Chemical Coordination and Integration
Chemical Coordination and Integration tests hormones as chemical messengers, their receptors, axes and feedback. Expect gland-hormone-target matching and feedback reasoning.
Core rules
- Peptide hormones act via membrane receptors and second messengers.
- Steroid hormones enter cells and act on intracellular receptors, altering gene transcription.
- Hypothalamus-pituitary axes control thyroid, adrenal cortex and gonads. Anterior pituitary secretes tropic hormones; posterior pituitary stores ADH and oxytocin made in the hypothalamus.
- Thyroid: T3 and T4; TRH from hypothalamus, TSH from anterior pituitary; negative feedback.
- Pancreas: insulin from beta cells lowers glucose; glucagon from alpha cells raises it.
- Pineal gland secretes melatonin.
Worked example
A patient has low T4 and high TSH. Explain the feedback pattern.
Reasoning: low T4 reduces negative feedback, so TRH and TSH rise. The thyroid gland is failing, which is primary hypothyroidism. If the pituitary failed, TSH would be low despite low T4. Answer: primary hypothyroidism.
Traps that cost marks
- ADH is made in the hypothalamus but released from posterior pituitary.
- Insulin lowers blood glucose; glucagon raises it.
- Steroid hormones act intracellularly, not through surface receptors.
- Anterior pituitary does not store ADH.
- Melatonin comes from pineal gland, not pituitary.