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Digestion
 The breaking down of food molecules for use by body cells
 Types:
o Mechanical: breaking down large food particles into smaller food
particles
o Chemical: chemical reactions that break down into usable
molecules
Digestive Functions
 Ingestion: introduction of food into stomach
 Mastication: chewing
 Propulsion: (movement- transportation of food throughout body)
o Deglutition: swallowing
o Peristalsis: moves material through digestive tract
 Mixing: segmental contraction that occurs in small intestine
 Secretion: lubricate, liquefy, digest
 Digestion: mechanical and chemical
 Absorption: bringing usable molecules into the bloodstream
 Elimination/Defaction: waste products removed from body
Names of Digestive System
 Continuous tube from the mouth to anus
 Approximately 30 feet long
 Known as…
o Digestive System
o Gastrointestinal (GI) tract
o Alimentary tract or canal
Four Layers of Tissues
 Mucosa: innermost, mucous membrane
 Submucosa: vascular, holds mucosa in place
 Muscularis: smooth muscle to move food
 Serosa: outermost layer continuous with the mesentery
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
1
Mouth
 Oral Cavity: opening surrounded by hard & soft palate, teeth, cheeks,
tongue
 Lips: lined with mucous membrane and covered with skin
o Labial frenulum- attaches lips to gums
o Uvula- prevents food from entering the nasal cavity when
swallowing
 Tongue: skeletal muscle covered with mucous membrane; involved in
speech, taste, mastication, swallowing
o Shapes chewed food with saliva into a ball – bolus
o Lingual frenulum- limits tongue movement
o Papillae- cover surface and sides of tongue
Salivary Glands
 Parotoid: (Largest) under skin in front of ears
 Submandibular: under base of tongue and below mandible
 Sublingual: (Smallest) under anterior portion of the tongue
 Saliva: 99.5% water, 0.5% other stuff
o Salts- to buffer chemicals
o Mucin- which forms mucous with matter (Lubrication)
o Lysozyme- kills bacteria
o Amylase- starch digesting enzyme
Digestion in Mouth
 Mechanical: mastication
o AKA chewing
 Chemical: salivary amylase
o breaks down starch
Pharnyx
 Common pathway for food and air
 Skeletal muscle lined by mucous membrane
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
2
Esophagus
 Muscular tube that lies closed behind the trachea
 Transports food from pharynx to stomach
 Secretes mucous to lubricate and aid transport
 Sphincters
o Upper & Lower
Degultition (Swallowing)
 Three Phases
o Voluntary- bolus of food moved by tongue from oral cavity to
pharynx
o Pharyngeal- involuntary; soft palate & uvula close off nasal
passage, epiglottis seals the larynx; breathing is interrupted as
food is pushed into the esophagus
o Esophageal- food is pushed down by waves of muscular movements
called Peristalsis
Stomach
 Regions
o Cardia- surrounds superior opening of stomach
o Fundus- above and to the left of the cardia
o Body- main portion of the stomach
o Pyloris- narrow, inferior portion
 Two muscular rings to regulate food passage – Sphincters
o Gastroesophageal sphincter (cardiac)- regulates food/chyme
into the stomach
o Pyloric sphincter- regulates food/chyme into the small intestine
Walls of Stomach
 Rugae- large folds in the stomach that help increase surface area
 Gastric glands- contain various cells and secrete gastric juice
o Pepsinogen: inactive enzyme
o Hydrochloric acid: converts pepsinogen into pepsin when at a pH
of 2
o Mucous
o Gastrin: hormone
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
3
Mechanical Digestion in Stomach
 Minutes after food enters the stomach, gentle mixing waves macerate
food and mix it with the gastric juice to form chyme
 Each wave will slosh the chyme around and splash it onto the rugae while a
small amount enters the small intestine
Chemical Digestion in Stomach
 Principal activity: protein digestion
 Pepsin breaks down the peptide bond b/w amino acids to form smaller
peptides
 Pepsin is only active in the acidic environment
 Gastric Lipase: aids in some lipid digestion
Digestion in the Stomach
 Absorbed in the stomach…
o Water
o Aspirin
o Alcohol
 Stomach empties within 2-6 hours into the small intestine
 Nutrient emptying order…
o Carbohydrates
o Proteins
o Lipids
Pancreas
 Secretes fluids to aid digestion in small intestine
 Lies behind the stomach
 Pancreatic duct sends fluids to small intestine
 Acini glands- secrete enzymes known as pancreatic juice
o Clear, colorless liquid
Pancreatic Juice
 Sodium Bicarbonate: makes it alkaline, which starts the action of
pepsin (pH 7.1 - 8.2)
 Pancreatic Amylase: digests carbohydrates
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
4
 Trypsin, Chemotrypsin, & Carboxypolypeptidase: digests proteins
 Pancreatic Lipase: digests lipids
 Ribonuclease & Deoxyribonuclease: digests nucleic acids
Liver
 Largest gland of the body! 
 Two lobes made up of lobules
 Hepatic (liver) cells produce bile
o Yellowish, brownish, or olive-greenish liquid
o pH of 7.6 – 8.6
o Bile salts aid in emulsification
 Breaking down fat droplets into smaller ones for increased
surface area
o Bilirubin: pigment
o Transported to the gallbladder and stored there
Liver Functions
 Carbohydrate Metabolism: maintains glucose levels
 Lipid Metabolism: breaks down some fatty acids
 Protein Metabolism: makes plasma proteins & converts ammonia to urea
 Removal of drugs & hormones: detoxify or excretes drugs into bile
 Excretes bile
 Makes bile salts
 Storage of vitamins & iron
 Phagocytosis of worn out RBC’s and WBC’s
 Activation of vitamin D
Gall Bladder
 Stores bile
 Can live w/o
Small Intestine
 Divisions
o Duodenum: smallest section
 stomach empties here
o Jejunum: middle section
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
5
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o Illeum: final section
 joins large intestine at ileocecal sphincter
21 feet of small intestine with added structures to increase surface area
o Almost all absorption occurs here
Circular folds: folds in mucosa to splash chyme & enhance absorption
Villi: fingerlike projections that contain capillaries, arteries, veins; all to
move absorbed substances quickly
Microvilli: smaller projections of the villi to further increase surface
area & absorption
Intestinal glands: in mucosa that secrete intestinal juice
o Clear, yellowish liquid quickly reabsorbed
o pH 7.6 with water and mucous
o Enzymes for Chemical Digestion…
 Maltase, Sucrose, Lactase: disaccharides to monosac.
 Peptidases: peptides to amino acids
 Ribonuclease, Deoxyribonuclease: nucleic acids
Mechanical Digestion of Small Intestine
 Segmentation: concentration of chyme & juice that sloshes b/w areas
of contraction of the muscularis
 Peristalsis: moves the chime steadily through intestines
Absorption in the Small Intestine
 Passage of digested substances and nutrients from the lumen to the blood
or lymph
 90% of all absorption takes place here
 Substances absorbed by diffusion, osmosis, & active transport
 Carbohydrates absorbed as monosaccharides
 Proteins absorbed as amino acids
 Lipids absorbed as monoglycerides & fatty acids
 Water – 9 Liters enter daily & 8 are reabsorbed
Large Intestine
 Main Functions
o Completion of absorption
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
6
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o Manufacture certain vitamins
o Formation of feces
o Elimination of feces
Cecum: pouch after ileocecal sphincter
Colon: ascending, transverse, descending, sigmoid
o Surface area increased by pouch like divisions; haustra
Rectum: last part; stores waste
o last inch is anal canal
Anus: opening to exterior
o Two sphincters: internal anal sphincter (involuntary) & external
anal sphincter (voluntary)
Chemical Digestion of Large Intestine
 No enzymes
 Bacterial ferment remaining carbohydrates
o Release hydrogen, carbon dioxide, & methane
 Vitamins K & some B’s are made and absorbed
Mechanical Digestion of Large Intestine
 Haustral churning: walls contract when haustra fill to a certain level
 Peristalsis: slower than other areas
 Mass peristalsis: strong muscular waves that pushes waste into the
rectum
Absorption & Feces Formation
 Chyme in the colon for 3-10 hours becomes rather solid; feces
o water, epithelial cells from mucosa, bacteria, undigested food
 All but 100mL of the 1L of water is absorbed
Defecation
 Emptying of the rectum
 Diarrhea: not enough water is absorbed because chyme travels too quickly
through intestine
o can cause dehydration
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
7
 Constipation: feces remains in colon too long, almost all the water is
absorbed
Digestive System Attachments
 Peritoneum & Serosa: secrete slippery fluid to glide organs over each
other
o outermost layer of the GI tract
 Visceral Peritoneum: covers some organs in abdominal cavity
 Parietal Peritoneum: the walls of the abdominal cavity
 Mesentary: binds small intestine to posterior abdominal wall
 Mesacolon: binds large intestine to posterior abdominal wall
 Falciform Ligament: attaches liver to the anterior abdominal wall and
diaphragm
Digestive Disorders
 Ulcers: lesions in a membrane
o Peptic: from gastric juice
o Gastric: in stomach
o Esophageal: in esophagus
o Duodenal: in small intestine
 Appendicitis: inflammation of appendix
 Cirrhosis: scarred liver due to chronic inflammation
 Colitis: inflammation of colon & rectum
 Hernia: protrusion of an organ through a membrane or cavity wall
LZHS McGraw Hill – Ch 24 Digestion Notes Filled-In
Anatomy H
8