Cellular communication is a complex signaling system of living organisms from single-celled fungi to massive bodies. Cells use signals to coordinate, cooperate, repel pathogens, colonize territory and respond to stress.
This is the foundation of forming a bacterial biofilms to triggering a nerve impulses in the brain. Bacteria and yeast use quorum sensing, with which they monitor their own population density.
Bacteria release autoinducers. As the population grows, concentration of autoinducers rises. When it reaches a threshold, autoinducers bind to receptors on or within the microbes to trigger changes in gene expression.
Bioluminescent bacteria Aliivibrio fischeri are symbiotic with the Hawaiian bobtail squid. The bacteria light up only when they reach a high enough population density inside the squid's light organs.
This coordinated luminescence helps the squid camouflage itself against predators. Bioluminescence can be used for counterillumination.
Photophores on the bottom side of an animal can match the dim light coming from the surface. This makes it harder for predators searching for prey silhouettes from below to see them.
Yeast reproduce asexually by budding. Occasionally they use a form of sexual reproduction. They cannot move on their own but pheromones signal the desire to mate.
Pheromones alert yeast cells of an opposite mating type. Haploid cells respond to pheromones. They enable mating between a and α cells, but prevent mating between cells of the same type.
Of the potentially millions of cells surrounding a cell, yeast partners may be within reach. They can stick to a substrate or travel with environmental forces like wind and water flow which mingle the cells.
Yeast can communicate effectively over distances up to 1 mm. Relative to the size of the microscopic cells this is a lot of ground. Stuck end to end, a thousand cells are needed, covering the human equivalent of up to five American football fields.
A yeast colony is abuzz with specialized signals. These help yeast coordinate responses to environmental stress, like changes in nutrient availability. Killer yeast is an example of cells producing toxins.
In multicellular organisms, the need for communication is amplified. Cells must coordinate actions to form tissues, organs and ultimately, a functioning being.
Cell signaling is specific. A signaling molecule will affect only cells with appropriate receptors.
Plants use chemical signals made of volatile organic compounds (VOCs). When a plant is attacked by consumers, it releases compounds to alert other parts of itself, or neighboring plants.
In 2020, Chinese Academy of Sciences researchers identify a pheromone called 4-vinylanisole(4-VA) which causes locusts to swarm. It's released by the insects and attracts nearby locusts into joining the swarm.
Among honeybees, the queen releases queen mandibular pheromone (QMP) in response to incoming signals. QMP regulates social behavior, hive maintenance, swarming, mating and prevents ovary growth in worker bees.
In other vertebrates cellular communication is a mix of hormonal and nerve signaling. Hormones are chemical messengers, released from glands into the bloodstream to enable long-distance communication.
During stressful situations, adrenal glands release cortisol. This hormone influences metabolism, immune response, behavior, often with emotional accompaniment. Cortisol levels can increase by 50% during high stress.
A hormone like adrenaline has different effects on tissues. In the heart, it increases heart rate and force of contraction. In the liver, it stimulates the breakdown of glycogen to release glucose.
Adrenaline makes the heart beat faster and blood pressure rises for more energy. Cortisol, the primary stress hormone, increases glucose in the bloodstream. It facilitates the brain's use of glucose and availability of substances to repair tissues.
Nerve cells use electrical signals or action potentials. These signals transmit rapidly, ensuring quick responses to stimuli.
Direct Contact: Cells can directly communicate by physically touching each other. This is important during development, as cells must recognize and interact with their neighbors to establish tissue boundaries and cell fate.
Gap junctions are tiny channels connecting cytoplasm of adjacent cells, allowing small molecules and ions to pass directly. This allows for rapid coordination of cellular activities, like muscle contraction in the heart.
Paracrine Signaling: Cells release signaling molecules affecting nearby cells. Cell growth and division occur through paracrine signaling, as in wound healing.
Endocrine Signaling: Hormones are long-distance messengers of large bodies. These signaling molecules are secreted into the bloodstream.
They travel to reach target cells with specific receptors for them. Insulin, released by the pancreas, signals cells throughout the body to take up glucose.
Synaptic Signaling: This specialized form of signaling occurs between neurons in the nervous system. Neurons communicate by releasing neurotransmitters, like dopamine or serotonin, into a small gap called the synapse.
The neurotransmitters bind to receptors on the receiving neuron, triggering an electrical signal. Synaptic signaling is responsible for diverse activities, from thought and emotion to muscle movement.
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