Endocrine Overview Flashcards
what is a hormone?
a chemical substance that is secreted into the internal body fluids by one cell or a group of cells and has a physiological control effect on other cells of the body.
what are the major endocrine glands?
- pituitary gland
- testes
- thyroid and parathyroid glands
- adrenal glands
- pancreas
- ovaries
whats the function of the endocrine glands?
they secrete hormones which regulate various functions throughout the body
how does feedback control work?
A sensor detects a regulated variable and responds by modulating its secretion of a hormone
This hormone, either acts on a target to modify another hormone or affect a second target.
when does GH peak?
night
when does cortisol peak?
morning
describe the release of hormones?
pulsatile and episodic (Frequency and amplitude) can vary daily (e.g. cortisol) or monthly (estradiol) or remain fairly constant (Thyroid hormone)
where is the clock with an intrinsic 24-25 hour cycle located?
in the suprachiasmatic nucleus (SCN) of the hypothalamus.
This free running clock is entrained by environmental light signals to the external 24-hour day.
name this gland and the hormone that is both an agent and regulator of the SCN
pineal gland; melatonin
what is the synergistic effect of hormones?
the effect of the two synergistic hormones is greater than that of either hormone alone (example is thyroid hormone and epinephrine on heart rate, since in addition to its direct effects of increasing heart rate, thyroid hormone increases the number of adrenergic receptors which can then respond to epinephrine).
what is the permissive effect of hormones?
thyroid hormone presence is necessary for aldosterone to stimulate Na+/K+ pumps, although TH has no stimulatory effect on these pumps by itself.
what is the antagonistic effect of hormones?
insulin vs. glucagon/epinephrine effects on glycogen synthesis
what are examples of cell-to-cell communication?
Direct contact
Synaptic
Chemical Signaling -Endocrine Signaling -Paracrine Signaling -Autocrine
how are hormones are removed from the blood and tissues by 6 basic methods?
- Enzymatic catabolism in blood and extracellular fluids
- Endocytosis of hormone-receptor complex by target cell with subsequent intracellular enzymatic catabolism and return of “cleared” receptor to plasma membrane
- Liver enzymatic degradation and/or excretion in bile
- Liver re-synthesis (example: aromatization of testosterone into estrogen)
- Kidney excretion into urine
- Hormonal binding to target sites
what are steroids?
Small lipid soluble molecules derived from cholesterol
T/F, steroids are not stored, synthesized de novo on demand
T
how do steroids circulate?
they circulate bound to globulins and other plasma proteins
what do steroids bind too?
bind intracellular receptors (cytosolic & nuclear)
describe the effects of steroids?
Effects are slow (hours), depend on gene transcription, protein synthesis, etc.
what are the four main domains of the steroid hormone receptor?
- The ligand (hormone) binding domain
- The DNA binding domain
- The N-terminal portion (transactivation domain)
- The DNA binding domain contains two Zinc Fingers which contain 4 cysteine residues which complex with zinc
how long are peptide/protein hormones?
3 to 200 amino acids long
how are peptide/protein hormones released?
- synthesized and stored, released in bursts
- generally circulate unbound in plasma, but there are exceptions (IGFs)
what do Peptide/Protein Hormones bind too?
extracellular receptors, and depend on 2nd messengers for signal transduction
what are the effects of peptide/protein hormones?
effects are very rapid (minutes), and initial effects do not depend on new protein synthesis
what are amino acid hormones synthesized from?
TYROSINE, they are also stored and secreted in bursts
describe how thyroid hormone is bound and its half life?
Thyroid Hormone circulates >99%bound, very long half-life (days)
what are the type of receptors that thyroid hormones bind too?
Binds to intracellular receptors (but plasma membrane transporter)
note that effects through gene transcription, slow
how does epinephrine and norepinephrine bind?
binds to extracellular receptors
effects through 2nd messengers, very rapid
how can we measure hormones?
Radioimmunassay
three levels of endocrine control?
Tertiary - hypothalamic stimulation
Secondary - pituitary stimulation
Primary - endocrine gland stimulation
what are the endocrine neoplasias?
type 1 and 2. Autosomal dominant, multifocal in a given endocrine organ.
what is type 1 neoplasia?
parathyroid tumors, pituitary tumors, pancreatic tumors
D/t inactivation of MEN1 gene on 11q13 affecting
- parathyroid (hyperplasia→ primary hyperparathyroidism)
- Pancreas (functional tumors, leading cause of death in MEN1, insulinoma → hypoglycemia, gastrinoma → Zollinger-Ellison syndrome)
- Pituitary - prolactinoma
what is type 2 neoplasia?
mutations of RET proto oncogene
Type 2a: medullary thyroid carcinoma, pheochromocytoma, parathyroid hyperplasia → hyperparathyroidism
Type 2b: medullary thyroid carcinoma, pheochromocytoma, mucosal neuromas
→ DO NOT develop parathyroid hyperplasia
→ develop extra endocrine manifestations: marfanoid habitus
