PBL - Obesity
Physiology of Appetite and Hunger and Stuff
Definitions in Physiology
Hunger = a craving for food, rhythmical contractions of the stomach, restlessness. A desire to search for adequate food supply
Appetite = a desire for food, usually of a particular type, and quality of food.
Satiety = success in achieving hunger and appetite.
Each of these is associated with specific centres in the brain, esp. the hypothalamus, which responds to environmental and cultural factors as well as neural, chemical and endocrine messengers.
There are two types of neurons in the arcuate nuclei of the hypothalamus that have really long complicated names and descriptions. POMC decreases food intake, increases energy expenditure. NPY-AGRP does the reverse. These are the major targets for appetite-regulating hormones such as leptin, insulin, CCK and grehlin.
Not Hungry:
Gastrointestinal filling: stretch receptors send inhibitory signals via the vagus nerve
Gastrointestial hormones that suppress hunger:
" CCK is released in response to fat in duodenum to stimulate gall bladder contractions, but also directly affects POMC.
" PYY is released mostly from ileum and colon, 1-2 hours after eating esp in response to fat.
" Insulin is released from beta-cells in the pancreas in the presence of glucose, and to some degree at food intake.
" GLP is released by intestines when filled with food, enhances insulin secretion from pancreas.
Leptin is a peptide hormone released from adipocytes that acts on POMCs and NPY-AgRP receptors as well as the pancreas re: insulin levels.
Hungry:
Grehlin is released from the fundus of the stomach in increasing amounts leading up to a meal. It stimulates NPY/AgRP receptors in the hypothalamus,
Appetite is also increased when blood levels of glucose, amino acids and fatty acids decrease.
Temperature also plays a role in hunger - when it's cold, we need more energy/food to keep warm. Temperature regulation occurs in the hypothalamus, so it's not too far for the to travel
Table 71-2 from guyton and hall summarises the neurotransmitters and hormones that influence feeding centres in the hypothalamus.
Anorexogenic:
-MSH, Leptin, Serotonin, Norepinephrine, CRH, Insulin, CCK, GLP, CART, PYY
Orexogenic:
NPY, AGRP, MCH, Orexin A + B, Endorphins, Galanin, Amino acids, Cortisol, Grehlin
refs:
Chapter 71 of Guyton and Hall - Dietary Balances; regulation of feeding obesity and starvation.
Wilcox, G "Food composition and its effect on human biology" - 21/9/2007 Monash MBBS 2042 Lecture
Saladin
Definitions in Physiology
Hunger = a craving for food, rhythmical contractions of the stomach, restlessness. A desire to search for adequate food supply
Appetite = a desire for food, usually of a particular type, and quality of food.
Satiety = success in achieving hunger and appetite.
Each of these is associated with specific centres in the brain, esp. the hypothalamus, which responds to environmental and cultural factors as well as neural, chemical and endocrine messengers.
There are two types of neurons in the arcuate nuclei of the hypothalamus that have really long complicated names and descriptions. POMC decreases food intake, increases energy expenditure. NPY-AGRP does the reverse. These are the major targets for appetite-regulating hormones such as leptin, insulin, CCK and grehlin.
Not Hungry:
Gastrointestinal filling: stretch receptors send inhibitory signals via the vagus nerve
Gastrointestial hormones that suppress hunger:
" CCK is released in response to fat in duodenum to stimulate gall bladder contractions, but also directly affects POMC.
" PYY is released mostly from ileum and colon, 1-2 hours after eating esp in response to fat.
" Insulin is released from beta-cells in the pancreas in the presence of glucose, and to some degree at food intake.
" GLP is released by intestines when filled with food, enhances insulin secretion from pancreas.
Leptin is a peptide hormone released from adipocytes that acts on POMCs and NPY-AgRP receptors as well as the pancreas re: insulin levels.
Hungry:
Grehlin is released from the fundus of the stomach in increasing amounts leading up to a meal. It stimulates NPY/AgRP receptors in the hypothalamus,
Appetite is also increased when blood levels of glucose, amino acids and fatty acids decrease.
Temperature also plays a role in hunger - when it's cold, we need more energy/food to keep warm. Temperature regulation occurs in the hypothalamus, so it's not too far for the to travel
Table 71-2 from guyton and hall summarises the neurotransmitters and hormones that influence feeding centres in the hypothalamus.
Anorexogenic:
-MSH, Leptin, Serotonin, Norepinephrine, CRH, Insulin, CCK, GLP, CART, PYY
Orexogenic:
NPY, AGRP, MCH, Orexin A + B, Endorphins, Galanin, Amino acids, Cortisol, Grehlin
refs:
Chapter 71 of Guyton and Hall - Dietary Balances; regulation of feeding obesity and starvation.
Wilcox, G "Food composition and its effect on human biology" - 21/9/2007 Monash MBBS 2042 Lecture
Saladin
posted by third year at
6:52 PM
1 Comments:
RECOMMENDATIONS
According to the Australian Clinical Practice Guidelines for the Management of Overweight and Obesity in Adults, surgery is the most effective treatment for severe obesity currently available. These guidelines advise that physicians should be aware of the following provisos issued by the US National Institutes of Health Consensus Development Conference Panel:
• Severely obese patients seeking therapy for the first time should be considered for treatment in a non-surgical program with integrated components of a dietary regimen, appropriate exercise, and behaviour modification and support. Surgery should be considered only if nonoperative measures for weight loss have failed.
• Bariatric surgery should be considered only for well-informed, motivated patients with acceptable operative risks.
• Candidates for surgical procedures should be selected after careful evaluation by a multi-disciplinary team with medical, surgical, psychiatric, and nutritional expertise.
• The operation should be performed by a surgeon who has substantial experience with the procedure and is working in a clinical setting with adequate support for all aspects of management and assessment.
• Lifelong medical surveillance after surgical therapy is essential.
These guidelines recommend that surgery is indicated for patients with a BMI greater than 40, or a BMI greater than 35 as well as serious medical comorbidities.
The effectiveness of bariatric surgery
• Results in greater overall weight loss than any other therapy many studies have demonstrated its long-term effectiveness
• One study has shown showed that surgery reduces the progression of and mortality from type 2 diabetes compared with non-surgically treated subjects
• In a recent meta-analysis, surgery has been shown to cause a mean reduction in BMI of 16.4 at one year, with reductions maintained at 13.3 in studies with a follow-up period of between nine months and seven years
• A preliminary analysis has shown that, despite the high cost of bariatric surgery, it is a cost-effective intervention for reducing diabetic medication costs over a five-year period
SURGICAL PROCEDURES
A variety of surgical procedures are used to treat obesity:
– Roux-en-Y gastric bypass (RYGB):
o involves creating a stomach pouch out of a small portion of the stomach and attaching it directly to the small intestine, bypassing a large part of the stomach and duodenum
o limits gastric capacity (stomach is physically smaller)
o causes mild malabsorption (fat absorption substantially reduced by avoiding the duodenum)
– Biliopancreatic bypass/diversion:
o combines limited gastroscopy with a long Roux limb intestinal bypass
o a larger portion of the stomach is left intact, including the pyloric valve. The duodenum is divided near this valve, and the small intestine divided as well.
the portion of the small intestine connected to large intestine is attached to the short duodenal segment next to the stomach
the remaining segment of the duodenum connected to the pancreas and gallbladder is attached to this limb closer to the large intestine
the ‘common channel’ is where contents from these two segments mix and ‘dumps’ into the large intestine
o restricts both food intake and the amount of calories and nutrients the body absorbs
– Laparoscopic adjustable gastric band:
o a device is fitted around the cardia of the stomach, restricting its capacity
o the band is adjustable to allow tailoring of the gastric pouch size to an individual’s need, and weight is lost through meal volume restriction does not interfere with the normal digestive process
o by far the most commonly utilised technique, making up approximately 95% of all procedures
– Vertically banded gastroplasty (gastric banding):
o performed more commonly in the past
o involves stapling the upper stomach to reduce gastric capacity
Bariatric surgery procedures: advantages and disadvantages (TABLE THAT DIDN'T COPY THROUGH)
From: http://www.health.gov.au/internet/wcms/Publishing.nsf/Content/obesityguidelines-guidelines-adults.htm/$FILE/adults_part9.pdf
RISKS
• In patients with acceptable operative risks, mortality as a consequence of bariatric surgery is low
• Bariatric surgery is, however, often associated with impaired absorption of micronutrients, which requires lifelong monitoring and often folate or vitamin B supplementation
LIPECTOMY
• With very rare exceptions, not a treatment for obesity per se
• Recent studies in animals suggest that lipectomy may have undesirable side effects
• Further research is needed to determine the effectiveness and safety of this surgical approach
SOURCES
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19500.htm, accessed 24/2/08.
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19268.htm, accessed 24/2/08.
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19497.htm, accessed 24/2/08.
http://www.nlm.nih.gov/medlineplus/ency/imagepages/19498.htm, accessed 24/2/08.
Snow V, Barry P, Fitterman N, Qaseem A, Weiss K. Pharmacologic and surgical management of obesity in primary care: a clinical practice guideline from the American College of Physicians. Ann Intern Med 2005 Apr 5;142(7):I55.
NHMRC Clinical Practice Guidelines for the Management of Overweight and Obesity in Adults, Part 9 – Treatment: Surgery; http://www.health.gov.au/internet/wcms/Publishing.nsf/Content/obesityguidelines-guidelines-adults.htm/$FILE/adults_part9.pdf, accessed 24/2/08.
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third year, At
February 24, 2008 at 3:12 PM
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