Human Nutrition Part 2

1. Human Nutrition Part 2

3. The Stomach • Muscular bag to store and digest food • Food enters through cardiac sphincter muscle • Can hold 1 litre of food for 4 hours

4. The Stomach • Lining of stomach is heavily folded forming millions of gastric glands • These produce gastricjuices • Mucousis made by gobletcells it prevents self digestion • Pepsinogenis made by zymogencells it is an inactive enzyme made active in the stomach it breaks proteins into peptides • Hydrochloricacid is made by oxyntic cells

5. Hydrochloric acid • This gives stomach a pH of 1 to 2! Very acidic • This acidity kills many bacteria, loosens fibrous and cellular foods, activates pepsinogen and denatures amylase from saliva • Too much acid in the stomach leads to heartburn – can be neutralised with alkalis such as alka seltzers or Rennies

6. Chyme • When the stomach is churning it turns food + gastric juices into a thick soupy mixture called Chyme • This leaves stomach in small amounts when the Pyloric Sphincter opens • Gastric juice could digest the stomach wall – this is prevented by mucous lining the stomach, mucous is alakaline, Pepsin is released as inactive pepsinogen, tightly packed cells line the stomach that can be replaced rapidly

7. If gastric juice does manage to digest the stomach wall ulcers can result • If ulcer becomes perforated bacteria could get into body and cause death

9. Small Intestine • 6 meter long tube! • First 25 cm is called the Duodenum (where most of the digestion takes place) • Remainder is Jejunumand Ileum these are the regions where absorption of digested food takes place

10. Small Intestine • Main function of duodenum is digestion • Cells that line the duodenum produce many enzymes • Products of the Liverand Pancreas also enter the duodenum

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12. The Pancreas • Secretes hormone insulin and digestive materials which form pancreatic juice • Pancreatic juice contains sodium bicarbonate salt to neutralise chyme from the stomach • Enzymes such as amylase and lipases are also present • The pancreatic duct leads from the pancreas to the duodenum

13. Liver – Complex organ Function • Makes Bile • Detoxifies the body – breaks down poisons such as alcohol and drugs • Breaks down excess amino acids to form urea • Converts glucose to glycogen for storage • Converts excess carbohydrate to fat • Stores vitamins (eg vit D) • Stores minerals (eg Iron) • Makes plasma proteins • Makes cholesterol for hormones • Produces heat to warm the blood and the body

15. Bile • Partly formed from remains of red blood cells • Consists of water salts and bile pigments (NO ENZYMES) • Made in the liver and stored in gall bladder • Gallstones in bile duct stop the release of bile • Functions • Emulsifies lipids – increases surface area (shake oil in a test tube to get emulsion) • Helps neutralise Chyme • Excretes pigments biliverdin and bilirubin made from dead red blood cells

16. Jejunum and Ileum • Food entering here is almost fully digested it is here that they will finally be absorbed into the body • Lining contains many villi to increase the surface area • The walls are only one cell thick and they have a rich blood supply to absorb the glucose, amino acids, vitamins and minerals

18. The capillaries carry the nutrients to the hepatic portal vein which takes them to the liver • The Liver acts like a giant warehouse allowing some nutrients out and storing others • Amino acids cannot be stored in the body so any that are not needed are broken down in a process called Deamination • This forms urea which is excreted in urine • Urea leaves through the Hepatic vein along with other wastes and goes to the kidneys

20. Villi • Lining of small intestine contains many foldings called villi (singular villus) • Each villus has approx600 microvilli! • This increases surface area for digestion and absorption • Intestinal glands between the villi produce intestinal juice

21. Inside each villus is a Lacteal containing lymph • Fatty acids and glycerol enter here are transported to the subclavian veins and distributed around the body

24. Large Intestine • 1.5 metres long • Food stays here for between 10 hours and a few days • Caecum and Appendix are Vestigial organs in humans - they have lost their function • Sometimes bacteria gather and grow in the apendix, bacterial waste builds up and causes pain if appendix ruptures it can be very serious

25. The Colon • This part of the large intestine reabsorbs water from the waste forming Faeces • Diarrhoea occurs if not enough water is reabsorbed • Constipation occurs if too much water is reabsorbed • Symbiotic bacteria in the colon produce vitamins while others digest cellulose

27. Rectum • Stores Faeces

28. A Balanced Diet • Seven components • Carbohydrate • Lipid • Protein • Minerals • Vitamins • Fibre • Water

29. The amount of food a person requires depends on age, activity, gender and health • Four food groups are: • Cereals breads and potatoes • Fruit and Vegetables • Milk cheese and yoghurt • Meat, fish and poultry

30. A Balanced Diet

31. Eating Disorders • Anorexia Nervosa and Bulimia Nervosa • Cause is unknown excessive desire to be thin • Bulimia involves binge eating and self – induced vomiting it is easier to disguise than anorexia • Both are extremely serious