Thyroid Endocrine Flashcards Preview

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Flashcards in Thyroid Endocrine Deck (25):
1

Hormones produced in the thyroid

T3 -triiodothyronine
T4 -thyroxine
Calcitonin -- peptide hormone from C-cells

2

How is Iodine transported into the follicle

Iodide in the blood
--> Na+/I- symporter --> apicial surface Pendrin channel (allows I- into colloid) --> oxidized to Iodine and iodinates Thyroglobulin (tyrosyl residues)

3

Thyroid cysts

Follicular or thyroglossal duct

4

4 causes of thyroid atrophy

-decreased TSH stimulation
1. 2ndary to lack of trophic hormone
2. Immune-mediated destruction
3. Compression/invasion by neoplasm
4. Colloid goiter

5

Causes of Thyroid hyperplasia

1. Iodine deficiency goiter
2. Feline hyperthyroidism

6

2 types of thyroid neoplasms

1. Follicular cell adenoma/carcinoma
2. C-cell adenoma/carcinoma

7

Causes of HYPOthryoidism

-2ndary
-Goiter
-Iodine-deficient goiter
-Iodine-excess or goitrogens
-Gongenital dyshormonogenetic goiter
-Follicular atrophy
-Iatrogenic
-Idiopathic (autoimmune)
-Lymphoplasmacytic thryoiditis

8

Microscopic features of Thyroid atrophy

-cuboidal epithelial cells
-dense colloid
-distended follicles

9

Congenital dyshormonogenetic goiter

Symmetrical hyperplastic goiter
-Hypothyroidism
-decreased growth rate = stillborn
-abnormal coat = hairless when born

-Autosomal recessive -ruminants, dog/cat
-defective Tgb synth or iodination

10

Microscopic features of hyperplasic goiter

- follicular epithelium
- tall columnar
- forms a papillary projection /endocytic vacuoles
- follicular lumen
-Pale colloid
-narrow follicular lumen

11

Feline Hyperthyroidism
(Thyroid lesions)

1. Follicular adenomas
2. Adenomatous hyperplasia

12

Non-thyroid lesions associated with Feline Hyperthyroidism

1. Increased Phos --> Reciprocal decrease in Ca
2. Increased PTH (due to low Ca) --> hyperparathyroidism
3. Hypertrophic cardiomyopathy

13

Thyroid tumors
(adenoma vs carcinoma?)
in Dog vs Cat vs Horse vs cattle

Dog = carcinoma
Cat = adenoma
Horse = C-cell adenoma --w/o clinical signs
Cattle = C-cell Carcinoma --Dairy bulls

14

What cell secretes PTH

Chief cell

15

Main target organs of PTH

1. Bone
2. Renal tubules
--Blocks Phos reabsorption
--Enhances Ca reabsorption
3. Intestines

-mobilizes Ca

16

Stimulating release of PTH

Recently synthesized PTH:
-released directly without entering the storage pool
- stimulated only by a decreased calcium ion concentration

PTH from the storage pool:
-mobilized by
-cAMP and β-agonists
- epi
- norepi
- isoproterenol
-lowered blood calcium ion

17

Parathyroid gland disorders

1. Parathryoid (Kursteiner's) cysts
2. Hyperparathryoidism --Most common
3. Hypoparathyroidism --Immune-mediated parathyroiditis

18

Causes of Hyperparathryoidism

- Primary
1. Chief cell adenoma
2. Chief cell carcinoma

-Secondary
1. Nutritional
2. Renal

19

Causes of Pseudohyperparathyroidism
aka Humoral hypercalcemia of malignancy

1. Lymphoma
2. Anal sac apocrine carcinoma

- does not have a true elevation of PTH
- persistant hypercalcemia
- should cause atrophy of Parathyroid gland

20

Secondary lesion due to Parathyroid adenoma

Severe thinning of cortical bone and large resorptive cavities

21

Lesion seen with Iodine deficiency

Early stage or fetus
-Hyperplastic goiter (enlarged, firm, dark red-brown)

After correction of iodine deficiency or maturation of the animal
-progresses to a colloid goiter (involutional stage)

22

Pathogenesis of Feline Hyperparathyroidism

IgG acts on TSH receptors --> proliferation of thyroid follicular cells --> multiple hyperplastic nodules or follicular adenomas

23

Common thyroid tumor in Dairy bull

Cell cell carcinomas
-Ca-rich diet

24

Pathogenesis: Renal Dz --> Hyperparathyroidism

-Decrease Phos excretion --> hyperphosphatemia --> decreased Ca:P --> stimulates PTH release
-Decreases Vitamin D3 production --> decrease intestinal absorption of Ca

25

Nutritional imbalances leading to Hyperparathyroid

1. Insufficient Ca
2. Excess Phos
3. Cholecalciferol deficiency