Thyroid Flashcards
Which gland is most important for basal metabolic regulation?
Thyroid gland
What is the isthmus?
Connecting tissue between the lobes of the thyroid. Hard to find in dogs and cats
What is the effect of thyroid hormone on oxygen?
Increase consumption of oxygen in target cells
What are some functions of thyroid hormone?
- Maintain function of organs
- Consumption of )2
- Lipid and carb metabolism
- Normal growth and maturation
- Regulation of calcium
What is the location of the thyroid gland?
Bilateral around trachea. Carotid sheath is lateral. Medial retropharyngeal is cranial. Deep to sternothyroideus muscle. and larynx is cranial
Where is the parathyroid gland?
Usually 4 and embedded in and is not normally palpable
What are follicular cells?
- Traps iodide and transport
- Synthesize and secrete thyroglobulin
- Remove and secrete T3 and T4
What are parafollicular cells?
In the thyroid.
- secrete calcitonin
- neural crest derivative
- decrease calcium levels
What is in follicles of the thyroid?
Colloid
What organ has the greatest blood flow per gram of tissue?
Thyroid
Which cells in the thyroid are pituitary independent?
Parafollicular cells
Were is iodine found in the body?
In the intestinal tract from feed and are trapped by follicular cells and through active transport enter the follicle
What happens to iodine when it enters the follicle?
Attached to Tyrosine by thyroperoxidase and makes either MIT (1 iodine) or DIT(2 iodines)
What is thyroglobulin?
In the colloid with many tyrosine residues and gets released to form T3 and T4
What is the ultimate effect of T3?
Increase basal metabolism
How do you get T3?
1 MIT + 1 DIT + thyroglobulin
Where does formation of MIT and DIT happen?
in the lumen???
How do you get T4?
DIT +DIT + thyroglobulin
What is reverse T3?
Order of addition of tyrosine is opposite. 3, 3’, 5’ tyrosines
Which thyroid hormone exists in the most amount?
T4
Where are receptors for thyroid hormone?
In the nucleus
How is thyroid hormone liberated from thyroglobulin?
- Endocytosis by thyroid epithelial cells
- Lysosomes fuse with endocytotic vesicles
- Free thyroid hormones diffuse from lysosomes into the blood.
What can transport thyroid hormones
- Thyroxine binding globulin (TBG) (70%)
- Transthyretin (10-15%)
- Albumin (20%)
What animals do not have TGB?
Rodents and cats
What cells produce calcitonin?
Thyroid parafollicular cells
What does calcitonin do?
Lower blood Ca and phosphorus
- Blocks osteoclasts action so it is stored in bones
- BLocks renal reabsorption of Ca and P
What it the antagonistic hormone to parathyroid hormone?
Calcitonin
What 3 hormones regulate calcium?
- Calcitonin (lower)
- Vitamin D (raise)
- Parathyroid hormone (raise)
What is a goiter?
Gross enlargement of the thyroid usually nonneoplastic and non-inflammatory
What animal is hyperthyroidism most common in?
Cats. Very rare in dog
How many months worth of thyroid hormone is stored in the thyroid?
6months
What is a primary hyperthyroidism?
Thyroid adenoma or enlargement
What is a secondary cause of hyperthyroidism?
Pituitary tumors or adenoma
What is a tertiary cause of hyperthyroidism?
Hypothalamic legion
What are some clinical signs of hyperthyroidism?
- increased metabolic rate (heat intolerance)
- Goiter
- Weight loss, polyphagia, PU
- Hyperactivity
- Tachycardia
- Cardiac murmur
- Diarrhea
- Serum enzymes elevated
- Low plasma cholesterol
- Bulging eyes in humans (sympathetic drive)
How can you diagnose hyperthyroidism?
- Serum T4
- TSH stimulation test
- Thyroid scan
- Needle biopsy
What is the treatment of hyperthyroidism?
- Antithyroid drugs (inhibit thyroperoxidase)
- Radioactive iodine
- Surgery
- Propanolol for tachycardia
What is hypothyroidism?
Deficiency of thyroid follicular hormones
What is cretinism?
Irreversible growth and metabolic retardation due to lack of thyroid hormones
Why is it important to catch hypothyroidism in young animals?
Without treatment there can be permanent growth damage and retardation
What are the signs of hypothyroidism?
- Elevated thyroglobulin antibodies
- Poor response to TSH
- High serum cholesterol
- Alopecia
- Lethargy
- Cold intolerance
- Obesity
- Bradycardia
What is treatment for hypothyroidism?
Thyroid replacement therapy
