Hormones

Question 1

Define hormone.

Answer 1

A hormone is a chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to one or more target organs where it exerts its effect(s). After hormones have performed their functions, they are eventually destroyed by the liver

Question 2

Explain what an endocrine gland is, with reference to the islets of Langerhans in the pancreas.

Answer 2

Endocrine glands are ductless glands that secrete hormones directly into the blood.

The pancreas contains special groups of cells known as the islets of Langerhans, which secrete insulin and glucagon hormones into the bloodstream.

Question 3

Explain how the hormone adrenaline is released and give examples of situations in which this may occur.

Answer 3

1. Stimuli when you are afraid, angry, anxious or stressed activate the hypothalamus in the brain.
2. Impulses are transmitted down the spinal cord.
3. The motor neurone transmits impulses to the adrenal gland.
4. The adrenal gland secretes adrenaline into the bloodstream.
5. Blood transports adrenaline to the target organs.

Question 4

State the effects of the hormone adrenaline.

Answer 4

• Stimulates the liver to convert glycogen to glucose so that more glucose is available for muscle contraction for energy release in tissue respiration.
• Increases metabolic rate for more energy release in tissue respiration
• Increases the rate of heartbeat and causes a rise in blood pressure so that oxygen and glucose are carried faster to the muscles
• Increases the rate and depth of ventilation, increasing the rate of uptake of oxygen by the lungs
• Increases the rate of blood clotting to prevent excessive loss of blood
• Constricts arterioles to the gut, thereby decreasing digestive activities
• Constricts arterioles in the skin, causing paleness, thus channeling more blood to the muscles
• Dilate pupils to enhance vision
• Contracts hair muscles, producing ‘goose bumps’ and causing hair to stand on end

Question 5

Explain how the blood glucose concentration is regulated by insulin and glucagon as a homeostatic mechanism

Answer 5

Insulin decreases blood glucose concentration by:
- increasing the permeability of cell membranes to glucose, thereby increasing the rate of glucose uptake by cells
- stimulating the liver and muscle cells to convert glucose into glycogen for storage
- increasing oxidation of glucose during tissue respiration

Glucagon increases blood glucose concentration by:
- stimulates the conversion of stored glycogen into glucose in the liver
- stimulates the conversion of fats and amino acids into glucose

Insulin and glucagon together regulate the blood glucose concentration and is an example of a homeostatic mechanism.

Question 6

Describe the signs and the treatment of diabetes mellitus

Answer 6

Signs:
- persistently high blood glucose level
- the presence of glucose in the urine after a meal
- healing of wounds is slow or difficult

Treatment:
Type 1 - regular insulin injection to decrease their blood glucose levels and consumption of sugary food to increase their blood glucose levels
Type 2 - exercise and regulation of carbohydrate content in their diet to control their blood glucose level, and medication and insulin injections if lifestyle changes fail

Question 7

What are the 2 main types of diabetes mellitus?

Answer 7

Type 1:
- early-onset diabetes
- the islets of Langerhans are unable to produce or secrete sufficient insulin to regulate blood glucose levels

Type 2:
- late-onset diabetes
- tends to develop in overweight people
- target cells like muscle cells do not respond well to insulin, decreasing their ability to regulate blood glucose levels