Receptor sites are proteins typically found on the surface of cells, which are capable of recognizing and bonding to specific molecules. A cell is a self-enclosed system, and it serves as the basic unit of life. All organs are made of different types of cells. For instance, skin is made of skin cells, muscles are made of muscle cells, and blood is made of blood cells.
Molecules that bind to receptor sites are known as ligands. Hormones, neurotransmitters, and drugs are examples of ligands. They are able to fit into specific receptor sites in the same way keys are able to fit into specific locks. Whenever a ligand binds to a receptor site, it alters the shape of the receptor and launches a cascade of chemical reactions known as signaling. A message from the ligand makes its way into the cell, which can induce a variety of responses, including changes in gene expression.
Membrane receptors are divided into three major classes: ion channel—linked receptors, G-protein-coupled receptors, and enzyme -linked receptors. Ion channel—linked receptors reside on the cell membrane. They have a channel that spans the cell membrane and enables ions—atoms and molecules with a negative or positive charge—to freely move in and out of the cell.
Examples of ions include sodium and calcium. When a ligand binds to the receptor site on the channel, the channel opens, allowing ions to travel through the channel in milliseconds. G-protein-coupled receptors are the largest class of receptors. Was this article helpful? Can we help guide you? How does this work? Learn more. Are these recommendations helpful? Take a quick survey. Last modified on September 21, at AM. In some cases, the mechanism of action for a receptor is not clear.
For example, hygroreceptors that respond to changes in humidity and osmoreceptors that respond to the osmolarity of fluids may do so via a mechanosensory mechanism or may detect a chemical characteristic of the environment. Sensory receptors perform countless functions in our bodies. During vision, rod and cone photoreceptors respond to light intensity and color.
During hearing, mechanoreceptors in hair cells of the inner ear detect vibrations conducted from the eardrum. During taste, sensory neurons in our taste buds detect chemical qualities of our foods including sweetness, bitterness, sourness, saltiness, and umami savory taste.
During smell, olfactory receptors recognize molecular features of wafting odors. During touch, mechanoreceptors in the skin and other tissues respond to variations in pressure. Adequate stimulus can be used to classify sensory receptors. Somatic sensory receptors near the surface of the skin can usually be divided into two groups based on morphology:. A tonic receptor is a sensory receptor that adapts slowly to a stimulus, while a phasic receptor is a sensory receptor that adapts rapidly to a stimulus.
As we exist in the world, our bodies are tasked with receiving, integrating, and interpreting environmental inputs that provide information about our internal and external environments. Our brains commonly receive sensory stimuli from our visual, auditory, olfactory, gustatory, and somatosensory systems.
Antagonist: Methysergide and ondansetron. Also increases blood flow to the kidneys, which allows for increased urine excretion. Agonist: Methoxamine and phenylephrine Antagonist: Doxazosin , prazosin , tamsulosin , and terazosin. Agonist: Clonidine Antagonist: Yohimbine. Agonist: Dobutamine and isoproterenol Antagonist: Beta-blockers Beta-blockers The heart muscle needs a constant supply of oxygen-rich blood.
Dilation of smooth muscle in the blood vessels, airways, digestive tract, and urinary tract Breakdown of glycogen in skeletal muscles releasing glucose for energy. Agonist: Albuterol , isoetharine, and terbutaline Antagonist: Propranolol. Agonist: Bethanechol and carbachol Antagonist: Atropine , ipratropium , and scopolamine. Contraction of skeletal muscles. Agonist: None commonly used Antagonist: Atracurium, pancuronium, and tubocurarine. Production of an allergic response Contraction of muscles in the airways and digestive tract Dilation of small blood vessels Drowsiness sedation.
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