors. These receptors are generally located on the arteries or at the postsynaptic area of our organs sympathetic neuroeffector in the splanchnic vessel contraction.

Beta receptors are another type of adrenergic receptors that are located postsynaptically at our organs. These receptors are again subdivided into Beta1 Beta2 and Beta3 Receptors. When these Beta receptors are activated the muscles of our body relax. The common activity of these receptors is an increase in heart rate, lipolysis, and renin release.

Table comparison between Alpha and Beta Receptors

What are Alpha Receptors?

Alpha Receptors are a group of receptors. They are located on the cell surface of some effectors tissue or organs innervated by the sympathetic nervous system that mediates certain physiological responses such as relaxation of intestinal muscles, vasocontraction, and contraction of smooth muscles. These Receptors are subtypes of Adrenergic Receptors which are generally involved in regulating responses in certain stimulators in our body.

Alpha Receptors are of two types namely Alpha1 Receptors and Alpha2 Receptors. The use of these receptors depends on the medication that indicates the targeted respondent organs. The Alpha1 receptors are most commonly used in all types of shock, heart failure decompensation, and cardiopulmonary resuscitation. Alpha1 receptors are again subdivided into Alpha1 agonists and Alpha1 blockers.

Alpha2 Receptors are used off-label for the treatment of post-traumatic stress disorder. Their stimulation reduces the outflow of the sympathetic nervous system from the vasomotor center and increases vagal tone. Sometimes these receptors also reduce sympathetic tone. It includes clonidine and guanfacine that are used as antihypertensives. They are of two types namely Alpha2 Agonists and Alpha2 Blockers.

Between 1906 and 1913, Henry Hallett dale explored the effect of adrenaline on animals. He injected it into the vessels which resulted in an increase in the blood pressure of these animals. He also exposed these animals to ergotoxine which resulted in a decrease in blood pressure. After these experiments he proposed, ergotoxine caused a fall of blood pressure and selective paralysis of smooth muscles. He also added that these components either cause contraction or relaxation depending on the responses of different types of the junction to the same component.

In the 20th century, it was agreed that the stimulation of sympathetic nerves causes different effects on body organs. They made two proposals to explain the phenomenon. Firstly, there were two types of neurotransmitters released from nerve terminals; or secondly, there were two types of detectors mechanisms. This hypothesis was introduced by Arturo Rosen and Walter Bradford Cannon.

What are Beta Receptors?

Beta receptors are a group of receptors that are present on the surface of the cells specifically located on some effector tissue and organs innervated by the sympathetic nervous system. These receptors mediate certain physiological responses such as relaxation of bronchial, vasodilation, increased heart rate, and uterine smooth muscles. These receptors are subtypes of Adrenergic Receptors subdivided into three different receptors namely Beta2, Beta2, Beta3 Receptors.

Bet1 Receptors are essential components for the normal physiological function of the Sympathetic nervous system. These receptors are activated through various hormones, medication, or signaling mechanisms.

Beta2 receptors are cell membrane-spanning adrenergic receptors. They generally activate g-protein-coupled receptors that bind norepinephrine and epinephrine.

Beta3 receptors are located in the urinary bladder, brown adipose tissue, and gallbladder. It relaxes the bladder and prevents urination.

Main Differences Between Alpha and Beta Receptors

1. Alpha Receptors are the Adrenergic Receptors that control physiological processes like intestinal relaxation and vasoconstriction. As against, Beta Receptors are a class of receptors that control the relaxation of bronchial, vasodilation, and increase heart rate.
2. Alpha Receptors stimulate effector cells whereas Beta Receptors relaxes effector cells.
3. Alpha Receptors are responsible for the contraction of blood vessels. On the other hand, beta receptors are responsible for the dilation of the blood vessels.
4. Alpha Receptors are located in the vascular smooth muscles and effectors tissue whereas beta receptors are located in the bronchial muscles, uterine muscles, and heart muscles.
5. There are two types of Alpha Receptors namely Alpha1 and Alpha2 Receptors. As against, Beta Receptors are of three types namely Beta1, Beta2, and Beta3 receptors.

Conclusion

Both Alpha and Beta Receptors occur at the sympathetic junction of different organs of our body such as the heart, lungs, fatty tissues, blood vessels, etc. although both of these receptors being part of adrenergic receptors, they both differ in several aspects such as their activities, types, and functions. The main difference being the effect of each type of receptors on effector cells.

References

1. https://europepmc.org/article/med/6253412
2. https://www.sciencedirect.com/science/article/pii/0024320577900662
3. https://nyaspubs.onlinelibrary.wiley.com/doi/abs/10.1111/j.1749-6632.1967.tb41229.x