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Human Biology

Human Biology. Digestive System. Interesting Facts. We eat about 500 kg of food per year We make approximately 1.7 litres of saliva every day Every day 11.5 litres of digested food, liquids and digestive juices flow through the digestive system, but only 100 mL is lost in feces,.

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Human Biology

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  1. Human Biology Digestive System

  2. Interesting Facts • We eat about 500 kg of food per year • We make approximately 1.7 litres of saliva every day • Every day 11.5 litres of digested food, liquids and digestive juices flow through the digestive system, but only 100 mL is lost in feces,

  3. Interesting Facts • Digestive problems cost Americans $50 billion each year in both direct costs and absence from work. • By age 50, many people will produce only 15% of the Hydrochloric Acid (stomach acid) they released at age 25. • Most of us pass somewhere between 200 and 2,000 mL of gas per day (average, about 600 mL) in roughly 13-14 passages

  4. How big is your stomach • An adults stomach holds about 2 litres of food • A child’s stomach holds a little bit less • Your stomach gets bigger the more you eat • A large adult can eat and drink up to 4 litres of food and liquid at one meal!

  5. How long are the intestines? • The small intestine is more than 3 times as long as the whole body • In an adult, this is about 21 fee long • The large intestine is another 5 feet long • The whole tube from the mouth to the anus is about 30 feet long.

  6. As a group, vegetarians produce more gas than meat-eaters because the intestinal enzymes can’t digest the cellulose in vegetables’ cell walls.

  7. Definitions • Anatomy – is the study of structures • Physiology – is the study of functions

  8. Functions of the Digestive System • Ingest (eat) our food • Secretes (enzymes, bile, HCl) to assist in digestion • Digest (breaks down) food • Absorbs our food • Used to make energy • Used to help us grow and repair ourselves • Eliminates our food (rids us of indigestible waste)

  9. Steps of Digestion

  10. Epiglottis Salivary Glands Esophagus Liver Stomach Gall bladder Pancreas Large Intestine Small Intestine Rectum

  11. The Function of the Mouth • Ingestion • To begin digestion: • Mechanical • Chemical

  12. The Structures of the Mouth • Teeth • Salivary Glands • Tongue

  13. The Structures of the Mouth • Teeth • Takes the food • Begins mechanical digestion by breaking the food in to smaller pieces

  14. The Structures of the Mouth • Salivary Glands: ducted glands that produce saliva, which: • Liquefies food • Contains amylase and begins chemical digestion • Lubricates and softens the bolus of food • Enzymes in saliva kill bacteria

  15. The Structures of the Mouth • Tongue: 3 functions • Contains taste buds, at the back of the tongue. This protects us against poisons as they most often taste bitter. • Moves the food around in the mouth and towards the teeth to mix the food and the saliva • Pushes the bolus of the food to the back of the throat to the ‘swallow reflex center’.

  16. Pharynx • Structure: the back of the throat. Opens to the respiratory and digestive system. • Functions: when food is placed on the ‘reflex center’ by the tongue, the following things happen: • The soft palate covers the opening to the nose • The epiglottis covers the trachea • Peristalsis of the esophagus begins

  17. Epiglottis • Covers the trachea (lungs) when we swallow food

  18. Esophagus Structure: • 30 cm long tube • Connects the pharynx to the stomach • No digestion occurs • At the beginning of the stomach there is a ring of muscle called the cardiac sphincter which stops food from re-entering the esophagus

  19. Esophagus Function: • Food moves through the esophagus by a process called peristalsis • This is a slow, rhythmic contraction that pushes the bolus along Peristalsis continues down the length of the entire digestive tract.

  20. Stomach Structure: • It is a ‘J’ shaped organ • It can hold 2.3 litres of food • It has 3 layers of muscle • Circular • Longitudinal • Transverse

  21. Stomach Function: • Churns food and liquefies it (mechanical digestion) • This process is aided by the ridges in the mucosa layer of the stomach

  22. Stomach Function: • Begins the chemical digestion of proteins with 3 cell types • One type makes the inactive enzyme pepsinogen. These cells have lots of mitochondria for active transport. • Chief cells produce 3M Hydrochloric Acid (HCl). • Mucous cells produce mucous to protect the mucosa cells (inner stomach lining) from the HCl.

  23. Gastric Juices • Gastric juices contain: • Pepsinogen • Hydrochloric Acid (HCl) • Mucous

  24. Stomach Function: • Hydrochloric Acid (HCl) is released when proteins enter the stomach. This creates a pH of 2.5 • This transforms pepsinogen into an active hydrolytic enzyme Pepsin, which begins the digestion of the proteins into smaller amino acid chains HYDROCHLORIC ACID PEPSIN Pepsinogen Protein smaller polypeptides

  25. Stomach Function: • HCl will also be released, however, when you are stressed and there is chronic stimulation of your autonomic nervous system • This dissolves the mucosa layer of the stomach, and results in an ulcer

  26. Stomach Function: • The stomach empties within 4 hours. What leaves the stomach is an acidic liquid called chyme. • The pyloric sphincter at the base of the stomach will meter out the chyme into the duodenum at a slow, controlled rate.

  27. Pancreas • The pancreas is a dual organ • Half of it is an endocrine gland which makes hormones such as insulin and glucagon • Half of it is an exocrine gland which make the enzymes to digest carbs, fats, proteins and nucleic acids

  28. Pancreas Endocrine Gland • Insulin and Glucagon are made by specialized cells of the pancreas called the islets of Langerhans • If there is a high blood sugar, the pancreas will release insulin • Causes the liver to store it as glycogen • Promotes formation of fats • Causes cells to absorb glucose • If there is low blood sugar, the pancreas will release glucagon • Causes the liver to break down glycogen and release glucose

  29. Pancreas Exocrine Gland • Pancreatic juices contain • Sodium Bicarbonate • Pancreatic Amylase • Lipase • Trypsin • Nucleases

  30. Pancreas Exocrine Gland • Sodium Bicarbonate (NaHCO3) is a base and is released to neutralize the stomach acid SODIUM BICARBONATE Chyme pH 2.5 pH 8.5

  31. Pancreas Exocrine Gland • Amylase is an enzyme that converts uncooked carbohydrates to maltose PANCREATIC AMYLASE Uncooked Starch Maltose

  32. Pancreas Exocrine Gland • Lipase is an enzyme that converts lipids into fatty acids and glycerol LIPASE Lipids Fatty Acids & Glycerol

  33. Pancreas Exocrine Gland • Trypsin is an enzyme that converts small protein chains into dipeptides and tripeptides TRYPSIN Small polypeptides Di, Tri peptides

  34. Pancreas Exocrine Gland • Nucleases are enzymes that convert nucleic acids (DNA and RNA) into nucleotides NUCLEASES Nucleic Acids Nucleotides

  35. Small Intestine - Structures There are 3 regions: • Duodenum: completes the chemical digestion • Jejenum: finishes digestion and begins absorption • Ileum: This is the longest section and its function is to absorb all of the nutrients into the circulatory and lymphatic systems

  36. Small Intestine - Structures • The small intestine has an increased rate of absorption (speeds up diffusion) due to its highly convoluted walls with a very large surface area • There are folds in the mucosa layer of the small intestine called villi • These villi also have smaller folds called microvilli

  37. Small Intestine - Structures • The absorption takes place through the columnar cells of the microvilli • This involves active transport and requires much energy • The total surface area of the small intestine is 180m2 (this is the size of a tennis court)

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