thyroid hormones - lecture 15

thyrotropin-releasing hormone (TRH)

in relation to the hypothalamic-pituitary-thyroid (HPT) axis, the hypothalamus releases ...

TRH activates the TRH receptors on the thyrotrophs

thyrotropin-releasing hormone travels a short distance to the anterior pituitary where the...

hormone 2 called thyroid-stimulating hormone (TSH)

once the TRH activates the anterior pituitary thyrotrophs, they are going to make and release ...

to the rest of the body

once the anterior pituitary thyrotrophs make and release TSH, it goes...

having a TSH receptor on a target cell that the TSH is going to bind to on the thyroid gland

because the TSH is going to circulate throughout the body, we want to make sure it only activates what it is supposed to activate, so we do that by...

thyroid hormones (T3 and T4)

once the thyroid gland is activated by the TSH receptors, it will release...

make sure there is not a nonstop release of these hormones when it is not needed

finally, the T3 and T4 will go around the body doing its job, but it will also circle back to the pituitary and hypothalamus in order to...

in front of the neck, wrapping around the trachea

where is the thyroid gland located

indication of hyperactive thyroid following injection of radioactive iodine and neck scan

what is this image showing

iodine and tyrosine

what are the important precursors for the thyroid gland

T3 and T4

amino acid derived hormones using tyrosine

iodine

mineral, there are public health interventional strategies to make sure we have enough of this

T3 and T4

when iodine and tyrosine are present, the thyroid gland will make ...

thyroid gland

made up of numerous follicles

colloid

a protein rich center where thyroid hormone is synthesized and stored

a store of iodine

human diets do not contain a lot of iodine, so the colloid of the thyroid gland also serves as...

follicular epithelial cells

surround the colloid and participate in almost all phases of thyroid hormone synthesis and secretion

follicle

an anatomical term, a small (often spherical) secretary cavity

follicle

the thyroid gland is made up of ...

blood vessels

transport hormones, nutrients to and from thyroid gland

thyroglobulin

a protein enriched in the thyroid gland, source of tyrosines for thyroid hormone, huge protein made of tyrosine amino acids

thyroglobulin

acts as a scaffold for thyroid hormone synthesis, physical support with tyrosine

INactive

T4 is...

Active

T3 is...

1. iodide is co-transported with sodium

2. iodide diffuses toward the follicle lumen

3. iodide transported to colloid and combines with tyrosines on thyroglobulin (pink worm looking thing)

***unidirectional transport of iodide (I-)

describe this image (steps 1-3)

4. the iodinated ring of one MIT/DIT is added to a DIT at another spot

5. endocytosis of thyroglobulin-containing T3 and T4 molecules (scissors coming in and clipping off thyroglobulin)

6. lysosomal enzymes cleave and release T3 and T4 from thyroglobulin

describe this image (steps 4-6)

DIT

di iodinated tyrosine

MIT

mono iodinated tyrosine

thyroid peroxidase

enzyme that takes tyrosine, adds iodine onto it (1 or 2)

thyroid peroxidase (TPO)

exclusively located in the thyroid colloid, presence int he blood is indicative of autoimmune destruction of the thyroid

thyroid peroxidase

how does iodide attach to tyrosine on thyroglobulin?

1. TRH activates TSH

2. TSH activates thyroid gland to make T3 and T4

3. T4 can become T3

4. negative feedback loop

***INCREASED METABOLISM

describe these images generally

increased metabolism

what is a main point of thyroid system?

are bound to binding proteins

hormones are inactive as long as they....

around 70% of thyroid hormones

bound to thyroxine-binding globulin (TBG)

around 30% of thyroid hormones

bound to other binding proteins

0.3% of thyroid hormones

unbound, free T3

0.03% of thyroid hormones

unbound, free T4

iodine (iodized salt, shrimp, seaweed)

necessary for thyroid hormone production

thyroid peroxidase

important enzyme required for thyroid hormone production

active

T3 is the biologically ________ form

1. metabolic actions (supporting metabolism)

2. permissive actions (thyroid works with another hormone to get max effect)

3. growth and development

what are the major actions of the thyroid hormones

1. brain and pituitary

2. heart

3. bone

4. adipose tissue

5. liver

thyroid hormone receptors are present in the nuclei of MOST cells of the body, and critically impact the following organs:

high affinity T3 receptors

metabolic and calorigenic actions:

present in most cells of the body

T3

metabolic and calorigenic actions:

stimulates a very diverse array of metabolic activities in most tissues

-increase overall metabolic rate

-increases oxygen consumption and ATP hydrolysis

-leads to increased thermogenesis

more than one hormone

keep in mind that most target cells in your body tend to have receptors for...

thyroid hormone

drastically increases the effectiveness of epinephrine at a target cell, due in large part to its ability to increase the number of cell surface receptors for epinephrine

nuclear

thyroid hormone receptors are __________ receptors

thyroid hormone signaling

acts on TH receptor to influence target gene expression

permissive

TH is ____________ on epinephrine's cellular actions

thyroid hormone

acts closely with growth hormone (GH) for body growth and development

growth and development

particularly important role in early brain structure development

hypothyroidism

deficits in neuronal layering and architecture

TSH

-binds to its receptor in the thyroid gland

-stimulates all steps involved in thyroid hormone synthesis and release

thyroid gland

-stores iodine and thyroid hormone in colloid

-produces more T4 (inactive) than T3 (active)

thyroid hormone

-synthesis and release are under negative feedback regulation by the HPT axis

-T4 (pro-hormone) is converted to T3 (hormone)

-binds to nuclear receptors and modulates gene expression

d. a and c

which nutrient precursors are needed in the body to produce T3 and T4?

a. tyrosine

b. cholesterol

c. iodine

d. a and c

d. b and c

besides blood levels of T3 and T4... what else could you measure in blood to diagnose alterations in thyroid hormone system function?

a. t3 receptors

b. TSH

c. thyroid peroxidase

d. b and c