BIOL1019 Chap.6 Thyroid, Parathyroid, Adrenal Glands and Pancreas
Thyroid, Parathyroid, Adrenal Glands and Pancreas
Four glands carry most of the endocrine regulation examined in this course. The thyroid sets metabolic rate through T3 and T4 and stores about 100 days of hormone, while calcium is held steady by three hormones: parathyroid hormone and calcitriol raise it and calcitonin lowers it.
The adrenal cortex produces aldosterone, cortisol and androgens in three zones, remembered as salt, sweet and sex, and the medulla releases adrenaline and noradrenaline under direct sympathetic control. The pancreatic islets balance blood glucose with insulin and glucagon. The chapter traces disorders such as Graves' disease, Cushing's syndrome and diabetes mellitus back to the hormone, gland and cell responsible.
The course's case activity trains a reasoning chain that runs from signs to hormone, gland and effect, and this chapter follows the same order, so you can work out an unfamiliar disorder from first principles instead of memorising a list of names.
What this chapter covers
- 01
Thyroid follicles, T3 and T4
- 02
Goitre, myxoedema and Graves' disease
- 03
Calcium balance: PTH, calcitriol and calcitonin
- 04
Adrenal cortex zones and their hormones
- 05
Adrenal medulla and the stress response
- 06
Insulin, glucagon and islet cells
- 07
Diabetes mellitus type 1 and type 2
- 08
Cushing's syndrome and aldosteronism
Worked example · free
Keeping blood glucose up between meals
- +1Alpha cells of the pancreatic islets secrete glucagon.
- +1Its release is stimulated by falling blood glucose, and also by high blood amino acids.
- +1Glucagon drives glycogen breakdown in the liver and triglyceride breakdown in adipose tissue.
- +1It also drives gluconeogenesis in the liver from amino acids, so new glucose enters the blood.
Key terms
- Thyroglobulin
- The protein stored as colloid in thyroid follicles from which T3 and T4 are made.
- Calcitonin
- A hormone from thyroid C cells that lowers blood calcium by inhibiting osteoclasts and increasing excretion.
- Zona fasciculata
- The middle zone of the adrenal cortex, which secretes glucocorticoids such as cortisol.
- Glucagon
- A hormone from pancreatic alpha cells that raises blood glucose through glycogen breakdown and gluconeogenesis.
- Polyuria
- Excessive urine production, seen in diabetes when glucose in the filtrate holds water in the nephron.
- Chromaffin cell
- An adrenal medulla cell that releases adrenaline and noradrenaline under sympathetic control.
Thyroid, Parathyroid, Adrenal Glands and Pancreas FAQ
What causes Graves' disease?
Graves' disease is a form of hyperthyroidism in which autoantibodies mimic TSH and stimulate the thyroid continuously. Because the stimulus does not depend on TSH, the normal negative feedback loop cannot switch secretion off, and excess T3 and T4 raise metabolic activity, producing weight loss, heat intolerance, nervousness, goitre and protruding eyes.
What is the difference between the adrenal cortex and the adrenal medulla?
The cortex makes steroid hormones from cholesterol in three zones: aldosterone, cortisol and androgens such as DHEA, with cortisol controlled through ACTH and negative feedback. The medulla's chromaffin cells make adrenaline and noradrenaline under direct sympathetic control through preganglionic fibres, releasing about 80% adrenaline and 20% noradrenaline in fight or flight.
How do type 1 and type 2 diabetes differ?
Type 1 diabetes is autoimmune destruction of the pancreatic beta cells, so insulin is absent and must be replaced. Type 2 diabetes begins as resistance of tissues to insulin, typically after age 40, with hereditary and diet or weight factors, and is usually treatable by diet and exercise. Both raise blood glucose and cause polyuria and thirst.
What is the difference between too much and too little calcium?
Low blood calcium increases the excitability of nerves and muscles, which can produce twitching, spasms and tetany. High calcium depresses the neuromuscular system and is linked with memory problems, depression, arrhythmias, bone softening and kidney stones, which the lecture summarises as stones, bones, abdominal moans and psychiatric overtones.
Exam move
Draw the calcium seesaw and the glucose loop from memory, labelling the gland, cell, hormone and target tissue on every arrow. Learn the adrenal zones with the lecture's mnemonic and pair each with its hormone. Then practise the reasoning chain the course's case sheet uses: from a sign to the hormone change, then to the gland or cell, then to the physiological effect.
Test yourself on the stress response by naming every hormone released, the gland zone that releases it and the effect on blood glucose, then do the same for a missed meal and for a large meal.
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