digestive system: overview
DESCRIPTION
Digestive System: Overview. The alimentary canal or gastrointestinal (GI) tract digests and absorbs food Alimentary canal – mouth, pharynx, esophagus, stomach, small intestine, and large intestine Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and pancreas. - PowerPoint PPT PresentationTRANSCRIPT
Digestive System: OverviewDigestive System: Overview The alimentary canal or gastrointestinal (GI) The alimentary canal or gastrointestinal (GI)
tract digests and absorbs foodtract digests and absorbs food Alimentary canal – mouth, pharynx, Alimentary canal – mouth, pharynx,
esophagus, stomach, small intestine, and large esophagus, stomach, small intestine, and large intestineintestine
Accessory digestive organs – teeth, tongue, Accessory digestive organs – teeth, tongue, gallbladder, salivary glands, liver, and gallbladder, salivary glands, liver, and pancreaspancreas
Digestive ProcessDigestive Process The GI tract is a “disassembly” line The GI tract is a “disassembly” line
Nutrients become more available to the body in Nutrients become more available to the body in each stepeach step
There are six essential activities: There are six essential activities: Ingestion, propulsion, and mechanical digestion Ingestion, propulsion, and mechanical digestion Chemical digestion, absorption, and defecationChemical digestion, absorption, and defecation
Gastrointestinal Tract ActivitiesGastrointestinal Tract Activities Ingestion – taking food into the digestive tract Ingestion – taking food into the digestive tract Propulsion – swallowing and peristalsisPropulsion – swallowing and peristalsis
Peristalsis – waves of contraction and relaxation of Peristalsis – waves of contraction and relaxation of muscles in the organ wallsmuscles in the organ walls
Mechanical digestion – chewing, mixing, and Mechanical digestion – chewing, mixing, and churning food churning food
Peristalsis and SegmentationPeristalsis and Segmentation
Figure 23.3
Gastrointestinal Tract ActivitiesGastrointestinal Tract Activities Chemical digestion – catabolic breakdown of Chemical digestion – catabolic breakdown of
foodfood Absorption – movement of nutrients from the Absorption – movement of nutrients from the
GI tract to the blood or lymphGI tract to the blood or lymph Defecation – elimination of indigestible solid Defecation – elimination of indigestible solid
wasteswastes
GI TractGI Tract External environment for the digestive processExternal environment for the digestive process Regulation of digestion involves:Regulation of digestion involves:
Mechanical and chemical stimuli – stretch Mechanical and chemical stimuli – stretch receptors, osmolarity, and presence of substrate in receptors, osmolarity, and presence of substrate in the lumenthe lumen
Extrinsic control by CNS centersExtrinsic control by CNS centers Intrinsic control by local centersIntrinsic control by local centers
Receptors of the GI TractReceptors of the GI Tract Mechano- and chemoreceptors respond to:Mechano- and chemoreceptors respond to:
Stretch, osmolarity, and pHStretch, osmolarity, and pH Presence of substrate, and end products of Presence of substrate, and end products of
digestiondigestion They initiate reflexes that:They initiate reflexes that:
Activate or inhibit digestive glands Activate or inhibit digestive glands Mix lumen contents and move them alongMix lumen contents and move them along
Nervous Control of the GI TractNervous Control of the GI Tract Intrinsic controlsIntrinsic controls
Nerve plexuses near the GI tract initiate short Nerve plexuses near the GI tract initiate short reflexesreflexes
Short reflexes are mediated by local enteric Short reflexes are mediated by local enteric plexuses (gut brain)plexuses (gut brain)
Extrinsic controlsExtrinsic controls Long reflexes arising within or outside the GI tract Long reflexes arising within or outside the GI tract CNS centers and extrinsic autonomic nervesCNS centers and extrinsic autonomic nerves
Peritoneum and Peritoneal Peritoneum and Peritoneal CavityCavity
Peritoneum – serous membrane of the Peritoneum – serous membrane of the abdominal cavityabdominal cavity Visceral – covers external surface of most Visceral – covers external surface of most
digestive organsdigestive organs Parietal – lines the body wallParietal – lines the body wall
Peritoneal cavityPeritoneal cavity Lubricates digestive organs Lubricates digestive organs Allows them to slide across one anotherAllows them to slide across one another
Peritoneum and Peritoneal Peritoneum and Peritoneal CavityCavity
Mesentery – double layer of peritoneum that Mesentery – double layer of peritoneum that provides:provides: Vascular and nerve supplies to the visceraVascular and nerve supplies to the viscera Hold digestive organs in place and store fatHold digestive organs in place and store fat
Retroperitoneal organs – organs outside the Retroperitoneal organs – organs outside the peritoneumperitoneum
Peritoneal organs (intraperitoneal) – organs Peritoneal organs (intraperitoneal) – organs surrounded by peritoneumsurrounded by peritoneum
Blood Supply: Splanchnic Blood Supply: Splanchnic CirculationCirculation
Splanchnic- pertaining to the digestive visceraSplanchnic- pertaining to the digestive viscera Arteries and the organs they serve includeArteries and the organs they serve include
The hepatic, splenic, and left gastric: spleen, liver, The hepatic, splenic, and left gastric: spleen, liver, and stomachand stomach
Inferior and superior mesenteric: small and large Inferior and superior mesenteric: small and large intestines intestines
Blood Supply: Splanchnic Blood Supply: Splanchnic CirculationCirculation
Hepatic portal circulation:Hepatic portal circulation: Collects nutrient-rich venous blood from the Collects nutrient-rich venous blood from the
digestive visceradigestive viscera Delivers this blood to the liver for metabolic Delivers this blood to the liver for metabolic
processing and storageprocessing and storage
Histology of the Alimentary Histology of the Alimentary CanalCanal
From esophagus to the anal canal the walls of From esophagus to the anal canal the walls of the GI tract have the same four tunicsthe GI tract have the same four tunics From the lumen outward they are the mucosa, From the lumen outward they are the mucosa,
submucosa, muscularis externa, and serosasubmucosa, muscularis externa, and serosa Each tunic has a predominant tissue type and a Each tunic has a predominant tissue type and a
specific digestive functionspecific digestive function
MucosaMucosa Moist epithelial layer that lines the lumen of Moist epithelial layer that lines the lumen of
the alimentary canalthe alimentary canal Three major functions:Three major functions:
Secretion of mucusSecretion of mucus Absorption of end products of digestionAbsorption of end products of digestion Protection against infectious diseaseProtection against infectious disease
Consists of three layers: a lining epithelium, Consists of three layers: a lining epithelium, lamina propria, and muscularis mucosaelamina propria, and muscularis mucosae
Mucosa: Epithelial LiningMucosa: Epithelial Lining Simple columnar epithelium and mucus-Simple columnar epithelium and mucus-
secreting goblet cellssecreting goblet cells Mucus secretions:Mucus secretions:
Protect digestive organs from digesting themselvesProtect digestive organs from digesting themselves Ease food along the tractEase food along the tract
Stomach and small intestine mucosa contain:Stomach and small intestine mucosa contain: Enzyme-secreting cells Enzyme-secreting cells Hormone-secreting cells (making them endocrine Hormone-secreting cells (making them endocrine
and digestive organs)and digestive organs)
Mucosa: Lamina Propria and Mucosa: Lamina Propria and Muscularis MucosaeMuscularis Mucosae
Lamina PropriaLamina Propria Loose areolar and reticular connective tissueLoose areolar and reticular connective tissue Nourishes the epithelium and absorbs nutrientsNourishes the epithelium and absorbs nutrients Contains lymph nodes (part of MALT) important Contains lymph nodes (part of MALT) important
in defense against bacteriain defense against bacteria Muscularis mucosae – smooth muscle cells Muscularis mucosae – smooth muscle cells
that produce local movements of mucosathat produce local movements of mucosa
Mucosa: Other SublayersMucosa: Other Sublayers Submucosa – dense connective tissue Submucosa – dense connective tissue
containing elastic fibers, blood and lymphatic containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nervesvessels, lymph nodes, and nerves
Muscularis externa – responsible for Muscularis externa – responsible for segmentation and peristalsissegmentation and peristalsis
Serosa – the protective visceral peritoneumSerosa – the protective visceral peritoneum Replaced by the fibrous adventitia in the esophagus Replaced by the fibrous adventitia in the esophagus Retroperitoneal organs have both an adventitia and Retroperitoneal organs have both an adventitia and
serosaserosa
Enteric Nervous SystemEnteric Nervous System Enteric- pertaining to the intestinesEnteric- pertaining to the intestines Composed of two major intrinsic nerve plexuses:Composed of two major intrinsic nerve plexuses:
Submucosal nerve plexus – regulates glands and smooth Submucosal nerve plexus – regulates glands and smooth muscle in the mucosamuscle in the mucosa
Myenteric nerve plexus – Major nerve supply that controls Myenteric nerve plexus – Major nerve supply that controls GI tract mobilityGI tract mobility
Segmentation and peristalsis are largely automatic Segmentation and peristalsis are largely automatic involving local reflex arcsinvolving local reflex arcs
Linked to the CNS via long autonomic reflex arcLinked to the CNS via long autonomic reflex arc
MouthMouth Oral or buccal cavity:Oral or buccal cavity:
Is bounded by lips, cheeks, palate, and tongue Is bounded by lips, cheeks, palate, and tongue Has the oral orifice as its anterior openingHas the oral orifice as its anterior opening Is continuous with the oropharynx posteriorlyIs continuous with the oropharynx posteriorly
MouthMouth To withstand abrasions: To withstand abrasions:
The mouth is lined with stratified squamous The mouth is lined with stratified squamous epithelium epithelium
The gums, hard palate, and dorsum of the tongue The gums, hard palate, and dorsum of the tongue are slightly keratinizedare slightly keratinized
Lips and CheeksLips and Cheeks Have a core of skeletal musclesHave a core of skeletal muscles
Lips: orbicularis oris Lips: orbicularis oris Cheeks: buccinatorsCheeks: buccinators
Vestibule – bounded by the lips and cheeks Vestibule – bounded by the lips and cheeks externally, and teeth and gums internallyexternally, and teeth and gums internally
Oral cavity proper – area that lies within the Oral cavity proper – area that lies within the teeth and gumsteeth and gums
Labial frenulum – median fold that joins the Labial frenulum – median fold that joins the internal aspect of each lip to the guminternal aspect of each lip to the gum
PalatePalate Hard palate – underlain by palatine bones and Hard palate – underlain by palatine bones and
palatine processes of the maxillaepalatine processes of the maxillae Assists the tongue in chewingAssists the tongue in chewing Slightly corrugated on either side of the raphe Slightly corrugated on either side of the raphe
(midline ridge)(midline ridge)
PalatePalate Soft palate – mobile fold formed mostly of Soft palate – mobile fold formed mostly of
skeletal muscleskeletal muscle Closes off the nasopharynx during swallowingCloses off the nasopharynx during swallowing Uvula projects downward from its free edgeUvula projects downward from its free edge
Palatoglossal and palatopharyngeal arches Palatoglossal and palatopharyngeal arches form the bordersform the borders
TongueTongue Occupies the floor of the mouth and fills the Occupies the floor of the mouth and fills the
oral cavity when mouth is closedoral cavity when mouth is closed Functions include:Functions include:
Gripping and repositioning food during chewingGripping and repositioning food during chewing Mixing food with saliva and forming the bolusMixing food with saliva and forming the bolus Initiation of swallowing, and speechInitiation of swallowing, and speech
TongueTongue Intrinsic muscles change the shape of the Intrinsic muscles change the shape of the
tonguetongue Extrinsic muscles alter the tongue’s positionExtrinsic muscles alter the tongue’s position Lingual frenulum secures the tongue to the Lingual frenulum secures the tongue to the
floor of the mouthfloor of the mouth
TongueTongue Superior surface bears three types of papillaeSuperior surface bears three types of papillae
Filiform – give the tongue roughness and provide Filiform – give the tongue roughness and provide friction friction
Fungiform – scattered widely over the tongue and Fungiform – scattered widely over the tongue and give it a reddish huegive it a reddish hue
Circumvallate – V-shaped row in back of tongueCircumvallate – V-shaped row in back of tongue
TongueTongue Sulcus terminalis – groove that separates the Sulcus terminalis – groove that separates the
tongue into two areas:tongue into two areas: Anterior 2/3 residing in the oral cavityAnterior 2/3 residing in the oral cavity Posterior third residing in the oropharynxPosterior third residing in the oropharynx
TongueTongue
Figure 23.8
Salivary GlandsSalivary Glands Produce and secrete saliva that: Produce and secrete saliva that:
Cleanses the mouthCleanses the mouth Moistens and dissolves food chemicals Moistens and dissolves food chemicals Aids in bolus formationAids in bolus formation Contains enzymes that break down starchContains enzymes that break down starch
Salivary GlandsSalivary Glands Three pairs of extrinsic glands – parotid, Three pairs of extrinsic glands – parotid,
submandibular, and sublingualsubmandibular, and sublingual Intrinsic salivary glands (buccal glands) – Intrinsic salivary glands (buccal glands) –
scattered throughout the oral mucosascattered throughout the oral mucosa
Salivary GlandsSalivary Glands Parotid – lies anterior to the ear between the Parotid – lies anterior to the ear between the
masseter muscle and skinmasseter muscle and skin Parotid duct opens into the vestibule next to second Parotid duct opens into the vestibule next to second
upper molarupper molar Submandibular – lies along the medial aspect Submandibular – lies along the medial aspect
of the mandibular bodyof the mandibular body Its ducts open at the base of the lingual frenulumIts ducts open at the base of the lingual frenulum
Sublingual – lies anterior to the submandibular Sublingual – lies anterior to the submandibular gland under the tonguegland under the tongue It opens via 10-12 ducts into the floor of the mouthIt opens via 10-12 ducts into the floor of the mouth
Salivary GlandsSalivary Glands
Figure 23.9a
Saliva: Source and CompositionSaliva: Source and Composition Secreted from serous and mucous cells of Secreted from serous and mucous cells of
salivary glandssalivary glands 97-99.5% water, hypo-osmotic, slightly acidic 97-99.5% water, hypo-osmotic, slightly acidic
solution containingsolution containing Electrolytes – NaElectrolytes – Na++, K, K++, Cl, Cl––, PO, PO44
2–2–, HCO, HCO33––
Digestive enzyme – salivary amylaseDigestive enzyme – salivary amylase Proteins – mucin, lysozyme, defensins, and IgAProteins – mucin, lysozyme, defensins, and IgA Metabolic wastes – urea and uric acidMetabolic wastes – urea and uric acid
Control of SalivationControl of Salivation Intrinsic glands keep the mouth moistIntrinsic glands keep the mouth moist Extrinsic salivary glands secrete serous, Extrinsic salivary glands secrete serous,
enzyme-rich saliva in response to: enzyme-rich saliva in response to: Ingested food which stimulates chemoreceptors Ingested food which stimulates chemoreceptors
and pressoreceptors and pressoreceptors The thought of food The thought of food
Strong sympathetic stimulation inhibits Strong sympathetic stimulation inhibits salivation and results in dry mouthsalivation and results in dry mouth
TeethTeeth Primary and permanent dentitions have formed Primary and permanent dentitions have formed
by age 21by age 21 Primary – 20 deciduous teeth that erupt at Primary – 20 deciduous teeth that erupt at
intervals between 6 and 24 monthsintervals between 6 and 24 months Permanent – enlarge and develop causing the Permanent – enlarge and develop causing the
root of deciduous teeth to be resorbed and fall root of deciduous teeth to be resorbed and fall out between the ages of 6 and 12 yearsout between the ages of 6 and 12 years All but the third molars have erupted by the end of All but the third molars have erupted by the end of
adolescenceadolescence Usually 32 permanent teethUsually 32 permanent teeth
Deciduous TeethDeciduous Teeth
Figure 23.10.1
Permanent TeethPermanent Teeth
Figure 23.10.2
Classification of TeethClassification of Teeth Teeth are classified according to their shape Teeth are classified according to their shape
and functionand function Incisors – chisel-shaped teeth for cutting or Incisors – chisel-shaped teeth for cutting or
nippingnipping Canines – fanglike teeth that tear or pierceCanines – fanglike teeth that tear or pierce Premolars (bicuspids) and molars – have broad Premolars (bicuspids) and molars – have broad
crowns with rounded tips; best suited for grinding crowns with rounded tips; best suited for grinding or crushingor crushing
During chewing, upper and lower molars lock During chewing, upper and lower molars lock together generating crushing forcetogether generating crushing force
2I2I 1C1C 2PM2PM 3M3M
XX 2 (32 teeth)2 (32 teeth)2I2I 1C1C 2PM2PM 3M3M
Dental Formula: Permanent Dental Formula: Permanent TeethTeeth
A shorthand way of indicating the number and A shorthand way of indicating the number and relative position of teethrelative position of teeth Written as ratio of upper to lower teeth for the Written as ratio of upper to lower teeth for the
mouthmouth Primary: 2I (incisors), 1C (canine), 2M (molars)Primary: 2I (incisors), 1C (canine), 2M (molars) Permanent: 2I, 1C, 2PM (premolars), 3M Permanent: 2I, 1C, 2PM (premolars), 3M
Tooth StructureTooth Structure Two main regions – crown and the rootTwo main regions – crown and the root Crown – exposed part of the tooth above the Crown – exposed part of the tooth above the
gingivagingiva Enamel – acellular, brittle material composed Enamel – acellular, brittle material composed
of calcium salts and hydroxyapatite crystals; of calcium salts and hydroxyapatite crystals; the hardest substance in the bodythe hardest substance in the body Encapsules the crown of the toothEncapsules the crown of the tooth
Root – portion of the tooth embedded in the Root – portion of the tooth embedded in the jawbonejawbone
Tooth StructureTooth Structure Neck – constriction where the crown and root Neck – constriction where the crown and root
come togethercome together Cementum – calcified connective tissue Cementum – calcified connective tissue
Covers the rootCovers the root Attaches it to the periodontal ligamentAttaches it to the periodontal ligament
Tooth StructureTooth Structure Periodontal ligamentPeriodontal ligament
Anchors the tooth in the alveolus of the jaw Anchors the tooth in the alveolus of the jaw Forms the fibrous joint called a gomaphosisForms the fibrous joint called a gomaphosis
Gingival sulcus – depression where the Gingival sulcus – depression where the gingiva borders the toothgingiva borders the tooth
Tooth StructureTooth Structure Dentin – bonelike material deep to the enamel Dentin – bonelike material deep to the enamel
cap that forms the bulk of the toothcap that forms the bulk of the tooth Pulp cavity – cavity surrounded by dentin that Pulp cavity – cavity surrounded by dentin that
contains pulp contains pulp Pulp – connective tissue, blood vessels, and Pulp – connective tissue, blood vessels, and
nervesnerves
Tooth StructureTooth Structure Root canal – portion of the pulp cavity that Root canal – portion of the pulp cavity that
extends into the rootextends into the root Apical foramen – proximal opening to the root Apical foramen – proximal opening to the root
canalcanal Odontoblasts – secrete and maintain dentin Odontoblasts – secrete and maintain dentin
throughout lifethroughout life
Tooth and Gum DiseaseTooth and Gum Disease Dental caries – gradual demineralization of Dental caries – gradual demineralization of
enamel and dentin by bacterial actionenamel and dentin by bacterial action Dental plaque, a film of sugar, bacteria, and mouth Dental plaque, a film of sugar, bacteria, and mouth
debris, adheres to teethdebris, adheres to teeth Acid produced by the bacteria in the plaque Acid produced by the bacteria in the plaque
dissolves calcium saltsdissolves calcium salts Without these salts, organic matter is digested by Without these salts, organic matter is digested by
proteolytic enzymes proteolytic enzymes Daily flossing and brushing help prevent caries by Daily flossing and brushing help prevent caries by
removing forming plaqueremoving forming plaque
Tooth and Gum Disease: Tooth and Gum Disease: PeriodontitisPeriodontitis
Gingivitis – as plaque accumulates, it calcifies Gingivitis – as plaque accumulates, it calcifies and forms calculus, or tartarand forms calculus, or tartar
Accumulation of calculus:Accumulation of calculus: Disrupts the seal between the gingivae and the teeth Disrupts the seal between the gingivae and the teeth Puts the gums at risk for infection Puts the gums at risk for infection
Periodontitis – serious gum disease resulting Periodontitis – serious gum disease resulting from an immune responsefrom an immune response
Immune system attacks intruders as well as Immune system attacks intruders as well as body tissues, carving pockets around the teeth body tissues, carving pockets around the teeth and dissolving boneand dissolving bone