Thyroid Hormones

tightly, housekeeping, contraction, secretion

metabolic processes are _______ regulated; the cell not only meets its basic metabolic "_______" needs; but also has to do its own special work in the body

(_______, _______, etc)

enzymatic, structural

During its life span, the cell continues to make the _______ and _________ proteins that ensure the maintenance of an appropriate rate of metabolism.

thyroid gland

endocrine gland, located at the front of the neck and below the Adam's apple

thyroxine (T4), triiodothyronine (T3)

the thyroid hormones are _________ and _______

-Regulation of body development

-Regulation of cellular metabolism

-They deliver their effect by gene regulation and affecting the cellular components needed for the normal rate of metabolism

roles of thyroid hormones:

False

true or false: the thyroid hormones are essential for life

slower

In the absence of thyroid hormones, the cellular housekeeping moves at a ______ pace, an event which eventually influences the ability of the cells to carry out their physiologic functions

colloid

The lumen of the follicle contains a high viscosity, proteinaceous gel-like substance called _________

thyroglobulin (Tg)

The colloid is a solution composed primarily of ________, a large protein that is a storage form of the thyroid hormones.

follicle

The thyroid ________ produces and secretes two thyroid hormones, T4 and T3

iodine, 3, 5, 3', 5'

T4 contains four ________ atoms on the ___,____,____, and _____ positions of the thyronine ring structure

iodine, 3, 5, 3'

T3 has only three ______ atoms, at ring positions ____, _____, and ______

calcitonin

The Parafollicular cells in the wall of the thyroid follicle synthesize _________

epithelial, parafollicular

In addition to the ________ cells that secrete T4 and T3, the wall of the thyroid follicle contains _________ cells that produce and secrete the hormone calcitonin

True

true or false: the thyroid follicle does not directly synthesize T4 and T3 in their final form

thyroglobulin

T4 and T3 are formed by modification of tyrosine residues in _________ as the follicular cells secrete it into the follicle lumen.

True

true or false: thyroglobulin is a 660 kDa, dimeric protein produced by the follicular cells of the thyroid and used entirely within the thyroid gland

pendrin

Once iodide ions are inside the follicular cells, they are transported by ________ into the follicle to be used for the iodination of the thyroglobulin precursor (Tg)

five, T4, T3

T3 is formed in only about one of _______ Tg molecules. As a result, the thyroid secretes substantially more _____ than _____

reservoir, buffer, sudden

The protein-bound T4 and T3 represent a large ________ of preformed hormone that can replenish the small amount of circulating free hormone as it is cleared from the blood.

This reservoir provides the body with a _______ against drastic changes in circulating thyroid hormone levels as a result of ______ changes in the rate of T4 and T3 secretion.

inactivation, excretion, half-lives

The protein-bound T4 and T3 molecules are also protected from metabolic ________ and ________ in the urine; thus, thyroid hormones have long _____-_____ in the bloodstream

7, 3

the half-life of T4 is about _____ days; the half life of T3 is about _____ day

40, deiodinase type 1 (D1)

About ______% of the T4 secreted by the thyroid gland is converted to T3 by the enzyme ________ ______ ______

trophic, atrophies, height

Evidence of this ______ effect of TSH is seen in the hypophysectomized patient, in whom the thyroid gland _______ as a result of a reduction in the _______ of the follicular cells

TSH, goiter

In contrast, chronic exposure to excessive amounts of ______ causes an increase in follicular cell height and number, resulting in an enlarged thyroid gland called ________

iodide

Dietary _______ is essential for the synthesis of thyroid hormones

table salt

To prevent iodide deficiency and consequent goiter formation, iodide is added to ______ _______

TRE (thyroid response elements), repress

Thyroid receptors bound to the ______ in the absence of T3 generally act to ________ gene expression

free, ATP

Target cells take up the ______ forms of T3 and T4 from the blood through a carrier-mediated process that requires ______

slow, hours, transcriptional, proteins

The transcriptional response to T3 is _______; thus when T3 is given to an animal or human, several _______ elapse before its physiologic effects can be detected; this delayed action reflects the time required for ______ changes and consequent synthesis of key _______ to occur.

slower, T3

When T4 is administered, its course of action is usually _______ than that of T3 because of the additional time required for the body to convert T4 to _____.

affinity

The mutant TRb does not bind T3 with high _______

TRb, mutations, Tra

The hypothalamic-pituitary axis is primarily regulated by ______ and thus is more sensitive to _________ in the receptor than tissues such as the heart, in which _____ is the dominant thyroid hormone receptor.

-Thyroid hormones are crucial for normal brain development, since they are essential for the differentiation and maturation of the neurons.

-If thyroid hormones are deficient during the prenatal and postnatal periods of differentiation and maturation of the brain, mental retardation occurs.

-Thyroid hormone therapy must be given to a thyroid hormone-deficient child during the first few months of postnatal life to prevent mental retardation

Thyroid hormone role in brain maturation:

growth, development

Body ______ and ________ require thyroid hormone

basal metabolic rate

thyroid hormones are a major determinant of _______ _____ _____

oxidative phosphorylation, heat production, thermogenic

Thyroid hormones regulate the basal rate at which ______ _______ (= ENERGY) takes place in cells and set the basal rates of body ______ ______. This is called the _________ action of thyroid hormones

carbohydrate, fat, protein

______, _______, and ______ metabolism are regulated by thyroid hormone

negative feedback

Thyroid hormones provide _______ _______ to control the hypothalamic-pituitary axis

-inhibit nerve cell replication

-stimulate growth of nerve cell bodies

-stimulate branching of dendrites

-stimulate rate of axon myelinization

actions of thyroid hormones in development of CNS:

-stimulate growth hormone gene expression in somatotrophs

-stimulate synthesis of many structural and enzymatic proteins

-promote calcification of bones

actions of thyroid hormones in body growth:

-regulate basal rates of oxidative phosphorylation

-body heat production

-oxygen consumption

basal energy expenditure

-stimulate synthetic and degradative pathways of carbohydrate, lipid, and protein metabolism

thyroid role in intermediary metabolism

-inhibit TSH secretion by decreasing sensitivity of thyrotrophs to thyrotropin-releasing hormone

thyroid hormone actions in regulating thyroid-stimulating hormone (TSH) secretion: