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Forms of Intracellular Signaling

Forms of intracellular signaling: a) Contact-dependent signaling b) Paracrine signaling c) Synaptic signaling d) Endocrine signaling
Cell-to-cell communication is the process of transmitting signals from one cell to another. The receiving and sending cells are not all immediately adjacent as well as all cell pairs do not exchange signals equally. Among multicellular organisms, chemical signaling can be divided into four basic categories: paracrine signaling, autocrine signaling, endocrine signaling, and contact signals. Signals from different categories of signaling are distinguished by the distance they travel through the organism to reach their target cells.

A) Contact-dependent signaling
Animals have gap junctions, while plants have plasmodesmata, which connect nearby cells. A small number of intracellular mediators can diffuse between cells when they are present in these water-filled channels. Molecular and ion movement between cells is easy, but larger molecules such as proteins and DNA cannot pass through channels without special help. By transmitting signaling molecules between cells, one cell tells the neighboring cell what its current state is. Having a coordinated response to a signal that only one cell receives allows a group of cells to work together and respond effectively. Most cells within a plant are connected by plasmodesmata, which makes the entire plant one large network.

An example of direct signaling is the binding of two cells because complementary proteins are present on their surfaces. The binding of one or both proteins changes the shape of the proteins, which then transmits a signal. A cell-surface marker is particularly important when it comes to signaling in the immune system, which uses it to recognize "self" cells (the body's cells) as well as cells infected with pathogens

B) Paracrine signaling
A chemical messenger (ligands) is often released by cells located near one another to communicate (for instance, signaling molecules). Signaling that occurs over relatively short distances, such as paracrine signaling, is known as paracrine signaling. Paracrine signaling allows cells to coordinate their activities with neighbors on a local level. While paracrine signals are present across a wide range of issues and contexts, they are particularly crucial during development, when one group of cells instructs another which cellular identity to adopt.

C) Synaptic signaling
Signals transmitted by nerve cells constitute paracrine signaling, which is unique. Synapses, the points of junction between two nerve cells where signals are transmitted, are named for this process. The sending neuron sends an electrical impulse along a long, fiber-like extension known as an axon that travels rapidly through the cell. Neurotransmitters are triggered when impulses reach synapse, as long as the small gap between nerve cells is not too large. Upon arrival at the receiving cell, neurotransmitters attach to receptors, causing a chemical change inside (often opening ion channels and altering the membrane's electrical potential). In response to the release of neurotransmitters at the chemical synapse, the sending cell degrades them or takes them back up. Essentially, this "resets" the system so that a synaptic connection is ready to respond to incoming signals.

D) Endocrine signaling
The circulatory system is often used as a distribution system for the messages that cells need to send over long distances. The long-distance endocrine signaling system involves specialized cells that release hormones into the bloodstream, carrying them to target cells far away from their source. In the body, hormones are substances that travel through the bloodstream to reach distant tissues. As well as the thyroid and hypothalamus, the pituitary gland releases hormones, as do both gonads (testes and ovaries), and the pancreas. There are several different types of hormones released by endocrine glands, some of which are important regulators of physiology and development.

Growth hormone (GH) allows bones and cartilage to grow as the pituitary gland releases it because Pituitary growth hormone (GH) is responsible for encouraging bone and cartilage growth... In addition to affecting different types of cells throughout the body, GH affects some of the smallest ones within the body. GH does, however, function in cartilage cells. This has to do with how it binds to receptors on their surface and urges them to divide.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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