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Endocrine 3
thyroid stuff
45
Physiology
Undergraduate 3
10/03/2015

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Term
What effects does thyroid hormone have on the anterior pituitary? On the hypothalamus?
Definition
inhibits responsiveness to TRH, prevents TSH secretion

inhibits secretion of TRH
Term
What is the largest purely endocrine gland?
Definition
the thyroid
Term
The 2 lobes of the thyroid are connected by the...
Definition
isthmus
Term
Describe the pathway leading to the release of thyroid hormone
Definition
Hypothalamus - TRH
Ant Pituitary - TSH
Thyroid - Thyroxine
Term
What else happens in response to stimulation of the thyroid by TSH?
Definition
the gland enlarges
Term
What does the parathyroid gland do?
Definition
secretes parathyroid hormone to increase Ca2+ concentration in the blood
Term
Describe the process of thyroid hormone production
Definition
see notes....
Term
1 I + tyrosine = ?
Definition
MIT
Term
2 I + tyrosine = ?
Definition
DIT
Term
How do we end up with T4 vs T3?
Definition
DIT + DIT = T4

MIT + DIT = T3
Term
How do T3/ T4 enter the bloodstream?
Definition
TSH stimulates follicular cells to take up colloid, which causes T3 & T4 to be hydrolyzed from thyroglobulin & released into blood

(they need carrier proteins to be transported within the bloodstream)
Term
Which is the 'active' form, T3 or T4?
Definition
T3
Term
What effect does thyroxine have?
Definition
increases BMR by:
-increasing cellular respiration rate
-increasing protein synthesis
-promoting nervous tissue maturation
Term
True or False

calcitonin is essential in regulating Ca2+ concenrations in the blood
Definition
false

unlike parathyroid hormone, calcitonin is not essential to regulate Ca2+
Term
Calcitonin is an ______ to parathyroid hormone
Definition
antagonist
Term
What does calcitonin do?
Definition
-inhibits osteoclast activity
-promotes urinary excretion of Ca2+
Term
What converts iodide to iodine?
Definition
TPO
Term

What transporter brings iodide into the follicular cells?

The colloid?

Definition

sodium-iodide transporter

 

pendrin transporter

Term
True or False

All thyroid hormones are bound to carriers in the blood
Definition
false

a small percentage are free
Term
Are thyroid hormones inactive active when bound to TBG?
Definition
inactive
Term
What does TBG do?
Definition
binds thyroxine to transport it within the blood
Term
In humans, secretion of thyroid hormones is highest when?
Definition
10AM - 2PM
Term
How is thyroid hormone secretion regulated?
Definition
-TRH is secreted in pulsatile fashion
-young animals secrete more
-stress/cold increases secretion
Term
Fetal development of what system relies on thyroid hormone in particular?
Definition
nervous system
Term
Can the gonads function properly without thyroid hormone?
Definition
no
Term
What hormone elevates BMR?
Definition
thyroid hormone
Term
If a person has weight gain/low BMR, is not tolerant of the cold, and is lethargic, what disease do they likely have?
Definition
hypothyroidism
Term
If a person has weight loss/high BMR, muscular weakness, nervousness etc., what disease do they likely have?
Definition
hyperthyroidism
Term
Bulging eyes is a sign of what disease?
Definition
hyperthyroidism
Term
What is the common cause of cretinism? what else can cause it?
Definition
maternal hypothyroidism

lack of iodine in the diet
Term
How could you distinguish between cretinism & dwarfism?
Definition
cretinism also has severe mental deficiency, dwarfism does not
Term
What phase of brain development relies on thyroid hormone, during pregnancy or after birth?
Definition
both
Term
What parts of brain formation rely on thyroid hormone?
Definition
-growth of dendrites & axons
-myelin formation
-synapsis formation
-neuronal migration
Term
At what age must cretinism be treated in order for this to be effective? What is the treatment?
Definition
-providing T4 at less than 1 month of age can restore normal function by age 5
Term
What causes goiter?
Definition
-lack of dietary iodide = low T3/T4 production
-TRH is produced in excess
-causes TSH to be produced in excess
-thyroid gland grows to try and produce more T3/T4
Term
Is graves disease associated with hypo or hyperthyroidism?
Definition
hyper
Term
Is high TRH & TSH associated with hypo or hyperthyroidism?
Definition
hypothyroidism
Term
_____thyroidism is more commmon in cats
_____thyroidism is more common in dogs
Definition
hyper
hypo
Term
What causes primary hypothyroidism in dogs?
Definition
destruction of the thyroid:

-lymphocytic thyroiditis
-idiopathic thyroid atrophy
Term
What causes secondary hypothyroidism in dogs?
Definition
-neoplasia causes secondary thyroid destruction
-congenital hypothyroidism/cretinism
Term
What dog breed is particularly susceptible to primary hypothyroidism?
Definition
doberman pinschers
Term
What stimulant might you administer to treat hypothyroidism? What does it do?
Definition
furosamide

increases conversion of T4 to T3
Term
What percentage of the thyroid must be damaged before signs of hypothyroidism become clinical?
Definition
75%+
Term
What is myxedema?
Definition
swelling of tissues seen with severe hypothyroidism
Term
What drug therapy can be used to treat hyperthyroidism?
Definition
administer thiocarbamides to decrease conversion of T4 to T3
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