Hormone life history Flashcards
hormone effects and hormone concentration
-they physiological effects of hormones depend on their concentration in blood/extracellular fluid
-almost inevitably, disease results when hormone conditions are either too high or too low
-therefore precise control over circulating concentrations of hormones is critical
-things that can affect amount: time of year, gender, size
-high=hyper, low=hypo
the concentration of hormones as seen by target cells it determined by what three factors
-rate of production
-rate of delivery
-rate of degradation + elimination
what is the life of a hormone cell
-endocrine cell
-can to a neutral or blood-borne stimulus
-can go to target cell
-can go to liver to either be excreted or to be metabolized to more active form
-can go to kidney for excretion
-can go to a hormone binding protein
rate of hormone production/secretion
-synthesis and secretion of hormones are the most highly regulated aspect of endocrine control
-such control is mediated by positive and negative feedback circuits
-this will be discussed in more detail within each endocrine axis
how are endocrine glands stimulated
-through the nervous system
-by other hormones
-humoral stimulation (other components: glucose, cytokines)
stimulation of hormone production: humoral stimulus
-hormone release caused by altered levels of certain critical ions or nutrients
-ie: stimulus: low concentration of Ca2+ in capillary blood
response: parathyroid gland secrete parathyroid hormone (PTH), which increases blood Ca2+
stimulation of hormone production: Neural stimulus
-hormone release caused by neural input
-ie: action potentials in preganglionic sympathetic fibres to adrenal medulla
-response: adrenal medulla cells secrete epinephrine and norepinephrine
stimulation of hormone production: hormone stimulus
-hormone released by another hormone (a trophic hormone)
-stimulus: hormones from hypothalamus
-response: anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones
feedback regulation: negative feedback
-hormone acts back onto the receptor to tell it to slow down via long or short loops
-imbalance
-hormone released
-correction
-negative feedback
-homeostasis
for a tissue to respond to feed back via hormone stimulus what does it need to have
-hormone receptor
-The hypothalamus + pituitary have lots of receptors
feedback regulation: positive feedback
-hormone acts back to increase production of the hormone
positive feedback vs stimulation
-pos feedback refers to further stimulation of the hormone/chmical which was the original source of the signal
-pos feedback and stimulation are not the same thing
rate of delivery example
an example of this effect is blood flow to a target organ or group of target cells- high blood flow delivers more hormone than blood flow
how do hormones circulate the blood
-either in the blood free or bound to LARGE proteins
-water-soluble hormones: no specific transport mechanism
-lipid soluble hormones: transport proteins
1) albumin & transthyretin: bind small ligands, general transport molecules
2) specific transport proteins:
-corticosteroid-binding globulins
-thyroxine-binding globulins
-sex hormone binding globulins
what does binding proteins impact
-metabolism and bioactivity of circulating hormones
-free hormone is the bioactive form
rate of degradation and elimination
-hormones, like all biomolecules, have characteristic rates of decay, and are metabolized and excreted form the body through several routes
how are hormones degraded (or metabolized)
-some are metabolized at their target cells (once job is done they get broken down)
-some are metabolized by enzymes in circulation (free is more susceptible)
-many are metabolized by enzymes in the liver or kidney
-most hormones are excreted via the kidneys (some via liver–>bile)
rate of degradation and elimination: what is a half life
-the time during which the concentration of hormone decreases to 50% of its initial volume
-doesnt take into account how its degraded just that it is degraded
-some are really short because you dont want to be stressed long where as others are long acting because it take awhile for them to get to their receptor
rate of degradation and elimination: metabolic clearance rate
-removal of hormones from circulation, the volume of plasma cleared of the hormone per unit time
-MCR=mg/min(removed)/ mg/mL(plasma) = mL plasma (cleared)/min
-volume of plasma cleared of hormone per unit of time
how is the half-life of a hormone related to MCR
high MCR doesn’t stick around long so they are inversely proportional
what is metabolic degradation
-mainly through the liver through enzymatic processes that include:
-phase I reactions (i.e. oxidation, reduction, hydroxylation decarboxylation)
-phase II reactions (ie. methylation, glucuronidation, sulfation)
excretion of hormone metabolites
-occurs through the bile or urine
-in addition the target cell may internalize the hormone and degrade it
-the role of the kidney is eliminating hormone and its degradation products from the body is important because anything small and water soluble is excreted by kidney
once a hormone arrives at a target cell what can it do
-alter plasma membrane permeability of membrane potential by opening or closing ion channel
-stimulate synthesis of proteins or regulatory molecules
-activate or deactivate enzyme systems
-induce secretory activity
-stimulate mitosis
-stimulates cell division
what does action of hormones depend on
-their chemical nature
-lipid-soluble hormones and water-soluble hormones
