chapter 17 digestive system

Chapter 17Lecture

PowerPoint

2402Anatomy and Physiology II

Chapter 17

Susan Gossett

sgossett@parisjc.edu

Department of Biology

Paris Junior College

Hole’s Human Anatomyand Physiology

Twelfth Edition

Shier Butler Lewis

Chapter 17

Digestive System

17.1: Introduction

• Digestion is the mechanical and chemical breakdown of foods into forms that cell membranes can absorb• Organs of the digestive system carry out these processes, as well as ingestion, propulsion, absorption and defecation• The digestive system consists of the alimentary canal extending from the mouth to the anus, plus accessory organs that empty into the alimentary canal

ACCESSORY ORGANSSalivary glandsSecrete saliva, which containsenzymes that initiate breakdownof carbohydrates

LiverProduces bile, whichemulsifies fat

GallbladderStores bile and introduces it into small intestine

PancreasProduces and secretes pancreatic juice, containing digestive enzymes and bicarbonate ions, into small intestine

ALIMENTARY CANAL

MouthMechanical breakdown of food; begins chemical digestion of carbohydrates

PharynxConnects mouth with esophagus

EsophagusPeristalsis pushes food to stomach

StomachSecretes acid and enzymes; mixes foodwith secretions to begin enzymaticdigestion of proteins

Small intestineMixes food with bile and pancreatic juice; final enzymatic breakdown of food molecules; main site of nutrient absorption

Large intestineAbsorbs water and electrolytes to form feces

RectumRegulates elimination of feces

17.2: General Characteristics of the Alimentary Canal

• The alimentary canal is a muscular tube about 8 meters long

.5 meter (from tongueto duodenum)

5.5 – 6.0 meters(small intestine)

1.5 meters(large intestine)

Esophagus

StomachGallbladder

PancreasDuodenum

Appendix

Tongue

Largeintestine

Ileum(3.3 – 3.6 m)

Jejunum(2.2 – 2.4 m)

Intestinal gland

Lacteal

Epithelium

Mucous gland in submucosa

Mucosa

Circular muscleLongitudinal muscle

Circular muscle

Longitudinal muscle

Serosa

Artery Mesentery

Circular fold

Mucosa

Submucosa

Serosa

Capillaries

Lacteal

Microvilli

Nucleus

Goblet cell

Lymph nodule

Nerveplexuses

Muscularlayer

Simple columnarepithelium

Movement of contents(b)

Digesting material

Wave ofcontraction

Innervation of the Tube

• Branches of the sympathetic and parasympathetic divisions of the autonomic nervous system extensively innervate the alimentary canal, including:

• Submucosal plexus – controls secretions • My enteric plexus – controls gastrointestinal motility

• Remember:• Parasympathetic impulses – increase activities of digestive system• Sympathetic impulses – inhibit certain digestive actions

17.3: Mouth

• The mouth:• Ingests food• Mechanically breaks up solid particles using saliva• Prepares food for chemical digestion

• This action is called mastication

Soft palate

Hard palate

Lingual frenulum

Palatinetonsils

Tongue

Vestibule

Cheeks and Lips

• The cheeks form the lateral walls of the mouth• The lips are highly mobile structures that surround the mouth opening

Tongue

• The tongue is a thick, muscular organ that occupies the floor of the mouth and nearly fills the oral cavity when the mouth is closed

Epiglottis

Lingual tonsils

Palatine tonsil

Papillae

Palate

• The palate forms the roof of the oral cavity and consists of a hard anterior part and a soft posterior part

Frontal sinus

Hard palate

Hyoid bone

Trachea

Esophagus

Laryngopharynx

Epiglottis

Lingual tonsil

Oropharynx

Palatine tonsilUvula

NasopharynxSoft palate

Opening of auditory tube

Pharyngeal tonsil

Sphenoidal sinus

LipTooth

Larynx

Nasal cavity

Vestibule

TongueOral cavity

• The teeth are the hardest structures in the body• There are primary (deciduous) teeth numbering 20• There are secondary (permanent) teeth numbering 32

b: © Nick Koudis/Getty Images

Incisors

Canine (cuspid)

Molars

Incisors(a)

Molars

Canines

Premolars(bicuspids)

Secondpremolars

Firstpremolars

Lateralincisors

Centralincisors

Gingiva

Root canal

Cementum

Dentin

Enamel

Alveolarprocess

Periodontalligament

Pulpcavity

17.1 Clinical Application

Dental Caries

17.4: Salivary Glands

• Salivary glands secrete saliva• This begins the digestion of carbohydrates• There are three pairs of major salivary glands, including:

• Parotid glands• Submandibular glands• Sublingual glands

• There are many minor glands scattered throughout the mucosa of the tongue, palate, and cheeks

Salivary Secretions

• The different salivary glands have varying proportions of two types of secretory cells, serous cells and mucous cells

• Serous cells produce a watery fluid with a digestive enzyme called salivary amylase• Mucous cells secrete mucous

• Parotid glands • Secrete clear watery, serous fluid• Rich in salivary amylase

• Submandibular glands• Secrete primarily serous fluid and some mucus

• Sublingual glands• Secrete primarily mucus

Major Salivary Glands

Sublingual glandMandible (cut)

Parotidgland

Massetermuscle

Submandibulargland

Tongue

Submandibularduct

Duct(a)

Serous cellDuct Mucous cell

Serous cellDuct

Serouscell

Mucouscell

a: © The McGraw-Hill Companies, Inc./Al Telser, photographer; figure b: © Biophoto Associates/Photo Researchers, Inc.; figure c: © The McGraw-Hill Companies, Inc./Al Telser, photographer

17.5: Pharynx and Esophagus

• The pharynx is a cavity posterior to the mouth from which the tubular esophagus leads to the stomach• Both the pharynx and esophagus muscular walls function in swallowing Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Mandible

TongueEpiglottis

Larynx

Esophagus

Superiorconstrictormuscles

Middleconstrictormuscles

Inferiorconstrictormuscles

Structure of the Pharynx

• The pharynx can be divided into the following parts:• Nasopharynx• Oropharynx• Laryngopharynx

Superior

Middle

Inferior

Tongue

Epiglottis

Trachea

Nasopharynxwith mucosaremoved toshow muscles

Pharyngealconstrictormuscles:

(a) The tongue forces food into the pharynx.

Foodmass

Hardpalate

Swallowing Mechanism

• Swallowing can be divided into three stages:• Voluntary stage where saliva is mixed with chewed food• Swallowing begins and the swallowing reflex is triggered• Peristalsis transports food in the esophagus to the stomach

• Specifically:• The palate and uvula raise• The hyoid bone and larynx elevate• The epiglottis closes off top of the trachea• The longitudinal muscles of pharynx contract• The inferior constrictor muscles relax and the esophagus opens• The peristaltic waves pushes food through the pharynx

Superior

Middle

Inferior

Tongue

Epiglottis

TracheaEsophagus

Soft palate

Larynx

Epiglottis

Hyoid bone

EsophagusLarynx

TonguePeristaltic wave

Stomach

Esophagus

Food mass

Nasopharynx with mucosa removed toshow muscles

Pharyngealconstrictormuscles:

Hardpalate

Foodmass

(a) The tongue forces food into the pharynx.

Softpalate

Superiorpharyngealconstrictormuscles

Foodmass

(c) Superior constrictor muscles contract and force food into the esophagus.

Foodmass

Inferiorpharyngealconstrictormuscles

(b) 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.

(d) Peristaltic waves move food through the esophagus to the stomach.

Esophagus

Diaphragm

Stomach

Esophagealhiatus

Mucosa

Submucosa

Muscularlayer

17.6: Stomach

• The stomach is a J-shaped, pouch-like organ, about 25-30 centimeters long• It hangs inferior to the diaphragm in the upper-left portion of the abdominal cavity• The stomach has two layers of smooth muscle

• An inner circular layer• An outer longitudinal layer• (There may be a third inner layer of oblique fibers.)

Fundus

Pylorus

Pyloric opening

Duodenum

Cardia

Esophagus

Circularfibers

Longitudinalfibers

Obliquefibers

Longitudinalfibers

Pyloricsphincter

Lessercurvature

Lower esophagealsphincter

Pyloriccanal

Pyloricantrum Gastric folds

(rugae)

Greatercurvature

Parts of the Stomach

Pyloric sphincter

Duodenum

Pylorus

Fundus

Gastric folds

Gastric Secretions• The mucous membrane of the stomach has tubular gastric glands that secrete:

• Pepsinogen• From the chief cells• Inactive form of pepsin

• Pepsin• From pepsinogen in the presence of hydrochloric acid• Is a protein splitting enzyme

• Hydrochloric acid• From the parietal cells• Needed to convert pepsinogen to pepsin

• Mucus• From the goblet cells and the mucous glands• Protective to stomach wall

• Intrinsic factor• From the parietal cells• Is required for vitamin B12 absorption

Gastric pits

Chief cell

(a) (b)

Parietal cell

Gastric gland

Mucous cellMucosa

Submucosa

Serosa

Mucous cell

Gastric pit

Parietal cell

Chief cell

Portion ofa gastric gland

Portion of agastric gland

Musclelayers

b: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Stimulation

Bloodstream

Release intobloodstreamParasympathetic

preganglionicnerve fiber (invagus nerve)

Gastrin stimulatesgastric glands torelease more gastricjuice

Parasympatheticpostganglionicimpulses stimulatethe release ofgastric juice fromgastric glands

Impulsesstimulatethe releaseof gastrin

Gastric Absorption

• Gastric enzymes begin breaking down proteins, but the stomach is not well-adapted to absorb digestive products

• Why not ???• The stomach does absorb:

• Some water• Certain salts• Certain lipid-soluble drugs• Alcohol

Mixing and Emptying Actions

Stomach

Duodenum

(a) (b) (c)

Pyloric sphincterrelaxed

Pyloric sphinctercontracted

Foodentering

From CNS

Nerve impulsesinhibit peristalsisin stomach wall

Duodenumfills with chyme

Sensory stretchreceptors arestimulated

Sensory nerveimpulses travelto centralnervous system

To CNS

Vagusnerve

Oh, My Aching Stomach!

17.7: Pancreas

• The pancreas has a dual function as both an endocrine gland and exocrine gland• The exocrine function is to secrete digestive juice called pancreatic juice

Right hepatic duct Left hepatic ductCystic duct Common hepatic ductBile duct

Bile duct

Gallbladder

Sphincter muscles

Head of pancreas

Duodenum

Major duodenal papilla

Intestinal lumen

Pancreatic duct

Pyloric sphincter

Minor duodenalpapilla

Major duodenalpapilla

Tail of pancreas

Pancreatic duct

Hepatopancreaticsphincter

Hepatopancreaticampulla

Pancreatic Juice

• Pancreatic juice contains enzymes that digest carbohydrates, fats, proteins, and nucleic acids, and include:

• Pancreatic amylase – splits glycogen into disaccharides• Pancreatic lipase – breaks down triglycerides• Trypsinogen, chymotrypsinogen, and carboxypeptidase

• Digest proteins• Nucleases – digest nucleic acids• Bicarbonate ions – make pancreatic juice alkaline

Bloodstream

Stimulation of effector organ

Acidic chymeentersduodenum

Bicarbonate ionsneutralize acidicchyme

Intestinal mucosareleases secretininto bloodstream

Secretin stimulatespancreas to secretebicarbonate ions

Hormonal signalsreleased into bloodstream

Pancreatic juice rich in bicarbonate ions passes downpancreatic ducts to the duodenum

17.8: Liver

• The liver is the largest internal organ• It is located in the upper-right abdominal quadrant just beneath the diaphragm

Liver Structure

Right lobe

Coronary ligament

Inferior vena cava

Left lobe

Inferior vena cava

Right lobe

Gallbladder Quadrate lobe

Cystic duct

Left lobe

Hepatic ductHepatic artery

Bile duct

Caudate lobe

Gallbladder

(b)(a)

Roundligament

Hepatic portalvein

Falciform ligament

Bile duct

Branch of hepatic arteryPlates of liver cells

Central vein

Bile canaliculi

Bile ductule

Bile duct

Sinusoids

Branch of hepatic portal vein

Hepaticsinusoids

Branches ofhepatic artery

Branch ofhepatic portal vein

c: © The McGraw-Hill Companies, Inc./Al Telser, photographer

Bile duct Bile ductuleBile canaliculi Kupffer cell Hepatic cells

Branchof hepaticportal vein

Branchof hepaticartery

Hepaticsinusoids

Blood flowinto liver

Central vein(blood flowout of liver)

Liver Functions

• The liver carries on many important metabolic activities, including:• Produces glycogen from glucose• Breaks down glycogen into glucose• Converts non-carbohydrates to glucose• Oxidizes fatty acids• Synthesizes lipoproteins, phospholipids, and cholesterol• Converts carbohydrates and proteins into fats• Deaminating amino acids • Forms urea• Synthesizes plasma proteins• Converts some amino acids to other amino acids• Stores glycogen, iron, and vitamins A, D, and B12

• Phagocytosis of worn out RBCs and foreign substances• Removes toxins such as alcohol and certain drugs from the blood

17.1 From Science to Technology

Replacing the Liver

Composition of Bile

• Bile is a yellowish-green liquid that hepatic cells continuously secrete• Bile contains:

• Water• Bile salts:

• Emulsify fats• Help absorb fatty acids, cholesterol, and fat-soluble vitamins

• Bile pigments• Cholesterol• Electrolytes

Hepatitis

Gallbladder

Bile duct

Cystic duct

Duodenum

Bloodstream

Chyme withfat entersduodenum

Cells from theintestinal mucosasecrete the hormonecholecystokinin (CCK)into the bloodstream

Hormonalsignals releasedinto bloodstream

Stimulation ofeffector organ

Pancreaticduct

Hepatopancreatic sphincter relaxes and bile enters duodenum

Bile passes down the cystic duct and bile duct to duodenum

CCK stimulates muscular layer of gallbladder wall to contract

Commonhepatic duct

Functions of Bile Salts

• Bile salts aid digestive enzymes• They reduce surface tension and break fat globules into droplets (like soap or detergent) and this is called emulsification• They enhance absorption of fatty acids and cholesterol• They help absorb fat-soluble vitamins A, D, E and K• Bile salts are recycled as they return to the liver

Gallbladder Disease

17.9: Small Intestine

• The small intestine is a tubular organ that extends from the pyloric sphincter to the beginning of the large intestine• It completes digestion of the nutrients in chyme, absorbs products of digestion, and transports the remaining residue to the large intestine• It consists of three parts that include:

• Duodenum• Jejunum• Ileum

Parts of the Small Intestine

Stomach

Jejunum

Duodenum

Ascending colon

Mesentery

Appendix

Stomach

Small intestine

Stomach

Gallbladder

Transverse colonunderneath

Greateromentum

Structure of the Small Intestinal Wall

Lacteal

Blood capillary network

Intestinal gland

Goblet cells

Simple columnarepithelium

VenuleArteriole

Lymph vessel

Villus

Intestinalgland

Villus

Microvilli

Cell membrane

Mitochondrion

Golgi apparatus

Nucleolus

Nucleus

Lumen Microvilli

Roughendoplasmicreticulum

Cytoplasm ofepithelial cell

Submucosa

Circular muscleLongitudinal muscle

Serosa

Plicaecirculares

Muscularlayer

Secretions of the Small Intestine

• In addition to mucous-secreting goblet cells, there are many specialized mucous-secreting glands (Brunner’s glands) that secrete a thick, alkaline mucus in response to certain stimuli• Enzymes in the membranes of the microvilli include:

• Peptidase – breaks down peptides into amino acids• Sucrase, maltase, lactase – break down disaccharides into monosaccharides• Lipase – breaks down fats into fatty acids and glycerol• Enterokinase – converts trypsinogen to trypsin• Somatostatin – hormone that inhibits acid secretion by stomach• Cholecystokinin – hormone that inhibits gastric glands, stimulates pancreas to release enzymes in pancreatic juice, and stimulates the gallbladder to release bile• Secretin – stimulates the pancreas to release bicarbonate ions in pancreatic juice

Regulation of Small Intestinal Secretions

• Regulation of small intestine secretion occurs by:• Mucus secretion is stimulated by the presence of chyme in the small intestine• Distension of the intestinal wall activates nerve plexuses in the wall of the small intestine• Parasympathetic reflexes triggering the release of intestinal enzymes

Absorption of the Small Intestine

• Villi increase the surface area for absorption• Small intestine absorption is so effective that very little reaches the organ’s distal end, noting that:

• Monosaccharides and amino acids absorb:• Through facilitated diffusion and active transport• Absorbed into blood

• Large proteins are broken down and absorbed into villi• Fatty acids and glycerol absorb by:

• Several steps involved as noted• Absorbed into lymph and blood

• Electrolytes and water absorb:• Through diffusion, osmosis, and active transport• Absorbed into blood

Maltose Glucose

MonosaccharidesDisaccharide

Glucose

Maltase

Amino acid Amino acid

Dipeptidase

Dipeptide(from protein digestion)

Lipase

C17H35 COO

Lipase+ +Fatty acids GlycerolFat

C17H35 COO

C17H35 C

Fatty acids

Lacteal

Nucleus

Chylomicrons

To blood

Lymph in lactealtransports chylomicronsaway from intestine

Chylomicronsleave epithelial celland enter lacteal

Fats collect in clustersencased in protein toform chylomicrons

Fatty acids areused to synthesizefats in endoplasmicreticulum

Fatty acidsresulting from fatdigestion enterepithelial cell

Endoplasmicreticulum

Lumen ofintestine

Epithelialcell

Movements of the Small Intestine

• The small intestine carries on mixing movements that include:

• Peristalsis – pushing movements that propel chyme• Segmentation – ring-like contractions that can move chyme back and forth

17.10: Large Intestine

• The large intestine is named because of its diameter• It has five parts that include:

• Cecum• Colon

• Ascending, transverse, descending and sigmoid• Rectum• Anus

Anal canal

Sigmoid colon

Haustra

Descending colon

Rectum

Appendix

Orifice of appendix

Ileocecal sphincter

Ascending colon

Serous layer Mucous membrane

Transverse colon

Muscular layer

Hepatic flexure

Tenia coli

Splenicflexure

Epiploicappendage

Structure of the Large Intestinal Wall

Submucosa

Muscular layer

Serosa

Mucosa

Functions of the Large Intestine

• The large intestine:• Has little or no digestive function• Absorbs water and electrolytes• Secretes mucus• Houses intestinal flora• Forms feces• Carries out defecation

Lumen oflargeintestine

Gobletcells

Movements of the Large Intestine

• Movements of the large intestine are similar to those of the small intestine• It is slower and less frequent than that of the small intestine• Movements include:

• Mixing movements • Peristalsis

• Mass movements usually follow meals• The defecation reflex relaxes the internal anal sphincter and then the external anal sphincter

Feces• Feces is composed of materials not digested or absorbed, and include:

• Water• Electrolytes• Mucus • Bacteria• Bile pigments altered by bacteria provide the color

• The pungent odor is produced by bacterial compounds including:

• Phenol• Hydrogen sulfide• Indole• Skatole• Ammonia

Disorders of the Large Intestine

17.11: Lifespan Changes

• Changes to the digestive system are slow and slight, and eventually include:

• Teeth may become sensitive• Gums may recede• Teeth may loosen, break or fall out• Heartburn may become more frequent• Constipation may become more frequent• Nutrient absorption decreases• Accessory organs age but typically not necessarily in ways that effect health

Important Points in Chapter 17:Outcomes to be Assessed

17.1: Introduction

Describe the general functions of the digestive system.

Name the major organs of the digestive system.

17.2: General Characteristics of the Alimentary Canal

Describe the structure of the wall of the alimentary canal.

Explain how the contents of the alimentary canal are mixed and moved.

17.3: Mouth

Describe the functions of the structures of the mouth.

Describe how different types of teeth are adapted for different functions, and list the parts of the tooth.

17.4-17.10: Salivary Glands – Large Intestine

Locate each of the organs and glands; then describe the general function of each.

Identify the function of each enzyme secreted by the digestive organs and glands.

Describe how digestive secretions are regulated.

Explain control of movement of material through the alimentary canal.

Describe the mechanisms of swallowing, vomiting, and defecating.

Explain how the products of digestion are absorbed.

17.11: Lifespan Changes

Describe aging-related changes in the digestive system.

Quiz 17

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