Digestive System Chapter 14

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Alimentary canal – digestive system that includes the mouth, pharynx, esophagus, stomach, intestines, and anus  About 30 feet in length

Mouth and Throat Digestion starts in the mouth Salivary gland – produces saliva that contains amylase  A digestive enzyme that breaks down carbohydrates Salivary glands are accessory organs

Mouth and Throat The mouth undergoes both chemical and mechanical digestions  Chemical digestion – the use of enzymes and chemicals to break down foodstuffs  Mechanical digestion – the use of teeth and muscular movements to break down foodstuffs

Mouth and Throat Teeth – bony structures used to break down foods mechanically Four different types  Incisors – used to pierce food  Canines – used to pierce and tear food (mainly meats)  Premolars and molars – used to grind food (Premolars)

Mouth and Throat Mastication – the process of chewing food Tongue – used to move food around during chewing; also contains taste buds Bolus – food mixed with saliva to form a wet lump

Mouth and Throat Hard and soft palates separate the oral cavity from the nasal cavity

Mouth and Throat Uvula – small, rounded muscular structure dangles from the palate; prevents food from entering the nasal cavity

Mouth and Throat Epiglottis – cartilaginous structure that protects the superior opening of the larynx  When food is swallowed, the larynx is pulled upward and the epiglottis blocks the larynx Breathing stops when swallowing occurs

Esophagus 10-inch long muscular tube that connects the pharynx to the stomach Boluses travel through the esophagus via peristalsis Peristalsis – a wave of muscular contractions that moves foodstuffs throughout the alimentary canal

Esophagus Takes about 4-8 seconds to move a bolus from the top to the bottom Two portions of the esophagus  Upper esophageal sphincter  Lower esophageal sphincter Sphincter – circular muscle that allow substances to enter and exit

Stomach Holds and digests food Protein digestion starts Muscular walls contract and churn food with hydrochloric acid that break down proteins

Stomach Food is converted into chyme (a soupy, partly digested material) which the stomach stores until it releases into the small intestine

Stomach Regions of the stomach  Cardiac – near the heart  Fundus – the bottom or base of an organ, or the part of a hollow organ  Body – midportion  Pylorus – funnel-shaped terminal end

Stomach Pyloric sphincter - a ring of muscles forms a valve between the stomach and small intestine Gastric folds (rugae) – help grind and digest food; increase the surface area of the stomach

Stomach Hydrochloric acid (HCl) has a pH level of 1-2 (highly acidic) Stomach has a pH level of 1-2 during digestion and 3-4 when food is absent

Stomach Gastric pits – millions of openings that line the stomach Gastric glands – secrete gastric juice  Gastric juice consists of enzymes and HCl

Stomach Chief cells – produce protein-digesting enzymes (pepsinogens)  Pepsinogen – inactive form of the enzyme  Pepsin – active form Parietal cells – produce HCl  HCl activates pepsinogen to pepsin

Accessory Organs Accessory organs aid in digestion Salivary glands – found in the mouth Liver – the body’s largest gland; detoxifies the blood and produces bile  Gland – an organ that secretes chemical substances (hormones, bile, etc.)  Bile – used to break down fats

Accessory Organs Gallbladder - green muscular sac that hangs from the liver; collects, stores, and concentrates bile from the liver Bile reaches the gallbladder from the common hepatic (referring to liver) duct Bile enters the duodenum via common bile duct

Accessory Organs Jaundice – Buildup of bile within the liver leading to bile pigments circulating through the body could cause tissues to turn yellow

Accessory Organs Pancreas – produces insulin and enzymes that aid in digestion  Insulin – helps regulate the amount of sugar in the blood  Enters the duodenum via pancreatic duct

Small Intestine Approximately 20 feet long and 1 inch in diameter Absorbs 90% of nutrients and water Villi – millions of fingerlike projections used to increase the surface area in the small intestine (used for absorption)

Small Intestine Duodenum – the first portion of the small intestine, where secretions from the liver (bile), pancreas (insulin), and stomach (chyme) are received;

Small Intestine Jejunum – the long, coiled middle portion of the small intestine Ileum – the final portion of the small intestine

Large Intestine Absorbs the remaining nutrients and water from indigestible foods, compacts the remaining matter, and eliminates it as feces Ascending colon – situated on the right side of the body that travels upward

Large Intestine Transverse colon – situated horizontally above the small intestine Descending colon – on the left side of the body; stores stool that will eventually empty into the rectum

Large Intestine Sigmoid colon – the s-shaped curve between the descending colon and the rectum Rectum – About 5 inches long; feces are stored here briefly prior to defecation

Large Intestine Anus – the sphincter through which fecal matter is expelled Peristaltic waves in the colon and contraction of the abdominal muscles trigger defecation Anus

Digestive Problems Diarrhea – the lack of absorbing water in feces resulting in a loose, watery stool Constipation – excessive water absorption of feces resulting in a dry stool Acid reflux – hydrochloric acid traveling up the esophagus Heartburn – a sensation of tightness, pain or discomfort in the middle of the chest