Endocrine System, Pt. 2

Question 1

What is the main composition of the thyroid gland?

Answer 1

• hormone-secreting epithelial cells lining colloid-filled follicles (follicle cells)
• parafollicular cells scattered between follicles (C cells)
• many capillaries
• internal parathyroid glands embedded within

Question 2

Thyroid gland, histology:

Answer 2

Question 3

What are 3 functions of the thyroid gland?

Answer 3

1. production of T3 and T4
2. thyroglobulin secretion stimulated by TSH
3. C cell secretion of calcitonin that lowers calcium levels in the blood

Question 4

In what animals is thyroid hyperplasia and adenoma nonfunctional? What is an exception?

Answer 4

older dogs and horses

CATS —> nodular hyperplasia to adenomas, can be cystic, rarely progesses into carcinomas —> feline hyperthyroidism

Question 5

What are the 2 most common signs of feline hyperthyroidism? Clinical pathology values? Associated pathology?

Answer 5

weight loss, polyphagia

high serum T4 and T3 concentrations

left ventricular hypertrophy due to an increase in metabolism caused by increased thyroid hormones

Question 6

How can left ventricular hypertrophy be differentiated from feline HCM and hyperthyroidism?

Answer 6

HCM is genetic and most common in younger cats

hyperthyroidism is most common in older cats

Question 7

How do thyroid follicular cell carcinomas compare to adenomas? In what animals are they most common?

Answer 7

• larger, malignant
• coarsely multinodular
• central area of necrosis and hemorrhage
• invades surrounding structures and vessels
• more likely to be bilateral
• 1/3 mobile, 2/3 fixed

dogs

Question 8

Where do thyroid follicular cell carcinomas typically metastasize?

Answer 8

lungs —> single or multiple “cannonball” pulmonary nodules

(lungs typically involved before retropharyngeal and caudal cervical LNs)

Question 9

What are ectopic thyroid carcinomas?

Answer 9

remnant thyroid tissue present along the ventral neck from the chin to the base of the heart (or within!)

Question 10

What is the most common cause of C-cell (ultimobranchial) tumors in cows? What is commonly a part of? In what animals is it most commonly an incidental finding?

Answer 10

adult to aged bulls on high-calcium diets possibly causing chronic stimulations

old horses, lab rats

multiple endocrine neoplasia syndrome: + bilateral pheochromocytomas + pituitary adenomas

Question 11

What is thought to be the cause of canine hypothyroidism? How does the affected thyroid look?

Answer 11

lymphocytic thyroiditis —> autoantibodies directed against thyroglobulin or TSH receptors that destroy the gland

tan, small/enlarged gland with multifocal to coalescing infiltrates of lymphocytes and plasma cells

Question 12

In what animals is idiopathic thyroid atrophy most common? What is it characterized by? What does the affected thyroid look like?

Answer 12

geriatric dogs

progressive loss of thyroid tissue with replacement by adipose tissue and minimal to no inflammation

smaller and lighter tan with collapsed follicles

Question 13

What are the 5 most common clinical signs of hypothyroidism? What pathology is associated?

Answer 13

1. weight gain, obesity
2. lethargy
3. alopecia (non-purulent, bilaterally symmetric)
4. hyperpigmentation
5. facial myxedema (tragic facial expression)

atherosclerosis due to hypercholesterolemia

Question 14

Hypothyroidism, histo:

Answer 14

• lymphocytic thyroiditis
• destroyed follicles
• increased lymphocytes

Question 15

Hypothyroidism pathologies:

Answer 15

• dilated coronary arteries
• myxedema with thickened facial folds = tragic expression

Question 16

Hypothyroidism:

Answer 16

• grey/white due to increased lymphocytes
• artherosclerosis
• atrophied

Question 17

What is goiter? What are 4 causes?

Answer 17

gross enlargement of thyroid glands due to diffuse hyperplasia or increased colloid with signs of hypothyroidism

1. dietary iodine deficiency
2. dietary iodine excess - interferes with absorption
3. goitrogenic compounds
4. genetic congenital goiter

Question 18

Goiter:

Answer 18

A = hyperplastic due to increased TSH and increased blood supply

B = near term bovine fetus with goiter, alopecia, and myxedema causing swelling of neck soft tissue

C = colloid goiter in foal

Question 19

In what animals is goiter common? When is it reversible?

Answer 19

• ruminants
• horses
• budgerigars (broccoli, cabbage, kale)

nutritional —> iodine deficiency correction induced colloid involution, but the gland remains enlarged and pale due to the accumulation of colloid and decreased vascularity

Question 20

What is the main composition of the parathyroid gland?

Answer 20

chief cells in active (small, dark) and inactive (large, pale cytoplasm) states

Question 21

What stimulated the parathyroid gland? When is hyperplasia common?

Answer 21

circulating calcium levels

low levels of calcium due to nutritional deficiencies or renal disease leads to chronic overstimulation (hyperplasia, adenoma, and carcinoma can be functional)

Question 22

What is diffuse hyperplasia of the parathyroid glands most commonly secondary to? How does it differ to nodular hyperplasia?

Answer 22

chronic stimulation by low calcium levels, commonly caused by renal disease (hyperphosphatemia) and phosphorus-rich and calcium-poor diets

diffuse hyperplasia is not considered an early transition to adenoma (single nodule is not indicative of renal disease/diet problems)

Question 23

Are parathyroid adenomas most commonly functional or nonfunctional? What do they look like? What are 2 common secondary changes?

Answer 23

functional —> secretes PTH, leading to hypercalcemia

well-demarcated and encapsulated, commonly solitary nodules that compress the adjacent gland

1. atrophy of other glands (functional)
2. C-cell hyperplasia

Question 24

How can parathyroid carcinoma be differentiated from adenomas?

Answer 24

• capsular invasion
• increased cellular pleomorphism
• increased mitoses
• vascular and local invasion

Question 25

What pathology is commonly associated with hyperparathyroidism or any etiology?

Answer 25

fibrous osteodystrophy with thinning of cortex and increased fracture rate in many bones and facial hyperostosis with loss of teeth - increased PTH activates osteoclasts to increase calcium resorption

Question 26

Fibrous osteodystrophy:

Answer 26

hyperparathyroidism - thin, poorly mineralized bone trabeculae with increased osteoclast activity and wide separation by fibroblasts and loose connective tissue

Question 27

What does pseudohyperparathyroidism cause? What is most commonly seen in dogs and cats? What needs to be a part of the differential diagnosis?

Answer 27

tumors associated with humoral calcemia of malignancy - DOGS: apocrine gland anal sac adenocarcinomas, lymphoma - CATS: lymphoma, bronchogenic carcinoma Ddx: multiple myeloma, osteosarcoma, abscesses

Question 28

Where are parathyroid (Kursteiner's) cysts most commonly found? What causes its formation? What is it lined by?

Answer 28

close to or in the parathyroid, cranial to the mediastinum duct between developing parathyroid and thymus persists and becomes dilated with fluid ciliated cuboidal epithlium

Question 29

What part of the pancreas is endocrine?

Answer 29

Islets of Langerhans ---> circular clusters of cells scattered among the acini of the exocrine pancreas with moderate amounts of pale eosinophilic to amphophilic cytoplasm - secrete insulin, glucagon, somatostatin, gastrin

Question 30

What cells produce each hormone in the pancreas?

Answer 30

- ALPHA = glucagon - BETA = insulin - DELTA = somatostatin - PP CELLS = pancreatic polypeptide

Question 31

What is the most common cause of islet tumor cells in the pancreas? What kind is most common in dogs? What other species is this common in?

Answer 31

beta cells ---> insulinoma (functional) ---> hypoglycemia ---> neuro signs carcinomas ---> invasive, large ruminants and ferrets

Question 32

What other tumor in the pancreas can appear but is less common? What are they derived from? What does it cause?

Answer 32

gastrinomas ---> ectopic APUD cells or multipotent stem cells Zollinger-Ellison syndrome - gastric acid hypersecretion that can lead to gastric ulceration (increased gastrin = increased HCl)

Question 33

When is islet vacuolar degeneration commonly seen? What happens to islet cells? Why does it develop?

Answer 33

chronic type II diabetic cats reduce in number and become vacuolated due to increased glycogen long-term overstimulation and exhaustion due to peripheral insulin resistance

Question 34

When is pancreatic necrosis common? What does it cause?

Answer 34

canine acute necrotizing pancreatitis type I diabetes (islets are destroyed by necrosis)

Question 35

What 4 pathologies are commonly associated with diabetes?

Answer 35

1. vacuolar hepatopathy (glycogen and lipid accumulation) 2. atherosclerosis 3. diabetic nephropathy and retinopathy due to damage of blood vessels leading to hypertension 4. cataracts due to metabolism of built-up glucose. inlens

Question 36

What are the 2 chemoreceptor organs? What do they do? What cells are they made up of?

Answer 36

carotid bodies and aortic bodies sense blood O2 and CO2 and regulate breathing with afferent nerve fibers sent to he brainstem - TYPE I = glomus, extensive autocrine and paracrine signaling - TYPE II = glial, endocrine

Question 37

What are chemodectomas? What species are predisposed?

Answer 37

aortic body tumors within the pericardial sac near the base of the heart = heart-base tumors brachycephalic dogs - hard to breath, so they are in a constant state of hypoxia which leads to overstimulation of the chemoreceptors

Question 38

Chemodectoma:

Answer 38

- aortic body tumor - brachycephalic - history or cardiac signs

Question 39

Where are carotid body tumors located? What do they look like?

Answer 39

bifurcation of the carotid artery, firmly adhered to the adventitia both carcinomas and adenomas are firm and white with areas of hemorrhage (carcinomas are larger with more local invasion)

Question 40

What are dispersed neuroendocrine system tumors? In what species are they most common?

Answer 40

tumors located within the respiratory, GI, and genital tract including the liver and pancreas (carcinoids), that can secrete vasoactive amines and gastrin dogs