Thyroid and Parathyroid Flashcards
Thyroid recap?
The thyroid gland, consisting of two bulky lateral lobes connected by a thin isthmus, is divided by fibrous septae into lobules, composed of about 20 to 40 follicles. Such follicles are the main unit of the thyroid and are lined by a single layer of cuboidal to low columnar epithelium. Thyroid hormones stimulate carbohydrate and lipid catabolism and protein synthesis, inducing an increase in the metabolic rate.
In case any structural or functional derangement interferes with the production of thyroid hormone, there is hypo functioning of the thyroid gland, causing Hypothyroidism: TSH levels are high while circulating levels of free T3 and T4 are low (primary hypothyroidism).
The opposite situation occurs instead in case of hyperfunctioning of the gland, the most common cause of Hyperthyroidism»_space; thyrotoxicosis characterized by hypermetabolic state caused by elevated free T4 and T3 levels and low TSH.
Both conditions mainly affect middle-aged women
What is Hashimoto’s thyroiditis?
It is the most common form of hypo function of the gland. It is an autoimmune disorder caused by CD8+ cytotoxic T cell. Patients suffer from tiredness, hair loss, weight gain and depression. Morphologically, the disease consists in a gradual atrophy of thyroid tissue following gland invasion with lymphocytic cells.
What are thyroid tumors?
The vast majority of thyroid tumors are benign follicular adenomas, discrete solitary masses derived from the follicular epithelium. Such tumors may be functional or non-functional, based on their ability to produce thyroid hormones. They are Papillary carcinoma, Follicular carcinoma, Anaplastic carcinoma and Medullary carcinoma.
What is papillary Carcinoma of the thyroid?
Account for the majority of thyroid carcinomas associate to ionizing radiation. Mainly occur between ages of 25 and 50. Generally asymptomatic and has good prognosis. May be solitary of multifocal with regions of fibrosis, cysts or calcifications.
What is Anaplastic carcinoma of the thyroid?
Very aggressive tumors, with a mortality rate approaching 100%. The mean age of onset is around 65 year of age. They present as rapidly enlarging bulging masses. TP53 inactivation and beta catenin.
What are follicular carcinomas of the thyroid?
It is the most frequent tumor in areas with dietary iodine deficiency, where they constitute 25% to 40% of thyroid cancers. They re more common in women and their incidence peaks in between 40 and 60 years of age. Follicular carcinomas present as slowly enlarging painless nodules.
What is medullary Carcinoma of the thyroid?
They derive from parafollicular C cells and are neuroendocrine neoplasms; they secrete calcitonin which helps decrease calcium levels in blood, causing paraneoplastic syndromes. They are sporadic in 70% of cases and familial in 30%. They are very aggressive, mainly occurring over the first decade of life and commonly metastasize. Contain deposition of amyloid.
Parathyroid recap?
The four parathyroid glands are composed of two cell types: Chief Cells and Oxyphil Cells. Chief cells predominate and they are characterized by central, round uniform nuclei and light to dark pink cytoplasm; sometimes due to the presence of abundant cytoplasmic glycogen they take on a water-clear appearance. Chief cells produce PTH and are the only component of parathyroid in early childhood. On the other hand, oxyphil cells are found either singly or in small clusters; they are slightly larger, with acidophilic cytoplasm tightly packed with mitochondria.
What is the function fo the parathyroid glands?
The function of the parathyroid gland is to regulate Ca2+ homeostasis, indeed PTH:
- Increases renal tubular Ca2+ absorption, thereby conserving free Ca2+
- Increases VitD conversion to its active form in the kidneys
- Increases urinary phosphate excretion, thereby lowering serum phosphate levels
- Increases Ca2+ absorption in the gastrointestinal tract
Hypo functioning of the parathyroid glands causes?
Hypo functioning of the glands causes a decrease in PTH, can be caused by :
• Autoimmune hypoparathyroidism
• Autosomal Dominant hypoparathyroidism.
• Familial Isolated hypoparathyroidism.
Clinical features are dental abnormalities, QT prolongation, muscle aches and cramps, hair loss, brittle nails.
Hyperparathyroidism causes?
Hyperparathyroidism is elevated levels of PTH :
• Primary hyperparathyroidism: autonomous overproduction of PTH, usually upon adenoma or parathyroid hyperplasia
• Secondary: compensatory increase in PTH secretion in response to prolonged hypocalcemia, most commonly from chronic kidney failure.
• Tertiary: persistent hypersecretion of PTH even after the cause of hypocalcemia has been corrected, for example after kidney transplant.
Primary hyperparathyroidism is caused by?
• Adenomas : 85 to 95% of cases.
• Primary Hyperplasia : Usually chief cell hyperplasia.
• Parathyroid Carcinoma : 1%, cells are uniform and resemble normal tissue.
Symptoms of hyper and hypo functioning of the thyroid gland?
Hyperfunctioning may cause tachycardia, palpitations, diarrhea, malabsorption, tremors. In more specific cases it can be associated to Graves’ disease where autoantibodies against TSH receptors cause hyperthyroidism.
Hypo functioning may cause tiredness, depression, hair loss, bradycardia and constipation.
What are acute and chronic thyroiditis?
Acute is a case of rare thyroiditis caused by infectious agents coming from the blood or lymphatics, usually caused by streptococcus. More common in children, and is preceded by an upper respiratory tract infection.
Chronic thyroiditis is characterized by an autoimmune disease like Hashimoto’s thyroiditis or riedels thyroiditis the latter is characterized by extensive fibrosis and IGG4 related disease.
