ScienceCBSE Class 10 · Control and Coordination

Hormones in Animals and the Endocrine System

Updated 14 October 2026 · Fact-checked

Hormones are chemical messengers released by endocrine glands directly into the blood and carried to target organs. Adrenaline prepares the body for emergencies, thyroxin regulates metabolism and needs iodine, growth hormone controls growth, insulin regulates blood sugar, and testosterone and oestrogen bring puberty changes. Feedback mechanisms control how much hormone is released.

Hormones travel in the blood from an endocrine gland to a target organ, and feedback tells the gland how much to release.

Illustration drawn for QuestionBuddy.

Understand Hormones in Animals

Why chemical signals? Electrical impulses are fast, but they have limits: they reach only cells connected by nervous tissue, and a cell needs time to reset before it can send another impulse. A chemical released into the body can reach all cells, regardless of nerve connections, and act steadily and persistently, though more slowly. Hormones do this job. In animals they are part of the endocrine system, the second way of control and coordination besides the nervous system.

Adrenaline: preparing for an emergency. Suppose a squirrel faces danger: it must either fight or run, and both need a lot of energy. Nerve impulses alone could instruct only a limited range of tissues, so the body also releases adrenaline from the adrenal glands. It is secreted directly into the blood and carried to target organs, including the heart:

the heart beats faster, supplying more oxygen to the muscles;
blood supply to the digestive system and skin is reduced, because muscles around the small arteries there contract; blood is diverted to the skeletal muscles;
breathing rate increases, as the diaphragm and rib muscles contract more.

Together these responses get the body ready for the situation.

Hormones and controlled growth. Animals grow in carefully controlled places; we do not grow fingers on our faces. Hormones help keep this design.

Thyroxin from the thyroid gland regulates carbohydrate, protein and fat metabolism to give the best balance for growth. Iodine is essential to make thyroxin. If the diet lacks iodine, a person may suffer from goitre, one symptom of which is a swollen neck (the thyroid sits in the neck). This is why iodised salt is advised.
Growth hormone from the pituitary regulates growth and development. Its deficiency in childhood leads to dwarfism.
Testosterone (testes, in males) and oestrogen (ovaries, in females) cause the changes of puberty seen around 10 to 12 years of age. Oestrogen also helps develop female sex organs and regulates the menstrual cycle.
Insulin from the pancreas regulates blood sugar. If it is not secreted in proper amounts, blood sugar rises, causing many harmful effects (diabetes); some patients are treated with insulin injections.
Releasing hormones (from the hypothalamus) stimulate the pituitary to release its hormones.

Feedback mechanisms. Hormones must be released in precise amounts at the right time. This is regulated by feedback. For example, when blood sugar rises, cells of the pancreas detect it and produce more insulin; as blood sugar falls, insulin secretion is reduced.

Nervous vs hormonal control. Nervous control uses electrical impulses along neurons; it is fast, reaches only connected cells, and its effects are short-lived. Hormonal control uses chemicals carried in blood; it is slower but reaches all cells and its effects last longer. Both work together, as when nerves and adrenaline prepare the body for an emergency.

Hormones in Animals: formulas and key facts

Adrenaline: $adrenal gland \to heart rate ↑, breathing ↑, blood to muscles ↑$; Blood to the digestive system and skin is reduced.
Thyroxin: $thyroid + iodine \to thyroxin (metabolism)$; Iodine deficiency → goitre (swollen neck).
Growth hormone: $pituitary \to growth and development$; Deficiency in childhood → dwarfism.
Insulin: $pancreas \to blood sugar regulation$; Too little → blood sugar rises (diabetes).
Sex hormones: $testes \to testosterone; ovaries \to oestrogen$; Changes at puberty.
Feedback: $blood sugar ↑\Rightarrow insulin ↑; blood sugar ↓\Rightarrow insulin ↓$; Keeps hormone levels precise.

How to solve Hormones in Animals questions

For hormone questions, build a gland-hormone-function link and then apply it.

1Name the gland and the hormone together (pituitary – growth hormone; thyroid – thyroxin; pancreas – insulin; adrenal – adrenaline; testes – testosterone; ovaries – oestrogen).
2State the function in one line.
3If a deficiency or excess is described, link it to the effect (goitre, dwarfism, high blood sugar).
4For 'how is it controlled', describe the feedback loop with the insulin example.
5For emergencies, list adrenaline's effects on heart, blood flow and breathing, and say why each helps.
6For comparisons with the nervous system, use: signal type, speed, reach, duration.

Hormones in Animals in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Feedback control of insulin

Suppose your uncle has been told to cut down on sugar and takes insulin injections. After a sweet-heavy festival lunch, he checks his blood sugar and finds it much higher than usual.

Explain what normally happens in a healthy person after a sugary meal, why your uncle's blood sugar stays high, and why insulin injections help.

Try it first, then show the solutionSolution

After a meal, blood sugar rises. In a healthy person, cells of the pancreas detect this and produce more insulin.
Insulin helps regulate the blood sugar level, bringing it down; as it falls, the pancreas reduces insulin secretion. This is a feedback mechanism.
In your uncle, insulin is not secreted in proper amounts, so the feedback cannot correct the rise and blood sugar stays high, which can cause many harmful effects.
Insulin injections supply the missing hormone so his blood sugar can be regulated.

Answer: Normally the pancreas responds to high blood sugar with more insulin (feedback). Without enough insulin, sugar stays high; injections replace the missing hormone.

Memory hook: Sugar up, insulin up; sugar down, insulin down: feedback keeps the balance.

Tricks to remember Hormones in Animals

Short memory aids. Say each one aloud once, then use it on a question the same day.

Gland-hormone pairs: 'Pituitary Grows, Thyroid Thinks Iodine, Pancreas Pumps Insulin'
Pituitary → growth hormone; thyroid → thyroxin (iodine); pancreas → insulin.
Use it when: Matching glands to hormones.
Adrenaline's three H's
Heart faster, Huffing (breathing) faster, Heading blood to muscles.
Use it when: Effects of adrenaline.
Nerves are texts, hormones are broadcasts
A nerve impulse goes to connected cells only; a hormone reaches every cell through blood.
Use it when: Comparing nervous and hormonal control.

Hormones in Animals: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Iodised salt · 2 marks · Very short answerBoard level

Why is the use of iodised salt advisable? Name the disease caused by iodine deficiency and one symptom.

Try it first, then show the solutionSolution

Iodine is needed by the thyroid gland to make thyroxin, which regulates carbohydrate, protein and fat metabolism for balanced growth (1 mark).
Iodine deficiency can cause goitre; one symptom is a swollen neck (1 mark).

Answer: Iodine is essential for thyroxin; deficiency causes goitre (swollen neck).

Example 2: Adrenaline in emergencies · 3 marks · Short answerHarder board level

How does our body respond when adrenaline is secreted into the blood? Why is a hormone used for this rather than nerves alone?

Try it first, then show the solutionSolution

Heart beats faster, supplying more oxygen to muscles (½ mark).
Blood to the digestive system and skin is reduced by contraction of muscles around small arteries, diverting blood to skeletal muscles (1 mark).
Breathing rate increases through contractions of the diaphragm and rib muscles (½ mark).
Nerve impulses reach only connected tissues; a hormone in the blood reaches all cells, producing the wide-ranging changes needed (1 mark).

Answer: Faster heartbeat, blood diverted to muscles, faster breathing; a hormone reaches all tissues at once.

Example 3: Complete the table · 5 marks · Long answerBoard level

Complete: (i) Growth hormone – gland – function; (ii) gland that makes thyroxin – function; (iii) Insulin – gland – function; (iv) Testosterone – gland – function; (v) Oestrogen – gland – function.

Try it first, then show the solutionSolution

(i) Pituitary; stimulates growth in all organs (1 mark).
(ii) Thyroid; regulates metabolism for body growth (1 mark).
(iii) Pancreas; regulates blood sugar level (1 mark).
(iv) Testes; changes at puberty in males (1 mark).
(v) Ovaries; development of female sex organs, regulates the menstrual cycle, changes at puberty (1 mark).

Answer: Pituitary/growth; thyroid/metabolism; pancreas/blood sugar; testes/male puberty; ovaries/female organs and menstrual cycle.

Example 4: Nervous vs hormonal · 4 marks · Short answerHarder board level

Compare and contrast nervous and hormonal mechanisms of control and coordination in animals (any four points).

Try it first, then show the solutionSolution

Signal: electrical impulses along neurons vs chemicals (hormones) in blood (1 mark).
Speed: nervous is very fast; hormonal is slower (1 mark).
Reach: nerve impulses reach only cells connected by nervous tissue; hormones reach all cells via blood (1 mark).
Persistence: a nerve cell cannot fire continuously and must reset; hormonal action is steady and persistent. Similarity: both coordinate body activities and respond to changes (1 mark).

Answer: Electrical vs chemical; fast vs slow; limited vs wide reach; short vs persistent effect.

Example 5: Diagnosing from symptoms · 3 marks · Short answerHOTS / competency

Three children are examined. P is much shorter than others of the same age, with normal body proportions. Q has a swelling at the front of the neck. R feels very thirsty and has high blood sugar. (a) Name the hormone most likely involved in each case and its gland. (b) For which child would a change in diet help most, and why?

Try it first, then show the solutionSolution

(a) P: growth hormone deficiency in childhood (pituitary) causing dwarfism (½ mark).
(a) Q: thyroxin, thyroid gland; goitre due to iodine deficiency (½ mark).
(a) R: insulin, pancreas; not secreted in proper amounts (1 mark).
(b) Q: iodine is needed to make thyroxin, so adding iodised salt to the diet can address the cause (1 mark).

Answer: P – growth hormone (pituitary); Q – thyroxin (thyroid, iodine); R – insulin (pancreas). Diet change (iodised salt) helps Q most.

Where students lose marks in Hormones in Animals

The slips examiners see most often, and what to write instead.

Mistake: Wrong gland for a hormone
Gland and hormone names are learnt separately.
Wrong working
Insulin is made by the thyroid.
Right working
Insulin is made by the pancreas; thyroxin by the thyroid.
Do this: Learn them as pairs from the NCERT table.
Usually costs: ½ to 1 mark each.
Mistake: Saying hormones travel through nerves
Confusion between the two systems.
Wrong working
Adrenaline is carried by nerves to the heart.
Right working
Adrenaline is secreted directly into the blood and carried to target organs.
Do this: Endocrine glands release hormones into the blood.
Usually costs: 1 mark.
Mistake: Linking goitre to the wrong cause
Students blame salt itself or sugar.
Wrong working
Goitre is caused by eating too much salt.
Right working
Goitre may result from iodine deficiency, since iodine is needed to make thyroxin.
Do this: Iodine → thyroxin → goitre if deficient.
Usually costs: 1 mark.
Mistake: Incomplete adrenaline effects
Only 'heart beats faster' is written.
Wrong working
Adrenaline makes the heart beat faster.
Right working
Faster heartbeat, less blood to digestive system and skin, more to skeletal muscles, faster breathing.
Do this: List all three effects.
Usually costs: 1-2 marks.

Exam tips

Learn NCERT Table 6.1 completely; questions often give one column and ask for the others.
Define a hormone as a chemical messenger secreted by an endocrine gland directly into the blood.
Always give the feedback example with insulin when asked how hormone secretion is controlled.
For comparison questions, write a table with at least four points.
The 'Do You Know?' box on the hypothalamus is not assessed, but releasing hormones appear in the NCERT table.

Practice questions on Hormones in Animals

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Which of the following is a plant hormone, not an animal hormone?
(a) insulin (b) thyroxin (c) oestrogen (d) cytokinin
Hint
One of these promotes cell division in plants.
Answer
(d) cytokinin.
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Some patients with diabetes are given insulin injections.
Reason (R): Insulin is produced by the thyroid gland and regulates metabolism.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Which gland makes insulin?
Answer
(c). Insulin is produced by the pancreas and regulates blood sugar.
Q3 · 3 marks · Short answerHarder board level
How is the timing and amount of hormone release regulated? Explain using the example of insulin.
Hint
Feedback.
Answer
By feedback mechanisms. When blood sugar rises, pancreatic cells detect the rise and secrete more insulin; as blood sugar falls, insulin secretion is reduced. So the hormone level follows the body's need.
Q4 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
Suppose a student hears a loud crash at night. Her heart pounds, she breathes quickly, and she feels ready to run, though her stomach feels 'empty'.
(a) Name the hormone and the gland responsible. (1 mark)
(b) Why does she breathe faster? (1 mark)
(c) Explain why her stomach feels 'empty' and why this response is useful in danger. (2 marks)
Hint
Where is the blood being sent?
Answer
(a) Adrenaline, adrenal glands. (b) Adrenaline increases breathing rate through contractions of the diaphragm and rib muscles, bringing in more oxygen. (c) Muscles around small arteries of the digestive system contract, reducing blood flow there and diverting blood to skeletal muscles; digestion can wait, while muscles need oxygen and energy to fight or run.
Q5 · 3 marks · Short answerHOTS / competency
Why do animals need hormones for growth when they do not show tropic (directional) growth like plants? Use one hormone as an example.
Hint
Growth in animals is also carefully controlled in place and amount.
Answer
Animals do not bend towards light or gravity, but their growth still happens in carefully controlled places and amounts; body design is maintained as children grow (we do not grow fingers on our faces). Hormones coordinate this. For example, growth hormone from the pituitary regulates growth and development; too little in childhood causes dwarfism.
Q6 · 2 marks · Very short answerBoard level
What changes occur at puberty and which hormones cause them? Name the glands.
Hint
Different hormones in males and females.
Answer
Dramatic changes in appearance around 10 to 12 years of age (puberty). Testosterone from the testes in males and oestrogen from the ovaries in females.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which gland secretes adrenaline?Show answer
Adrenal gland.
2.Which element is needed to make thyroxin?Show answer
Iodine.
3.Deficiency of growth hormone in childhood causes?Show answer
Dwarfism.
4.Which hormone regulates blood sugar?Show answer
Insulin, from the pancreas.
5.What regulates the amount of hormone released?Show answer
Feedback mechanisms.
6.Hormone responsible for puberty changes in females?Show answer
Oestrogen (ovaries).

Hormones in Animals: frequently asked questions

What are hormones?

Chemical messengers released by endocrine glands directly into the blood, which carry them to target organs to bring about specific effects.

What does adrenaline do in our body?

It makes the heart beat faster, diverts blood from the digestive system and skin to the skeletal muscles, and increases breathing rate, preparing the body for an emergency.

Why is iodised salt important?

The thyroid needs iodine to make thyroxin, which regulates metabolism for growth. Lack of iodine can cause goitre.

How does a feedback mechanism work?

The body detects the level of something, such as blood sugar, and adjusts the hormone accordingly: more insulin when sugar rises, less when it falls.

What is the difference between nervous and hormonal coordination?

Nervous coordination uses fast electrical impulses that reach only connected cells; hormonal coordination uses slower chemical signals in the blood that reach all cells and act more persistently.