PSL-Week 3 Flashcards
What is definition of homeostasis?
the process of maintaining constant internal environement despite changing conditions
What is the difference between positive and negative feedback?
negative feedback works for homeostasis by turning off the stimuli when the system has returned to within the normal range but positive feedback is different because it acts for change, it reinforces effect of stimuli and can only be turned off by outside factors
What is an example of negative feedback in our endocrine system which involves the hypothalamus?
cortisol secretion, where when there is enough cortisol in body, cortisol itself will start suppressing the upstream processes like action of hypothalamus secreting CRH and stop release of cortisol so it doesn;t deviate from normal
What is an example of positive feedback loop?
even though it is rare feedback, it occurs during childbirth when baby drops lower in uterus, that will initiate labour and that will stimulate oxytocin which respond by causing uterine contractions and those contractions will push baby even lower in uterus which will cause cervical stretch and that process keeps going until baby is delivered which is the external force taht will stop this positive feedback lopp
Imagine a hormone is released in response to low blood pressure and acts to reduce blood pressure, what is this example of?
positive feedback because the response is reinforcing the change of low blood pressure which is moving away from homeostasis so it is reinforcing new change which means it is positive feedback
Maintaining homeostasis isn’t possible without intercellular communication, what are the two types of communications that we have in our system?
local and long distance
What are three ways for local control type of intercellular communication
through gap junctions, by contact dependant where membrane protein bind membrane protein, and by autocrine where molecules move through interstitial fluid
Why are neuroendocrine/neurohormones distinct from neurotransmitters and hormones?
neuroendocrines are chemicals secreted by neurons but are secreted into bloodstream and act on its target as a hormone
What are the two types of long distance communication in our body and how do they differ?
the two types are our endocrine system and nervous system:
1- endocrine system is slower acting than nervous system since its hormones travel through bloodstream
2- endocrine system secrete hormones while nervous sytem secrete neurotransmitters which are chemicals
Differences between simple and complex reflexes?
simple reflezes are mediated either by nervous or endocrine system while complex are mediated by both and go through several integrating systems
What is difference between local change and systemic change?
in local change the repsonse due to stimulus is mediated by local cells close to area or repsonse
in systemic change the repsonse is mediated by cells that are further from teh area of stimuli
Stimuli has to be sensed to ilicit a response, so what sense these stimuli?
sensors in opur body can vary from being specialized cells or structures that can convert stimuli into electrical signal to being a cell membrane receptor or intracellular receptor
All are reflex pathways the same, where there is a signal, then interegating center, and then a response?
not quite, reflex systems can be as simple as having only an intergating system to ilicit teh reponse, but they can also become more complicated where there could be intergating center involved to release a hormone for example, but then that hormone will act on another cell to have it release another substance and then that susbstance, hormone for example, will go to target and then have a response
so reflex pathways can vary
What are some characteristics of hormones?
can be made in different places in body
made by cells in specific endocrine glands/tissues
transported using the blood
bind specific targets
can act on multiple tissues
alter activity of target cell
terminated by negative feedback
help with maintaining homeostasis or percipetate a change
What are the two classes of hormones?
Hydrophobic/lipophilic
Hydrophilic/lipophobic
What are characteristics of hydrophilic hormone?
get released by exocytosis, can travel freely in blood, cannot cross membrane freely, can be made in advance and stored
Whata re examples of hydrophilic hormones
peptide hormones, protein hormones, and catecholamines
What are chractersitics of hydrophbic hormones?
are released by diffusion from the cell cytoseol, can cross plasma membrane without help, cannot be made in advance and stored as they can cross freely, boudn by carrier proteins in blood to be get transported as it si hydrophobic
What are examples of hydrophobic hormones
steroid hormones and thyrpid hormones
What are the three main types of hormones based on tehir biochemical properties?
peptide/protein- made from 3 or more amino acids
steroid- made from cortisol
amine- made from single amino acid type
What are some of the distinct features of peptie hormones?
they ahve short life span in plasma and can bind membrane receptoires
How are the three types of hormones different?
steroid are different from amine and peptide because they are made form cortisol while amine and peptide are made from amino acids, steroid are also trasnported using transport proteins while amine and peptide can mix easily with blood plasma
What is difference between preporhormone, prohormone, and homrone of the peptide hormones?
preprohormone is the initial peptide sewuence that is sequenced and released by ribosome
prohormone is the preprohormone after it loses teh signal sequence which happens when preprohormone makes its way to ER as that is purpose of the signal sequence
hormone is the final product that gets released and the type of hormone that gets released from that prohormone depends on protolytic processing enzymes
What is distinct features of steroid hormones?
they are all made from same molecules, the cholestrol, so all of them have teh same backbone but end up as different hormones because of the enzymatic acivity of teh cell it is in and teh cells that make steroid hormones have large amount opf Smooth ER since that is where tehy get synthesized, and this type of hormone can act on cytosol and nucleus receptores and some plasma membrane receptores
Insulin is degraded in body extremly quickly and is difficult to measure because of this, how else could we indirectly measure insulin release?
by measuring the C-peptide levels because the proinsulin consist of insulin and C-peptide before it gets cleaved so knowing C-peptide amounts will correpsond to insulin amount as well
What makes amine hormones different from peptide hormones?
they are made from either of the two amino acids, tryptophan or tyrosine
What is a type of amine hormone that is tryptophan derivative?
metatonin which can behave as peptide or steroid depending on receptor and its target and also known as darkness hromone because it is secreted at night by pineal gland and it is to govern the biological clock
What are two types of amine hormones that are tyrosine derivatives?
catecholamines which behave like peptides and are neurohormones that are made in adrenal medulla
thyroid hormones which behave like steroid
How do stimuli trigger hormone release?
using intracellular pathways such as:
changing membrane potential
increasing cystolic Ca
changing enzymatic activity
increasing transporr of hormone subtrate into cell
altering transcription of genes coding for hormones
promoting survival and growth
How does glucose stimulate release of insulin?
as blood sugar increase, the receptor in pancriatic beta cells called GLUT2 will open by binding glucose and let glucose in
the intake of glucose will increase ATP/ADP ration because of glucokinase and this increasing ATP will block K channels and build up of K will depolarize teh cell and open Ca voltge gated channels
entering of Ca into cell will signal exosytosis of insulin vesicles and release insulin
Sulfonylurea blocks K atp channels, what affect could this have?
enhance insulin secretion
Which is the actual pituitary gland that secrete hormones, the anterior or the posterior?
the anterior pituitary gland is teh atucal gland that secrete hormones while the posterior is only used a storage for hormones send from hypothalamus and then transport tehm to appropriate target
What part fo teh endocrine system is responsible for teh release of the trophic hormones which are in control of inhibiting and releasing of other hormones?
the hypothalamus
What are the three types of interactive effects that are experienced by cells due to being sensitive for more than one hormone?
1- synergetic effect: hormones act together for greater effect, add up their affect
2- permissive effect: one hormone enhances the target’s repsonse to second hormones
3- antagonistic effects: one hormone opposes action of another
What is teh general idea of how hormones signal?
they bind receptor, change receptor’s conformation and activity, changing in hormone’s conformation and activity alters activity of intercellular pathways which acn end up in chaning synthesisi of target proteins and or modifying existing target proteins
What are teh characteristics shared by receptores?
are made by large proteins, comes from families of proteins, have variable number of target cells, can be activated and inhibited, can be found in membrane, cytoplasm, and nucleus, and they can be saturated
Hormone A binds receptor B which causes response C. The [ ] of hormone A doubles in body casuing doubling in response C. The [ ] doubles again for hormone A, but there was no change in response C. What could’ve happened?
receptor B was saturated
What are teh two main types of receptores?
intracellular receptores and plasma membrane receptores
What are the differences between intracellular receptores and plasma membrane receptores?
intracellular bind lipid solubel hormones, are found in cytosol and in nucleus so they can directly alter gene trasncription while plasma membrane receptores are G protein couples receptores, receptor enzyme receptores, receptor channels, and intergin receptores
How does the intracellular receptores bind lipophilic hormone and cause change?
the lipophilic hormone can diffuse directly into cell and eitehr bidn the cyctolic receptor or diffuse into nucleus and bind nuclear receptor, but in the end will form a hormone receptor complex that ahs specific DNA sequence which will allow it to bind hormone receptor element in DNA and then cause transcription of whatever it is needed
How does Gs coupled receptores activate adenylyl cyclase?
signal binding the G protein complex will activate G protein and alpha subunit will convert GDP to GTP which turns on the adenylyl cyclase and that converts ATP into cAMP which activated protein kinase A and then protein Kinase A will phosphorylate other proteins to lead teh cellular response
How does Gq of the GPCR activate phospholipase C?
signal bind GPCR to activate G protein and activated G protein will activate phospholipase C which is amplifier enzyme and then PL-C converts menbrane phospholipid to DAG that remains in membrane and also convert membrane phospholipid to IP3 which diffuse into cytoplasm, and then DAG activate protein kinase PK-C that phosphorylate proteins and IP3 causes release of Ca from organnels to create Ca signal
How do Galpha i inactivate adenylyl cyclase?
the inhibitory regulatory G protein will be activated by Ri which cause it to inhibit adenylyl cycclase so it doesn’t convert ATP into cAMP
How does epinephrine binding alpha receptor on intestinal blood vessels instead of beta 2 receptores like in skeletal muscle blod vessel affect its activity?
epinephrine binding alpha receptor on intestinal blood vessels constrict the vessel
epinephrine binding beta 2 receptor on skeletal muscle blood vessel cause it to dilate
That is because alpha 2 receptor has Gi protein coupled recetor so it inhibits the adenylyl cyclase while beta receptores have Gs coupled protein receptor so they activate adenylyl cyclase
What are some ways to modulate signalling?
degrading hormones, up/down regulating receptor, receptor desentization, breaking down the second messengers, modifying any components in pathway
How are receptores on the membrane downregulated?
one way is by endocytosis of the receptores, where the receptors ligan migrates to clathrin ciated pit and get endocytosed, then the vesicle loses the clathrin coat which leads to receptor and ligand seperating, the ligand go to lysosome to get degraded while the recetores stay in trasnport vesicle and move to cell membrane to get exocytosed when needed.
How is the most rapid intracellular response of all receptores activated?
teh fasted intracellular response is reached by receptor channels where binding of receptor cause it to become an open channel and let vthe appropriate ions flow like Na and K to depolarize cell
