The digestive system

Random Fact Stomach growling is called borborygmic and happens all the time, but it is just louder when your stomach is empty because there is no food to muffle it.

Enzymes in digestion Digestive enzymes are classified based on their target substrates: Proteases and peptidases split proteins into small peptides and amino acids. Lipases split fat into three fatty acids and a glycerol molecule. Amylases split carbohydrates such as starch and sugars into simple sugars such as glucose. Nucleases split nucleic acids into nucleotides.

Enzymes in the mouth Lingual lipase: Salivary amylase: Salivary glands secrete enzymes and substances that aid in digestion and also disinfection. Lingual lipase: Lipid digestion starts in the mouth. Starts the digestion of the lipids/fats. Salivary amylase: Carbohydrate digestion starts initiates in the mouth. Breaks complex carbohydrates to smaller chains

Pepsin - the main gastric enzyme Protein digestion first starts in the stomach Chief cells produce pepsinogen – inactive form of pepsin Activated by the stomach acid  pepsin. Breaks down the protein in the food into smaller particles Peptide fragments and amino acids.

Hydrochloric acid (HCl) Stomach acid produced by parietal cells. Functions to denature the proteins ingested, to destroy any bacteria or virus that remains in the food, and also to activate pepsinogen into pepsin.

Intrinsic factor (IF) Produced by the parietal cells of the stomach. Is used to bind Vitamin B12, for absorption at the terminal portion of the ileum.

Mucin & Gastrin Mucin and bicarbonate are secreted by mucous cells to protects the lining of the stomach from HCl Gastrin is a hormone produced by the G cells of the stomach in response to stomach stretching occurring after food enters it, and also after stomach exposure to protein. It is an endocrine hormone that enters the bloodstream and eventually returns to the stomach where it stimulates parietal cells to produce hydrochloric acid (HCl) and Intrinsic factor (IF).

Gastric lipase Acidic lipase secreted by the gastric chief cells in the fundic mucosa in the stomach. pH optimum of 3–6. Gastric lipase & lingual lipase = the two acidic lipases

Cells and their function summary Parietal cells: Produce hydrochloric acid and intrinsic factor. Gastric chief cells: Produce pepsinogen. Chief cells are mainly found in the body of stomach Mucous neck and pit cells: Produce mucin and bicarbonate to create a "neutral zone" G cells: Produce gastrin in response to distention or protein stimulate parietal cell secretion Located in the antrum of the stomach

Words to know Enzymes Hormone Lingual lipase Salivary amylase Pepsin Pepsinogen Intrinsic factor Bicarbonate Parietal cell Gastric chief cell Mucous neck and pit cells G cells Gastrin Esophagus Hydrochloric acid Peristalsis Bicarbonate Bolus Parietal cell Upper and lower esophageal sphincters Gastric chief cell Fundus Body Muscle layers Mucous membrane Antrum Pyloric sphincter

Using the information provided… With a partner, draw the digestive system from the mouth to the stomach on a window Stages 1 & 2 Make sure to label the parts of the body we have discussed (words to know at the end of both PowerPoints) Include all of the enzymes and hormones in these areas

Questions to think about How do the layers in the stomach contribute to digestion? What factors may alter how digestion takes place?

Small intestine Named for its small diameter It is very long (avg. 6 m – 18 ft.)

Duodenum Most of digestion takes place here Ducts from liver, gallbladder and pancreas join to form the pancreatic duct (controlled by sphincter of Odi) Bile from liver & gallbladder - emulsifies fat Pancreatic juices from pancreas – has sodium bicarbonate  slightly basic environment that neutralizes chime

Digestive enzymes & hormones From pancreas and liver - enter by the pancreatic duct. Pancreatic enzymes and bile from the gallbladder = a response to the hormone cholecystokinin (produced in response to the presence of nutrients). Secretin (hormone) promotes the release of bicarbonate from pancreas Gastrointestinal inhibitory peptide (GIP) (hormone) believed to stimulate insulin secretion

Digestion of Proteins Degraded into small peptides and amino acids before absorption. Proteolytic enzymes (trypsin and chymotrypsin): secreted by the pancreas and cleave proteins into smaller peptides. Proteo – protein Lytic – break apart Carboxypeptidase: pancreatic brush border enzyme Splits one amino acid at a time.

Lipid digestion Lipids degraded into fatty acids and glycerol. Pancreatic lipase breaks triglycerides into free fatty acids and monoglycerides. Help from bile secreted by the liver and stored in the gall bladder. Bile salts attach to triglycerides to help emulsify them

Carbohydrate digestion Pancreatic amylase: breaks down starch into oligosaccharides. Brush border enzymes: Sucrase, maltase and lactase Other carbohydrates pass undigested into the large intestine and further handling by intestinal bacteria.

Carbohydrates that go undigested Lactase is absent in some adult humans lactose is not digested Some carbohydrates (cellulose) are digested Humans lack the enzyme for splitting the bonds between the glucose molecules.

Jejunum & Ileum Jejunum: 2nd part Ileum: 3rd part Area where the majority of absorption takes place Ileum: 3rd part Absorption of vitamins Small Intestine: Structure, Digestion, Absorption https://www.youtube.com/watch?v=0ygBLRNKxEY

Villi Increase surface area (SA) Absorb nutrients Outer wall of epithelial cells Each cell has thousands of microvilli (brush border) Increase surface area (SA) Absorb nutrients Sugars and amino acids enter the blood capillaries Glycerol and fatty acids enter epithelial cells. They are packaged as lipoprotein droplets and enter the lacteal.

Words to know Enzymes: Hormones: Gastrin Secretin GIP CCK Duodenum Jejunum Ileum Chime Bile Villi Microvilli Brush border Blood capillaries Lacteal Emulsification Pancreatic amylase Maltase Lactase Sucrase Pepsinogen Pepsin Trypsin Carboxypeptidase Gastric lipase Lipase Nuclease Nucleosidase Gastrin Secretin GIP CCK