Endocrine System Physiology 1 - Teel Flashcards
2 Hormones secreted by pituitary gland:
AVP
Oxytocin
Regulatory factors of Hypothalamic releasing hormones
___ stimulates secretion of ___
CRH (corticotropin) : ACTH, also stimulates expression of POMC gene
TRH (thyrotropin): TSH / PRL
GHRH (Growth hormone) : HGH
GnRH (Gonadotropin) : Stimulates secretion of FSH and LH
Regulatory factors of Hypothalamic releasing hormones
____ inhibits secretion of ____
Somatostatin: GH TSH
Dopamine: PRL
Hormones of Anterior Pituitary
ACTH (Adrenocorticotropic hormone)
Regulates function of adrenal cortex
Derived from POMC
Regulated by CRH
Related to stress
Glucocorticoids inhibit ACTH synthesis / secretion
Diurnal rhythm exists
Hormones of Anterior Pituitary
TSH (Thyroid-stimulating hormone)
Regulates function of thyroid gland
TRH regulates synthesis / secretion of TSH
Exhibits diurnal variation, stimulated by cold temps
Negative feedback regulation by thyroid hormones
Hormones of Anterior Pituitary
HGH (Human growth hormone)
Regulates growth in childhood
Stimulates secretion of insulin-like growth factor 1 (IGF-1)
Displays pulsatile secretory pattern with peaks during sleep
Hormones of Anterior Pituitary
Gonadotropic hormones
LH (Luteinizing hormones)
FSH (Follicle-stimulating hormone)
Both regulate testes / ovaries
Both regulated by GnRH (Gonadotropin-releasing hormone)
Hormones of Anterior Pituitary
Prolactin
Regulates synthesis of milk of the breast
Significance of Somatotrophs
In anterior pituitary, these synthesize prohormone that is converted to HGH
Stored in little granules
What influences growth hormone?
Blood glucose levels. You can have peaks of growth hormone during day depending on your blood glucose levels.
Somatotroph mechanism
GHRH from hypothalamus stimulate somatotrophs in anterior pituitary to make HGH.
Somatostatin also produced here
Contains both GHRH receptor and SS receptor. Secondary messengers are needed (cAMP)
Metabolic Effects of HGH
Skeletal muscle increases in glucose production, but decreases glucose uptake from adipose tissue. Decreasing uptake means there’s more glucose in blood. So basically less glucose in skeletal muscle
Adipose tissue: increased lipolysis
Liver (hepatocytes): increased gluconeogenesis (making glucose)
All of these effects have an insulin resistant reaction. These are all insulin antagonists
Importance of IGF with HGH
Growth promoting actions of growth hormone (HGH) have to include IGF 1 and 2, particularly 1.
Mechanisms of IGF-1
binds to proteins synthesized by liver
levels in plasma are fairly stable
acts through specific receptor
begins to regulate growth by age 3-4
Note: IGF-2 has similar actions to IGF-1, but has less dependence on HGH.
Stages of Growth
In utero:
Important things:
IGF-II, placental lactogen, fetal insulin, cortisol, T4 and nutritional factors
Stages of Growth
In early childhood:
HGH, IGF-1, cortisol, insulin, T4, nutritional factors
Stages of Growth
Puberty:
HGH, IGF-1, cortisol, insulin, T4, gonadal steroids, nutritional factors
Mechanism of production of T3/T4
TRH released from hypothalamus, traveling down blood supply to thyrotrophs (cell in anterior pituitary), producing TSH
TSH released into circulation, travels to thyroid gland.
Thyroid responds to TSH by producing T3 / T4
Thyrotroph mechanism
Contain TRH receptors. Secondary messenger mediated. Release TSH
Follicular Cell
functional part of the thyroid gland. Absolutely dependent on dietary iodine.
TSH receptor in basolateral side.
Thyroid follicular cell and glandular function
mechanism
Iodine / Na+ from blood cotransported via basolateral membrane of follicular cell. I- then goes into lumen converting into I2
Thyroglobulin (TG) synthesized within thyroid follicular epithelial cell, then gets transported into lumen.
In follicular lumen, TG links up with Iodine, forming either MIT and DIT (moniodotyrosine, diiodotyrosine)
TG reassembles MIT and DIT to form either T3 or T4 (still attached to TG).
T3 / T4 attached to TG from colloid now travels back into follicle cell
T3 / T4 cleaved inside cell, then travel out of cell on basolateral side
Mechanism after T3/T4 transported out of follicle cell
Binds to Thyroid-binding globulin (TBG) / albumin
Actions of Thyroid hormones
T4 converts to T3. T3 binds to thyroid hormone receptor which is linked to retinoid X receptor in target cells.
Binding affects alteration of gene transcription and synthesis of proteins that initiate action of thyroid hormones.
Tons of effects, mainly metabolism effects. Same with cardiovascular. Upregulates a bunch of stuff.
Thyroid gland dysfunction
Hyperthyroidism
Disease associated with this
moist skin, palpitations, arrythmias, murmurs of heart, CHF, decreased VC / lung compliance, Diarrhea, nervousness, neutropenia, splenomegaly
upregulate gluconeogenesis / glycogenolysis / more
Gain too much stuff
Example: Grave’s Disease. Antibodies bind to and stimulate TSH receptors.
Thyroid Gland dysfunction
Hypothyroidism
Disease associated with this
dry skin, bradycardia (heart rate too slow), slow reflexes, hypoventilation, gain weight,
downregulate gluconeogenesis / glycogenolysis / more
Lose a lot of stuff
Example: Hashimoto’s disease. TSH blocking antibodies.
