Hypothyroidism
How the thyroid makes hormones that set the pace of metabolism, why autoimmune destruction or iodine deficiency leaves too little hormone, and how a slowed metabolism explains tiredness, cold intolerance, weight gain and the rest of the picture.
By the end, you can
- Describe how the thyroid makes T4 and T3 and how the hypothalamic-pituitary-thyroid axis controls it.
- Explain the main causes of hypothyroidism, especially autoimmune (Hashimoto’s) thyroiditis and iodine deficiency.
- Relate the symptoms to reduced metabolic rate and reduced sympathetic sensitivity.
- Explain why TSH rises and why a goitre may form.
- Explain why newborns are screened for congenital hypothyroidism.
- Recognise the classic morphology, hormone patterns and tests of hypothyroidism, and explain how thyroid hormone replacement acts on its mechanism and why it needs care.
What it is
Hypothyroidism is deficient production of thyroid hormone. It is usually primary, from disease of the thyroid itself, most often autoimmune (Hashimoto’s) thyroiditis where iodine is sufficient and iodine deficiency worldwide. Secondary hypothyroidism, from pituitary or hypothalamic failure, is rare. Severe, long-standing hypothyroidism is called myxoedema.
3 types to tell apart
- Primary (overt)
- Low thyroid hormone with high TSH.
- Subclinical
- High TSH with thyroid hormone still in range; may progress, especially with thyroid antibodies.
- Congenital
- Present from birth, from an absent or underdeveloped gland or a defect in hormone synthesis.
US spelling: myxoedema → myxedema.
Normal function
The thyroid sets the metabolic pace
The , two lobes joined by an in front of the trachea, is made of follicles: spheres of cells around a store of colloid. The cells trap iodide from the blood and attach it to the protein thyroglobulin, forming thyroxine (T4) and triiodothyronine (T3).
Thyroid-stimulating hormone (TSH) from the pituitary drives every step. Thyroid hormone feeds back on the pituitary and hypothalamus to keep its own level steady.
In tissues, T4 is converted to the more active T3, which enters the nucleus and switches on genes that raise oxygen use, heat production, sodium-potassium pump activity and the number of beta-adrenergic receptors. It also drives growth and brain development in childhood.
In primary hypothyroidism the thyroid fails, feedback weakens and TSH rises.
Underlying change · Step 1 of 4
Why too little hormone is made
The full lesson is part of Student Pro
It takes you through all 4 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 2 of 4
Metabolism slows
The full lesson is part of Student Pro
It takes you through all 4 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 3 of 4
Swollen tissues and a goitre
The full lesson is part of Student Pro
It takes you through all 4 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 4 of 4
Diagnosis, children and severe disease
The full lesson is part of Student Pro
It takes you through all 4 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 4 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 4 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 4 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 4 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 4 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 .