Thyroid (Endocrine 2) Flashcards
Thyroid Gland:
Structure
- Two lobes with narrow isthmus
- Thyroid epithelail cells
- arranged in follicles
- produce thyroid hormone
- Thyroid-C cells
- Small affrefates of cells between follicles
- Produce calcitonin
Thyroid Gland:
Function:
Thyroid Hormones
- Increased metabolism
- Stimulate heart and neural function
Thyroid Gland:
Function:
Calcitonin
- Regulateion of serum calcium concentrations
- inhibition of osteoclasts and bone resorption and synergistic with parathormone to decrease renal phosphorus absorption
Thyroid Gland:
Function:
Regulation of Adrenal Function
- Hypothalamic releasing factors
- Pituitary hormones
- TSH
Thyroid Gland:
Dysfunction:
Hyperfunction (Hyperthyroidism)
- Usually primary thyroid involvement
- Polyphagia, weight loss, weak, thachycardia
- Most common in cats
Thyroid Gland:
Dysfunction:
Hypofunction (Hypothyroidism)
- usually primary thyroid involvement
- Inactivity, alopecia, lethargy, weight gain, obesity
- Most common in dogs
Thyroid Gland:
Pathogenesis:
Metabolic
Thyroid dysfunction will result in metabolic alterations
Thyroid Gland:
Pathogenesis:
Neoplasia
Usually functional, sometimes non-functional
Thyroid gland:
Pathogenesis:
Cell Alteration and injury
Hyperplasia and atrophy are common
Thyroid Gland:
Pathogenesis:
Immunopathology
Autoimmune destruction of the thyroid
Thyroid Glands:
Pathogenesis:
Developmental
Ectopic Thyroid tissue
Thyroid Gland:
Causes:
Genetic Predisposition
- Thyroid neoplasia, hyperplasia, and autoimmunity
Thyroid Gland:
Causes:
Nutritional
- Deficiency of Iodine, tyrosine or other thyroglobulin components
Thyroid Gland:
Causes:
Chemical
- Goitrogenic compounds
- thiouracil, sulfonamides, cyanogenic plants
Thyroid Gland Neoplasia:
Thyroid Follicular adenoma and Carcinoma
- Most common in old cats
- these are often functional resulting in hyperthyroidism
- There can be nodules in one or both lobes
- Distinction between hyperplasia is sometimes difficult
- Less common in dogs
- These are often large, invasive, and metastatic to regional lymph nodes
Thyroid follicular adenoma/carcinoma
Thyroid Gland Hyperplasia:
Thyroid Follicular nodular hyperplasia
- Most common as an age-related change in horses, dogs, and cats
- Most are non-functional and of minimal significance
- in cats, some of these may progress to adenoma
Hyperthyroidism
- Functional neoplasms result in hyperthyroidism
- increased basal metabolic rate
- Polyphagia with weight loss
- Hyperacticity and nervousness
- Weakness and heat intolerance
- Tachycardia
- May be due to mutation in the gene coding for the TSH receptor
- this is different than Graves disease in humans since theera re no auto-antibodies to the TSH receptor in cats
Thyroid Gland C-Cell Neoplasia:
Parafollicular C-cell Neoplasia
- Most common in old bulls and horses
- often amlignant in bulls, but incidental in horses
- Bulls:
- these may arise due to long-term infestion of high calcium rations
- high calcium rations also induce hyperplasia initially
- Pituitary or adrenal medulla neoplasia may occur concurrently
- these may arise due to long-term infestion of high calcium rations
- Some can be functional:
- Hypercalcitoninism
- Vertebral osteophytes and osteosclerosis
- Hypercalcitoninism
Goiter
- Inhibition of thyroid hormone formation
- nutritional deficiency of iodone or tyrosine
- Goitrogenic compound ingestion
- cruciferous plants
- Drugs
Goiter:
Diffuse
Excessive TSH stimulus due to decreased thyroid hormones
Iodine deficiency is a common cause
Goiter:
Multinodular
Idependent of TSH
Mainly in old cats
Goiter:
Dyshormonogenic
Defective synthesis with normal iodine levels
Due to genetic defect in thyroglobulin synthesis or thyroid peroxidase
Autosomal recessive in sheep and goats
Goiter:
Thyroid Hyperplasia is the lesion
- cause varies
- Results in hypothyroidism in postnatal animals
- Stillbirth is most common when affected in utero
- Neonates can also hav esigns of hypothyroidism
- myxedema
Goiter:
Images
Thyroid Gland Atrophy:
Idiopathic Follicular Atrophy
- Most common in dogs
- There is primary degeneration and atrophy of the thyroid gland
- Results in hypothyroidism
- accounts for approximately 50% of hte cases of canine hypothyroidism
Thyroid Gland Atrophy:
Lymphocytic thyroiditis
- Most common in dogs
- Autoimmune destruciton of the thyroid gland
- there is fibrosis, atrophy, and lymphocytic infiltration of the gland
- Results in hypothyroidism
- Accounts for approximately 50% of these cases in dogs
- Similar to Hashimoto’s thyroiditis
- Auto-antibodies to thyroglobulins
Lymphocytic Thyroiditis
Hypothyroidism
- Clinical syndrome characterized by decreased T3/T4 levels
- Signs include:
- weight gain
- inactivity
- Alopecia
- Reproductive abnormalities
- Hypercholesterolemia
Hypothyroidism:
Systemic lesions associated with disease
- Hyperkeratosis and adnexal atrophy of the skin
- Myexedema
- Atherosclerosis
- Hepatic lipidosis
Is the cause for approximately 50% of the cases of hypothyroidism in dogs
Parathyroid Gland:
Structure
- Chief cells:
- comprise most of the gland
- Produce parathormone
- Oxyphil Cells
- modified cheif cells
Parathyroid Gland:
Function
- Control and maintenance of serum calcium levels
- Parathyroid Hormone
- Released in response to low serum calcium
- Stimulates GI absorption and resorption of Ca++ from none, increased renal retention of Ca++ and inhibits phophorus reabsorption
- Calcitonin
- Released in response to high serum Calcium
- Decreased GI absorption and resorption from bone, decreased renal retention
- Viramin D
- conversion to calcium in the kidney
- Synergistic wth parathormone
- Parathyroid Hormone
Parathyroid Gland:
Dysfunction:
Hyperfunction
- Primary or secondary parathyroid involvement
- usually secondary
- Increased lameness and fractures, facial bone enlargement and weakening
Parathyroid Gland:
Dysfunction:
Hypofunction
- Usually primary parathyroid involvement
- Variable signs, including anorexia, weakness, or tetany of convulsions
