Endocrine: Thyroid gland anatomy
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