Disease and response · GCSE Biology
Endocrine system
Map GCSE Biology hormones: glands, blood transport, target organs, pituitary as master gland, and how chemical control is slower but longer-lasting than a nerve impulse.
Gland secretes hormone into blood. Hormone binds receptors on a target organ. Pituitary is the master gland. Adrenaline is the fast emergency hormone; many others are slower than reflexes.
The important bits
What you need to know
- 1
The endocrine system is made of glands that secrete hormones (chemical messengers) directly into the blood. Hormones travel to target organs that have matching receptors.
- 2
Compared with nerves: hormones are slower, travel in blood, and often have a longer-lasting effect. Useful for growth, metabolism, blood glucose and the menstrual cycle — not for pulling a hand off a stove.
- 3
Pituitary gland (in the brain) is the master gland: it secretes several hormones that control other glands (for example TSH controlling the thyroid, FSH and LH controlling the ovaries).
- 4
Thyroid: thyroxine, controls metabolic rate. Adrenal glands: adrenaline, increases heart rate, breathing, and glucose to muscles (fight or flight). Pancreas: insulin (and glucagon on Higher). Ovaries: oestrogen (and progesterone). Testes: testosterone.
- 5
Adrenaline is a useful contrast with a reflex: still fast for a hormone, but it affects the whole body via blood, not a single muscle via one motor neurone.
- 6
Negative feedback keeps levels in range: if thyroxine is high, TSH from the pituitary falls, so the thyroid releases less thyroxine. Higher-tier papers expect this loop.
- 7
Reproductive hormones (Triple/Combined depending on route): FSH ripens an egg, LH causes ovulation, oestrogen and progesterone build and maintain the uterus lining. Contraceptive pills use oestrogen/progesterone to inhibit FSH.
- 8
Hormones are not enzymes and not antibodies. They are not used up as food. They bind, cause a change, and are broken down (often in the liver).
Quotations worth analysing
Short evidence. Real method.
“Hormones are chemical messengers secreted by glands into the blood and acting on target organs.”
Gland, blood, target: three marks hiding in one sentence. “Hormones are chemicals in the body” is too thin.
“The pituitary is the master gland.”
It controls other glands with tropic hormones such as TSH, FSH and LH. Do not say the pituitary makes insulin.
“Adrenaline increases heart rate and the delivery of oxygen and glucose to muscles.”
Link to respiration: more aerobic respiration for a sudden energy transfer. This is not a reflex arc.
Go deeper
How do I compare nervous and hormonal control in a table answer?
Speed: nervous faster (milliseconds) versus hormones seconds to hours. Pathway: neurones versus blood. Duration: brief impulse versus longer-lived chemical. Target: a specific effector versus any tissue with the receptor (can be widespread). Example: dropping a hot dish is nervous; puberty is hormonal; blood glucose is hormonal (insulin); a startle that makes your heart race is adrenaline, hormonal but still quick. In six marks, fill the table then add one named example each. Do not write that hormones are “electricity in the blood”. Do not write that nerves are slower. Homeostasis uses both: temperature uses nerves and effectors (sweat glands, muscles); glucose uses hormones.
Go deeper
What does negative feedback look like for thyroxine?
Low thyroxine → pituitary releases more TSH → thyroid releases more thyroxine → metabolic rate rises. High thyroxine → less TSH → less thyroxine. That loop keeps metabolism stable. Iodine is needed to make thyroxine; deficiency can cause a goitre (enlarged thyroid) in some courses. If a question gives TSH and thyroxine blood levels, read which way the feedback has gone. Graves’ disease and underactive thyroid appear more at A-level; at GCSE, stick to the loop and to “thyroxine controls metabolic rate”. Adrenaline is not primarily a negative-feedback exam story; it is a short-term override in an emergency, then is broken down.
Go deeper
Where do FSH, LH, oestrogen and progesterone fit if my paper includes them?
FSH from the pituitary: follicle (egg) matures in the ovary and oestrogen is produced. Oestrogen: uterus lining thickens and inhibits FSH (so only one egg), then stimulates LH surge. LH: ovulation. Progesterone from the corpus luteum: maintains lining, inhibits FSH and LH. If no fertilisation, progesterone falls, lining is shed (period). Combined pill: oestrogen and progesterone keep FSH low, no egg. Fertility drugs may contain FSH. This is a cycle of hormones, not a reflex. Learn it as a sequence of days if Triple demands it. Combined papers vary; if the specification lists the menstrual cycle, this paragraph is not optional.
See the idea in action
Compare how a person withdraws a hand from a flame with how adrenaline prepares them to run. Withdrawal: receptor in skin, sensory neurone, relay in spinal cord, motor neurone, muscle contracts — milliseconds, local. Adrenaline: adrenal glands secrete the hormone into blood, heart rate and breathing rise, glycogen to glucose in liver, more oxygen and glucose reach many muscles — slower than the reflex but body-wide and longer than one impulse. Both protect, but only one is a reflex arc. Insulin would be the wrong hormone here; it lowers blood glucose rather than preparing for flight.
Exam technique
Turn knowledge into marks
Define hormone as a chemical from a gland in the blood to a target organ. Contrast speed and duration with nerves. Learn pituitary, thyroid, adrenal, pancreas, ovaries, testes and one hormone each. Use negative feedback where the paper is Higher.
Common mistakes
Do not give these marks away
- 01
Saying hormones travel along neurones, or that the pituitary makes insulin.
- 02
Calling adrenaline a reflex, or saying hormonal control is faster than nervous control.
- 03
Mixing up FSH/LH with insulin, or oestrogen with testosterone’s gland.
How do hormones travel to their target organs?
AAlong sensory neurones only
BIn the blood from the gland that secreted them
CThrough stomata
DBy osmosis through a cell wall
Show the answer
In the blood from the gland that secreted them. Endocrine glands secrete hormones into the blood. Nerves use neurones. Stomata and cell walls are plant structures.
Quick questions
If this is the bit you searched
What is a hormone GCSE Biology?
A chemical messenger secreted by a gland into the blood, which acts on a target organ that has the matching receptors.
Why is the pituitary called the master gland?
It produces hormones that control many other glands, including TSH for the thyroid and FSH and LH for the ovaries.
What does adrenaline do?
It increases heart rate, breathing rate and the supply of glucose and oxygen to muscles, preparing the body for fight or flight.
How is hormonal control different from nervous control?
Hormones are slower, travel in blood and often last longer. Nerve impulses are electrical, faster and usually shorter-lived.