How do errors in communication impact homeostasis

These together produce an emotional and motivational quality that drives the need for survival. The cognitive component involves the attitudes, beliefs, and expectations of pain to determine how noxious stimulus information is processed and conveyed into a response or output [ 19 - 22 ]. Consequently, an important aspect of cognition in pain processing is related to higher order cognitive functioning, such as decision making, and the interaction of decision-making processing during pain.

Each of the components of pain provides a critical aspect of the pain experience and functioning together, produce a holistic perceptual experience of pain. In addition to this multidimensionality perspective, pain has also been described as a homeostatic emotion [ 5 ].

Like homeostatic drives, homeostatic emotions evoke behavior in response to changes in homeostasis. Pain, of course, is adaptive and motivational in nature especially when acute [ 12 , 24 , 25 ]. Acute pain is short in duration, self-limited, and deficient in psychosocial or biological changes disproportionate to the pain intensity [ 26 , 27 ]. Due to these qualities, acute pain also contains sensory qualities that alert changes to the ideal state.

While chronic pain may no longer retain this quality since this pain persists longer than the removal of the noxious stimulus or beyond tissue damage repair, chronic pain may still preserve its unpleasantness and motivation despite sensory, emotional, and behavioral alterations [ 27 - 29 ]. It is the affective and unpleasant qualia of pain that is the strongest contender in promoting behavior by providing a negative motivational state [ 5 , 30 ]. Thus, within these qualifications, pain can be considered a driving force in homeostasis and plays an essential role in motivating an organism through emotional, attentional, and sensory mechanisms.

The importance of pain and its quality as a homeostatic emotion can be further explained through drive-reduction theory Fig. Pain creates an imbalanced state and an unpleasant affect needing to be resolved. This, in turn, motivates an organism to maintain internal stability by reacting in favor of survival. In other words, the affective-motivational component of pain is directly associated with the homeostatic and adaptive nature of pain.

When pain i. As a result, pain demands attention and requires a response that drives the organism to resolve, maintain, or revert to homeostasis by means of either escape or avoidance of the painful situation [ 5 , 16 , 31 - 35 ]. Decision-making is regarded as the cognitive process that involves identifying and assessing possible alternatives in order to solve a problem or achieve some objective [ 36 ].

Good decision-making processing is especially advantageous and is critical for survival. Under normal circumstances, decision-making involves evaluating an almost unlimited number of alternatives to a current situation to assess the best outcome of long-term behavioral consequences [ 37 - 39 ]. When decisions are suitable, cognition ensures that the ratio of benefits, costs, and consequences are favorable to current needs and optimizing utility at small costs [ 40 - 42 ].

Information regarding homeostatic status, sensory input, and prediction of future threats or benefits are required for decision processes. This is essential in ensuring the maximum number of ongoing, and possibly competing for homeostatic needs are met.

Emotional or somatic processes also aid in guiding behavior and decisions. This occurs in a biased manner even in situations where there are no definitive right or wrong answers and instead cause intuitions that lead to a more perceived correct choice [ 43 - 45 ]. Therefore, like pain, decision-making is also influenced by cognitive and emotional processes along with homeostatic information. Such overlap strongly suggests a strong association among homeostasis, pain, and decision-making processing Fig.

As seen above, pain and decision-making share very similar qualities. Decision-making directly reflects two of the three modalities that comprise pain - both containing aspects of emotional and cognitive processes.

Pain is associated with the affective-motivational component that mirrors the emotional processing that occurs within decision-making, and general cognitive processes that are required for decision-making reflects the cognitive-evaluative component of pain. Emotional and cognitive processes are also key players that may modulate pain experiences and behavioral outcomes.

In fact, emotions and mood influence both pain and decisions where negative emotional states may increase the unpleasantness of pain even though intensity is maintained [ 23 , 46 , 47 ] or increase the likelihood for risky decisions [ 17 , 48 - 50 ]. These negative states, however, do signal homeostatic imbalances that are most likely related to survival so these outcomes may not be unreasonable considering the imperfect state. To further complicate this interrelated relationship, changes in cognitive functions are also associated with pain, particularly with chronic pain and these cognitive alterations may either be a direct result of pain or pain may indirectly cause effects on cognitive function [ 48 ].

This may be driven in part to a purely emotional response, lacking in rational choice, utilization of limited resources, the interaction of neuromodulators, neuroplasticity, or a combination of all these factors [ 56 ]. Therefore, although the behavioral outcomes may not always be immediately beneficial to the individual, changes to morphology, concentration of neurotransmitters and other cellular activity are sanctioned in hopes to aid and modulate pain.

Furthermore, reorganization and plasticity resulting from incoming stimuli have also been implicated in acute pain suggesting that modulation of the pain experience may be critical to survival [ 57 , 58 ]. It is understood however that processes have optimal thresholds and if pain remains despite cortical changes as with chronic pain, these alternations may disrupt other homeostatic states causing more harm than good causing a positive feedback loop to address new homeostatic disturbances.

Nonetheless, it should be apparent that pain and decision-making are interconnected and are greatly involved in increasing our fitness and survival through homeostatic processes especially in regard to acute pain.

As one would predict, this relationship should be reflected through common neurobiological substrates, where a host of neural correlates that aid in pain processing is also involved in decision-making processes Table 1 [ 59 - 64 ]. Since decision-making and pain have the common goal to engage behavior to maintain homeostasis, and imbalances of homeostasis impact decision-making and pain processes, various cortical and subcortical areas that subserve basic needs, somatic and autonomic responses, and behavioral expressions must be involved [ 50 , 65 , 66 ].

For example, the hypothalamus and autonomic brainstem nuclei basal forebrain, ventral striatum, Periaqueductal Gray PAG , and other brain-stem nuclei are responsible for generating the corresponding somatic responses from stimuli in the presence of a decision [ 67 ]. The amygdala provides the negative or positive valence of the stimuli, promotes exploration, and demands attention towards a particular stimulus. Since the amygdala encodes the somatic valence or importance of the stimuli, it also serves as a convergence-divergence zone where the stimulus primary inducer or thought of the stimulus secondary inducer is coupled with a response [ 68 , 69 ].

This processing is important to help guide future decisions since previous associations and outcomes play a major role in directing future decisions. Additional areas of the prefrontal cortex, including the anterior cingulate, ventromedial prefrontal, lateral and dorsolateral prefrontal, and orbitofrontal cortex are also responsible for higher processing in regards to decision-making [ 69 ].

As a whole, the prefrontal cortex is proposed to be responsible for executive functions of cognition, especially regarding making decisions and controlling attention [ 70 , 71 ]. Within the prefrontal cortex, the anterior cingulate cortex is critical for detecting an error, conflict, or task difficulty. Thus, the anterior cingulate cortex plays a critical role in pain affect and evaluating our decisions by assessing multiple factors.

The ventromedial prefrontal cortex also plays a role in decision-making [ 74 , 75 ] and is involved in the integration of emotion and cognition. Regardless if there are no correct answers on moral tasks, emotions ultimately provide a decision that feels more correct.

Though this heuristic can enhance decisions, emotions can also reduce the efficacy of rational decisions. The lateral prefrontal cortex is critical for executive control and, along with the anterior cingulate cortex and the parietal cortex, is partly responsible for control of attention [ 70 ].

Although the lateral prefrontal cortex and especially the dorsolateral prefrontal cortex is thought to be primarily involved in purely cognitive functioning, recent studies have revealed evidence for the integration of cognition and emotion in this area [ 77 , 78 ]. In fact, emotional valence photos could modulate activity in these areas where pleasant photos increased activity and unpleasant photos decreased activity compared to control photos [ 79 ].

The orbitofrontal cortex, like the amygdala, can discriminate positive and negative values of stimuli by integrating sensory and affective information. This stimulus evaluation provided by the amygdala and the orbitofrontal cortex appears to also be responsible for action strategies for current and also future anticipatory occurrences [ 53 , 80 - 82 ].

As a result, both regions refer to critical associations with previous decisions and consequences such that current decisions will be better suited to the wanted outcome. Homeostasis, pain, and cognition can individually impact behavior through powerful biological mechanisms. However, these systems do not act in isolation. Indeed, there is considerable conceptual and neurobiological overlap that highlights the close interaction of decision-making, pain, and homeostasis.

Reductively, this relationship is founded upon pain requiring and eliciting a decision. Yet this interplay becomes more profound when the rationale for similarity is extended further to include the shared characteristics of homeostasis and emotional and cognitive qualities.

Ultimately then, the decision to either escape or allow pain entirely depends on the current homeostatic information which includes current affective, attentional, motivational influences.

Under this idea, it is no wonder that pain is a multidimensional phenomenon that directly impacts homeostasis through its three modalities. To summarize entirely, the sensory component of pain allows an organism to be aware of where and how the homeostatic disturbance occurs, while the affective-motivational component demands attention and motivates an organism to resolve the pain, and the cognitive-evaluative component provides the organism with a solution- a behavioral choice based on previous and current pain situations and what outcomes that are associated with those choices.

Thus, pain disturbs the ideal state homeostasis requires and as a result, drives a decision. This positive feedback loop is necessary for survival. Even more, under this same notion, decision-making is considered the aiding force of homeostasis. Decisions utilize homeostatic information to cognitively and emotionally assess which alternatives provide a more ideal state determined by cost versus benefit.

As a result, decisions promote homeostasis and aid in reverting to the ideal state. Pain, in this case, is a stressor and changes the ideal state, whereas the decision to escape or avoid pain returns homeostatic equilibrium. Additionally, because homeostasis can be reduced to a mechanism of maintenance, resistance, and survival, pain and decision-making are necessary for completing that loop [ 1 , 5 , 32 , 83 ]. This then could suggest that these entities may not be truly separate systems, but rather interconnected.

Evolutionarily, this concept makes sense. By design, each of these biological mechanisms plays a role in increasing the odds of survival.

Functionally, it is anatomically and behaviorally efficient to combine similar like mechanisms along parallel, if not overlapping biological pathways especially when each component revolves around a central goal of survival. Thus, the link between homeostasis, pain, and cognition can be further expounded through the perspective of survival through three means: an alerting system through pain, a mechanism of checks and balances provided by homeostasis, and requirement of action driven by decision-making.

The undeniable overlap in both neural signatures and a conceptual understanding of these phenomenon suggests the importance of survival. However, the numerous factors that can individually influence pain, decisions, and homeostasis, may also play a role in modulating survival. Thus, it may be imperative to consider this complex and integrated relationship when attempting to understand the multi-dimensionality of pain and may provide further insight into how pain and pain treatments may differ across individuals.

Ke Ren completed his Ph. He has nearly 40 years of experiences in biochemical research focusing on Neurosciences and Pain. He has published more than manuscripts and book chapters. He has been serving as an editorial board member of Pain, Journal of Pain, Evidence-Based complementary and alternative Medicine, Pain Research and treatment, and Odontology. The partnership allows the researchers from the university to publish their research under an Open Access license with specified fee discounts.

Bentham Open welcomes institutions and organizations from world over to join as Institutional Member and avail a host of benefits for their researchers. It is known as one of the oldest universities in Malaysia. UPSI was later upgraded to a full university institution on 1 May, , an upgrade from their previous college status.

Their aim to provide exceptional leadership in the field of education continues until today and has produced quality graduates to act as future educators to students in the primary and secondary level. Bentham Open publishes a number of peer-reviewed, open access journals. These free-to-view online journals cover all major disciplines of science, medicine, technology and social sciences. Bentham Open provides researchers a platform to rapidly publish their research in a good-quality peer-reviewed journal.

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Bentham Open welcomes institutions and organizations from the world over to join as Institutional Member and avail a host of benefits for their researchers.

The first Ministry of Health in Jordan was established in The Ministry began its duties in , the beginning of the health development boom in Jordan. The first accomplishment was the establishment of six departments in the districts headed by a physician and under the central administration of the Ministry. All peer-reviewed, accepted submissions meeting high research and ethical standards are published with free access to all. The Porto University was founded in Porto University create scientific, cultural and artistic knowledge, higher education training strongly anchored in research, the social and economic valorization of knowledge and active participation in the progress of the communities in which it operates.

The Open Pain Journal is an Open Access online journal, which publishes research articles, reviews, letters, case reports and guest-edited single topic issues in all areas of pain research.

Bentham Open ensures speedy peer review process and accepted papers are published within 2 weeks of final acceptance. The Open Pain Journal is committed to ensuring high quality of research published. We believe that a dedicated and committed team of editors and reviewers make it possible to ensure the quality of the research papers. The overall standing of a journal is in a way, reflective of the quality of its Editor s and Editorial Board and its members.

The Open Pain Journal is seeking energetic and qualified researchers to join its editorial board team as Editorial Board Members or reviewers. Proficiency in English language. Submit or solicit at least one article for the journal annually. Peer-review of articles for the journal, which are in the area of expertise 2 to 3 times per year. If you are interested in becoming our Editorial Board member, please submit the following information to info benthamopen.

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The equivalent value of NH 4 2 Cr 2 O 7 can then be calculated by dividing 1. Thus, for NH 4 2 Cr 2 O 7 , dissolving 0. What are the concentrations of all ionic species derived from the solutes in these aqueous solutions? Given: molarity. Asked for: concentrations.

A Classify each compound as either a strong electrolyte or a nonelectrolyte. B If the compound is a nonelectrolyte, its concentration is the same as the molarity of the solution. If the compound is a strong electrolyte, determine the number of each ion contained in one formula unit. Find the concentration of each species by multiplying the number of each ion by the molarity of the solution.

A Sodium hydroxide is an ionic compound that is a strong electrolyte and a strong base in aqueous solution:. Recall from Section 4. Thus alcohols are nonelectrolytes. One of the great wonders of the cell membrane is its ability to regulate the concentration of substances inside the cell.

The phospholipids are tightly packed together, and the membrane has a hydrophobic interior. This structure causes the membrane to be selectively permeable. A membrane that has selective permeability allows only substances meeting certain criteria to pass through it unaided.

In the case of the cell membrane, only relatively small, nonpolar materials can move through the lipid bilayer remember, the lipid tails of the membrane are nonpolar.

Some examples of these are other lipids, oxygen and carbon dioxide gases, and alcohol. However, water-soluble materials—like glucose, amino acids, and electrolytes—need some assistance to cross the membrane because they are repelled by the hydrophobic tails of the phospholipid bilayer. All substances that move through the membrane do so by one of two general methods, which are categorized based on whether or not energy is required. Passive transport is the movement of substances across the membrane without the expenditure of cellular energy.

In contrast, active transport is the movement of substances across the membrane using energy from adenosine triphosphate ATP. You have seen examples of these types of transport mechanisms in Chapter 4, where we learned about the generation of an action potential within a neuron. In order to understand how substances move passively across a cell membrane, it is necessary to understand concentration gradients and diffusion. A concentration gradient is the difference in concentration of a substance across a space.

When molecules move in this way, they are said to move down their concentration gradient. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. A couple of common examples will help to illustrate this concept. Imagine being inside a closed bathroom. If a bottle of perfume were sprayed, the scent molecules would naturally diffuse from the spot where they left the bottle to all corners of the bathroom, and this diffusion would go on until no more concentration gradient remains.

Another example is a spoonful of sugar placed in a cup of tea. Eventually the sugar will diffuse throughout the tea until no concentration gradient remains. In both cases, if the room is warmer or the tea hotter, diffusion occurs even faster as the molecules are bumping into each other and spreading out faster than at cooler temperatures. Having an internal body temperature around Whenever a substance exists in greater concentration on one side of a semipermeable membrane, such as the cell membranes, any substance that can move down its concentration gradient across the membrane will do so.

Consider substances that can easily diffuse through the lipid bilayer of the cell membrane, such as the gases oxygen O 2 and CO 2. O 2 generally diffuses into cells because it is more concentrated outside of them, and CO 2 typically diffuses out of cells because it is more concentrated inside of them. Neither of these examples requires any energy on the part of the cell, and therefore they use passive transport to move across the membrane. Before moving on, you need to review the gases that can diffuse across a cell membrane.

Because cells rapidly use up oxygen during metabolism, there is typically a lower concentration of O 2 inside the cell than outside. As a result, oxygen will diffuse from the interstitial fluid directly through the lipid bilayer of the membrane and into the cytoplasm within the cell. On the other hand, because cells produce CO 2 as a byproduct of metabolism, CO 2 concentrations rise within the cytoplasm; therefore, CO 2 will move from the cell through the lipid bilayer and into the interstitial fluid, where its concentration is lower.

This mechanism of molecules moving across a cell membrane from the side where they are more concentrated to the side where they are less concentrated is a form of passive transport called simple diffusion Figure 8.

Simple Diffusion across the Cell Plasma Membrane. The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion. Large polar or ionic molecules, which are hydrophilic, cannot easily cross the phospholipid bilayer.

Very small polar molecules, such as water, can cross via simple diffusion due to their small size. Charged atoms or molecules of any size cannot cross the cell membrane via simple diffusion as the charges are repelled by the hydrophobic tails in the interior of the phospholipid bilayer. Solutes dissolved in water on either side of the cell membrane will tend to diffuse down their concentration gradients, but because most substances cannot pass freely through the lipid bilayer of the cell membrane, their movement is restricted to protein channels and specialized transport mechanisms in the membrane.

A common example of facilitated diffusion is the movement of glucose into the cell, where it is used to make ATP. Although glucose can be more concentrated outside of a cell, it cannot cross the lipid bilayer via simple diffusion because it is both large and polar.

To resolve this, a specialized carrier protein called the glucose transporter will transfer glucose molecules into the cell to facilitate its inward diffusion. There are many other solutes that must undergo facilitated diffusion to move into a cell, such as amino acids, or to move out of a cell, such as wastes. Because facilitated diffusion is a passive process, it does not require energy expenditure by the cell. Water also can move freely across the cell membrane of all cells, either through protein channels or by slipping between the lipid tails of the membrane itself.

Osmosis is the diffusion of water through a semipermeable membrane Figure 8. The movement of water molecules is not itself regulated by cells, so it is important that cells are exposed to an environment in which the concentration of solutes outside of the cells in the extracellular fluid is equal to the concentration of solutes inside the cells in the cytoplasm.

T onicity is used to describe the variations of solute in a solution with the solute inside the cell. Three terms— hypotonic, isotonic, and hypertonic —are used to compare the relative solute concentration of a cell to that of the extracellular fluid surrounding the cells. In a hypotonic solution , such as tap water, the extracellular fluid has a lower concentration of solutes than the fluid inside the cell, and water enters the cell.

Note that water is moving down its concentration gradient If this occurs in an animal cell, the cell may burst, or lyse. Because the cell has a lower concentration of solutes, the water will leave the cell. In effect, the solute is drawing the water out of the cell. This may cause an animal cell to shrivel, or crenate. In an isotonic solution , the extracellular fluid has the same solute concentration as the cell.

If the concentration of solutes of the cell matches that of the extracellular fluid, there will be no net movement of water into or out of the cell. Blood cells in hypertonic, isotonic, and hypotonic solutions take on characteristic appearances as shown in Figure 8. Various organ systems, particularly the kidneys, work to maintain this homeostasis. Some organisms, such as plants, fungi, bacteria, and some protists, have cell walls that surround the plasma membrane and prevent cell lysis.

The plasma membrane can only expand to the limit of the cell wall, so the cell will not lyse. In fact, the cytoplasm in plants is always slightly hypertonic compared to the cellular environment, and water will always enter a cell if water is available.

This influx of water produces turgor pressure, which stiffens the cell walls of the plant Figure 8. In nonwoody plants, turgor pressure supports the plant. If the plant cells become hypertonic, as occurs in drought or if a plant is not watered adequately, water will leave the cell. Plants lose turgor pressure in this condition and wilt. Another mechanism besides diffusion to passively transport materials between compartments is filtration. Unlike diffusion of a substance from where it is more concentrated to less concentrated, filtration uses a hydrostatic pressure gradient that pushes the fluid—and the solutes within it—from a higher pressure area to a lower pressure area.

Filtration is an extremely important process in the body. For example, the circulatory system uses filtration to move plasma and substances across the endothelial lining of capillaries and into surrounding tissues, supplying cells with the nutrients.

Furthermore, filtration pressure in the kidneys provides the mechanism to remove wastes from the bloodstream. For all of the transport methods described above, the cell expends no energy. Membrane proteins that aid in the passive transport of substances do so without the use of ATP. During active transport, ATP is required to move a substance across a membrane, often with the help of protein carriers, and usually against its concentration gradient. One of the most common types of active transport involves proteins that serve as pumps.

Similarly, energy from ATP is required for these membrane proteins to transport substances—molecules or ions—across the membrane, usually against their concentration gradients from an area of low concentration to an area of high concentration. These pumps are particularly abundant in nerve cells, which are constantly pumping out sodium ions and pulling in potassium ions to maintain an electrical gradient across their cell membranes.

An electrical gradient is a difference in electrical charge across a space. In the case of nerve cells, for example, the electrical gradient exists between the inside and outside of the cell, with the inside being negatively-charged at around mV relative to the outside.

This process is so important for nerve cells that it accounts for the majority of their ATP usage. Active transport pumps can also work together with other active or passive transport systems to move substances across the membrane. For example, the sodium-potassium pump maintains a high concentration of sodium ions outside of the cell.

Therefore, if the cell needs sodium ions, all it has to do is open a passive sodium channel, as the concentration gradient of the sodium ions will drive them to diffuse into the cell.

In this way, the action of an active transport pump the sodium-potassium pump powers the passive transport of sodium ions by creating a concentration gradient. When active transport powers the transport of another substance in this way, it is called secondary active transport. Symporters are secondary active transporters that move two substances in the same direction.

Because cells store glucose for energy, glucose is typically at a higher concentration inside of the cell than outside. However, due to the action of the sodium-potassium pump, sodium ions will easily diffuse into the cell when the symporter is opened. The flood of sodium ions through the symporter provides the energy that allows glucose to move through the symporter and into the cell, against its concentration gradient.

Conversely, antiporters are secondary active transport systems that transport substances in opposite directions. Other forms of active transport do not involve membrane carriers. Once pinched off, the portion of membrane and its contents becomes an independent, intracellular vesicle. A vesicle is a membranous sac—a spherical and hollow organelle bounded by a lipid bilayer membrane.

Endocytosis often brings materials into the cell that must to be broken down or digested. Many immune cells engage in phagocytosis of invading pathogens. Like little Pac-men, their job is to patrol body tissues for unwanted matter, such as invading bacterial cells, phagocytize them, and digest them.

Phagocytosis and pinocytosis take in large portions of extracellular material, and they are typically not highly selective in the substances they bring in.

Cells regulate the endocytosis of specific substances via receptor-mediated endocytosis. Receptor-mediated endocytosis is endocytosis by a portion of the cell membrane that contains many receptors that are specific for a certain substance.

Iron, a required component of hemoglobin, is endocytosed by red blood cells in this way. Iron is bound to a protein called transferrin in the blood. Specific transferrin receptors on red blood cell surfaces bind the iron-transferrin molecules, and the cell endocytoses the receptor-ligand complexes. Many cells manufacture substances that must be secreted, like a factory manufacturing a product for export.

These substances are typically packaged into membrane-bound vesicles within the cell. When the vesicle membrane fuses with the cell membrane, the vesicle releases it contents into the interstitial fluid. The vesicle membrane then becomes part of the cell membrane. Cells of the stomach and pancreas produce and secrete digestive enzymes through exocytosis Figure 8.

Endocrine cells produce and secrete hormones that are sent throughout the body, and certain immune cells produce and secrete large amounts of histamine, a chemical important for immune responses. To ensure that you understand the material in this chapter, you should review the meanings of the bold terms in the following summary and ask yourself how they relate to the topics in the chapter.

A solution is a homogeneous mixture. The major component is the solvent , while the minor component is the solute. Solutions can have any phase; for example, an alloy is a solid solution. Solutes are soluble or insoluble , meaning they dissolve or do not dissolve in a particular solvent. The terms miscible and immiscible , instead of soluble and insoluble, are used for liquid solutes and solvents.

The statement like dissolves like is a useful guide to predicting whether a solute will dissolve in a given solvent. Dissolving occurs by solvation , the process in which particles of a solvent surround the individual particles of a solute, separating them to make a solution. For water solutions, the word hydration is used. If the solute is molecular, it dissolves into individual molecules. If the solute is ionic, the individual ions separate from each other, forming a solution that conducts electricity.

Such solutions are called electrolytes. If the dissociation of ions is complete, the solution is a strong electrolyte. If the dissociation is only partial, the solution is a weak electrolyte. Solutions of molecules do not conduct electricity and are called nonelectrolytes. The amount of solute in a solution is represented by the concentration of the solution. The maximum amount of solute that will dissolve in a given amount of solvent is called the solubility of the solute.

Through a process called excitotoxicity, glutamate spreads through the brain and kills cells that were not affected by the blockage, often leading to widespread brain damage. Many mechanisms maintain appropriate cell growth: Cell division occurs in response to external signals 1. Enzymes repair damaged DNA 2. Cells make connections with their neighbors 3. If these connections suddenly change, neighboring cells send out an alert. Cells respect and stay within tissue boundaries 4. If a cell is beyond repair, it initiates its own death 5.

Cell growth and division is such an important process that it is under tight control with many checks and balances. But even so, cell communication can break down. The result is uncontrolled cell growth, often leading to cancer. Cancer can occur in many ways, but it always requires multiple signaling breakdowns. Often, cancer begins when a cell gains the ability to grow and divide even in the absence of a signal.

Ordinarily this unregulated growth triggers a signal for self-destruction. But when the cell also loses the ability to respond to death signals, it divides out of control, forming a tumor. Later cell communication events cause blood vessels to grow into the tumor, enabling it to grow larger. Additional signals allow the cancer to spread to other parts of the body. During an asthma attack, signaling molecules cause a narrowing of breathing passages in the lungs, making it difficult to breathe.

Many drugs that treat asthma mimic natural signals that tell muscle cells in the lungs to relax, allowing breathing passages to open. Just as cell communication can go wrong resulting in disease, many disease treatments rely on cell communication. If you think of disease as a roadblock in cell communication, treatment is an alternate route.