Hormones and the endocrine system - TCE Biology (Tasmania)
“Hormones alter the metabolism of target cells, tissues or organs by increasing or decreasing their activity; in animals, most hormones are produced in endocrine glands as a result of nervous or chemical stimulation and travel via the circulatory or lymph system to the target cells, tissues or organs”
Hormones are chemical messengers made by endocrine glands and released into the blood (or lymph) in response to nervous or chemical stimulation. They travel throughout the body but only affect target cells that have receptors matching the hormone, where they increase or decrease the cells' activity. The course focuses on three hormones: insulin and glucagon from the pancreas (blood glucose), and antidiuretic hormone (ADH), made in the hypothalamus and released by the posterior pituitary (water balance).
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What this dot point is asking
Hormones are part of criterion 6 (Section C of the TASC exam). The external assessment specifications limit the endocrine glands to the pancreas, hypothalamus and pituitary, and the hormones to insulin, glucagon and ADH. Other endocrine organs, the names of lipid-soluble and water-soluble hormones, and the hormone-receptor complex and transcription are excluded.
What makes something a hormone
- Produced by an endocrine gland (a ductless gland that secretes directly into the blood).
- Released in response to a stimulus, which may be nervous (a nerve impulse) or chemical (a change in blood composition, such as blood glucose concentration).
- Transported in the blood (or lymph) to all parts of the body.
- Acts only on target cells with specific receptors whose shape matches the hormone.
- Effect: increases or decreases the activity (metabolism) of the target cells, tissues or organs.
A hormone reaches almost every cell, but only cells with complementary receptors respond. This is why one hormone can have a precise effect.
The hormones in the course
| Hormone | Gland that releases it | Stimulus for release | Target | Effect |
|---|---|---|---|---|
| Insulin | Pancreas | Blood glucose above the normal range | Liver, muscle and other body cells | Cells take up glucose; liver converts glucose to glycogen; blood glucose falls |
| Glucagon | Pancreas | Blood glucose below the normal range | Liver | Glycogen broken down to glucose and released; blood glucose rises |
| ADH (antidiuretic hormone) | Posterior pituitary (made in the hypothalamus) | Blood too concentrated (water deficit), detected by the hypothalamus | Kidney collecting ducts | More water reabsorbed into the blood; less, more concentrated urine |
See glucose regulation and osmoregulation and the nephron for the full feedback loops.
Nervous and hormonal control working together
The hypothalamus links the two systems. It receives information from receptors, can send nerve impulses to effectors, and makes ADH that is released from the posterior pituitary into the blood. Hormonal responses are slower to start and last longer than nervous responses, which suits variables such as blood glucose and water balance that need sustained adjustment.
Classifying responses
- A hand is pulled away from a hot stove within a fraction of a second: nervous (fast, short-lived, specific muscles).
- Blood glucose falls over an hour after insulin is released: hormonal (slower, carried in the blood to many cells).
- Urine becomes darker and less in volume on a hot day: hormonal (ADH acting on the kidneys), triggered by the hypothalamus detecting concentrated blood.
Marker's note: justify with speed, the type of signal and how it travels.
- Saying hormones travel along nerves
- Hormones travel in the blood (or lymph).
- Saying ADH is made in the pituitary
- It is made in the hypothalamus and released by the posterior pituitary.
- Saying the pancreas releases cells into the blood
- The pancreas releases hormones (insulin and glucagon), not cells. TASC's 2025 assessment report noted this error.
Exam-style questions
Questions in the style of TASC exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Original4 marksInsulin travels to every part of the body in the blood, yet it affects only some cells. Explain why.Show worked answer →
Explanation (4 marks). Hormones are chemical messengers released into the blood, so they reach almost all cells (1). A hormone only affects target cells that have specific receptors with a shape complementary to the hormone (1). Insulin binds to its receptors on target cells such as liver, muscle and fat cells (1), triggering changes inside those cells (such as increased glucose uptake), while cells without insulin receptors are not affected (1).
Original3 marksIdentify the gland that releases antidiuretic hormone (ADH) into the blood, the part of the brain where it is made, and its target organ.Show worked answer →
One mark each: released by the posterior pituitary gland; made in the hypothalamus; target organ is the kidney (the collecting ducts of the nephrons).