Insulin & Glucagon
Introduction to Hormones
- A hormone is a chemical substance produced by an endocrine gland and carried by the blood
- The endocrine glands that produce hormones in animals are known collectively as the endocrine system
- A gland is a group of cells that produces and releases one or more substances (a process known as secretion)
- Hormones are chemicals which transmit information from one part of the organism to another and that bring about a change
- They alter the activity of one or more specific target organs
- Hormones only affect cells with receptors that the hormone can bind to
- These are either found on the cell surface membrane, or inside cells
- Receptors have to be complementary to hormones for there to be an effect
- Hormones are used to control functions that do not need instant responses
Insulin and Glucagon
- The pancreas is an organ found in the abdomen of mammals
- It functions as both an endocrine gland and an exocrine gland
- Endocrine glands secrete hormones directly into the blood, whereas exocrine glands secrete substance via a duct
- The exocrine function of the pancreas is to produce digestive enzymes to be delivered to the small intestine
- The endocrine function of the pancreas is to produce the hormones glucagon and insulin
- Within the pancreas, these two functions are performed by different tissues
- Most of the cells of the pancreas secrete digestive enzymes, but throughout the organ, there are small sections of cells known as the islets of Langerhans that produce hormones
- The islets of Langerhans contain two cell types: alpha cells (α cells), which secrete glucagon, and beta cells (β cells), which secrete insulin
The location and structure of the pancreas
The control of blood glucose by glucagon and insulin
- If the concentration of glucose in the blood decreases below a certain level, cells may not have enough glucose for respiration and so may not be able to function normally
- If the concentration of glucose in the blood increases above a certain level, this can also disrupt the normal function of cells, potentially causing major problems
- The control of blood glucose concentration is a key part of homeostasis
- Blood glucose concentration is controlled by glucagon and insulin:
- Glucagon is synthesised and secreted by α cells when blood glucose falls and stimulates liver and muscle cells to convert stored glycogen into glucose to be released into the blood, increasing blood glucose concentration
- Insulin is synthesised and secreted by β cells when blood glucose rises and stimulates liver and muscle cells to convert excess glucose into glycogen to be stored, decreasing blood glucose concentration
Control of blood glucose levels
Examiner Tip
The terms glucagon and glycogen are very often mixed up by students as they sound similar. Remember:
- Glucagon is the hormone
- Glycogen is the polysaccharide that glucose is stored as
Learn the differences between the spellings and what each one does so you do not get confused in the exam!