Download 10.2 - The Human Digestive System - SV.pptx

2014-­‐07-­‐17 Recall The Diges)ve System Learning About Our Guts! •  Diges-on has four stages – Inges-on – Diges-on (mechanical and chemical) – Absorp-on – Elimina-on The Alimentary Canal Inges)on/Diges)on •  Adult humans have a diges-ve tract that ranges from 6.5m to 9m •  Although it is one con-nuous tube, it can be broken down into specialized segments •  Inges-on occurs when food is put into the mouth •  Mechanical and chemical diges-on both begin in the oral cavity (mouth) Mechanical –  Food is mas)cated (ground down by teeth) and formed into bolus by tongue Chemical diges-on –  Saliva aids the chemical breakdown of carbohydrates (by salvary amylase enzyme) Diges)on -­‐Chemical-­‐ Diges)on -­‐Chemical-­‐ Saliva – a watery secre-on in the mouth that begins the diges-ve process •  Contains amylase enzymes – break down starches (complex carbs) •  Lubricates food for swallowing •  Dissolves par-cles & makes food tas-ng possible •  Dissolved par-cles penetrate cells of taste buds on tongue and cheeks •  Nerve cells for taste s-mulated when receptor sites filled by chemical compounds with complementary shape
Salivary Glands •  Sublingual glands release saliva into mouth through smaller ducts 1 2014-­‐07-­‐17 Diges)on -­‐Mechanical-­‐ Teeth Diges)on •  Glands in the lining of the esophagus produce mucus which keeps the passage moist and aids in swallowing •  The bolus then enters into the stomach through the esophageal sphincter (aka cardiac sphincter) Diges)on •  Esophagus – muscular tube through which food passes from the mouth to the stomach •  Bolus ac-vates peristalsis –  Involuntary rhythmic muscle contrac-on moves the bolus down esophagus into the stomach Diges)on •  Sphincters – regulate movement of food into and out of the stomach •  Cardiac sphincter– relaxa-on allows food to enter the stomach •  Pyloric sphincter – allows food to exit stomach (enter duodenum) Diges)on •  Stomach – 1.5L capacity, “j” shaped, food storage •  Located in the abdominal cavity •  Rugae -­‐ stomach walls are folded, allows for expansion when full •  Stomach also undergoes peristalsis to con-nue mechanical diges-on and mixing of food with gastric juices •  3 layers of muscle fibres that contract and then relax to churn and mechanically break up pieces of food •  Chyme – a thick liquid produced in the stomach and made of digested food combined with gastric juice 2 2014-­‐07-­‐17 Diges)on Chemical Diges-on •  Gastric juices – secreted by glands in stomach •  Mixture of HCl(aq), salts, enzymes, water, and mucus •  Alkaline mucus protects stomach lining from being digested by gastric juices Absorp)on is made possible by enzymes Diges)on HCl •  Kills harmful substances •  Converts pepsinogen (protein diges-ng enzyme) to its ac-ve form pepsin •  PH ranges from 2.0 – 3.0 Absorp-on •  Diges)ve enzymes – help break down food substances into forms that can be absorbed and used by the body •  Diges)ve enzymes are normally secreted… •  In the mouth (part of saliva) •  By the stomach •  Released into small intes-nes from liver and pancreas Enzymes Involved in Diges)on Enzymes Involved in Diges)on •  Amylase: •  Protease: –  breaks down of –  breaks down protein starches. –  Secreted by pancreas –  (secreted in the saliva and the pancrea-c •  Pepsin juices) –  Breaks down protein •  Mycozyme: –  Released in stomach –  Breaks down starches –  (secreted in stomach) •  Lipase: –  breakdown fats (lipids) –  (secreted by the pancreas) 3 2014-­‐07-­‐17 Absorp)on •  Most diges-on occurs in the small intes-ne •  Up to 7m in length, 2.5cm in diameter •  Three dis-nct parts: –  Duodenum –  Jejunum –  Ileum •  Contains folds (villi) Absorp)on SMALL INTESTINE Duodenum •  First 25 – 30 cm •  Not mucus lined (cannot handle stomach acids) •  Liver and pancrea-c secre-ons bring pH up to between 5-­‐6 Absorp)on: Accessory Organs Liver •  Largest internal organ (1.5kg) •  Secretes bile, a greenish-­‐ yellow fluid •  Helps to digest fat •  Green colour from destruc-on of old RBCs (pigment eliminated as waste) Absorp)on •  Villi – finger like projec-ons lining the surface of the small intes-ne that increase the surface area to improve the absorp-on of nutrients Absorp)on: Accessory Organs Pancreas •  Secretes 1L of pancrea-c fluid into duodenum daily •  Pancrea-c fluid contains: –  Enzymes to digest carbohydrates, lipids, proteins –  Bicarbonate (helps to regulate enzyme func-on and pH in duodenum) Absorp)on: Accessory Organs Gall Bladder •  Stores bile that is created in liver •  Contains bile salts –  Essen-al for diges-on of fats –  Fats are insoluble, are suspended in chime as small droplets –  Bile salts act like detergent and allow for emulsifica-on 4 2014-­‐07-­‐17 Absorp)on SMALL INTESTINE Jejunum •  Next 2.5m •  Contains lots of folds of the inner wall •  Breaks down remaining proteins and carbohydrates •  pH between 7 – 9 Absorp)on The Importance of pH on Enzyme Ac)vity •  Enzyme func-on and rate of ac-vity is governed by: –  Temperature –  pH Absorp)on SMALL INTESTINE Ileum •  Last 3m •  Contains fewer and smaller villi than duodenum or jejunum •  Func-on is to absorb nutrients, as well as to push remaining undigested material into large intes-ne •  pH between 7-­‐9 Absorp)on LARGE INTESTINE •  Also known as colon •  Absorb water from alimentary canal •  About 90% of H2O is absorbed back into the blood •  Volume of indiges-ble food mostly (indiges-ble plant maher) is reduced by about 2/3 Absorp)on LARGE INTESTINE •  Three sec-ons: –  Ascending –  Transverse –  Descending •  Billions of anerobic bacteria •  Some of these bacteria produce vitamins: folic acid, B vitamins, vitamin K ELIMINATION 5