Human Digestive Digestive System - YouTube.flv System

1. Human DigestiveDigestive System - YouTube.flv System http://vimeo.com/76306734 Video link

2. 5 Digestion Processes (IDAAE) • Ingestion: taking in of food into the body. • Digestion: breaking down of food into simpler substances • Absorption: diffusion of food from small intestine into the blood • Assimilation: using digested nutrients to make new material • Egestion: removal of undigested waste material

3. Recall. . . What are the main organs of the alimentary canal? • Mouth • Oesophagus • Stomach • Small intestine • Large intestine • Anus Although not part of the alimentary canal, the liver, gall bladder and pancreas are closely associated with it. They play an important role in digestion by secreting digestive enzymes.

4. Digestion • Mechanical / physical digestion physically breaks down the food in the mouth (chewing). Smaller pieces of food increase surface area for digestion. It also takes place in the stomach (churning of food by the muscular stomach walls) • Chemical digestion uses enzymes to chemically break down complex food substances into their simplest form. e.g. Starch maltose amylase

5. Chemical digestion: • Starch (carbohydrate) digestion: in mouth and small intestine. • Protein digestion: in stomach and small intestine • Fat digestion: only in small intestine Why must food be digested??? Large molecules of food are unable to pass through cell membranes, thus must be broken down into small molecules so that they can diffuse through cell membranes into the blood stream

6. Mouth (Ahhh....) • Mouth ingests food • Teeth masticates food into small pieces to increase surface area for digestion • Saliva (pH 7) moisten and soften food • Starch maltose • Tongue mixes food with saliva and rolls food into a bolus before swallowing • Saliva - water, mucus, salivary amylase Salivary amylase

8. https://vimeo.com/76306735 Swallowing

9. What Happens During Breathing and Swallowing? Normally, air passes into the trachea (windpipe)while food passes into the oesophagus. pharynx During breathing, the larynx is lowered and the glottis is open. air larynx (voice-box) oesophagus glottis trachea (windpipe)

10. What Happens During Breathing and Swallowing? During swallowing, the larynx is raised and the glottis is covered by the epiglottis. This prevents food particles from entering the trachea. pharynx food particles epiglottis oesophagus glottis larynx (voice-box) trachea (windpipe)

11. What Happens During Breathing and Swallowing? Occasionally, small particles of food or water may get into the larynx or trachea. food particles larynx (voice-box) trachea (windpipe)

12. What Happens During Breathing and Swallowing? This automatically induces violent coughing to force the food particles or water out and to prevent choking. food particles larynx (voice-box) trachea (windpipe)

13. Oesophagus • Minimal digestion • Carries food from mouth to stomach by peristalsis • Oesophagus has circular and longitudinal muscles which are antagonistic. • When circular muscles contract, longitudinal muscles relax and vice-versa.

14. Peristalsis Part of the gut wall • The two layers of muscles cause rhythmic, wave-like contractions of the gut walls. Such movements are known as peristalsis. • Peristalsis: • enables food to be mixed with the digestive juices; and • moves the food along the gut. circular muscles longitudinal muscles

15. Wall here dilates Direction of movement of food Circular muscles relax Wall here constricts. Circular muslces contract; longitudinal muscles relax Longitudinal muscles contract

16. Peristalsis – Move the food down! • When circular muscles contract, longitudinal muscles relax. Gut wall constricts i.e. gut becomes narrower and longer. Food is squeezed or pushed forward. • Gravity and slippery mucous lining helps push food down too. • http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.html

17. Stomach • Stores food temporarily • Stomach muscles churns and mixes food (also by peristalsis) with gastric juice to form chyme. • Gastric juice contains hydrochloric acid (HCl) and enzymes like rennin and pepsin • HCl is very acidic (pH2), thus it kills bacteria and other microorganisms, as well as stopping the action of salivary amylase • Provides acidic medium for gastric enzymes to work • Only protein digestion here

18. The stomach is “guarded” at the entrance and exit points by sphincter muscleswhichcontrol the amount of food entering and leaving the stomach. https://vimeo.com/76306734

19. Small Intestine • Subdivided into duodenum, jejunum and ileum • In the small intestine, chyme stimulates • Pancreas to secrete pancreatic juice • Gall bladder to secrete bile • Intestinal glands to secrete intestinal juice • All three juices secreted are alkaline, pH 8.5

20. 2 bile 1 bile duct pancreatic juice • Pancreatic and intestinal juice contain many digestive enzymes. • Bile does not contain • enzymes. Bile emulsifies fats, increasing the • surface area for lipase • action pancreatic duct 3 intestinal juice

22. Villi – absorption by diffusion Diffusion To liver From intestine To

23. Large Intestine (colon) • Large inverted U shaped tube. • No digestion takes place here • Absorbs water and minerals salts • Stores the faeces (dead cells, mucus, germs, undigested food)

24. Is the colon the main region for water absorption? No! About 94% of the total amount of water passing through the alimentary canal is absorbed by the small intestine! The large intestine absorbs most of the remaining 6% of water. Rectum – temporarily stores faeces Anus – egests (= removal of undigested matter) faeces

25. Organs associated with the alimentary canal These organs do not digest food but aid in digestion • Gall bladder • Pancreas • Liver

26. One cell thick epithelium – for efficient absorption of food particles Blood capillaries – transport sugars and amino acids away from the small intestine Lacteal – fatty acids and glycerol recombine in the epithelium to form fat which then enters the lacteal as fine fat droplets This continual transport of digested food substances maintains the concentration gradient for the absorption of digested food substances.

27. Gall bladder • Temporarily stores bile (smelly green substance) secreted by liver. • Secretes bile in the presence of chyme. • Bile breaks up large fat droplets into very small fat droplets to increase surface area for lipase action (Emulsification) Bile emulsifies fats • *Bile is not an enzyme, so it is not affected by temperature

28. Pancreas • Connects to small intestine by pancreatic duct • Produces pancreatic juice • Secretes hormones like insulin (controls blood glucose concentration) and glucagon (controls carbohydrate metabolism) Liver • Produces bile, which is stored in the gall bladder

30. Absorption Adaptations of the small intestine • Small intestine is very long (~5 m) • Internal surface of the small intestine has many folds. • On these folds, there are many finger-like projections called villi • These 3 adaptations increase surface area for absorption

31. Assimilation • After travelling through the blood stream to the rest of the body, cells can now make use of • glucose as source of energy • amino acids to build new cytoplasm and tissue cells • fatty acids to build new cell membranes