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What are the main steps in the digestive process?
Ingestion, digestion, movement, absorption, and elimination
Ingestion
Intake of food via the mouth
Digestion
Mechanically or chemically breaking down foods into their subunits
Movement
Food must be moved along the GI tract in order to fulfill all functions
Absorption
Movement of nutrients across the GI tract wall to be delivered to cells via the blood
Elimination
Removal of indigestible molecules
What are the 4 major layers that make up the wall of the GI tract?
Mucosa, submucosa, muscularis, and serosa
Lumen
Central space right below the mucosa containing food being digested
Mucosa
Innermost layer that produces mucus to protect the lining and also produces digestive enzymes
Submucosa
2nd layer of loose connective tissue that contains blood vessels, lymphatic vessels, and nerves
Muscularis
3rd layer made of 2 layers of smooth muscle that move food along the GI tract
Serosa
Outer lining that is part of the peritoneum
What are the accessory organs of the digestive system?
Salivary glands, liver, gallbladder, and pancreas
What are the digestive tract organs?
Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus
Salivary Glands (Diagram definition)
Secrete saliva which contains digestive enzyme for carbohydrates
Liver (Diagram definition)
Major metabolic organ; processes and stores nutrients; produces bile for emulsification of fats
Gallbladder (Diagram definition)
Stores bile from liver, sends it to the small intestine
Pancreas (Diagram definition)
Produces pancreatic juice; contains digestive enzymes, and sends it to the small intestine; produces insulin and secretes it into the blood after eating
Mouth (Diagram definition)
Teeth chew food; tongue tastes and pushes food for chewing and swallowing
Pharynx (Diagram definition)
Passageway where food is swallowed
Esophagus (Diagram definition)
Passageway where peristalsis pushes food to stomach
Stomach (Diagram definition)
Secretes acid and digestive enzyme for protein; churns, mixing food with secretions, and sends chyme to small intestine
Small Intestine (Diagram definition)
Mixes chyme with digestive enzymes for final breakdown; absorbs nutrient molecules into body; secretes digestive hormones into blood
Large Intestine (Diagram definition)
Absorbs water and salt to form feces
Rectum (Diagram definition)
Stores and regulates elimination of feces
What is the pathway that food follows
Mouth → pharynx → esophagus → stomach → small intestine → large intestine → rectum → anus
How many pairs of salivary glands do humans have?
3
What do the salivary glands secrete?
Salivary amylase
What does salivary amylase begin in the digestive process?
Carbohydrate digestion
What do tonsils do?
Fight diseases
What type of tissue are tonsils made of?
Lymphatic tissue
What is the teeth’s function?
Mechanical breakdown of food
What is the tongue covered in?
Taste buds
What does the tongue assist in doing?
The mechanical breakdown and movement of food
The tongue forms ____ and moves it toward the pharynx
Bolus
Bolus
Mass of chewed food created by the tongue
How many teeth are in adults?
32
How many deciduous teeth are in babies?
20
What is each tooth made of?
A crown and a root
What covers the crown of teeth?
Enamel and dentin
Pharynx
A cavity between the mouth and esophagus that serves as a passageway for food (and air)
Esophagus
A long muscular tube that carries food to the stomach
What are the two ways we style food?
Voluntarily and involuntarily
What is the voluntary phase of swallowing food?
In the beginning, when food is being swallowed from the mouth into the pharynx is a voluntary act
What is the involuntary phase of swallowing food?
Once the food in the pharynx, swallowing becomes a reflex
Epiglottis
Covers the voice box to make sure food is routed into the esophagus
How does food move down the esophagus?
Peristalsis
Peristalsis
The rhythmic contraction of the GI tract
Stomach Functions
Store food, start digestion of proteins, and control movement of chyme into the small intestine
Stomach Physical Description
J-shaped organ with a thick wall
How many layers of muscle in the muscularis layer of the stomach wall are there?
3
What do the 3 layers of muscle in the stomach wall help with?
Mechanical digestion and allow it to stretch
The mucosa layer of the stomach has deep folds called ____, and _____ pits that lead into _____ glands that secrete _____ juice
Rugae; gastric
What does gastric juice contain?
Pepsin, HCl, and mucus
Pepsin
An enzyme that breaks down proteins
What does HCl in the stomach do?
Gives the stomach a pH of 2 which activates pepsin and helps kill bacteria found in food
What bacterium lives in the mucus of gastric juice?
Helicobacter pylori
What can helicobacter pylori in stomach mucus cause?
Gastric ulcers
What substance does the stomach empty into the small intestine?
Chyme
How long does it take for the stomach to empty chyme into the small intestine?
2-6 hours
How long is the average small intestine?
6 m/18 ft
What do the enzymes secreted by the pancreas into the small intestine do?
Digest carbs, proteins, and fats
What is secreted by the gallbladder into the small intestine?
Bile
What does the bile from the gallbladder in the small intestine do?
Emulsify fats
What does the absorption of digested food depend on in the small intestine?
A large surface area
How is a large surface area created in the small intestine?
Numerous villi and microvilli
Where do amino acids and sugar enter after being absorbed in the microvilli?
Capillaries
Where do fatty acids and glycerol enter after being absorbed in the microvilli?
Lacteals (small lymphatic vessels)
What is the process of carbohydrate digestion?
Carbohydrate → Pancreatic amylase → maltase → glucose → villi → blood capillary
What is the process of protein digestion?
Protein → trypsin → peptides → peptidase → amino acids → villi → blood capillary
What is the process of fat digestion?
Bile + fat globules → emulsification droplets → lipase → monoglycerides and free fatty acids → chylomicron → lymphatic capillary
Carbohydrate digestion major digestive enzymes
Salivary amylase, pancreatic amylase, maltase, and lactase
Protein digestion major digestive enzymes
Pepsin, trypsin, and peptidases
Fat digestion major digestive enzymes
Lipase
Nucleic acids digestion major digestive enzymes
Nuclease and nucleosidases
What is salivary amylase produced by and its site of action?
Salivary glands and mouth
What is pancreatic amylase produced by and its site of action?
Pancreas and small intestine
What is maltase produced by and its site of action?
Small intestine and small intestine
What is lactase produced by and its site of action?
Small intestine and small intestine
What is pepsin produced by and its site of action?
Gastric glands and stomach
What is trypsin produced by and its site of action?
Pancreas and small intestine
What is peptidases produced by and its site of action?
Small intestine and small intestine
What is nuclease produced by and its site of action?
Pancreas and small intestine
What is nucleosidases produced by and its site of action?
Small intestine and small intestine
What is lipase produced by and its site of action?
Pancreas and small intestine
What does salivary amylase digest?
Starch + water → maltose
What does pancreatic amylase digest?
Starch + water → maltose
What does maltase digest?
Maltose + water → glucose + glucose
What does lactase digest?
Lactose + water → glucose + glucose
What does pepsin digest?
Protein + water → peptides
What does trypsin digest?
Protein + water → peptides
What does peptidases digest?
Peptide + water → amino acids
What does nuclease digest?
RNA and DNA + water → nucleotides
What does nucleosidases digest?
Nucleotide + water → base + sugar + phosphate
What does lipase amylase digest?
Fat droplet + Water → monoglycerides + fatty acids
What is the pH of salivary amylase?
Neutral
What is the pH of pancreatic amylase?
Basic
What is the pH of maltase?
Basic
What is the pH of lactase?
Basic
What is the pH of pepsin?
Acidic
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