Chapter 18: Homeostasis

Question 1

Action of effectors when LESS glucagon and MORE insulin is secreted by the pancreas

Answer 1

At liver cells and muscle cells:
- take up more glucose from blood
- promotes the conversion of excess glucose into glycogen by an enzyme

Body cells
- increase glucose uptake for respiration
- increase rate of respiration per unit time

Question 2

Action of effectors when MORE glucagon and LESS insulin is secreted by the pancreas

Answer 2

At liver cells and muscle cells:
- take up less glucose from blood
- promotes the conversion of glycogen into glucose by an enzyme

Body cells
- decrease glucose uptake for respiration
- decrease rate of respiration per unit time

Question 3

Why does the blood glucose level returns to normal 5 hours after the meal?

Answer 3

• The insulin in blood is degraded and loses its stimulatory effect
• The decrease in insulin level in blood plasma lowers its inhibitory effect on glucagon secretion
• resulting in a higher level of glucagon in blood plasma
• that stimulates liver cells to promote the conversion of glycogen to glucose
• thus blood glucose level rises again.

Question 4

Why is glucose present in the urine of diabetic patients?

Answer 4

• Patients with diabetes do not secrete sufficient insulin compared to a healthy person
• The liver cannot convert excess glucose to glycogen efficiently
  → High level of glucose is preset in the glomerular filtrate
• The kidney tubues fail to absorb all the glucose from the filtrate

Question 5

Why do diabetic patients urinate frequently?

Answer 5

• The unabsorbed glucose lowers the water potential of the glomerular filtrate.
• Hence, a smaller amount of water is reabsorbed. The
• greater amount of urine produced thus causes frequent urination.
• Diabetic patients usually feel very thirsty and tired.

Question 6

Blood glucose level in a diabetic patient
1. rises to a higher level after glucose consumption
2. remains high for a longer time
compared to a healthy person
compared to a healthy person.

Account for the phenomeona.

Answer 6

• With insufficient stimulatory effect from insulin, there is less uptake of glucose from blood by body cells for respiration/liver cells for conversion into glycogen compared to a healthy person
• With insufficient inhibitory effect of insulin, the pancreas secretes a larger amount of glucagon. A higher level of glucagon stimulates liver cells to promote the conversion of glycogen from glucose compared to a healthy person

As a result, the blood glucose concentration
1. rises to a higher level after glucose consumption
2. remains high for a longer time
compared to a healthy person

Question 7

Food suggestions for diabetic patients

Answer 7

• Take in complex carbohydrates in a normal meal
• Consume a diet low in carbohydrates e.g. ketogenic diet
• Eat plenty of vegetables at each meal
• Take small but frequent meals

Question 8

Why should diabetic patients take in complex carbohydrates in a normal meal?

Answer 8

• It takes more time for starchy foods to be broken down before digestion
• A small amount of glucose is absorbed gradually
• Smaller fluctuation of blood glucose level
• lowers the chance of having a high blood glucose lvl

Question 9

Why should diabetic patients consume a diet low in carbohydrates e.g. ketogenic diet?

Answer 9

• Low carbohydrate content → smaller amount of glucose after digestion and absorption
• consumption of ketogenic diets will not lead to a sharp rise in blood glucose level

Question 10

Why should diabetic patients eat plenty of vegetables at each meal?

Answer 10

• Vegetables contain indigestable dietary fibre → Will NOT contribute to the rise in blood glucose level
• Slow down the digestion of other carbohydrates and reduces the absorption of glucose into the blood
• The fibre also gives a sense of fullness, thus reducing food intake and thus helps restrict the increase in glucose level.

Question 11

A man diagnosed with a kind of pancreatic cancer which is characterised by an overgrowth of endocrine pancreatic cells. He sometimes felt dizzy but became less dizzy after drinking solution of glucose.

Based on the above observation, suggest why this pancreatic cancer would cause dizziness in the man.

Answer 11

• Due to uncontrolled growth of insulin-secreting cells, this pancreatic cancer probably leads to an excessive secretion of insulin.
• As insulin stimulates the uptake of blood glucose by cells, excessive insulin secretion would reduce the blood glucose to a low level.
• As a result of insufficient blood glucose supply to the brain, which depends solely on glucose for respiration, The man would feel dizzy.

Question 12

After having an operation to remove a large part of the pancreas, the man was advised to take a low protein and low fat diet. Explain the biological reasons behind this advice.

Answer 12

Some tissues of the pancreas secrete protease and lipase. They may be removed together with the cancerous tissue, and this would make the digestion of protein and fat difficult

Question 13

Some people believe that diabetes mellitus is caused by excessive intake of sugary food. Discuss whether
this idea is valid based on your own knowledge of the two different types of diabetes mellitus.

Answer 13

• Too much sugary food will lead to obesity (1)
• and increases the risk of non-insulin-dependent diabetes mellitus. (1)
• Sugary food will not lead to insulin-dependent diabetes mellitus (1)
• because it is due to an autoimmune response. (1)

Question 14

2018DSE Q7: Explain why diabetic patients should consume low GI meals

Answer 14

• Low GI food will lead to small fluctuations in blood glucose level. (1)
• The chance of having too high blood glucose level/glucose appearing in urine is reduced. (1)

Question 15

Blood glucose level of diabetic has a larger increase in the first hour compared with the healthy person. Why?

Answer 15

• In the healthy person, the initial rise in blood glucose stimulated the secretion of more insulin by the pancreas
• While there is no/less insulin secretion in the diabetic person (Type I diabetes)
  In the healthy person,
• With insufficient stimulatory effect from insulin, there is:
• less uptake of glucose from blood by body cells for respirationliver cells for conversion into glycogen compared to a healthy person
• less uptake of glucose from blood by liver cells for conversion into glycogen compared to a healthy person

Question 16

(Basal level of blood glucose in normal person is always lower than that in a diabetic person)

Amy is diabetic while Mike is not. They both drank glucose solution after fasting overnight.
Explain why Amy has a higher fasting blood glucose level than Mike.

Answer 16

• During fasting, the low blood glucose level stimulated the pancreas to produce more glucagon (and less insulin)
• Glucagon stimulated liver cells and muscle cells to convert stored glycogen into glucose.
• The glucose was released into the blood and blood glucose level increased.
• Since glucose uptake by liver cells and other body cells was inefficient in Amy, her blood glucose level remained high after fasting.

Question 17

What would be the shape of each curve if both subjects had ingested 100mL of an aqueous solution containing 80g of glucose instead of administering glucose directly into the bloodstream?

Answer 17

Shapes of the curves would be similar except that there will be a delay in attaining peak glucose level in both subjects. This is because it takes time for the ingested glucose to reach the small intestine, where it is absorbed.

Question 18

Why do Type-1 diabetic patients may feel dizzy after prolonged exercise (insufficient blood, nutrients, or oxygen)

Answer 18

• Diabetic patients lack insulin in their blood (1)
• and hence the liver cells and muscle cells fails to convert glucose into glycogen for storage. (1)
• During intense exercise, blood glucose is consumed for muscle activities. (1)
• The blood glucose level drops continuously without replenishment from the glycogen stored. (1)