Endocrine Glands II Flashcards
What is the structure of the thyroid gland?
Sits anterior to trachea in neck - 2 lobes connected by the isthmus
CT capsule send extensions (septa) inward - subdivide the thyroid lobes into lobules
Each lobule contains follicles
What is the histology of thyroid gland?
Parenchyma - thyroid follicles which contain endocrine cells (follicular cells) and contains colloid
Areas between follicles are fenestrated capillaries and endocrine cells called parafollicular cells
What is the basic structural unit of the thyroid gland?
Follicles
Walls are simple cuboidal epithelium and these cells are follicular cells
Contents are colloid
What is the structure and function of follicular cells?
Form the follicle wall and synthesize the thyroid hormones T3 and T4
T3 and T4 increase metbaolic rate and influence body growth and development
What is colloid?
Thyroglobulin
Storage form of T3 and T4 hormones
What is the areas between thyroid follicles?
Fenestrated capillaries
Parafollicular cells (clear cells and C cells) - they synthesize calcitonin and release it when blood calcium levels are high
What does calcitonin do and what is it released?
Inhibits osteoclast activity so there is less bone resorption and lowers calcium in blood
released by parafollicular cells
What are the parathyroid glands?
4 small glands embedded in CT capsule of thyroid gland
Each gland has a CT capsule that sends short extensions (septa) inward
What are the main cells of the parathyroid glands?
Endocrine cells - cheif cells
Oxyphil cells - function unknown
What is the structure and function of chief cells?
Smaller cells, basophilic cytoplasm
Synthesize, store, and release parathyroid hormone (PTH, parathormone)
What does PTH do?
Stimulates osteoclast activity which means more bone resorption and raises calcium in blood
Also causes a decrease in kidney calcium excretion by stimulating calcium reabsorption
What is the structure and function of oxyphils?
Function is unknown
Larger cells, acidophilic cytoplasm and isolated in clusters
Do PTH and calcitonin have the same or opposite effects?
Opposite!
PTH - chief cells of parathyroid
Calcitonin - parafollicular cells of thyroid gland
What is the structure of the suprarenal gland?
Lies in fat lobule atop kidney
Dual embryonic origin - cortex from mesoderm and medulla from neural crest (ectoderm)
CT capsule sends longer extensions (trabeculae) deep inward
What do the trabeculae of the suprarenal gland do?
Anchor the capsule in deeper tissues
Pathways for vessels and nerves that supply the gland
What is the parenchyma of the suprarenal gland?
Cortex with 3 distinct zones - zona glomerulosa, zona fasciculata, and zona reticularis
Medulla has endocrine cells called chromaffin cells
What do all endocrine cells in cortex synthesize?
Corticosteroids (from cholesterol)
Syntehtic activity regulated by anterior pituitary
Cells in each zone form clusters that are separate by fenestrated capillaries
What is the zona glomerulosa and what is its function?
Outer zone of cortex
Cells synthesize 2 mineralocorticoids:
Aldosterone - regulates water and electrolyte balance by stimulating sodium absorption and potassium excretion in the distal convoluted tubules of the kidneys
Deoxycorticosterone - promotes sodium absorption
What is the zona fasciculata and its function?
Middle and largest zone of the cortex
Cells are spongiocytes that contain numerous lipid droplets
Cells synthesize 2 glucocorticoids that regulate carbohydrate, protein, and fat metabolism - cortisol and corticosterone
What are the effects of cortisol? A BIG FIB
Increase
Appetite
Blood pressure
Insulin resistance
Gluconeogenesis while decreasing glucose utilization
Decrease
Fibroblast activity (decrease collagen and elastin synthesis and slows healing)
Inflammatory and immune system responses
Bone formation (decrease osteoblast activity)
How is cortisol stimulated to be released?
CRH from hypothalamus stimulates corticotrophs to make and release ACTH
ACTH stimulates spongiocytes to make and release cortisol
Excess cortisol suppresses release of CRH, ACTH, and cortisol
What is the structure and function of the zona reticularis?
Inner zone of cortex with strongly acidophilic cells
The cells synthesize 2 weak androgens:
Dehydroepiandrosterone (DHEA) and androstenedione
These hormones have masculinizing effects in males and females but the effect is weaker in males
Cells also synthesize small amounts of glucocorticoids
What are the cells and functions of the suprarenal medulla?
Chromaffin cells that synthesize 2 catecholamine that synthesize epinephrine (adrenaline) and norepinephrine (noradrenaline)
Medulla also has sympathetic ganglion cells whose axons innervate smooth muscle cells in cortical blood vessels and also modules cortical activity
What is the pineal gland and its functions?
Neuroendocrine organ - neurons secrete hormones that regulate day/night cycles
Each pineal gland has a CT capsule that send septa inward. Septa mainly serve as pathways for the vessels and nerves that supply the gland
What is in the parenchyma of the pineal gland?
Endocrine cells - pinealocytes
Neuroglial cells
Pineal sand
What is the function of the pinealocytes?
Receive info about current light levels and synthesize 2 hormones that regulate circadian rhythms
Convert tryptophan into serotonin, which is converted into melatonin
Melatonin synthesize is organelles called synaptic ribbons
What is the function of neuroglial cells of pineal gland?
Functions are similar to those of astrocytes and microglia
What is the function of pineal sand?
Calcified concretions
Function unknown
What are the dual glands of the pancreas? What is the other part of its structure?
Exocrine pancreas - serous acini that secrete digestive enzymes
Endocrine pancreas - pancreatic islets (islets of Langerhans)
CT capsule sends septa inward that subdivide lobes into smaller lobules. Septa forms paths for vessels and nerves that supply the gland and forms path for larger ducts carrying exocrine secretions
What is part of the stroma and the parenchyma of the endocrine pancreas?
Stroma: Capsule and septa (dense irregular CT), Internal scaffold (reticular fibers)
Each islet surrounded by reticular fibers
Parenchyma - islets. contains fenestrated capillaries
What are the pancreatic islet cells?
Alpha cells
Beta cells
Delta cells - D and D1
Epsilon cells
PP cells (F cells)
Gastrin producing cells (G cells)
What do alpha cells secrete and synthesize?
Glucagon which increases blood glucose levels
What do beta cells secrete and synthesize?
Insulin - lowers blood glucose levels
Amylin - inhibits stomach emptying and glucagon release
What do delta cells secrete and synthesize?
D cells - somatostatin which reduces smooth muscle contraction in the GI tract and gallbladder after a meal
D1 cells - vasoactive intestinal peptide - induces glycogenolysis and modulates smooth muscle contraction in the GI tract
What do epsilon cells secrete and synthesize?
Ghrelin - induces the sensation of hunger
What do PP cells secrete and synthesize?
Pancreatic polypeptide which inhibits the secretion of digestive enzymes by the pancreas
What do gastrin producing cells secrete and synthesize?
Gastrin - stimulates parietal cells in mucosa layer of stomach wall to synthesize and release HCl
