PowerPoint Lecture Slides prepared by Jason LaPres Lone Star College North Harris Introduction to the Digestive System Acquires nutrients from environment Anabolism Uses raw materials to synthesize essential compounds ID: 777427
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Slide1
Slide2C h a p t e r
22
The Digestive System
PowerPoint® Lecture Slides prepared by Jason LaPres
Lone Star College - North Harris
Slide3Introduction to the Digestive System
Acquires nutrients from environment
AnabolismUses raw materials to synthesize essential compounds
CatabolismDecomposes substances to provide energy cells need to function
Slide4Introduction to the Digestive System
Catabolic Reactions
Require two essential ingredients:OxygenOrganic molecules broken down by intracellular enzymes:
e.g., carbohydrates, fats, and proteins
Slide5Digestive Tract
Digestive tract
also called gastrointestinal (GI) tract or alimentary canalIs a muscular tubeExtends from oral cavity to anus Passes through pharynx, esophagus, stomach, and small and large intestines
Slide6Digestive Tract
Figure 22–1 The Components of the Digestive System.
Slide7Digestive Tract
Figure 22–1 The Components of the Digestive System.
Slide8Digestive Tract
Functions of the Digestive System
Ingestion: Occurs when materials enter digestive tract via the mouth
Mechanical processing:
Crushing and shearing
Makes materials easier to propel along digestive tract
Digestion
:
The chemical breakdown of food into small organic fragments for absorption by digestive epithelium
Slide9Digestive Tract
Functions of the Digestive System
Secretion:
Is the release of water, acids, enzymes, buffers, and salts By epithelium of digestive tract
By glandular organs
Absorption
:
Movement of organic substrates, electrolytes, vitamins, and water
Across digestive epithelium
Into interstitial fluid of digestive tract
Excretion
:
Removal of waste products from body fluids
Slide10Digestive Tract
Lining of the digestive tract protects surrounding tissues against
Corrosive effects of digestive acids and enzymesMechanical stresses, such as abrasion
Bacteria either ingested with food or that reside in digestive tract
Slide11Digestive Tract
The Digestive Organs and the Peritoneum
Lined with serous membrane consisting ofSuperficial mesothelium covering a layer of areolar tissueSerosa, or visceral peritoneum:covers organs within peritoneal cavity
Parietal peritoneum:lines inner surfaces of body wall
Slide12Digestive Tract
Peritoneal Fluid
Is produced by serous membrane liningProvides essential lubricationSeparates parietal and visceral surfacesAllows sliding without friction or irritation
Slide13Digestive Tract
Mesenteries
Are double sheets of peritoneal membraneSuspend portions of digestive tract within peritoneal cavity by sheets of serous membraneThat connect parietal peritoneumWith visceral peritoneum
Slide14Digestive Tract
Mesenteries
Areolar tissue between mesothelial surfacesProvides an access route to and from the digestive tractFor passage of blood vessels, nerves, and lymphatic vessels Stabilize positions of attached organs
Prevent intestines from becoming entangled
Slide15Digestive Tract
Mesentery Development
During embryonic developmentDigestive tract and accessory organs are suspended in peritoneal cavity by:dorsal mesentery
ventral mesenterylater disappears along most of digestive tract except at the
lesser omentum
and at the
falciform ligament
Slide16Digestive Tract
Figure 22–2 Mesenteries.
Slide17Digestive Tract
The Lesser Omentum
Stabilizes position of stomachProvides access route for blood vessels and other structures entering or leaving liverThe Falciform Ligament Helps stabilize position of liver
Relative to diaphragm and abdominal wall
Slide18Digestive Tract
The Dorsal Mesentery
Enlarges to form an enormous pouch, called the greater omentumExtends inferiorly between:
the body wall and the anterior surface of small intestineHangs like an apron:
from lateral and inferior borders of stomach
Adipose tissue in greater omentum:
conforms to shapes of surrounding organs
pads and protects surfaces of abdomen
provides insulation to reduce heat loss
stores lipid energy reserves
Slide19Digestive Tract
The
Mesentery Proper Is a thick mesenterial sheet
Provides stabilityPermits some independent movementSuspends all but first 25 cm (10 in.) of small intestine
Is associated with initial portion of small intestine (duodenum) and pancreas
Fuses with posterior abdominal wall, locking structures in position
Slide20Digestive Tract
The
Mesocolon A mesentery associated with a portion of the large intestineTransverse mesocolon supports transverse colon
Sigmoid mesocolon supports sigmoid colonDuring development, mesocolon of ascending colon, descending colon, and the rectum
Fuse to dorsal body wall
Lock regions in place
Slide21Digestive Tract
Figure 22–2b Organization of Mesenteries in an Adult.
Slide22Digestive Tract
Figure 22–2c Mesenteries: Anterior View of the Empty Peritoneal Cavity.
Slide23Digestive Tract
Figure 22–2d Sagittal Section Showing the Mesenteries of an Adult.
Slide24Digestive Tract
Histological Organization of the Digestive Tract
Major layers of the digestive tractMucosaSubmucosaMuscularis externa
Serosa
Slide25Digestive Tract
Figure 22–3 The Structure of the Digestive Tract
Slide26Digestive Tract
The Mucosa
Is the inner lining of digestive tractIs a mucous membrane consisting ofEpithelium, moistened by glandular secretionsLamina propria of areolar tissue
Slide27Digestive Tract
The Digestive Epithelium
Mucosal epithelium is simple or stratifiedDepending on location, function, and stresses: oral cavity, pharynx, and esophagus:
mechanical stresseslined by stratified squamous epithelium
stomach, small intestine, and most of large intestine:
absorption
simple columnar epithelium with mucous (goblet) cells
Slide28Digestive Tract
The Digestive Epithelium
Enteroendocrine cellsAre scattered among columnar cells of digestive epitheliumSecrete hormones that:coordinate activities of the digestive tract and accessory glands
Slide29Digestive Tract
Lining of Digestive Tract
Folding increases surface area for absorption: Longitudinal folds, disappear as digestive tract fills
Permanent transverse folds (plicae circulares)
Slide30Digestive Tract
The Mucosa
Lamina PropriaConsists of a layer of areolar tissue that contains:blood vesselssensory nerve endings
lymphatic vesselssmooth muscle cellsscattered areas of lymphoid tissue
Slide31Digestive Tract
The Lamina Propria
Muscularis mucosaeNarrow band of smooth muscle and elastic fibers in lamina propriaSmooth muscle cells arranged in two concentric layers:
inner layer encircles lumen (circular muscle)outer layer contains muscle cells parallel to tract (longitudinal layer)
Slide32Digestive Tract
The Submucosa
Is a layer of dense, irregular connective tissueSurrounds muscularis mucosaeHas large blood vessels and lymphatic vesselsMay contain exocrine glands
Secrete buffers and enzymes into digestive tract
Slide33Digestive Tract
Submucosal Plexus
Also called plexus of MeissnerInnervates the mucosa and submucosaContainsSensory neurons
Parasympathetic ganglionic neuronsSympathetic postganglionic fibers
Slide34Digestive Tract
The Muscularis Externa
Is dominated by smooth muscle cellsAre arranged inInner circular layerOuter longitudinal layer
Slide35Digestive Tract
The Muscularis Externa
Involved inMechanical processingMovement of materials along digestive tract
Movements coordinated by enteric nervous system (ENS)Sensory neurons
Interneurons
Motor neurons
Slide36Digestive Tract
The Muscularis Externa
ENSInnervated primarily by parasympathetic division of ANS:sympathetic postganglionic fibers:the mucosa
the myenteric plexus (plexus of Auerbach)
Slide37Digestive Tract
The Serosa
Serous membrane covering muscularis externaExcept in oral cavity, pharynx, esophagus, and rectum:where adventitia,
a dense sheath of collagen fibers, firmly attaches the digestive tract to adjacent structures
Slide38Digestive Tract
The Movement of Digestive Materials
By muscular layers of digestive tractConsist of visceral smooth muscle tissueAlong digestive tract:
has rhythmic cycles of activitycontrolled by pacesetter cells
Cells undergo spontaneous depolarization:
triggering wave of contraction through entire muscular sheet
Slide39Digestive Tract
Pacesetter Cells
Located in muscularis mucosae and muscularis externaSurrounding lumen of digestive tractPeristalsis
Consists of waves of muscular contractionsMoves a
bolus
along the length of the digestive tract
Slide40Digestive Tract
Peristaltic Motion
Circular muscles contract behind bolus:While circular muscles ahead of bolus relax
Longitudinal muscles ahead of bolus contract:Shortening adjacent segments
Wave of contraction in circular muscles:
Forces bolus forward
Slide41Digestive Tract
Segmentation
Cycles of contractionChurn and fragment the bolusMix contents with intestinal secretions
Does not follow a set patternDoes not push materials in any one direction
Slide42Digestive Tract
Figure 22–4 Peristalsis.
Slide43Digestive Tract
Figure 22–4 Peristalsis.
Slide44Digestive Tract
Control of Digestive Function
Neural mechanismsControl:movement of materials along digestive tract
secretory functionsMotor neurons:
control smooth muscle contraction and glandular secretion
located in myenteric plexus
Slide45Digestive Tract
Neural Mechanisms
Short reflexesAre responsible for local reflexesControl small segments of digestive tract
Operate entirely outside of CNS control:sensory neurons
motor neurons
interneurons
Slide46Digestive Tract
Neural Mechanisms
Long reflexesHigher level control of digestive and glandular activitiesControl large-scale peristaltic waves
Involve interneurons and motor neurons in CNSMay involve parasympathetic motor fibers that synapse in the myenteric plexus:
glossopharyngeal, vagus, or pelvic nerves
Slide47Digestive Tract
Hormonal Mechanisms
At least 18 peptide hormones that affectMost aspects of digestive functionActivities of other systems
Are produced by enteroendocrine cells in digestive tractReach target organs after distribution in bloodstream
Slide48Digestive Tract
Local Mechanisms
Prostaglandins, histamine, and other chemicals released into interstitial fluid, may affect adjacent cells within small segment of digestive tractCoordinating response to changing conditionsFor example,
variations in local pH, chemical, or physical stimuliAffect only a portion of tract
Slide49Digestive Tract
Figure 22–5 The Regulation of Digestive Activities.
Slide50Functions of Oral Cavity
Sensory analysis
Of material before swallowingMechanical processingThrough actions of teeth, tongue, and palatal surfaces
LubricationMixing with mucus and salivary gland secretions
Limited digestion
Of carbohydrates and lipids
Slide51Oral Cavity
Oral Mucosa
Lining of oral cavityHas stratified squamous epitheliumOf
cheeks, lips, and inferior surface of tongueIs relatively thin, nonkeratinized, and delicate
Inferior to tongue is thin and vascular enough to rapidly absorb lipid-soluble drugs
Cheeks are supported by pads of fat and the buccinator muscles
Slide52Oral Cavity
Labia
Also called lipsAnteriorly, the mucosa of each cheek is continuous with that of the lipsVestibule
Space between the cheeks (or lips) and the teeth
Slide53Oral Cavity
Gingivae
(Gums) Ridges of oral mucosaSurround base of each tooth on alveolar processes of maxillary bones and mandible
Slide54Oral Cavity
Figure 22–6a The Oral Cavity.
Slide55Oral Cavity
Figure 22–6b The Oral Cavity.
Slide56Oral Cavity
The Tongue
Manipulates materials inside mouthFunctions of the tongue
Mechanical processing by compression, abrasion, and distortionManipulation
to assist in chewing and to prepare material for swallowing
Sensory analysis
by touch, temperature, and taste receptors
Secretion
of mucins and the enzyme
lingual lipase
Slide57Oral Cavity
Salivary Glands
Three pairs secrete into oral cavity Each pair has distinctive cellular organizationAnd produces saliva with different properties
Slide58Oral Cavity
Parotid Salivary Glands
Inferior to zygomatic archProduce serous secretionEnzyme salivary amylase (breaks down starches)
Drained by parotid duct (Stensen duct)Which empties into vestibule at second molar
Slide59Oral Cavity
Sublingual Salivary Glands
Covered by mucous membrane of floor of mouthProduce mucous secretionActs as a buffer and lubricantSublingual ducts
(Rivinus ducts)Either side of lingual frenulum
Slide60Oral Cavity
Submandibular Salivary Glands
In floor of mouthWithin mandibular groove
Secrete buffers, glycoproteins (mucins), and salivary amylaseSubmandibular ducts (Wharton ducts)
Open immediately posterior to teeth
Either side of lingual frenulum
Slide61Oral Cavity
Salivary Glands
Produce 1.0–1.5 liters of saliva each day70% by submandibular glands25% by parotids5% by sublingual glands
Slide62Oral Cavity
Figure 22–7 The Salivary Glands.
Slide63Oral Cavity
Saliva
99.4% water0.6% includesElectrolytes (Na
+, Cl-, and HCO
3
-
)
Buffers
Glycoproteins (mucins)
Antibodies
Enzymes
Waste products
Slide64Oral Cavity
Functions of Saliva
Lubricating the mouthMoistening and lubricating materials in the mouthDissolving chemicals that stimulate taste buds and provide sensory information
Initiating digestion of complex carbohydrates by the enzyme salivary amylase
(ptyalin or alpha-amylase)