Which type of feedback promotes homeostasis

This ensures that the tissue will have enough oxygen to support its higher level of metabolism. Maintaining internal conditions in the body is called homeostasis from homeo-, meaning similar, and stasis, meaning standing still. But if you think about anatomy and physiology, even maintaining the body at rest requires a lot of internal activity. Your brain is constantly receiving information about the internal and external environment, and incorporating that information into responses that you may not even be aware of, such as slight changes in heart rate, breathing pattern, activity of certain muscle groups, eye movement, etc.

Any of these actions that help maintain the internal environment contribute to homeostasis. We can consider the maintenance of homeostasis on a number of different levels. For example, consider what happens when you exercise, which can represent challenges to various body systems.

Yet instead of these challenges damaging your body, our systems adapt to the situation. At the whole-body level, you notice some specific changes: your breathing and heart rate increase, your skin may flush, and you may sweat. If you continue to exercise, you may feel thirsty. These effects are all the result of your body trying to maintain conditions suitable for normal function:. Feedback loop is defined as a system used to control the level of a variable in which there is an identifiable receptor sensor , control center integrator or comparator , effectors, and methods of communication.

Terminology in this area is often inconsistent. For example, there are cases where components of a feedback loop are not easily identifiable, but variables are maintained in a range. Such situations are still examples of homeostasis and are sometimes described as a feedback cycle instead of a feedback loop. Feedback Cycle is defined as any situation in which a variable is regulated and the level of the variable impacts the direction in which the variable changes i.

With this terminology in mind, homeostasis then can be described as the totality of the feedback loops and feedback cycles that the body incorporates to maintain a suitable functioning status. Air conditioning is a technological system that can be described in terms of a feedback loop. The thermostat senses the temperature, an electronic interface compares the temperature against a set point the temperature that you want it to be.

If the temperature matches or is cooler, then nothing happens. If the temperature is too hot, then the electronic interface triggers the air-conditioning unit to turn on. Once the temperature is lowered sufficiently to reach the set point, the electronic interface shuts the air-conditioning unit off.

For this example, identify the steps of the feedback loop. Cruise control is another technological feedback system. The idea of cruise control is to maintain a constant speed in your car. If the speed is too slow, the interface stimulates the engine; if the speed is too fast, the interface reduces the power to the tires. Remember that homeostasis is the maintenance of a relatively stable internal environment.

When a stimulus, or change in the environment, is present, feedback loops respond to keep systems functioning near a set point, or ideal level. Feedback is a situation when the output or response of a loop impacts or influences the input or stimulus. Positive feedback loops are inherently unstable systems.

Because a change in an input causes responses that produce continued changes in the same direction, positive feedback loops can lead to runaway conditions. The muscle contractions of shivering release heat while using up ATP.

The brain triggers the thyroid gland in the endocrine system to release thyroid hormone, which increases metabolic activity and heat production in cells throughout the body. The brain also signals the adrenal glands to release epinephrine adrenaline , a hormone that causes the breakdown of glycogen into glucose, which can be used as an energy source.

The breakdown of glycogen into glucose also results in increased metabolism and heat production. A deviation from the normal range results in more change, and the system moves farther away from the normal range. Positive feedback in the body is normal only when there is a definite end point.

Childbirth at full term is an example of a situation in which the maintenance of the existing body state is not desired. The events of childbirth, once begun, must progress rapidly to a conclusion or the life of the mother and the baby are at risk. The extreme muscular work of labor and delivery are the result of a positive feedback system Figure 1.

The first contractions of labor the stimulus push the baby toward the cervix the lowest part of the uterus. The cervix contains stretch-sensitive nerve cells that monitor the degree of stretching the sensors. These nerve cells send messages to the brain, which in turn causes the pituitary gland at the base of the brain to release the hormone oxytocin into the bloodstream.

Oxytocin causes stronger contractions of the smooth muscles in of the uterus the effectors , pushing the baby further down the birth canal. This causes even greater stretching of the cervix. The cycle of stretching, oxytocin release, and increasingly more forceful contractions stops only when the baby is born.

At this point, the stretching of the cervix halts, stopping the release of oxytocin. A second example of positive feedback centers on reversing extreme damage to the body. The endocrine system helps regulate and maintain various body functions by synthesizing and releasing hormones. It is composed of glands located through out the body that secrete chemicals called hormones directly into the blood. Hormones stimulate various body tissues. The hormone levels in the blood are regulated by a highly specialized homeostatic mechanism called feedback.

Information regarding the hormone level or its effect is fed back to the gland that the hormone secreted from. Due to positive and negative feedback, our body will be in homeostasis. In negative feedback, the response will reverse or cause the opposite effect of the original stimulus. Negative feedback can be explained with the process of insulin production and release.

After a meal the blood sugar level will be elevated due to the absorption of sugars from the digestive tract. This triggers the release of insulin from pancreas.

Insulin converts sugar into cells and hence the blood sugar level drops. Solutes that dissolve into individual neutral molecules without dissociation do not impart additional electrical conductivity to their solutions and are called nonelectrolytes. Polar covalent compounds, such as table sugar C 12 H 22 O 11 , are good examples of nonelectrolytes.

The term electrolyte is used in medicine to mean any of the important ions that are dissolved in aqueous solution in the body. Sports drinks such as Gatoraid have combinations of these key electrolytes, to help replenish electrolyte loss following a hard workout.

Similarly, solutions can also be made by mixing two compatible liquids together. The liquid in the lower concentration is termed the solute, and the one in higher concentration the solvent. When two similar solutions are placed together and are able to mix into a solution, they are said to be miscible. Liquids that do not share similar characteristics and cannot mix together, on the other hand, are termed immiscible. For example, the oils found in olive oil, such as oleic acid C 18 H 34 O 2 have mainly nonpolar covalent bonds which do not have intermolecular forces that are strong enough to break the hydrogen bonding between the water molecules.

Thus, water and oil do not mix and are said to be immiscible. Other factor such as temperature and pressure also affects the solubility of a solvent. Thus, in specifying solubility, one should also be aware of these other factors. Back to the Top. In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. All of us have a qualitative idea of what is meant by concentration.

Anyone who has made instant coffee or lemonade knows that too much powder gives a strongly flavored, highly concentrated drink, whereas too little results in a dilute solution that may be hard to distinguish from water.

Quantitatively, the concentration of a solution describes the quantity of a solute that is contained in a particular quantity of that solution.

Knowing the concentration of solutes is important in controlling the stoichiometry of reactants for reactions that occur in solution, and are critical for many aspects of our lives, from measuring the correct dose of medicine to detecting chemical pollutants like lead and arsenic.

Chemists use many different ways to define concentrations. In this section, we will cover the most common ways of presenting solution concentration.

These include: Molarity and Parts Per Solutions. The most common unit of concentration is molarity , which is also the most useful for calculations involving the stoichiometry of reactions in solution. The molarity M of a solution is the number of moles of solute present in exactly 1 L of solution. Note that the volume indicated is the total volume of the solution and includes both the solute and the solvent. For example, an aqueous solution that contains 1 mol g of sucrose in enough water to give a final volume of 1.

In chemical notation, square brackets around the name or formula of the solute represent the concentration of a solute. Calculate the number of moles of sodium hydroxide NaOH needed to make 2. This will allow you to cancel out your units when doing the calculation. Asked for: amount of solute in moles. Strategy: 1 Rearrange the equation above to solve for the desired unit, in this case for moles.

Perform any conversions that are needed so that the units match. The given values for this equation are the volume 2. The volume units for both of these numbers are in Liters L and thus, match. Therefore, no conversions need to be made. There is no piece of equipment that can measure out the moles of a substance.

For this, we need to convert the number of moles of the sample into the number of grams represented by that number. We can then easily use a balance to weigh the amount of substance needed for the solution. For the example above:. To actually make the solution, it is typical to dissolve the solute in a small amount of the solvent and then once the solute is dissolved, the final volume can be brought up to 2.

If you were to add 10 g of NaOH directly to 2. Remember that the final volume must include both the solute and the solvent. Note that the volume of the solvent is not specified. Since the solute occupies space in the solution, the volume of the solvent needed is less than the desired total volume of solution. To make a solution, start by addition a portion of the solvent to the flask. Next, weigh out the appropriate amount of solute and slowly add it to the solvent.

Once it is dissolved in the solvent, the volume of the solution can be brought up to the final solution volume. For the volumetric flask shown, this is indicated by the black line in the neck of the flask. In this case, it indicates mL of solution. Volumetric flasks exist in many different sizes to accommodate different solution volumes. Graduated cylinders can also be used to accurately bring a solution to its final volume.

Other glassware, including beakers and Erlenmeyer flasks are not accurate enough to make most solutions. The solution in Figure 7. Given: mass of solute and volume of solution. Asked for: concentration M.

In the consumer and industrial world, the most common method of expressing the concentration is based on the quantity of solute in a fixed quantity of solution. Percent solutions define the quantity of a solute that is dissolved in a quantity of solution multiplied by When making a percent solution, it is important to indicate what units are being used, so that others can also make the solution properly. Also, recall that the solution is the sum of both the solvent and the solute when you are performing percent calculations.

Thus, the following equation can be used when calculating percent solutions:. As an example, a 7. How much water is in the solution? Thus, we can fill in the values and then solve for the unknown.

How many grams of NaCl are required to make mL of a For more dilute solutions, parts per million 10 6 ppm and parts per billion 10 9 ; ppb are used. These terms are widely employed to express the amounts of trace pollutants in the environment.

There are also ppm and ppb units defined with respect to numbers of atoms and molecules. The mass-based definitions of ppm and ppb are given here:. Both ppm and ppb are convenient units for reporting the concentrations of pollutants and other trace contaminants in water. Concentrations of these contaminants are typically very low in treated and natural waters, and their levels cannot exceed relatively low concentration thresholds without causing adverse effects on health and wildlife.

For example, the EPA has identified the maximum safe level of fluoride ion in tap water to be 4 ppm. Inline water filters are designed to reduce the concentration of fluoride and several other trace-level contaminants in tap water Figure 8. This can be very useful as it is easier for us to think about water in terms of its volume, rather than by its mass. In addition, the density of water is 1. For example, if we find that there is lead contamination in water of 4 ppm, this would mean that there are:.

Concentrations of ionic solutes are occasionally expressed in units called equivalents Eq. One equivalent equals 1 mol of positive or negative charge.

In a more formal definition, the equivalent is the amount of a substance needed to do one of the following:. By this definition, an equivalent is the number of moles of an ion in a solution, multiplied by the valence of that ion. The valence of calcium is 2, so for that ion you have 1 mole and 2 equivalents. A solution of a desired concentration can also be prepared by diluting a small volume of a more concentrated solution with additional solvent.

A stock solution , which is a prepared solution of known concentration, is often used for this purpose. Diluting a stock solution is preferred when making solutions of very weak concentrations, because the alternative method, weighing out tiny amounts of solute, can be difficult to carry out with a high degree of accuracy.

Dilution is also used to prepare solutions from substances that are sold as concentrated aqueous solutions, such as strong acids. The procedure for preparing a solution of known concentration from a stock solution is shown in Figure 8. It requires calculating the amount of solute desired in the final volume of the more dilute solution and then calculating the volume of the stock solution that contains this amount of solute.

Remember that diluting a given quantity of stock solution with solvent does not change the amount of solute present, only the volume of the solution is changing. The relationship between the volume and concentration of the stock solution and the volume and concentration of the desired diluted solution can therefore be expressed mathematically as:.

Where M s is the concentration of the stock solution, V s is the volume of the stock solution, M d is the concentration of the diluted solution, and V d is the volume of the diluted solution. What volume of a 3. Given: volume and molarity of dilute solution, and molarity of stock solution.

Asked for: volume of stock solution. Strategy and Solution:. For Dilution problems, as long as you know 3 of the variables, you can solve for the 4th variable. Next, check to make sure that like terms have the same units. For example, Md and Ms are both concentrations, thus, to be able to perform the calculations, they should be in the same unit in this case they are both listed in Molarity.

If the concentrations were different, say one was given in Molarity and the other in percent or one was in Molarity and the other was in Millimolarity, one of the terms would need to be converted so that they match.

That way, the units will cancel out and leave you with units of volume, in this case. Finally, fill in the equation with known values and calculate the final answer. Note that if mL of stock solution is needed, that you can also calculate the amount of solvent needed to make the final dilution. Thus far, we have been discussing the concentration of the overall solution in terms of total solute divided by the volume of the solution.

When ionic compounds dissolve in a solution, they break apart into their ionic state.