A Gland With No Duct Posts Its Message Into the Blood
Learn how an endocrine gland differs from an exocrine one, where the pituitary, thyroid, adrenal, pancreas and gonads lie, which hormone each secretes and what it does, and which disorder follows from too little or too much.
Why does a gland with no duct still get its secretion where it is needed?
Because it uses the blood as its delivery system instead of a pipe.
A salivary gland has a duct — a tube that carries saliva to one specific place, the mouth. An endocrine gland has no duct at all. It releases its secretion straight into the blood, which then carries it to every part of the body.
That sounds wasteful, and it is not. The secretion — a hormone — only affects the particular target organ built to respond to it, so a thyroid hormone can circulate everywhere and act only where it should. This page covers the first part of the ICSE Class 8 Biology chapter on the endocrine system: the two kinds of gland, where the endocrine glands are, and what each one's hormone does.
A salivary gland has a duct — a tube that carries saliva to one specific place, the mouth. An endocrine gland has no duct at all. It releases its secretion straight into the blood, which then carries it to every part of the body.
That sounds wasteful, and it is not. The secretion — a hormone — only affects the particular target organ built to respond to it, so a thyroid hormone can circulate everywhere and act only where it should. This page covers the first part of the ICSE Class 8 Biology chapter on the endocrine system: the two kinds of gland, where the endocrine glands are, and what each one's hormone does.
What is the difference between an exocrine and an endocrine gland?
Exocrine glands have ducts; endocrine glands do not.
Exocrine glands pour their secretion into a duct, which carries it to a specific site where it acts locally.
- Salivary glands — saliva into the mouth
- Gastric glands — gastric juice into the stomach
- Sweat glands — sweat onto the skin
- Tear glands — tears onto the eye
- Liver — bile into the small intestine
- Sebaceous glands — oil onto the skin and hair
Their secretions are mostly enzymes and other substances needed in quantity at one place.
Endocrine glands are ductless. They release hormones directly into the blood, which carries them throughout the body to their target organs.
- Pituitary, thyroid, parathyroid, adrenal, pineal, thymus
Mixed glands do both jobs, and there are two important ones:
- The pancreas secretes pancreatic juice through a duct into the small intestine (exocrine), and the hormones insulin and glucagon into the blood (endocrine).
- The gonads produce gametes (testes make sperm, ovaries make ova) and hormones released into the blood.
A hormone is a chemical messenger, secreted in very small amounts by an endocrine gland directly into the blood, which travels to a target organ and controls or coordinates a particular activity there.
Four properties of hormones worth knowing:
- They are needed in minute quantities — a tiny amount produces a large effect.
- They act slowly but their effects are long-lasting, unlike a nerve impulse which is fast and brief.
- They are not stored in the body; they are used up after acting and must be secreted afresh.
- They act only on their target organ, even though they reach every organ.
Why the body needs both a nervous and a hormonal system. The nervous system handles anything needing an immediate, short response — pulling your hand from a hot pan. The endocrine system handles anything needing a slow, sustained one — growth over years, or the menstrual cycle over weeks. Neither could do the other's job, which is why both exist and why they are called the two coordinating systems of the body.
Exocrine glands pour their secretion into a duct, which carries it to a specific site where it acts locally.
- Salivary glands — saliva into the mouth
- Gastric glands — gastric juice into the stomach
- Sweat glands — sweat onto the skin
- Tear glands — tears onto the eye
- Liver — bile into the small intestine
- Sebaceous glands — oil onto the skin and hair
Their secretions are mostly enzymes and other substances needed in quantity at one place.
Endocrine glands are ductless. They release hormones directly into the blood, which carries them throughout the body to their target organs.
- Pituitary, thyroid, parathyroid, adrenal, pineal, thymus
Mixed glands do both jobs, and there are two important ones:
- The pancreas secretes pancreatic juice through a duct into the small intestine (exocrine), and the hormones insulin and glucagon into the blood (endocrine).
- The gonads produce gametes (testes make sperm, ovaries make ova) and hormones released into the blood.
A hormone is a chemical messenger, secreted in very small amounts by an endocrine gland directly into the blood, which travels to a target organ and controls or coordinates a particular activity there.
Four properties of hormones worth knowing:
- They are needed in minute quantities — a tiny amount produces a large effect.
- They act slowly but their effects are long-lasting, unlike a nerve impulse which is fast and brief.
- They are not stored in the body; they are used up after acting and must be secreted afresh.
- They act only on their target organ, even though they reach every organ.
Why the body needs both a nervous and a hormonal system. The nervous system handles anything needing an immediate, short response — pulling your hand from a hot pan. The endocrine system handles anything needing a slow, sustained one — growth over years, or the menstrual cycle over weeks. Neither could do the other's job, which is why both exist and why they are called the two coordinating systems of the body.
Where are the main endocrine glands in the body?
Working downwards from the head:
- Pituitary gland — a very small gland at the base of the brain, hanging just below it. Despite its size it is called the master gland.
- Thyroid gland — in the neck, in front of the windpipe, shaped like a butterfly with two lobes joined across the middle. It is the largest endocrine gland.
- Parathyroid glands — four tiny glands lying behind the thyroid, embedded in its surface.
- Adrenal glands — a pair, one sitting like a cap on top of each kidney. This is why they are also called the suprarenal glands.
- Pancreas — a long gland lying behind the stomach, between the stomach and the small intestine.
- Gonads — the testes, in the scrotum outside the body cavity in males; the ovaries, a pair in the lower abdomen in females.
Two more are named in the syllabus in passing:
- Pineal gland — in the brain
- Thymus gland — in the chest, behind the breastbone
Why the pituitary is called the master gland. Along with its own hormones, it secretes hormones whose job is to control other endocrine glands — instructing the thyroid, the adrenals and the gonads when to secrete. So a fault in the pituitary can disturb several glands at once, while a fault in the thyroid affects only the thyroid's own work.
This is also why the pituitary sits where it does. Being attached to the base of the brain lets the nervous system influence it directly, and through it the whole endocrine system — which is how the two coordinating systems are joined together.
A locating detail worth remembering. The thyroid is the one gland you can point to on yourself, in the front of the neck. Its swelling is visible from outside, which is exactly why goitre is such a recognisable disorder and why it appears in every question on this chapter.
- Pituitary gland — a very small gland at the base of the brain, hanging just below it. Despite its size it is called the master gland.
- Thyroid gland — in the neck, in front of the windpipe, shaped like a butterfly with two lobes joined across the middle. It is the largest endocrine gland.
- Parathyroid glands — four tiny glands lying behind the thyroid, embedded in its surface.
- Adrenal glands — a pair, one sitting like a cap on top of each kidney. This is why they are also called the suprarenal glands.
- Pancreas — a long gland lying behind the stomach, between the stomach and the small intestine.
- Gonads — the testes, in the scrotum outside the body cavity in males; the ovaries, a pair in the lower abdomen in females.
Two more are named in the syllabus in passing:
- Pineal gland — in the brain
- Thymus gland — in the chest, behind the breastbone
Why the pituitary is called the master gland. Along with its own hormones, it secretes hormones whose job is to control other endocrine glands — instructing the thyroid, the adrenals and the gonads when to secrete. So a fault in the pituitary can disturb several glands at once, while a fault in the thyroid affects only the thyroid's own work.
This is also why the pituitary sits where it does. Being attached to the base of the brain lets the nervous system influence it directly, and through it the whole endocrine system — which is how the two coordinating systems are joined together.
A locating detail worth remembering. The thyroid is the one gland you can point to on yourself, in the front of the neck. Its swelling is visible from outside, which is exactly why goitre is such a recognisable disorder and why it appears in every question on this chapter.
Which hormone does each gland secrete, and what does it do?
Pituitary gland — growth hormone. It controls the growth of the bones and of the body as a whole. The pituitary also secretes hormones that control the other endocrine glands, and one that acts on the kidney to regulate water.
Thyroid gland — thyroxine. It controls the rate of metabolism — how fast the body releases energy from food — and is also needed for normal physical and mental growth and development. Thyroxine contains iodine, so the gland cannot make it without iodine in the diet.
Parathyroid glands — parathormone. It regulates the level of calcium and phosphorus in the blood and bones.
Adrenal glands — adrenaline. Called the emergency hormone or the fight-or-flight hormone, it prepares the body for sudden action by raising the heart rate, raising the breathing rate, raising blood pressure and raising blood glucose, and by sending more blood to the muscles.
This is the hormone behind what you feel when startled — a thumping heart, quick breathing and a burst of strength. Since it acts through the blood, it takes a second or two to arrive and its effects persist for minutes, which is exactly the difference between a hormone and a nerve impulse.
Pancreas — insulin and glucagon.
- Insulin lowers blood glucose, by helping cells take glucose in and the liver store it.
- Glucagon raises blood glucose, by releasing stored glucose from the liver.
The two work against each other, which is how the level is held steady between meals and after them.
Testes — testosterone. It controls the male secondary sexual characters and is needed for sperm production.
Ovaries — oestrogen and progesterone. Oestrogen controls the female secondary sexual characters; both control the menstrual cycle, and progesterone maintains pregnancy.
The pattern across the list. Every hormone regulates a rate or a level rather than performing an action itself. Thyroxine sets a rate, insulin holds a level, growth hormone controls a rate of growth. Nothing here builds or moves anything — hormones give instructions, and the target organs do the work. That is what coordination means, and it is why so many different disorders arise from too little or too much of a single substance.
Thyroid gland — thyroxine. It controls the rate of metabolism — how fast the body releases energy from food — and is also needed for normal physical and mental growth and development. Thyroxine contains iodine, so the gland cannot make it without iodine in the diet.
Parathyroid glands — parathormone. It regulates the level of calcium and phosphorus in the blood and bones.
Adrenal glands — adrenaline. Called the emergency hormone or the fight-or-flight hormone, it prepares the body for sudden action by raising the heart rate, raising the breathing rate, raising blood pressure and raising blood glucose, and by sending more blood to the muscles.
This is the hormone behind what you feel when startled — a thumping heart, quick breathing and a burst of strength. Since it acts through the blood, it takes a second or two to arrive and its effects persist for minutes, which is exactly the difference between a hormone and a nerve impulse.
Pancreas — insulin and glucagon.
- Insulin lowers blood glucose, by helping cells take glucose in and the liver store it.
- Glucagon raises blood glucose, by releasing stored glucose from the liver.
The two work against each other, which is how the level is held steady between meals and after them.
Testes — testosterone. It controls the male secondary sexual characters and is needed for sperm production.
Ovaries — oestrogen and progesterone. Oestrogen controls the female secondary sexual characters; both control the menstrual cycle, and progesterone maintains pregnancy.
The pattern across the list. Every hormone regulates a rate or a level rather than performing an action itself. Thyroxine sets a rate, insulin holds a level, growth hormone controls a rate of growth. Nothing here builds or moves anything — hormones give instructions, and the target organs do the work. That is what coordination means, and it is why so many different disorders arise from too little or too much of a single substance.
Which disorders come from too little or too much of a hormone?
Because a hormone acts in minute amounts, even a small departure from the right level causes a recognisable disorder. Each one below is named for its cause.
Thyroxine — too little.
- Goitre — the thyroid swells into a visible lump in the neck. The usual cause is a shortage of iodine in the diet, without which the gland cannot make thyroxine and enlarges as it tries.
- In children, severe deficiency causes cretinism — stunted physical and mental growth.
- In adults, it causes myxoedema — a slowed metabolism, with weight gain, puffiness, tiredness and intolerance of cold.
Thyroxine — too much. An overactive thyroid, with a fast metabolism: weight loss despite a good appetite, a rapid heartbeat, restlessness, and in some cases protruding eyes.
Growth hormone — too little in childhood. Dwarfism — the body stops growing to its normal height, with the proportions remaining roughly normal and mental development unaffected.
Growth hormone — too much in childhood. Gigantism — abnormally excessive growth in height.
Growth hormone — too much in adulthood. Acromegaly — the long bones can no longer lengthen, so the bones of the hands, feet and jaw thicken instead.
Insulin — too little. Diabetes mellitus — blood glucose stays high because cells cannot take it in. Glucose then appears in the urine, and the symptoms are excessive thirst, frequent urination, tiredness and weight loss. It is managed with diet, exercise and, where needed, insulin.
Parathormone — too little. Muscle cramps and spasms, from a fall in blood calcium.
Why goitre is the one that can be prevented from the kitchen. It is caused by a dietary deficiency rather than by a fault in the gland. Adding a tiny quantity of iodine to common salt supplies what the thyroid needs, and this is why iodised salt is sold and recommended, particularly in inland and hilly regions where soil and water are naturally low in iodine.
The distinction to keep straight. Dwarfism and gigantism both come from growth hormone, one from too little and one from too much, and both must begin in childhood while the bones can still lengthen. Diabetes comes from insulin, and goitre from thyroxine and iodine. Attaching the disorder to the wrong hormone is the commonest error in this chapter, and each pairing is a separate one-mark answer.
Thyroxine — too little.
- Goitre — the thyroid swells into a visible lump in the neck. The usual cause is a shortage of iodine in the diet, without which the gland cannot make thyroxine and enlarges as it tries.
- In children, severe deficiency causes cretinism — stunted physical and mental growth.
- In adults, it causes myxoedema — a slowed metabolism, with weight gain, puffiness, tiredness and intolerance of cold.
Thyroxine — too much. An overactive thyroid, with a fast metabolism: weight loss despite a good appetite, a rapid heartbeat, restlessness, and in some cases protruding eyes.
Growth hormone — too little in childhood. Dwarfism — the body stops growing to its normal height, with the proportions remaining roughly normal and mental development unaffected.
Growth hormone — too much in childhood. Gigantism — abnormally excessive growth in height.
Growth hormone — too much in adulthood. Acromegaly — the long bones can no longer lengthen, so the bones of the hands, feet and jaw thicken instead.
Insulin — too little. Diabetes mellitus — blood glucose stays high because cells cannot take it in. Glucose then appears in the urine, and the symptoms are excessive thirst, frequent urination, tiredness and weight loss. It is managed with diet, exercise and, where needed, insulin.
Parathormone — too little. Muscle cramps and spasms, from a fall in blood calcium.
Why goitre is the one that can be prevented from the kitchen. It is caused by a dietary deficiency rather than by a fault in the gland. Adding a tiny quantity of iodine to common salt supplies what the thyroid needs, and this is why iodised salt is sold and recommended, particularly in inland and hilly regions where soil and water are naturally low in iodine.
The distinction to keep straight. Dwarfism and gigantism both come from growth hormone, one from too little and one from too much, and both must begin in childhood while the bones can still lengthen. Diabetes comes from insulin, and goitre from thyroxine and iodine. Attaching the disorder to the wrong hormone is the commonest error in this chapter, and each pairing is a separate one-mark answer.
Exam tip
Exam tip: pair every disorder with its hormone and its gland
Answer a disorder question with three things: the hormone, whether there is too little or too much, and the gland. Goitre — deficiency of thyroxine from the thyroid, usually due to a lack of iodine in the diet.
Learn the four headline pairings cleanly: goitre — thyroxine, diabetes mellitus — insulin, dwarfism — too little growth hormone, gigantism — too much growth hormone.
Say that dwarfism and gigantism both arise in childhood, and that excess growth hormone in an adult gives acromegaly instead.
Define a hormone with all its parts — a chemical messenger, secreted in small amounts, directly into the blood, acting on a target organ.
For exocrine versus endocrine, lead with the duct: exocrine glands have one, endocrine glands are ductless.
Name the pancreas and the gonads as mixed glands and say what each does on both sides.
Give the location precisely when asked: pituitary at the base of the brain, thyroid in front of the windpipe, adrenals on top of the kidneys, pancreas behind the stomach.
Call the pituitary the master gland and give the reason — it controls other endocrine glands.
And contrast the two coordinating systems in one line: nerve impulses are fast and brief, hormones are slow and long-lasting.
Learn the four headline pairings cleanly: goitre — thyroxine, diabetes mellitus — insulin, dwarfism — too little growth hormone, gigantism — too much growth hormone.
Say that dwarfism and gigantism both arise in childhood, and that excess growth hormone in an adult gives acromegaly instead.
Define a hormone with all its parts — a chemical messenger, secreted in small amounts, directly into the blood, acting on a target organ.
For exocrine versus endocrine, lead with the duct: exocrine glands have one, endocrine glands are ductless.
Name the pancreas and the gonads as mixed glands and say what each does on both sides.
Give the location precisely when asked: pituitary at the base of the brain, thyroid in front of the windpipe, adrenals on top of the kidneys, pancreas behind the stomach.
Call the pituitary the master gland and give the reason — it controls other endocrine glands.
And contrast the two coordinating systems in one line: nerve impulses are fast and brief, hormones are slow and long-lasting.
Did you know
Why does a fright make your heart pound before you have decided anything?
Step near a snake on a path and your heart is already hammering before you have worked out what you saw.
The nervous system detects the danger in a fraction of a second and, among other things, signals the adrenal glands. They release adrenaline into the blood, and within a second or two it has reached the heart, the lungs, the liver and the muscles.
Every effect it produces prepares the body for sudden effort. The heart beats faster to move blood quickly, breathing speeds up to take in more oxygen, the liver releases stored glucose so the muscles have fuel, and blood is diverted to the muscles from organs that can wait. None of it is decided; all of it is automatic.
What makes the feeling last is the hormone itself. A nerve impulse would have finished in milliseconds, but adrenaline has to be carried away and broken down, which takes minutes. That is why you stay shaky long after the snake has gone — and it is the clearest everyday demonstration of the difference between nervous and hormonal control.
The nervous system detects the danger in a fraction of a second and, among other things, signals the adrenal glands. They release adrenaline into the blood, and within a second or two it has reached the heart, the lungs, the liver and the muscles.
Every effect it produces prepares the body for sudden effort. The heart beats faster to move blood quickly, breathing speeds up to take in more oxygen, the liver releases stored glucose so the muscles have fuel, and blood is diverted to the muscles from organs that can wait. None of it is decided; all of it is automatic.
What makes the feeling last is the hormone itself. A nerve impulse would have finished in milliseconds, but adrenaline has to be carried away and broken down, which takes minutes. That is why you stay shaky long after the snake has gone — and it is the clearest everyday demonstration of the difference between nervous and hormonal control.
Key takeaways
Glands, hormones and their disorders: quick revision
- Exocrine glands have ducts carrying secretions to a specific site — salivary, gastric, sweat, tear, sebaceous glands and the liver.
- Endocrine glands are ductless and release hormones into the blood — pituitary, thyroid, parathyroid, adrenal, pineal, thymus.
- Mixed glands: the pancreas (pancreatic juice by duct, insulin and glucagon into blood) and the gonads (gametes plus hormones).
- A hormone is a chemical messenger secreted in small amounts directly into the blood, acting on a target organ. Hormones act slowly with long-lasting effects, are not stored, and are used up after acting.
- Nerve impulses are fast and brief; hormones are slow and sustained — hence two coordinating systems.
- Locations: pituitary at the base of the brain, thyroid in front of the windpipe, four parathyroids behind it, adrenals on top of the kidneys, pancreas behind the stomach, gonads in the scrotum or lower abdomen.
- The pituitary is the master gland because it controls other endocrine glands.
- Hormones and functions — growth hormone: growth of bones and body. Thyroxine: rate of metabolism, growth and development; contains iodine. Parathormone: calcium and phosphorus. Adrenaline: the emergency hormone, raising heart rate, breathing, blood pressure and blood glucose. Insulin lowers and glucagon raises blood glucose. Testosterone: male secondary sexual characters and sperm. Oestrogen and progesterone: female characters, the menstrual cycle and pregnancy.
- Disorders — goitre: too little thyroxine, usually from iodine deficiency; cretinism in children and myxoedema in adults. Excess thyroxine gives weight loss, a rapid heartbeat and protruding eyes.
- Dwarfism: too little growth hormone in childhood. Gigantism: too much in childhood. Acromegaly: too much in adulthood.
- Diabetes mellitus: too little insulin — high blood glucose, sugar in the urine, thirst and frequent urination.
- Parathormone deficiency: muscle cramps and spasms.
- Iodised salt prevents goitre, because the cause is dietary and not a fault in the gland.
Test yourself by writing the gland, hormone and function for each of the six main glands, then matching four disorders to their hormones — those two tables are what this chapter is marked on.
- Endocrine glands are ductless and release hormones into the blood — pituitary, thyroid, parathyroid, adrenal, pineal, thymus.
- Mixed glands: the pancreas (pancreatic juice by duct, insulin and glucagon into blood) and the gonads (gametes plus hormones).
- A hormone is a chemical messenger secreted in small amounts directly into the blood, acting on a target organ. Hormones act slowly with long-lasting effects, are not stored, and are used up after acting.
- Nerve impulses are fast and brief; hormones are slow and sustained — hence two coordinating systems.
- Locations: pituitary at the base of the brain, thyroid in front of the windpipe, four parathyroids behind it, adrenals on top of the kidneys, pancreas behind the stomach, gonads in the scrotum or lower abdomen.
- The pituitary is the master gland because it controls other endocrine glands.
- Hormones and functions — growth hormone: growth of bones and body. Thyroxine: rate of metabolism, growth and development; contains iodine. Parathormone: calcium and phosphorus. Adrenaline: the emergency hormone, raising heart rate, breathing, blood pressure and blood glucose. Insulin lowers and glucagon raises blood glucose. Testosterone: male secondary sexual characters and sperm. Oestrogen and progesterone: female characters, the menstrual cycle and pregnancy.
- Disorders — goitre: too little thyroxine, usually from iodine deficiency; cretinism in children and myxoedema in adults. Excess thyroxine gives weight loss, a rapid heartbeat and protruding eyes.
- Dwarfism: too little growth hormone in childhood. Gigantism: too much in childhood. Acromegaly: too much in adulthood.
- Diabetes mellitus: too little insulin — high blood glucose, sugar in the urine, thirst and frequent urination.
- Parathormone deficiency: muscle cramps and spasms.
- Iodised salt prevents goitre, because the cause is dietary and not a fault in the gland.
Test yourself by writing the gland, hormone and function for each of the six main glands, then matching four disorders to their hormones — those two tables are what this chapter is marked on.