Hormones and blood glucose | OCR Gateway GCSE Biology Notes

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The key idea

Hormones are chemical messengers carried in blood. Negative feedback keeps internal conditions close to optimum.

Blood glucose negative feedbackInsulin and glucagon reverse opposite changes.

Revision notes

The bit that matters

Learn the process in clean chunks. If a sentence explains a cause, make sure you can say the effect too.

The endocrine system

The endocrine system is made of glands that secrete chemicals called hormones directly into the bloodstream.The blood carries the hormone to a target organ where it produces an effect.Hormonal responses are usually slower than nervous responses but their effects last longer.The $pit$ uitary gland in the brain is the master gland because it secretes hormones that control other glands.

Controlling blood glucose

Blood glucose concentration is monitored and controlled by the pancreas.If blood glucose is too high the pancreas releases insulin, which causes glucose to move from the blood into the cells, and excess glucose is stored as glycogen in the liver and muscles.If blood glucose is too low the pancreas releases glucagon, which causes glycogen to be converted back into glucose and released into the blood.

Diabetes

Type 1 diabetes is caused by the pancreas failing to produce enough insulin, leading to dangerously high blood glucose, and it is controlled by insulin injections.Type 2 diabetes is caused by body cells no longer responding properly to insulin, and risk factors include obesity.Type 2 diabetes is controlled by a carbohydrate controlled diet and exercise.

Negative feedback

Blood glucose control is an example of negative feedback, where a change in a level triggers a response that returns it towards normal.When glucose rises insulin lowers it, and when glucose falls glucagon raises it.This continual adjustment keeps blood glucose within narrow limits, which is part of homeostasis.

Key terms

Definitions to learn

Hormone

A chemical messenger secreted by a gland into the blood that acts on a target organ.

Endocrine system

The system of glands that secrete hormones into the bloodstream.

Insulin

A hormone from the pancreas that lowers blood glucose by moving it into cells.

Glucagon

A hormone from the pancreas that raises blood glucose by breaking down glycogen.

Homeostasis

The regulation of internal conditions to maintain a stable environment for cells.

Negative feedback

A response that reverses a change and returns a level towards normal.

Worked example

Explain how insulin lowers blood glucose concentration after a meal.

The pancreas detects a rise in blood glucose.

It releases insulin.

Cells take up glucose and the liver stores glucose as glycogen.

Final answer

Insulin lowers blood glucose by increasing uptake and glycogen storage.

Exam habit

Specify insulin (lowers blood glucose) vs glucagon (raises it).Name the target organ (liver) and the conversion (glycogen ↔ glucose).Always link the hormone to the gland that secretes it.

Watch out

Insulin lowers blood glucose. Glucagon raises it.

Examiner tips

How to score full marks

1Be precise: insulin moves glucose into cells and stores it as glycogen; glucagon converts glycogen back to glucose.
2Distinguish Type 1, where no insulin is produced, from Type 2, where cells stop responding to insulin.
3When describing negative feedback, state both directions of the response so it is clear the level returns to normal.

Practice questions

Try these yourself

Open each answer only after you have explained the full biological process.

1What gland releases insulin?

Mark scheme

1.Recall the organ involved in blood glucose control.

The pancreas.

2How does glucagon increase blood glucose?

Mark scheme

1.Link glycogen stores to glucose.

It causes glycogen in the liver to be converted into glucose and released into the blood.

3Why is negative feedback important?

Mark scheme

1.Explain stable internal conditions.

It reverses changes and keeps conditions near an optimum.

4Name the organ that monitors and controls blood glucose concentration.[1 mark]

Mark scheme

1.Recall the gland that makes insulin and glucagon.

Pancreas (1)

5Name the hormone released when blood glucose is too high.[1 mark]

Mark scheme

1.Recall the hormone that lowers glucose.

Insulin (1)

6Describe how the body responds when blood glucose concentration becomes too high.[3 marks]

Mark scheme

1.State the hormone and its effects.

The pancreas releases insulin (1); glucose moves from the blood into the cells (1); and excess glucose is stored as glycogen in the liver and muscles (1)

7Explain the difference between the causes of Type 1 and Type 2 diabetes.[3 marks]

Mark scheme

1.State the cause of each type.

In Type 1 diabetes the pancreas does not produce enough insulin (1); in Type 2 diabetes the body cells stop responding properly to insulin (1); a risk factor for Type 2 is obesity (1)

8A person has not eaten for several hours and their blood glucose falls below normal. Explain how their body uses negative feedback to return blood glucose to normal.[5 marks]

Mark scheme

1.Identify the hormone and gland.
2.Describe the action and the feedback principle.

The fall in blood glucose is detected by the pancreas (1); the pancreas releases glucagon (1); glucagon causes glycogen stored in the liver to be converted back into glucose (1); the glucose is released into the blood raising the concentration back towards normal (1); this is negative feedback because the response reverses the original change (1)

9Explain why a person with untreated Type 1 diabetes has a very high concentration of glucose in their urine.[4 marks]

Mark scheme

1.Explain why glucose is not removed from the blood.
2.Link to kidney filtration.

Without insulin the person's cells do not take up glucose from the blood (1); blood glucose concentration rises to very high levels (1); when blood is filtered in the kidneys the glucose concentration is too high for all of it to be reabsorbed (1); so some glucose remains in the filtrate and is excreted in the urine (1).

10Compare the nervous system and the endocrine system as methods of communication in the body.[4 marks]

Mark scheme

1.Give two differences related to speed, pathway and duration of response.

The nervous system uses electrical impulses along neurones whereas the endocrine system uses hormones carried in the blood (1); nervous responses are faster (milliseconds) while hormonal responses are slower (seconds to minutes) (1); nervous responses are short-lived while hormonal effects can last much longer (1); nervous responses are localised to a specific effector while hormones act on target organs anywhere in the body (1).

11Explain why Type 2 diabetes cannot be treated with insulin injections in the same way as Type 1 diabetes.[4 marks]

Mark scheme

1.Link Type 2 to cell receptor response rather than insulin production.

In Type 2 diabetes the body cells no longer respond properly to insulin (1); the problem is with the cells' receptors for insulin, not with insulin production (1); injecting more insulin would not restore the cells' ability to respond to it (1); instead treatment focuses on diet to control blood glucose and exercise to improve cell sensitivity to insulin (1).

12Adrenaline is released by the adrenal glands in response to danger. Describe two effects of adrenaline on the body and explain how each helps prepare the body to respond.[4 marks]

Mark scheme

1.Give two specific physiological effects.
2.Link each to fight-or-flight response.

Adrenaline increases heart rate (1), delivering more oxygen and glucose to muscles for rapid contraction (1); it stimulates the conversion of glycogen to glucose in the liver (1), increasing the blood glucose available for respiration (1). (Any two effects with explanation.)

13Explain the principle of negative feedback using blood glucose control as an example, and suggest why maintaining glucose within narrow limits is important for cells.[5 marks]

Mark scheme

1.Define negative feedback.
2.Apply it to insulin and glucagon.
3.State why stable glucose matters.

Negative feedback means a change in a level triggers a response that reverses the change and returns it to normal (1); when blood glucose rises, insulin is released to lower it; when it falls, glucagon is released to raise it (1); this keeps glucose within narrow limits (1); cells need a constant supply of glucose for respiration (1); too little glucose starves cells of energy while too much can damage cells by osmosis (1).

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