Archive for March, 2012

Negative feedback is a naturally occurring / automatic off-switch in the body.

English: Electric water boiler Deutsch: Wasser...

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Imagine you are boiling water in a modern electric kettle.

  • Your aim is to heat the water up to boiling temperature to, say, make a cup of tea.
  • When you switch the kettle on, this has the effect of heating an element in the kettle and heat is gradually transferred to the water causing it to boil.
  • If you keep the element on permanently, the water will gradually become steam, there will be no water left for your cup of tea and your will have wasted a lot of energy.
  • Instead, as the water becomes steam, it passes through vents at the top of the kettle – the steam heats up a thermostat and when it reaches the set temperature, the kettle switches off.

This is negative feedback because the very water which you were heating, once at the required temperature, causes the heating process to switch off.

So, relating that to processes which occur in nature (of which there are many), here’s an example of biological negative feedback:

  • If an animal’s blood glucose begins to rise, cells in the pancreas (called Beta Cells) detect this increase and release insulin.
  • The effect of insulin is to allow glucose to be taken from the blood, into the cells, so that the cells can use it for energy.
  • As the cells take up glucose, the glucose levels in the blood begin to fall.
  • Falling levels of glucose are detected by the Beta Cells in the pancreas and – this is the Negative Feedback partinsulin release is switched off.
  • This helps to prevent glucose levels falling to dangerously low levels.

Negative Feedback Mechanism
Other examples of negative feedback include, temperature regulation (under central nervous influence), blood pressure control (by the Renin-Angiotensin-Aldosterone System), blood calcium control and many others.

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A common cause of confusion in anatomy is the difference between cilia and villi.  Both of these are finger-like projections found in the body but they are found in different places and have entirely different jobs to do.

Cilia are tiny hair-like structures which are found on the surface of cells lining the upper-airways (the trachea and bronchi).  The job of the cilia is to WIGGLE!  The airways are coated with a thin layer of mucus which traps dust and particles stopping them from getting into the lungs.  The cilia wiggle to move the mucus up the airways toward the mouth so that it can be coughed up and swallowed.

Cilia

Villi are finger like structures found in the wall of the intestine [villus = one; villi = many].  Because they come out from the wall of the intestine, they have the effect of creating more space for absorption of nutrients; that is: they increase the surface area.  Villi are filled with blood vessels to take away the nutrients to the circulation.  They also contain a structure called a lacteal which absorbs fats from the intestine for delivery to the blood stream.

Villi

The surface area of the villus is increased even further by the presence of microvilli.  Microvilli are tiny structures on the surface of the villi.

NOTE: VILLI DO NOT WIGGLE – THEY DO NOT MOVE FOOD THROUGH THE INTESTINE.