Digestive System Overview
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Questions and Answers

Which part of the digestive system is the primary site for absorption?

  • Stomach
  • Small intestine (correct)
  • Large intestine
  • Oral cavity

    • What is the primary function of mechanical digestion?

  • To physically break food into smaller pieces (correct)
  • To facilitate the elimination of waste
  • To provide taste sensations
  • To chemically alter food for nutrient absorption

    • Which accessory organ is responsible for producing bile?

  • Liver (correct)
  • Salivary glands
  • Pancreas
  • Gallbladder

    • What role do enzymes play in digestion?

    <p>They help break down complex chemicals into simpler forms</p> Signup and view all the answers

    What structure stores and releases saliva?

    <p>Sublingual glands</p> Signup and view all the answers

    What is a bolus?

    <p>A chewed mass of food mixed with saliva</p> Signup and view all the answers

    Which statement is true about the pharynx?

    <p>It connects the oral cavity to the esophagus, with no digestion occurring.</p> Signup and view all the answers

    Which part of the tooth contains blood vessels and nerves?

    <p>Pulp cavity</p> Signup and view all the answers

    What is the primary function of amylase?

    <p>Digests starch into maltose.</p> Signup and view all the answers

    Which part of the large intestine is attached to the cecum?

    <p>Appendix.</p> Signup and view all the answers

    What prevents backflow between the small and large intestines?

    <p>Ileocecal valve.</p> Signup and view all the answers

    What role does bile play in digestion?

    <p>Emulsifies fats.</p> Signup and view all the answers

    Which type of muscle controls the external anal sphincter?

    <p>Striated muscle.</p> Signup and view all the answers

    What is the main nutrient absorbed in the small intestine?

    <p>Carbohydrates.</p> Signup and view all the answers

    What component of pancreatic juice neutralizes gastric acid in the duodenum?

    <p>Bicarbonate juice.</p> Signup and view all the answers

    What function does the liver serve related to detoxification?

    <p>Synthesizes enzymes that detoxify substances.</p> Signup and view all the answers

    Which structures in the small intestine increase surface area for absorption?

    <p>Villi and microvilli.</p> Signup and view all the answers

    What is primarily absorbed by the large intestine?

    <p>Vitamins.</p> Signup and view all the answers

    What is the primary role of the medulla during swallowing?

    <p>Coordinate pharynx muscle contraction</p> Signup and view all the answers

    Which function is performed by the lower esophageal sphincter (LES)?

    <p>Prevents backflow of stomach contents</p> Signup and view all the answers

    What occurs if the LES doesn't close properly?

    <p>Gastroesophageal reflux (heartburn)</p> Signup and view all the answers

    What is the main role of the gastric pits in the stomach?

    <p>Secrete gastric juice</p> Signup and view all the answers

    What stimulates the secretion of gastric juice in the stomach?

    <p>The sight or smell of food</p> Signup and view all the answers

    Which part of the small intestine is primarily involved in digestion completion?

    <p>Ileum</p> Signup and view all the answers

    What is the function of bile in the digestive system?

    <p>Emulsifies fats</p> Signup and view all the answers

    Which hormone stimulates bile production when food enters the small intestine?

    <p>Secretin</p> Signup and view all the answers

    What structure ensures the controlled passage of chyme into the duodenum?

    <p>Pyloric sphincter</p> Signup and view all the answers

    Where are Peyer's patches primarily located?

    <p>Ileum</p> Signup and view all the answers

    What is the main purpose of the muscular tube known as the esophagus?

    <p>Conduction of food to the stomach</p> Signup and view all the answers

    Which part of the digestive system does the gallbladder belong to?

    <p>Accessory organ system</p> Signup and view all the answers

    Which layer of the alimentary tube contains blood vessels and lymphatic vessels?

    <p>Submucosa</p> Signup and view all the answers

    What effect does sympathetic stimulation have on digestive secretions?

    <p>Decreases secretions</p> Signup and view all the answers

    Which of the following statements about the oral cavity is incorrect?

    <p>The oral cavity includes the pharynx.</p> Signup and view all the answers

    What is the role of chemical digestion in the digestive system?

    <p>To convert complex chemicals into simpler chemicals usable by the body.</p> Signup and view all the answers

    How many teeth do humans have upon the complete eruption of permanent teeth?

    <p>32 permanent teeth</p> Signup and view all the answers

    Which part of the digestive process occurs mainly in the small intestine?

    <p>Absorption of nutrients primarily</p> Signup and view all the answers

    Which accessory organ functions primarily to produce digestive enzymes and hormones?

    <p>Pancreas</p> Signup and view all the answers

    What is the primary role of enamel in the anatomy of the tooth?

    <p>Provides a hard surface for chewing and is resistant to decay</p> Signup and view all the answers

    How does the tongue assist in the digestion process?

    <p>By keeping food between the teeth and mixing it with saliva</p> Signup and view all the answers

    Which function does the pharynx NOT perform during swallowing?

    <p>Facilitates the digestion of food particles</p> Signup and view all the answers

    What mechanism allows the esophagus to transport food even when positioned upside down?

    <p>Peristalsis propels food towards the stomach</p> Signup and view all the answers

    What is the composition of saliva primarily made of?

    <p>Water mixed with digestive enzymes</p> Signup and view all the answers

    Study Notes

    Digestive System Divisions

    • The alimentary tube is a continuous tube starting at the mouth and ending at the anus.
    • It consists of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine.
    • The large intestine eliminates undigested material as feces.
    • Digestion occurs in the oral cavity, stomach, and small intestine.
    • Absorption primarily takes place in the small intestine.
    • Accessory organs aid in digestion. These include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

    Mechanical vs. Chemical Digestion

    • Mechanical digestion physically breaks down food into smaller pieces.
    • Chemical digestion changes complex chemicals into simpler ones the body can use.
    • Enzymes play a role in aiding digestion.

    Oral Cavity

    • The oral cavity, also known as the buccal cavity, is the entrance to the digestive system.
    • It's bounded by the hard and soft palate (top), cheeks (sides), and floor of the mouth (bottom).
    • It contains the teeth, tongue, and openings to salivary gland ducts.
    • The teeth (20 deciduous, 32 permanent) mechanically break down food and mix it with saliva.

    Oral Cavity

    • The root of a tooth is enclosed in a socket within the mandible (lower jaw) or maxilla (upper jaw).
    • The pulp cavity contains blood vessels and nerves from the trigeminal nerve.
    • Enamel, the hardest substance in the body, protects the tooth and is resistant to decay.
    • Dentin forms the root of the tooth.
    • The tongue, a skeletal muscle, is innervated by the hypoglossal nerve.
    • Papillae, located on the tongue's surface, contain taste buds.
    • The tongue mixes food with saliva and keeps food between the teeth.
    • Elevation of the tongue is the first step in swallowing.
    • A bolus is a chewed-up mass of food mixed with saliva.

    Salivary Glands

    • Saliva is produced by three pairs of salivary glands: parotid, submandibular, and sublingual.
    • The parotid glands are located below and in front of the ears.
    • The submandibular glands are at the posterior corners of the mandible.
    • The sublingual glands are under the floor of the mouth.
    • Saliva secretion is continuous but increases with the presence or smell of food.
    • Saliva is mainly water but contains digestive enzymes.

    Pharynx

    • The oropharynx and laryngopharynx are food passageways connecting the oral cavity to the esophagus.
    • No digestion occurs in the pharynx.
    • During swallowing, the medulla coordinates the:
      • Contraction of the pharynx muscles
      • Cessation of breathing
      • Elevation of the soft palate to block the nasopharynx
      • Elevation of the larynx and closure of the epiglottis
    • Talking or laughing while eating can interfere with swallowing and lead to choking.

    Esophagus

    • The esophagus is a muscular tube connecting the pharynx to the stomach.
    • No digestion occurs in the esophagus.
    • Peristalsis propels food towards the stomach, even when upside down.
    • The lower esophageal sphincter (LES) relaxes to allow food into the stomach and contracts to prevent backflow.
    • Gastroesophageal reflux (heartburn or dyspepsia) occurs when the LES doesn't close properly.

    Layers of the Alimentary Tube

    • The mucosa of the alimentary tube has an epithelium that secretes mucus and digestive enzymes.
    • Lymph nodules containing lymphocytes and macrophages are found below the epithelium.
    • The submucosa contains:
      • Blood vessels and lymphatic vessels
      • The Meissner's plexus, a network of nerve fibers that innervate the mucosa and regulate secretions.
    • Parasympathetic stimulation increases secretions.
    • Sympathetic stimulation decreases secretions.
    • The external muscle layer contracts, breaking up food and mixing it with digestive juices.
    • Peristalsis is one-way contraction from the mouth to the anus.
    • The Auerbach's plexus is part of the enteric nervous system and regulates peristalsis.
    • Parasympathetic stimulation increases peristalsis.
    • Sympathetic stimulation decreases peristalsis.
    • The serosa is a serous membrane made up of the mesentery and peritoneum.
    • The parietal peritoneum lines the abdominal cavity.
    • The mesentery (visceral peritoneum) covers the organs in the abdominal cavity.

    Stomach

    • The stomach is located in the upper left quadrant of the abdominal cavity, to the left of the liver and in front of the spleen.
    • The stomach acts as a reservoir for food and carries out both mechanical and chemical digestion.
    • The cardiac orifice is the opening from the esophagus into the stomach.
    • The fundus is the upper portion of the stomach, mainly for storage.
    • The body is the central area of the stomach, also mainly for storage.
    • The pylorus is the lower portion of the stomach, adjacent to the duodenum.
    • Digestion occurs in the pylorus.
    • The pyloric sphincter controls the passage of chyme into the duodenum.
    • Rugae are folds in the stomach lining that allow it to expand.
    • Gastric pits are glands in the stomach that secrete gastric juice.
    • Mucous glands secrete mucus to protect the stomach lining from acidic gastric juices.
    • Chief cells secrete pepsinogen, an inactive form of pepsin.
    • Parietal cells secrete hydrochloric acid, which activates pepsinogen to pepsin and begins protein digestion.
    • Hydrochloric acid is highly acidic (pH 1-2), killing most microorganisms.
    • Parietal cells also secrete intrinsic factor, necessary for vitamin B12 absorption.
    • The smell or sight of food stimulates the secretion of gastric juice.
    • Gastrin, a hormone secreted by G cells, stimulates gastric juice production.
    • The stomach has three layers of smooth muscle that churn and mix food.
    • Churned food is called chyme.
    • The pyloric sphincter contracts during churning, but relaxes periodically to release chyme into the duodenum.

    Small Intestine

    • The small intestine is about 20 feet long and 1 inch in diameter.
    • It extends from the stomach to the cecum of the large intestine.
    • The duodenum, the first 10 inches of the small intestine, is where the common bile duct enters.
    • The jejunum is 8 feet long.
    • The ileum is about 11 feet long.
    • Digestion is completed in the small intestine.
    • Absorption of digested nutrients into the blood and lymph occurs mainly in the small intestine.
    • The mucosa of the small intestine contains:
      • Cells with microvilli, which increase surface area for absorption
      • Goblet cells, which secrete mucus
      • Enteroendocrine cells, which secrete hormones
    • Peyer's patches, abundant in the ileum, are lymph nodules that destroy absorbed pathogens.
    • The external muscle layer mixes chyme with digestive secretions and propels it toward the colon.

    Liver

    • The liver has two lobes (right and left) and is located in the upper right and center of the abdominal cavity, below the diaphragm.
    • The liver lobule is the basic unit of the liver.
    • Hepatic arteries and portal veins branch within the liver.
    • The sinusoids are large capillaries in the liver.
    • The liver's digestive function is the production of bile.
    • Bile is secreted into small bile ducts, which join to form the hepatic duct.
    • The hepatic duct carries bile out of the liver.
    • The hepatic duct joins the cystic duct of the gallbladder to form the common bile duct, which delivers bile to the duodenum.
    • Bile is mainly water and contains bilirubin and cholesterol.
    • Bile salts, contained in bile, emulsify fats in the small intestine, assisting in the mechanical digestion of fats.
    • The hormone secretin, produced in the duodenum, stimulates bile production when food enters the small intestine.
    • The liver also regulates blood glucose, amino acids, stores vitamins, and removes toxins from the blood.

    Gallbladder

    • The gallbladder is a 3-4 inch organ located on the under surface of the right lobe of the liver.
    • Bile flows from the hepatic duct into the cystic duct and then into the gallbladder.
    • The gallbladder stores bile and concentrates it by absorbing water.
    • When food enters the duodenum, the hormone cholecystokinin stimulates the gallbladder to contract, releasing bile into the cystic duct, common bile duct, and duodenum.

    Pancreas

    • The pancreas is located in the upper left quadrant of the abdominal cavity, between the curve of the duodenum and the spleen.
    • Pancreatic enzymes include:
      • Amylase, which digests starch into maltose
      • Lipase, which digests emulsified fats into fatty acids and glycerol
      • Trypsin, which digests polypeptides into shorter amino acid chains
    • Pancreatic juice is carried through ducts to the pancreatic duct, which joins the common bile duct in the duodenum.
    • The pancreas also secretes bicarbonate juice, an alkaline substance that neutralizes gastric acid in the duodenum.

    Absorption

    • Most absorption of digested nutrients occurs in the small intestine.
    • Plica circularis (circular folds), villi, and microvilli increase the surface area for absorption.
    • Microvilli are folds of the small intestine's mucosa.
    • Each villus contains a capillary network and a lacteal, a dead-end lymph capillary.
    • Nutrients are absorbed into the blood through the capillaries surrounding the villi.
    • Blood from the villi travels to the liver through the portal vein.

    Large Intestine (Colon)

    • The large intestine is 5 feet long and extends from the ileum of the small intestine to the anus.
    • The cecum is the first portion of the large intestine.
    • The ileocecal valve prevents backflow between the small and large intestines.
    • The appendix, attached to the cecum, is a small dead-end tube of lymphatic tissue.
    • Appendicitis occurs when the appendix becomes impacted with stool.
    • The parts of the colon include:
      • Ascending colon
      • Transverse colon
      • Descending colon
      • Sigmoid colon
      • Rectum (6 inches)
      • Anal canal (last inch)
    • No digestion occurs in the large intestine.
    • The mucus secreted in the large intestine provides lubrication.
    • Taenia coli, three bands of longitudinal smooth muscle, gather the large intestine into pouches called haustra.
    • The normal flora of the large intestine consists of bacteria that produce Vitamin K, which is absorbed.
    • The large intestine absorbs water, minerals, and vitamins.
    • Undigested material becomes feces.

    Defecation

    • Defecation is the elimination of feces.
    • Feces consist of:
      • Cellulose and other undigestable material
      • Dead and living bacteria
      • Water
    • The defecation reflex is a spinal cord reflex that can be controlled voluntarily.
    • Peristalsis moves feces into the rectum.
    • Stretch receptors in the rectum stimulate the defecation reflex when feces enter.
    • The internal anal sphincter, a smooth muscle, relaxes during defecation.
    • The external anal sphincter, a skeletal muscle, controls voluntary closure of the anus.
    • Diarrhea occurs when large amounts of water are not absorbed in the large intestine, resulting in loose stools..

    Functions of the Liver

    • Carbohydrate metabolism:
      • Regulates blood glucose levels
      • Converts excess sugar to glycogen for storage
      • Converts glycogen to glucose when blood sugar is low
    • Amino acid metabolism:
      • Regulates blood levels of amino acids
      • Produces 12 of the 20 amino acids needed for protein synthesis
    • Lipid metabolism:
      • Synthesizes plasma proteins, including albumin, which maintains blood volume
    • Formation of bilirubin:
      • Macrophages in the liver break down old red blood cells
      • Bilirubin is produced from the heme portion of hemoglobin
    • Phagocytosis:
      • Kupffer Cells, fixed macrophages in the liver, phagocytize old red blood cells, pathogens, and foreign material.
    • Storage:
      • Stores fat-soluble vitamins (A, D, E, and K)
      • Stores water-soluble vitamin B12
      • Stores iron and copper
    • Detoxification:
      • Synthesizes enzymes that detoxify harmful substances such as alcohol and medications.

    Digestive System Divisions

    • The alimentary tube is a continuous passage starting at the mouth and ending at the anus.
    • The alimentary tube consists of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine.
    • The large intestine eliminates waste as feces.
    • Digestion happens in the oral cavity, stomach, and small intestine.
    • Absorption primarily occurs in the small intestine.
    • Accessory organs help digestion, including teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

    Mechanical vs. Chemical Digestion

    • Mechanical digestion physically breaks down food.
    • Chemical digestion converts complex chemicals into simpler ones the body can use.
    • Enzymes aid in digestion.

    Oral Cavity

    • The mouth, or buccal cavity, is the digestive system's entrance.
    • Bounded by the hard and soft palate (top), cheeks (sides), and floor of the mouth (bottom).
    • Contains teeth, tongue, and openings to salivary gland ducts.
    • Teeth (20 deciduous, 32 permanent) mechanically break down food and mix it with saliva.

    Tooth Structure

    • The root of a tooth is enclosed in a socket within the mandible (lower jaw) or maxilla (upper jaw).
    • The pulp cavity holds blood vessels and nerves from the trigeminal nerve.
    • Enamel, the body's hardest substance, protects the tooth and resists decay.
    • Dentin forms the tooth's root.

    Tongue

    • The tongue, a skeletal muscle, is innervated by the hypoglossal nerve.
    • Papillae, on the tongue's surface, contain taste buds.
    • The tongue mixes food with saliva and keeps food between teeth.
    • Elevation of the tongue is the first step in swallowing.
    • A bolus is a chewed-up food mass mixed with saliva.

    Salivary Glands

    • Saliva is produced by three pairs of salivary glands: parotid, submandibular, and sublingual.
    • The parotid glands are located below and in front of the ears.
    • The submandibular glands are at the posterior corners of the mandible.
    • The sublingual glands are under the floor of the mouth.
    • Saliva secretion is continuous but increases with food presence or smell.
    • Saliva is primarily water, containing digestive enzymes.

    Pharynx

    • The oropharynx and laryngopharynx are food passageways connecting the oral cavity to the esophagus.
    • No digestion occurs in the pharynx.
    • During swallowing, the medulla coordinates:
      • Pharynx muscle contraction
      • Breathing cessation
      • Soft palate elevation to block the nasopharynx.
      • Larynx elevation and epiglottis closure.
    • Talking or laughing during eating can interfere with swallowing and lead to choking.

    Esophagus

    • The esophagus is a muscular tube connecting the pharynx to the stomach.
    • No digestion occurs in the esophagus.
    • Peristalsis propels food towards the stomach, even when upside down.
    • The lower esophageal sphincter (LES) relaxes to allow food into the stomach and contracts to prevent food backflow.
    • Gastroesophageal reflux (heartburn or dyspepsia) occurs when the LES doesn't close properly.

    Layers of the Alimentary Tube

    • The alimentary tube's mucosa has epithelium that secretes mucus and digestive enzymes.
    • Lymph nodules with lymphocytes and macrophages are found beneath the epithelium.
    • The submucosa contains:
      • Blood vessels and lymphatic vessels.
      • The Meissner's plexus, a network of nerve fibers innervating the mucosa and regulating secretions.
      • Parasympathetic stimulation increases secretions.
      • Sympathetic stimulation decreases secretions.
    • The external muscle layer contracts, breaking up food and mixing it with digestive juices.
    • Peristalsis is a one-way contraction from the mouth to the anus.
    • The Auerbach's plexus is part of the enteric nervous system and regulates peristalsis.
    • Parasympathetic stimulation increases peristalsis.
    • Sympathetic stimulation decreases peristalsis.
    • The serosa is a serous membrane made up of the mesentery and peritoneum.
    • The parietal peritoneum lines the abdominal cavity.
    • The mesentery (visceral peritoneum) covers organs in the abdominal cavity.

    Stomach

    • The stomach is located in the upper left quadrant of the abdominal cavity, to the left of the liver and in front of the spleen.
    • The stomach stores food and carries out mechanical and chemical digestion.
    • The cardiac orifice is the opening from the esophagus into the stomach.
    • The fundus is the stomach's upper portion, mainly for storage.
    • The body is the stomach's central area, also primarily for storage.
    • The pylorus is the stomach lower portion, adjacent to the duodenum.
    • Digestion takes place in the pylorus.
    • The pyloric sphincter controls the passage of chyme into the duodenum.
    • Rugae are folds in the stomach lining that allow for expansion.
    • Gastric pits are stomach glands that secrete gastric juice.
    • Mucous glands secrete mucus to protect the stomach lining from acidic gastric juices.
    • Chief cells secrete pepsinogen, an inactive form of pepsin.
    • Parietal cells secrete hydrochloric acid, which activates pepsinogen to pepsin and begins protein digestion.
    • Hydrochloric acid is highly acidic (pH 1-2), killing most microorganisms.
    • Parietal cells also secrete intrinsic factor, necessary for vitamin B12 absorption.
    • The smell or sight of food stimulates gastric juice secretion.
    • Gastrin, a hormone secreted by G cells, stimulates gastric juice production.
    • The stomach has three layers of smooth muscle that churn and mix food.
    • Churned food is called chyme.
    • The pyloric sphincter contracts during churning but relaxes periodically to release chyme into the duodenum.

    Small Intestine

    • The small intestine is about 20 feet long and 1 inch in diameter.
    • It extends from the stomach to the cecum of the large intestine.
    • The duodenum, the first 10 inches of the small intestine, is where the common bile duct enters.
    • The jejunum is 8 feet long.
    • The ileum is about 11 feet long.
    • Digestion is completed in the small intestine.
    • Absorption of digested nutrients into the blood and lymph mainly occurs in the small intestine.
    • The mucosa of the small intestine contains:
      • Cells with microvilli, which increase surface area for absorption
      • Goblet cells, which secrete mucus
      • Enteroendocrine cells, which secrete hormones
    • Peyer's patches, abundant in the ileum, are lymph nodules that destroy absorbed pathogens.
    • The external muscle layer mixes chyme with digestive secretions and propels it toward the colon.

    Liver

    • The liver has two lobes (right and left) and is located in the upper right and center of the abdominal cavity, below the diaphragm.
    • The liver lobule is the liver's basic unit.
    • Hepatic arteries and portal veins branch within the liver.
    • The sinusoids are large capillaries in the liver.
    • The liver's digestive function is the production of bile.
    • Bile is secreted into small bile ducts, which join to form the hepatic duct.
    • The hepatic duct carries bile out of the liver.
    • The hepatic duct joins the gallbladder's cystic duct to form the common bile duct, which delivers bile to the duodenum.'
    • Bile is primarily water and contains bilirubin and cholesterol.
    • Bile salts, in bile, emulsify fats in the small intestine, aiding in the mechanical digestion of fats.
    • The hormone secretin, produced in the duodenum, stimulates bile production when food enters the small intestine.
    • The liver also regulates blood glucose and amino acids, stores vitamins, and removes toxins from the blood.

    Gallbladder

    • The gallbladder is a 3-4 inch organ located on the underside of the right lobe of the liver.
    • Bile flows from the hepatic duct into the cystic duct, and then into the gallbladder.
    • The gallbladder stores bile and concentrates it by absorbing water.
    • When food enters the duodenum, the hormone cholecystokinin stimulates the gallbladder to contract, releasing bile into the cystic duct, common bile duct, and duodenum.

    Pancreas

    • The pancreas is located in the upper left quadrant of the abdominal cavity, between the curve of the duodenum and the spleen.
    • Pancreatic enzymes include:
      • Amylase, which digests starch into maltose
      • Lipase, which digests emulsified fats into fatty acids and glycerol.
      • Trypsin, which digests polypeptides into shorter amino acid chains.
    • Pancreatic juice travels through ducts to the pancreatic duct, which joins the common bile duct in the duodenum.
    • The pancreas also secretes bicarbonate juice, an alkaline substance that neutralizes gastric acid in the duodenum.

    Absorption

    • Most absorption of digested nutrients happens in the small intestine.
    • Plica circularis (circular folds), villi, and microvilli increase the surface area for absorption.
    • Microvilli are folds of the small intestine's mucosa.
    • Each villus contains a capillary network and a lacteal, a dead-end lymph capillary.
    • Nutrients are absorbed into the blood through the capillaries surrounding the villi.
    • Blood from the villi travels to the liver via the portal vein.

    Large Intestine (Colon)

    • The large intestine is 5 feet long and extends from the ileum of the small intestine to the anus.
    • The cecum is the first portion of the large intestine.
    • The ileocecal valve prevents backflow between the small and large intestines.
    • The appendix, attached to the cecum, is a small dead-end tube of lymphatic tissue.
    • Appendicitis occurs when the appendix becomes impacted with stool.
    • The colon's parts include:
      • Ascending colon
      • Transverse colon
      • Descending colon
      • Sigmoid colon
      • Rectum (6 inches)
      • Anal canal (last inch).
    • No digestion occurs in the large intestine.
    • The mucus secreted in the large intestine provides lubrication.
    • Taenia coli, three bands of longitudinal smooth muscle, gather the large intestine into pouches called haustra.
    • The normal flora of the large intestine are bacteria that produce Vitamin K, which is absorbed..
    • The large intestine absorbs water, minerals, and vitamins.
    • Undigested material becomes feces.

    Defecation

    • Defecation is the elimination of feces.
    • Feces consist of:
      • Cellulose and other undigestible material
      • Dead and living bacteria
      • Water.
    • The defecation reflex is a spinal cord reflex controllable voluntarily.
    • Peristalsis moves feces into the rectum.
    • Stretch receptors in the rectum stimulate the defecation reflex when feces enter.
    • The internal anal sphincter, a smooth muscle, relaxes during defecation.
    • The external anal sphincter, a skeletal muscle, controls voluntary closure of the anus.
    • Diarrhea happens when large amounts of water are not absorbed in the large intestine, resulting in loose stools.

    Functions of the Liver

    • Carbohydrate metabolism:
      • Regulates blood glucose levels.
      • Converts excess sugar to glycogen for storage.
      • Converts glycogen to glucose when blood sugar is low.
    • Amino acid metabolism:
      • Regulates blood levels of amino acids.
      • Produces 12 of the 20 amino acids needed for protein synthesis.
    • Lipid metabolism:
      • Synthesizes plasma proteins, including albumin, which maintains blood volume.
    • Formation of bilirubin:
      • Macrophages in the liver break down old red blood cells.
      • Bilirubin is produced from the heme portion of hemoglobin.
    • Phagocytosis:
      • Kupffer Cells, fixed macrophages in the liver, phagocytize old red blood cells, pathogens, and foreign material.
    • Storage:
      • Stores fat-soluble vitamins (A, D, E, and K).
      • Stores water-soluble vitamin B12.
      • Stores iron and copper.
    • Detoxification:
      • Synthesizes enzymes that detoxify harmful substances like alcohol and medications.

    Digestive System Divisions

    • The alimentary tube is a long tube running from the mouth to the anus, including the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine.
    • The primary function of the digestive system is to break down food, starting in the oral cavity, stomach, and small intestine, and absorbing nutrients into the bloodstream.
    • The large intestine removes undigested materials as feces.
    • The small intestine is responsible for the majority of absorption.
    • Accessory organs of the digestive system include teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

    Digestion

    • Digestion uses mechanical and chemical processes to break down food.
    • Mechanical digestion physically breaks down food into smaller pieces, often assisted by chewing.
    • Chemical digestion uses enzymes to convert complex chemicals into simpler chemicals that the body can use.

    Oral Cavity

    • The oral cavity, or mouth, is the beginning of the digestive system.
    • The mouth contains teeth and the tongue, which are essential for initial food processing.
    • Teeth use mechanical force to break down food into smaller pieces.
    • The tongue mixes food with saliva and helps position food between teeth.
    • The salivary glands secrete saliva, which contains digestive enzymes, beginning chemical digestion.
    • The tongue helps elevate food during swallowing.

    Anatomy of the Tooth

    • The root of the tooth anchors into the mandible or maxilla.
    • The pulp cavity contains blood vessels and nerves.
    • Enamel forms the outer surface of the tooth, making it resistant to decay.
    • Dentin provides the structure for the root.

    The Tongue

    • The tongue is a skeletal muscle that is essential for chewing, swallowing, and taste sensation.
    • Taste buds on the surface of the tongue detect different flavors.

    Salivary Glands

    • Three pairs of salivary glands (parotid, submandibular, and sublingual) continuously produce saliva, increasing secretion when food is present.

    The Pharynx

    • The oropharynx and the laryngopharynx are passageways for both air and food.
    • The pharynx connects the oral cavity to the esophagus, transporting food.
    • No digestion occurs in the pharynx.
    • Swallowing reflexes are coordinated in the medulla.

    The Esophagus

    • The esophagus is a muscular tube that transports food from the pharynx to the stomach.
    • Peristalsis, coordinated muscle contractions, moves food towards the stomach, even when upside down.
    • No digestion occurs in the esophagus.
    • The lower esophageal sphincter controls the entrance of food into the stomach and prevents reflux.

    Layers of the Elementary Tube

    • The mucosa lining of the elementary tube contains:
      • Epithelium: produces mucus for lubrication and digestive enzymes
      • Lymph nodules: contain lymphocytes that produce antibodies
      • Macrophages: phagocytize bacteria.
    • The submucosa contains blood vessels, lymphatic vessels, and the Meissner's plexus, a nerve network that regulates secretions.
    • The muscular layer contracts to break up food and mix it with digestive juices.
    • Peristalsis uses muscle contractions to move food through the digestive tract.

    The Stomach

    • The stomach is located in the upper left quadrant of the abdominal cavity, and connects to the esophagus and the small intestine.
    • The stomach is crucial for mechanical and chemical digestion.
    • Rugae are folds in the stomach mucosa that allow for expansion.
    • Gastric pits secrete gastric juice, which contains:
      • Mucus: Protects the stomach lining from acidity
      • Pepsinogen: An inactive form of pepsin
      • Hydrochloric acid: Converts pepsinogen to pepsin, kills microorganisms, lowers pH
      • Intrinsic factor: Necessary for vitamin B12 absorption.
    • Three layers of smooth muscle provide for mechanical digestion in the stomach.
    • Chyme is the mixture of food and gastric juice in the stomach.
    • The pyloric sphincter releases chyme into the small intestine.

    The Small Intestine

    • The small intestine is about 20 feet long and 1 inch in diameter, and is responsible for the majority of digestion and nutrient absorption.
    • The small intestine has three sections: the duodenum, jejunum, and ileum.
    • The duodenum receives bile from the liver and gallbladder, and pancreatic juice from the pancreas.
    • The mucosa of the small intestine contains cells with microvilli that increase surface area for absorption.
    • The ileum contains Peyer's patches, which provide important immune function.

    The Liver

    • The liver is located in the upper right quadrant of the abdominal cavity and is the largest organ in the body.
    • The liver has many important metabolic functions, including producing bile.
    • The liver regulates blood glucose, amino acids, stores vitamins, and removes toxins from the blood.
    • Bile is produced by the liver cells and transported through the common bile duct to the duodenum.
    • The gallbladder stores and concentrates bile.

    The Gallbladder

    • The gallbladder is located on the under surface of the right lobe of the liver.
    • The function of the gallbladder is to store and concentrate bile.
    • When food enters the duodenum, cholecystokinin stimulates the gallbladder to release bile into the duodenum.

    The Pancreas

    • The pancreas is located in the upper left abdominal quadrant and produces pancreatic enzymes and bicarbonate.
    • Pancreatic juice is released through the pancreatic duct into the duodenum.

    Absorption and Metabolism

    • Digestion is completed and absorbed in the small intestine, with nutrients entering the blood and lymph systems.
    • Capillaries in the villi of the small intestine absorb nutrients into the blood.

    The Large Intestine

    • The large intestine, or colon, is about 5 feet long and is responsible for water, mineral, and vitamin absorption.
    • No digestion occurs in the large intestine.

    Defecation

    • Defecation is the process of eliminating undigested material.
    • The defecation reflex is controlled voluntarily, and coordinated by the internal and external anal sphincters.

    Other Liver Functions

    • The liver regulates blood glucose levels, regulating the breakdown of glycogen and its conversion into glucose.
    • The liver synthesizes plasma proteins and removes toxins from the blood.
    • Kupffer cells in the liver phagocytize old red blood cells, pathogens, and foreign materials.

    Aging of the GI System

    • As we age, the gastrointestinal system can experience changes to digestive enzyme activity, motility, nutrient absorption, and immune function.

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    Description

    Explore the crucial divisions of the digestive system, including the roles of the alimentary tube and accessory organs. Understand the difference between mechanical and chemical digestion, alongside the significance of the oral cavity. This quiz covers essential concepts vital for mastering human biology.

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