DOC PREVIEW
USC BISC 307L - Pancreas
Type Lecture Note
Pages 8

This preview shows page 1-2-3 out of 8 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 8 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 8 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 8 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 8 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

BISC 307L 2nd Edition Lecture 15 Current LectureMetabolism and Metabolic FuelThere are two states of the body:1. you have just eaten and food is being absorbed. This is the absorptive/fed state, when there is an excess of fuel flooding blood. Also known as the anabolic state2. Post absorptive/fasted state. You are not eating, and catabolic reactions are predominating. Flow of Moleculesthrough MetabolismFood molecules enterthe body as three majormacromolecules: fats,carbs, and protein. Thetubs immediatelyunderneath themrepresent theimmediately availablepools in the bloodplasma of free fattyacids, glucose, andamino acids. The pools at the bottomare what the body cellsuse for their needs, and just above them are the storage forms of these fuel molecules, with fatty acids stored as fat, glucose stored as glycogen, and the amino acids stored in the body protein (protein stores in the body are all the cells that have protein in them - mainly skeletal muscle, which can be broken down when necessary to restore the protein pool.This doesn’t greatly reduce their function – even if you got rid of half of the protein in your skeletal muscle, you would be weaker but still functional).Connecting the storage pool with the immediately available pools are the systems of reactions/processes that breaks one down into another. -Lipolysis breaks down fat to form free fatty acids. Free fatty acids and excess glucose can also be esterified into new fats through lipogenesis. -Glycogen(carbohydrate stores) is replenished by glycogenesis from the glucose pool, mostly down in the liver. And glycogen is broken down by glycogenolysis to break glucose. -Amino acids are broken down by proteolysis, which isn’t shown. Other lateral pipes exist, for example gluconeogenesis; glucose can be synthesized from amino acids. If you take the amino group off amino acids, they look like carbohydrates. The liver can transmogrify those amino acids and convert them into glucose (gluconeogenesis). For normal metabolism in most tissues, which is powered by glucose or fatty acids, any excess nutrients are recycled back into their storage forms. The red lines in the glucose pool represent the levels of normal plasma glucose. The pipe coming out of the left can only take glucose out ofthe pool when glucose levels are above the lower pipeline level. You can also see that the brain metabolism is privileged, and it is at a lower pipeline level, meaning it can continue drawing glucose even after levels have fallen down below the normal range. This is because brain metabolism is so important – it depends on glucose more than any other tissue. CNS tissues are highly metabolically active, and they do not store any form of energy – there are no glycogen or fats or proteins up there for fuel. Since it has such a high metabolic rate, it is completely dependent on an adequate supply of glucose. Control of Appetite and SatietySatiety is the opposite ofhunger. This is one of the mostimportant things we do –ensure there is adequate fuelavailability to power our entire metabolism. Therefore, the control of appetite is highly complicated. Control resides in several nuclei of the hypothalamus (the box is meant to represent the hypothalamic nuclei). In those nuclei, there are neurons that are characterized by their release of principal NT’s of three types: 1. Neuropeptide Y, which directly stimulates hunger and eating. 2. Melanocortin peptides, which decrease hunger, or stimulate satiety. They release various melanocortin peptides. What is melanocortin? It is a family of peptides that are posttranslationally processed from POMC. POMC is synthesized, processed, and cleaved. The products are hormones or NT’s – one important one being ACTH. - the most important melanocortin peptide in the control of satiety is the alpha MSH, or melanocyte stimulating hormone. Alpha MSH released from these neurons increases satiety. 3. agouti-related protein, which stimulates hunger. Agouti is a signaling peptide that controls skin color in infants. This has a homologous structure to that protein, hence the name. It antagonizes the effects of alpha MSH. Whether you feel hungry or not is a balance between stimulatory and inhibitory influences.These feeding and satiety centers in the hypothalamus are subject to complex regulation due to hormone mechanisms. The hormones come from adipocyte/fat cells, which release the four things on the upper left and leptin. The hormones at the bottom of the figure are the gut hormones, or gastrointestinal hormones: 1. Ghrelin – a hungerstimulating hormone. This is acirculating hormone that isproduced by the stomachwhen it is empty. It works bystimulating Neuropeptide Yand Agouti-related proteinsecreting neurons in thehypothalamus. But when youeat a meal, ghrelin secretiondrops significantly. -interesting fact:people who are overweighthave stomachs that have beenhabituated to being overfilled. So even though their stomachs are filled they still secreteGhrelin. This may be part of the reason why people who lose weight, especially rapidly, have a hard time keeping it off.The two hormones on the bottom right inhibit hunger. They are both from the intestine and exert their effect by stimulating the neurons that decrease hunger (melanocortin peptides) and by inhibiting neuropeptide Y neurons, which secrete NYY, which stimulates hunger. They are:2. CKK(cholecystokinin) which is secreted by the intestine after it is full after a meal. The intestine also secretes the other hormone - not necessarily when it is full of food, but when it is full of food from a high calorie meal. Secretion of 3. polypeptide YY is correlated with the caloric content of the meal, and not volume, whereas CCK is more related to volume. An intestine full of high calorie foods (like fat), will cause PYY to activate and decrease hunger.Ghrelin and the two hormones on the right are antagonistic, but they work on different time scales. Ghrelin and CCK are secreted in the same time span and exert their effects quickly, so they are truly antagonistic. However, PYY creates a much more long term effect. So PYY and CCK operate on different time scales. PYY on hours (12 hours) and CCK on minutes. At the very top of our diagram we have adipocytes. The first hormone in this whole figure that was discovered was leptin. Leptin is a hunger-inhibiting hormone released by adipocytes. It stimulates satiety and decreases hunger by stimulating alpha MSH and inhibiting


View Full Document

USC BISC 307L - Pancreas

Documents in this Course
Load more
Download Pancreas
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Pancreas and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Pancreas 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?