Lecture 14 - Thyroid, Parathyroid and Adrenal Glands Flashcards
Thyroid structure and location
two lobes joined by an isthmus. Just below the larynx. anterior to the parathyroid.
Thyroid development
developed by the foramen cecum (same as tongue). will be in place after 7 weeks, below the larynx.
Colloid
gelatin like substance that fills the follicles of the thyroid. Is surrounded by follicular cells which secrete the colloid.
Follicular cells shape
typically squamos to columnar
Parafollicular cells (or C cells)
stain clearer. Produce calcitonin. can be embedded into the epithelium or can form bunches outside. Neural crest origin.
Vascularity of thyroid cells
frequent capillary openings with fenestrated endothelium.
Follicular cells contents
lots of RER, golgi, and microvilli
Thyroid hormones
T3 (triiodothryonine) and T4 (thyroxine), calcitonin.
T3 and T4
increase basal metabolic rate (T3 - mitochondrial number, cristae density and activity), influence body growth and nervous system development in the fetus. Stored in colloid. T4 most abundant. T3 most potent.
Calcitonin
produced and secreted by parafollicular cells or C cells. induced by increases in blood calcium levels, lowers blood calcium by inhibiting bone resorption (osteoclasts)
Iodine absorption in follicular cells
have iodide pumps (transporters) that concentrate iodide in the thyroid gland to make T3 and T4.
Thyroglobulin
glycoprotein that is synthesized by RER and secreted into the colloid.
Synthesis of thyroid hormones
Thyroglobulin produced, uptake of iodide by Na/I symporter on basolateral membrane, oxidation of iodine by thyroid peroxidase and transported into the follicle by pendrin, iodination by thyroid peroxidase occurs.
Pendrin
anion transporter to get oxidized iodine into the follicle
Thyroid peroxidase
oxidation of iodine in the cell and iodination of thyroglobulin in the follicle.
Thyroid feedback loop
hypothalamus releases TReleasingH which stimulates the anterior pituitary gland to release TSH (thyrotropin). TSH causes a release of T3/T4 into the blood stream and target cells. Feedback to the anterior pituitary and hypothalamus inhibit TRH.
Thyroid hormone secretion
upon stimulation of thyrotropin, follicular cells take up colloid by endocytosis. digested by lysosomal enzymes. Proteases free T3 and T4 to the cytoplasm and secreted basally into the blood. Rest is recycled.
T or F: Thyroid produces there products extracellularly
True.
Hyperactive thyroid follicle appearance
colloid is decreased. more of columnar epithelium.
Hypoactive thyroid follicle appearance
lots of colloid present. squamous epithelium since pushed by the colloid.
Parathyroid structure and location
4 small glands. posterior to thyroid.
Parathyroid development
derived from the parapharyngeal pouches. Inferior come from 3rd pouch, superior come from 4th pouch.
Two cell types of the parathyroid
chief (principal) cells and oxyphil cells
Chief (principal) cells
produce parathyroid hormone which promotes bone reabsorption. dark staining. arranged in cords.
Oxyphil cells
function is unknown, but abundance mitochondria. Light staining. accumulate in age, along with fat cells
parathyroid hormone feedback loop
low blood calcium, stimulates parathyroid hormone secretion, PTH will cause bone to release calcium, kidneys to converse calcium, and intestine to increase absorption. Once calcium rises, PTH inhibited
PTH 3 main targets
bone, kidney, and intestine
PTH and bone
osteoblasts are the main target, which will produce osteoclast stimulating factor (paracrine mechanism) which induces the proliferation of osteoclasts - mobilizing calcium into the blood stream.
PTH and kidney
kidneys conserve calcium in the tubule cells
PTH and intestines
PTH induces the synthesis of vitamin D, which helps with the absorption of calcium.
Adrenal structure and location
medulla, cortex, and capsule. two glands capping the kidneys but with no connection. Lots of adipose tissue but does not increase with age.
Adrenal gland development
cortex - celomic epithelium (mesothelium) derived from mesoderm
medulla - neural crest cells derived from ectoderm
3 layers of adrenal cortex
zona glomerulosa (15%), zona fasciculata (65%) with cords, and zona reticularis (7%)
Zona glomerulosa
bent cords. interconnection between two segments. secrete mineralcorticoids.
zona fasciculata
linear cord arrangement. Glucocorticoids and the androgens are secreted
Zona reticularis
no specific cord arrangement. Lots of capillaries. also secrete glucocorticoids and androgens.
Adrenal gland vascularization
highly vascularized. suprarenal vein in the medulla. arterial (via medullary arteries) and venous (via cortical veins) blood
Aldosterone
(mineralcorticoid) secreted by columnar or pyramidal cells in the ZG. stimulates sodium reabsorption in the distal convoluted tubule of the kidney. Induced by angiotensin II.
cortisol (hydrocortisone)
(glucocorticoid) secreted from ZF. increases blood sugar levels through gluconeogenesis. Suppress the immune system, and aid in fat, protein and carbohydrate metabolism.
DHEA (dihydroepiandrosterone)
a weak androgen secreted by the ZR. converted into testosterone elsewhere in the body.
Endocrine control of the ZF/ZR
hypothalamus is stimulated, induces ATCH from the anterior pituitary to the adrenal gland where it secretes glucocorticoids. Will feedback to hypothalamus and anterior pituitary
Endocrine control of ZG
Aldosterone is controlled by angiotensin II (lung) which is derived from angiotensin I (kidney) which signal initially comes from the liver.
Adrenal medulla
specialized postganglionic sympathetic neurons. produce epinephrine and norepinephrine
Type of cells in the renal medulla
polyhedral parenchymal cells
what is produced by medulla
epi, norepi, ATP, chromagranins, catecholamine-binding proteins, dopamine-B-hydroxylase, and enkephalins
Staining of epinephrine and norepinephrine
epi: dark and regular/organized.
Noreip: very dark and irregular/disorganized.
Fetal adrenal glands
much larger than in adults compared to body weight. secrete androgens and estrogens
Short term response to stress of adrenal gland
epi and norepi released, heartbeat and blood pressure increase. blood glucose levels rise. muscles become energized.
Long term response to stress of adrenal gland
glucocorticoids - protein and fat metabolism instead of glucose breakdown, reduction in inflammation, immune cells suppressed.
Mineralocorticoids - sodium ions and water are reabsorbed by kidney. blood volume and pressure increase.
Hypophysectomy and the appearance of the adrenal cortex
removal of the hypothalamus causes cortical atrophy.
Stress and appearance of the adrenal cortex
stress induces the hypothalamus and ACTH which causes thickening of the cortex.