Lecture 2+3 Flashcards
3 classes of anterior pituitary hormones?
glycoproteins:
FSH, LH, and hCG (pregnancy)
alpha chains are identical, beta differ
POMC:
ACTH
lactogens:
GH, PRL, and hPL (pregnancy)
growth hormone?
secreted by?
stimulators? inhibitors?
secreted by somatotrophs
inhibited by somatostatin
stimulated by hypoglycemia, ghrelin, and GHRH (major)
mechanism of GHRH
binds to receptor
increase cAMP and Ca
thus increased GH synthesis and exocytosis
mechanism of somatostatin on GH
decreased cAMP and decreased Ca
inhibits DNA transcription and GH exocytosis
mechanism of GH on target cell
activate tyrosine kinase receptor
increase gene expression
direct actions of GH on the liver, fat, and muscle
Liver:
increase blood glucose
increase IGF
increase IGF-BP
fat:
increase lipid breakdown
decreased glucose intake
muscle:
increase AA uptake
increased protein synthesis
decreased glucose intake
blood glucose vs insulin
increased blood glucose leads to increased insulin
GH always increases blood glucose
insulin is needed for growth
IGF1 or somatomedin C
role of IGF’s
produced mainly in the liver in response to growth hormone
role:
promote linear growth
increase organ size and function
low amounts of IGF will lead to dwarfism
hypersecretion of GH
usually due to tumor in AP
the result can be giantism or acromegaly
giantism occurs before the closure of the epiphyseal plates
how phenylalanine can produce dopamine, norepinephrine, and epinephrine?
phenylalanine is converted to tyrosine by phenylalanine hydroxylase (H4 is a cofactor)
tyrosine is converted to DOPA by tyrosine hydroxylase (H4 is a cofactor)
DOPA to dopamine is done by DOPA decarboxylase (PLP or B6 is the cofactor)
dopamine to norepinephrine by dopamine Beta hydroxylase (vitamin C is cofactor)
norepi to epinephrine by Phenylethanolamine N methyl transferase (SAM is cofactor)
Parkinson’s disease
neurodegenerative disorder due to loss of dopamine producing cells in the basal ganglia
characterized by movement disorders
how to measure norepinephrine or epinephrine?
how are they broken down?
urinary VMA levels
both catecholamines are broken down by either MAO or COMT
vma =Vanillylmandelic acid
what is the end product of dopamine degradation?
HVA by either MAO or COMT
HVA is homovanillic acid
what may high urinary VMA point to?
pheochromocytoma
seen to have overproduction of epinephrine
symptoms:
headache, sweating, tachycardia, hypertension
how is serotonin synthesized?
how is melatonin?
how is serotonin excreted?
tryptophan is converted to 5 hydroxy tryptophan by tryptophan hydroxylase (BH4 is cofactor)
5 hydroxy tryptophan is converted to serotonin by amino acid decarboxylase (B6 is cofactor)
serotonin is converted to 5-HIAA by MAO for excretion
melatonin is derived from serotonin
Carcinoid syndrome?
tumor of the serotonin producing cells in the gut (APUD cells)
seen to have flushing, sweating, diarrhea, bronchospasm
increased 5-HIAA in urine
reactions that need Tetrahydrobiopterin (BH4)?
- phenylalanine hydroxylase (phe to tyr)
- tyrosine hydroxylase (Tyr to DOPA)
- tryptophan hydroxylase (Trp to 5-hydroxy trp)
Tetrahydrobiopterin deficiency
decreased synthesis of neurotransmitters
results in severe mental impairment
T3 and T4 hormones?
tyrosine residues (3 / 4) are Iodinated
T4, less active, is converted to T3, more active, by 5’ Deiodinase
steps in formation of thyroid hormone?
trapping iodine in cell
iodinate the thyroglobin protein (post-translational)
coupling of the tyrosine side chains
release
functions of TPO or thyroperoxidase?
- TPO fixes iodine to thyroglobulin
2. then acts as a peroxidase (link the tyrosine chains)
iodine deficiency
result in hypothyroidism and goiter due to increased TSH secretion
if occurring during fetal development congenital hypothyroidism can occur
graves disease
a form of hyperthyroidism that occurs due to overproduction of thyroid hormone
(antibody that mimics TSH)
