Pathology of Endocrine System 1 Flashcards
What is the endocrine system?
Integrated network of glands that secrete chemical messengers (hormones) into the bloodstream
What do hormones act on?
Target cells distant to site of synthesis, binding to receptors and changing their activity
What are some examples of effects that hormones may have?
Regulation of metabolism, growth and development, tissue function
Maintain functional balance (homeostasis)
Where are hormones synthesised and stored?
In glands, which are packets of cells with secretory granules that are vascular and ductless
How are levels of hormones maintained?
Negative feedback
What are examples of organs in the endocrine system?
- Pineal gland
- Hypothalamus
- Pituitary gland
- Thyroid gland
- Parathyroid gland
- Adrenal glands
- Pancreas
- Includes other organs, such as ovary, testes and kidneys, and also diffuse endocrine cells such as those in the lungs and GIT
Endocrine organs are linked by feedback axis, what are some major systems?
- TRH -> TSH -> T3/4
- GnRH -> LH/FSH -> sex hormones
- CRH -> ACTH -> cortisol
- Renin -> angiotensin -> aldosterone
What are examples of classificaitons of endocrine disease?
- Dysregulated hormone release
- Hyperfunction
- Hypofunction
- Effect of a mass lesion
- Hyperplasia
- Increased number and secretory activity of cells
- Atrophy
- Diminution of cells due to lack of stimulation
- Tissue damage
- Inflammation, autoimmune disease, compression, trauma, infarction
- Neoplasia
- Adenoma, functioning or non-functioning (benign)
- Carcinoma (malignant)
- Congenital abnormality
What is hyperplasia in terms of the endocrine system?
Increased number and secretory activity of cells
What is atrophy?
Diminution of cells due to lack of stimulation
What are examples of causes of tissue damage?
Inflammation
Autoimmune disease
Compression
Trauma
Infarction
How can diseases on one endocrine gland have multiorgan clinical effects?
Due to hormones acting on several tissues
What is the thyroid responsible for the release of?
Thyroxine (T3) and triiodothyronine (T3)
Calcitonin
What is the function of T4 and T3?
Regulates basal metabolic rate
What is the function of calcitonin?
Regulates calcium homeostasis
What is T3 also known as?
Triiodothyronine
What is T4 also known as?
Thyroxine
What can be seen in the histology of the thyroid gland?
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What are the epithelial cells of the thyroid gland resonsible for?
TG synthesis
Iodination
Resorption and release of T3 and T4
What cells in the thyroid gland secrete calcitonin?
C-cells
How are epithelial cell of the thyroid gland arranged?
Follicles filled with colloid (contains thyroglobulin)
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What is contained in the colloid of the thyroid gland?
Thyroglobulin
Explain the process of the hypothalamus-pituitary-thyroid axis?
- TRH from hypothalamus stimulated by cold, stress
- Stimulates TSH leading to stimulation of thyroid to produce T3 and T4 (increase the number, size and activity of thyroid follicular cells)
- TSH/TRH levels feedback of T3 and T4 respond to circulating
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What is TRH from hypothalamus stimulated by?
Cold
Stress
How does TSH lead to stimulation of thyroid to produce T3 and T4?
Increases the number, size and activity of thyroid follicular cells
What supplies the feedback of TSH/TRH?
T3 and T4
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What are some manifestations of thyroid disease?
- Hyperthyroidism
- Thyrotoxicosis
- Hypothyroidism
- Myxoedema, cretinism, subclinical
- Thyroid enlargement
- Goitre, isolated nodule/mass
- Thyroiditis
- Autoimmune
- Gland destruction
- Multinodular goitre
- Tumours
- Benign, malignant
What does hyperthyroidism lead to?
Thyrotoxicosis (excess thyroid hormone in the body)
What does hypothyroidism lead to?
Myxoedema
Cretinism
Subclinical hypothyroidism
What is myxoedema?
Severely advanced hypothyroidism
What is cretinism?
Condition characterised by deformity and learning difficulties due to congenital hypothyroidism
What does thyroid enlargement lead to?
Goitre
Isolated nodule/mass
What is thyroiditis?
Inflammation of the thyroid gland
What are some causes of hyperthyroidism?
Diffuse toxic hyperplasia (Grave’s disease) 70%
Toxic multinodular goitre 20%
Toxic adenoma
What is the most common cause of hyperthyroidism?
Grave’s disease
What is Grave’s disease also known as?
Diffuse toxic hyperplasia
Does Grave’s disease impact more males or females?
Females > males
What is the pathogenesis of Grave’s disease?
- Autoimmune production of anti-TSH receptor antibodies
- Stimulate activity, growth, inhibit TSH binding
- Ophthalmopathy immune mediated, ocular fibroblasts have TSH receptor
- Affects the thyroid by causing diffuse hyperplasia and hyperfunction
What are some causes of hypothyroidism?
Hashimoto’s thyroiditis
Iatrogenic
Iodine deficiency
Congenital hypothyroidism
What is Hashimoto’s thyroiditis?
- Autoimmune destruction of thyroid epithelial cells
- Cytotoxic T cells, cytokine and antibody mediated destruction
- Circulating autoantibodies to thyroglobulin and thyroid peroxidase
What is the commonest cause of hypothyroidism?
Hashimoto’s thyroiditis
Does Hashimoto’s thyroiditis affect more males or females?
M>F
What age group is most affected by Grave’s disease?
20-40
What age group is most affected by Hashimoto’s thyroiditis?
45-65
What impact does Hashimoto’s thyroiditis have on the thyroid?
Causes diffuse enlargement and gradual failure
What is seen in the histology of Hashimoto’s thyroiditis?
Intense infiltrate of lymphocytes and plasma cells
Hurthle cell change
What is goitre?
Enlarged thyroid
Explain the pathogenesis of goitre?
- Iodine deficiency, goitrogens -> impaired synthesis of T3 and T4 -> increased TSH concentration -> hypertrophy and hyperplasia of thyroid epithelium (simple epithelium becomes multinodular)
What is the most common cause of goitre?
Iodine deficiency
What is seen in the histology of goitre?
Crowded follicles
Distended colloid filled follicles
Haemorrhage
Fibrosis
Cystic change
Nodular appearance
What is the thyroid nodule?
The dominant nodule in multinodular goitre
What can the thyroid nodule be?
Cyst, follicular adenoma or carcinoma
What are the different kinds of thyroid carcinoma?
- Differentiated thyroid carcinoma
- Papillary carcinoma 75-85%
- Follicular carcinoma 10-20%
- Anaplastic carcinoma <5%
- Medullar carcinoma (lymphoma) 5%
What can the thyroid nodule be investigated by?
TFTs
Ultrasound
FNA - cytology
What are risk factors for thyroid carcinoma?
Family history
Chrominc inflammatory conditions
Radiation exposure
Obesity
What is a neoplasm?
A new and abnormal growth of tissue in a part of the body, especially as a characteristic of cancer
Are most thyroid neoplasms functioning or non-functioning?
Non-functioning
What does DTC stand for?
Differentiated thyroid cancer
What are 2 kinds of differentiated thyroid cancer (DTC)?
Follicular carcinoma
Papillary carcinoma
Where does follicular carcinoma often metastasis to?
Blood or bones
Does follicular carcinoma have a genetic predisposition?
RAS mutation
or PAX8/PPARG translocation
What age group usually gets papillary carcinoma?
<50
Is there a genetic predisposition to papillary carcinoma?
BRAF mutation
or RET/PTC gene rearrangement
What is papillary carcinoma associated with?
Ionising radiation
What is seen in the histology of papillary carcinoma?
- Papillary projections, empty nuclai, psammoma bodies, may be cystic
What is thyroid medullar carcinoma?
Malignant tumour of C-cells
Produces calcitonin
Does thyroid medullar carcinoma have a genetic predisposition?
RET proto-oncogene
What does thyroid medullar carcinoma produce?
Calcitonin (with or without production of other polypeptides)
What is the treatment of thyroid carcinoma?
- Surgery
- Follicular and PTC, medullary (with external radiotherapy)
- Radioactive iodine
- Unsafe during pregnancy
- External radiotherapy
- Chemotherapy
When is it unsafe to use radioactive iodine as a treatment for thyroid carcinoma?
During pregnancy
How many parathyroid glands do most people have?
4
What do parathyroid glands produce?
PTH which regulates plasma calcium
What is the function of PTH?
Regulate plasma calcium
What are the different classifications of hyperparathyroidism?
- Primary hyperparathyroidism
- Often asymptomatic hypercalcaemia
- Sporadic or familial (MEN-1)
- Adenoma 85-95%
- Hyperplasia 5-10%
- Carcinoma rare
- Secondary hyperparathyroidism
Is there a genetic predisposition to primary hyperparathyroidism?
MEN-1
What is secondary hyperparathyroidism?
Physiological response to decreased calcium in renal failure