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Homeostasis: 2. The negative feedback mechanism involving the hormone insulin for controlling the concentration of blood glucose

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Sub-index of notes on homeostasis: Blood sugar level control, insulin, diabetes


(2) The negative feedback mechanism for controlling the concentration of blood glucose

How does the body control blood sugar level ?

For glucose level read 'the blood concentration of the sugar glucose' C6H12O6

The pancreas is always checking on the concentration of glucose in the blood that flows through it.

(a) If your glucose level in the blood is too high the 1st hormone insulin is secreted by the pancreas.

After a meal the glucose concentration in the blood rises and insulin causes it to move into the cells in the body for respiration.

BUT, the insulin also causes cells in liver and muscle to convert some of the glucose into glycogen - an chemical energy store.

So, prompted by the pancreas detecting a high level of blood sugar, the insulin secreted promotes cellular uptake of glucose for respiration AND the formation of glycogen.

If the glucose concentration is too high, the pancreas secretes insulin.

Therefore, the conversion of glucose to glycogen, reduces the glucose concentration in the blood.

When the glucose level reduces, insulin is no longer secreted by the pancreas and the conversion of glucose to glycogen stops and the blood glucose level is stabilised.

(b) If the pancreas detects your blood glucose level is too low the 2nd hormone glucagon is secreted by the pancreas into the bloodstream.

Glucagon makes the liver and muscle cells convert glycogen into glucose and transported to where it is needed.

So the blood level of glucose increases - it needs to if you are engaged in vigorous exercise!

When the glucose concentration reaches an appropriate level, secretion of either insulin or glucagon stops and so does the interconversion of glycogen and glucose, thus stabilising the glucose level.

Note:

(i) Don't mix up or misspell the hormone glucagon and the 'energy store' glycogen !

(ii) Insulin hormone reduces glucose level and glucagon hormone increases glucose level.

(iii) When two effectors or substances work in opposite ways to restore something in the body to normal, they are said to be antagonistic.

The two hormones insulin and glucagon are working antagonistically because they have opposite effects, but both effects are trying to return the glucose level to normal.

The control of blood sugar levels is described below in terms of a 'homeostasis mechanism' - a 'negative feedback mechanism' using both a tabular and graphical representation of the process.

The homeostasis negative feedback system for glucose level control

(a) The homeostasis negative feedback system for too high a glucose level - insulin is added (b) The homeostasis negative feedback system for too low a glucose level - glucagon added
1. The pancreas detects the blood sugar level is too high. 1. The pancreas detects the blood sugar level is too low.
2. Insulin is secreted by the pancreas to mix with the excess glucose. 2. Glucagon is secreted by the pancreas.
3. The excess glucose is now moved from the blood into liver and muscle cells - triggered by the insulin. 3. There is too little glucose but there is glycogen stored in the liver
4. The glucose level is now reduced to the appropriate level. 4. The secreted glucagon triggers the breakdown of glycogen into glucose sugar - using the liver's energy store.
5. Overall the secreted insulin makes the liver turn the excess glucose into glycogen - effectively a store of chemical potential energy for future use. 5. Overall the glucose level is increased in the blood to meet the respiration demands of the body.
This is all automatically done by the organism's complex control systems and enables the organism e.g. your body, to maintain as near as possible the 'ideal' glucose level for healthy life!

BUT it all depends on insulin production - and there may be diabetic problems - read on

A simplified graphical representation of controlling the concentration of glucose in blood.

Both the hormones insulin and glucagon are made and secreted from the pancreas.


Keywords, phrases and learning objectives for this part on the insulin negative feedback mechanism to control blood sugar level

In terms of homeostasis be able to describe and explain the negative feedback mechanism involving the hormone insulin, which is secreted from pancreas, and controls the concentration of glucose (for respiration) in the blood stream. Be able to interpret the body's response (insulin feedback mechanism) from a diagram if the glucose level in the blood becomes too high or too low.


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