L25. Endocrine 3 Flashcards
What are the similarities between thyroid and adrenal?
- both are catabolic in nature, exert converging stimulatory influence on metabolism
- both respond to homeostatic threat
- have distinct regulatory mechanisms
what is the function of the thyroid hormone?
Thyroid hormone increases cellular activity
What is the function of cortisol
mobilizes glucose
What are the regulatory mechanisms of thyroid and adrenal systems?
feed-forward elements
negative feedback regulation
Trace the path of thyroid hormone release
The paraventricular neuron in the hypothalamus releases TRH. TRH is released from the median eminence into the anterior pituitary where the thyrotrope releases TSH. the TSH stimulates the follicular cells in the thyroid to release thyroid hormones
What are the constituents in the follicular unit?
- Follicle cells
2. Colloid
What is the function of follicle cells in the follicular unit?
- captures iodine
- synthesizes thyroglobulin (TGB)
- produces TH
- cubodial (active)
What is the function of colloid in the follicular unit?
- thyroglobulin-rich protein
2. stores TH precursor
Describe thyroid hormone synthesis
- TSH binds to receptors found on the follicle cells
- selective absorption of the iodide ions
- Thyroglobulin is produced in the RER and is sent to the golgi body. tyrosine-iodide coupling occurs
- the TGB-iodide is released into the colloid lumen through exocytosis
- TGB reuptake and digestion occurs
- thyroid hormone is released from TGB and enters the general circulation
Describe thryroid hormone synthesis
- TGB-iodide enters the cell through endocytosis
- lysosomal digestion occurs
- T3 and T4 is released
Draw out T3
L25 pg 8b
What is TGB
-it is the constructed scaffold (storage molecule) that contains iodinated tyrosine residues
-protein produced by and used entirely by the thyroid galnd
in the colloid, TGB is iodinated at the tyrosine residues
-pairs of tyrosine residues are linked to form complexes containing 3 or 4 iodine atoms
What happens to TGB/ the scaffold during release
TGB is deconstructed to release iodinated tyrosine residues as T3 and T4.
Describe the histology of follicular units
- tall cuboidal
- microvilli ( needed for colloid recapture)
- colloid droplets
Describe the histology of parafolliclar cells
- squamous in shape
2. contains granules
What does the parafollicular cell produce
calcitonin
What are the differences between T3 and T4
- T4 is released more abundantly than T3
- T4 activity is less than T3
- T4 has greater affinity to TGB ( protection from gradation)
- target cells than convert T4 to T3
What are the functions of the thyroid hormones
- oxygen consumption
- growth, development and reproduction
- Na/K channel opening
- response to adrenaline
- heart and respiratory rate
- lipid/carbohydrate metabolism
What happens when we lack iodine in the diet?
- insufficient iodine to make thyroid hormone
2. enlarged thyroid gland (goiter)
Why is there an enlarged thyroid when we lack iodine in the diet?
lack of T3 and T4 (because no iodine to iodinate the tyrosine) negative feedback causes increased in TRH and TSH. accumulation of TSH in the thyriod
What is Grave’s disease?
hyperthyroidism
immune system produces a molecule that mimics the TSH and causes T3 and T4 release by the thyroid
independent of PVN and pituitary
Describe the path of cortisol release
- PVN in the hypothalamus produces CRH
- CRH is released into the median eminence and causes the corticortope to release ACTH
- ACTH stimulates the adrenal gland to release cortisol
What are the 2 components of the adrenal gland
adrenal cortex
adrenal medulla
What is the function of the adrenal cortex
- steroid producing (cortisol)
2. pituitary regulated (ACTH)
What is the function of the adrenal medulla
- regulated by the sympathetic nervous system (CNS)
2. catecholamine producing
between the stomach and the adrenal gland state which is pre-ganglionic and which is post ganglionic sympathetic
stomach: post-ganglionic sympathetic
adrenal gland: pre-ganglionic sympathetic
What are the 3 zones of the adrenal cortex
Z. Reticularis (innermost : towards the medulla)
Z Fasciculata
Z Glomerulosa (outermost)
Name the corticoids that are produced by the respective adrenal cortex layer
- Z. glomerulus: mineralcorticoids- aldosterone
- Z. fascicles: gluccocorticoids-cortisol
- Z. reticularsis: androgrens- dhea
What are the catecholamines produced by the medulla
adrenaline and noradrenaline
What are the functions of aldosterone
- mineralcorticoid
2. Na + retention
What are the functions of cortisol
- glucorticoid
2. glucose mobilization
Describe adrenal-steroid biosynthesis
cholesterol is converted to pregnenolone
pregnenolone is then used to synthesize make aldosterone cortisol and androgens
* all regulated by ACTH
What are the precursors for steroid synthesis
cholesterol and pregnolone
What regulates steroid synthesis/release (steroid synthesis refers to the hormones released by the adrenal cortex)
ACTH
aldosterone is regulated by both ACTH and angiotensin
Describe the histology of adrenocortical
- steroid producing
- steroid storage
- lipid droplets present
Describe the adrenomedullary
- secretory granules producing
2. catecholamine producing
What is the similarity between thyroid hormone and cortisol?
- circulate blood while attached to carrier proteins (specific)
What is the carrier protein for thyroid hormone
TBG thyroid binding globulin
What is the carrier protein for cortisol
cortisol binding globulin CBG
What is the function of a carrier protein for hormone aside from transport
prevents hormone degradation
Describe the parathyroid galnd
4 nodules that are embedded posterior to the thyroid
produce parathyroid hormone
