Endocrine System, Pt. 2 Flashcards
What is the main composition of the thyroid gland?
- hormone-secreting epithelial cells lining colloid-filled follicles (follicle cells)
- parafollicular cells scattered between follicles (C cells)
- many capillaries
- internal parathyroid glands embedded within
Thyroid gland, histology:
What are 3 functions of the thyroid gland?
- production of T3 and T4
- thyroglobulin secretion stimulated by TSH
- C cell secretion of calcitonin that lowers calcium levels in the blood
In what animals is thyroid hyperplasia and adenoma nonfunctional? What is an exception?
older dogs and horses
CATS —> nodular hyperplasia to adenomas, can be cystic, rarely progesses into carcinomas —> feline hyperthyroidism
What are the 2 most common signs of feline hyperthyroidism? Clinical pathology values? Associated pathology?
weight loss, polyphagia
high serum T4 and T3 concentrations
left ventricular hypertrophy due to an increase in metabolism caused by increased thyroid hormones
How can left ventricular hypertrophy be differentiated from feline HCM and hyperthyroidism?
HCM is genetic and most common in younger cats
hyperthyroidism is most common in older cats
How do thyroid follicular cell carcinomas compare to adenomas? In what animals are they most common?
- 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
Where do thyroid follicular cell carcinomas typically metastasize?
lungs —> single or multiple “cannonball” pulmonary nodules
(lungs typically involved before retropharyngeal and caudal cervical LNs)
What are ectopic thyroid carcinomas?
remnant thyroid tissue present along the ventral neck from the chin to the base of the heart (or within!)
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?
adult to aged bulls on high-calcium diets possibly causing chronic stimulations
old horses, lab rats
multiple endocrine neoplasia syndrome: + bilateral pheochromocytomas + pituitary adenomas
What is thought to be the cause of canine hypothyroidism? How does the affected thyroid look?
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
In what animals is idiopathic thyroid atrophy most common? What is it characterized by? What does the affected thyroid look like?
geriatric dogs
progressive loss of thyroid tissue with replacement by adipose tissue and minimal to no inflammation
smaller and lighter tan with collapsed follicles
What are the 5 most common clinical signs of hypothyroidism? What pathology is associated?
- weight gain, obesity
- lethargy
- alopecia (non-purulent, bilaterally symmetric)
- hyperpigmentation
- facial myxedema (tragic facial expression)
atherosclerosis due to hypercholesterolemia
Hypothyroidism, histo:
- lymphocytic thyroiditis
- destroyed follicles
- increased lymphocytes
Hypothyroidism pathologies:
- dilated coronary arteries
- myxedema with thickened facial folds = tragic expression
Hypothyroidism:
- grey/white due to increased lymphocytes
- artherosclerosis
- atrophied
What is goiter? What are 4 causes?
gross enlargement of thyroid glands due to diffuse hyperplasia or increased colloid with signs of hypothyroidism
- dietary iodine deficiency
- dietary iodine excess - interferes with absorption
- goitrogenic compounds
- genetic congenital goiter
Goiter:
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
In what animals is goiter common? When is it reversible?
- 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
What is the main composition of the parathyroid gland?
chief cells in active (small, dark) and inactive (large, pale cytoplasm) states
What stimulated the parathyroid gland? When is hyperplasia common?
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)
What is diffuse hyperplasia of the parathyroid glands most commonly secondary to? How does it differ to nodular hyperplasia?
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)
Are parathyroid adenomas most commonly functional or nonfunctional? What do they look like? What are 2 common secondary changes?
functional —> secretes PTH, leading to hypercalcemia
well-demarcated and encapsulated, commonly solitary nodules that compress the adjacent gland
- atrophy of other glands (functional)
- C-cell hyperplasia
How can parathyroid carcinoma be differentiated from adenomas?
- capsular invasion
- increased cellular pleomorphism
- increased mitoses
- vascular and local invasion
What pathology is commonly associated with hyperparathyroidism or any etiology?
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
Fibrous osteodystrophy:
hyperparathyroidism - thin, poorly mineralized bone trabeculae with increased osteoclast activity and wide separation by fibroblasts and loose connective tissue
What does pseudohyperparathyroidism cause? What is most commonly seen in dogs and cats? What needs to be a part of the differential diagnosis?
tumors associated with humoral calcemia of malignancy
- DOGS: apocrine gland anal sac adenocarcinomas, lymphoma
- CATS: lymphoma, bronchogenic carcinoma
Ddx: multiple myeloma, osteosarcoma, abscesses
Where are parathyroid (Kursteiner’s) cysts most commonly found? What causes its formation? What is it lined by?
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
What part of the pancreas is endocrine?
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
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?
beta cells —> insulinoma (functional) —> hypoglycemia —> neuro signs
carcinomas —> invasive, large
ruminants and ferrets
What other tumor in the pancreas can appear but is less common? What are they derived from? What does it cause?
gastrinomas —> ectopic APUD cells or multipotent stem cells
Zollinger-Ellison syndrome - gastric acid hypersecretion that can lead to gastric ulceration (increased gastrin = increased HCl)
When is islet vacuolar degeneration commonly seen? What happens to islet cells? Why does it develop?
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
When is pancreatic necrosis common? What does it cause?
canine acute necrotizing pancreatitis
type I diabetes (islets are destroyed by necrosis)
What 4 pathologies are commonly associated with diabetes?
- vacuolar hepatopathy (glycogen and lipid accumulation)
- atherosclerosis
- diabetic nephropathy and retinopathy due to damage of blood vessels leading to hypertension
- cataracts due to metabolism of built-up glucose. inlens
What are chemodectomas? What species are predisposed?
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
Chemodectoma:
- aortic body tumor
- brachycephalic
- history or cardiac signs
Where are carotid body tumors located? What do they look like?
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)
What are dispersed neuroendocrine system tumors? In what species are they most common?
tumors located within the respiratory, GI, and genital tract including the liver and pancreas (carcinoids), that can secrete vasoactive amines and gastrin
dogs
