BCH2022 Chap.10 Hormone Signalling and Metabolic Disease
Hormone Signalling and Metabolic Disease
Hormone signalling begins with receptor recognition and continues through intracellular relays to enzyme, transporter or gene responses. Water-soluble hormones usually signal through membrane receptors and second messengers, while lipid-soluble hormones can engage intracellular receptors. Response depends on receptor abundance, coupling efficiency, cell-specific machinery and signal termination.
Agonists, antagonists and partial agonists must be distinguished through binding and concentration-response evidence. The disease method locates the earliest abnormal link between hormone, receptor, relay, target and phenotype rather than using a broad label in place of mechanism. Hormone signalling questions should follow information from ligand to response without skipping the transduction steps.
First identify whether the receptor is at the cell surface or intracellular, because ligand properties and receptor location constrain how the signal reaches its target. Then trace the activated receptor to a defined second messenger, kinase, phosphatase or transcriptional response and state the time scale.
Amplification means a small receptor input can generate a larger downstream signal, but pathway branching and feedback mean the final response is not inferred from receptor occupancy alone. Agonists, antagonists and partial responses are best separated with dose-response logic. Potency concerns the concentration range required for an effect, whereas efficacy concerns the maximum response under the assay conditions.
A rightward shift, a reduced maximum and a changed baseline can therefore imply different mechanisms. Receptor number, coupling efficiency, ligand removal and downstream enzyme capacity can all reshape the curve. Desensitisation and signal termination are active parts of the pathway; persistent ligand does not guarantee an indefinitely increasing response. In metabolic disease, distinguish hormone deficiency from resistance.
A high hormone concentration alongside an inadequate tissue response is different from failure to produce the signal, and tissue responses may not change uniformly. Experimental evidence should include vehicle and positive controls, a concentration range, repeated biological samples and a readout close to the proposed mechanism. Protein abundance alone does not establish receptor activity, and one endpoint does not show order.
A time course plus receptor-proximal and metabolic readouts provides a stronger chain. Finish the explanation by linking the signalling lesion to a named pathway change and then to the whole-body fuel pattern, while stating what alternative result would challenge the interpretation.
What this chapter covers
- 01
Hormone classes
- 02
Membrane receptors
- 03
Intracellular receptors
- 04
Second messengers
- 05
Agonists and antagonists
- 06
Signalling lesions in disease
Worked example · free
Localise a signalling defect
- +1Use high hormone to reject simple hormone deficiency as the leading explanation.
- +1Use normal binding to support receptor presence and ligand recognition.
- +1Place the suspected lesion between receptor activation and target-enzyme phosphorylation.
- +1Measure receptor activation and an intermediate relay to divide that interval further.
Key terms
- Membrane receptor
- A membrane receptor binds an external ligand and transmits information across the plasma membrane.
- Intracellular receptor
- An intracellular receptor binds a cell-permeable ligand and often influences gene regulation.
- Second messenger
- A second messenger is an intracellular molecule that relays and amplifies receptor activation.
- Agonist
- An agonist binds a receptor and promotes a signalling state that produces a response.
- Antagonist
- An antagonist binds or interferes with signalling and reduces agonist action without the same activation.
- Desensitisation
- Desensitisation reduces responsiveness during persistent stimulation through receptor or relay changes.
Hormone Signalling and Metabolic Disease FAQ
How does hormone chemistry predict receptor location?
Water-soluble hormones cannot freely cross the lipid bilayer and commonly use membrane receptors. Lipid-soluble hormones can enter cells and bind intracellular receptors, often producing transcription-linked responses.
What does a competitive antagonist do?
A surmountable competitive antagonist reduces agonist action at a given concentration and can shift the concentration-response curve right. Adding sufficient agonist may preserve the maximum response.
Why can the same messenger have different effects?
Cells express different target proteins, scaffolds, enzymes and genes. The same intracellular signal can therefore reach different effectors and produce tissue-specific metabolic outcomes after receptor activation.
How is hormone resistance identified?
Resistance is suggested when hormone concentration is adequate or high but target response remains weak. Receptor binding, activation, relay measurements and target modification are needed to locate the defect.
Exam move
Draw five boxes labelled hormone, receptor, relay, target and phenotype. For each experiment, mark the last normal box and first abnormal box, then place the lesion between them. Compare water-soluble and lipid-soluble hormones by receptor location, relay and time course. Practise full concentration-response curves rather than one-dose interpretations, and separate affinity, efficacy and maximum response.
Add signal termination through receptor internalisation, messenger degradation and dephosphorylation. For disease questions, state the measured evidence before the mechanism and finish with a discriminating test. When discussing therapy, predict both immediate target engagement and longer-term compensation so that loss of response is not mistaken automatically for failed binding.
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