What are the main principles of homeostasis?

Question

ie, how is temperature, blood sugar levels and water content in blood controlled?

Answer 1

Homeostasis

The relatively constant conditions within organisms, or the physiological processes by which such conditions are maintained in the face of external variation.

Similar homeostatic controls are used to keep factors such as temperature and blood pressure nearly constant despite changes in an organism's activity level or surroundings. Such systems operate by detecting changes in the variable that the system is designed to hold constant and initiating some action that offsets any change. All incorporate a sensor within the system that responds when the actual condition differs from the desired one, a device to ensure that any action taken will reduce the difference between actual and desired, and an effector to take the needed action as directed. The crucial aspect is that information is fed back from effector to sensor and action is taken to reduce any imbalance—hence the term negative feedback.

Blood pressure is, at least on a moment-to-moment basis, regulated by a system for which the sensors are stretch-sensitive cells located in the neck arteries that carry blood from heart to brain. An increase in blood pressure triggers sensor activity; their signal passes to the brain; and, in turn, the nerve supplying the heart (the vagus) is stimulated to release a chemical (acetylcholine) that causes the heart to beat more slowly—which decreases blood pressure.

The volume of the blood is subject to similar regulation. Fluid (mainly plasma) moves between the capillaries and the intercellular fluid in response to changes in pressure in the capillaries. A decrease in blood volume is detected by sensors at the base of the brain; the brain stimulates secretion of substances that cause contraction of tiny muscles surrounding the blood vessels that lead into the capillaries. The resulting arteriolar constriction reduces the flow of blood to, and the pressure within, the capillaries, so fluid moves from intercellular space into capillaries, thus restoring overall blood volume.

Answer 2

BASIC PRINCIPLES OF HOMEOSTASIS

HOMEOSTASIS = maintenance of constancy of the INTERNAL ENVIRONMENT

1.Whenever a condition (e.g.. temp; glucose level in blood etc.) deviate from a set point or NORM (e.g.. 37 C; 90mg glucose per 100cm blood) the corrective mechanism is triggered by the very entity which is to be regulated, ie. homeostasis involves a self-adjusting mechanism of the control process being built into the system.

2.In the case of e.g.. glucose regulation an increase in the amount of glucose triggers a process to decrease it. Conversely, a decrease in the glucose level triggers a process to increase it. In both cases the result is a reasonably constant level of glucose. When a change in an entity brings about the OPPOSITE EFFECT this is known as a NEGATIVE FEEDBACK mechanism.

Sometimes the corrective mechanism leading to NEGATIVE feedback breaks down with the result that a deviation from the norm initiates FURTHER deviation. This is known as POSITIVE FEEDBACK.

e.g.. Once the temperature regulating mechanisms fail ,the metabolic rate goes on climbing even if the environmental temp. is no longer increased. This is because every time the metabolic rate increases it generates more heat which increases the metabolic rate a bit more, and so on.

It is difficult to think of any household situation in which positive feedback systems operate. When a baby is born, contractions of the womb become progressively stronger as the head is pressed down into the vagina (birth canal); this is a positive feedback system that results in the expulsion of the baby from the mother's womb.

Another physiological example can be seen in the generatic of a nerve impulse where Na+ (sodium ions) crossing the nerve cell membranes stimulate further Na+ to cross. (see later) This process only lasts for a brief moment.

It is clear from the examples of POSITIVE FEEDBACK (above) that (i) under normal conditions it is UNCOMMON since (ii) the end result is a further increase or further decrease in the entity concerned and hence CONSTANCY IS AVOIDED.

3.Homeostasis must necessarily involve FLUCTUATIONS, small though these may be.
Only by deviating form the NORM can the mechanism be brought into play.

4.The feedback system must have:

·RECEPTORS (or SENSORS) capable of detecting the change;
·a CONTROL MECHANISM (or MONITOR) capable of initiating the appropriate corrective measure;
·EFFECTORS which can carry out these corrective measures.

As a simplified example, consider the movement of fluid through a pump - to make this a physiological system, assume that the fluid is blood and the pump is a heart. The function to be controlled homeostatically is the rate of outflow of blood from the heart, so this is the output and there must be a sensor that measures the rate of outflow. This sensor transmits its measurements to the monitor, which compares the actual with the required output; the monitor sends signals to the pump - the heart muscle - and so adjusts the rate of pumping when the output is different from the set level.

Answer 3

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RE:
What are the main principles of homeostasis?
ie, how is temperature, blood sugar levels and water content in blood controlled?

Answer 4

The purpose of homeostasis is to maintain a constant internal environment, and this is so the enzymes in the body are allowed to work at their optimum levels.

Temperature is controlled by sweating and expansion of blood vessels near the skin (vasodilation) when it is hot. And by shivering and shrinking of blood vessels near the skin (vasoconstriction).

Blood sugar levels are maintained by the hormone insulin, this converts glucose (a sugar) to glygogen (storage). See
http://www.scienceaid.co.uk/biology/humans/hormones.html

Water content is controled by the hormone ADH and the kidneys. It is a much more complicated process, but explained well here:
http://www.scienceaid.co.uk/biology/humans/homeostasis.html

Answer 5

The control of body temperature in humans is a good example of homeostasis in a biological system. In humans, normal body temperature fluctuates around the value of 98.6° F, but various factors can affect this value, including exposure, hormones, metabolic rate, and disease, leading to excessively high or low temperatures. The body's temperature regulation is thought to be controlled by a region in the brain called the hypothalamus. Feedback about body temperature is carried through the bloodstream to the brain and results in compensatory adjustments in the breathing rate, the level of blood sugar, and the metabolic rate. Heat loss in humans is aided by reduction of activity, by perspiration, and by heat-exchange mechanisms that permit larger amounts of blood to circulate near the skin surface. Heat loss is reduced by insulation, decreased circulation to the skin, and cultural modification such as the use of clothing, shelter, and external heat sources. The range between high and low body temperature levels constitutes the homeostatic plateau—the “normal” range that sustains life. As either of the two extremes is approached, corrective action (through negative feedback) returns the system to the normal range.

Answer 6

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Answer 7

The skeletal muscles can shiver to produce heat if the body temperature is too low.
Non-shivering thermogenesis involves the decomposition of fat to produce heat.
Sweating cools the body with the use of evaporation.
The pancreas produces insulin and glucagon to control blood-sugar concentration

Answer 8

Bacteria maintain homeostasis with their cell membrane and lipid bilayer. Nonpolar tails of the Phospholipids make the up the interior of the lipid bilayer because Polar water, both inside and outside the cell repels the nonpolar tails.

Answer 9

By hormones, look up Human Anatomy details for exacts. The obvious one is insulin for blood sugar, and also ADH help regulate water loss via the kidneys

Answer 10

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