Overview of the digestive system (Pg. 473): The process of breaking food down into particles by mechanical and chemical means so that they are small enough to be used by cells.
○ 2 groups of Organs:
1) Gastrointestinal Tract/ GI tract/ Digestive tract/ Ailimentary Canal:
1) One continuous tube from mouth to anus that passes through the body (not INSIDE of the body)
□ Mouth/Oral cavity
□ Oropharynx- where the tonsils are
□ Esophagus
□ Stomach
□ Small Intestine
® Duodenum
® Jejunum
® Ileum
□ Large Intestine
® Cecum
® Colon
◊ Ascending
◊ Transverse
◊ Descending
◊ Sigmoid
◊ Rectum/Anus
2) Accessory Organs:
□ Teeth: Crush food, digestion starts within the mouth
□ Tongue: Swallowing/Speech, Muscles in the floor of the mouth
® Taste buds
□ Salivary glands: 3 sets
® Parotoid
® Sub-mandibular
® Sublingual:
◊ Saliva: 95% H20, 5% enzymes, and is controlled by the ANS
□ Pancreas:
® Pancreatic juices that are secreted into the small intestine
□ Liver:
® Produces bile
□ Gall Bladder:
® Stores bile.
○ Functions (Pg 473) 6 Basic Processes:
1) Ingestion:
1) Mouth
2) Secretion:
1) Happens at all levels, the enzymes breakdown, water mixes and hydrolyzes
3) Mixing/Propulsion:
1) Chewing, Stomach
4) Digestion:
1) Mechanical:
a) Starts in the mouth with chewing
2) Chemical:
a) Stomach enzymes (acids), Saliva in the mouth, S.I> pancreatic juice and bile.
5) Absorption:
1) Primary site of nutrient absorption is in S.I.
a) Water absorption: L.I. (Colon)
6) Defecation:
1) Removal and expulsion of waste products
○ 4 layers that form the wall of the GI tract (Pg 474-475):
§ (In order from innermost to outermost):
§ Mucosa:
□ Innermost layer of mucous membrane that lines the lumen.
® 3 layers:
◊ Epithelium
◊ Lamina Propia (connective tissue)
◊ Muscularis mucosae (smooth muscle)
□ Structures found in this tissue:
® Gland that secrete
® Lymph nodes
® Smooth Muscle that creates folds.
§ Submucosa:
□ Made of areolar (loose and fluffy) C.T.
□ Binds blood vessels and lymphatic's
□ Receives absorbed molecules
□ Contain nerves that control secretions of the ANS
§ Muscularis:
□ Primarily 2 thick layers of smooth muscle whose function is to mix and propel the food w/ the exception of the tube in the mouth and external anal sphincter.
§ Serosa:
□ Serous membrane->Part of the peritoneum, the largest serous membrane in the body
○ Segments of the GI tract (Pg 476):
§ Mouth (476):
§ Oropharynx (478):
§ Esophagus:
§ Stomach (480):
§ Small Intestine (486):
□ Duodenum
□ Jejunum
□ Ileum
§ Large Intestine (491):
□ Cecum:
□ Colon:
® Ascending
® Transverse
® Descending
® Sigmoid
® Rectum/Anus
• Digestive System Continued:
○ Overview:
§ Ingestion: Process of taking in food. Eating.
§ Secretion: Water, Acids, Buffer, and enzymes. Chemical digestion
§ Motility: Mixing, propulsion, movement. Mechanical digestion.
§ Digestion: Nutrients broken down so they can be absorbed.
§ Absorption: Movement of molecules passing through the mucosa into our internal environment.
§ Excretion: Removal of material that has not been absorbed into the body.
○ Mechanical Digestion:
§ Mastication: chewing of food, mixing with saliva.
§ Deglution: Swallowing (Bolus)
§ Peristalsis: wave like rippling movement of muscle layer, propels the product through the tract
§ Stomach: mixing waves (segmentation)
§ Colon: Haustral churning
§ Emulsification: Bile breaks down lipids so enzymes can work chemically (breaks them into smaller molecules)
○ Chemical Digestion:
§ When we eat we take in six main types of chemical substances.
□ Protein
□ Carbs (simple sugars)
□ Fats
□ Vitamins
□ Mineral
□ Water
§ Only 3 have to be further broken down, they need to be chemically digested to be absorbed.
□ Protein
□ Carbs
□ Fats
§ Enzymes:
□ Organic "catalyst"
□ Proteins that accelerate chemical reactions without becoming part of the product.
□ -Ase (suffix) : means that it is an inactive enzyme.
® Carbohydrates: Amylase: found in pancreatic juice, saliva, and the small intestine. (inactivated by acids)…so none are found in the stomach.
® Proteins: larger molecules and we use proteases to break down those. Gastric juice (stomach) pancreatic juice and the small intestine.
® Fats/Lipids: lingual lipase. Large fats must be mechanically broken down first in order to emulsify by bile salts.
○ Residue of digestion:
§ After we have chemically and mechanically broken everything down so that whatever nutes are available so they can be absorbed, and go where they need to go , we are going to have a product left in the tract that can not be used, this is called the residue of digestion.
§ Components of food that resist digestion and are thus eliminated from the intestines in the feces.
□ What we primarily find:
® Cellulose (dietary fiber), binds water and helps things move through our tract.
® Undigested connective tissue from meat, fascia fibers and ( mostly) collagen (fibers)
○ Digestive Secretion:
§ The release of various substances; Water, enzymes, acids, buffers.
§ Released from exocrine glands.
§ Saliva.
§ Gastric Juice.
§ Pancreatic juice.
§ Bile.
§ Intestinal Juice.
○ Control of digestive gland secretion:
§ 3 Overlapping phases
§ Cephalic: thought, sight, smell, taste.
§ Starts the gastric phase while that one is going on…
§ Gastric: stimulated by stretching of the stomach wall… as you put food in there are special Proprioceptors that stimulate glands.
§ Intestinal: Stretching of the intestinal wall.
○ Absorption:
§ The passage of substances through the intestinal mucosa into the blood and lymph
□ In the stomach there is very little absorption, alcohol and aspirin can go right through the stomach lining.
§ Most nutrients are absorbed in the small intestine.
§ Water is primarily absorbed in the large intestine.
○ Elimination:
§ Expulsion of the residue of digestion.
§ The residue is referred to as feces.
§ The act of elimination is referred to as defecation.
