Chapter 17 - Digestive System Flashcards

Chapter 17 – Digestive System Part 1 – General Characteristics

• Digestion is the mechanical and chemical breakdown of foods into forms that cell membranes can absorb.
  • Mechanical digestion: Breaks down large pieces of food into smaller ones without changing the chemical composition.
  • Chemical digestion: Uses enzymes to break down food particles, changing them into simpler chemicals.
    • Carbohydrates are broken down into monosaccharides.
    • Proteins are broken down into amino acids.
    • Lipids are broken down into fatty acids and glycerol.
    • Nucleic acids are broken down into nucleotides.

Digestive System Portions

• The digestive system consists of two portions:
  • Alimentary canal:
    • The food passageway.
    • Consists of organs that extend from the mouth to the anus.
    • Includes the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anal canal.
    • It is a muscular tube, about 8 meters long.
  • Accessory organs:
    • Consists of organs that empty secretions into the alimentary canal.
    • Food does not pass through them.
    • Includes the salivary glands, liver, gallbladder, and pancreas.

Alimentary Canal and Accessory Organs Functions

• Alimentary Canal:
  • Mouth: Mechanical breakdown of food; begins chemical digestion of carbohydrates.
  • Pharynx: Connects mouth with esophagus.
  • Esophagus: Peristalsis pushes food to the stomach.
  • Stomach: Secretes acid and enzymes; mixes food with secretions to begin enzymatic digestion of proteins.
  • Small intestine: Mixes food with bile and pancreatic juice; final enzymatic breakdown of food molecules; main site of nutrient absorption.
  • Large intestine: Absorbs water and electrolytes to form feces.
  • Rectum: Regulates elimination of feces.
  • Anus
• Accessory Organs:
  • Salivary glands: Secrete saliva, which contains enzymes that initiate the breakdown of carbohydrates.
  • Liver: Produces bile, which emulsifies fat.
  • Gallbladder: Stores and concentrates bile and releases it into the small intestine.
  • Pancreas: Produces and secretes pancreatic juice, containing digestive enzymes and bicarbonate ions, into the small intestine.

Wall of Alimentary Canal

• The wall of the alimentary canal is composed of 4 layers; from innermost to outermost, the layers are:
  • Mucosa: The innermost layer, a mucous membrane.
    • Folded in some areas to increase surface area.
    • Absorbs dietary nutrients and secretes mucus and enzymes.
  • Submucosa: Connective tissue layer.
    • Nourishes cells and transports absorbed food molecules.
  • Muscularis (externa): Muscle tissue; contains circular and longitudinal layers.
    • Moves the tube and food materials.
  • Serosa: The outermost layer; serous fluid eliminates friction.
    • Visceral peritoneum of organs within the abdominal cavity.

Mucosa Details

• Includes:
  • Epithelium
  • Villi
  • Lacteal
  • Lymph nodule
  • Intestinal gland
  • Nerve plexuses
  • Microvilli
  • Goblet cell
  • Simple columnar epithelium
  • Capillaries

Movement in the Alimentary Canal

• Two types of movement in the alimentary canal:
  • Mixing movements:
    • Muscle in small sections contracts rhythmically.
    • Does not move materials in one direction.
    • Example: segmentation in the small intestine, churning in the stomach.
  • Propelling movements:
    • Moves materials in one direction.
    • Peristalsis: Ring of contraction progresses down the tube.
      • Propels food particles down the tract in a wavelike motion.

Nervous System Control

• Branches of the sympathetic and parasympathetic divisions of the autonomic nervous system extensively innervate the alimentary canal.
  • Autonomic control of digestive activity:
    • Parasympathetic impulses: Increase activities of the digestive system (secretion and motility).
    • Sympathetic impulses: Inhibit digestive actions (secretion and motility).
  • Many postganglionic fibers are organized into a nerve plexus:
    • Submucosal plexus: Controls secretions.
    • Myenteric plexus: Controls gastrointestinal motility.
  • Enteroendocrine cells:
    • Found in the stomach and small intestine.
    • Secrete hormones to regulate GI organs and processes.

Digestive System Part 2 – Mouth, Pharynx, and Esophagus

• The mouth is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking down food into smaller pieces and mixing them with saliva.
  • Mastication is the process of chewing.
  • The oral cavity is enclosed by the cheeks, lips, palate, and tongue.
    • The oral vestibule is the space between the cheeks, lips, and teeth.
  • The mouth also functions as an organ of speech and has sensory receptors.

Mouth Anatomy

• Includes:
  • Lip
  • Hard palate
  • Soft palate
  • Uvula
  • Palatine tonsils
  • Tongue
  • Oral vestibule
  • Epiglottis
  • Lingual tonsils
  • Papillae

Teeth

• Deciduous (baby) teeth:
  • Central incisor: Eruption at 6-9 months
  • Lateral incisor: Eruption at 7-11 months
  • Canine: Eruption at 16-20 months
  • 1st molar: Eruption at 12-16 months
  • 2nd molar: Eruption at 20-26 months
• Permanent teeth:
  • Central incisor: Eruption at 6-8 years
  • Lateral incisor: Eruption at 7-9 years
  • Canine: Eruption at 9-12 years
  • 1st premolar: Eruption at 10-12 years
  • 2nd premolar: Eruption at 10-12 years
  • 1st molar: Eruption at 6-7 years
  • 2nd molar: Eruption at 11-13 years
  • 3rd molar (wisdom tooth): Eruption at 17-25 years

Tooth Structure

• Includes:
  • Enamel
  • Dentin
  • Crown
  • Pulp (in pulp cavity)
  • Gingiva
  • Root
  • Alveolar process
  • Periodontal ligament
  • Root canal
  • Cementum

Salivary Glands

• Salivary glands secrete saliva.
  • Saliva lubricates and binds food together into a bolus.
  • Saliva also has an enzyme called salivary amylase, which begins the chemical digestion of carbohydrates.
  • Each salivary gland is composed of 2 types of cells:
    • Mucous cells secrete mucus.
    • Serous cells secrete a watery substance containing the salivary amylase.
  • Major salivary glands include:
    • Parotid glands: Largest glands found anterior and slightly inferior to the ears.
    • Submandibular glands: Are in the floor of the mouth on the inside surface of the mandible.
    • Sublingual glands: Small salivary glands located on the floor of the mouth inferior to the tongue.

Pharynx

• The pharynx, commonly called the “throat”, is posterior to the oral cavity and extends from the nasal cavity to the esophagus.
  • Passageway for food and air and does not assist in food digestion.
  • Divided into three parts:
    • Nasopharynx: Superior to the soft palate.
      • Passageway for air only.
      • Connected to the middle ear through the auditory (eustachian) tube.
    • Oropharynx: Posterior to mouth down to the epiglottis.
      • Passageway for food and air.
    • Laryngopharynx: Inferior to the oropharynx from the epiglottis to the cricoid cartilage.
      • Passageway for food and air.
  • The inner circular muscles of the pharynx form the constrictor muscles (superior, middle, and inferior) which are needed for swallowing.

Pharynx Anatomy

• Includes:
  • Nasal cavity
  • Pharyngeal tonsil
  • Opening of auditory tube
  • Soft palate
  • Nasopharynx
  • Oral cavity
  • Uvula
  • Palatine tonsil
  • Oropharynx
  • Lingual tonsil
  • Epiglottis
  • Laryngopharynx
  • Esophagus
  • Trachea
  • Mandible
  • Superior constrictor muscles
  • Skull
  • Middle constrictor muscles
  • Posterior surface of the tongue
  • Larynx
  • Inferior constrictor muscles
  • Circular esophageal muscle

Swallowing

• Steps:
  • The tongue forces food into the pharynx.
  • The soft palate, hyoid bone, and larynx are raised, the tongue is pressed against the palate, the epiglottis closes, and the inferior constrictor muscles relax so that the esophagus opens.
  • Superior constrictor muscles contract and force food into the esophagus.
  • Peristaltic waves move food through the esophagus to the stomach.

Esophagus

• The esophagus is a straight, muscular tube, mostly located in the mediastinum, posterior to the trachea.
  • Connects the pharynx to the stomach and does not assist in digestion.
  • Peristalsis and gravity aid the movement of food and fluid through the esophagus.
  • Passes through the diaphragm in an opening called the esophageal hiatus.
    • Hiatal hernia: When part of the stomach protrudes through the esophageal hiatus and into the thoracic cavity.
  • The lower esophageal sphincter (cardiac sphincter) relaxes to allow the passage of food and fluid into the stomach.

Esophagus Anatomy

• Includes:
  • Esophagus
  • Diaphragm
  • Esophageal hiatus
  • Stomach

Digestive System Part 3 – Stomach

• The stomach is a J-shaped, pouchlike organ that hangs inferior to the diaphragm in the upper-left portion of the abdominal cavity.
  • Has a capacity of about 1 liter or more.
    • The inner lining of the stomach has thick gastric folds (rugae) that unfold when the stomach distends.
  • Receives food from the esophagus and mixes it with gastric juice.
    • Initiates chemical digestion of proteins.
    • Has limited absorption of nutrients like water, salts, lipid-soluble drugs, and alcohol.
    • Moves food to the small intestine.
  • Has three layers of muscle to help mix (churn) the food with acid and enzymes:
    • Circular layer, longitudinal layer, and oblique layer.

Stomach Anatomy

• Includes:
  • Duodenum
  • Lower esophageal sphincter
  • Esophagus
  • Fundus
  • Cardia
  • Body
  • Pyloric sphincter
  • Lesser curvature
  • Pyloric opening
  • Pylorus
  • Pyloric canal
  • Pyloric antrum
  • Gastric folds (rugae)
  • Greater curvature

Stomach Wall Muscle Layers

• Esophagus
  • Circular layer of smooth muscle cells
  • Longitudinal layer of smooth muscle cells
  • Oblique layer of smooth muscle cells
    Esophagus
  • Longitudinal layer of smooth
    muscle cells

Gastric Glands

• The surface of the inner layer of the stomach is studded with many small openings called gastric pits located at the ends of tubular gastric glands.
  • Gastric glands contain four types of secretory cells:
    • Mucous neck cells secrete mucus.
      • Mucus protects the inner lining of the stomach.
    • Chief cells secrete pepsinogen and gastric lipase.
      • Pepsinogen is a zymogen enzyme that is a precursor to pepsin, which digests proteins.
      • Gastric lipase is a lipid-digesting enzyme that is minimally active in the stomach.
    • Parietal cells secrete hydrochloric acid (HCl) and intrinsic factor.
      • HCl converts pepsinogen into pepsin and denatures the proteins found within food.
      • Intrinsic factor is needed for the absorption of vitamin B12 (cobalamin) in the small intestine.
        • A lack of intrinsic factor leads to pernicious anemia.
    • Enteroendocrine cells secrete hormones that regulate gastric secretion and/or motility:
      • Gastrin and histamine increase gastric secretion.
      • Somatostatin inhibits gastric secretion.
  • Gastric gland secretions combine to form gastric juice.
    • Gastric juice combines with partially digested food to form chyme.

Gastric Gland Anatomy

• Includes:
  • Mucous neck cell
  • Gastric gland
  • Gastric pits
  • Mucosa
  • Submucosa
  • Muscularis
  • Parietal cell
  • Chief cell
  • Serosa
  • Enteroendocrine cell

Gastric Secretion

• Gastric secretion is controlled by nerves and hormones and occurs in three phases:
  • Cephalic phase: Increased parasympathetic activity (via the Vagus nerve) due to sight, taste, smell, and thought of food.
  • Gastric phase: Stretch of the stomach wall increases gastrin secretion, which increases gastric secretions.
    • HCl released from parietal cells comes from blood. This leads to an alkaline tide in the blood.
  • Intestinal phase: Initially releases intestinal gastrin, which increases gastric secretions.
    • As the duodenum fills, a sympathetic reflex inhibits gastric release.
    • Enterogastric reflex: Ensures the stomach slows down as the duodenum fills. Proteins and fats in the duodenum stimulate cholecystokinin release, which decreases gastric motility.

Regulation of Gastric Secretion

• Cephalic phase:
  • Vagus nerve stimulates gastric secretion even before food is swallowed.
• Gastric phase:
  • Food stretches the stomach and activates myenteric and vagovagal reflexes. These reflexes stimulate gastric secretion. Histamine and gastrin also stimulate acid and enzyme secretion.
• Intestinal phase:
  • Intestinal gastrin briefly stimulates the stomach, but then secretin, CCK, and the enterogastric reflex inhibit gastric secretion and motility while the duodenum processes the chyme already in it. Sympathetic nerve fibers suppress gastric activity, while vagal (parasympathetic) stimulation of the stomach is now inhibited.

Digestive System Part 4 – Pancreas, Liver, and Gallbladder

• The pancreas functions as an endocrine organ and an exocrine organ.
  • As an endocrine gland, the pancreas secretes insulin and glucagon to regulate blood glucose levels.
  • As an exocrine gland of the digestive system, it secretes digestive fluid called pancreatic juice.
  • Structure of exocrine pancreas:
    • Pancreatic acinar cells make up most of the pancreas and release pancreatic juice into tiny ducts which lead to the pancreatic duct.
    • The pancreatic duct (along with the common bile duct from the liver and gallbladder) empties into the duodenum of the small intestine.
    • The pancreatic duct and the common bile duct join at a dilated tube called the hepatopancreatic ampulla (of Vater).
      • The hepatopancreatic sphincter (of Oddi) surrounds the ampulla and controls the movement of bile and pancreatic juice into the duodenum.

Pancreas Anatomy

• Includes
  • Minor duodenal papilla
  • Major duodenal papilla
  • Duodenum
  • Accessory pancreatic duct
  • Sphincter muscles
  • Head of pancreas
  • Intestinal lumen
  • Main pancreatic duct
  • Tail of pancreas
  • Bile duct
  • Hepatopancreatic ampulla
  • Hepatopancreatic sphincter

Pancreatic Juice

• Pancreatic juice contains enzymes that digest carbohydrates, fats, proteins, and nucleic acids.
  • Components of pancreatic juice:
    • Pancreatic amylase: Splits starch and glycogen into disaccharides.
    • Pancreatic lipase: Breaks down triglycerides.
    • Trypsin: Digests proteins.
      • Released as inactive trypsinogen, which is activated by enterokinase in the small intestine.
    • Chymotrypsin: Digests proteins.
      • Released as inactive, activated by trypsin.
    • Carboxypeptidase: Digests proteins.
      • Released as inactive, activated by trypsin.
    • Nucleases: Digest nucleic acids.
    • Bicarbonate ions: Make pancreatic juice alkaline; buffer stomach acid.

Regulation of Pancreatic Secretion

• Hormones that help regulate the release of pancreatic juice:
  • Secretin: Stimulates the pancreas to release pancreatic juice high in bicarbonate ions.
  • CCK: Stimulates the pancreas to release pancreatic juice high in enzymes.
• Nervous system regulation: During the cephalic and gastric phases, parasympathetic impulses stimulate the pancreas to secrete digestive enzymes.

Liver

• The liver, the largest internal organ, is in the upper right quadrant of the abdominal cavity, just inferior to the diaphragm.
  • The term hepatic refers to the liver.
    • Hepatocytes = liver cells
  • A fold of visceral peritoneum called the coronary ligament attaches the liver to the diaphragm on its superior border.
  • The liver is divided into four lobes:
    • A large right lobe and a smaller left lobe.
      • The falciform ligament is a fold of visceral peritoneum that separates the right and left lobes and fastens the liver to the abdominal wall anteriorly.
      • The round ligament (ligamentum teres) is a fibrous remnant of the umbilical vein
    • The quadrate lobe is a minor lobe near the gallbladder
    • The caudate lobe is a minor lobe near the inferior vena cava

Liver Anatomy

• Includes:
  • Inferior vena cava
  • Coronary ligament
  • Quadrate lobe
  • Falciform ligament
  • Gallbladder
  • Right lobe
  • Left lobe
  • Round ligament
  • Caudate lobe

Hepatic Lobules

• Each lobe of the liver is separated into many tiny hepatic lobules, which are the liver’s functional units.
  • Hepatic lobule components:
    • Contain hepatocytes (liver cells) around a central vein.
    • Hepatic sinusoids are channels for blood, between plates of cells.
    • The hepatic portal vein brings absorbed nutrients to sinusoids.
    • The hepatic artery brings oxygen-rich blood, which mixes with oxygen-poor blood from the portal vein.
    • Kupffer cells are macrophages found within the lobules.
  • Blood flows from sinusoids to central veins, then to hepatic veins.
  • Bile flows from ductules to hepatic ducts, then to the common hepatic duct.

Liver Functions

• The Liver's Main Functions Include:
  • Removes toxins from the blood (Detoxification)
  • Polymerizes glucose to glycogen; breaks down glycogen to glucose; converts noncarbohydrates to glucose (Carbohydrate Metabolism)
  • Oxidizes fatty acids; synthesizes lipoproteins, phospholipids, and cholesterol; converts excess portions of carbohydrate molecules into fat molecules (Lipid Metabolism)
  • Deaminates amino acids; forms urea; synthesizes plasma proteins; converts certain amino acids into other amino acids (Protein Metabolism)
  • Stores glycogen, vitamins A, D, and B12, iron, and blood (Storage)
  • Removes damaged red blood cells and foreign substances by phagocytosis (Blood filtering)
  • Produces and secretes bile (Secretion)

Bile

• Bile is a yellowish-green liquid that hepatic cells continuously secrete.
  • Components of Bile:
    • Water
    • Bile salts:
      • Produced from cholesterol.
      • Emulsify fats.
      • Only bile component that has a digestive function (act as fat-emulsifying agents).
    • Bile pigments: Bilirubin and biliverdin, derived from hemoglobin breakdown.
    • Cholesterol
    • Electrolytes
  • Jaundice is a yellowing of the skin, eye sclerae, and mucous membranes.
    • Caused by blockage of bile ducts, diseases such as cirrhosis or hepatitis, or rapid red blood cell destruction.

Gallbladder

• The gallbladder is a pear-shaped sac found on the inferior surface of the liver.
  • Stores and concentrates bile.
    • CCK stimulates the gallbladder to contract and release bile.
    • Releases bile into the duodenum of the small intestine via the common bile duct at the hepatopancreatic ampulla.
  • Gallstones:
    • The gallbladder normally concentrates bile salts, bile pigments, and cholesterol.
    • Sometimes cholesterol precipitates and forms solid crystals.
      • Crystals can enlarge, forming gallstones.
    • Causes: Excess bile concentration, too much cholesterol secretion by the liver, or inflammation of the gallbladder.

Gallbladder Anatomy

• Includes
  • Gallbladder
  • Duodenum
  • Right hepatic duct
  • Cystic duct
  • Bile duct
  • Left hepatic duct
  • Common hepatic duct
  • Hepatopancreatic sphincter
  • Pancreatic duct

Regulation of Bile Release

• Chyme with fat enters the duodenum.
• Cells of the intestinal mucosa secrete the hormone cholecystokinin (CCK) into the bloodstream.
• CCK stimulates the muscular layer of the gallbladder wall to contract.
• Bile passes down the cystic duct and bile duct to the duodenum.
• The hepatopancreatic sphincter relaxes and bile enters the duodenum.

Digestive System Part 5 – Small Intestine

• The small intestine connects the stomach to the large intestine and receives secretions from the pancreas and liver.
  • The small intestine is divided into three regions:
    • Duodenum: Is about 25 centimeters long and is the shortest and most fixed portion of the small intestine.
      • Receives acidic chyme from the stomach and secretions from the pancreas and liver.
    • Jejunum: The mid-region.
      • There is no distinct separation between the jejunum and ileum, but the diameter of the jejunum is usually greater, and its wall is thicker, more vascular, and more active than that of the ileum.
    • Ileum: Near the large intestine.
      • The distal end of the ileum narrows to form the ileocecal valve (sphincter muscle between the small and large intestines).
• The jejunum and ileum are attached to the posterior abdominal wall by folds in the peritoneum called the mesentery.

Small Intestine Anatomy

• Includes:
  • Duodenum
  • Stomach
  • Jejunum
  • Ascending colon
  • Cecum
  • Mesentery
  • Appendix
  • Ileum
  • Liver
  • Gallbladder
  • Transverse colon
  • Greater omentum

Intestinal Wall

• 90% of nutrient absorption occurs in the small intestine due to the tremendous amount of surface area of the small intestinal wall.
  • Structure of the intestinal wall:
    • Intestinal villi project into the lumen (increasing surface area).
      • Each villus is composed of simple columnar epithelium, with microvilli and connective tissue with many blood & lymphatic vessels (lacteals).
      • Absorbed nutrients are carried away by blood vessels & lacteals.
    • Submucosal folds called plicae circulares also further increase the surface area.
• The total surface area of the small intestine is about 200 m^2.
  • Absorption is so effective that very little absorbable material reaches the organ’s distal end.

Intestinal Secretions

• Secretions of the small intestine:
  • Mucus:
    • Secreted by goblet cells.
    • Also secreted by specialized Brunner’s glands that secrete a thick, alkaline mucus in response to certain stimuli.
  • Enzymes in the membranes of the microvilli:
    • Enterokinase: Converts trypsinogen from the pancreas into trypsin.
    • Peptidases: Break down peptides into amino acids.
    • Sucrase, maltase, lactase: Break down disaccharides into monosaccharides.
    • Lipase: Breaks down fats into fatty acids and glycerol.

Fat Absorption

• Fat absorption by the small intestine:
  • Fat digestion and absorption:
    • Emulsified by bile salts.
      • Digested mainly by lipase enzymes from the pancreas and small intestine.
      • Digested into glycerol and fatty acids.
  • Micelles and chylomicrons:
    • Micelles: Loose complexes of fatty acids and bile salts, from which fatty acids can migrate to microvilli and be absorbed.
    • Fatty acids + glycerol are resynthesized into triglycerides in the smooth ER.
    • New triglyceride clusters are encased in protein, forming chylomicrons.
      • Chylomicrons are absorbed by lacteals.

Digestive Enzymes

• Salivary amylase:
  • Source: Salivary amylase
  • Digestive Action: Begins carbohydrate digestion by breaking down starch to disaccharides
• Pepsin:
  • Source: Gastric chief cells
  • Digestive Action: Begins protein digestion
• Pancreatic amylase:
  • Source: Pancreas
  • Digestive Action: Breaks down starch into disaccharides
• Pancreatic lipase:
  • Source: Pancreas
  • Digestive Action: Breaks down fats into fatty acids and glycerol
• Proteolytic enzymes:
  • Source: Pancreas
  • Digestive Action: Break down proteins or partially digested proteins into peptides
    • Trypsin
    • Chymotrypsin
    • Carboxypeptidase
• Nucleases:
  • Source: Pancreas
  • Digestive Action: Break down nucleic acids into nucleotides
• Peptidase:
  • Source: Intestinal mucosal cells
  • Digestive Action: Breaks down peptides into amino acids
• Sucrase, maltase, lactase:
  • Source: Intestinal mucosal cells
  • Digestive Action: Break down disaccharides into monosaccharides
• Intestinal lipase:
  • Source: Intestinal mucosal cells
  • Digestive Action: Breaks down fats into fatty acids and glycerol
• Enterokinase:
  • Source: Intestinal mucosal cells
  • Digestive Action: Converts trypsinogen into trypsin

Digestive System Part 6 – Large Intestine

• The large intestine (colon) is so named because its diameter is greater than that of the small intestine; it is about 1.5 meters long.
• Parts of the large intestine include:
  • Cecum: Nearest the ileum of the small intestine; the appendix is a blind pouch in this region. Appendicitis is inflammation of the appendix.
  • Colon: The majority of the length and is divided into four parts.
    • Ascending colon: From cecum to liver (right).
    • Transverse colon: Runs across the top of the abdomen.
    • Descending colon: From spleen downward (left).
    • Sigmoid colon: S-shaped portion, which becomes the rectum.
  • Rectum: The distal region of the colon.
  • Anal canal: Narrowing of the rectum and opening to the outside.

Large Intestine Structure

• Structure of the large intestinal wall:
  • The wall has the same 4 layers as other tubular organs of the alimentary canal.
    • Does not have villi and plicae circulares.
  • Longitudinal muscle is organized into 3 bands, taeniae coli, that run down the entire length of the colon.
    • Muscle bands create pouches called haustra, which help form feces.
  • Also has small collections of fat called epiploic appendages in the serosa on its outer surface.

Large Intestine Functions

• Has little or no digestive function.
  • Contains tubular glands containing goblet cells; secrete mucus, the only significant secretion of the large intestine.
  • Absorbs water (about 90% of water that enters it) and electrolytes.
  • Houses intestinal flora, bacteria that break down contents such as cellulose and produce vitamins K, B12, and thiamine.
• Forms feces and carries out defecation.
  • Feces are composed of materials not digested or absorbed and contain:
    • Water (approximately 75% of feces)
    • Electrolytes
    • Mucus
    • Bacteria
    • Bile pigments, which provide the color after bacterial alteration
  • Intestinal gas: A mixture of nitrogen, oxygen, methane, carbon dioxide, hydrogen, ammonia, and hydrogen sulfide (causes an unpleasant odor).

Large Intestine Movement

• Movements of the large intestine:
  • Similar to those of the small intestine, but slower and less frequent.
  • Types of movements:
    • Mixing movements
    • Mass movements: Peristaltic waves, 2 to 3 times/day, which usually follow meals.
  • Defecation reflex:
    • Eliminates feces from the body.
    • Involves holding a deep breath and contracting abdominal muscles.
    • Feces move into the rectum, relaxing the internal anal sphincter and then the external anal sphincter.