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

• 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

Pharynx

Teeth

Mouth Cavity

During swallowing the Trachea moves up and forces the Epiglottis to close over the trachea’s opening

Swallowing• 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

Pharynx

Epiglottis

Trachea

Esophagus

Trachea

Bolus

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

aCardiac Sphincter

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 NaHCO3 turns 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

• 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• 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.

DescendingColon

Transverse Colon

Ascending Colon

Cecum

Appendix

Rectum

Anus

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

Identify all the parts

Review• 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

• Pancreas– 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.

• Liver– 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

=O

Optimal pH for the EnzymeEnzyme Location pHSalivary Amylase Mouth. Salivary Gland NeutralPancreatic Amylase Duodenum. Pancreas BasicPepsin Stomach AcidicTrypsin Pancreas. Duodenum BasicPeptidase Small Intestine BasicNuclease Pancreas. Duodenum BasicNucleosidase Small Intestine BasicLipase Pancreas, Duodenum Basic

SOURCE ENZYME FOOD PRODUCT

MOUTH (salivary glands)

Salivary amylase Polysaccharides Maltose

STOMACH Pepsin Proteins Peptides

PANCREAS Pancreatic amylase TrypsinLipase

Polysaccharides ProteinsFats

Maltose PeptidesFatty acidsand glycerol

SMALL INTESTINE Maltase Peptidases

Maltose Peptides Glucose Amino acids

FOOD TYPE ENZYME SOURCE PRODUCTS

CARBOHYDRATES Salivary amylase Pancreatic amylaseMaltase

Salivary glands PancreasSmall intestine

Maltose MaltoseGlucose

PROTEINS Pepsin TrypsinPeptidases

Stomach mucosa Pancreas Intestinal mucosa

Peptides PeptidesAmino acids

FATS Lipase Pancreas Fatty acidsand glycerol

Polysaccharides Maltose Glucose

Proteins Peptides Amino Acids

Fats Glycerol + Fatty Acids

Salivary amylasePancreatic Amylase

Maltase

PepsinTrypsin

Peptidase

Lipase

Name the Enzyme Involved

Remember to Drink lots of water