5.1.4 - HORMONAL COMMUNICATION

Question 1

What is the hormonal system?

Answer 1

• Made up of endocrine glands (groups of cells that secrete hormones) + hormones (‘chemical messengers’, usually proteins or peptides. some are steroids)
• Hormones are secreted when an endocrine gland is stimulated —> can be stimulated by a change in concentration of a specific substance (can be another hormone or electrical impulse)
• Hormones diffuse directly into the blood, then they’re taken around the body by the circulatory system
  ^— they diffuse out of the blood all over the body but each hormone will only bind to specific receptors for that hormone (found on membranes of some cells called target cells) + trigger a response

Question 2

What is a first messenger?

Answer 2

• A hormone
  ^— because it carries the chemical message the first part of the way, from the endocrine gland to the receptor on the target cells

Question 3

Describe the process of hormones binding to receptors

Answer 3

• When a hormone binds to its receptor, it activates an enzyme in the cell membrane
• The enzyme catalyses the production of a molecule inside the cell called a signalling molecule —> this molecule signals to other parts of the cell to change how the cell works
• The signalling molecule activates a cascade (chain reaction) inside the cell

Question 4

What is a second messenger?

Answer 4

• Signalling molecule inside the target cell
  ^— because it carries the chemical message the second part of the way, from the receptor to the other parts of the cell

Question 5

Describe the structure of the adrenal glands

Answer 5

• Adrenal glands are endocrine glands that are found just above the kidneys
• Each adrenal gland has an outer part called the cortex + an inner part called the medulla

Question 6

Describe the role of the adrenal cortex in the response to stress

Answer 6

Secretes steroid hormones (cortisol + aldosterone) when stressed
^— have a role in short-term + long-term stress response:
- Stimulates breakdown of proteins + fats into glucose —> increases amount of energy available so the brain + muscles can response to the situation
- Increases blood volume + pressure by increasing the uptake of sodium ions + water by kidneys
- Suppresses the immune system

Question 7

Describe the role of the adrenal medulla in the response to stress

Answer 7

Secretes catecholamine hormones (modified amino acids) such as adrenaline + noradrenaline when stress short-term:
- Increase heart + breathing rate
- Cause cells to break down glycogen into glucose
- Constrict some blood vessels so that blood is diverted to the brain + muscles

Question 8

Describe the role of the pancreas as an endocrine gland

Answer 8

• Areas of the pancreas that contain endocrine tissue are called islets of Langerhans
  ^— found in clusters around blood capillaries
  ^— made of 2 types of cell: α cells secreting glucagon and β cells secreting insulin
• Insulin + glucagon help control blood glucose conc.

Question 9

Outline the fluctuation of blood glucose concentration after eating and exercise

Answer 9

• All cells need a constant energy supply to work, so blood glucose concentration must be carefully controlled
• Conc. of blood glucose is normally 90mg per 100cm³ - monitored by cells in pancreas
• Blood glucose rises after eating food containing carbs
• Blood glucose falls after exercise as more glucose use in respiration to release energy

Question 10

Outline the role of insulin as a hormone when blood glucose concentration is too high

Answer 10

• Insulin binds to specific receptors on the cell membranes of liver cells + muscle cells
• Increases the permeability of cell membranes to glucose, so cells take up more glucose
• Insulin also activates enzymes that convert glucose into glycogen
• Cells are able to store glycogen in their cytoplasm as an energy source
• Insulin also increases rate of respiration of glucose, especially in muscle cells

Question 11

What is the process of forming glycogen from glucose called?

Answer 11

Glycogenesis

Question 12

Outline the role of glucagon as a hormone when blood glucose concentration is too low

Answer 12

• Glucagon binds to specific receptors on the cell membranes of liver cells
• Glucagon activates enzymes that break down glycogen into glucose
• Glucagon also promotes the formation of glucose from glycerol + amino acids
• Glucagon decreases the rate of respiration of glucose in cells

Question 13

What is the process of breaking down glycogen into glucose called?

Answer 13

Glycogenolysis

Question 14

What is the process of forming glucose from non-carbohydrates called?

Answer 14

Gluconeogenesis

Question 15

Explain the negative feedback mechanism when blood glucose concentration is too high

Answer 15

• When blood glucose conc. is high, more glucose enters β cells by facilitated diffusion
• More glucose on a β cell causes the rate of respiration to increase, making more