Core Ch 18 Homeostasis
18.1 Concepts of homeostasis
Definition of homeostasis:
the ability of an organism to maintain a constant internal environment to enable normal
functioning of cells
Importance of homeostasis:
an organism as a whole will function more efficiently because its cells are maintained at
stable optimum conditions
18.2 Parameters of the internal environment
1. Glucose level in blood
-∵glucose is the main source of energy for cells
∴steady glucose level in blood ensures constant supply of glucose to cells for
respiration
-change in glucose level in blood also affects the water potential of the blood and
tissue fluid
-regulated by the pancreas & liver
2. Gas content in blood
-oxygen is required for respiration to oxidize food
-CO2 produced during respiration affects the p H in blood and thus affects the activity
of enzymes
-regulated by controlling breathing rate & heart rate
3. Water content
-content of water in the body affects the water potential of the blood & tissue fluid
-regulated by the kidney
4. Body temperature
-keeping the body temp constant is essential for enzymes to function properly
-skin is the main organ to regulate heat lossmaintain a constant body temp
18.3 Negative feedback mechanism
-homeostasis is brought about by negative feedback mechanismresults in responses
that have opposite effects to the changes in the parameter, so that the level of the
parameter can be restored to normal
18.4 Regulation of blood glucose level
a. Blood glucose level higher than normal
-an increase in blood glucose level stimulates the pancreas to secrete more insulin into
the blood
stimulates liver cells to convert more glucose to glycogen/increases oxidation of
glucose in respiration by body cells
reduction of blood glucose level
b. Blood glucose level lower than normal
-a decrease in blood glucose level stimulates the pancreas to secrete more glucagon
into the blood
stimulates liver cells to convert more glycogen to glucose (glucose released into the
blood)
rise in blood glucose level
18.5 Diabetes
Type I diabetes: caused by the inability of the pancreas to produce sufficient amount of
insulin
Type II diabetes: caused by the insensitivity to insulin of body cells (body cells do not
respond to insulin)
blood glucose level rises to such a high level after a meal that the kidneys cannot
reabsorb all the glucosesome glucose are excreted in the urine
blood glucose level rises, which makes the water potential in blood dropsbody cells
will lose water to the blood by osmosisincrease in blood volumeincrease in urine
production & excessive thirst
Question bank
1. Referring to the specific organs and hormone involved, describe the sequence
of events that leads to a decrease in blood glucose level.
-an increase in blood glucose level stimulates the pancreas to (1)
-secrete more insulin into the blood stream (1)
-insulin stimulates liver cells (1)
-to convert more blood glucose into liver glycogen (1)
-and stimulates the increase in rate of oxidation of glucose in respiration by body
cells (1)
resulting in a decrease in blood glucose level
2. Explain why the blood glucose level increases after a meal of rice.
-the starch in rice is first digested into glucose (1)
-glucose is then absorbed into the blood in the small intestine
3. Based on your biological knowledge, explain why the urine of a diabetic person
usually contains glucose.
-In the diabetic person, the pancreas cannot produce enough insulin (1)
-thus the liver cannot convert excess glucose in the blood into glycogen (1)
-his blood glucose concentration remains high (1)
-leading to a high level of glucose in the glomerular filtrate (1)
-the kidney tubules cannot reabsorb all the glucose from the filtrate (1)
thus glucose is excreted in the urine
4. Explain why the healthy person had a smaller increase in blood glucose level in
the first hour when compared with the diabetic person.
-In the healthy person, the initial rise in blood glucose level stimulates the secretion
of insulin (1)
-by the pancreas (1)
-while there is less insulin secretion in the diabetic person (1)
-insulin stimulates the conversion of glucose into glycogen in the liver/uptake of
glucose by body cells (1)
-so the increase of blood glucose level in the healthy person is smaller
5. Explain the change in glucose consumption during exercise.
-glucose consumption increases during exercise (1)
-because glucose is used in respiration (1)
-to provide more energy for muscle contraction (1)
6. Explain why a diabetic patient may suffer from hypoglycaemia if he has taken
more exercise than usual.
-diabetic patients lack insulin/do not have enough insulin in their blood (1)
-and hence the liver fails to convert glucose into glycogen for storage (1)
-during intense exercise, blood glucose is consumed for muscle activities (1)
-the blood glucose drops continuously without replenishment from the glycogen
stored (1)
7. Suggest why diabetic patients are advised to take in complex carbohydrates in
normal meal.
-it takes time for starchy food to be digested before absorption (1)
-as a result, a small amount of glucose is absorbed gradually (1)
-the fluctuation of blood glucose level is less/blood glucose level will not increase too
fast after a normal meal (1)
8. Suggest why diabetic patients are advised to take in sugar when
hypoglycaemia occurs.
-sugar is easily digested/absorbable (1)
-blood glucose level can be raised immediately to alleviate the symptoms of
hypoglycaemia (1)
Homeostasis (★★★★★)
1. Blood glucose level regulation
{DSE 15 P1-8, DSE 12 P1-7, AL 06 PIB-10, AL 07 PIIC-8, CE 02-1(c), CE 05-9(a)}
(a) The roles of pancreas and liver in blood glucose regulation
(b) The antagonistic roles of insulin & glucagon
(c) The appearance of glucose in urine under different circumstances
(d) The consequences of the failure in keeping blood glucose level constant
(e) The cause & treatment of diabetes (insulin-dependent diabetes vs
insulin-independent diabetes)
(f) The use of recombinant DNA technology in making insulin
