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Digestive System Chapter 14
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The Digestive System – Overview
Is a long, hollow pathway called the alimentary canal. Begins at mouth and ends with the anus Consists of primary and periphery organs Food passes through primary organs Periphery organs only play a role, food does not enter these organs.
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The Digestive Tract Periphery Organs Fig. 14.1
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4 Stages of Digestion Ingestion Digestion taking in of food;
breaking down of food into smaller pieces Mechanical digestion Physical change only Breaks food into smaller pieces to increase surface area Chemical digestion Enzymatic breakdown to small organic molecules Enzymes – protein that chemically breaks down food Produced by the body's glands and organs. Results in simple molecules that easily pass into the blood.
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4 Stages of Digestion cont’d
Absorption transporting of molecules into the blood; Egestion removing of solid, undigested materials from the body.
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Digestive Tract – Mouth
Overall functions of mouth Begins process of digestion Mechanical digestion Chewing food Mixing with saliva Bolus formation Chemical digestion Begin digestion of starches to disaccharides
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Adult mouth Fig. 14.2
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Digestive Tract – Mouth cont’d
Tongue Taste buds- chemical sensation of taste Rough surface- aids in mechanical digestion Composed of skeletal muscle Roof of mouth Hard palate- composed of bone ridges for mechanical digestion Soft palate- composed of muscle Uvula Closes off nares during swallowing
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Digestive Tract – Mouth cont’d
Tonsils Lymphoid tissue Help protect against infection 3 Types Palatine- on both sides of pharynx Pharyngeal (Adenoids)- in nasopharynx Lingual - at base of tongue Tonsillitis- inflammation of tonsils
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Digestive Tract – Mouth cont’d
Salivary glands 3 pairs Collective secretions are called saliva Lubricates food so it can pass through canal Dissolves food particles Allows us to taste food! Contains amylase enzyme for starch digestion
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Digestive Tract – Mouth cont’d
Teeth Mechanical digestion 20 Deciduous teeth Baby teeth, first 2 years 32 adult teeth Tooth structure Crown Outer enamel covering Dentin Pulp Root pulp Fig. 14.2
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Digestive Tract – Mouth cont’d
Teeth cont’d 4 Types, each with a purpose Incisors Chisel shaped for cutting an slicing Canines Forms a single point used to hold and tear food. Premolars & Molars Broad flat teeth Crushing and grinding
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Digestive Tract – Mouth cont’d
Teeth cont’d Dental caries Cavities in teeth Prevented by flouride Brushing and flossing can help prevent development
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Digestive Tract - Pharynx
Connects nasal and oral cavities Part of both respiratory and digestive systems Muscular structure, actively pushes food down Swallowing reflex Uvula closes off nares Trachea moves upward under epiglottis Epiglottis closes airway off Bolus of food moves down into esophagus Esophagus
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Digestive Tract – Esophagus
Passes from pharynx to stomach Peristalsis Rhythmic wave of contraction throughout tract Propels bolus down esophagus to stomach Sole purpose is conduction of food
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Digestive Tract – Esophagus cont’d
Sphinctors Muscles that encircle tubes Act like valves Contraction-closes tube Relaxation- opens tube Esophageal sphinctor At entrance to stomach Not well developed Relaxes with peristaltic wave Bolus pushed through into stomach
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Digestive Tract – Esophagus cont’d
Heartburn Gastroesophageal reflux Acidic contents enter esophagus Causes irritation Vomiting Abdominal muscles contract Diaphragm contracts Positive pressure pushes stomach contents upward through esophagus
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Walls of Digestive Tract
Mucosa Epithelium supported by connective tissue Lines lumen Glandular epithelial cells produce enzymes Goblet cells produce mucous Submucosa Loose connective tissue Contains blood vessels Lymph nodes- Peyer’s patches
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Walls of Digestive Tract cont’d
Muscularis- 2 layers of smooth muscle Longitudinal –outer, runs along length of gut Circular-inner, encircles tube
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Walls of Digestive Tract cont’d
Serosa Squamous epithelium Supported by connective tissue Secretes serous fluid Lacking in esophagus
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Wall of digestive tract
Fig. 14.4
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The Stomach Thick-walled J-shaped organ Lies on left side of abdomen
Overall function of the stomach Mechanical digestion Mixing of food with gastric juice Forms semi-liquid called chyme Chemical digestion Initiation of protein digestion Storage of food
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The Stomach cont’d Rugae: folds in wall 3 muscle layers
Aid in mechanical digestion-friction Allows expansion 3 muscle layers Longitudinal Oblique Circular
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The stomach cont’d. Gastric glands Mucous cells Produce gastric juice
Chief cells Pepsinogen Inactive form of proteolytic enzyme Parietal cells HCl Activates pepsinogen to pepsin Decreases bacterial growth Mucous cells Produce thick protective mucus layer
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The Stomach cont’d. Fig. 14.5
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The Stomach cont’d. Ulcers Open sore in stomach wall
Helicobacter pyloris Infection decreases mucus production
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The Small Intestine Duodenum First 25 cm
Principal site of digestion of nutrients Receives bile from the liver Emulsification of fats Receives pancreatic juice from pancreas Many enzymes for digestion of nutrients Bicarbonate to neutralize pH
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The Small Intestine cont’d.
Jejunum and ileum Principal site of absorption of nutrients Lining has villi Increases surface area Outer layer of columnar epithelium Cells have microvilli- more surface area Villi contain lymph lacteals Absorb fatty acids and glycerol Villi contain blood capillaries Absorb sugars and amino acids
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Anatomy of the small intestine
Fig. 14.6
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Regulation of Digestive Secretions
Neurological control Pressure and distension Presence of particular types of food Hormonal control Gastrin Produced by stomach Stimulates gastric secretion Gastric inhibitory peptide (GIP) Produced by duodenum Inhibits gastric secretion
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Regulation of Digestive Secretions cont’d
Secretin and cholecystokinin (CCK) Produced by duodenum Acid stimulates secretin release Digested protein and fat stimulate CCK Effects of both hormones Increased pancreatic secretion Increased bile secretion
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Regulation of Digestive Secretions cont’d
Hormonal control of digestive gland secretions Fig. 14.7
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The Large Intestine Cecum Colon
Blind end of the large intestine, at juncture of s.i. Appendix Projection of cecum May play a role in fighting infections Rupture may cause peritonitis Colon Ascending, transverse, and descending portions Absorption of water, salts Terminates at the rectum
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The Large Intestine cont’d.
Fig. 14.8
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The Large Intestine cont’d.
Defecation reflex Feces forced into rectum by peristalsis Stretching of walls initiates reflex Rectal muscles contract Anal sphinctors relax Defecation occurs
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The Large Intestine cont’d.
Fecal composition 75% water Indigestible materials Intestinal flora (bacteria) 99% facultative anaerobes Produce vitamin K Color from breakdown of bilirubin and oxidized iron
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Defecation reflex cont’d
Fig. 14.9
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Accessory organs The pancreas Endocrine function Exocrine function
Insulin and glucagon Regulate blood glucose Exocrine function Sodium bicarbonate Pancreatic amylase-starch digestion Trypsin-protein digestion Lipase-fat digestion
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Accessory organs cont’d.
The liver Largest gland in the body Lobules-structural and functional units Triads Located in lobules A bile duct A branch of the hepatic artery A branch of the hepatic portal vein Detoxifies poisonous substances in blood Removes and stores iron and vit. A, D, E, K, and B12 Makes plasma proteins Regulates cholesterol
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Accessory organs cont’d
The liver cont’d. Glucose regulation Excess glucose stored as glycogen in the liver Glycogen broken down to glucose when needed When glycogen is depleted Converts fats and amino acids to glucose Requires deamination of amino acids Liver combines ammonia with carbon dioxide Forms urea
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Hepatic lobules Fig
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Accessory organs cont’d
The liver cont’d. Bile production Stored in gall bladder Composition Bilirubin From breakdown of hemoglobin Greenish color Bile salts Derived from cholesterol Emulsify fats
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Hepatic portal system Fig
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Accessory organs cont’d
The gall bladder Excess bile stored Secreted through common bile duct Cholesterol can precipitate out of solution Forms crystals Can become gall stones Obstructive jaundice
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