What is the largest pure endocrine gland?
Thyroid
Describe the composition of the thyroid gland
A gland made up of follicles that are made of epithelial cells
storage unit called a colloid- store thyroglobulin
parafollicular cells- make calcitonin
What role does the thyroid gland play in the body?
Major metabolic regulator
How does the thyroid gland act like a metabolic regulator?
- increases metabolic rate and heat production
- calorigenic effect
- maintain blood pressure
- regulates tissue growth and development
- influences reproductive systems
What is the calorigenic effect?
- oxidation of glucose to make ATP
How does the thyroid gland maintain blood pressure?
- increase the # of adrenergic receptors
- increase vasoconstriction: results in high blood pressure b/c it decreases size of blood vessels
Why is the thyroid gland unique?
-Unlike other glands it can store the hormones that it produces
What is the diurnal cycle?
TSH peaks before sleep and remains high at night
TH is produced at night
production is inhibited by sun
What type of hormone is TH
Amino-acid based but acts like a steroid requires transporter proteins
What is TBG
- Thyroid binding globulins
- Transport T3 and T4
- produced in liver
How does TH move through the body
T3 and T4 bind to TBG which carry them to the target cells where they bind to an intracellular receptor, then transcription cfan occur
What inhibits TH
- High levels of T4 inhibits
the production of TSH (in
adenohypophysis)
What type of mechanism is used for thyroid feedback
humoral mechanism
What are some things that can inhibit TSH
- GHIH (somatostatin)
- high levels of
glucocorticoid - high levels of sex
hormones - high levels of iodine
What are some things that can stimulate the production of TH
- Low levels of TH activates adenohypophysis to produce TSH
- Falling levels of T4 stimulate TH production
What do parafollicular cells produce?
- Produce calcitonin
What does calcitonin do?
- Lowers blood calcium
- inhibit osteoclast activity
- stimulates calcium uptake out of the blood deposit into cells
Why is calcitonin important
- Plays a large role in childhood development
- Most important in periods of rapid skeletal growth and reformation
What acts as an antagonist to calcitonin?
PTH (parathyroid)
What kind of cells can be found in parathyroid?
Glandular: chief cells and oxyphill cells
Under what conditions will aldosterone be secreted?
- High potassium
- Low sodium levels, low blood volume, and low blood pressure
What does acinar cells produce?
Produce enzymes, exocrine
What do the islets of langherhans produce? What kind of cells can be found here?
- Produce glucagon and insulin
- Alpha and Beta cells
What kind of stimulation is the glucagon feedback? (Answer in regards to parasympathetic or sympathetic)
Sympathetic stimulation of medulla will promote release
