Endocrinology Overview Flashcards
hypothalamus - releasing hormones
- thyrotropin releasing hormone (TRH)
- growth hormone releasing hormone (GHRH)
- gonadotropin releasing hormone (GnRH)
- corticotropin releasing hormone (CRH)
*target: stimulate the anterior pituitary to make/release other hormones
hypothalamus - inhibitor hormones
- dopamine (prolactin-inhibiting factor)
- somatostatin (growth hormone-inhibiting factor, GHIH)
*target tissues = anterior pituitary (both) & GI tract (somatostatin only)
anterior pituitary - hormones
- follicle stimulating hormone (FSH)
- luteinizing hormone (LH)
- adrenocorticotrophic hormone (ACTH)
- thyroid stimulating hormone (thyrotropin, TSH)
- prolactin
- growth hormone (somatotropin)
posterior pituitary - hormones
- antidiuretic hormone (ADH, vasopressin)
- oxytocin
intermediate pituitary - hormones
- melanocyte stimulating hormone
thyroid gland - follicular cell hormones
- thyroxine (T4)
- tri-iodothyronine (T3)
thyroid gland - parafollicular cell (C-cell) hormones
- calcitonin
parathyroid gland - hormones
- parathyroid hormone (PTH)
adrenal medulla - hormones
- catecholamines (including epinephrine, norepinephrine)
adrenal cortex - hormones
- glucocorticoids (including cortisol)
- mineralocorticoids (including aldosterone)
- androgens
gonads - hormones
- ovaries: estrogen, progesterone
- testes: testosterone
pancreas - hormones
- insulin (from beta cells)
- glucagon (from alpha cells)
- somatostatin (from delta cells)
negative feedback loops (general principles)
*hormone products INHIBIT further hormone release
*most signaling pathways in the endocrine system utilize negative feedback loops (ex. cortisol, thyroid hormone)
positive feedback loops (general principles)
*hormone products STIMULATE further hormone release
*ex. oxytocin hormone during childbirth
secretory patterns of hormones (general principles)
different hormones have different secretory patterns; some examples include:
1. release in a pulsatile fashion: e.g. GnRH, LH
2. diurnal variation (influenced by light / sleep-wake cycle): e.g. ACTH, cortisol, GH, TSH, prolactin
3. release in response to specific stimuli (injury, stress, etc): e.g. cortisol, GH
4. changes in secretion over one’s lifetime: e.g. testosterone
dynamic testing - defined
*refers to the concept of trying to stimulate or inhibit the release of a certain hormone to see if a person’s body is making too much or too little of that hormone
*not all hormone levels can be checked with a simple blood draw
*ex: the cosyntropin stimulation test tried to stimulate the adrenal gland to produce cortisol
endocrine cellular communication - defined
*a factor is secreted into a capillary bed and transported to a distant site
*“traditional” hormone secretion
paracrine cellular communication - defined
*a factor is secreted and acts at a local site, targeting neighboring cells of a different type
autocrine cellular communication - defined
*a factor is produced by a cell and acts on the same cell, often as a means of regulation
endocrine signaling - key concepts
*hormones travel through blood, exposing many cells to various hormones, in order to cause effects at a distance from their source glands, BUT hormones only affect cells with the appropriate receptors
steroid hormones - defined
*derived from cholesterol
*lipophilic & hydrophobic
*membrane permeable; use INTRACELLULAR receptors
*enter cells to create a response: gene transcription
*require binding proteins for blood transport, which:
-increase hormone half-life
-serve as a storage pool
-regulate active hormone availability
non-steroid hormones - defined
- amines: derived from single amino acid (usually tyrosine)
- peptides: derived from short chains of amino acids
steroids hormones - examples
- progesterone
- estrogen
- testosterone
- cortisol
- aldosterone
- thyroid hormone (T3/T4)
- vitamin D
types of hormone receptors
- intracellular receptors
- cell-surface receptors:
a. G-protein-couple receptors (GPCRs)
b. receptor tyrosine kinases
c. nonreceptor tyrosine kinases
intracellular hormone receptors (overview)
*located in nucleus or cytoplasm
*used by lipophilic hormones that can permeate cell membranes (including ALL steroid hormones)
*effect is to regulate gene transcription
hormones that use intracellular receptors
ALL steroid hormones:
*progesterone
*estrogen
*testosterone
*cortisol
*aldosterone
*thyroid hormones (T3/T4)
*vitamin D
G protein-coupled receptors (GPCRs) that use cAMP (overview)
*located on the cell surface
*GPCRs have 7 transmembrane domains and signal through G-proteins that activate enzymes (adenylyl cyclase) to convert ATP to cAMP (second messenger), which activates protein kinase A, whiich increases intracellular calcium
hormones that signal via cAMP
*FSH
*LH
*ACTH
*TSH
*CRH
*hCG
*ADH
*MSH
*PTH
*calcitonin
*histamine (H2)
*GHRH
*glucagon
*catecholamines
G protein-coupled receptors (GPCRs) that use IP3 (overview)
*GPCRs (alpha-q subunit) activate phospholipase C enzyme which produces second messengers IP3 and DAG which activates protein kinase C
hormones that signal via IP3/DAG
*GnRH
*oxytocin
*ADH/vasopressin
*TRH
*histamine (H1)
*angiotensin II
*gastrin
receptor tyrosine kinases (RTKs) - overview
*activated by ligand-induced dimerization, leading to auto-phosphorylation of tyrosine residues → signaling cascade via MAP kinase pathway
hormones that use receptor tyrosine kinases
*insulin
*IGF-1
*FGF
*PDGF
*EGF
*TGF-B
nonreceptor tyrosine kinases - overview
*doesn’t have it’s own tyrosine kinase, so it couples with TK from a JAK protein → phosphorylation and dimerization of STAT gene transcription
hormones that use nonreceptor tyrosine kinases and JAK/STAT pathway
*G-CSF
*erythropoietin
*thrombopoietin
*prolactin
*immunomodulators: IL-2, IL-6, interferons
*growth hormone
*leptin
