Chapter 17Digestive System

Digestive System

Functions of Digestive System• ingestion• mechanical digestion• chemical digestion• propulsion• absorption• defecation

Major Organs

Alimentary Canalvs.

Accessory Organs• Mouth• Pharynx• Esophagus• Stomach• Small Intestine (SI)• Large Intestine (LI)• Anus

• Teeth• Tongue• Salivary glands• Pancreas• Liver• Gall bladder

Alimentary Canal

Alimentary Canal Wall

Movements of the Tube

• mixing movements• peristalsis

Innervation of the Tube

• parasympathetic impulses – increase activities of digestive system

• sympathetic impulses – inhibit certain digestive actions

Mouth

• ingestion• mechanical

digestion• prepares food for

chemical digestion

Palates & Pharynx

Swallowing Mechanism

• soft palate and uvula raise

• hyoid bone and larynx elevate

• epiglottis closes off top of trachea

• longitudinal muscles of pharynx contract

• inferior constrictor muscles relax and esophagus opens

• peristaltic waves push food through pharynx

Swallowing Mechanism

Esophagus

Stomach

Radiograph of Stomach

Gastric Secretions

• pepsinogen• from chief cells• inactive form of pepsin

• pepsin• from pepsinogen in presence of

HCl• protein splitting enzyme

• hydrochloric acid• from parietal cells• needed to convert

pepsinogen to pepsin

• mucus• from goblet cells and mucous

glands• protective to stomach wall

• intrinsic factor• from parietal cells• required for vitamin B12

absorption

Mixing and Emptying Actions

Three Parts of Small Intestine

Mesentery

• suspends portions of the small intestine from the posterior abdominal wall

Intestinal Villus

Wall of Small Intestine

Large Intestine

Large Intestinal Wall

Functions of Large Intestine

• little or no digestive function• absorbs water and electrolytes• secretes mucus• forms feces• carries out defecation

Feces

• water• electrolytes• mucus • bacteria• bile pigments altered by bacteria provide color• smell produced by bacterial compounds

Accessory Organs

• Tongue• Teeth• Salivary glands• Pancreas• Liver• Gall bladder

Tongue

Primary Teeth

• 8 incisors• 4 cuspids• 8 molars

Secondary Teeth

Section of a Tooth

Salivary Glands

Secretions of Salivary Glands

• Parotid glands • clear• water, serous fluid• rich in amylase

• Submandibular glands• primarily serous fluid• some mucus

• Sublingual glands• primarily mucus• most viscous

Pancreas

Pancreatic Juice

• pancreatic amylase – splits glycogen into disaccharides (carbs)

• pancreatic lipase – breaks down triglycerides (fats)• trypsin, chymotrypsin, and carboxypeptidase – digests

proteins• nucleases – digest nucleic acids

Liver

Liver Functions

• produces glycogen (storage form) from glucose• breaks down glycogen into glucose• converts noncarbohydrates to glucose• oxidizes fatty acids• synthesizes lipoproteins, phospholipids, and cholesterol• converts carbohydrates and proteins into fats• deaminates amino acids • forms urea• synthesizes plasma proteins• converts some amino acids to other amino acids• stores glycogen, vitamins A,D, B12, iron, and blood

• **Makes, converts and stores many things!!!!**• **phagocytosis of worn out RBCs and foreign substances**• **removes toxins from blood**

Composition of Bile

• water• bile salts

• emulsification of fats• absorption of fatty acids, cholesterol, and fat-soluble

vitamins• bile pigments• cholesterol• electrolytes

Gallbladder

Regulation of Bile Release

• fatty chyme entering duodenum stimulate gallbladder to release bile