Hormones and homeostasis

Hormones are chemical messengers produced by endocrine glands and carried in the blood to target organs.

Key endocrine glands

Gland	Hormone(s)	Effect
Pituitary (brain)	FSH, LH, ADH, TSH, growth hormone	"Master gland" — controls other glands
Thyroid	Thyroxine	Sets metabolic rate
Pancreas	Insulin, glucagon	Regulates blood glucose
Adrenal glands	Adrenaline	Fight-or-flight response
Ovaries	Oestrogen, progesterone	Female secondary sexual characteristics, menstrual cycle
Testes	Testosterone	Male secondary sexual characteristics, sperm production

Hormonal vs nervous control

Feature	Nervous	Hormonal
Speed	Fast (milliseconds)	Slower (seconds to days)
Duration	Short-lived	Long-lasting
Path	Electrical impulses along neurones	Chemical messengers in blood
Specificity	Localised to target	Travels everywhere; only target cells with receptors respond

Blood glucose regulation

Normal blood glucose is around 90 mg/dL. Two pancreatic hormones keep it stable.

When glucose rises (after a meal):

• Pancreas releases insulin.
• Insulin causes liver and muscle cells to absorb glucose from the blood and store it as glycogen.
• Blood glucose returns to normal.

When glucose falls (between meals):

• Pancreas releases glucagon.
• Glucagon causes the liver to break down glycogen back into glucose, releasing it into the blood.
• Blood glucose returns to normal.

This is a negative feedback system.

Diabetes

Two main types:

Type 1:

• Pancreas produces little or no insulin (autoimmune destruction of beta cells)
• Usually diagnosed in childhood
• Treated by insulin injections + carbohydrate-controlled diet

Type 2:

• Body cells become resistant to insulin (or pancreas produces too little)
• Strongly linked to obesity and lifestyle
• Usually diagnosed in adults
• First-line treatment: diet, exercise, weight loss; medication (metformin); insulin in advanced cases

WJEC exam tip

Always say "blood glucose" rather than "blood sugar" in answers. And be precise about which hormone does which: insulin LOWERS blood glucose; glucagon RAISES it. Mixing them up is the most common single error in WJEC mark schemes.