These notes contain all the information regarding Homeostasis which is outlined in both Grade 11 and 12. It contains flow charts as well as bulleted explanations. However, thermoregulation has not been included in this document.
Homeostasis
(the ability to maintain internal stability in an organism in response to environmental changes)
Controlled by: nervous and endocrine system
Negative feedback mechanism:
(a normal biological response in which the effects of a reaction slow/stop the reaction)
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Sequence of events:
1. Imbalance is detected by the receptor
(stimulus)
2. Control centre is stimulated
3. Control centre responds
4. Message sent to target organs
(effectors)
5. Effector responds
6. Reverses the imbalance
7. Balance is restored
Important variables and homeostatic mechanisms:
Stimulus: Reason for importance of regulation: Effectors:
Water All metabolic reactions require a balance of water Kidney (nephron-
and salt concentrations in the blood and tissue fluid collecting duct)
Skin
Salt Salt concentration in blood and tissue fluid Kidney (nephron-
determines the osmotic pressure which affects the loop of henle)
cell losing or gaining water via osmosis
Carbon dioxide Carbon dioxide produced during CR affects the PH Lungs (breathing
of blood and tissue fluid. Enzymes are very sensitive muscles)
to PH variations Heart
Glucose Glucose levels need to be maintained to ensure Liver
energy levels are maintained + metabolic functions Pancreas
can continue
Thyroxin Variations in thyroxin levels have an effect on your Thyroid
metabolic rate
Temperature Increase and decrease of normal body temperature Skin (sweat
affects metabolism due to effect on enzyme activity. glands, blood
High temp= denature vessels)
Low temp= slow down
1. Blood glucose regulation:
(regulated by the liver and pancreas: secrete pancreatic hormones, insulin and glucagon)
Blood glucose levels are affected by:
1. Food eaten
, 2. Exercise
3. Adrenalin secretion
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High blood glucose levels:
1. Imbalance- increased blood glucose
levels
2. Control centre- detected by the Islets
of Langerhans in pancreas (beta cells)
3. Responds- Islets of Langerhans
secrete insulin into bloodstream
4. Message to target organs (effectors)-
insulin transported to liver + muscle
cells
5. Responds- enzymes in the liver
catalyse the conversion of excess
glucose into glycogen+ stored
6. Reverses the imbalance- glucose
levels in blood decrease
7. Balance is restored- glucose levels
return to normal
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Low blood glucose levels:
1. Imbalance- decreased blood glucose
levels
2. Control centre- detected by the Islets
of Langerhans in pancreas (alpha cells)
3. Responds- Islets of Langerhans
secrete glucagon into bloodstream
4. Message to target organs (effectors)-
glucagon transported to liver + muscle
cells
5. Responds- glycogen is broken down
into free glucose
6. Reverses the imbalance- glucose
levels in blood increase
7. Balance is restored- glucose levels
return to normal
Diabetes Mellitus (pancreatic disorder):
(causes high blood glucose levels)
Long term effects:
Damage to blood vessels leading to circulatory problems and organ damage
Wounds on skin do not heal well
Negatively affects eyes leading to poor vision and eventually blindness
Type 1: pancreas does not secrete insulin. Affects young children and adults up to 30. Rely on
insulin injections
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