Medical Physiology Block 7 Week 1 Flashcards
What are the endocrine glands?
pituitary, thyroid, parathyroid, testes, ovary, the adrenal cortex and medulla, and endocrine pancreas
Name the paracrine factors.
interleukins, lymphokines, PDGF, FGF
What is the main neuropeptide?
somatostain released from pancreas and hypothalamus
Name the peptide hormones.
pancreas: insulin, glucagon, and somatostain
pituitary: growth hormone, gonadotropin hormones (LH and FSH), adrenocorticotropic hormone (ACTH), thyrotropin, and prolactin
parathyroid: PTH
thyroid: calcitonin
hypothalamus: somatostatin and several releasing hormones
What are catecholamines derived from? steroid hormones?
tyrosine; cholesterol
What cells in the anterior pituitary can secrete more than one hormone?
gonadotropin-producing cells (FSH and LH)
Which hormones require binding proteins?
thyroid hormones, steroid hormones, IGF-1 and -2, and growth hormone
What is the function of binding proteins in serum?
provides a reservoir or pool of the hormone; extends the half-life of the hormone
Is there a trend that hormones that have a primary action of long term modulation of gene transcription are bound to plasma proteins?
Yes; peptide hormones and catecholamines produce rapid responses and circulate freely
What hormones complement each other during exercise? growth? which hormones have antagonistic actions?
glucagon, epinephrine, and cortisol; GH, insulin, IGF-1, thyroid hormone, and sex hormones; insulin and glucagaon
Describe the anatomy of the pituitary lobe.
highly vascular; Posterior pituitary receives arterial blood, whereas the anterior pituitary receives only portal venous inflow from the median eminence (outside the BBB);
Which hormone secreted by the pituitary has no endocrine feedback mechanism?
prolactin
How are neurohypophysis hormones synthesized?
produced as prohormones and cleaved during transport along the axons
Is peptide hormone synthesis increased following stimuli that induce secretion?
primarily yes
What is the signaling cascade for glucagon? AVP? TSH? TRH? ANP? insulin? IGF? PDGF? EGF? GH? LIF? erythropoitin? angiotension?
Gs; Gq; Gq; Gq (PLA2); guanylyl cyclase; RTK; RTK; RTK; RTK; tyrosine kinase-associated receptors; same as GH; same as GH; mutliple signaling cascades
Do catecholamines have hierarchic feedback system?
no; controlled by the CNS
What tissues in the body have the capacity to form hormones from cholesterol?
adrenal cortex makes cortisol, aldosterone, and androgen; the gonads make either estrogen and progesterone (ovary) or testosterone (testes)
Do cholesterol-based hormones have cellular storage pools?
no
Describe steroid receptors.
monomeric phosphoproteins; homology among receptors, particularly C DNA binding domain; dimerize on binding to their target sites on DNA (two zinc fingers)
What are the effects of steroid hormones?
regulate gene transcription; stabilize specific mRNA molecules (increasing half-life)
How do tissues specify the response to steroid hormones?
abundance of specific steroid receptors
genes for steroid receptor proteins do not have steroid response element in their 5’ flanking region (gene transcription must occur following hormone binding to receptor; sometimes the receptor is recycled from the nucleus back to the cytoplasm)
Do steroid and thyroid hormones have nongenomic actions?
yes; through PI3K mediated phosphorylation (example: estrogen receptor alpha binds strongly to PI3K stimulating phosphorylation of PIP2 to PIP3 and modulation of NO synthase activity)
Where are the adrenal glands located?
above the upper pole of each kidney in the retroperitoneal space
Describe the anatomy of the adrenal glands.
cortex is derived from mesoderm, whereas the medulla is derived from neural crest cells that migrate into the developing cortex
Describe the adrenal cortex.
glomerulosa layer near surface produces aldosterone, the fasciculata layer in the midcortex produces cortisol, and the reticularis layer near the cortical-medullary junctions also produces cortisol
What are the three major classes of steroid hormones?
glucocorticoids (increase plasma glucose levels), mineralocorticoids (promotes salt and water retention by the kidney), and sex steroids
Does aldosterone at physiological concentrations have glucocorticoid activity? does cortisol have mineralocorticoid activity?
No; yes
How does the adrenal cortex obtain cholesterol?
imported from circulation via LDL receptor-mediated endocytosis or synthesized de novo from acetate by way of acetyl coA
T/F: Enzymes utilized for conversion of cholesterol to steroid hormone belong to the cytochrome P-450 oxidase family?
True; exception is 3beta-hydroxysteroid dehydrogenase
How is cortisol synthesized?
SCC enzyme removes long side chain on C-20 (rate-limiting step) in the mitochondria producing pregnenolone; the SER enzyme 3beta hydroxysteroid dehydrogenase oxidizes pregnenolone generating a ketone, progesterone; 17alpha-hydroxylase in the SER adds a hydroxyl group; 21alpha-hydroxylase produces 11-deoxcycortisol (SER); 11beta-hydroxylase produces cortisol
Is 17alpha-hydroxylase present in the glomerulosa layer?
No
What other products can be formed from 17alpha-hydroxylpregnenolone and 17alpha-hydroxyprogesterone? What enzyme is required? Can these products be converted to other hormones?
weak androgens: dehdroepiandrosterone and androstenedione; 17,20 desmolase (17alpha-hydroxylase); yes, peripheral tissue may use 17-ketosteroid reductase to androstenedione to testosterone
How is cortisol transported in blood?
most bound to transcortin (produced in the liver) or albumin (also produced in the liver); less than 5% is free in the circulaton
How is cortisol inactivated? Why is this important in the clinical setting?
SER enzyme 11beta-HSD; 11beta-HSD-1 is reversible meaning that administration of cortisone can produce cortisol; 11beta-HSD-2 irreversibly converts cortisol to cortisone in the kidney