Thyroid (Endocrine 2)

Question 1

Thyroid Gland:

Structure

Answer 1

• 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

Question 2

Thyroid Gland:

Function:

Thyroid Hormones

Answer 2

• Increased metabolism
• Stimulate heart and neural function

Question 3

Thyroid Gland:

Function:
Calcitonin

Answer 3

• Regulateion of serum calcium concentrations
  
  • inhibition of osteoclasts and bone resorption and synergistic with parathormone to decrease renal phosphorus absorption

Question 4

Thyroid Gland:

Function:

Regulation of Adrenal Function

Answer 4

• Hypothalamic releasing factors
• Pituitary hormones
  
  • TSH

Question 5

Thyroid Gland:

Dysfunction:

Hyperfunction (Hyperthyroidism)

Answer 5

• Usually primary thyroid involvement
• Polyphagia, weight loss, weak, thachycardia
• Most common in cats

Question 6

Thyroid Gland:

Dysfunction:

Hypofunction (Hypothyroidism)

Answer 6

• usually primary thyroid involvement
• Inactivity, alopecia, lethargy, weight gain, obesity
• Most common in dogs

Question 7

Thyroid Gland:

Pathogenesis:

Metabolic

Answer 7

Thyroid dysfunction will result in metabolic alterations

Question 8

Thyroid Gland:

Pathogenesis:

Neoplasia

Answer 8

Usually functional, sometimes non-functional

Question 9

Thyroid gland:

Pathogenesis:

Cell Alteration and injury

Answer 9

Hyperplasia and atrophy are common

Question 10

Thyroid Gland:

Pathogenesis:

Immunopathology

Answer 10

Autoimmune destruction of the thyroid

Question 11

Thyroid Glands:

Pathogenesis:

Developmental

Answer 11

Ectopic Thyroid tissue

Question 12

Thyroid Gland:

Causes:

Genetic Predisposition

Answer 12

• Thyroid neoplasia, hyperplasia, and autoimmunity

Question 13

Thyroid Gland:

Causes:

Nutritional

Answer 13

• Deficiency of Iodine, tyrosine or other thyroglobulin components

Question 14

Thyroid Gland:

Causes:

Chemical

Answer 14

• Goitrogenic compounds
  
  • thiouracil, sulfonamides, cyanogenic plants

Question 15

Thyroid Gland Neoplasia:

Thyroid Follicular adenoma and Carcinoma

Answer 15

• 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

Question 16

Thyroid follicular adenoma/carcinoma

Answer 16

Question 17

Thyroid Gland Hyperplasia:

Thyroid Follicular nodular hyperplasia

Answer 17

• 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

Question 18

Hyperthyroidism

Answer 18

• 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

Question 19

Thyroid Gland C-Cell Neoplasia:

Parafollicular C-cell Neoplasia

Answer 19

• 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
• Some can be functional:
  
  • Hypercalcitoninism
    
    • Vertebral osteophytes and osteosclerosis

Question 20

Goiter

Answer 20

• Inhibition of thyroid hormone formation
  
  • nutritional deficiency of iodone or tyrosine
  • Goitrogenic compound ingestion
    
    • cruciferous plants
    • Drugs

Question 21

Goiter:

Diffuse

Answer 21

Excessive TSH stimulus due to decreased thyroid hormones

Iodine deficiency is a common cause

Question 22

Goiter:

Multinodular

Answer 22

Idependent of TSH

Mainly in old cats

Question 23

Goiter:

Dyshormonogenic

Answer 23

Defective synthesis with normal iodine levels

Due to genetic defect in thyroglobulin synthesis or thyroid peroxidase

Autosomal recessive in sheep and goats

Question 24

Goiter:

Thyroid Hyperplasia is the lesion

Answer 24

• cause varies
• Results in hypothyroidism in postnatal animals
  
  • Stillbirth is most common when affected in utero
  • Neonates can also hav esigns of hypothyroidism
    
    • myxedema

Question 25

Goiter: Images

Answer 25

Question 26

Thyroid Gland Atrophy: Idiopathic Follicular Atrophy

Answer 26

* 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

Question 27

Thyroid Gland Atrophy: Lymphocytic thyroiditis

Answer 27

* 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

Question 28

Lymphocytic Thyroiditis

Answer 28

Question 29

Hypothyroidism

Answer 29

* Clinical syndrome characterized by decreased T3/T4 levels * Signs include: * weight gain * inactivity * Alopecia * Reproductive abnormalities * Hypercholesterolemia

Question 30

Hypothyroidism: Systemic lesions associated with disease

Answer 30

* Hyperkeratosis and adnexal atrophy of the skin * Myexedema * Atherosclerosis * Hepatic lipidosis Is the cause for approximately 50% of the cases of hypothyroidism in dogs

Question 31

Parathyroid Gland: Structure

Answer 31

* Chief cells: * comprise most of the gland * Produce parathormone * Oxyphil Cells * modified cheif cells

Question 32

Parathyroid Gland: Function

Answer 32

* 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

Question 33

Parathyroid Gland: Dysfunction: Hyperfunction

Answer 33

* Primary or secondary parathyroid involvement * usually secondary * Increased lameness and fractures, facial bone enlargement and weakening

Question 34

Parathyroid Gland: Dysfunction: Hypofunction

Answer 34

* Usually primary parathyroid involvement * Variable signs, including anorexia, weakness, or tetany of convulsions