Pathology of Endocrine System

Question 1

What is the definition of Primary Hyperfunction?

Answer 1

Cells of lesion autonomously synthesize and release hormone at an excess rate

e.g. primary hyperparathyroidism: adenoma or adenocarcinoma in the parathyroid gland

Question 2

What is the definition of Secondary Hyperfunction?

Answer 2

Excess trophic hormone production in another organ

e.g Pituitary tumor increasing ACTH release and increasing cortisol production + release

Question 3

What is the definition of Primary Hypofunction?

Answer 3

Reduced hormone secretion by an organ, can be due to:

• destruction of secretory cells of the organ: e.g. immune-mediated injury
• failure of normal development of the organ: e.g. Pituitary dwarfism
• biochemical defect in the synthesis pathway: e.g. Vitamin D dependent rickets in pigs

Question 4

What is the definition of Secondary Hypofunction?

Answer 4

Interference with the secretion of trophic hormones

e.g. pituitary neoplasm that is non-functional (not releasing hormone) but is destroying surrounding secretory cells

Question 5

What is another name for the Pars distalis of the Pituitary gland?

Answer 5

• Adenohypophysis
• Anterior pituitary

note: produces and releases the majority of the pituitary hormones: GH, Prolactin, LH, FSH, TTH, ACTH

Under control of the Hypothalamus via Releasing Hormones, which are secreted into the rostral hypophyseal artery

Question 6

What is another name for the Pars nervosa of the Pituitary gland?

Answer 6

• Neurohypophysis
• Posterior pituitary

note: storage and secretory site of oxytocin and ADH

Question 7

What are the potential underlying causes of Hypopituitarism of the pars nervosa specifically?

Answer 7

• Compression and destruction of the pars nervosa, infundibular stalk, or supraoptic nucleus in the hypothalamus

Can be due to neoplasia, cysts, inflammation, or trauma

Question 8

What clinical signs would you expect to see with a disease in the pars nervosa?

Answer 8

• Diabetes insipidus: due to inadequate ADH production

- PUPD –> hypotonic urine

Question 9

What are the potential underlying causes of Hypopituitarism of the pars distalis specifically?

Answer 9

• Aplasia: seen in Guernsey and Jersey cattle mainly, leading to a prolonged gestation. The fetus’ pituitary didn’t develop fully and therefore no ACTH is released to cause the cortisol surge needed for parturition
• Cysts: can lead to pituitary dwarfism
• Non-secretory neoplasia
• Inflammation: abscess or meningitis

Question 10

What are the most common causes of hyperpituitarism?

Answer 10

• Functional adenomas, either in the pars distalis or the pars intermedia
  e. g. Functional adenoma of ACTH-secretion, which stimulates both adrenal glands, leading to hyperplasia and Cushing’s disease
  e. g. Functional adenoma of the pars intermedia. Occurs in horses. This functional adenoma produces excess pro-OMC peptides, leading to docility and a diminished response to pain
  e. g. Functional adenoma of the pars distalis, leading to hypersecretion of GH and somatotropin –> Acromegaly in cats

Question 11

What hormones does the Zona Glomerulosa release?

What is the most common dysfunction/ disease of this zone?

Answer 11

• Releases mineralcorticoids: aldosterone + deoxycorticosterone independent of ACTH

These hormones are responsible for Na + water reabsorption, and K secretion from the kidneys

• Most commonly: hypofunction = Addison’s Disease

Question 12

What hormones does the Zona Fasciculata release?

What is the most common dysfunction/ disease of this zone?

Answer 12

• Releases glucocorticoids: cortisol, cortisone and corticosteroid

Responsible for glucogenesis, lipolysis, protein catabolism and anti-inflammatory

• Most commonly: hyperfunction = Cushing’s Disease

Question 13

What hormones does the Zona Reticularis release?

What is the most common dysfunction/ disease of this zone?

Answer 13

• Releases sex hormones

No significant malfunctions

Question 14

You notice the adrenal glands of an older dog/ cat/ horse have focal enlargements on U/S, but the dog does not present with any clinical signs, what could this be?

Answer 14

Nodular hyperplasia
Non-functional, often an incidental finding, usually find multiple nodules on both adrenal glands and they can be up to 2cm wide

Question 15

What are the possible causes of Primary hypoadrenocorticism?

Answer 15

• Idiopathic adrenocortical atrophy: thought to be an auto-immune disease
• Metastatic Neoplasia
• Adrenal cortex necrosis/ haemorrhage: common in DIC, viral infections, overexertion or stress in wild animals
• Fungal infections or Tuberculosis

Question 16

What are the possible causes of Secondary hypoadrenocorticism?

Answer 16

• Hypopituitarism: disease in the pituitary gland

- Iatrogenic adrenocortical atrophy: overtreatment of Cushing’s, rapid withdrawal from steroids, use of progestagens

Question 17

What is the function of the adrenal medulla?

Answer 17

• Production of catecholamines: epinephrine/ adrenaline

Question 18

What is the most commonly seen disease of the adrenal medulla?

Answer 18

• Pheochromocytoma
  A tumor of the chromaffin cells in the adrenal medulla
• Seen in horses and dogs
• Usually malignant

Question 19

What are the most common causes of Hypoparathyroidism?

Answer 19

Dogs:

• Lymphocytic parathyroiditis: immune-mediated disease leading to the destruction of the parathyroid (most common cause in dogs)
• Infarction/ inflammation

Cats:
- Iatrogenic: usually removal of the parathyroid during thyroid surgery

Question 20

What are some causes of Primary Hyperparathyroidism?

Answer 20

• Functional parathyroid neoplasm: usually an adenoma, less likely a carcinoma

Surgery is usually curative

Question 21

What are some causes of Secondary Hyperparathyroidism?

Answer 21

This is the excessive secretion of PTH in response to hypocalcemia

• Renal: increased retention of P, or a decrease in active Vitamin D leads to the increased P and decrease in Ca+ which overstimulates the production of PTH
• Nutritional: Diets high in Phosphorus (e.g. Bran) or Malabsorption of Ca+

Question 22

What are some causes of Pseudo- Hyperparathyroidism?

Answer 22

This is a type of Paraneoplastic Syndrome

Tumors that cause this include:

• Lymphosarcoma
• Adenocarcinoma of the anal glands
• Multiple myeloma
• Any neoplasia that metastisizes to the bone and causes necrosis leading to Ca+ release

Question 23

What are the possible causes and the most common cause of Hypothyroidism?

Answer 23

Dogs:
Most commonly
- Lymphocytic thyroiditis: an autoimmune reaction to thyroglobulin. There is a breed/ genetic predisposition in Goldens, Doberman Pinschers, Cocker Spaniels and Airedales

Less commonly:

• Bi-lateral non-functional thyroid neoplasia
• Pituitary disease e.g. Pituitary dwarfism
• Diffuse hyperplasia of the thyroid follicular cells: iodine deficiency or ingestion of goitrogenic compounds (clover, brassica, seaweed)
• Nodular hyperplasia in the thyroid glands: these are endocrinologically inactive in dogs and horses, EXCEPT in cats, which causes hyperthyroidism in cats

Question 24

What are the possible causes and the most common causes of Hyperthyroidism in cats and dogs?

Answer 24

Cats:

• Functional Adenomas/ hyperplastic lesions
• Carcinomas are less likely

Dogs:

• Functional adenocarcinoma, BUT most are non-functional
• Adenomas are less likely