Hyperthyroidism
How excess thyroid hormone, from TSH-receptor antibodies in Graves’ disease, autonomous nodules or a damaged, leaking gland, speeds metabolism and amplifies adrenergic effects, and why the cause changes the findings.
By the end, you can
- Describe thyroid follicles, how T4 and T3 are made, and the hypothalamic–pituitary–thyroid axis with its negative feedback.
- Explain why TSH is suppressed in almost all hyperthyroidism.
- Explain how TSH-receptor antibodies cause Graves’ disease, and contrast toxic nodules and thyroiditis.
- Relate excess thyroid hormone to a raised metabolic rate and increased sensitivity to catecholamines.
- Explain why eye disease points to Graves’ disease rather than to thyrotoxicosis in general.
- Recognise the classic morphology, hormone patterns and tests of hyperthyroidism, and explain how antithyroid drugs, beta-blockers, iodide, radioactive iodine, surgery and orbitopathy treatments act on its mechanism.
What it is
Thyrotoxicosis is the state caused by too much thyroid hormone acting on the tissues; hyperthyroidism is thyrotoxicosis caused by the thyroid gland making too much hormone. The commonest causes are Graves’ disease, toxic multinodular goitre and a single toxic adenoma. In thyroiditis, stored hormone leaks from an inflamed gland without any increase in production; taking too much thyroid hormone medicine has the same effect from outside.
3 types to tell apart
- Graves’ disease
- Autoimmune: antibodies stimulate the TSH receptor, so the whole gland enlarges and overproduces. Only Graves’ disease causes the characteristic eye disease and pretibial myxoedema.
- Toxic multinodular goitre and toxic adenoma
- One or more nodules make hormone without needing TSH, often because of mutations that switch on the TSH-receptor pathway. Commoner in older people and where iodine intake was low.
- Thyroiditis
- Inflammation damages the follicles, which release their stored hormone (after a viral illness, after pregnancy or with some medicines). Thyrotoxicosis is temporary and may be followed by hypothyroidism.
Normal function
Thyroid follicles make and store hormone
The lies in front of the , below the : two lobes joined by an . It is made of thousands of spherical follicles, each a single layer of follicular cells round a store of colloid rich in the protein thyroglobulin.
Follicular cells trap iodide from the blood, and the enzyme thyroid peroxidase attaches iodine to tyrosines in thyroglobulin and couples them. The hormone stays stored in the colloid, enough for weeks, until TSH signals the cells to take it back in and release thyroxine (T4) and a smaller amount of triiodothyronine (T3). Tissues convert T4 to T3, the more active form.
T3 enters cells and binds nuclear receptors, changing which genes are expressed. It sets the basal metabolic rate, heat production, heart rate and contractility, and is needed for normal growth and brain development. Most T4 and T3 in the blood is bound to proteins; only the small free fraction acts.
Underlying change · Step 1 of 5
Hormone production escapes the feedback loop
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 2 of 5
Graves’ disease: antibodies switch on the TSH receptor
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Underlying change · Step 3 of 5
Nodules and thyroiditis: different routes to excess hormone
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Disrupted function · Step 4 of 5
Metabolism speeds up and adrenergic effects are amplified
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Consequences · Step 5 of 5
Graves’ orbitopathy: swelling inside the orbit
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Symptoms and signs
Symptoms, signs and findings
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Exam detail
Exam detail
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Treatment
How treatment works
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Recap
Recap
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .
Self-check
Check your understanding
The full lesson is part of Student Pro
It takes you through all 5 steps of the mechanism, explains the symptoms, signs and findings each step causes, adds the exam detail and how treatment works where the lesson has them, then recaps it and lets you check yourself with 10 self-check questions. The full pathophysiology library: guided lessons with self-check questions comes with Student Pro, with 100 tutor answers a month and the full available catalogue.
Free to read: the introduction and .