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Chapter 12. Digestion. The Start of Digestion. The Mouth  Food enters here The Teeth  mechanically breaks down food The Tongue  Chemically recognizes food. Moves food around the mouth. Assists in swallowing

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chapter 12

Chapter 12


the start of digestion
The Start of Digestion
  • The Mouth Food enters here
  • The Teeth  mechanically breaks down food
  • The Tongue  Chemically recognizes food. Moves food around the mouth. Assists in swallowing
  • Salivary Glands  Releases Saliva into the mouth. Saliva starts chemical breakdown and moistens food for swallowing.
The Pharynx The area in the very back of the mouth that receives air from the nasal cavities (air from the nose) and food from the mouth.
  • Esophagus  The food tube. The tube that goes from the mouth to the stomach. Many muscles surround this tube to help swallow. When muscles work to swallow its called Peristalsis
  • Trachea  Tube that goes down to the lungs to breath. This has cartridge rings so it is always open.
  • Epiglottis  covers the Trachea when swallowing so food does not go down into the lungs.
Nasal Cavity



Mouth Cavity

During swallowing the Trachea moves up and forces the Epiglottis to close over the trachea’s opening
  • Step 1: food is chewed in the mouth. Saliva is added for lubrication. Saliva also contains the digestive enzyme Salivary amylase. This enzyme breaks down starches into disaccharides like maltose
  • Step 2: Food is turned into a Bolus ( a ball of food) and pushed back of mouth by tongue.
  • Step 3: Muscles move the bolus down the esophagus. This is called peristalsis. The trachea moves up and the epiglottis closes access to the trachea. A muscle in the pharynx closes access to the nasal cavity
Nasal Cavity







into the stomach
Into the Stomach
  • The bolus moves down the esophagus and into the stomach.
  • The cardiac sphincter prevents the food from going from the stomach back up the esophagus.
  • A sphincter is a muscle that goes around a tube to act as a valve.
  • The cardiac sphincter is located at the joining of the stomach and the esophagus
The stomach has many gastric glands the release gastric juices into the stomach
  • Gastric Juice Contains:
    • Pepsin  enzyme breaks proteins to peptides
    • HCl acid  the acid kills some bacteria, activates pepsin, and breaks up food (but does not digest)
    • Mucus  slime that covers your stomach wall to protect it against the acid
  • Muscles around the stomach help mix the food with the gastric juices

Cardiac Sphincter

into the small intestine
Into the Small Intestine
  • After the stomach the pyloric sphincter opens and lets Chyme pass on into the small intestine
  • The first part of the small intestine is called the duodenum
  • The duodenum has ducts that enter the duodenum that release many different chemicals
Duodenum releases
    • Bile comes from liver. Bile is often stored in the Gall Bladder Emulsifies fat.
    • Pancreatic Juices
      • Juices from the organ called the pancreas
      • Sodium bicarbonate NaHCO3turns the acidic chyme basic
      • Pancreatic amylase  breaks down starch into disaccharides. Enzyme.
      • Trypsin  breaks down protein into peptides. Enzyme
      • Lipase  breaks down fat. Enzyme
      • Nuclease  breaks down nucleic acid into nucleotides
The small intestine is designed to absorb nutrients.
    • It has a huge surface area. This is because the inside of the small intestine has finger-like projections called villi. Each villi has finger-like projections called microvilli
  • The small intestine has a thin layer of mucus over it. Under the mucus are the villi and microvilli. Sugars and amino acids pass through the mucus and get moved into the blood vessels.
enzymes of the small intestine
Enzymes of the Small Intestine
  • The small intestine has many enzymes that work there to help let materials pass through the wall of the small intestine
    • Maltase digests maltose into glucose
    • Peptidase  digests peptides into amino acids
    • Nucleosidases  digests nucleotides into bases, sugar, and phosphate
Amino acids, sugars, and components of nucleotides, move into the blood by going through the microvilli
  • The parts of Fat (glycerol and fatty acids ) get moved into the Lacteal.
  • The lacteal is part of the lymphatic system.
moving into the large intestine
Moving into the Large Intestine
  • The Large Intestine is shorter in length but wider in diameter
  • Made up of several parts
    • Ascending colon – part of colon that goes up
    • Transverse colon – part of colon that goes along side
    • Descending colon – part of colon that goes down
    • Cecum – attached to ascending colon. Goes nowhere
    • Appendix – attached to cecum. Can get infected.
    • Rectum – where all the feces is stored. End of colon.
    • Anus – the muscular opening to expel feces.
Transverse Colon









what happens in the large intestine
What happens in the Large Intestine
  • The large intestine is full of bacteria. A lot the bacteria are anaerobic bacteria.
    • Anaerobic bacteria  bacteria that do not use oxygen. Bacteria that will die in the presence of oxygen.
  • These bacteria break down indigestible materials. They also produce some vitamins that are then absorbed by the large intestine wall.
  • The large intestine absorbs water out of the waste
  • Salivary Glands
    • Salivary amylase, moistens food
  • Stomach
    • Gastric Juices: Pepsin, HCl, Mucus
  • Pancreas
    • Pancreatic Juices: NaHCO3, Trypsin, Lipase
    • Insulin hormone is secreted into the blood
      • This hormone tells cells in the body to take up glucose
      • This hormone is released after eating when there is high glucose levels in the blood
    • Blood glucose levels are high  releases Insulin
      • Insulin causes cells to take up glucose
    • Blood glucose levels are low  releases Glucagon
      • Tells body to break down glycogen into glucose. Glycogen is found in the liver
      • Tells body to break down fat into glycerol and fatty acids.
    • Makes Bile
    • Removes any poisons from the blood
    • Stores Iron and many vitamins
    • Stores glycogen. This can be made into glucose
    • Regulates blood cholesterol levels
    • Produces Urea:
      • 2NH3 + CO2 H2N-C-NH2 + H2O


Salivary amylase

Pancreatic Amylase


Name the Enzyme Involved

Polysaccharides  Maltose  Glucose

Proteins  Peptides  Amino Acids

Fats  Glycerol + Fatty Acids