14.3 Hormones
- Syllabus
- 0610–2026–2027
- Topic
- 14.3
- Level
- —
Learning objectives
14.3.1Hormone as a chemical substance• Describe a hormone as a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs14.3.2Specific endocrine glands and state• Identify in diagrams and images specific endocrine glands and state the hormones they secrete, limited to: (a) adrenal glands and adrenaline (b) pancreas and insulin (c) testes and testosterone (d) ovaries and oestrogen14.3.3Adrenaline as the hormone secreted• Describe adrenaline as the hormone secreted in ‘fight or flight’ situations and its effects, limited to: (a) increased breathing rate (b) increased heart rate (c) increased pupil diameter14.3.4Nervous and hormonal control• Compare nervous and hormonal control, limited to speed of action and duration of effect14.3.5Glucagon is secreted by the pancreas• State that glucagon is secreted by the pancreas14.3.6Role of adrenaline in the control• Describe the role of adrenaline in the control of metabolic activity, limited to: (a) increasing the blood glucose concentration (b) increasing heart rate
Define a hormone
A hormone is a chemical substance produced by a gland, carried by the blood, and able to alter the activity of one or more specific target organs.
gland produces hormone → blood carries hormone → specific target organ changes activity
A hormone travels in the blood, but only target organs with the appropriate response are affected.
Match endocrine glands to their hormones
Identify each required endocrine gland by its position and match it to its named hormone.
| Endocrine gland | Position cue | Hormone |
|---|---|---|
| adrenal glands | on top of the kidneys | adrenaline |
| pancreas | across the upper abdomen | insulin |
| testes | male reproductive organs | testosterone |
| ovaries | female reproductive organs | oestrogen |
The adrenal glands sit above the kidneys but are separate glands; the pancreas secretes insulin, while glucagon is introduced separately in objective 14.3.5.
Describe adrenaline in fight-or-flight situations
Adrenaline is secreted in fight-or-flight situations to prepare the body for rapid action.
| Effect | Change |
|---|---|
| breathing rate | increases |
| heart rate | increases |
| pupil diameter | increases |
For this objective, the required fight-or-flight effects are limited to increased breathing rate, increased heart rate and increased pupil diameter.
Compare nervous and hormonal control
Nervous and hormonal control differ in speed of action and duration of effect.
| Control system | Speed of action | Duration of effect |
|---|---|---|
| nervous | fast | short-lived |
| hormonal | slower | longer-lasting |
A fast response is not necessarily long-lasting: nervous control is the faster but shorter-lived system.
State where glucagon is secreted
Glucagon is secreted by the pancreas.
The pancreas is an endocrine gland that secretes both insulin and glucagon.
The pancreas secretes glucagon; the liver is a target organ in blood-glucose control but does not secrete glucagon.
Describe the metabolic effects of adrenaline
Adrenaline prepares the body for increased metabolic activity by increasing blood glucose concentration and increasing heart rate.
| Adrenaline effect | Immediate value |
|---|---|
| increases blood glucose concentration | makes more glucose available for respiration |
| increases heart rate | circulates blood and glucose more rapidly |
The required metabolic-control effects here are increased blood glucose concentration and increased heart rate; detailed blood-glucose homeostasis belongs to the next Topic.