Hormones — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions

Section 1 of 36What a hormone is

What a hormone is

Hormone

Hormone a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.

• Hormones are chemical messengers that carry information from one part of the body to another.

Endocrine system

• Endocrine system all the hormone-producing glands of the body together.
• Endocrine glands have a good blood supply so hormones enter the blood plasma quickly.

Section 2 of 36How hormones reach their targets

Transport

• Transport hormones are carried around the whole body in the blood plasma.

Target cells

• Target cells only cells with receptors complementary to the hormone respond to it.
• Receptors may be on the cell membrane or inside the cell.

Removal

• Removal the liver breaks down or transforms excess hormone in the blood.

Section 3 of 36Main endocrine glands and hormones

Hormone	Gland	Role	Effect
Adrenaline	Adrenal glands	Prepares the body for fight or flight	Increases heart rate and breathing rate; dilates pupils
Insulin	Pancreas	Lowers blood glucose	Liver and muscle cells take up glucose and store it as glycogen
Glucagon	Pancreas	Raises blood glucose	Liver converts glycogen to glucose
Testosterone	Testes	Main male sex hormone	Development of male secondary sexual characteristics
Oestrogen	Ovaries	Main female sex hormone	Development of female secondary sexual characteristics; controls the menstrual cycle

Section 4 of 36Adrenaline: the fight or flight hormone

1Adrenaline

• Adrenaline secreted by the adrenal glands in situations of danger or stress.
• Flight means removing oneself rapidly from danger, for example running away.
• Fight means physical combat to overcome danger when flight is not possible.

2Increased breathing rate and heart rate

• Increased breathing rate and heart rate oxygen and glucose reach muscle cells faster and carbon dioxide is removed faster.

3Increased pupil diameter

• Increased pupil diameter more light reaches the retina so more information reaches the brain.

4Increased blood glucose concentration

• Increased blood glucose concentration more glucose is available for respiration in muscle cells.

5Blood flow diverted

• Blood flow diverted blood is directed towards muscles and away from non-essential parts such as the alimentary canal.

Section 5 of 36Nervous and hormonal control compared

Feature	Nervous system	Endocrine system
Made up of	Neurones, brain and spinal cord	Glands
Type of message	Electrical impulses	Chemical hormones
Speed of action	Very fast	Slower
Duration of effect	Short, until impulses stop	Longer, until the hormone is broken down
Target	Specific muscles or glands	Target organs with matching receptors

Section 6 of 36More from the specification

More from the specification

Synaptic reflex action contrasting with auxin

• Synaptic reflex action contrasting with auxin rapid neurotransmitter release at chemical synapses enables millisecond motor reflexes, contrasting with slow directional transport of plant auxin.

Endocrine Communication Principles

• Hormones are chemical messengers synthesized by ductless endocrine glands, secreted directly into blood plasma,
  • and transported systemically to alter metabolic activities in specific target organs.

Dual Antagonistic Regulation of Blood Glucose

• Insulin secreted by pancreatic beta cells promotes cellular glucose uptake and glycogenesis,
• while glucagon stimulates glycogenolysis in the liver to elevate circulating glucose levels.

Adrenaline and the Fight-or-Flight Response

• Rapid adrenaline secretion from the adrenal medulla elevates heart rate, boosts breathing rate, dilates bronchioles,
  • and redirects blood flow toward skeletal muscles during emergencies.

Synapse

• A junction between two neurones where an impulse passes by neurotransmitter diffusing across a gap.

Ciliary muscle

• Muscle that changes the tension on the lens.

Suspensory ligaments

• Fibres that connect the ciliary muscle to the lens.

Negative feedback

• A mechanism in which a change from the set point triggers a response that returns the factor to the set point.

Motor neurone

• Neurone carrying impulses from the CNS to effectors.

Radial muscle

• Iris muscle that widens the pupil when it contracts.

Sense organ

• An organ containing groups of receptors.

Nerve impulse

• Electrical signal passing along a neurone.

Reflex

• Rapid, involuntary and automatic response to a stimulus.

Growth

• A permanent increase in size and dry mass.

Homeostasis

• The maintenance of a constant internal environment.

Section 7 of 36What is a hormone?

Hormone

Hormone a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.

Endocrine glands

• Endocrine glands glands that release hormones directly into the blood.

Target cells

• Target cells hormones are carried everywhere in the plasma but only cells with matching receptors respond.

Section 8 of 36Main endocrine glands

Gland	Hormone	Effect
Adrenal glands	Adrenaline	Prepares the body for fight or flight
Pancreas	Insulin	Lowers blood glucose
Testes	Testosterone	Male secondary sexual characteristics
Ovaries	Oestrogen, progesterone	Female characteristics, menstrual cycle, maintaining pregnancy
Pituitary gland	FSH, LH, ADH and others	Controls other glands and water balance

Section 9 of 36Hormone action step by step

1

A change (stimulus) is detected.

2

The gland releases the hormone into the blood.

3

The blood carries the hormone around the body.

4

Target cells with specific receptors respond.

5

The response removes the stimulus, so the gland stops releasing hormone (negative feedback).

Section 10 of 36Hormone chemistry and removal

Hormone chemistry and removal

Chemical type

• Chemical type most hormones are proteins or peptides, such as insulin;
  • testosterone and oestrogen are steroids.

Breakdown

• Breakdown hormones are broken down in the liver and excreted by the kidneys, so effects are not permanent.

Pituitary

• Pituitary the master gland, because many of its hormones control other glands such as the ovaries and testes.

Hypothalamus

• Hypothalamus part of the brain that controls the pituitary and monitors blood composition and temperature.

Section 11 of 36Hormones in homeostasis

Hormone	Source	Target	Main effect
Insulin	Pancreas	Liver, muscle	Glucose converted to glycogen
Adrenaline	Adrenal glands	Heart, liver, muscle	Fight or flight
ADH	Pituitary	Kidney	More water reabsorbed

• ADH
  • released when the blood becomes too concentrated, so the kidneys reabsorb more water and the blood is diluted.

Section 12 of 36Nervous and hormonal control compared

Feature	Nervous system	Endocrine system
Message	Electrical impulses	Chemical hormones
Pathway	Neurones	Bloodstream
Speed	Very fast	Slower
Duration	Short	Longer lasting
Target	Specific muscles or glands	Widespread target organs

Section 13 of 36More from the specification

More from the specification

Hormonal Homeostasis in Animals

• Homeostasis is the maintenance of a constant internal environment; hormones such as insulin, adrenaline,
• and ADH regulate target tissue metabolism, blood solute levels,
• and arterial blood pressure.

Auxin Action in Plant Shoots

• Auxin is synthesized at growing apical shoot tips and diffuses basipetally; unequal distribution causes extended cell expansion, directing shoots towards light and upward against the pull of gravity (negative gravitropism).
  • (positive phototropism)

Involuntary Pupil Reflex Arc

• The pupil reflex adjusts pupil diameter to regulate light entering the retina: circular and radial iris muscles contract reflexively without conscious intervention via sensory and motor cranial nerves.

Gravitropic Responses in Roots and Shoots

• In roots, high auxin levels inhibit cell elongation on the lower side,
• causing roots to bend downward towards gravity, opposite to the response seen in aerial shoots.
  • (positive gravitropism)

Hormonal Homeostasis in Animals

• Homeostasis is the maintenance of a constant internal environment; hormones such as insulin, adrenaline,
• and ADH regulate target tissue metabolism, blood solute levels,
• and arterial blood pressure.

Auxin Action in Plant Shoots

• Auxin is synthesized at growing apical shoot tips and diffuses basipetally; unequal distribution causes extended cell expansion, directing shoots towards light and upward against the pull of gravity (negative gravitropism).
  • (positive phototropism)

Involuntary Pupil Reflex Arc

• The pupil reflex adjusts pupil diameter to regulate light entering the retina: circular and radial iris muscles contract reflexively without conscious intervention via sensory and motor cranial nerves.

Gravitropic Responses in Roots and Shoots

• In roots, high auxin levels inhibit cell elongation on the lower side,
• causing roots to bend downward towards gravity, opposite to the response seen in aerial shoots.
  • (positive gravitropism)

Circular muscle

• Iris muscle that narrows the pupil when it contracts.

Synapse

• A junction between two neurones where an impulse passes by neurotransmitter diffusing across a gap.

Pupil reflex

• Change in pupil diameter in response to light intensity.

Ciliary muscle

• Muscle that changes the tension on the lens.

Suspensory ligaments

• Fibres that connect the ciliary muscle to the lens.

Motor neurone

• Neurone carrying impulses from the CNS to effectors.

Radial muscle

• Iris muscle that widens the pupil when it contracts.

Sense organ

• An organ containing groups of receptors.

Nerve impulse

• Electrical signal passing along a neurone.

Reflex

• Rapid, involuntary and automatic response to a stimulus.

Growth

• A permanent increase in size and dry mass.

Homeostasis

• The maintenance of a constant internal environment.

Retina

• Layer of the eye containing light receptors.

Section 14 of 36Source and trigger

Adrenaline

• Adrenaline a hormone secreted by the adrenal glands above the kidneys.

Trigger

• Trigger fear, danger, anger, excitement or stress.

Start of the response

• Start of the response the sense organs detect a threat and the brain sends nerve impulses to the adrenal glands.

Section 15 of 36Sequence of events

1

A threat is detected by the sense organs.

2

The brain stimulates the adrenal glands through nerves.

3

Adrenaline is released into the bloodstream.

4

It reaches the target organs: heart, liver, muscles and iris.

5

The body responds within seconds.

6

Once danger passes, adrenaline is broken down and the effects fade.

Section 16 of 36Effects of adrenaline

Organ	Effect	Benefit
Heart	Beats faster and harder	More oxygenated blood to muscles
Lungs	Faster breathing rate	More oxygen taken in and carbon dioxide removed
Liver	Glycogen converted to glucose	Raises blood glucose for respiration
Skin and gut arterioles	Constrict	Blood is diverted to the muscles
Eyes	Pupils dilate	More light reaches the retina

Section 17 of 36Why these effects help

1Muscles need more energy

• Muscles need more energy respiration needs oxygen and glucose, so adrenaline raises the supply of both.

2Waste removal

• Waste removal faster blood flow and breathing remove carbon dioxide more quickly.

3Fight or flight

• Fight or flight the changes prepare the body to run away or to fight.

4Adrenaline does not give energy itself

• Adrenaline does not give energy itself it increases the supply of the raw materials for respiration.

Section 18 of 36Speed, scope and duration

Speed

• Speed adrenaline reaches its targets within seconds, fast for a hormone.

Duration

• Duration effects last minutes, longer than a nerve response.

Scope

• Scope heart, lungs, liver, skin, gut, muscles and eyes respond together.

Chronic stress

• Chronic stress frequent adrenaline release may raise blood pressure.

Section 19 of 36Other contexts

Non-dangerous situations

• Non-dangerous situations before an exam or sports event the heart pounds, the mouth goes dry and hands sweat.

Medical use

• Medical use injected to treat severe allergic reactions because it opens airways and raises blood pressure.

Section 20 of 36More from the specification

1Endocrine vs nervous coordination

• Endocrine glands secrete chemical hormones into circulating blood, providing widespread, slower,
• and longer-lasting regulatory effects than fast electrical nerve impulses.

2Adrenaline and the fight-or-flight response

• Secreted by the adrenal glands during acute stress, adrenaline increases heart rate, breathing rate,
• and blood glucose concentration to prepare muscles for exertion.

3Glucagon and blood glucose maintenance

• When blood glucose falls below set-point levels, pancreatic alpha cells release glucagon, stimulating hepatic glycogenolysis to restore homeostasis.

4Auxin and cell elongation

• Auxin and cell elongation auxin promotes plant shoot growth by stimulating cellular elongation rather than rapid cell division.

5Sensory and motor neurones

• Sensory and motor neurones sensory neurones transmit electrical action potentials towards the central nervous system to coordinate rapid reflexes.

6Thermoregulation in mammals

• Thermoregulation in mammals hypothalamus monitors blood temperature, triggering sweat secretion or shivering to maintain constant internal core levels.

7Circular muscle

• Iris muscle that narrows the pupil when it contracts.

8Homeostasis

• The maintenance of a constant internal environment.

9Synapse

• A junction between two neurones where an impulse passes by neurotransmitter diffusing across a gap.

10Ciliary muscle

• Muscle that changes the tension on the lens.

11Suspensory ligaments

• Fibres that connect the ciliary muscle to the lens.

12Negative feedback

• A mechanism in which a change from the set point triggers a response that returns the factor to the set point.

13Muscle cell

• Mitochondria

14Motor neurone

• Neurone carrying impulses from the CNS to effectors.

15Radial muscle

• Iris muscle that widens the pupil when it contracts.

16Neurone

• A nerve cell that carries electrical impulses.

17Reflex

• Rapid, involuntary and automatic response to a stimulus.

18Growth

• A permanent increase in size and dry mass.

19Insulin

• A pancreatic hormone that lowers blood glucose.

20Control

• A test on distilled water used for comparison.

Section 21 of 36Insulin and glucagon

Insulin

• Insulin secreted by the pancreas after a meal;
  • liver and muscle cells take up glucose and convert it to glycogen.

Glucagon

• Glucagon secreted when blood glucose falls; the liver breaks glycogen down to glucose.

Negative feedback

• Negative feedback the two hormones have opposite effects, so blood glucose stays within narrow limits.

Normal level

• Normal level about 90 mg per 100 cm³ of blood.

Section 22 of 36Diabetes

Diabetes

Type 1 diabetes

• Type 1 diabetes the pancreas cannot make enough insulin, so blood glucose stays high.
• Glucose appears in the urine and the person is thirsty and tired.
• It is controlled by insulin injections, careful diet and exercise.

Type 2 diabetes

• Type 2 diabetes body cells respond poorly to insulin, and it is linked to obesity.
• It is managed by diet, exercise and sometimes drugs.

Section 23 of 36Sex hormones

Hormone	Made in	Role
Testosterone	Testes	Sperm production, deep voice, facial hair, muscle growth at puberty
Oestrogen	Ovaries	Breast development, widening hips, thickening the uterus lining
Progesterone	Ovaries (and placenta)	Maintains the uterus lining, especially in pregnancy

Section 24 of 36Other hormones

ADH

• ADH from the pituitary gland; increases water reabsorption in the kidney so less urine is made.

FSH

• FSH stimulates egg development in the ovary.

LH

• LH stimulates ovulation.

Section 25 of 36Hormones of the menstrual cycle

1

FSH stimulates a follicle to develop and the ovary to release oestrogen.

2

Oestrogen repairs and thickens the uterus lining and stimulates the pituitary to release LH.

3

LH triggers ovulation around day 14.

4

The empty follicle becomes the corpus luteum, which secretes progesterone.

5

Progesterone maintains the uterus lining.

6

If no pregnancy occurs, progesterone falls and menstruation begins.

Section 26 of 36Nervous or hormonal control

Nervous control

• Nervous control suits rapid reactions, such as removing a hand from a hot object, because impulses travel in milliseconds along specific pathways.

Hormonal control

• Hormonal control suits long-term changes, such as growth at puberty, because hormones act more slowly on many cells for longer.

Both together

• Both together in fight or flight, nerves trigger the release of adrenaline.

Section 27 of 36More from the specification

More from the specification

Endocrine system vs nervous system signalling

• Hormones are chemical messengers transported in the bloodstream to target organs, acting slower and longer-term than electrical impulses conducted along neurones in a reflex arc.

Hormonal control of blood glucose concentration

• Endocrine cells in the pancreas monitor blood sugar levels, releasing insulin when concentration rises and glucagon when levels fall to preserve homeostasis.

Pupil reflex and autonomic nervous coordination

• Unlike slow hormonal control, the pupil reflex relies on rapid transmission along a sensory neurone and motor neurones to constrict the iris in high light intensity.

Extended plant hormone function of auxin

• In contrast to animal endocrine systems, plants produce auxin in shoot tips to regulate directional cell elongation, influenced by external stimuli rather than circulating blood.

Endocrine system vs nervous system signalling

• Hormones are chemical messengers transported in the bloodstream to target organs, acting slower and longer-term than electrical impulses conducted along neurones in a reflex arc.

Hormonal control of blood glucose concentration

• Endocrine cells in the pancreas monitor blood sugar levels, releasing insulin when concentration rises and glucagon when levels fall to preserve homeostasis.

Pupil reflex and autonomic nervous coordination

• Unlike slow hormonal control, the pupil reflex relies on rapid transmission along a sensory neurone and motor neurones to constrict the iris in high light intensity.

Extended plant hormone function of auxin

• In contrast to animal endocrine systems, plants produce auxin in shoot tips to regulate directional cell elongation, influenced by external stimuli rather than circulating blood.

Circular muscle

• Iris muscle that narrows the pupil when it contracts.

Retina

• Layer of the eye containing light receptors.

Synapse

• A junction between two neurones where an impulse passes by neurotransmitter diffusing across a gap.

Pupil reflex

• Change in pupil diameter in response to light intensity.

Ciliary muscle

• Muscle that changes the tension on the lens.

Suspensory ligaments

• Fibres that connect the ciliary muscle to the lens.

Motor neurone

• Neurone carrying impulses from the CNS to effectors.

Radial muscle

• Iris muscle that widens the pupil when it contracts.

Sense organ

• An organ containing groups of receptors.

Neurone

• A nerve cell that carries electrical impulses.

Reflex

• Rapid, involuntary and automatic response to a stimulus.

Homeostasis

• The maintenance of a constant internal environment.

Section 28 of 36Hormones and the endocrine system

Hormones and the endocrine system

Hormone

Hormone a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.

Endocrine glands

• Endocrine glands glands that secrete hormones directly into the blood.

Response

• Response slower than a nervous response, but it usually lasts longer and can affect many organs.

Section 29 of 36Key hormones

Hormone	Gland	Main effect
Adrenaline	Adrenal glands	Prepares the body for fight or flight
Insulin	Pancreas	Lowers blood glucose
Glucagon	Pancreas	Raises blood glucose
Testosterone	Testes	Male secondary sexual characteristics and sperm production
Oestrogen	Ovaries	Female secondary sexual characteristics; controls the menstrual cycle
Progesterone	Ovaries	Maintains the uterus lining
ADH	Pituitary	More water reabsorbed in the kidneys

Section 30 of 36Adrenaline effects

1Heart

• Heart beats faster and harder, increasing blood flow to muscles.

2Breathing

• Breathing rate increases, bringing in more oxygen.

3Liver

• Liver converts glycogen to glucose, raising blood glucose for respiration.

4Pupils and blood flow

• Pupils and blood flow the pupils dilate and blood is diverted from the digestive system to the muscles.

Section 31 of 36Hormonal and nervous control compared

Feature	Nervous	Hormonal
Transmitted by	Neurones	Blood
Speed	Rapid	Slower
Response length	Brief	Longer
Area affected	Precise	Widespread

• No direct connection
  • an endocrine gland has no direct link to its target, so the signal travels in the blood.

Section 32 of 36Menstrual cycle and contraception

1FSH

• FSH stimulates egg development and oestrogen secretion.

2Oestrogen

• Oestrogen repairs the uterus lining and, at its peak, triggers LH release, which causes ovulation.

3Progesterone

• Progesterone maintains the lining, and menstruation follows when it falls.

4Contraceptive pill

• Contraceptive pill keeps oestrogen and progesterone high to prevent ovulation.

5Fertility treatment

• FSH is injected to stimulate egg production.

Section 33 of 36Medical uses and misuse

Insulin

• Insulin given to people with type 1 diabetes.

Sex hormones

• Sex hormones used in hormone therapy.

Anabolic steroids

• Anabolic steroids similar to testosterone;
  • build muscle but cause liver damage, mood changes and shrinking testes, and are banned in sport.

Plant hormones (auxins)

• Plant hormones (auxins) used to promote root growth in cuttings and as selective weedkillers.

Section 34 of 36More from the specification

1Reflex Arc and Nerve Impulses

• In a reflex action, sensory receptors detect a stimulus and transmit rapid electrical impulses along sensory neurones to the spinal cord or brain, bypassing conscious thought to trigger a rapid protective response via motor impulses.

2Negative Feedback and Homeostatic Control

• Homeostasis maintains internal environmental levels within narrow limits through negative feedback mechanisms that detect deviations and activate corrective responses.
  • (such as body temperature and blood glucose concentration)

3Hormonal Regulation vs Nervous Coordination

• Endocrine glands secrete chemical hormones into the blood to target specific cells,
• producing slower, longer-lasting physiological responses compared to the rapid electrical impulse conduction of the nervous system.

4Sense organ

• An organ containing groups of receptors.

5Nerve impulse

• Electrical signal passing along a neurone.

6Circular muscle

• Iris muscle that narrows the pupil when it contracts.

7Retina

• Layer of the eye containing light receptors.

8Synapse

• A junction between two neurones where an impulse passes by neurotransmitter diffusing across a gap.

9Ciliary muscle

• Muscle that changes the tension on the lens.

10Suspensory ligaments

• Fibres that connect the ciliary muscle to the lens.

11Negative feedback

• A mechanism in which a change from the set point triggers a response that returns the factor to the set point.

12Muscle cell

• Mitochondria

13Motor neurone

• Neurone carrying impulses from the CNS to effectors.

14Radial muscle

• Iris muscle that widens the pupil when it contracts.

15Reflex

• Rapid, involuntary and automatic response to a stimulus.

16Homeostasis

• The maintenance of a constant internal environment.

Section 35 of 36Key terms

Term	Meaning
Hormone	A chemical substance produced by a gland and carried by the blood that alters the activity of specific target organs.
Endocrine gland	A gland that releases hormones directly into the blood.
Target organ	An organ with cells whose receptors match a particular hormone.
Adrenaline	The fight or flight hormone secreted by the adrenal glands.
Insulin	A pancreatic hormone that lowers blood glucose.
Glucagon	A pancreatic hormone that raises blood glucose.
Testosterone	The main male sex hormone, made in the testes.
Oestrogen	The main female sex hormone, made in the ovaries.

Term	Meaning
Hormone	A chemical substance produced by a gland and carried by the blood that alters the activity of target organs.
Endocrine gland	A gland that secretes hormones directly into the blood.
Target organ	An organ with cells that have receptors for a particular hormone.
Pituitary gland	The master gland whose hormones control other glands.
Hypothalamus	Part of the brain that controls the pituitary gland.
ADH	A pituitary hormone that increases water reabsorption in the kidney.

Term	Meaning
Adrenaline	The fight or flight hormone secreted by the adrenal glands.
Adrenal glands	Glands above the kidneys that secrete adrenaline.
Fight or flight	The body's preparation to confront or escape danger.
Dilate	To widen, as the pupils do in the adrenaline response.
Target organ	An organ whose cells respond to a hormone.

Term	Meaning
Insulin	A pancreatic hormone that lowers blood glucose.
Glucagon	A pancreatic hormone that raises blood glucose.
Testosterone	The main male sex hormone, made in the testes.
Oestrogen	A female sex hormone from the ovaries.
Progesterone	A hormone that maintains the uterus lining.
FSH	A pituitary hormone that stimulates egg development.
LH	A pituitary hormone that triggers ovulation.

Term	Meaning
Hormone	A chemical substance produced by a gland and carried in the blood to alter the activity of target organs.
Endocrine gland	A gland that secretes hormones into the blood.
Adrenaline	A hormone preparing the body for fight or flight.
Anabolic steroid	A synthetic hormone similar to testosterone that builds muscle.
Auxin	A plant hormone used in rooting powder and selective weedkillers.

Section 36 of 36Exam technique

1

Saying hormones travel along nerves — hormones are carried in the blood plasma.

2

Saying a hormonal response is faster than a nervous one — hormones act more slowly but last longer.

3

Saying adrenaline lowers heart rate or blood glucose — it raises both.

4

Confusing glucagon with glycogen — glucagon is the hormone, glycogen is the stored carbohydrate.

1

Saying hormones travel along nerves — they travel in the blood plasma.

2

Saying all body cells respond to every hormone — only cells with complementary receptors respond.

3

Saying endocrine glands have ducts — they release hormones straight into the blood.

4

Believing hormone effects are always quick — they are slower but longer lasting than nerve impulses.

1

Saying adrenaline is made in the pituitary — it is made in the adrenal glands.

2

Saying adrenaline lowers blood glucose — it raises it.

3

Saying the pupils constrict — they dilate.

4

Saying the adrenaline response is slow to start — it begins within seconds.

1

Saying insulin raises blood glucose — it lowers it.

2

Mixing up glycogen and glucagon — glycogen is the stored carbohydrate and glucagon is the hormone.

3

Saying testosterone is made in the adrenal glands — it is made in the testes.

4

Saying insulin cures diabetes — it only controls it.

1

Saying hormones travel through nerves — they travel in the blood.

2

Saying adrenaline lowers heart rate — it raises it.

3

Saying hormonal responses are faster than nervous ones — they are slower.

4

Confusing the gland with the target organ — the gland secretes the hormone, the target responds.