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 in a β cell causes the rate of respiration to increase, making more ATP
• The rise in ATP trigger the potassium ion channels in the β cell plasma membrane to close
• This means potassium ions (K⁺) can’t get through the membrane - so they build up inside the cell
• This makes the inside of the β cell less negative because there are more positively-charged K⁺ ions inside the cell - so the plasma membrane of the β cell is depolarised
• Depolarisation triggers calcium ion channels to open, do calcium ions diffuse into the β cell
• This causes the vesicles to fuse with the β cell plasma membrane, releasing insulin (by exocytosis)

Question 16

What is diabetes mellitus?

Answer 16

A condition where blood glucose concentration can’t be controlled properly

Question 17

What are the two types of diabetes mellitus?

Answer 17

• Type 1 diabetes
• Type 2 diabetes

Question 18

What is Type 1 Diabetes?

Answer 18

• No insulin is produced
  ^— auto-immune disease, in which the body attacks + destroys the β cells in the islets of Langerhans —> means no insulin production
• After eating blood glucose concentration rises + remains high, which can result in death if untreated
  ^— kidneys can’t reabsorb all of this glucose, so some is excreted in the urine

Question 19

What is the cause of Type 1 Diabetes?

Answer 19

• Usually develops in children or young adults
• Risk of developing Type 1 Diabetes is slightly increased if there’s a close family history of the disease

Question 20

How is Type 1 Diabetes treated?

Answer 20

• Insulin therapy
  ^— many ppl require regular insulin injection throughout the day | some use an insulin pump (continuously delivers insulin into the body via a tube inserted beneath the skin)
• Some people have been successfully treated by islet cell transplantation (healthy islet cells received from a donor so their pancreas can produce insulin - although some insulin therapy is sometimes needed)
• Ppl with type 1 need to regularly monitor their blood glucose concentration + need to think about:
  ^— Diet - healthy, balanced diet reduces amount of insulin that needs to be injected | have a carefully planned diet so they can manage glucose intake
  ^— Activity - regular exercise reduce amount of insulin needed to be injected by using up blood glucose

Question 21

What is Type 2 Diabetes?

Answer 21

• Occurs when β cells don’t produce enough insulin or when the body’s cells don’t respond properly to insulin
• Cells don’t respond properly because the insulin receptors on their membranes don’t work properly, so the cells don’t take up enough glucose
  ^— means the blood glucose concentration is higher than normal

Question 22

What is the cause of Type 2 Diabetes?

Answer 22

• Usually acquired later in life that type 1
  ^— linked to obesity
• Risk is increased in people from certain ethnic groups (e.g. African and Asian, + people with a close family history of the disease)

Question 23

How is Type 2 Diabetes treated?

Answer 23

• Lifestyle changes (e.g. healthy, balanced diet, regular exercise + losing weight)
• If blood glucose can’t be controlled through lifestyle changes, then medication may be prescribed:
  ^— Metformin - first prescription choice —> acts on liver cells to reduce the amount of glucose that they release into the blood + acts to increase sensitivity of cells to insulin so more glucose can be taken up with the same amount of insulin
  ^— Sulfonylureas (e.g. gliclazide) - stimulate the pancreas to produce more insulin
  ^— Thiazolidinediones (pioglitazone) - make the body cells more sensitive to insulin
• Sometimes medication isn’t enough so insulin therapy is used in addition or instead

Question 24

Describe how genetically modified bacteria can be used to treat diabetes

Answer 24

• Insulin used to be extracted from animal pancreases (e.g. pigs + cattle) to treat people with type 1
  ^— but now, human insulin can be made by genetically modified (GM) bacteria —> much better:
• Producing insulin using GM bac. is cheaper than from animals
• Larger quantities can be produced using GM bac.
• GM bac. make human insulin —> more effective than using pig/cattle insulin (slightly different to humans) _ less likely to trigger an allergic response or be rejected
• Some ppl prefer insulin from GM bac. due to ethical/ religious reasons (e.g. vegetarians)

Question 25

Describe how stem cells could be used to cure diabetes

Answer 25

• Stem cells could be grown into β cells
• β cells would then be implanted into the pancreas of a person with type 1 diabetes
  ^— means the person would be able to make insulin as normal
• Still being developed, but if effective it’ll cure type 1