Digestion & Absorption of Carbohydrates PDF

Digestion and absorption of carbohydrates Dr. Mohammed Abdullah Hassan Assistant Professor of Biochemistry  Digestion Digestion – The process of changing food into simple components which the body can absorbed Digestion is a form of catabolism that...

Digestion and absorption of carbohydrates Dr. Mohammed Abdullah Hassan Assistant Professor of Biochemistry  Digestion Digestion – The process of changing food into simple components which the body can absorbed Digestion is a form of catabolism that is often divided into two processes: – Mechanical digestion Refers to the physical breakdown of large pieces of food into smaller pieces. – Chemical digestion The enzymes breakdown food into the small molecules the body can use, using digestive enzymes. Why is food chemically broken down? – The macromolecules are too large to pass through cell membranes Dr. Mohammed Abdullah Hassan Food processing Dr. Mohammed Abdullah Hassan  Stage of digestion Digestion is a multistage process in the digestive system that separated into four steps: 1. Ingestion: placing food into the mouth and entry to the digestive system 2. Mechanical and chemical breakdown: mastication and the mixing of the resulting bolus with water, acids, bile and enzymes in the stomach and intestine to break down complex molecules into simple structures 3. Absorption: transport of nutrients from the digestive system to the circulatory and lymphatic capillaries through osmosis, active transport, and diffusion. 4. Excretion: Removal of undigested materials from the digestive tract through defecation. Dr. Mohammed Abdullah Hassan  Digestive system (mouth) Mouth: ingestion of food; mastication & swallowing Saliva: water, salts, enzymes, that secreted by salivary glands Saliva, contains salivary amylase, an enzyme which starts the digestion of starch in the food. Dr. Mohammed Abdullah Hassan  Digestive system (stomach & intestine) Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. In small intestine, pancreas release pancreatic enzymes, in which digestion continues. After fully digested, 95% of absorption of nutrients occurs in the small intestine. Waste material is eliminated from the rectum during defecation. Dr. Mohammed Abdullah Hassan  Digestive hormones Gastrin – The secretion of gastrin is stimulated by food arriving in the stomach. – stimulates secretion of pepsinogen and hydrochloric acid. Secretin – Stimulates the secretion of sodium bicarbonate by pancreas and the bile synthases in the liver. Cholecystokinin (CCK) – Stimulates the release of digestive enzymes in the pancreas – Stimulates the emptying of bile in the gall bladder. Dr. Mohammed Abdullah Hassan  Absorption Dr. Mohammed Abdullah Hassan  Digestion of dietary carbohydrates Digestive processes convert all the dietary carbohydrates to their constituent monosaccharides by hydrolyzing glycosidic bonds between the sugar unites The digestion of starch begins in the mouth and complete at small intestine – The salivary gland releases salivary a-amylase, which converts starch to smaller polysaccharides called α-dextrins. At stomach, the salivary α-amylase is inactivated by the acidity of the stomach (HCl) At small intestine, pancreas secreted: – Bicarbonate that neutralizes the gastric secretions – Pancreatic α-amylase, which complete digestion of carbohydrate Dr. Mohammed Abdullah Hassan  Digestion of dietary carbohydrates Pancreatic α-amylase converting α- dextrins to disaccharides (maltose, lactose, and sucrose) and oligosaccharides (limit dextrins) Intestinal brush border enzymes complete the digestion process, which cleaves disaccharides to monosaccharides 1. Maltase cleaves maltose to 2 glucoses 2. Isomaltase cleaves isomaltose to 2 glucoses 3. Lactase cleaves lactose to glucose and galactose 4. Sucrase cleaves sucrose to glucose and fructose Dr. Mohammed Abdullah Hassan  Transport of dietary carbohydrates  Only monosaccharides are absorbed and transported via blood to the liver and peripheral tissues  What are the types of mechanism???  In liver, fructose and galactose are rapidly converted to glucose  Glucose enters most cells by specific carrier; glucosetrnsported (GLUT), that transports it from out of the cell to the cytosol. Dr. Mohammed Abdullah Hassan  Maintenance of Blood glucose The source of glucose in the blood is from …….: Glucose is the major metabolic fuel of mammals and a universal fuel of the fetus It is the precursor for synthesis of all the other carbohydrates in the body: – Glycogen for storage; ribose and deoxyribose in nucleic acids; and galactose in lactose of milk, in glycolipids, and in glycoproteins. Dr. Mohammed Abdullah Hassan  Blood sugars Blood sugar: is a sugar that the bloodstream carries to all cells in the body to supply energy. A person needs to keep blood sugar levels within a safe range to reduce the risk of diabetes and heart disease. Result HA1C test Fasting blood sugar test Diabetes 6.5% or above 126 mg/dL or above Prediabetes 5.7 – 6.4% 100 – 125 mg/dL Normal Below 5.7% 99 mg/dL or below Dr. Mohammed Abdullah Hassan  Blood glucose disorders Blood glucose level reach a maximum of about 140-160 mg/dl about one hour after carbohydrate-containing meal, and returns to normal after 2-2.5 hours Hypoglycemia: occurs when blood glucose level are below the normal fasting level Hyperglycemia: occurs when blood glucose level are above the normal fasting level Lactose intolerance or lactase deficiency: People with lactose intolerance are unable to fully digest lactose in milk. As a result, they have diarrhea, gas and bloating after eating or drinking dairy products. Dr. Mohammed Abdullah Hassan  Hormonal control of blood glucose Insulin: – Polypeptide hormones produced by β cells of pancreatic islets of Langerhans – Enhances the entry of blood glucose into the cells (liver, muscles, and adipose tissue) and increased glucose metabolism – Lead to reduce blood glucose – Referred to as a hypoglycemic agent. Glucagon – Polypeptide hormones secreted by the a cells of pancreatic islets of Langerhans – Stimulate glycogenolysis and gluconeogenesis in the liver. – Lead to increasing plasma glucose levels, – Referred to as a hyperglycemic agent Dr. Mohammed Abdullah Hassan  Hormonal control of blood glucose Epinephrine Secreted from adrenal gland in response to fasting and chronic stress Inhibiting insulin secretion, increasing glycogenolysis, and promoting lipolysis. Lead to increases plasma glucose Glucocorticoids as Cortisol and ACTH – Cortisol released from the adrenal cortex on stimulation by adrenocorticotropic hormone (ACTH). – Both lead to increases plasma glucose level – Decreasing intestinal glucose entry into the cell and increasing gluconeogenesis, liver glycogenolysis, and lipolysis. Dr. Mohammed Abdullah Hassan  Hormonal control of blood glucose Growth hormone – Promote increased plasma glucose. – Decreasing the entry of glucose into the cells and increasing glycolysis. Other hormones as thyroxine and somatostatin: – Thyroxine Produced by thyroid gland Increases plasma glucose levels by increasing glycogenolysis, gluconeogenesis, and intestinal absorption of glucose. – Somatostatin, Produced by the d-cells of the islets of Langerhans of the pancreas Increases plasma glucose levels by the inhibition of insulin, glucagon, growth hormone, and other endocrine hormones. Dr. Mohammed Abdullah Hassan Dr. Mohammed Abdullah Hassan Blood glucose, insulin and glucagon levels Dr. Mohammed Abdullah Hassan  Home work Search in scientific databases about the glucose transports (GLUTs) at this points as example: – Number of GLUTs in human – How this transporter is produced – Types and functions of this transporters in different tissues – Association between GLUTs and different diseases NOTE: 1. Use up to date reference(s) (2021-2023) 2. Summarize that in one or few pages Dr. Mohammed Abdullah Hassan Dr. Mohammed Abdullah Hassan