Summary of chemical breakdown of food by hydrolytic enzymes (Protein enzymes).

Transcription

1 Biology 12 Digestive System Digestion Overview: The digestive process can be divided into 4 phases: 1. ingestion - includes swallowing and peristalsis 2. digestion - the physical (by teeth) and chemical (by enzymes) breakdown of food into nutrients (unit molecules) small enough to diffuse into cells 3. absorption - diffusion and active transport of nutrients into blood 4. defecation - removal of undigested material Summary of chemical breakdown of food by hydrolytic enzymes (Protein enzymes).

2 Digestive System Anatomy

3 Mouth Food is ingested and the teeth begin mechanical breakdown of food into smaller pieces. tongue pushes food against hard palate (roof of mouth) further physically break food to smaller pieces Salivary glands secrete saliva Saliva contains: 1. Mucus to make the food slippery for swallowing 2. Hydrolytic enzyme salivary amylase - begins the chemical breakdown of starch into maltose (disaccharide) making the food taste sweet and therefore taste better. The tongue pushes food to pharynx, which starts the swallowing reflex, food is called a bolus. swallowing reflex: 1. As bolus is swallowed, soft palette pushes upward to close the nasal cavity. 2. Uvula, often mistaken for the tonsils, is a small flap that projects down into the pharynx and acts to kick food away from the nasal cavity. 3. Epiglottis closes entrance to trachea (windpipe) so that food does not enter here. Esophagus 1. Food enters the esophagus a muscular tube which leads to the stomach. Wave-like contractions (called peristalsis) of the smooth muscle, which surrounds the esophagus, pushes the food towards the stomach. 2. At entrance to the stomach the cardiac sphincter (a ring of muscle), prevents food from leaving the stomach back into the esophagus. Heartburn occurs when acid from the stomach escapes through the cardiac sphincter into the unprotected esophagus.

4 Stomach Food enters the stomach the gastric glands of the stomach secrete gastric juice Gastric juice contains: 1. Hydrochloric acid (HCl) - HCl creates acidic environment of stomach (ph = 3), acidic environment kills bacteria in food but its main function is to convert the inactive enzyme pepsinogen into the active enzyme pepsin. 2. mucus coats the stomach wall protecting the cells from HCl 3. pepsinogen an inactive enzyme pepsinogen (an inactive enzyme) + HCl = pepsin Pepsin begins breakdown of protein into peptides. An ulcer is caused by the digestion of proteins in the stomach (gastric) cell membranes, effectively eating a hole in the stomach lining (caused mainly by bacteria, not excess stomach acid). Food leaving stomach called acid chyme - travels out of stomach through pyloric sphincter to Small Intestine.

5 Small intestine (S.I.) 1. Duodenum - first part of small intestine, where enzymes and the absorption of nutrients into the blood chemically break down the rest of food begins. 2. As acid chyme (containing fats and partially digested protein) enters the small intestine, the liver increases production of bile and causes the release of bile from the gall bladder where bile is stored. 3. Bile enters the duodenum (through a duct or tube) where it emulsifies fat, causing fat to be broken down into smaller droplets. Emulsification is defined as the process of causing fat to disperse in water. Emulsification increases the surface area of fat (many smaller droplets), therefore increasing the surface area for fat enzymes (lipase) to work. 4. Pancreas secretes pancreatic juice, which enters the duodenum through the pancreatic duct. 5. Pancreatic juice contains: 1. Sodium bicarbonate (NaHCO 3 ) 2. Amylase (pancreatic) 3. Lipase 4. Trypsin An easy way to remember the components of pancreatic juice is to remember the acronym SALT SALT = Sodium bicarbonate neutralizes acid chyme to a ph of 8 (slightly basic), provides an appropriate environment (ph) for the pancreatic enzymes, amylase, lipase, and trypsin. Pancreatic amylase continues breakdown of starch to maltose (started in the mouth). Lipase breaks down fats to fatty acids and glycerol (unit molecules) which is helped by the emulsification of fat into smaller droplets by bile. (Bile is not an enzyme) Trypsin continues the breakdown protein into peptides, which was started in the stomach. At this stage the only food to be completely broken down are fats.

6 Intestinal Juice: produced by cells lining the small intestine 1. Includes enzymes needed to finish the breakdown of protein and carbohydrates. These include a group of enzymes called peptidases which breakdown peptides into amino acids. 2. Also, a group of enzymes that breakdown carbohydrates into glucose are found here. The most notable of these is maltase, which breaks down maltose into glucose. Lactase is also found here and it breaks down lactose to glucose. Someone who is lactose intolerant cannot produce this protein hormone called lactase. 3. Also includes nucleases to break down nucleic acids to nucleotides Villi Nutrients are absorbed through the villi, the tiny folds in the surface of small intestine. Villi - increase surface area for absorption. Fatty acids and glycerol diffuse into the lacteal, part of the lymphatic system, which eventually empties into the blood stream. This prevents the tiny capillaries in the villi from becoming clogged. Glucose and amino acids (as well as vitamins and minerals like calcium and potassium) diffuse into the capillaries (blood vessels) found inside the villi. Glucose and amino acids can also be actively transported into the blood from the small intestine; of course, this requires ATP (energy) and allows transport from low to high concentration (against the concentration gradient). This ensures that the blood absorbs as much glucose as possible. Active transport is accomplished by carrier proteins, which act like pumps.

7 Large Intestine - Colon 1. The remaining undigested material travel into the colon or large intestine. 2. Here water and salt are absorbed and the feces is compacted and temporarily stored. 3. Helpful bacteria called E. coli are found in the colon where they breakdown some of the undigested material and produce vitamins and amino acids for our use. 4. Finally, the undigested material is removed in a process called defecation. Defecation is the removal of undigested material, which has never entered the blood; this is technically different from excretion or the removal of waste products from the blood by the kidneys. The Liver: The Gatekeeper - 6 major functions 1. Produce bile which is then stored in the gall bladder 2. Destroys old red blood cells and converts hemoglobin breakdown products which become part of bile 3. Stores glucose as glycogen after eating and breaks down glycogen to glucose between eating. This maintains blood glucose levels at about 0.1%. 4. Detoxifies blood by removing and metabolizing poisonous substances like alcohol. 5. Produces blood proteins like some blood clotting proteins 6. Produces urea - deaminates amino acids - removal of amine group forming NH3, which is toxic. NH 3 is converted to urea, a less toxic substance, by the liver. The rest of the amino acid can be converted to glucose to meet emergency energy needs.

8 Enzyme Chart - Summarize major enzymes used in the digestive process Enzyme Where it is Where it works Substrate Product Preferred ph produced Salivary amylase Salivary Glands Mouth Starch Maltose 7 or 8 Pepsin Gastric glands Stomach Protein Peptides 2 or 3 Pancreatic Pancreas Small intestine Starch Maltose 8 amylase Lipase Pancreas Small intestine Lipids Fatty acids 8 Trypsin Pancreas Small Intestine Protein Peptides 8 Peptidases Intestinal glands Small intestine Peptides Amino acids 8 Maltase Intestinal glands Small intestine Maltose Glucose 8 Nucleases Intestinal glands Small intestine Nucleic acids Nucleotides 8

9 The homeostasis of blood glucose (sugar) levels- Insulin and Glucagon Hormones Insulin: 1. After eating and digesting carbohydrates, blood glucose levels rise. 2. This causes the pancreas to secrete insulin. Insulin (a hormone = chemical messenger) is secreted into blood vessels and travels throughout the bloodstream. 3. Insulin attaches to receptors on various cells of the body (like liver and muscle cells). Insulin causes these cells to take in glucose. Inside these cells, glucose can be used to produce ATP or stored as glycogen. 4. These actions of glucose cause the blood glucose levels to drop. This drop in blood glucose inhibits (shuts off) further insulin secretion. This is an example of negative feedback.

10 Glucagon: 1. Between meals, blood glucose levels drop. 2. This causes the pancreas to secrete glucagon. Glucagon (a hormone = chemical messenger) is secreted into blood vessels and travels throughout the bloodstream. 3. Glucagon causes the liver and muscles to convert glycogen back to glucose and release this glucose into the blood stream. 4. These actions cause blood glucose to rise. This rise in blood glucose inhibits (shuts off) further glucagon secretion. This is an example of negative feedback. Insulin and Glucagon Summary Metabolic Actions of Insulin and Glucagon Action Insulin Glucagon Fatty acid use Triglyceride production Stimulates synthesis of triglycerides from free fatty acids; inhibits release of free fatty acids from triglycerides. (increases fat storage) Stimulates release of free fatty acids from triglycerides. (decreases fat storage) Liver glycogen Blood glucose Increases glycogen synthesis; increases glucose uptake and storage. Stimulates breakdown of glycogen so that glucose can be released into blood. Glucose uptake Skeletal muscle glycogen Stimulates glucose uptake and storage of glucose as glycogen. No receptors, no effect. Amino acid uptake Protein synthesis Stimulates amino acid uptake by cells and is necessary for protein synthesis. No receptors, no effect.

11 So How Does Insulin Increase Body Fat? Insulin Action Insulin is a storage hormone. 1. Insulin attaches to receptor sites on the cell membrane. 2. This signals the glucose channels to open so glucose can diffuse into the cell. 3. Glucose can be used to produce ATP to provide energy for cellular functions. 4. Some glucose can be stored as glycogen. This glycogen can be reconverted back to glucose if the cell is low on glucose and needs ATP. 5. Extra glucose is converted to fat (triglycerides). This fat can be reconverted back to glucose like substances and used to produce ATP. If glucose is always present, then this fat stays stored in the cell. Adipose cells fill with fat, especially in the abdominal region. 6. If the insulin receptors are not functioning (and/or insulin is not present), then there is no signal to open glucose channels. Without glucose entering cells, ATP production is severely limited. Fats become the next energy source for ATP but with limited fat storage, the cell will turn to amino acids (proteins) to supply emergency glucose. 7. Insulin also promotes the uptake of amino acids by muscles cells, therefore, assisting in muscle protein synthesis (muscle growth.

12 So How Does Glucagon Decrease Body Fat? Glucagon Action: 1. When there are many fatty acids (FA) in the blood, these fatty acids diffuse into fat cells (adipose cells) and are turned into triglycerides (TG). Therefore, fat cells grow in size, especially abdominal fat cells. 2. Between meals, glucagon hormone is secreted from the pancreas. Glucagon attaches to receptor sites on fat cells 3. Through some complex biochemical events (cascade), ATP is used to phosphorylate (add phosphate to) HSL (hormone sensitive lipase). This activates HSL. 4. Activated HSL will hydrolyze (digest) stored triglycerides into free fatty acids. 5. These free fatty acids diffuse out of the cell and can be used to produce ATP in other cells (like muscle cells). Adipose (fat cells) shrink in size meaning less body (abdominal) fat.

13 Turning down insulin and increasing glucagon tips. 1. Eat low glycemic carbohydrates: Low glycemic carbohydrates results in slower absorption of glucose and lower insulin release. Therefore, less fat storage. This link is a good place to start your research: 2. Eat carbohydrates with protein and fat: This also slows the absorption of glucose and results in lower insulin levels after each meal. Therefore, less fat storage. 3. Eat more whole foods like fruit and vegetables rather than processed carbohydrates (including juices and so called energy drinks). 4. Avoid fat free foods that contain high fructose corn syrup. High fructose corn syrup results in insulin spike and increased fat storage. 5. Change your exercise routine to include body weight circuits that help build muscle. Reduce long slow cardio exercises. 6. Understand the concept of biochemical individuality what works for others might not work for you. 7. Keep researching and asking questions if it was easy then everyone would do it!