18.2 Endocrine System Flashcards
4 Mechanisms of intercellular communication
direct, paracrine, endocrine, synaptic
Both nervous & endocrine systems regulated mainly by what type of feedback?
negative feedback
3 classes of hormones
- amino acid derivatives
- peptide hormones
- lipid derivatives
amino acid derivatives synthesized from
tyrosine and tryptophan
hormones synthesized from tyrosine
thyroid hormones
catecholamines: E, NE, & dopamine
hormones synthesized from tryptophan
melatonin
groups of peptide hormones
- glycoproteins (>200 amino acids long)
2. short polypeptides, small proteins
classes of lipid derivatives
- eicosanoids
2. steroid hormones
eicosanoids
signalling molecules derived from arachadonic acid..strong paracrine effects.. leukotrienes, prostaglandins, thromboxanes, prostacyclins
steroid hormones
derived from cholesterol.. released by reproductive organs (androgens, estrogens, progestins), cortex of adrenal glands (corticosteroids), and kidneys (calcitrol)
which hormones are likely to attach to transport proteins in the bloodstream?
thyroid hormones and steroid hormones
glycoproteins
> 200 amino acids long.. ex: TSH, LH, FSH
short chain polypeptides/small proteins
-includes all hormones secreted by hypothalamus, heart, thymus, digestive tract, pancreas, and posterior pituitary gland.
ADH, OXT (each 9 amino acids long)
GH (191 amino acids), PRL (198 amino acids)
Hormones with receptors in plasma membranes
extracellular: catecholamines, peptide hormones
intracellular: eicosanoids
first messenger
hormone
second messengers
- cAMP
- cGMP
- Calcium ions
down regulation
presence of hormone decreases number of receptors
up-regulation
absence of a hormone triggers increase in receptors.
G protein
enzyme complex coupled to a membrane receptor..binds to GTP
G protein & cAMP
- g protein activates adenylate cyclase, which converts ATP to cAMP, which functions as a second messenger to activate a kinase, leading to phosphorylation
- g protein stimulates PDE, inhibiting adenylate cyclase activity
phosphodiesterase (PDE)
inactivates cAMP
G proteins and Calcium ions
g protein activates phospholipase C (PLC), which triggers a cascade:
- production of diacylglycerol (DAG) and inositol triphosphate (IP3)
- IP3 triggers release of Ca2+ from intracellular reserves
- DAG and Ca2+ activate Protein Kinase C (PKC), which opens channels to extracellular Ca2+
- Ca2+ serve as messengers with calmodulin (protein)
hormones with intracellular receptors
Steroid hormones diffuse through membrane (receptors in cytoplasm or nucleus), Thyroid hormones transported across membrane (receptors at mitochondria increase ATP production, nucleus)
endocrine reflexes can be triggered by:
- humoral stimuli
- hormonal stimuli
- neural stimuli
endocrine reflexes are usually controlled by what type of feedback?
negative feedback
simple endocrine reflexes control the hormone secretion of which organs/tissues?
heart, pancreas, parathyroid glands, and digestive tract.
regulatory hormones of the hypothalamus control..
endocrine cells of anterior pituitary
hormones secreted by anterior pituitary control..
endocrine cells in thyroid, adrenal cortex, and reproductive organs
hypothalamus exerts direct neural control over..
endocrine cells of adrenal medullae
