Endocrine System Review

What does the endocrine system consist of?

glands

What do the glands produce and secrete?

hormones

What do hormones regulate inside of the body?

• growth

• metabolism

• sexual development and function

Where is the thyroid located inside of the body and what is it shaped like?

anterior, butterfly

True or false: the thyroid is the largest gland in the body

true

What does the thyroid produce?

T3 and T4 hormones

What do thyroid hormones regulate inside the body?

cellular activity - metabolism of cells

In accordance with physiology of the thyroid, what is absrobed into the bloodstream from the digestive tract?

iodine

Blood transports iodine in the form of iodide to thyroid gland where it is trapped and organified by the thyroid follicular cells.

What is produced when iodide is oxidized?

◦ MIT (monoiodotyrosine)

◦ DIT (diiodotyrosine)

4.T-3 is formed from _____ MIT molecule and _____ DIT molecule.

1 and 1

T-4 is formed from _____ DIT molecules.

2

True or false: thyroid cells are the only cells in the body which can absrob iodine

true

 _____ of released thyroid hormone is T4 and _____is in the form of T3

90% and 10%

What determines the metabolic activity of thyroid hormonoe

the amount of free T3 and T4

What is the normal serum thyroxine lab values?

4.6-12 ug/dl

What feedback mechanism is used within the endocrine system?

negative feedback mechansim

What does TRH stand for?

thyrotropin releasing hormone

What does TRF stand for?

thryotropin releasing factor

What does TSH stand for?

thyroid stimulating hormone

what does TSH stimulate?

stimulates the thyroid to produce T3 and T4

 ____ circulating hormone (T3, T4) will signal the pituitary gland to _______the amount of TSH it is producing.

increased;decreased

decreased; increased

 Blood Work:  Elevated TSH

 Diagnosis:  Hypo or hyper?

hypo

 Blood Work:  Decreased TSH

 Diagnosis:  Hyper or hypo?

hyper

examples of hormone production problems

hypo or hyper

examples of mechanism issues

swollen gland

examples of nodules or lumps

cancer

cancerous lumps or lesions

What will the TSH and T4 lab values show in accordance to hypothyroidism?

TSH will be elevated and T4 will be low

What are the possible causes of hypothyroidism?

• iodine deficiency or excess

• inherited enzyme deficiency

• post ablation

• end stage toxic

• mets

• thyroiditis

• pituitary or hypothalamus dysfunction

What are the two types of hypothyroidism?

Primary and Secondary hypothyroidism

What is primary hypothyroidism?

failure of the thyroid glans to synthesize and release thyroid hormone

What is secondary hypothyroidism?

TSH deficiency, congetial or from pituitary tumor

What will the TSH and T4 lab values show in accordance to hyperthyroidism?

TSH wil be low, T4 will be elevated

What are the possible causes of hyperthyroidism?

• graves disease

• solitary nodule

• multinodular goiter (MNG)

• thyroiditis

What are some possible symptoms associated with hyperthyroidism?

• elevated metabolic rate

• excessive perspiration

• rapid, irregular heartbeat

• nervousness

• weight loss

• exophthalmos

What are some possible symptoms associated with hypothyroidism?

• low mwtabolic rate

• always cold

• constipation

• dry skin

• weight gain

• puffy face

• hair loss

What is exophthalmos ?

protrusion of the eyeballs caused by swollen tissue behind the eyes

Define myxedema

swelling of the body or face that often accompanies hypothyroidism

Define thyroid storm

sudden release of large amounts of thyroid hormones

Define exophthalmos

bulging of the eys that often accompanies hyperthyroidism

Define goiter

swelliing of the thyroid gland

Define cretinism (infantile hypothyroidism)

stunted growth, thickened facial features, abnormla bone development, mental retardation

What are possible treatment options for hyperthyroidism?

• beta blockers (ONLY manages symptoms does NOT treat)

• antothyroid medications

• radioactive iodine treatment

• surgical resection

What are possible treatment options for hypothyroidism?

• hormone replacement medications

What are the characterisitcs of benign thyroid nodules?

• family history of hashimoto’s thyroiditis

• family history of benging thyroid nodule or goiter

• symptoms of hyperthroidism or hypothyroidism

• pain or tenderness

• soft, smooth, mobile

• MNG

• produces normal amount on thyroid scan (warm)

• Toxic = above 35%

• simple cyst on ultrasound

What are characteristics of malginant nodules?

•age < 20 or age > 70

•More popular with male gender

•new onset of swallowing difficulties or hoarseness

•history of external neck irradiation during childhood

•firm, irregular and fixed nodule

•presence of cervical lymphadenopathy (swollen hard lymph nodes in the neck)

•previous history of thyroid cancer

•nodule that is "cold" on scan

solid or complex onultrasound

What percentage of solitary cold nodules are malignant?

15-25%

What percentage of solitary hot nodules are malignant?

1%

What percentage of multi nodules are malignant?

5%

What are the different types of thyroid images that can be done?

Thyroid uptake and scan

Whole body scan

When performing a thyroid uptake and scan, does the patient have a thyroid?

yes

When performing a whole body scan, does the patient have a thyroid?

no

What radiopharmaceuticals are used to perform thyroid uptake and scans?

123I, 131I, 99mTcO4, or a combination

What radiopharmaceuticals are used to perform a whole body scan>

can be done with either 123I or 131I

When can a whole body scan be done in accordance with other treatments?

pre ablation (treatment), post treatment, or a routine follow up

What is the half life of I131?

8.1 days

What is the half life of I123?

13.2 hours

What is the half life of 99mTc?

6.02 hours

What kind of emisison is associated with 131I?

gamma and beta

What kind of emisison is associated with 123I?

gamma

What kind of emisison is associated with 99mTc?

gamma

What is the energy of 131I?

364 keV

What is the energy of 123I?

159 keV

What is the energy of 99mTc?

140 keV

What is the mechansim of uptake of 131I or 123I?

ionic trapping - bound to thyroglobin

What is the mechansim of uptake of pertechnetate?

active transport - trapped in the follicle

What are contraindications to thyroid imaging?

• allergy to iodine

• medication ha snot been stopped

What is relavent patient history to be obtained for thyroid imaging?

family history or cancer/thyroid disease

taking any thyroid medications or anything that contains iodine

neck swelling or lumps

weight changes / comfort or discomfort With base tempature

recent x-rays

taking vitamins

lab work

What is the patient prep required for thyroid imaging?

• pump and dump when using Tc and 123I

• Stop breastfeeding when using 131I

• restrict stable iodine, antithyroid medication, and hormone replacement

What is the dose used when administerinf a capsule of I131 for thyroid uptake?

5-10 uCi

What is the dose used when administerinf a capsule of I123 for thyroid uptake?

200-300 uCi

When can a thyroid uptake be taken hours based?

2, 4, 6, 24, and 48 hours post admin

For what radiopharmaceutcials when used should we decay correct for when obtaining thyroid uptake?

123I and 131I

What does a thyroid uptake probe measure?

how much iodine is absorbed in by the thyroid gland

What is the formula for determining % uptake?

% Uptake  =

  [(net neck counts - net thigh counts)x 100]

(net standard counts) (decay factor)

 *higher the iodine uptake, the more active the gland

Calculate the uptake

 4 hour uptake: 4 hour decay factor= 0.810

 Capsule   734,915 cpm

 Bkgd   103 cpm

 Thyroid  29,760 cpm

 Thigh  683 cpm

      29,760 cpm – 683cpm

    %uptake=   -----------------------------------------------  x 100 = 4.8%

     (734,915cpm– 103cpm)(0.810)  

What is a normal range of thyroid uptake 4-6 hours after capsule admin?

5-20%

What is a normal range of thyroid uptake 24 hours after capsule admin?

7-35%

What is an abnormal range of thyroid uptake 4-6 hours after capsule admin?

<7% hypo

What is an abnormal range of thyroid uptake 24 hours after capsule admin?

>35% hyper

What radiopharmaceuticals can be used to perofmr a thyroid scan?

• I-123

• pertechnetate

What is the dose for pertechnetate when used for a thyroid scan?

2-10 mCi IV

What is the imaging procedure used when obtaining a thyroid scan using pertechnetate?

• 15-30 minute delay

• pin hole collimtor

• 100,000-200,00 counts per image or 5 minutes

• Views: anterior, anterior with marker, LAO, RAO

What is the dose when using I-123 for a thyroid scan?

200-500uCi orally

What is the imaging procedure used when obtaining a thyroid scan when using I-123?

• 4hrs or 18-24 hrs delay

• pinhole collimator

• 50,000-100,00 counts or 10 minutes

• views: anterior, anterior with marker, LAO, RAO

What is a normal interpretation of a thyroid scan?

• euthyroid/homogenous uptake

• left smaller than right lobe plus pyramidal lobe

• location - inferior thyroid cartilage and superior to supra sternal notch

• uptake = or > salivary gland

What is a abnormal interpretation of a thyroid scan?

• plmmers - autonomous MNG 0 hot or cold solitary or multiple

• non visualization - thyroiditis

• graves disease - enlarged high uptake

• hasimotos thyroiditis - enlarged, mottled

• thyroid cancer - solitary cold, 4% hot

What are possible artifacts that could be present on a thyroid scan?

• iodine contaminants I-123

• pertechnetate less accurate due to lower uptake high bakcground

• metal on neck

• improper collimator

• incorrect markers

• patient movement

What are the charactersitcs of thyroid cancer?

• cancerous thyroid tissue will always act like thyroid tissues = take up iodine, found in single nodule

• 11,000 ner cases per year in the US

• 3:1 female to male ratio

• olfer than 30 years old

• no symptoms

What are the two kinds of thyroid cancer?

papillary and follicular

What are the characteristics of papillary thyroid cancer?