Downing: Pineal, Thyroid and Parathyroid Flashcards
When is the pineal gland the largest?
first decade of life
Describe the gross structure of the pineal gland.
Cone shaped
Attached by a STALK to the roof of the 3rd ventricle
What composes 95% of cells in the pineal gland?
pinealocytes
What do pinealocytes produce?
melatonin
What are the supporting elements in the pineal gland?
glial cells (astrocytes)
What happens to the pineal gland as you get older?
Brain sand!
concretions of hydroxyapetite and Ca that increase w/ age (good tumor markers)
*displacement from midline is evidence of cerebral tumor
What is the nerve supply to the pineal galnd?
Sympathetic (Epi) that END on pinealocytes
What are the functions of the pineal gland
produces melatonin
- low light periods
- suppresses gonadotrophin secretion via hypo inhibition
- retards gonadal growth and fxn
What may be associated w/ SAD?
pineal gland
What is the embryological growth of the thyroid gland?
downgrowth at FLOOR of pharynx (pouches I and II)> vascular mesenchyme separates diverticulum into follicles> ultimobranchial body (pouch IV) fuses with downgrowth from pharynx (primordium)> which brings in C cells
What is the origin of C cells?
NCC
What makes up the follicles of the thyroid?
simple low cuboidal cells
contain colloid
Where do you store the precursor to T4 and T3?
colloid
Wha synthesizes thyroid hormones?
follicular cells
What surrounds all off the thyroid follicles?
fenestrated capillaries providing RICH vascularization
A normal/resting follicular cells have what characteristics?
Makes small amt of thyroid hormone
Low cuboidal
few mito, small golgi
some RER in base of cells
What are the characteristics of a TSH stimulated follicle (active)?
TSH from the pars distalis> columnar cells increase in representation lipid droplets PAS + colloid apical lysozymes
What is the origin of parafollicular cells?
NCC
What synthesizes calcitonin (high Ca)?
parafollicular cells
SLOWS down the activity of osteclasts–> decreased Ca
How does calcitonin lower Ca?
inhibits bone resorption
decreases osteoclast motility/numbers
promotes excretion of Ca and PO4 from the kidneys
What is the only gland that stores large quantities of product extracellularly?
Thyroid
Stores in colloid (3 mo supply)
Where is thyroglobulin composed of?
glycoprotein
3% are tyrosyl residues that are available for iodination
How is iodine taken up?
Basal portion of follicular cells have an active iodide transport>
concentates>
oxidation to iodine at cell surface via TPO
What gets iodated in thyroglobulin?
tyrosyl residues
EXTRACELLULARLY
