Digestion Mouth to Small Intestine

Mouth Mouth starts mechanical digestion – Teeth grind and cut food Saliva starts chemical digestion – Salivary amylase breaks down amylose into disaccharides After chewing, tongue forms a ball from the food, called a bolus

Swallowing Reflex Epiglottis is a flap of tissue meant to prevent food from entering the trachea

Peristalsis Rhythmic contracts of smooth muscle around esophagus pushes food toward the stomach

Stomach Muscular and J-shaped Mechanical digestion (contractions of muscle to churn food) Chemical digestion (enzymes such as pepsin)

Stomach Stomach contains gastric pits, which have different cells specializing in different secretions

Gastric secretions CellSecretionPurpose/Function Mucus CellsMucus, Bicarbonate Protect the stomach lining from acid Ensure proper activity of some enzymes G CellsGastrinHormone that stimulates the release of HCl from parietal cells Parietal CellsHClHCl lowers pH of stomach, which denatures protein and activates pepsinogen into pepsin Chief CellsPepsinogenPepsinogen is activated by low pH into pepsin

Digestion in Stomach Salivary Amylase inactivated by low pH of stomach HCl denatures proteins (denaturing is the unfolding/breakdown of the 3D structure of proteins) Pepsin digests long polypeptides into shorter polypeptides

Small Intestine Anatomy Divided into three components: – Duodenum – Jejunum – Ileum 6-8 meters long 1.5” in diameter

Villi to Microvilli What benefit does having villi and microvilli give to the organism?

Small Intestine Liquid leaving the stomach is called chyme Chyme has a low pH, and must be neutralized to ensure it doesn’t damage the small intestine Secretin, a hormone from the stomach, has stimulated the release of bicarbonate from the pancreas Bicarbonate released by the pancreas into the small intestine, neutralizes the chyme (weakly basic pH8)

Stomach Pancreas Duodenum Gall Bladder Liver (Not shown) Liver ducts Common Bile Duct Pancreatic Duct

Secretin bicarbonate

Bile (made in liver) Bile (stored in gall bladder) Bile is made in the liver, stored in the gall bladder Bile is released when fat is digested Bile emulsifies fats.

Pancreatic Secretions: Pancreatic amylase – digests starch Pancreatic lipase – digests lipids Trypsinogen (trypsin) – digests small polypeptides into small peptides Chymotrypsin – digests small polypeptides into small peptides Peptidases – digest small peptides into smaller peptides/amino acids Small Intestine Secretions: Carbohydrases -Sucrase -Lactase -Maltase Peptidases – digest small peptides into smaller peptides and amino acids All of these enzymes work best at pH 8

Absorption Once all macromolecule polymers have been broken down into their monomer subunits, the subunits are small enough to be absorbed into the blood MonosaccharidesAmino acidsFatty acids/glycerol Transported to liver to be converted to glucose Some are converted into glucose for energy Used to provide energy to cells Extra glucose is converted to glycogen Some are transported throughout the body to be used to make body proteins/enzymes

Formative Quiz Answer the questions on the following slides as best as you can.

B F E C A D G 1.

2. Match the enzyme/secretion with the description Enzyme/SecretionDescription A – Pancreatic lipaseI – emulsifies fats B – Salivary amylaseII – stimulates release of bicarbonate in pancreas C – PepsinIII – digest small polypeptides into amino acids D – PeptidasesIV– digests polypeptides into smaller polypeptides E – bileV – product is glucose and fructose F – sucraseVI – protects stomach from HCl G – Pancreatic amylaseVII – stops working in the stomach H - SecretinVIII – digests fats in small intestine I - MucusIX – digests starch in small intestine

3. List three ways in which the body contributes to mechanical digestion.

4. Where is bile created?

5. Summarize the digestion of proteins.

6. Which of the following are secreted by the pancreas? a)Bile b)Amylase c)Lipase d)Bicarbonate e)Secretin f) Pepsin g) Trypsin h) Mucus j) Sucrase k) Fructase

7. How does the small intestine increase its surface area?