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Embeds 0 No embeds. No notes for slide. The originating cell produces the chemical signal that diffuses throughout the tissue nearby. The chemical is not stable and deteriorates if it has to travel long distances. The chemical that the cell produces is targeted at other specific cells. The targeted cells have receptors on their cell membranes for the secreted chemical. Non-targeted cells don't have the required receptors and are not affected.
Original Research ARTICLE
The secreted chemical attaches itself to the receptors of targeted cells and triggers a reaction inside the cell. The reaction in turn influences targeted cell behavior. For example, skin cells grow in layers with the top layer made up of dead cells. Cells of a different tissue lie underneath the bottom layer of skin cells. Local cell signaling ensures that the skin cells know in which layer they are located and whether they have to divide to replace dead cells.
Paracrine signaling is also used to communicate inside muscle tissue. A paracrine chemical signal from the nerve cells in the muscle causes the muscle cells to contract, allowing for muscle movement in the larger organism. Autocrine signaling is similar to paracrine signaling but acts on the cell that initially secretes the signal.
The original cell produces a chemical signal, but the receptors for the signal are on the same cell. As a result, the cell stimulates itself to change its behavior. For example, a cell could secrete a chemical that promotes cell growth. The signal diffuses throughout the local tissue but is captured by receptors on the originating cell. The cell that secreted the signal is then stimulated to engage in more growth.
Introduction to cell signaling (article) | Khan Academy
This feature is useful in embryos where growth is important, and it also promotes effective cell differentiation, when autocrine signaling reinforces a cell's identity. Autocrine self-stimulation is rare in adult healthy tissue but can be found in some cancers. In endocrine signaling, the originating cell secretes a hormone that is stable over long distances. The hormone diffuses through the cell tissue into capillaries and travels through the circulatory system of the organism.
Endocrine hormones spread throughout the body and target cells in locations that are remote from the signaling cell. The targeted cells have receptors for the hormone and change their behavior when the receptors are activated. For example, cells in the adrenal gland produce the hormone adrenaline, which causes the body to enter the "fight or flight" mode. The hormone spreads throughout the body in the blood and causes reactions in targeted cells. They typically interact with internal receptors. Steroid hormones are an example.
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Water soluble hydrophilic ligands can not pass directly through the cell membrane. They typically interact with cell-surface receptors. Peptide protein hormones are an example. There are a variety of other ligands such as nitric oxide NO gas. Nitroglycerin and Viagra affect the NO pathway. Kinases are a type of enzyme that adds a phosphate group to another molecule including other proteins. This is called phosphorylation. Phosphorylation can activate or deactivate other proteins.
Second messengers are small molecules that help to spread a signal through the cytoplasm after a ligand binds to a receptor.
Signals Travel Into Cells
They do this by altering the behavior of certain cellular proteins. There are several categories of cellular responses to signals. Changes in gene expression : an increase or decrease in the production of a protein produced by a specific gene. An increase in cellular metabolism : the conversion of glucose to glycogen and back can be regulated depending on the energy needs of the cell.