Control of blood glucoseOxford AQA IGCSE Biology: Revision notes

Section 1

What is a hormone and how does the endocrine system work?

A hormone is a chemical messenger produced by an endocrine gland. Hormones are transported through the bloodstream to reach their target organs, where they cause a response. The endocrine system works slowly but has long-lasting effects, making it ideal for processes that need sustained control.

Key characteristics of hormonal communication:

Hormones are produced in small amounts but have powerful effects
They travel throughout the body in the blood
Only target cells with the correct receptors respond
Effects develop slowly but last longer than nervous responses

Key termshormoneendocrine glandtarget organchemical messengerbloodstream

Exam tip

Examiners test whether you understand hormones are chemical messengers. Always write 'chemical messenger' in your definition – this is the key phrase on the mark scheme.

Think of it like this

Think of hormones like broadcast radio signals – they travel everywhere but only receivers (target cells) tuned to the right frequency (with the right receptors) will respond.

Section 2

Which glands produce hormones and what do they do?

The major endocrine glands and their locations and functions are:

Gland	Location	Hormones Produced	Function
Pituitary	Base of brain	FSH, LH, growth hormone	Controls other glands; regulates growth, reproduction and metabolic rate
Thyroid	Neck	Thyroxine	Increases metabolic rate and heat production; controls growth and development
Adrenal	Top of kidneys	Adrenaline, cortisol	Prepares body for stress (fight or flight); controls response to danger
Pancreas	Abdomen (near stomach)	Insulin, glucagon	Regulates blood glucose concentration
Ovaries	Pelvis (females)	Oestrogen, progesterone	Controls female sexual development and menstrual cycle
Testes	Scrotum (males)	Testosterone	Controls male sexual development and sperm production

Remember: The pituitary gland is the 'master gland' because it controls the function of many other glands.

Key termspituitary glandthyroid glandadrenal glandpancreasovariestestesthyroxineadrenalineinsulinglucagonoestrogenprogesteronetestosterone

Exam tip

You must be able to state the location AND the function of each gland. Examiners often ask 'where is the gland?' and 'what does it do?' in separate parts, so learn both.

Common mistake

Students often confuse the pancreas as only a digestive organ. Remember: it is an endocrine gland that produces insulin and glucagon, not just digestive enzymes.

Section 3

How do nervous and hormonal communication compare?

The nervous and hormonal systems both coordinate body functions but work in very different ways:

Feature	Nervous System	Hormonal System
Speed	Very fast (milliseconds)	Slow (seconds to minutes)
Duration	Short-lived effects	Long-lasting effects
Specificity	Very specific – targets precise cells via neurones	Less specific – affects all cells with matching receptors
Type of messenger	Electrical and chemical (neurotransmitters)	Chemical (hormones)
Reversibility	Quickly reversible when stimulus stops	Slower to reverse

Key insight: The nervous system is ideal for rapid, precise responses (e.g. reflex actions), while the hormonal system is better for sustained, widespread effects (e.g. growth, reproduction).

Key termsnervous systemhormonal systemspecificityneurotransmitterreceptor

Exam tip

Examiners test comparative language. Use phrases like 'faster than', 'lasts longer than' and 'more specific than' when comparing systems. Avoid vague statements like 'different'.

Example

If you touch a hot plate: the nervous system causes an instant reflex withdrawal (fast, precise), but the hormonal system simultaneously releases adrenaline for prolonged stress response (slow, widespread).

Section 4

What is the fight or flight response and the role of adrenaline?

The fight or flight response is a rapid physiological reaction to danger or stress. The adrenal gland releases the hormone adrenaline into the bloodstream, which prepares the body to either confront the threat (fight) or escape it (flight).

Effects of adrenaline:

Increases heart rate – pumps blood faster to muscles
Increases breathing rate – supplies more oxygen to muscles
Dilates (widens) blood vessels supplying muscles – increases blood flow to muscles
Constricts blood vessels supplying digestive system – blood diverted away from digestion
Increases blood glucose concentration – provides energy for muscles
Dilates pupils – improves vision

Why these changes occur:

Adrenaline prepares muscles for rapid action
Oxygen and glucose delivery to muscles is maximised
Functions not needed in emergency (digestion) are shut down
The body is in a state of high alert

Key point: This is a short-term response; once the danger passes, adrenaline is broken down and normal body functions resume.

Key termsfight or flight responseadrenalineadrenal glandheart ratebreathing rate

Exam tip

Examiners want you to explain WHY each change occurs, not just list them. Always link effects back to preparation for danger – e.g. 'heart rate increases so blood reaches muscles faster, providing oxygen and glucose for rapid action'.

Think of it like this

Adrenaline is like a building's emergency alarm – it triggers multiple systems (lights, doors, speakers) simultaneously to prepare for danger, not just one single response.

Section 5

How do insulin and glucagon control blood glucose, and what are diabetes and its treatments?

Blood glucose regulation:

The pancreas detects changes in blood glucose and responds with two hormones:

Hormone	Released when	Effect	Action
Insulin	Blood glucose is high (after eating)	Decreases blood glucose	Allows glucose to enter cells for respiration or storage as glycogen; stimulates liver to convert glucose to glycogen
Glucagon	Blood glucose is low (during fasting)	Increases blood glucose	Stimulates liver to break down glycogen into glucose; stimulates conversion of other substances into glucose

Negative feedback control (Higher Tier):

Both hormones work via negative feedback:

High blood glucose → pancreas releases insulin
Insulin lowers blood glucose
Once glucose returns to normal, insulin secretion stops (feedback switches off the response)
Similarly, low glucose → glucagon released; once glucose rises, glucagon stops being produced

This system maintains blood glucose in a narrow range (approximately 90–100 mg/100cm³ blood at rest).

Diabetes – Type 1:

Cause: Pancreas produces little or no insulin (autoimmune destruction of insulin-producing cells)
Symptoms: High blood glucose, fatigue, excessive thirst, frequent urination
Treatment: Insulin injections (usually multiple times daily); regular monitoring; controlled diet and exercise

Diabetes – Type 2:

Cause: Body cells become resistant to insulin; pancreas may produce some insulin but not enough
Risk factors: Obesity, age, family history, sedentary lifestyle
Symptoms: Similar to Type 1 but often develop slowly
Treatment: Lifestyle changes (diet, exercise, weight loss); oral medications; some cases may require insulin injections

Key difference: Type 1 is autoimmune (insulin deficiency); Type 2 is insulin resistance (cells don't respond to insulin).

Key termsblood glucoseinsulinglucagonpancreasnegative feedbackType 1 diabetesType 2 diabetesglycogen

Exam tip

To explain negative feedback, use this structure: state the stimulus → state the response → explain how the response reduces the stimulus. Higher Tier students must show this three-step reasoning.

Common mistake

Students often say 'insulin removes glucose from the blood' – this is vague. Say 'insulin allows cells to take up glucose' or 'insulin stimulates the liver to convert glucose to glycogen'.

Example

After a meal: glucose rises → pancreas releases insulin → insulin allows cells to absorb glucose and liver to store it as glycogen → blood glucose returns to normal → insulin secretion decreases. This is negative feedback.

Section 6

What is the menstrual cycle and how do hormones control it?

The menstrual cycle is a monthly cycle in females (approximately 28 days) that prepares the uterus for pregnancy. Four hormones control the cycle:

Hormone	Produced by	Effects
FSH (Follicle-Stimulating Hormone)	Pituitary gland	Stimulates development of follicles (egg sacs) in ovaries; stimulates oestrogen production
Oestrogen	Ovarian follicles	Builds up uterine lining (endometrium); inhibits FSH; triggers LH surge
LH (Luteinising Hormone)	Pituitary gland	Triggers ovulation (release of egg); stimulates formation of corpus luteum
Progesterone	Corpus luteum	Maintains thick uterine lining; inhibits FSH and LH

The four phases of the cycle:

Menstruation (Days 1–5): Uterine lining breaks down and leaves the body as blood; oestrogen and progesterone levels are low
Follicular phase (Days 1–13): FSH rises → stimulates follicle growth → follicles produce oestrogen → oestrogen builds uterine lining and rises
Ovulation (Day 14): High oestrogen triggers LH surge → ovulation occurs (egg released from ovary)
Luteal phase (Days 15–28): LH stimulates corpus luteum formation → corpus luteum produces progesterone → progesterone maintains uterine lining; if egg not fertilised, progesterone and oestrogen drop → cycle restarts

Hormonal regulation (Higher Tier):

Positive feedback: Rising oestrogen in mid-cycle triggers the LH surge (the response amplifies the stimulus)
Negative feedback: High progesterone inhibits FSH and LH, preventing new follicles from developing

Contraceptives – how hormones prevent pregnancy:

Contraceptive	Hormones	How it works
Combined pill	Oestrogen + progesterone	Inhibits FSH and LH → prevents follicle development and ovulation; maintains uterine lining
Progesterone-only pill (POP)	Progesterone only	Inhibits LH → prevents ovulation; thickens cervical mucus (prevents sperm entry)

Fertility treatments:

FSH injections: Used to stimulate development of multiple follicles in women with low FSH or irregular cycles; increases chance of ovulation
LH injections: Trigger ovulation after FSH treatment; ensures egg is released at optimal time
In vitro fertilisation (IVF):
1. FSH administered to stimulate multiple follicles
2. Eggs collected from ovaries
3. Eggs fertilised with sperm in the laboratory
4. Embryos grown for 2–3 days
5. Healthy embryos inserted into uterus
6. Progesterone given to support uterine lining and maintain pregnancy

Key termsmenstrual cycleFSHLHoestrogenprogesteroneovulationfolliclecorpus luteumuterine liningcombined pillprogesterone-only pillIVF

Exam tip

Examiners test whether you can link hormone changes to observable events (e.g. 'oestrogen rises → uterine lining thickens'). Always connect the hormone to its effect on a target organ.

Exam tip

Higher Tier students must distinguish between positive and negative feedback in the cycle. Learn: high oestrogen causes positive feedback (LH surge), but high progesterone causes negative feedback (inhibits FSH/LH).

Common mistake

Students confuse when each hormone is high. Oestrogen peaks mid-cycle (causes ovulation); progesterone is highest in the luteal phase (after ovulation).

Example

If a woman takes the combined pill: oestrogen and progesterone levels stay artificially high → FSH and LH are inhibited via negative feedback → follicles don't develop → ovulation doesn't occur → pregnancy prevented.

Must Know

A hormone is a chemical messenger produced by an endocrine gland, transported in the blood to target organs. This definition is fundamental and appears in every exam.
Major glands and their functions: Pituitary (controls other glands), thyroid (metabolic rate), adrenal (adrenaline for fight-or-flight), pancreas (blood glucose regulation), ovaries/testes (sex hormone production). You must know locations and functions.
Hormonal vs. nervous communication: Hormones are slower but longer-lasting and less specific than nervous signals. Use comparative language in exam answers.
Blood glucose control: Insulin lowers glucose (released when high); glucagon raises glucose (released when low). Both work via negative feedback to maintain glucose in a narrow range. Type 1 diabetes = no insulin; Type 2 = insulin resistance.
Menstrual cycle hormones: FSH and oestrogen build the uterine lining; LH triggers ovulation; progesterone maintains the lining. Combined pill prevents ovulation by inhibiting FSH/LH; progesterone-only pill works mainly by inhibiting LH. Fertility treatments use FSH/LH injections or IVF.
Adrenaline increases heart rate, breathing rate, and blood glucose while reducing digestion – all to prepare muscles for rapid action in emergencies.

That's the notes covered.

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