Unit 1 human nutrition(2)
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The document summarizes the key structures and processes involved in human digestion. It describes the major organs that make up the human digestive tract, from the mouth to the anus. It then explains the five main stages of digestion - ingestion, mechanical and chemical digestion in the mouth, stomach and small intestine, absorption in the small intestine, and excretion from the large intestine and anus. Accessory organs like the liver, pancreas and gallbladder are also discussed.
Unit 1 human nutrition(2)
- 2. STRUCTURE OF HUMAN DIGESTIVE TRACT Humans have a complete digestive tract begins with mouth & ends with anus. The major structures of human digestive tract: mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus.
- 3. The accessory organs of digestion are the Liver Salivary glands gall bladder pancreas
- 5. Why is digestion important? To convert large (insoluble molecules) of food smaller soluble molecules absorbed into the blood or lymph capillaries & used for various metabolic processes.
- 6. DIGESTIVE PROCESS INGESTION DIGESTION MECHANICAL AND CHEMICAL ABSORPTION ASSIMILATION EXCRETION
- 7. PATHWAY OF FOOD AND RELATED PROCESSES IN THE BODY
- 8. MOUTH Ingestion: Food is placed in mouth. Teeth: - Incisors cut or bite the food. - Canines used to tear meat. - Molars and pre-molars grind the food fine. Mechanical digestion
- 9. STRUCTURE OF A MOLAR
- 10. SALIVA Secreted by the salivary glands (parotid gland, sublingual gland & sub- maxillary gland) Mix with the food to form bolus. Saliva contains enzyme (amylase) breaks down cooked starch into maltose. Chemical digestion.
- 11. TONGUE Mixes food with saliva & pushes food between teeth. Makes swallowing easier.
- 12. ESOPHAGUS Bolus forced down esophagus when muscular pharynx contract swallowing process. NB!!! Peristalsis (contraction & relaxation of circular & longitudinal muscles) of the esophagus pushes food downwards into stomach, through cardiac valve. No absorption takes place The epiglottis covers the trachea prevents food from going into the trachea when you swallow.
- 13. EPIGLOTTIS
- 15. PERISTALSIS
- 16. STOMACH (Isisu) Food enters the stomach (fundus region) through the cardiac valve. Remains 30 min before stomach muscles (circular-, longitudinal- and oblique muscles) starts contracting & relaxing (peristalsis). Food move with circular movements through stomach (corpus and pyloric regions) & mixes with gastric juices. Mechanical digestion
- 17. Gastric juices secreted after the hormone, gastrin (stimulates parietal cells in the fundus region of stomach). Gastric juices consist of: 1.HCl (Acidify stomach &neutralizes bolus, antiseptic solution, emulsifies fats), 2.digestive enzymes (pepsin, rennin & lipase), 3.mucus (help protect inner lining of stomach against enzyme activity) & 4.water.
- 18. Gastric juices help with chemical digestion of food (bolus) now called chym. Some absorption occurs in stomach: water, glucose, salt and certain drugs and alcohol pass into blood capillaries of stomach wall.
- 20. SMALL INTESTINE Chym enters duodenum (1st part of small intestine) through pyloric valve. Mix with bile (secreted from liver/gall bladder) & pancreatic juices.
- 21. CHEMICAL DIGESTION Secretin hormone that stimulates pancreas to secrete pancreatic juice into duodenum. Pancreatic juice contain: sodium bicarbonate (neutralizes the chym, antiseptic) & digestive enzymes (Trypsin, amylase and lipase) Bile produced in liver & stored by the gall bladder. When fatty rich food enters small intestines bile is secreted by gall bladder & transported to duodenum.
- 23. FUNCTIONS OF BILE Neutralizes acid from stomach Emulsifies fats (increase surface area of fats for better digestion) Aid in absorption of fats. Reduce fluidity of chym Antiseptic prevent decomposition Assist in absorption of fat-soluble vitamins.
- 24. Chym moves through jejunum (2nd part of small intestines) Mixes with intestinal juice (succus entericus)
- 25. MECHANICAL DIGESTION The 2 muscle layer of the small intestine helps with the process of peristalsis. Cross section through the small intestine
- 26. FUNCTIONS OF THE LIVER - Isibindi Produces & secretes bile. Stores glucose in form of glycogen & controlled by hormone insulin. When body requires glucose glycogen changed back into glucose. The liver also converts glycerol, into glucose. Convert excess carbohydrates into fatty acids which combine with glycerol to form fats.
- 27. Stores blood temporarily blood also formed in liver of embryos. Manufactures plasma proteins e.g. albumen & fibrinogen. Forms heparin prevents clotting of blood inside blood vessels. Detoxifies the body.
- 28. Liver breaks down surplus amino acids through process of deamination: Change amino acid ammonia. 2 x ammonia molecules combine with 1 molecule of CO2 urea & water. Urea conveyed to kidneys for excretion. Deaminated amino acids converted into glucose (glucose converted to glycogen & stored in liver)
- 29. BLOOD SUPPLY OF THE LIVER Hepatic portal vein transports digested food from small intestine to liver The hepatic portal vein is a blood vessel that conducts blood from the digestive system to the liver. This blood is rich in nutrients that have been extracted from food, and the liver processes these nutrients; it also filters toxins that may have been ingested with the food. Hepatic artery transports O2 & nutrients to the liver (enter the liver). Inside liver blood of these 2 blood vessels mix & products transported is exchanged between blood and the liver cells. Waste moves out of liver cells & transported away from the liver by hepatic vein which joins up with inferior vena cava.
- 30. BLOOD SUPPLY TO THE LIVER CELLS
- 31. ABSORPTION FROM THE SMALL INTESTINE Food mainly absorbed from small intestine where all final digestive processes take place & end-products of digestion is formed. The final products of digestion: glucose, amino acids, fatty acids and glycerol formed in small intestine.
- 32. Adaptations of the small intestine for the absorption of food. The absorptive surface area is increased by: The great length of the small intestine (6- 7m) The circular folds of the mucosa lining of the small intestine. The millions of villi lining the folds. The chym is pushed along very slowly through the small intestine, allowing time for absorption to take place.
- 34. STRUCTURE OF THE VILLUS Villus consist of several capillary arteries supply villus with O2 & capillary veins carry food away from the villus. Lacteals (lymph vessels) found in center of each villus used for the absorption of fats. Vessels surrounded by connective tissue & a layer of columnar epithelial cells with goblet cells
- 35. STRUCTURE OF THE VILLUS
- 36. The process of absorption in the small intestine The columnar epithelial cells play active part in absorption & able to allow substances to enter villi Amino acids, glucose, mineral salts, water & vitamins absorbed directly into the blood.
- 37. FAT ABSORPTION FROM SMALL INTESTINE Fatty acids (insoluble) combine with bile salts To form fatty acid-bile salt complex which is (soluble) in water. This complex plus glycerol component of fat absorbed by columnar epithelial cells of villi. Inside villus fatty acids freed from the bile salts & recombine with glycerol to form tiny fat globules.
- 38. FAT ABSORPTION FROM SMALL INTESTINE Some of the fat globules are absorbed directly into the blood capillaries. Most fat globules are absorbed by the lacteals. The lacteals unite to form small lymph vessels which enter main lymphatic system. Fat in lacteal now known as chyle, & it reaches bloodstream in the end.
- 39. LARGE INTESTINE No digestion takes place in the colon. Undigested food particles from small intestine enter the caecum through ileocaecal valve. In colon water is absorbed chym becomes semi-solid.
- 40. LARGE INTESTINE Symbiotic bacteria present in colon act upon food rests decomposing them & turning them into faeces. Bacteria synthesize vitamins Bgroups and K essential for blood clotting process. Peristalsis in colon facilitated by mucus produced by numerous mucous glands. Mucus assists the movement of feces & protects the wall of the colon.
- 41. HUMAN COLON
- 42. RECTUM By the time feces reach the rectum consist of approximately 70% water. Bacteria account for about 30% of dry mass of feces Remainder made up of food residue (mainly cellulose).
- 43. FAECES STORED IN RECTUM
- 44. ANUS Defecation (excretion) brought about by contraction of the circular muscles of rectum & relaxation of the muscles which make up the anal sphincter.