Endocrine: Thyroid gland anatomy

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These cells absorb iodine from the bloodstream

Follicular cells

Hormones of C cells:

Calcitonin

Hypothyroid = low ________ and high _______

T3 and T4, TSH

Follicular cell hormones

Triiodothyronine (T3) and Tetraiodothyronine (T4)

PTH raises

serum calcium levels

Calcitriol is produced by the

skin, liver and kidneys

At the same time that they absorb iodine, Follicular cells synthesize

thyroglobulin

Calcitonin Cells (C cells) found in the

thyroid gland, along with Follicular cells

The Hypothalamus secretes

thyrotropin releasing hormone

Calcitonin effects/MOA:

-osteoclast inhibition (break down) -osteoblast stimulation (build-up)

The Hypothalamic-Pituitary-Thyroid Axis

-The hypothalamus secretes Thyrotropin releasing hormone -TRH stimulates the anterior pituitary to secrete Thyroid stimulating hormone -TSH stimulates the thyroid gland to secrete T3 and T4 -T3 and T4 stimulate the target cells to increase metabolic activity -If T3 and T4 are present in appropriate amounts in the bloodstream, they feed back to the anterior pituitary gland and hypothalamus and inhibit further release of TSH and TRH (negative feedback inhibition)

PTH raises serum calcium levels via four mechanisms:

-increases osteoclast population and thus bone resorption -promotes calcium reabsorption by kidneys -inhibits osteoblasts, thus inhibiting bone deposition of calcium -promotes final step of Calcitriol synthesis by the kidneys

Calcitonin antagonizes

Parathyroid hormone

Metabolically active Thyroid hormone

T3

Tyrosine and iodine combine to form

T3

Percentage of T3 and T4 in the bloodstream

T3 = 10% T4 = 90%

Hyperthyroid = low _________ and high _______

TSH, T3 and T4

Thyroid hormone secreted in response to

Thyroid-stimulating hormone (TSH)

T3 increases

aerobic respiration, stimulates DNA transcription, and increases the rate of protein sythesis

Transport proteins:

albumins and globulins

Thyroid-stimulating hormone produced by

anterior pituitary gland

Specific effects of Thyroid hormone

calorigenic effect, increases heart rate and strength of contraction, increases respiratory rate, stimulates appetite, accelerates breakdown of fat, carbs and proteins for fuel, promotes alertness, promotes bone growth and remodeling, assists in development of skin, hair, nails and teeth, stimulates fetal nervous and skeletal development, stimulates the pituitary gland to secrete growth hormone

Calcitonin is very active in _________ due to constant bone remodeling and turnover

children

Calcitriol synthesis

epidermal keratinocytes use UV radiation to produce vitamin D3, which is transported to the liver and converted into calcidiol, then it is transported to the kidneys and converts to calcitriol (skin to liver to kidneys) (vitamin D3 to calcidiol to calcitriol)

Thyroid gland composed of

hormone-secreting Follicular cells and Calcitonin Cells

Calcitonin secreted in response to

hypercalcemia

Effects of calcitriol

increase calcium reabsorption by the small intestine, inhibit urinary calcium excretion, promote phosphate excretion (calcium binds to phosphate for bone deposition), stimulate osteoclasts to reabsorb (break down) bone

Primary effect of Thyroid hormine

increases body's metabolic rate and increases oxygen consumption

Calorigenic effect

increasing heat production

The Parathyroid glands are _______ from the Thyroid gland

independent

Need ______ to make Thyroid hormone

iodine

Parathyroid hormone is secreted by the ________ in response to _________

parathyroid glands, hypocalcemia

T3 and T4 bind to hormone receptors on target cells and penetrate their

phospholipid membranes

An enzyme in the target cell cytoplasm...

removes one iodine from T4, turning it into T3 (the metabolically active form)

Calcitriol

the most active form of Vitamin D

T3 and T4 collectively known as

thyroid hormone

T3 and T4 bind to ___________ ___________ which carry them to target cells

transport proteins (bound hormones)

Thyroglobulin is composed of large quantities of the amino acid

tyrosine


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