1215 Week 22

1215 Week 22

1. Lecture 1

   • Carbohydrate Digestion
     • accounts for about 50% of calorie intake
     • polysaccharides, disaccharides, monosaccharides
     • enzymes that breakdown carbohydrates - salivary/pancreatic amylase, brush border enzymes
     • there is no breakdown in the stomach and only monosaccharides can be absorbed
     • brush border enzymes: maltase - maltose to 2 glucose, sucrase - sucrose to glucose and fructose, lactase - lactose to glucose and galactase
     • monosaccharides are absorbed by facilitated diffusion and cotransport
     • facilitated diffusion moves fructose across the membrane using GLUT5
     • cotransport moves glucose and galactose across the membrane using sodium ions
     • simple sugars cross the basolateral membrane via GLUT2 facilitated diffusion and monosaccharides by diffusion
   • Protein/Amino Acid Digestion
     • proteins are digested by: endopeptidases - split polypeptides at interior bonds, exopeptidases - cleave terminal amino acids
     • protein digestion starts in the stomach - 15%
     • protein digestion continues in the duodenum - trysin, chymotrysin, elastase, carboxypeptidase
     • zymogens are the inactive precursor to the active enzyme
     • amino acids are transported via sodium ion cotransport, peptides by hydrogen ion cotransport
     • peptides are brokendown iside the cell and amino acids transported across the basolateral membrane into the capillaries
   • Fat Digestion
     • triglycerides, phopholipids and cholesterol are digested by lingual, pancreatic and gastric lipases
     • lipases remove 2 fatty acids from triglycerides
     • lipases are water soluble and digestion requires bile salts to form an emulsion in the duodenum by making micelles so they can't be absorbed
     • fats diffuse into enterocytes and in the ER are made into triglycerides which are packaged into cylomicrons and leave the cell via exocytosis into lacteals
   • Hunger and Satiety
     • peripheral satiety signals originate in the gut and travel via the vagus nerve to the nTS in the brain stem: activation of stretch receptors, chemical content of the gut, peptides/hormones released during eating (cholecystokinin and peptide YY)
     • long term signals include insulin and leptin ( based on adipose levels)
     • anorexigenic - switches off eating
     • peripheral hunger signals come the GI and occurs about 2-4 hours after emptying - examples include ghrelin and neuropeptide Y
     • orexigenic - switches on hunger

2. Lecture 2

   • Starvation
     • 870 million people are chronically malnurished worldwide - developing 15%, developed 1.4%
     • in the UK there are 5 million people in food poverty, risk groups - elderly, chronically ill and low income families
     • it takes 63 days to die of starvation
     • carbohydrates run out in a week and then protein and fat breakdown occurs
     • there is a 65-80% decrease in gluconeogenesis and an increase in ketone bodies (provides 2/3 of the brain's energy)
     • proteins needed for cell function are the last to be depleted and when 50% of all proteins are lost you can no longer survive
     • consequences - FFA to ketone bodies, vitamin deficiences, metabolic acidosis, increased ventilation, muscle atrophy, increased ammonium secretion, risk of hypothermia, weak and apathetic, confusion and cognitive deficits, decreased ability to work, respiratory function, HR, CO and blood volume
   • Obesity
     • there are multiple overlapping pathways in the gut-brain axis
     • there are no satiety or feeding centres in the hypothalamus
     • obesity is on the rise in the UK
     • physiological consequences - increased O2 cost of exercise, cardio-respiratory response to exercise, ventilatory work, decreased maximum response to external exercise, cardiovascular reserve, VC and FRC, hypoxemia at rest and pulmonary vascular resistance, increased weight circumfrence
     • pathophysiological consequences: muscloskeletal system - osteoarthritis, lower back pain
     • pathophysiological consequences: cardiovascular system - high BP, increased risk of heart disease, stroke and deep vein thrombosis
     • pathophysiological consequences: metabolic and endocrine systems - high risk of developing type 2 diabetes
     • pathophysiological consequences: cancers, liver and gastrointestinal disease
     • pathophysiological consequences: reproductive and urilogical systems - disturbed periods, erectile dysfunction, polycystic ovaries, infertility, incontinence
     • pathophysiological consequences: respiratory system - sleep apnea
     • pathophysiological consequences: psychological - depression