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Homeotasis
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Concept of Homeotasis
Homeostasis is the maintenance of a constant
internal environment within a living organism.
Homeostatic mechanisms maintain optimal
physical and chemical conditions in the body
to allow normal enzymatic and other cellular
activities to be carried out.
In biological systems, homeostasis usually
achieved by negative feedback.
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inputReceptor(sensor)
Coordinator(control)
Effector(output)
Feedback loop
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(a) A stimulus is a change in the level of the factor(parameter) being regulated.This detectablechange is known as the input.
(b) The receptor (sensor ) detect a stimulus.
(c) A coordinator (control) receives and controlinformation from the receptor.It triggers the
action that will correct the change. (d) An effector (output) carries out the action
(corrective mechanism) that restore condition toits optimum.
(e) The feedback loop enables the sensor tomonitor any changes brought about the effector.
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Control of Blood Glucose Level
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When blood glucose concentration
rises above the set point, insulin issecreted by the beta cells of the
islets of Langerhans in the pancreas
The insulin molecules bind to
receptor on the cell membrane
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And bring about changes in both cell
surface membrane permeability and
enzyme activity which leads to the
following effects:
An increase in the uptake of glucoseand amino acids into cells
An increase in the rate of conversion of
glucose to fat in adipose cells
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An increase in the rate of
conversion of glucose to glycogen
in liver and muscle cells
(glycogenesis)
An increase in the rate of cellularrespiration (conversion of glucose
to O and HO)
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Insulin affects all the cells but
muscle, fat and liver cells are its main
targets
When blood glucose concentrationfalls below the set point, the alpha
cells of the islets of Langerhans in
the pancreas secrete glucagon
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DIABETES MELLITUS
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Diabetes mellitus is caused by the failure of
beta cells in the pancreas to produce insulin or
the failure/reduction of target cells to respondto insulin.
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The liver and other cells are unable to take up
and metabolise glucose. The blood glucose
level rises to above normal level(hyperglycaemia).
The patients feels thirsty as more water is
needed to dilute the blood and to lower theosmotic concentration of the blood.
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The kidney tubules are unable to reabsorb the
high level of glucose. Excess glucose is
removed in the urine (glycosuria).
Fats and proteins are used as respiratory
substrates resulting in the patient losing
weight.
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Diabetes Mellitus
Type 1 (insulindependent
diabetes mellitus)
Type 2 (non-
insulin dependentdiabetes mellitus)
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TYPE 2 DIABETES MELLITUS (non-
insulin dependent diabetes mellitus)
The remaining 80-90% of the patients has thistype of diabetes.
It is due to defiency in insulin secretion or the
failure of insulin receptor on the plasmamembrane of target cells to respond to insulin.
This is often associated with inherited geneticfactors, diet, obesity and increasing age.
Some patients control their blood glucose levelby regulating their diet and exercise. In severecase they still need daily insulin injections.
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Long term complications of diabetes
mellitus if not treated include kidney
disease, cataracts, blindness andcardiovascular disorders.
Reduced circulation can lead to gangrene
in the arm and legs. Excessive metabolism of fats lead to high
concentration of ketones in the blood,
acidosis (acidic metabolites accumulate in
the blood) and the lowering of blood pH
which can lead to coma and death
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Blood glucose levels can now be
monitored using dipsticks and electronic
biosensors. Human insulin used in treating diabetics
can now be produced on a large scale by
genetic engineering.
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