Hormones Ex

1.
The figure above illustrates a generalized pattern of response towards an internal stimulus.

(a) Response to a rise in blood glucose level follows the pattern in Fig. 3.1.
(i) State the regulator and the effector involved in the restoration of blood glucose to its normal level. [2]
(ii) Describe the sequence of events that leads to the lowering of blood glucose concentration to its normal level. [2]

(b) What is the importance of the negative feedback mechanism to the body? [1]

(c) Explain why the response towards an external stimulus e.g. knee jerk reflex, occurs much faster than the response towards changes in the blood glucose level. [2]

ANSWERS
1(a)(i) Regulator: pancreas; Effector: liver and muscles;
(ii) Rise in blood glucose levels is detected by the pancreas, which secretes insulin/increases insulin secretion;
Insulin causes the liver and muscles to convert glucose into glycogen, and increases permeability of cells to glucose, and hence lowers blood glucose levels back to normal;

(b) To maintain a constant internal environment, and stop corrective mechanisms from overcorrecting the imbalance;

(c) The response towards external stimuli involves electrical nerve impulses transmitted along neurones at high speed;
Changes in blood glucose level involves hormones transported by blood which takes a longer time;

2. Identify the receptors and effectors involved in the lowering of glucose in the blood / describe how plasma glucose concentration is lowered.
ANSWER
Receptors: Cells in the pancreas (Islet of Langerhans);
Effectors: Mainly liver cells / muscle cells;
Mechanism: Insulin is secreted into bloodstream by Islet of Langerhans in pancreas;
Glucose uptake from the blood by body cells is increased due to increased permeability to glucose;
Use of glucose in respiration by these cells is increased;
Liver and muscle cells convert glucose into glycogen;

3. Read the following passage, which is taken from an advice book for diabetics.

Hypoglycaemia, or ‘hypo’ for short, occurs when there is too little sugar in the blood. It is important to always carry some form of sugar with you and take it immediately you feel a ‘hypo’ start. A hypo may start because:

• You have used to much insulin
• You are late for a meal, have missed a meal altogether, have eaten too little at a meal, or you have taken a lot more exercise than usual.

The remedy is to take some sugar.

An insulin reaction usually happens quickly and the symptoms vary - sweating, trembling, tingling of the lips, palpitations, hunger, pallor, blurring of vision, slurring of speech, irritability, difficulty in concentration.

Do not wait to see if it will pass off, as an untreated ‘hypo’ could lead to unconsciousness.

(a) Many diabetics use insulin.
(i) How does insulin help diabetics with their condition? [1]
(ii) Explain why there is too little sugar in the blood if the person exercises more than usual? [2]

(b) Suggest why sugar is recommended for a ‘hypo’, rather than starchy food. [3]

ANSWERS
3(a)(i) Insulin helps to lower blood glucose concentration by promoting the conversion of excess blood glucose into glycogen at the muscles and liver, and increasing the uptake of glucose by cells;
(ii) During exercise, the muscles use more glucose from the blood for extra respiration to provide the body with energy, which means there may be less glucose in the bloodstream;;
(b) Sugar molecules are simpler and require no digestion or less digestion than starch;
This means they will be absorbed faster into the blood at the small intestine which corrects the "hypo" faster;
Compared to starch which will require a longer time for digestion and hence absorption will occur later;

4(a) Explain how in a healthy person, the blood sugar, are returned to normal after they have risen above the normal levels. [3]

(b) Explain why it is important for man to maintain a constant body temperature of 37 deg C. [2]

ANSWERS

(a)• Pancreas detect the rise in blood glucose level.
• Islets of Langerhans secrete insulin which is sent via the blood stream to the liver/muscles.
• Liver/muscles cells stimulated to increase the permeability of the cell membrane to glucose thereby increase the rate of glucose uptake by cells.
• Cause the conversion of glucose to glycogen for storage in the muscles and organs.
• Cause increased oxidation of glucose during tissue respiration.
• These mechanisms help to lower blood glucose levels back to normal;
(b)
• Enables Man to be active at all times/throughout the year, no need to hibernate.
• In all temperature zones, can colonize many areas.
• Biochemical reactions run by enzymes can take place near optimum temperature.
• Enzymes inactive at lower temperature and denatured at higher temperatures.