CSB325 Lecture 8 Notes

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Cell and Systems Biology
David Lovejoy

CSB325 Lecture 8 Energy and Stress Slide 1 Energy production in terms of food and digestion is a PSNS effect You have money coming in and you are putting it into the bank The SNS and the stress system is taking the money out of the bank and spending it to deal with certain stresses Slide 3Do not memorize the biochemistry You should know the key components that are coming in and knowing that they all eventually feed into the citric acid cycle If there is a lack of glucose in the diet then glucose can be made by gluconeogenesis In most cases if there is a lack of glucose in the diet then a number of organisms will utilize fatty acids as an energy sourceSlide 4 GH is produced by the anterior lobe of the pituitarySomatotrophs have two effective controls that come from the hypothalamus Somatotrophs are either under positive control or negative control When there is a positive control coming in from the hypothalamus then it induces the somatotrophs to synthesize and release GH When there is a negative control then it shuts it off GH is released in a pulsatile fashion throughout the day It generally follows the circadian rhythm It also changes concentrations to a certain degree during a period of quiescence It is most active in the quiescent period When you are sleeping GH is more preferentially released There is a certain amount of GH that is released after feeding GHRH is the primary hormone that causes the release of GH GHRH is released from the arcuate nucleus in the hypothalamus into the median eminence into the portal system where it makes its way into the adenohypophysis anterior pituitary and stimulates the somatotrophsPACAP is another primary hormone and is very closely related to GHRH GHRH and PACAP are paralogs to each other due to gene duplication In mammals GHRH is the fundamental GHreleasing factor In fishes PACAP is the fundamental GHreleasing factor They are both effective Depending upon the physiological need one or both can be released GnRH dopamine and TRH are modulatory factorsSRIF somatostatin is the key releasing inhibitory factor that is acting in the arcuate nucleus which is acting to inhibit GH As GHRH or PACAP is released then GH increases As GH goes high then SRIF brings GH back down The normal pulse that occurs throughout the day can be explained primarily by those two hormones GHRH or PACAP are positive hormone releasing factors SRIF is an inhibitory factorSerotonin norepinephrine and glutamate are modulatory factorsGH is released into the blood stream The primary target of GH from an endocrine point of view is the liver The liver will respond in an endocrine fashion to release two principle peptides IGFI and IGFII IGFI and IGFII are paralogs of insulin These will feedback to further inhibit the release of GH IGFI and IGFII will also act on a number of tissues of the body to stimulate growth There will be a direct action on growth and maintenance by GH and then a secondary action by IGFI and IGFII There are other modulatory factors From the stomach one of the principle endocrine feedback mechanisms is ghrelin Ghrelin has a positive feedback on the somatotrophs to release more GH During feeding when the stomach is active and starting to digest ghrelin tells the somatotrophs that more GH is required Leptin is one of the feedback hormones from fat cells Leptin acts to further stimulate a number of hormones directly within the brain NPY CCK and bombesin CCK and bombesin are paralogs of each other This will further act to modulate the release of GHRH or PACAPGhrelin is acting directly on the somatotrophs Leptin is acting indirectly through its actions on a series of hormones in the arcuate nucleusWithin the somatotrophs themselves activin causes a shortloop autocrine positive feedback As the somatotrophs become active it releases activin to the surrounding cells and then it feeds back to further stimulate the release of GH GH itself will also do the same thingGH is going to be released whenever there is a need for tissue growthSlide 5 GH has a number of effects You can ignore the signal transduction pathways You should know what happens at the organismal level GH acts on several types of tissues GH is also associated with amino acid transport and muscle development in skeletal muscle GH is acting on the storage components of the denser tissues eg bone mass cartilage and skeletal muscle Slide 6 PSNS Digestion growth maintenance Storing energy Nonstress related component SNS Stress related component Acts through a series of nerve systems but primarily through the vagus nerveThe two systems are in opposition to each other and they will inhibit each other If the PSNS is active enough then it will inhibit the SNS The SNS will act to inhibit the PSNS It depends on what the needs of
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