Digestion

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Digestion

• Mechanical and Chemical Breakdown of Ingested Food

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3 Stages in Digestion

• Digestion - breakdown of food into
  particles/molecules small enough to pass into the
  blood stream.
• 2 types of digestion
• mechanical (Mastication)
• chemical (Enzymes)
• Absorption of nutrients into the blood stream
• Elimination of indigestible nutrients

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Organs and Glands of the Digestive System

• Mouth
• Salivary Glands
• Esophagus
• Stomach
• Small intestine
• Liver
• Pancreas
• Gall bladder
• Intestinal Glands
• Large intestine

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Enzymes of the Digestive System

• Salivary amylase (starch ? sugar)
• Pepsin (proteins ? peptones and proteoses)
• Bile (emulisification of lipids)
• Pancreatic Juice
• Amylase (polysacchardies ? disacchardies)
• Trypsin (peptones and proteoses ? peptides)
• Lipase (lipids ? gylcerol and fatty acids)
• Intestinal Juice
• Peptidase (peptides ? amino acids)
• Maltase (Disaccharide ? Monosacchardies)

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The Mouth

• Mechanical breakdown of nutrients begins in the
  mouth by chewing (Mastication).
• The purpose of chewing is to increase the surface
  area of food.
• Chemical breakdown of starch also begins in
  mouth. Starch is converted into glucose by
  salivary amylase (secreted by the salivary
  glands)
• This mixture of food and saliva is made into a
  mass of food called a bolus and then pushed into
  the pharynx by the tongue which triggers
  involuntary swallowing.
• The esophagus is a muscular tube whose muscular
  contractions (peristalsis) propel food to the
  stomach.
• Peristalsis the wave action of muscle that
  moves food through the digestive system.

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The Stomach ( Churn, Churn, Churn)

• During a meal, the stomach gradually fills to a
  capacity of 1 liter, from an empty capacity of
  50-100 milliliters.
• At a price of discomfort, the stomach can distend
  to hold 2 liters or more.
• The stomach secretes about 2 liters of gastric
  juices per day.
• Gastric juice contains hydrochloric acid,
  pepsinogen, and mucus
• Hydrochloric acid (HCl) lowers pH of the stomach
  to activate pepsinogen ? pepsin. The acidic
  environment also helps to liquefy foods.
• Pepsin is an enzyme that controls the hydrolysis
  of proteins into peptides.
• The stomach also mechanically churns the food.
  Chyme, (liquefied food) the mix of acid and food
  in the stomach, leaves the stomach and enters the
  small intestine.

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The Small Intestine

• The small intestine is the major site for
  digestion and absorption of nutrients.
• 98 of digestion and 100 of absorption of
  nutrients occurs in the small intestines.
• Small intestine is made up of 3 parts
• Duodenum
• Jejunum
• Ileum

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From Stomach to Duodenum

• Chyme Liquefied food
• Acidic Chyme is pushed from the lower part of the
  stomach through the pyloric sphincter into the
  Duodenum (first part of small intestines).
• The stomach empties over a 1 to 2 hour period.

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Small Intestines (Doudenum)

• Chyme is pushed out of the stomach into the small
  intestines. The acid chyme stimulates the Liver
  and the Pancreas.
• The pancreas secretes digestive enzymes and
  stomach acid-neutralizing sodium bicarbonate.(2
  pH ? 8 pH)
• Enzymes - Lipase, Amylase, Trypsin
• The liver produces bile, which is stored in the
  gall bladder before entering the bile duct into
  the duodenum.
• Bile emulsifies fats (breaks fats into little
  pieces)

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Carbohydrate Digestion step by step

• The chyme is pushed into your small intestines
  (duodenum) which triggers the release of
  Pancreatic juice from the pancreas
• Amylase is one of the enzymes in the pancreatic
  juice which breaks down Polysaccharides into
  disaccharides
• Finally the intestinal glands release intestinal
  juice which includes the enzyme maltase.
  (jejunum)
• Maltase breaks down the disaccharides into
  monosaccharide which are absorbed by the blood
  stream.
• Monosaccharides are absorbed into blood stream
  and carried to the cells (ileum)

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Protein Digestion Step by Step

• Proteins begin to be digested by Pepsin in the
  stomach while being liquefied by the acid HCL.
• The chyme is pushed into your small intestines
  (duodenum) which triggers the release of
  Pancreatic juice from the pancreas
• Trypsin is one of the enzymes in pancreatic juice
  which continues the breakdown of proteins into
  Peptide bonds
• Finally the intestinal glands release intestinal
  juice which includes peptidase which breaks
  peptide bonds into amino acids. (jejunum)
• Those amino acids are absorbed into the blood
  stream and carried to the cells (ileum)

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Digestion of Lipids

• The chyme is pushed into your small intestines
  (duodenum) which triggers the release of
  Pancreatic juice from the pancreas and bile from
  your gall bladder.
• Bile emulsifies (chews) the lipids to increase
  surface area
• Lipase that is found in pancreatic juice
  hydrolyses lipids into a glycerol and 3 fatty
  acids
• The products are absorbed by the small
  intestines and carried to the cells for use.
  (jejunum and ileum)

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Enzymes and were they are Used

• Salivary amalyase (starch ? sugar) MOUTH
• Pepsin (proteins ? Polypeptides) STOMACH
• Bile (emulisification of lipids) DUODENUM
• Pancreatic Juice DOUDENUM
• Amylase (polysacchardies ? disacchardies)
• Trypsin (peptones and proteoses ? peptides)
• Lipase (lipids ? gylcerol and fatty acids)
• Intestinal Juice JUJUMIN and ILEUM
• Peptidase (peptides ? amino acids)
• Maltase (Disaccharide ? Monosacchardies)

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Villi and MircoVilli

• The small intestine is lined with vill and
  microvilli
• The purpose of villi and microvilli are to
  increase surface area in the small intestines.
  Increase the speed at which nutrients are
  absorbed
• The small intestines a 6 meter long tube has a
  surface area of 300 square meters or the surface
  area of a 500-600m long tube.
• Each villus has a capillary network supplied by a
  small artery. Absorbed nutrients pass through the
  microvilli into the capillary (blood stream),
  usually by passive transport (diffusion).

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The Large Intestine

• The large intestine is made up by the cecum,
  appendix, colon, and rectum.
• Digested food is pushed from the small intestines
  into the large intestine.
• No digestion takes place in the large intestines
• Material in the large intestine is mostly
  indigestible residue and liquid.
• Water, and salts are absorbed, the remaining
  contents form feces (mostly cellulose, bacteria,
  bilirubin).
• Bacteria in the large intestine, such as E. coli,
  produce vitamins (including vitamin K) that are
  absorbed.

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• There are 3 parts to the Colon
• Ascending Colon
• Transverse Colon
• Descending Colon

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The Liver and Gall Bladder

• The Liver makes Bile and stores it in the gall
  bladder.
• The Gall bladder sends bile to the small
  intestine when the acidic chyme from the stomach.
  Bile contains bile salts, which emulsify fats,
  making them susceptible to enzymatic breakdown.
• The liver also stores excess glucose in the form
  of glycogen.

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The Pancreas

• When the acidic chyme is pushed out of the
  stomach into the small intestines. IT simulates
  the pancreas to send pancreatic juice, which
  neutralizes the chyme, begins digestions of
  Carbohydrates, Lipids and continues digestion of
  protein.
• Pancreatic juice also contains Lipase which
  digested emulsified Lipids

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Stomach HCl

• Hydrochloric acid does not directly function in
  digestion
• it kills microorganisms that cause food
  poisoning.
• lowers the stomach pH to between 1.5 and 2.5
• activates pepsinogen (to pepsin) Pepsin is an
  enzyme that starts protein digestion.
• HCl inhibits further carbohydrate breakdown
  started by salivary amylase.
• HCl aids in the liquefaction of masticated food
• Epithelial cells secrete mucus that forms a
  protective barrier between the cells lining the
  inside of the stomach and the stomach acids.

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Ulcers

• Peptic ulcers result when the protective mucus
  fails and the HCl eats away at the lining of the
  stomach.
• Bleeding ulcers result when tissue damage is so
  severe that bleeding occurs into the stomach.
• Perforated ulcers are life-threatening situations
  where a hole has formed in the stomach wall.
• At least 90 of all peptic ulcers are caused by
  Helicobacter pylori (bacteria). Other factors,
  including stress and ibuprofen, can also produce
  ulcers.