Carbohydrate digestion, absorption and blood sugar homeostasis Flashcards
what are the 3 types of carbohydrates
- monosaccharides (glucose, fructose, galactose)
-disaccharides (maltose,sucrose,lactose) - polysaccharide (starch,glycogen,cellulose)
what are the structures of polysaccharides
- starch in potatoes,rice, cornflakes
- amylose and amylopectin
- amylose- 1 chain
- attached by alpha 1,4
- branched chain has different bonds
- then there’s alpha 1-6
- glycogen found in the body of animal we consume
- linear chain connected by alpha 1-4
- cellulose - linear attached with alpha 1-4 but the branches chains 1-4
what is glands are important in the carbohydrate digestion in the oral cavity
parotid gland, submandibular gland, = both mechanical
serous cells- salivary alpha amylase
what enzyme is involved in carbohydrates digestion in the mouth
salivary amylase
- secreted by serous acini of parotid and sub mandibular salivary glands
- optimal pH=6.7
- action begins in the oral cavity and is assisted by mechanical breaking up of polysaccharides during chewing
- mode of action; hydrolysis of alpha 1-4 linkage in polysaccharides producing a mixture of oligosacharides
- works for 1-2 hours in the stomach before being deactivated by the gastric acids
what enzymes are involved in intestinal digestion of carbohydrates
- pancreatic amylase
- secreted form the pancreatic exocrine acini into the duodenum through he pancreatic duct
- optimum pH=6.7-7.0
- mode of action: hydrolysis of alpha 1-4 linkage
- responsible for digestion of more complex carbohydrate that take longer to break down to disaccharides or oligo saccharides
what are the brush border enzymes
maltase, sucrase and lactose
- found on the membrane surface of the micro villi of the epithelial cells lining the small intestines
- optimal pH =7.8
- mode of action: hydrolysing disaccharides into monosaccharides
how are carbohdyrate digested in the GIT
- lactase break down lactose to glucose and galactose
-lactose intolerance - deficiency in lactase - avoiding milk and dietary products
how are carbohydrates absorbed
- occurs in small intestine
- villi
-microvilli - increases SA which facilitates absorption - the absorbable form of carbohydrates is monosaccharides
- glucose and galactose enter the epithelial cells of the intestine through the apical border via active transport using sodium dependant co transporters, Sodium potassium pump requires energy
- they leave the cells through the basolateral side using faciliated diffusion and glucose co-trasnporter 2 (GLUT-2) into the circulation
- Fructose enters (GLUT-5) and leaves (GLUT-2) the epithelial cells using facilitated diffusion (no energy required)
what are the 3 mechanisms of diffusion
passive diffusion
facilitated diffusion
active transport
how is glucose and galactose absorbed
- epithelial cells and brush bordere
- glucose cannot enter cell membrane so is carried by SGLT1 using sodium
- enter cell together , sodium released releasing energy so the glucose will be released
- fructose binds with sodium and the SLGT2 leave
how is fructose absorbed
- uses Glut5
- released inside by facilitated diffusion
what factors affect carbohydrate absorption
- faster through intact mucosa
- absorption is decreased if there is some inflammation or injury to the mucosa
- Thyroid hormones increase the rate of absorption of glucose
- Mineralocorticoid: e.g. Aldosterone increase the rate of absorption
- Sodium concentration : high concentrations increase the rate of absorption
what is th main nutrient for the brain and retina
under non starvation conditions, GLUCOSE is the main nutrient for the Brian and retina
what is the sole nutrient for red blood cells?
glucose
describe briefly the Krebs cycle
Glucose molecule is taken and broken down into pyruvate and ATP
what is glucagon and what is it secreted by
Glucagon is a hormone secreted by the alpha cells in the islets of Langerhans of the pancreas; and is responsible for converting glycogen stored in the liver to glucose and releasing it in the blood when blood glucose levels are low
what is the structure and synthesis of insulin?
- insulin is a small protein: MWT =6000
- 2 pp chains A &B linked by a disulphide bond
what is the role of insulin in glucose uptake by body cells
- insulin works through stimulating GLUT4
