A Sudden Fright Can Flood Your Blood With Adrenaline Within Seconds
Learn the hormones of the adrenal cortex, why adrenaline is called the emergency hormone, what growth hormone, tropic hormones, ADH and oxytocin do, and how too little or too much of them upsets the body, plus the feedback loop that controls TSH.
How do the adrenal and pituitary glands keep the body ready and in balance?
A dog suddenly barks behind you and your heart pounds before you have even turned round. That rush comes from the adrenal glands. Meanwhile, a pea-sized gland under your brain, the pituitary, quietly controls your growth, your water balance and several other glands.
This part covers adrenal hormones, adrenaline's emergency role, the pituitary hormones, and what happens when growth hormone or ADH is out of balance, ending with the feedback loop that controls the thyroid.
This part covers adrenal hormones, adrenaline's emergency role, the pituitary hormones, and what happens when growth hormone or ADH is out of balance, ending with the feedback loop that controls the thyroid.
Which hormones does the adrenal gland secrete, and what does each do?
The adrenal cortex secretes corticoids that control sugar use, salt and water balance and some sexual characters, while the adrenal medulla secretes adrenaline and noradrenaline.
Adrenal cortex — the corticoids
- Glucocorticoids, such as cortisol — control the use of carbohydrates, proteins and fats, raise blood sugar and reduce inflammation
- Mineralocorticoids, such as aldosterone — control sodium and potassium levels, and so the body's water balance and blood pressure
- Sex corticoids — small amounts that support secondary sexual characters
Adrenal medulla
- Adrenaline and noradrenaline — prepare the body for emergencies
An everyday example. Doctors prescribe steroid medicines for severe allergies or swelling because they act like glucocorticoids and calm inflammation.
The boundary case. The adrenal cortex is essential for life, because without its hormones salt and water balance fails; the medulla is not essential, since sympathetic nerves can produce similar effects.
Adrenal cortex — the corticoids
- Glucocorticoids, such as cortisol — control the use of carbohydrates, proteins and fats, raise blood sugar and reduce inflammation
- Mineralocorticoids, such as aldosterone — control sodium and potassium levels, and so the body's water balance and blood pressure
- Sex corticoids — small amounts that support secondary sexual characters
Adrenal medulla
- Adrenaline and noradrenaline — prepare the body for emergencies
An everyday example. Doctors prescribe steroid medicines for severe allergies or swelling because they act like glucocorticoids and calm inflammation.
The boundary case. The adrenal cortex is essential for life, because without its hormones salt and water balance fails; the medulla is not essential, since sympathetic nerves can produce similar effects.
Why is adrenaline called the emergency hormone, and what does it do to the body?
Adrenaline is called the emergency hormone because it is released in fear, anger or danger and rapidly prepares the body to fight or run away.
Effects of adrenaline:
- Heart beats faster and more strongly; blood pressure rises
- Breathing speeds up and air passages widen
- Liver converts glycogen to glucose, so more fuel reaches muscles
- Blood is diverted from the skin and gut to the muscles, so the skin looks pale
- Pupils dilate to let in more light
- Digestion slows down
- Hairs stand on end
Control. The adrenal medulla is stimulated by sympathetic nerves, so adrenaline and the sympathetic system work together.
An everyday example. After a near-miss with a speeding scooter, your hands tremble and your heart races for a while even though the danger has passed.
The link. These are the same changes the sympathetic nervous system makes; adrenaline in the blood reinforces and prolongs them, which is why you stay shaky after the nerve signals stop.
Effects of adrenaline:
- Heart beats faster and more strongly; blood pressure rises
- Breathing speeds up and air passages widen
- Liver converts glycogen to glucose, so more fuel reaches muscles
- Blood is diverted from the skin and gut to the muscles, so the skin looks pale
- Pupils dilate to let in more light
- Digestion slows down
- Hairs stand on end
Control. The adrenal medulla is stimulated by sympathetic nerves, so adrenaline and the sympathetic system work together.
An everyday example. After a near-miss with a speeding scooter, your hands tremble and your heart races for a while even though the danger has passed.
The link. These are the same changes the sympathetic nervous system makes; adrenaline in the blood reinforces and prolongs them, which is why you stay shaky after the nerve signals stop.
What do growth hormone, tropic hormones, ADH and oxytocin do?
Growth hormone controls body growth, tropic hormones stimulate other endocrine glands, ADH makes the kidneys save water, and oxytocin contracts the uterus during childbirth and releases milk.
Anterior pituitary
- Growth hormone — growth of bones and muscles
- Tropic hormones — act on other glands:
- TSH stimulates the thyroid
- ACTH stimulates the adrenal cortex
- FSH and LH stimulate the ovaries and testes
Posterior pituitary
- ADH (antidiuretic hormone) — increases water reabsorption in the kidney tubules, reducing urine volume
- Oxytocin — makes the uterus contract during childbirth and causes milk to flow when a baby suckles
An everyday example. On a hot day without enough water, more ADH is released and your urine becomes darker and scantier.
The substance. Tropic means acting on another gland — that is how the pituitary earns the name master gland.
Anterior pituitary
- Growth hormone — growth of bones and muscles
- Tropic hormones — act on other glands:
- TSH stimulates the thyroid
- ACTH stimulates the adrenal cortex
- FSH and LH stimulate the ovaries and testes
Posterior pituitary
- ADH (antidiuretic hormone) — increases water reabsorption in the kidney tubules, reducing urine volume
- Oxytocin — makes the uterus contract during childbirth and causes milk to flow when a baby suckles
An everyday example. On a hot day without enough water, more ADH is released and your urine becomes darker and scantier.
The substance. Tropic means acting on another gland — that is how the pituitary earns the name master gland.
What happens with too little or too much growth hormone or ADH, and how does feedback control TSH?
Too little growth hormone causes dwarfism and too much causes gigantism or acromegaly; too little ADH causes diabetes insipidus; and TSH is controlled by negative feedback from thyroxine levels.
Growth hormone
- Hyposecretion in childhood — dwarfism: very short but well-proportioned body, with normal intelligence
- Hypersecretion in childhood — gigantism: excessive height
- Hypersecretion in adults — acromegaly: enlarged hands, feet and jaw, since long bones can no longer lengthen
ADH
- Hyposecretion — diabetes insipidus: large volumes of dilute urine and great thirst, with no sugar in urine
- Hypersecretion — the body retains too much water, giving small amounts of concentrated urine
Feedback control of TSH
The result is a steady level, because the output of the system switches off its own trigger.
An everyday example. An electric iron's thermostat cuts the current when the iron is hot and switches it on when it cools.
The link. In iodine deficiency, thyroxine stays low, so TSH stays high and keeps stimulating the thyroid until it swells into a goitre.
Growth hormone
- Hyposecretion in childhood — dwarfism: very short but well-proportioned body, with normal intelligence
- Hypersecretion in childhood — gigantism: excessive height
- Hypersecretion in adults — acromegaly: enlarged hands, feet and jaw, since long bones can no longer lengthen
ADH
- Hyposecretion — diabetes insipidus: large volumes of dilute urine and great thirst, with no sugar in urine
- Hypersecretion — the body retains too much water, giving small amounts of concentrated urine
Feedback control of TSH
The result is a steady level, because the output of the system switches off its own trigger.
An everyday example. An electric iron's thermostat cuts the current when the iron is hot and switches it on when it cools.
The link. In iodine deficiency, thyroxine stays low, so TSH stays high and keeps stimulating the thyroid until it swells into a goitre.
Exam tip
What earns full marks on adrenal and pituitary hormones?
Give each hormone its gland region and function, list adrenaline's effects organ by organ, and write the feedback loop as a cycle with arrows.
- Cortex: glucocorticoids, mineralocorticoids, sex corticoids; medulla: adrenaline
- List at least five effects of adrenaline
- Anterior pituitary: growth hormone and tropic hormones; posterior: ADH and oxytocin
- Disorders: dwarfism, gigantism, acromegaly, diabetes insipidus
- Feedback: show both the low-thyroxine and high-thyroxine branches
The trap. Writing acromegaly for a tall child. Gigantism happens in childhood; acromegaly happens in adults.
- Cortex: glucocorticoids, mineralocorticoids, sex corticoids; medulla: adrenaline
- List at least five effects of adrenaline
- Anterior pituitary: growth hormone and tropic hormones; posterior: ADH and oxytocin
- Disorders: dwarfism, gigantism, acromegaly, diabetes insipidus
- Feedback: show both the low-thyroxine and high-thyroxine branches
The trap. Writing acromegaly for a tall child. Gigantism happens in childhood; acromegaly happens in adults.
Did you know
Why do you get goosebumps when you are scared or cold?
A spooky story or a chilly breeze can make tiny bumps rise all over your arms.
At the base of each hair is a very small muscle. Adrenaline and sympathetic nerves make these muscles contract, pulling the hairs upright and raising the skin around them.
In furry animals, raised hair traps a warmer layer of air or makes the animal look bigger to an enemy. Humans have too little body hair for this to help much, but the old reflex still works.
At the base of each hair is a very small muscle. Adrenaline and sympathetic nerves make these muscles contract, pulling the hairs upright and raising the skin around them.
In furry animals, raised hair traps a warmer layer of air or makes the animal look bigger to an enemy. Humans have too little body hair for this to help much, but the old reflex still works.
Exam relevance
How do adrenal and pituitary hormones lead into NEET Biology?
This is foundation work for Class 11 Chemical Coordination and Integration in NEET Biology.
What gets built on. The chapter describes releasing and inhibiting hormones from the hypothalamus, the adenohypophysis and neurohypophysis of the pituitary, the three zones of the adrenal cortex, and disorders such as Addison's disease, diabetes insipidus and acromegaly. Hormonal control of this kind returns in the menstrual cycle in Class 12 Human Reproduction.
Question types. Match-the-column items pairing hormones with glands, targets and disorders, and assertion-reason questions on feedback.
The trap that costs marks. ADH and oxytocin are made in the hypothalamus and only stored and released by the posterior pituitary.
What gets built on. The chapter describes releasing and inhibiting hormones from the hypothalamus, the adenohypophysis and neurohypophysis of the pituitary, the three zones of the adrenal cortex, and disorders such as Addison's disease, diabetes insipidus and acromegaly. Hormonal control of this kind returns in the menstrual cycle in Class 12 Human Reproduction.
Question types. Match-the-column items pairing hormones with glands, targets and disorders, and assertion-reason questions on feedback.
The trap that costs marks. ADH and oxytocin are made in the hypothalamus and only stored and released by the posterior pituitary.
Key takeaways
What must you be able to do from this part?
- Adrenal cortex: glucocorticoids for metabolism and inflammation; mineralocorticoids for salt and water; sex corticoids
- Adrenal medulla: adrenaline, the emergency hormone
- Adrenaline: faster heart and breathing, more blood glucose, blood to muscles, dilated pupils, slower digestion
- Growth hormone: growth; TSH, ACTH, FSH, LH: stimulate other glands
- ADH: water reabsorption; oxytocin: uterine contraction and milk flow
- Dwarfism, gigantism, acromegaly from growth hormone imbalance
- Diabetes insipidus from too little ADH
- TSH feedback: low thyroxine raises TSH; high thyroxine lowers it
Picture yourself at the start line of a race and see if you can list every change adrenaline makes before the whistle blows.
- Adrenal medulla: adrenaline, the emergency hormone
- Adrenaline: faster heart and breathing, more blood glucose, blood to muscles, dilated pupils, slower digestion
- Growth hormone: growth; TSH, ACTH, FSH, LH: stimulate other glands
- ADH: water reabsorption; oxytocin: uterine contraction and milk flow
- Dwarfism, gigantism, acromegaly from growth hormone imbalance
- Diabetes insipidus from too little ADH
- TSH feedback: low thyroxine raises TSH; high thyroxine lowers it
Picture yourself at the start line of a race and see if you can list every change adrenaline makes before the whistle blows.