Physiological Aspects of Appetite and Body Weight Lecture 2 PDF

Lecture 2: Physiological Aspects of Appetite and Body Weight Adult Weight Management, CLNP 413. Collegeof Applied Medical Sciences, Clinical NutritionSciencesProgram Overview • What is food? • Neural and hormonal control of appetite. • Body weight regulation: set point theory. What is Food? H...

Lecture 2: Physiological Aspects of Appetite and Body Weight Adult Weight Management, CLNP 413. Collegeof Applied Medical Sciences, Clinical NutritionSciencesProgram Overview • What is food? • Neural and hormonal control of appetite. • Body weight regulation: set point theory. What is Food? Here • Food is any substance consumed by an organism for nutritional support. • The decision on what to eat is complex! • “Normal” or “desirable” is determined by: ‫األشياء اللي تأثر على اختيارنا للطعام‬ – Religious or cultural rules – Experience – Allergies and intolerances ‫عدم االرتياح ألكل هذا الطعام املحدد‬ – Availability – Education levelAwarnes – Emotional associations Eating disorders Hunger • It is usually an unpleasant sensation that compels a person to seek food and eat it. • It is a physiological condition associated with the stomach's contraction (demand for energy). ‫تكون االنقباضات قوية وتحدث لفترة و‬ .‫بمثابة وسيلة للمعدة لالنتقال إلى مرحلة الراحة‬ • The contractions are forceful and occur for a period and the act as a way for the stomach to pass into a resting stage. • Hunger conditions that subside with eating will reappear ‫تهدأ مع األكل سوف تظهر مرة أخرى‬ later with greater intensity. .‫في وقت الحق وبكثافة أكبر‬ • Symptoms: stomach contractions, weakness, irritability, occasional headache. Satiety • It is a sensation accompanying the satisfaction of the desire for food after eating. • Satiety is the other side of hunger and appetite. • Satiety is the physiological and psychological experience of “fullness” after eating and drinking. • While hunger builds up slowly, satiety occurs rapidly. Phases of GI Control • Cephalic • Gastric • Intestinal CEPHALIC PHASE CEPHALIC PHASE • The cephalic phase of gastric secretion is initiated by the sight, smell, thought or taste of food. • Neurological signals originate from the cerebral cortex and in the appetite centers of the amygdala and hypothalamus. • This enhanced secretory activity is a conditioned reflex. • This phase of secretion normally accounts for about 20 percent of the gastric secretion associated with eating a meal. Taste • Signaled by taste cells – Receptor cells (taste buds) with microvilli that interact with fluid in the mouth – Supporting cell sends a signal through nerve fibers to the brain • Taste cells present in the tongue, palate, pharynx, larynx, and sometimes cheeks – The tongue perceives salt, sweet, bitter, and sour – The palate is more receptive to sour and bitter • Small chemical changes affect the ability to bind with receptor cells – “After taste” ‫إن الطعم يتغير بعد تناول اللحم خصوصا عند املرأة الحامل‬ • Rapid turnover decreases with age Brain Control ‫نواة مقوسة‬ Protein + protiens • Hypothalamus (arcuate nucleus) integrates information from tissues • Sends signal to start or stop eating – Ex: Neuropeptide Y INTESTINAL PHASE • The intestinal phase is a stage in which the duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes. • 5-10% of gastric secretion occurs during this phase. • The duodenum initially enhances gastric secretion, but soon inhibits it. GASTRIC PHASE • The gastric phase is a period in which swallowed food and semidigested protein (peptides and amino acids) activate gastric activity • 50-60% of total gastric acid secretion occurs during this phase. ‫ عن طريق التمدد‬:‫يحفز الطعام املتناول نشاط املعدة بطريقتني‬ .‫املعدة وعن طريق محتويات املعدة تحفيز املستقبالت في معدة‬ • Ingested food stimulates gastric activity in two ways: by stretching the stomach and by gastric contents stimulating receptors in the ،‫منعكس قصير يتوسط من خالل الضفيرة العصبية العضلية املعوية‬ stomach. ‫ويتوسط منعكس طويل من خاللها األعصاب املبهمة وجذع الدماغ‬ • Stretch activates two reflexes: a short reflex mediated through the myenteric nerve plexus, and a long reflex mediated through the vagus nerves and brainstem Ghrelin (Appetite Stimulating Hormone) • Ghrelin produced by the stomach and small amounts also released by the small intestine increases just before a meal. • Stimulates gastric motility and acid secretion • Increases with weight loss decrease with weight gain • Ghrelin levels increase after dieting, which may explain why diet-induced weight loss can be challenging to maintain. Leptin (Appetite-Suppressing Hormone) • Hormones secretedby adipose tissue • Signals satiety to the hypothalamus • When fat cells produce a high level of leptin a message will be transmitted to the hypothalamus and appetite will be inhibited (satiation). • An increase in adipose tissue mass with weight gain results in a significant increase in circulating leptin. • Obesity – Leptin resistance – Generates oxidative stress • Leptin circulates in the blood and acts on the brain to regulate food intake. • When fat mass falls, plasma leptin concentrations fall too, stimulating appetite and suppressing energy expenditure until fat mass is restored. • When fat mass increases, leptin is then secreted and circulates through the body, eventually activating leptin receptors in the “arcuate nucleus” of the hypothalamus. • This system enables mammalian organisms to maintain optimal levels of stored energy (fat) under a wide range of environmental conditions. ‫• يدور اللبتني في الدم ويعمل على الدماغ لتنظيم تناول الطعام‪.‬‬ ‫• عندما تنخفض كتلة الدهون‪ ،‬ينخفض تركيز هرمون الليبتني في البالزما ً‬ ‫أيضا‪ ،‬مما يحفز الشهية‬ ‫وقمع إنفاق الطاقة حتى يتم استعادة كتلة الدهون‪.‬‬ ‫• عندما تزداد كتلة الدهون‪ ،‬يتم إفراز هرمون الليبتني ويدور عبره‬ ‫الجسم‪ ،‬مما يؤدي في النهاية إلى تنشيط مستقبالت اللبتني في "النواة املقوسة" للجسم‬ ‫تحت املهاد‪.‬‬ ‫• يم ّكن هذا النظام الكائنات الثديية من الحفاظ على املستويات املثلى من مخزونها‬ ‫الطاقة )الدهون( في ظل مجموعة واسعة من الظروف البيئية‪.‬‬ Leptin's effects Because of a gene defect, the boy doesn't make leptin, but treatment with the hormone, begun when he was 3.5 years old (top), brought his weight down to normal levels, as shown at age 8. Insulin (Appetite-suppressing hormone) • It is a hormone secreted by the beta cells in the pancreas. • A higher level of insulin temporarily suppresses appetite. • It aims to transform the consumed food (metabolism of carbohydrates and fats) into glucose, the simple sugar on which the body can run, and then to move the glucose into body cells. Peptide YY (PYY) (Appetite-Suppressing Hormone) • It is secreted from the endocrine L cells of the small and large bowel and released into circulation after meals. • It acts as an appetite suppressant that cancels out Ghrelin’s appetite-stimulating effects. Set-point theory ‫ثبات الوزن‬ ‫تنص على أن هناكطريقة املكافحة البيولوجية في البشر‬ .‫الذي ينظم الوزن بشكل فعال نحو الوزن املحدد مسبقا لكل فرد‬ • Set point theory states that there is a biological control method in humans that actively regulates weight towards a predetermined set weight for each individual. • This may occur through the regulation of energy intake (e.g., via increased or decreased appetite) or energy expenditure (e.g., via reduced metabolism). ‫قد يحدث هذا من خالل‬ ‫ عبر زيادة أو نقصان الشهية( أو‬،‫تنظيم استهالك الطاقة )على سبيل املثال‬ .(‫االس ِت ْقالب‬ ‫ عن طريق خفض‬،‫استهالك الطاقة )على سبيل املثال‬ ْ Required Reading: Zhang et al. Appetite controland energy balance regulation in the modern world: reward-driven brain overrides repletion signals. International Journal of Obesity, 2009 References • Advanced Nutrition: Macronutrients, Micronutrients, and Metabolism by Berdanier and Zempleni. CRC Press. 2009 • Control of Food Intake and Appetite by Hussain, Silva, and Bloom. Modern Nutrition in Health and Disease, 11th edition • Vander’s Human Physiology: The Mechanisms of Body Function by Widmaier, Raff, and Strang, 12th edition