18: Homeostasis

Question 1

State the meaning of homeostasis.

Answer 1

Homeostasis is the maintenance of a relatively constant internal environment in an organism.

Question 2

State the meaning of internal environment in humans.

Answer 2

Tissue fluid and blood

Question 3

State the importance of homeostasis.

Answer 3

Homeostasis ensures that our cells are in a stable environment suitable for their survival and normal functioning. If homeostasis fails, we will get sick or even die.

Question 4

State four parameters of our internal environment under homeostatic regulation.

Answer 4

Body temperature, water content in blood, gas content in blood, glucose levels in blood.

Question 5

Explain the importance of controlling our body temperature.

Answer 5

Our metabolic activities are controlled by enzymes, which only work efficiently within a narrow range of temperatures around 37ºC. A stable body temperature within the range is important for keeping enzyme activities and hence the metabolic rate steady. This allows us to stay active in different seasons and environments of different temperatures.

Question 6

State the organ responsible for the homeostasis regulation of body temperature.

Answer 6

Skin.

Question 7

State the possible outcomes if homeostasis fails to control our body temperature.

Answer 7

If our body temperature becomes too high, heatstroke may occur. If our body temperature becomes too low, hyperthermia may occur.

Question 8

Explain the importance of controlling the water content in our blood.

Answer 8

Changes in the water content in blood alter the water potential of tissue fluid surrounding the cells. This in turn affects the movement of water into and out of the of the cells by osmosis.

Question 9

State the main organ responsible for the homeostasis regulation of water content in blood.

Answer 9

Kidneys

Question 10

State the possible outcomes if homeostasis fails to control the water content in our blood.

Answer 10

If there is too much water content in our blood, the water potential of the tissue fluid becomes higher than that of the surrounding cells. This causes too much water to enter the cells, and the cells may burst.
If there is too little water content in our blood, the water potential of the tissue fluid becomes lower than that of the surrounding cells. This causes water to be drawn out of the cells, and the cellular metabolism in affected cells will slow down or even stop.

Question 11

Explain the importance of controlling the gas content in our blood.

Answer 11

Cells need oxygen in order to release energy from glucose in respiration. A stable oxygen content in blood ensures a steady supply of oxygen to our cells for respiration.
On the other hand, carbon dioxide lowers the pH of blood and hence the pH of tissue fluid when it dissolves in blood. These changes in pH may affect enzyme activities because enzymes can only function within a narrow range of pH. A stable carbon dioxide content in blood ensures that the pH in blood and tissue fluid allows the functioning of enzymes.

Question 12

State the systems responsible for the homeostasis regulation of gas content in blood.

Answer 12

The breathing system and circulatory system.

Question 13

State the possible outcomes if homeostasis fails to control the oxygen content in our blood.

Answer 13

If there is insufficient oxygen content in blood, then our cells will not obtain enough oxygen for respiration. Less energy is released in respiration and our cells may not be able to function normally.

Question 14

Explain the importance of controlling the glucose level in our blood.

Answer 14

Glucose is the main energy source for cells. A stable glucose level ensures a steady supply of glucose to our cells for respiration. Glucose is also soluble in water and its presence lowers the water potential of a solution. Thus keeping a stable blood glucose level can avoid changes in the water potential of blood, and hence that of tissue fluid and cells.

Question 15

State the main organs responsible for the homeostasis regulation of glucose levels in blood.

Answer 15

Pancreas and liver

Question 16

Name the mechanism which brings about homeostasis.

Answer 16

Negative feedback mechanism

Question 17

State the systems which may be involved in the negative feedback mechanism.

Answer 17

Nervous system and endocrine system

Question 18

State the components of a negative feedback mechanism.

Answer 18

A receptor, a control centre (eg. the brain or an endocrine gland), an effector.

Question 19

State the functions of a receptor in a negative feedback mechanism.

Answer 19

It detects a stimulus, which is a change in the level of a parameter from the set point. It then sends neural or hormonal messages to a control centre.

Question 20

State the functions of a control centre in a negative feedback mechanism.

Answer 20

It compares the level of the parameter with the set point. It then sends neural or hormonal messages to initiate a response.

Question 21

State the functions of an effector in a negative feedback mechanism.

Answer 21

It received messages from the control centre and produces a response.

Question 22

Explain why the negative feedback mechanism is described as negative.

Answer 22

The response has an opposite (negative) effect on the change in the level of a parameter. This beings the level closer to the set point.

Question 23

State whether the level of a parameter stays constant when homeostasis is achieved.

Answer 23

No, it fluctuates within the normal limits of the set point.

Question 24

Explain how a negative feedback mechanism is similar to the operation of an air conditioner.

Answer 24

The temperature sensor detects the room temperature. The control board then compares this room temperature with the set temperature.
If the room temperature is above the set temperature, the control board turns on the cooling system.
If the room temperature is below the set temperature, the control board turns off the cooling system.
By turning on or off the cooling system, the air conditioner produced an opposite effect to the change in room temperature, which brings the room temperature closer to the set temperature. This ensures that the room temperature is kept relatively constant.

Question 25

State an example of positive feedback mechanism in humans.

Answer 25

The process of labour in humans.

Question 26

Name the hormones used regulate blood glucose levels.

Answer 26

Insulin and glucagon

Question 27

State the nature of insulin and glucagon.

Answer 27

They are **protein hormones**.

Question 28

State the actions brought about by insulin.

Answer 28

1. It stimulates liver cells and other body cells to **take up more glucose** from the blood 2. It stimulates liver cells and muscle cells to **convert more glucose into glycogen** for storage. 3. It stimulates the body cells to **consume more glucose** for respiration.

Question 29

State the actions brought about by glucagon.

Answer 29

It stimulates liver cells and muscle cells to **convert stored glycogen into glucose**.

Question 30

Describe the changes when an increase in the blood glucose level is detected.

Answer 30

When **chemoreceptors** in the pancreas detect an **increase** in the blood glucose levels the pancreas produces **more insulin and less glucagon**. More insulin stimulates liver cells and muscle cells to convert more glucose into glycogen for storage. Insulin also stimulates body cells to consume more glucose for respiration. As more glucose is taken up from the blood, the blood glucose level **decreases** and returns to the set point.

Question 31

Describe the changes when a decrease in the blood glucose level is detected.

Answer 31

When chemoreceptors in the pancreas detect a **decrease** in the blood glucose level, the pancreas produces **less insulin and more glucagon**. More glucagon stimulates liver cells and muscle cells to convert more stored glycogen into glucose. As more glucose is released into the blood, the blood glucose level **increases** and returns to the set point.

Question 32

State a disease in which the patient's body fails to regulate blood glucose levels.

Answer 32

Diabetes mellitus

Question 33

Describe the blood glucose level of a diabetic patient after drinking a glucose solution.

Answer 33

Glucose uptake from the blood by liver cells and other body cells is inefficient. The blood glucose level rises more quickly and to a higher peak. The peak occurs later compared to that of a normal person. Glucose is excreted in urine. The blood glucose level decreases slowly and is still higher than the initial level after 4 hours.

Question 34

Name the two types of diabetes mellitus.

Answer 34

Type 1 diabetes (insulin-dependent diabetes), type 2 diabetes (non-insulin-dependent diabetes)

Question 35

State the difference between the two types of diabetes mellitus.

Answer 35

In patients having insulin-dependent diabetes / type 1 diabetes, the pancreas **produces too little or no insulin**. Thus, the patient has to rely on **regular insulin injections** to control the blood glucose level. In patients having non-insulin-dependent diabetes / type 2 diabetes, the body cells are **insensitive to insulin**.

Question 36

State three ways to manage diabetes mellitus.

Answer 36

Eating healthy, regular physical activity, monitoring of blood glucose levels.

Question 37

Explain why diabetics may have hypoglycaemia.

Answer 37

Diabetics may have hypoglycaemia after **prolonged exercise** because they do not have enough stored glycogen to replenish the glucose used for muscle activities. Eating too little or injecting too much insulin may also lead to hypoglycaemia.