BIOL1019 Chap.5 Hormones, the Hypothalamus and the Pituitary
Hormones, the Hypothalamus and the Pituitary
The endocrine system is the body's second communication system, slower to start and longer lasting than the nervous system and able to reach virtually every cell.
This chapter sets out the three chemical classes of hormone and the two routes into a target cell: water-soluble hormones bind surface receptors and act through second messengers such as cAMP, while lipid-soluble hormones cross the membrane and change gene expression.
It then turns to the hypothalamus, the master gland that controls the anterior pituitary through releasing hormones in portal blood and sends ADH and oxytocin down its own axons to the posterior pituitary, and lays out the axis chains and feedback signs the course expects you to draw.
Because so many later topics depend on pituitary hormones, including the thyroid, adrenal cortex, kidney and reproductive cycle, this chapter is worth mastering early; the course itself suggests tackling the endocrine system with flow diagrams and tables rather than long notes.
What this chapter covers
- 01
Nervous versus endocrine communication
- 02
Three hormone classes
- 03
Second messengers and intracellular receptors
- 04
Free and protein-bound hormones
- 05
Hypothalamic releasing and inhibiting hormones
- 06
Anterior and posterior pituitary
- 07
Axis chains and feedback signs
- 08
Growth hormone and its disorders
Worked example · free
Comparing the two pituitary lobes
- +1Hypothalamic neurosecretory cells release releasing or inhibiting hormones into the hypophyseal portal system.
- +1The anterior lobe synthesises and secretes its own hormones in response, for example TSH acting on the thyroid.
- +1The posterior lobe makes no hormones; ADH and oxytocin are produced in hypothalamic nuclei and travel down axons.
- +1They are released from the axon terminals in the posterior lobe, for example ADH acting on the kidneys.
Key terms
- Hypophyseal portal system
- The blood vessels that carry hypothalamic releasing and inhibiting hormones directly to the anterior pituitary.
- Tropic hormone
- A hormone that controls the secretion of another endocrine gland, such as TSH acting on the thyroid.
- Steroid hormone
- A lipid-soluble hormone made from cholesterol that binds an intracellular receptor and alters gene expression.
- Oxytocin
- A posterior pituitary hormone that contracts smooth muscle of the uterus and mammary glands and acts in positive feedback.
- Antidiuretic hormone
- A hypothalamic hormone released from the posterior pituitary that increases water reabsorption by the kidneys.
Hormones, the Hypothalamus and the Pituitary FAQ
Why does the course compare the endocrine and nervous systems?
The two systems both regulate the body but in different ways. Nervous signals are direct, act close to where they are released and begin within milliseconds, while hormones travel in the blood, act on distant targets with receptors and take seconds to days to act but last longer. Expect a comparison question on mediators, targets, onset and duration.
Why do thyroid and steroid hormones last longer in the blood?
Most free hormones remain functional for less than an hour. More than 99% of thyroid and steroid hormones travel bound to transport proteins, which protect them from removal and release them gradually, so they circulate much longer. Effective concentration also depends on rates of secretion, metabolism and excretion.
Are the prolactin and growth hormone axes positive feedback?
The course's axis answers note that these axes might be argued as positive because inhibiting hormones are produced, but technically the products reduce the releasing hormones, so both are classed as negative feedback. The oxytocin pathway from the posterior pituitary is the course's example of positive feedback.
What does growth hormone do and what happens when it is out of balance?
Growth hormone, released in bursts especially during sleep, drives growth and metabolism largely through IGF produced by the liver. The lecture links its disorders to growth outcomes: too little in childhood causes dwarfism, too much before growth ends causes gigantism, and excess in adults causes acromegaly, with a pronounced brow, enlarged jaw, hands and feet.
Exam move
Follow the course's advice to think in flow diagrams and tables. Draw each axis as hypothalamic hormone, pituitary hormone, target gland, product and a feedback arrow with its sign, and make a table of the seven anterior hormones with targets and effects. Then explain aloud, once for adrenaline and once for cortisol, how each reaches and changes a target cell.
Spend a final session on the hypothalamus alone, explaining its three links to the endocrine system, because the lectorial asks exactly that and the answer connects this chapter with the autonomic nervous system.
Working through Hormones, the Hypothalamus and the Pituitary in BIOL1019? Sia is AskSia’s AI Anatomy & Physiology tutor — ask any BIOL1019 Hormones, the Hypothalamus and the Pituitary question and get a clear, step-by-step explanation grounded in how BIOL1019 is taught and assessed. Read this chapter free, then take your hardest questions to Sia.