endocrine 1.2 Flashcards
stretch reflex have different reflex arcs - patellar tendon*
stimulus on tendon
muscle spindle stretch and fire in quad
afferent path : AP travels through sensory neuron
sensory neuron synapses in spinal cord
2 different efferent paths : somatic motor neuron and interneuron
somatic motor neuron goes to quad and fires
interneuron inhibits somatic motor neuron going to hamstring (relaxes, reciprocal inhibition)
endocrine secretion regulation : negative feedback between 2 hormones
A produces hormone A which acts on tissue B that produces hormone b and stops A from making hormone A
negative feedback - between a hormone and a metabolite
tissue makes a hormone that increase the amount of compound which can be a metabolite, once the metabolite increases its going to stop the production of the original hormone
negative feedback between antagonistic pairs of hormones
2 hormones that are going to work with a compound or metabolite
eg. release glucagon when sugar level low to increase
release insulin when sugar levels high to decrease
positive feedforward
increase in estrogen cause positive feedforward to FSH and LH
hormone transport in blood - water solubility
most peptide and all catecholamine hormones are water-soluble
-dissolve in plasma
- *steroid and thyroid hormones**
- bound to large proteins so they are not water soluble
total hormone concentration in plasma
= free hormones + bound hormones
free hormones
only free hormones can diffuse out of capillaries and encounter its target cells
-free hormones are what we look at in tests
when hormones are attached to large proteins in the blood they have to dissolve all to enter into a cell
peptides and catecholamimes
- free (unbound) in plasma
- receptors on plasma membrane
signaling mechanisms :
most common signaling mechanisms
second messengers -cAMP, Ca, IP3
enzyme activation by receptor (JAK)
intrinsic enzymatic activity of receptor
steroid and thyroid hormones
protein bound in plasma
receptor in intracellular
signaling mechanisms :
-intracellular receptors directly alter gene transcription
hormones concentration in the plasma depends on
- its rate of secretion by the endocrine gland
- its rate of removal from the blood (metabolic transformation or excretion)
what happens after the hormone acts on the target tissue
we clear the hormone
can have dangerous effects from prolonged exposure to target tissue if we don’t clear
removal by excretion or metabolic transformation
- by the liver, kidneys or cells it acts upon
- enzymes in the blood and tissues rapidly breakdown catecholamine and peptide hormones
→ free vs protein-bound hormones (protein-bound hormones hard to get rid of)
-metabolism of a hormone can activate it instead of inactivating it
released hormone secreted gets to blood then…
- excreted in urine/feces
- inactivated by metabolism
- bind to receptor and produce a cellular response
- activated by metabolism
hormone receptors
- in order for a response to a hormone, need the SPECIFIC receptors to be present on or in target cells
- peptide hormones and catecholamines receptors on plasma membrane of target cells
- steroid and thyroid hormone receptors locateed inside the target cells
regulation of hormone receptors
upregulate : increase number of a hormones receptors in a cell
→ because of prolonged exposure to low concentration of target tissue, we want to increase the sensitivity to the hormone
down-regulate : decrease the number of a hormones receptors in a cell
→ help prevent over stimulation
permissiveness
your hormones can regulate its own receptors up and down regulation, but it can also up or down regulate another hormones receptor
- thyroid hormone increases the number of beta-adrenergic receptors on the cell, which epinephrine attaches to
- up-regulating so they become more sensitive to epinephrine
effects of peptide hormones and catecholamines - activated receptor can directly influence..
- enzyme activity that is part of the receptor
- activity of cytoplasmic janus kinases associated with the receptor
- G proteins coupled in the plasma membrane to effector protein-ion channels and enzymes that generate 2nd messengers such as cAMP and Ca2+
can exert both rapid and slower actions on the same target cell
enzyme activity that is part of the receptor
Enzyme activity is part of the receptor itself
first messenger binds to a specific receptor, has a conformational change to receptor so enymatic side is activated
- results in phosphorylation of the receptor because it gets phosphate group from ATP
- makes phosphotyrosine and acts as a docking site for cytoplasmic proteins
- docking proteins climb behind to activate cells response to signalling pathway
activity of cytoplasmic janus kinases associated with the receptor
janus kinase attached to receptor but not on it
- first messenger (peptide hormone or catacolamine) makes conformational change to receptor
- activation of janus kinase
- will phosphorylate different target proteins by taking phosphate from ATP and adding it to proteins and activating them
- results in a protein + ADP that carries out the cell’s response
G proteins
G proteins coupled in the plasma membrane to effector proteins-ion channels and enzymes that generate 2nd messengers such as cAMP and Ca2+
-G proteins (alpha, beta, gamma) activate when first messenger binds
- Alpha leaves when activated and binds to GTP lined to plasma membrane
- leads to different events towards cell response such as secondary mesengers and change in membrane potential
G proteins
G proteins coupled in the plasma membrane to effector proteins-ion channels and enzymes that generate 2nd messengers such as cAMP and Ca2+
-G proteins (alpha, beta, gamma) activate when first messenger binds
- Alpha leaves when activated and binds to GTP lined to plasma membrane
- leads to different events towards cell response such as secondary mesengers and change in membrane potential
effects of steroid and thyroid hormone
- leads to activation or inhibition of the transcription of particular genes
- when we change the concentration of proteins, we see an activation or inhibition of particular processes the cell carries out or a change in the cell’s rate of protein secretion
- receptors can be in nucleus or cytosol (will move to the nucleus)
- binds to DNA to do gene transcription