Receptors: definition, meaning, Functions, Types, Topics

Definition Of Receptors

Receptors are highly specialised proteins found either on or inside the cells that change conformation upon specific molecule binding. They form an integral part of physiological processes and mediate interactions between the cell and its environment.

Receptors are proteins that participate in detecting signals, among them hormones, neurotransmitters, and sensory stimuli, and acting accordingly. They allow the cell to respond to the changes and thus maintain homeostasis; they participate in growth, immune responses, and sensing.

Types Of Receptors

Receptors can be classified in several ways. Knowing the classifications is associated with the functions and mechanisms connected with the different kinds of receptors.

Classification Based On Location

• Cell Surface Receptors: These are present on the plasma membrane and the receptor binds to the extracellular molecules.

• Intracellular Receptors: These are present inside the cell and the receptors bind to those molecules which can cross the plasma membrane.

Based On Function

• Sensory Receptors: These are sensitive to light, sound, temperature, etc.

• Neurotransmitter Receptors: These mediate the actions of neurotransmitters within the nervous system.

• Hormone receptors: These bind with the hormone and mediate a diversity of physiological processes.

Structure And Function Of Receptors

The structure of receptors is very closely linked to their function. This section looks at the general structure of receptors and their mechanism of action.

General Structure Of A Receptor

• Ligand-Binding Domain: The region that binds the signalling molecule.

• Transmembrane Domain: It spans the cell membrane in cell surface receptors.

• Intracellular Domain: Binds intracellular signaling molecules.

Mechanism Of Action

• Ligand Binding: The event where a receptor binds its specific ligand, the signalling molecule.

• Signaling cascades also known as signal transduction pathways: It's a series of molecular activities that results in a cellular response, which is triggered by the interaction between the receptor and its ligand.

Cell Surface Receptors

Cell surface receptors are responsible for inter- and intracellular communication and signal transduction through binding with other molecules outside the cell.

Types Of Cell Surface Receptors

• G Protein-Coupled Receptors: The activated receptor triggers the G protein to activate an intracellular signalling cascade.

• Receptor Ion Channels: Opening of the ion channel allows ions to move into or out of the cell, which changes the activity of the cell.

• Enzyme-Linked Receptors: Either one has intrinsic enzymatic activity or is associated with enzymes.

Function And Significance

• These receptors take part in various activities, such as sensory perception, immune response, and hormone action.

Intracellular Receptors

The intracellular receptors reside inside the cell and almost always interact with small hydrophobic molecules that can diffuse through the plasma membrane.

Types Of Intracellular Receptors

• Cytoplasmic Receptors: These are located in the cytosol and move into the nucleus after activation.

• Nuclear Receptors: Located in the nucleus, they directly affect gene expression.

Function And Significance

• Intracellular receptors participate in gene expression and cellular responses to hormones and other signalling molecules.

Sensory Receptors

Sense environmental stimuli and send them as neural signals.

Types Of Sensory Receptors

• Mechanoreceptors: Detect mechanical changes, such as pressure and stretch.

• Thermoreceptors: Detect changes in temperature.

• Photoreceptors: Detect light; found in the eyes.

• Chemoreceptors: Detect chemical changes, including taste and smell.

Function And Role In Sensory Perception

• The process through which physical stimuli are changed or transduced into the electrical signals that are processed by the nervous system.

Neurotransmitter Receptors

Neurotransmitter receptors play an essential role in neural communication and thus also in the functioning of the nervous system.

Types Of Neurotransmitter Receptors

• Ionotropic Receptors: Those forming ion channels that open upon binding of neurotransmitter, allowing ions to flux through.

• Metabotropic Receptors: Activate

• G proteins or other secondary messengers mediate cellular responses.

Role In Nervous System

• These receptors, on binding neurotransmitters, either directly modulate ion channels or induce signal cascades that impact neuronal activity.

Hormone Receptors

Hormone receptors mediate the effects of hormones and thus control a wide variety of physiological processes.

Types Of Hormone Receptors

• Peptide Hormone Receptors: Mostly at the surface of the cell, they bind to peptide hormones.

• Steroid Hormone Receptors: Intracellularly located, these receptors join with steroid hormones, which diffuse through the cell membrane.

Role In Endocrine System

• Hormone-Receptor Interaction: The event of hormone binding induces a conformational change in the receptor that will activate downstream pathways.

• Hormone Signal Transduction Pathway: This takes place with the binding of hormone receptors, thereby relaying an intracellular response that in turn produces a specific cellular response.

Receptor-Associated Disorders And Diseases

• This can lead to a wide range of diseases or disorders in the organism.

• Diabetes: Genetic defects in insulin receptors result in resistance to insulin and consequently, type 2 diabetes follows.

• The deregulation of neurotransmitter receptors is widely implicated in a diversity of diseases that include but are not limited to depression, schizophrenia, and Parkinson's disease.

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