How do hormones coordinate the body, and how is blood glucose concentration controlled by insulin and glucagon?
5.1.4 Hormonal communication: the principles of hormonal coordination and the contrast with nervous coordination; the structure and function of the adrenal glands and pancreas; the control of blood glucose concentration by insulin and glucagon (glycogenesis, glycogenolysis and gluconeogenesis); the second messenger model of adrenaline and glucagon; and the causes of type 1 and type 2 diabetes.
A focused answer to the OCR H420 5.1.4 dot point on hormonal communication. Covers hormonal versus nervous coordination, the adrenal glands and pancreas, the control of blood glucose by insulin and glucagon, the second messenger model, and the causes of type 1 and type 2 diabetes.
Reviewed by: AI editorial process; not yet individually human-reviewed
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What this dot point is asking
OCR wants you to explain the principles of hormonal coordination and how it differs from nervous coordination, describe the adrenal glands and pancreas, explain the control of blood glucose by insulin and glucagon (including glycogenesis, glycogenolysis and gluconeogenesis), describe the second messenger model, and explain the causes of type 1 and type 2 diabetes.
The answer
Hormonal versus nervous coordination
Hormones are chemical messengers secreted by endocrine glands directly into the blood, which carries them to target cells that have complementary receptors. Compared with nervous coordination, hormonal coordination is slower to act, longer-lasting, and more widespread (it travels in the blood to many cells), whereas nervous coordination is fast, short-lived and localised (it travels along neurones to specific effectors).
The adrenal glands and pancreas
- The adrenal glands (above the kidneys) release adrenaline (from the medulla) in the "fight or flight" response, raising heart rate and blood glucose, among other effects, and steroid hormones from the cortex.
- The pancreas is both an exocrine gland (digestive enzymes) and an endocrine gland. The islets of Langerhans contain beta cells (secrete insulin) and alpha cells (secrete glucagon).
Control of blood glucose
Blood glucose is kept near a set point by negative feedback:
- When blood glucose rises (after a meal), beta cells secrete insulin. Insulin makes liver and muscle cells take up more glucose (more GLUT4 channels) and convert it to glycogen (glycogenesis), and increases respiration and fat storage. Blood glucose falls.
- When blood glucose falls (fasting, exercise), alpha cells secrete glucagon. Glucagon makes the liver break glycogen down to glucose (glycogenolysis) and make glucose from non-carbohydrates such as amino acids and glycerol (gluconeogenesis). Blood glucose rises.
Adrenaline also raises blood glucose (by stimulating glycogenolysis), preparing the body for activity.
The second messenger model
Glucagon and adrenaline act by the second messenger model, because they cannot enter the cell:
- The hormone (the first messenger) binds to a specific receptor on the cell-surface membrane.
- This activates adenylyl cyclase, which converts ATP into cyclic AMP (cAMP), the second messenger.
- cAMP activates protein kinase, triggering a cascade of enzymes that carry out glycogenolysis, releasing glucose.
The enzyme cascade gives amplification: one hormone molecule leads to the release of many glucose molecules.
Diabetes
- Type 1 diabetes: the beta cells cannot produce insulin (often an autoimmune destruction), usually starting in childhood; blood glucose rises uncontrollably. It is treated with insulin injections and diet control.
- Type 2 diabetes: the cells lose their responsiveness to insulin (insulin resistance), often linked to obesity, poor diet, age and inactivity; it is usually controlled by diet, exercise and sometimes drugs. After a glucose meal, a diabetic's blood glucose rises higher and stays high for longer than a healthy person's.
Examples in context
Example 1. Adrenaline before a race. Adrenaline released before exercise stimulates glycogenolysis in the liver, raising blood glucose so muscles have fuel for respiration, an example of hormonal preparation for activity.
Example 2. Insulin pumps. People with type 1 diabetes may use an insulin pump that delivers insulin to mimic the beta cells, controlling blood glucose where their own pancreas cannot.
Try this
Q1. State two ways in which hormonal coordination differs from nervous coordination. [2 marks]
- Cue. Hormonal is slower to act and longer-lasting and more widespread (via the blood); nervous is fast, short-lived and localised (via neurones).
Q2. Explain how insulin lowers the blood glucose concentration. [2 marks]
- Cue. It makes liver and muscle cells take up more glucose (more GLUT4 channels) and convert it to glycogen (glycogenesis), and increases its use in respiration, so blood glucose falls.
Q3. Name the second messenger in the action of glucagon. [1 mark]
- Cue. Cyclic AMP (cAMP).
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR H420/01 20196 marksExplain how the blood glucose concentration is returned to normal after it rises following a meal.Show worked answer →
Run the negative feedback loop through insulin and its effects.
A rise in blood glucose is detected by the beta cells in the islets of Langerhans of the pancreas, which secrete insulin into the blood.
Insulin binds to receptors on target cells (liver and muscle), causing more glucose channels (GLUT4) to be inserted so cells take up more glucose, and activating enzymes that convert glucose to glycogen (glycogenesis) in the liver and muscle. It also increases the use of glucose in respiration and its conversion to fat.
As glucose is removed, the blood glucose concentration falls back to normal; the beta cells then secrete less insulin (negative feedback). Markers reward beta cells detecting the rise, insulin secretion, increased uptake, glycogenesis, and the return to normal by negative feedback.
OCR H420/01 20214 marksDescribe the second messenger model by which glucagon (or adrenaline) raises the blood glucose concentration in a liver cell.Show worked answer →
Trace the signal from the receptor to the response inside the cell.
Glucagon (or adrenaline) is the first messenger; it binds to a specific receptor on the cell-surface membrane of the liver cell (it does not enter the cell). This activates the enzyme adenylyl cyclase, which converts ATP into cyclic AMP (cAMP), the second messenger.
cAMP activates protein kinase, which activates a cascade of enzymes that catalyse the breakdown of glycogen to glucose (glycogenolysis). The glucose leaves the cell and raises the blood glucose concentration.
The cascade gives amplification: one hormone molecule leads to many glucose molecules. Markers reward first messenger binding the receptor, adenylyl cyclase making cAMP, protein kinase activation, glycogenolysis and amplification.
Related dot points
- 5.1.2 Homeostasis and excretion: the principles of homeostasis and negative feedback; the role of the liver in deamination and detoxification; the structure of the nephron and the processes of ultrafiltration and selective reabsorption; and osmoregulation by ADH acting on the collecting duct.
A focused answer to the OCR H420 5.1.2 dot point on homeostasis and the kidney. Covers negative feedback, the liver's role in deamination and detoxification, the nephron, ultrafiltration and selective reabsorption, and osmoregulation by ADH acting on the collecting duct.
- 5.1.3 Neuronal communication: the structure of a neurone; the establishment of the resting potential by the sodium-potassium pump; the generation of an action potential by voltage-gated channels (depolarisation and repolarisation); the all-or-nothing principle and the refractory period; saltatory conduction in myelinated neurones; and synaptic transmission by acetylcholine at a cholinergic synapse.
A focused answer to the OCR H420 5.1.3 dot point on neuronal communication. Covers neurone structure, the resting potential, the action potential and its ionic basis, the all-or-nothing principle and refractory period, saltatory conduction, and synaptic transmission by acetylcholine.
- 5.1.5 Plant and animal responses: tropisms and the role of auxin (IAA) in phototropism; the structure and function of the mammalian nervous system (central and peripheral, voluntary and autonomic), the reflex arc and the fight-or-flight response; and the structure and the sliding filament mechanism of skeletal muscle contraction.
A focused answer to the OCR H420 5.1.5 dot point on plant and animal responses. Covers tropisms and the role of auxin in phototropism, the organisation of the mammalian nervous system, the reflex arc and fight-or-flight, and the sliding filament mechanism of muscle contraction.
- 2.1.4 Enzymes: the role of enzymes as biological catalysts in metabolic reactions; the mechanism of enzyme action including the lock-and-key and induced-fit models; the effects of temperature, pH, enzyme and substrate concentration on the rate of reaction; the action of competitive and non-competitive inhibitors; the roles of cofactors, coenzymes and prosthetic groups.
A focused answer to the OCR H420 2.1.4 dot point on enzymes. Covers enzymes as catalysts, the lock-and-key and induced-fit models, activation energy, the effects of temperature, pH and concentration, competitive and non-competitive inhibition, and cofactors.
- 5.2.2 Respiration: the four stages of aerobic respiration (glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation); the role of decarboxylation, dehydrogenation, reduced NAD and FAD, the electron transport chain, chemiosmosis and ATP synthase; the synthesis of ATP and the role of oxygen as the final electron acceptor; and anaerobic respiration in animals (lactate) and in yeast (ethanol).
A focused answer to the OCR H420 5.2.2 dot point on respiration. Covers the four stages of aerobic respiration (glycolysis, the link reaction, the Krebs cycle and oxidative phosphorylation), chemiosmosis and ATP synthase, the role of oxygen, and anaerobic respiration producing lactate or ethanol.
Sources & how we know this
- OCR A Level Biology A (H420) Specification — OCR (2023)