The Better Fitness Through Nutrition Glossary
Physical regulatory system: A system that will maintain its internal consistency even though external things try to change it.
System variable: This is the variable that is changed or reprinted in a system.
Set point: This is the optimal/optimum value of the system variable.
Correctional mechanism: This is the part of the system that actually changes the system variable and can return it to the set point.
Detector: This is the part of a system that will monitor or watch the system variable, and find out when the correctional mechanism is to be used to return the system variable to the set point.
Negative feedback: When the system variable returns to the optimal value designated by the set point, negative feedback will alert the correctional mechanism to SHUT OFF.
Satiety mechanism: Delayed mechanisms in the body like ingestion, that the body actually uses to MAKE A GUESS about the potential water and food taken in.
Intracellular fluid: More commonly called the cytoplasm, this is simply the fluid in the cells. The solute levels in the intracellular fluid rarely change because of the difficulty in getting solutes to pass through the cell wall.
Intravascular fluid: This is the blood plasma, or the fluid in the circulatory system, which includes the heart and the blood vessels.
Cerebrospinal fluid: The spinal fluid. It is a very small fluid reservoir when compared to the other three major fluid compartments. Everyday the entire fluid amount in the human body rebuilds itself five times a day.
Isotonic solution: This solution is balanced. Two different solutions that meet with differing concentrations will mix, and the water will flow from one to another, and in isotonic solutions no water flows either way.
Interstitial fluid: This fluid is also called the lymphatic fluid. It "bathes the cells" and both solutes and water can flow in and out it. The levels of concentration in this fluid affect the most systems in the body, and must be monitored closely.
Hypertonic solution: This is a solution that has a higher concentration than the normal concentration, or isotonic. Solutions that are hypertonic DRAW water from other areas, by osmosis, to try and make the concentration difference between two areas smaller, and finally when they are equal, it is isotonic. These hypertonic solutions can dry out the cells.
Hypotonic solution: A hypotonic solution is DILUTE. it will release water out of it, in an attempt to raise the concentration level in the solution compared to surrounding systems. These solutions can burst a cell from water flowing into the cell.
Hypovolemia: It is a condition the human body suffers from, it is literally: a low volume of the blood.
Osmometric thirst: Osmometric thirst is derived from thirst created from water loss by sweating and osmosis in the cells, between the interstitial fluid and the intercellular fluid. It is also a drop in the fluid in the cells, which just happens to be caused by a drop in the intracellular fluid.
Volumetric thirst: Volumetric thirst is caused by a drop in the blood plasma, or intravascular fluid.
Osmoreceptors: These were found my Varney in 1947, they are nerves that are responsible for detecting the concentration of the interstitial fluid.
AV3V: This is an acronym for "anteroventrical tip of the third ventricle" which is located in the hypothalamus. The osmoreceptors for the human body are mostly located here.
OVLT: This is the acronym for "organum vasculosum of the lamina terminalis" which is a circumventricular organ. Meaning that the "organ" is located on the blood side of the blood-brain barrier, and this is the structure in the AV3V that is related to osmometric thirst.
Blood-brain barrier: The blood-brain barrier is the "divider" between... well, the blood stream and the brain (SUPRISE !!!). There are things about the blood and volumetric and osmometric thirst that could be detected if the brain could actually "see" into the blood, but it is very separated from that. Specialized structures like the SFO and the OVLT detect these concentrations and fluid levels.
Angiotensin: This is a hormone that is created from angiotensinogen, which is a protein in the blood. Instigated by the kidneys releasing renin, which is the catalyst for this conversion, angiotensin is responsible for several things in the human body stimulates the SFO to start drinking, causes hormones to be secreted by the pituitary glands and the adrenal glands, increases blood pressure, and it causes the kidney to stop secreting sodium and water, leading to an appetite of both salt and water.
Atrial baroreceptors: These are located in the larger veins of the body (the superior and inferior vena cavas) and the atria of the heart, which actually detect the "stretch" and thus blood level. If stretch drops below a certain level, it usually is caused by a drop in the intravascular fluid. Thus these cause volumetric thirst to be initiated.
Renin: This is the catalyst that initiates the creation of angiotensin from angiotensinogen. This is secreted by the kidneys in response to volumetric thirst.
Median preoptic nucleus: The median preoptic nucleus is the part of the human anatomy which is responsible for initiating drinking because of volumetric thirst. It is utilized by both the SFO and the nucleus of the solitary tract. This is also located on the brain side of the blook-brain barrier BY THE WAY.
SFO: The "subfornical organ" is a structure that is responsible for volumetric thirst which is initiated by the kidneys, when they secrete renin and start the process. Angiotensin stimulates the SFO on the blood side, and it send a message across the barrier to the median preoptic nucleus which then initiates volumetric thirst.
Nucleus of the solitary tract: And when the other path is taken, the atrial baroreceptors send a signal to the nucleus, and this is on the blood side again. Just like the SFO, it sends a signal across the blood-brain barrier to the median preoptic nucleus.
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