Digestive System

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Digestive system

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Food Intake - Ingestion

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Digestive Process

1. Ingestion

2. Peristalsis

3. Digestion

4. Absorption

5. Defication

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Digestion:• The breaking down of food molecules

1. mechanical digestion –

2. Chemical digestion –

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Composition

• Main Organs –

• Accessory Organs –

• Length – 6

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Structure

• Lumen –

• Digestive Wall – 4 layers– Mucosa or mucous membrane– Submucosa– Muscularis– Serosa

• Peritoneum

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Mucosa• Inner layer composed of– Surface Epithelium –

– Lamina Propria –

– Musculari mucosa –

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Submucosa

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• Contains:– – –

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Muscularis

• Consists of– –

• contractions help break down food physically, mix it with…

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Serosa

• Outermost layer• Composed of …

• AKA: the visceral peritoneum

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Peritoneum

• Serous Membrane– Parietal peritoneum:

– Visceral peritoneum:

– Peritoneum forms…

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Important folds of the peritoneum• Mesentary-

• Falciform ligament-

• Lesser omentum-

• Greater Omentum –

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Mouth

• Oral or buccal cavity formed by…

• Cheeks –

• Lips –

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Mouth cont.

• Vestibule – • Roof of Mouth– Hard palate –

– Soft palate –

– Uvula –

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Tongue

• Forms the floor of the oral cavity; skeletal muscle

• Extrinsic muscle –

• Intrinsic muscles –

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Tongue cont.

• Lingual Frenulum –

• Papillae –

• Taste Buds -

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Salivary glands

• 3 pairs of glands that produce saliva– Parotid –• mumps – •

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Salivary Glands cont.

• Submandibular –

• Sublingual –

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Composition of Saliva

• continuously secreted by salivary glands• secretion increases when…

• Volume: in 24 hours…– 99.5% H20 solvent + mucin = mucous– 0.5% solutes

• Usually controlled by…

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0.5% of solutes

• Salts – • Some organic compounds• Mucin-

• Salivary amylase – • Lysozyme –

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Teeth

• Dentition• Typical tooth consists of– Crown – – Root –– Cervix or neck –

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Teeth

• Composition– Dentin:

– Pulp cavity:

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Teeth

• Composition cont.– Root canals:

– Enamel:

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Tooth

• Dentitions: 2 sets of teeth– Decidnous, • Incisors – • Cuspids(canines) – • First and second molars –

– Permanent teeth (23)• Incisors (8)• Cuspids (4)• Bicuspids (8)• Molars (12) first second and third (wisdom teeth)

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Digestion in Mouth

• Mechanical–

• Chemical– • •

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Swallowing or Deglutition

• Moves food from mouth to stomach in 3 phases– Volutary stage:– Pharyngual stage:

– Esophagual stage:

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Esophagus

• A muscular, collapsible tube that lies behind the trachea and is about 10 inches long, that connects the pharynx to the stomach; leaves thoracic cavity through opening in diaphragm esophageal hiatus

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Esophagus cont.

• No enzyme secretion or absorption• Secretes…

• Passage of food is regulated sphincters–

– –

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Stomach

• J-shaped enlargement of the digestive tract; the superior portion is a continuation of the esophagus as the inferior portion connects to the duodenum

• Function– Primary -– Secondary -

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Stomach

• Anatomy– Cardia -

– Fundus –

– Body –

– Pylorus –

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Stomach

• Wall made of 4 layers with certain modifications– Mucosae – large folds-rugae; composed of

– Gastric Pits –

• Zymogenic (chief) cells: • Parietal cells:

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Stomach– Gastric pits• Parietal cells cont.

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– Intrinsic factor –

• Mucous cells –• Enteroendocrine cells –

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Stomach

– Muscularis – 3 layers• • •

• These allow for mechanical digestion, mixing with gastric juices and movement of food to duodenum

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Stomach Digestion

• Mechanical –

• Food remains in fundus …

Chemical – pH of 2Pepsin – Gastric lipase –

Very little digestion of lipids in adult stomach40

Stomach

• Gastric Secretion Regulation– – –

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Stomach

• Empties contents into duodenum 2-6 hours after ingestion– CH2O – – Protein – – Fats –

• Absorption–

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Pancreas

• Dual-function organ– Soft oblong gland 6 inches long 1 inch think– Lies posterior to the greater curvuture of the

stomach and is connected to duodenum by a duct– Divided into head, body, and tail– Islets of langerhans-

– 99% of cells are…

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Pancreas• Pancreatic Juice 1200-1500 mL per 24 hours– Clear, colorless liquid– pH 7.1-8.2– Compound mostly…– Enzymes

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Pancreas

• Secretion–

– Secretin –

• Rich in Na HCO– Cholecystokinin –

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Liver

• Located under the diaphragm and is divided into the right and left lobes by falciform ligament

• Common bile duct–

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Liver

• Common bile duct– Hepatic duct – – Cystic duct –

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Liver

• Composition– Many functional units called lobules which consist

of cords of:• Hepatic cells –

• Sinusoids –

• Kupffer cells –

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Liver

• Blood comes from hepatic artery and hepatic portal vein

• Bile:– –

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Liver

• Bile composition– H2O– Electrolytes (dilute and help buffer acids in chyme)– Bilirubin –

– Assortment of lipids –

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Liver

• Function – over 200– Manufactures bile salts– Manufactures…

– Phagocytosis of…– Break down…– Forms glycogen from…– Storage of…

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Liver

• Gallbladder– Stores and concentrate…

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Small Intestine

• Majority of digestion and absorption occurs; 20 feet long and 5-7.5 cm in diameter– Divisions• Duodenum (10 inches) secretions from pncreas and

liver• Jejunum – 8 feet• ileum

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Small intestine

• Plica– Transverse folds…

• Each supports a series of fingerlike projections• Intestinal villi -

– Mucosa• Contains intestinal glands –

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Small intestine

• Duodenum’s submucosa contains Brunner’s glands which

• Chyme in small intestine 3-5 hours• pH...

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Small intestine

• Peyer’s patches –

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Small intestine

• Chemical digestion – Table 14-2– CH2O –– Proteins – – Lipids –– Nucleic Acids –

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Small intestine• Absorption –

– Diffusion, facilitated diffusion, osmosis, active transport• • • • •

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Large Intestine

• “Colon” 5 feet in length x 2.5 inches wide; no villi, still have microvilli on exposed surfaces of epithelium– Functions• • • •

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Large Intestine

• 4 regions, ascending colon starts – ileocecal valve controls passage of chyme ito cecum– Cecum (3 in) -

– Colon –

– Rectum (8 in)– Anal canal (1 in)

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Large intestine

• Movement of Chyme 3-10 hours– Peristalsis– Mass peristalsis – – Bacterial digestion – – – Chyme –

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Large intestine

• Feces composition– – –

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