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  1. 1. Digestion and Sports Nutrition Digestion
  2. 2. Your Digestive System The story we are about to tell is of stormy seas, acid rains, and dry, desert-like conditions. It’s an arduous journey that traverses long distances and can take several days. It’s one in which nothing comes through unchanged. It’s the story of your digestive system whose purpose is to turn the food you eat into something useful – for your body. Down the Hatch It all starts with that first bite of pizza. Your teeth tear off that big piece of crust. Your saliva glands start spewing out spit like fountains. Your molars grind your pizza crust, pepperoni, and cheese into a big wet ball. Chemicals in your saliva start chemical reactions. Seemingly like magic, starch in your pizza crust begins to turn to sugar! A couple more chews, and then your tongue pushes the ball of chewed food to the back of your throat. A trap door opens, and there it goes, down to your gullet! Next, your muscles squeeze the wet mass of food down, down, down a tube, or oesophagus, the way you would squeeze a tube of toothpaste. It’s not something you tell your muscles to do – they just do it – in a muscle action called peristalsis. Then the valve to the stomach opens up and pizza mush lands in your stomach.
  3. 3. Inside the Stomach Imagine being inside a big, pink muscular bag – sloshing back and forth in a sea of half digested mush and being mixed with digestive chemicals. Acid rains down from the pink walls, which drip with mucus to deep them from being eroded. Sounds a little like an amusement park ride gone crazy? Every time you think you’ve got your equilibrium back, the walls of muscles fold in on themselves again. Over and over again, you get crushed under another wave of slop. Every wave mixes and churns the food and chemicals together more – breaking food into even smaller and smaller bits. Then another valve opens. Is the end in sight you ask, as the slop gets pushed into the small intestine? Inside the small intestine, chemicals and liquids from places like the liver and pancreas break down and mix up leftovers. The small intestine looks like a strange underwater world filled with things that resemble small finger like cactuses. But they’re not cactuses, they’re villi. Like sponges, they’re able to absorb tremendous amounts of nutrients from the food you eat. From the villi, the nutrients will flow into your bloodstream.
  4. 4. But hold on!! The story is still not over yet – the leftovers that your body cannot use still have more travelling to do! Next, they’re pushed into the large intestines. It’s much wider and much drier. You find that the leftovers are getting smaller, harder and drier as they are pushed through the tube. After all, this is the place where water is extracted and recycled back into your body. In fact, the leftovers that leave your body are about 1/3 the size of what first arrived in your intestines. Where food turns into poop Finally, the end of the large intestine is in sight! Now the drier leftovers are various handsome shades of brown. They sit at the end of their journey, waiting for you to expel them – out your anus. Of course, you know the rest! A glorious, if slightly stinky, journey, don’t you think??
  5. 5. Factoids • How long are your intestines?? At least 8 metres in an adult. Be glad you’re not a full-grown horse – their coiled up intestines are 29 metres long!! • Chewing food takes from 5 – 30 seconds • Swallowing takes about 10 seconds • Food sloshing in the stomach can last 3 – 4 hours • It takes 3 hours to food to move through the intestine • Food drying up and hanging out in the large intestine can last 18 hours to 2 days. • Americans eat about 333 million kgs of peanut butter • Americans eat over 1 billion kgs of chocolate a year • In your lifetime, your digestive system may handle about 50 tons.
  6. 6. Digestive System The digestive system is often referred to as a food refinery – purifying the raw material foods to provide fuels and building materials for the cells. It is the process that breaks down food into substances that can be absorbed by the body for energy, growth and repair. The digestive system prepares food for use by hundreds of millions of body cells. Two processes occur; ingestion, food is taken into the digestive system and swallowed, and digestion, when food enters the alimentary canal (full length of the digestive pipe). There are two types of digestion; mechanical, the breakdown of food by the action of the teeth and alimentary canal (squeezing, turning and tossing food), and chemical (breaking bonds of large molecules), the breakdown of food by enzymes, acid and bile in the mouth, stomach and small intestine. The gut modifies food physically and chemically and disposes of unusable waste.
  7. 7. Structures of the Digestive System The alimentary canal consists of four layers of tissue: • Mucosa – made up of epithelial cells (an internal skin which absorbs molecules of nutrients and produces digestive secretions – liquids) and thin layers of connective tissue, varies along the alimentary canal according to what role it has to play eg one cell thick in the small intestine where absorption of food molecules occurs. • Submucosa – a layer of connective tissue lying beneath the mucosa (protein containing fluid). Collects and supplies lymph (protein containing fluid). • Muscle layer – found under the submucosa, is responsible for mixing food and mechanical digestion. • Outer membrane – outer most layer of the canal and is a thin membrane (thick skin of protective sheath), connects and anchors to the wall of the abdominal cavity.
  8. 8. Organs of the Alimentary Canal - Mouth, Pharynx and Salivary Glands • Teeth cut and crush food and mix food with saliva. Saliva travels to the mouth through ducts from the salivary glands. Saliva contains an enzyme called amylase, water and minerals and some mucus, which helps to lubricate the food. • Once swallowing begins, it is an automatic or reflex event, over which we have no conscious control. It occurs in four stages: – The tongue pushes against the top of the mouth (hard palate) and pushes the food to the back of the mouth or pharynx. – Soft palate is pushed upwards by the tongue, closing the opening to the nasal cavity. – Larynx is pulled upwards against the epiglottis, to prevent food from entering the respiratory passages. – Food is then squeezed backwards and down and guided through the pharynx to the oesophagus.
  9. 9. http://www.youtube.com/watch?v=fCQ_MrhhGvI Why does chewing gum prevent tooth decay?
  10. 10. • It is a simple straight tube with very muscular walls • Solid foods are moved down the oesophagus by waves of peristalsis and reach the stomach in 6 seconds (liquids travel much more rapidly) • Sphincters are found in the alimentary canal, where one organ joins with another. They act like a rubber band around the top of a bag. – Demonstrate squeezing a plastic bag, therefore touch sensitive • By their contraction or relaxation they control the passage of small quantities of digested food from one organ to the next. • Examples: between the oesophagus and the stomach, between the stomach and the small intestine. Organs of the Alimentary Canal - Oesophagus
  11. 11. • The stomach is a large muscular sac. • It has three mechanical tasks: – It stores or acts as a reservoir for the swallowed food and liquid. This requires the muscles of the upper part of the stomach to relax and accept large volumes of swallowed material. Food may remain in the stomach for 3 – 4 hours and may hold over 2 litres of food and gastric juices. – The lower part of the stomach mixes the food, liquid and gastric juices (acid, pepsin and mucus) together by waves of peristaltic contractions to pound and churn the contents. This is converted into a semi-fluid mixture called chyme (slurry). – Through the pyloric sphincter the chyme is slowly released into the small intestine. Organs of the Alimentary Canal - Stomach
  12. 12. HCl: Acid on meat activity – observation Acid is neutralized in the duodenum by pancreatic bicarb to prevent small intestine damage Acid activates pepsin to break down protein Mucous (secreted by goblet cells) protects lining of stomach from self destruction Ulcers – due to bacteria
  13. 13. • It is a very long tube – up to 8 metres in adults, which is coiled up inside the abdominal cavity. • It is divided into 3 parts – Duodenum – Jejunum – Ileum • The duodenum is the main site of chemical digestion in the gut tube. Digestive secretions enter the duodenum from: – The liver, via the bile duct – The pancreas, via the pancreatic duct. – Gland cells in the wall of the intestines • The sodium bicarbonate of pancreatic juice soon neutralises the acid chyme from the stomach. The digestive enzymes, assisted by the bile salts from the liver, and then complete the breakdown of food molecules to small soluble compounds. These products of digestion can pass through the intestinal lining and enter the bloodstream, • Digestive foods are absorbed into the ileum. Organs of the Alimentary Canal – Small Intestine Food intolerance (gluten, lactose) gut gets upset, causing inflammation, fatigue etc, can cause at the brain level (mood and depression) Coke angle can be helpful in stabilizing – potassium phosphate???
  14. 14. Membrance scenario Show semipermeable dialysis tube allowing one way flow of some things Into blood or lymph (fats) Osmotic pull – no energy used (passive process), high to low concentration. Show the rate of flow and differences with concentrations. How strong can you make sports drinks?
  15. 15. • Material that is not absorbed by the ileum is passed through to the large intestine. These are vegetable fibres and cellulose (roughage), bacteria and mucus (Recovers H2O – solvent carrying medium – if not diarrhoea. Vitamin manufacture bacteria – if CHO gets too thick or roughage too high) • The large intestine consists of three main areas: – Caecum and appendix – Colon – Rectum • The caecum and appendix have no special features • There is no secretion of enzymes in the large intestine and it can absorb very little food. However, it does absorb a great deal of water which then leaves the undigested residue which passes on to the rectum in a semi-solid state, known as faeces. • Remaining food material may spend up to 24 hours in the large intestine, before it is expelled through the anus after temporary storage in the rectum. Organs of the Alimentary Canal – Large Intestine
  16. 16. You tube – Slow emptying of viscous meal – http://www.youtube.com/watch?v=QDrzs1bZSWI Vomiting reverse giant contractions - http://www.youtube.com/watch?v=f6y5SykbqJE&
  17. 17. Accessory Organs 1. The Liver It produces bile, cleans poisonous substances such as alcohol and lactic acid from the blood and stores nutrients such as glycogen. The liver acts as a filter system for the body. 2. The Gall Bladder Muscular pouch that stores bile from the liver, then releases it into the small intestine. Bile breaks down large droplets of fat. 3. The Pancreas It produces several digestive enzymes and hormones and releases them into the small intestine. Insulin is one of these. It controls the blood glucose levels. – Exocrine part produces many enzymes, which enter the duodenum via the pancreatic duct. – Endocrine part produces insulin.
  18. 18. Organ Gland Secretion Function Mouth Salivary Glands Saliva • Amylase Polysaccharides Disaccharides (starch and glycogen broken down to maltose) Stomach Gastric Glands Gastric juice • HCl • Pepsin Acid environment for pepsin Proteins polypeptides Liver Liver Bile • Bile salts Emulsification of fats (green) Pancreas Exocrine pancreas Pancreatic juice • NaHCO3 • Amylase • Lipase • Trypsin Neutralises HCl Polysaccharides to disaccharides Fats to fatty acids and glycerol Proteins to polypeptides Small Intestine Intestinal Glands Intestinal juice • Peptidase • Maltase • Sucrase • Lactase Peptides to amino acids Disaccharides to monosaccharides Secretions of the Digestive System
  19. 19. Absorption • Absorption of small molecules takes place in the small intestine. • For absorption to be efficient and complete, a large area of contact between the digested food molecules and the intestinal lining is necessary. • There are four ways in which the structure of the small intestine provides a huge surface area for absorption: – Great length – Large circular folds – Villi (finger like projections of mucosal lining) – Microvilli (tiny folds on the surface of each cell) • In addition the small intestine has a very large supply of blood vessels to transport the absorbed food molecules from the gut to the tissues of the body. • From the small intestine, absorbed molecules are carried in the hepatic portal vein to the liver • Here the food molecules may be stored by the liver cells or changed before joining the general circulation of the body.
  20. 20. Absorption and Surface Area SA Surface Area model Huge increase in contact area but then must slow down the flow, compared to flat Therefore pre-digested protein in the first 2 hours when most needed (post exercise)
  21. 21. Organ Action Process Mouth Biting, chewing, and tasting • Mechanical Digestion mixes salivary juice and breaks food down in size • Chemical Digestion of STARCH begins and salivary juice breaks down to a simpler form Oesophagus Swallowing • Mechanical movement is caused by muscular contraction called PERISTALSIS which forces food into the STOMACH Stomach Churning and mixing movement • Mechanical mixing of the DIGESTIVE juices, which enter the stomach; HYDROCHLORIC ACID kills any dangerous bacteria and ENZYMES begin to act on PROTEINS Small Intestine • Duodenum • Jejunum • Ileum Mixing movement • Mechanical peristalsis continues • Chemical BILE from the GALL BLADDER begins to chemically change FATS into smaller fat particles; PANCREATIC JUICE (from the PANCREAS) containing ENZYMES begin to act on proteins, fats and starch (each one has a particular enzyme, which causes the changes). PANCREATIC JUICE also contains INSULIN, which controls the amount of sugar in the blood by controlling sugar metabolism. Absorption Absorption begins soon after food enters the small intestine PROTEINS and CARBOHYDRATES enter the capillaries in the walls of the intestine. FATS enter the LYMPH vessels, which are also in the walls of the intestine. Proteins and carbohydrates are carried directly to the LIVER. FATS will enter the bloodstream directly after being removed from the intestines by the lymph vessels. Large Intestine Movement WATER only is absorbed from what remains in the large intestine. The remainder (mostly waste materials and some water) is passed along for storage in the RECTUM, ready for elimination through the ANUS. • If too much water is removed, CONSTIPATION results. • If too little water is removed, DIARRHEA results. Digestive System Summary