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Digestion review
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Figure 23.1
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Salivary Glands• Produce and secrete saliva ‐ Function:
– Cleanses the mouth– Moistens and dissolves food chemicals – Chemical digestion ‐ contains enzymes that break down starch –AMYLASES
– Defense against bacteriaComposition:‐ Mostly water‐ Salivary amylase (breaks down starch)‐ Antibodies (IgA) and lysozyme (antibacterial enzyme)
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Salivary Glands ‐ Know the names of the three major glands
Figure 23.9a
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• Four layers of alimentary canal – These 4 basic layers are present throughout the tube!
• Mucosa• Submucosa• Muscularis externa• Serosa
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Mucosa• Moist epithelial layer that lines the lumen of the alimentary canal
• Three major functions:– Secretion of mucus(protect lining and ease food along)
– Absorption of end products of digestion– Protection against infectious disease (lymphatic tissue here – contains white blood cells which will react against foreign materials)
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• Submucosa – dense connective tissue containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nerves
• Muscularis externa – at least 2 muscle layers (circular and longitudinal)
• responsible for segmentation and peristalsis• Serosa – the protective visceral peritoneum (outer lining)
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Peristalsis
• What?• Where? (between mouth and stomach)
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Mouth through esophagus
• Mechanical? Where?
• Chemical? Where?• Enzymes?
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Figure 23.14a
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Stomach• Sphincters?
• Rugae?
THREE Muscle layers?function?
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Microscopic Anatomy of the Stomach
Figure 23.15b
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Microscopic Anatomy of the Stomach
Figure 23.15c
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Glandular cells of the Stomach– Chief cells – produce pepsinogen
• Pepsinogen is activated to pepsin by HCl• Pepsin‐ digests proteins to amino acids
– Parietal cells‐ produce HCl• HCl kills bacteria• Activates pepsin
‐Enteroendocrine cells – secrete gastrinstimulates digestive activity in stomach and small intestine
‐Mucous secreting cells ‐
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Stomach• Mechanical digestion?
• Chemical digestion?
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Small Intestine: Gross Anatomy
• Runs from pyloric sphincter to the ileocecalvalve
• Has three subdivisions: duodenum jejunumileum
Most digestion and absorption is completed by the ileum
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Small Intestine• Functions?• Digestion of all nutrients• Absorption of all nutrients
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Small Intestine: Microscopic Anatomy
Figure 23.21
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Small Intestine: Microscopic Anatomy
• Structural modifications of the small intestine wall increase surface area– Plicae circulares: deep circular folds of the mucosa and submucosa
– Villi – fingerlike extensions of the mucosa– Microvilli – tiny projections of absorptive mucosal cells’ plasma membranes
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Small Intestine: Microscopic Anatomy
Figure 23.21
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Small Intestine‐cell types• Simple columnar cells‐
Secretion (specialized cells)‐enzymes Absorption‐ digested nutrients
• Goblet cells – mucous Function?
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Small Intestine‐Absorption• Lacteals?
• Capillary network?
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Small intestine ‐ enzymes• Brush border enzymes
– Amylases: Carbs to sugars– Peptidases: Proteins to amino acids– Nucleases: Nucleic acids to sugars, phosphates and N‐bases
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Figure 23.34
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Hormones from small intestine
• Secretin and Cholecystokin (CCK) – stimulate pancreatic and bile secretion
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Small Intestine ‐Movement• Segmentation
• Pertistalsis
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Duodenum and Accessory Organs
Figure 23.20
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Liver:Functions
• Hepatocytes’ (liver cells) functions include:– Production of bile – this is the digestive function– Processing bloodborne nutrients– Storage of fat‐soluble vitamins– Detoxification– Production of blood proteins
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Composition of Bile• A yellow‐green, alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes
• Bile salts are cholesterol derivatives that:– Emulsify fat– Facilitate fat and cholesterol absorption
• The chief bile pigment is bilirubin, a waste product of heme
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The Gallbladder
• Thin‐walled, green muscular sac on the ventral surface of the liver
• Stores and concentrates bile by absorbing its water and ions
• Releases bile via the cystic duct, which flows into the bile duct –which flows into the duodenum
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Pancreas
• Exocrine function (in digestion)–Secretes pancreatic juice which contains enzymes for the breakdown of all types of food
• The pancreas also has an endocrine function –release of insulin and glucagon –to regulate blood sugar levels
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Composition and Function of Pancreatic Juice
• Bicarbonate solution of enzymes and electrolytes – Neutralizes acid chyme– Provides optimal environment for pancreatic enzymes
• Enzymes catalyze breakdown of carbs, lipids, proteins and nucleic acids
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Large Intestine
Figure 23.29a
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Large Intestine
• Functions:– Some chemical digestion by bacterial flora– Absorption of water and salts– Vitamin synthesis‐ K and B vitamins by bacterial flora
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Bacterial Flora• The bacterial flora of the large intestine consist of:– Bacteria surviving the small intestine that enter the cecum and
– Those entering via the anus• These bacteria:
– Colonize the colon– Ferment indigestible carbohydrates– Release irritating acids and gases (flatus)– Synthesize B complex vitamins and vitamin K