Exercise 41 Digestive System 1. Digestion and absorption It is the physical and chemical break down...

Exercise 41

Digestive System

1

Digestion and absorption

It is the physical and chemical break down of food

AbsorptionIt is the passing of the digested food

through the epithelial cells into the blood stream

2

Digestive system

3

Gastrointestinal tract

It is the alimentary canal Mouth Pharynx Esophagus Stomach Small intestine Large instestine

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Accessory digestive organs

Salivary glands Gallbladder Liver Pancreas Teeth

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General histology of the gastrointestinal tract

It has 4 tunicsMucosa

• Epithelium – simple columnar• Lamina propria – areolar tissue• Muscularis mucosa

• Smooth muscle that enables movement of the mucosa

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• Functions of the mucosa are secretion, absorption, protection

Submucosa• Dense connective tissue• Blood vessels• Lymph nodes and vessels• Submucosal plexus • Functions are nutrition and

protection of the mucosa7


Muscularis externa• Inner circular layer of smooth

muscle• Outer longitudinal layer of smooth

muscle• Myenteric plexus• Allows GI movements

8


Serosa (abdominal organs)• Most outer layer• Mesothelium – areolar tissue• Functions is to reduce friction

between GI organsAdventitia

• Coarse fibrous tissue that binds the GI organs to the surrounding tissues. Anchors and protects them9

Oral cavity

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Macroscopy of the digestive tract

Oral cavity or mouthOral cavityLips or labia

• Superior and inferior labial frenulumCheeksPalate

• Soft with uvula• Hard• Palatine raphe

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Macroscopy of the digestive tractTongue

• Lingual frenulumVestibulePalatine tonsil

• Palatoglossal arch• Palatopharyngeal arch

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Lingual tonsilSalivary glands

• Saliva• Salivary amylase

PharynxNasopharynxOropharynxLaryngopharynx

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Macroscopy of the digestive tract Esophagus

PeristalsisGastroesophageal sphincterAdventitia and not serosa

StomachCardiac regionFundusBody

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Pyloric region• Pyloric sphincter

Greater curvatureGreater omentum

• From the greater curvature down to the abdominal organs

Lesser curvature

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Lesser omentumFrom the lesser curvature to the liverGastric pitGastric rugaeFunction of the stomach is to

process the food forming the chyme

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Histology of the stomach

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MucosaGastric glands

• Chief or zymogenic cells: • Located on the fundus• Produce pepsinogen

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• Parietal cells:• Located on the fundus• Produce HCL• Produce intrinsic factor

Enteroendocrine cells:• Located on the pyloric region• Release hormones

Submucosa

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Muscularis externaOblique layerCircular layerLongitudinal layer

Gastroesphageal junction (Cardioesophageal)Stratified squamous epithelium on

the esophagusSimple columnar on the stomach

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Small intestine

From the pyloric sphincter to the ileocecal valve

Mesentery Proper• Double layer of peritoneum that

attaches the small intestine to the posterior body wall

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Small intestine

PlicaeDeep folds of the mucosa and

submucosaThey cause the chyme to spiral

through the intestine slowing and mixing it

Intestinal crypts of crypts of LieberkuhnIt is the invaginated area of the

mucosa between the villi

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Small intestine

LactealIt is the lymphatic capillary present in

each villus Function of the small intestine

Nutrients absorption

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PART B

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Subdivisions of the small intestine

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Small intestine

DuodenumPancreatic ductBile ductHepatopancreatic ampullaMajor duodenal papillaHepatopancreatic sphincter or

sphincter of OddiDuodenal glands or Brunner’s

glands – located in the submucosal layer

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Small intestine

JejunumWhere the food is most absorbed

IleumIleocecal valvePeyer’s patches

• Aggregation of lymphoid tissue more prominent in the ileum

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Small intestine

Superficial structures of the small intestine that increases the absorptive area of the mucosaVilli

• Fingerlike projections of the mucosa

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Small intestine

Microvilli or brush border• Projections of the cell membrane

of the columnar epithelium• Brush border enzymes

Plicae

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Histology of the small intestine

Identify these structures on the slide:PlicaCriptsVilliBrush borderLayers of the intestine

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Histology of the small intestine

DuodenumSubmucosa with Brunner’s glands

JejunumLongest, leafy villi

IleumSubmucosa with Peyer’s patches

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The large intestine

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Large intestine

From the ileocecal valve to the anus Mesocolon

Attaches the large intestine to the body wall

CecumIt is the first part

AppendixA blind tube like structure connected

to the cecum33

Large intestine

Colon: Ascending

Right side of the abdominal cavityRight colic (hepatic) flexureIt is retroperitoneal

TransverseCross the abdominal cavityLeft colic (splenic) flexure

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Large intestine

DescendingIt is retroperitoneal

SigmoidS-shaped Located in the pelvis

Rectum

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Large intestine

AnusExternal sphincter - skeletal muscle

• VoluntaryInternal sphincter – smooth muscle

• involuntary

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Large intestine - structures

Tenia coliIt is the longitudinal muscle layer of

muscularis externaIt is in the shape of a muscle band

HaustraPocket like sacs of the large intestineIt is caused by the tenia coli

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Large intestine - structures

Epiploic appendagesFat-filled pouches of visceral

peritoneum hanging for the colon’s surface

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Large intestine

Functions of the large intestineConsolidate and propel the fecal

matter to the anusSite for intestinal bacteria to

synthesize vitamins B and KSite for water absorption

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Histology of the large intestine

Lumen Crypts Layers of the digestive tract Mucosa with the maximum amount of

goblet cells No villi

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Teeth:Deciduous (milk teeth)

• They appear between 6 month and 2 ½ years of age

• They begin to shed at 6 years of age

• They are completely shed by the age of 12

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Permanent• They begin to appear at 6 years of

age• They last for a lifetime

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Types of teeth

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Classification of the teethIncisors

• Chisel shaped• Shearing action when biting• 4 superiors and 4 inferiors (2

centrals and 2 laterals)• Single-rooted

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CaninesCone-shapedIt tears the food2 superiors and 2 inferiorsSingle-rooted

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PremolarsTwo cuspsIt grinds the food4 superiors and 4 inferiors

• 2 first premolars• 2 second premolars

Generally single-rooted• 1st premolar may have 2 roots

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MolarsThey have broad crownsRounded cusps6 superiors and 6 inferiors

• 2 first molars• 2 second molars • 2 third molars or wisdom teeth

They have 2 roots They grind food into fine pieces

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Dental formula: Deciduous

2,1,0,2

2,1,0,2 Permanent

2,1,2,3

2,1,2,3

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Anatomy of the teethCrown

• Clinical• Anatomical

Enamel• It consists mainly of calcium salts

Gum or gingival• Gingival sulcus and margin

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Neck Root Cementum Periodontal ligament Dentin Pulp

Contain blood vessels and nerves Pulp cavity

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Odontoblasts Root canal Apical foramen

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PART C

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Salivary glandsParotid glands

• Anterior to the ear• He parotid duct open at the level

of the second superior molar• Mainly a serous gland

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Submandibular gland• Located on the floor of the mouth• He submandibular duct opens at

the base of the lingual frenulum• Serous and mucous gland

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Sublingual glandLocated on the floor of the mouthThere are many sublingual ducts that

open under the tongueSerous and mucous gland

Saliva compositionMucin - Forms the bolusSerous fluid – contain amylase

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Histology of the salivary glandsMucous cells forming the aciniSerous cells forming demilunes

around the mucous cellsDucts with cuboidal epithelium

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Salivary glands

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LiverLocated mainly in the right

hypochondriac region4 lobes

• Right, left, caudate, quadrateFalciform ligament

• Suspend the liver from the diaphragm and anterior abdominal wall

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Bile duct system

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BileProduced by the liver Responsible for emulsification of the

lipid from the diet Bile duct system

Bile canaliculus• Carries the bile to the duct of the

nearest portal area

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Bile ducts carry bile to the:Right and left hepatic ducts Common hepatic duct

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Histology Lobules

• Structural and functional units of the liver

• They have cords of hepatocytes running away from the central vein

• Hexagonal shapeCentral vein

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Histology of the liver

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Portal triad or portal tract• Located at each of the six corners

of the lobule• Hepatic artery• Hepatic portal vein• Bile duct

Sinusoids• Blood-filled

Kupffer cells• Macrophage lining the sinusoids

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GallbladderStores the bile not being usedConcentrates the stored bileCystic duct

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PancreasIt is a retroperitoneal organEndocrine and exocrine organSecretes the pancreatic juice into the

duodenumIt alkalinizes the chyme coming from

the stomachPancreatic duct or duct of WirsungAccessory pancreatic duct or duct of

Santorini66


Histology of the pancreasAcinar or exocrine pancreasIslets or endocrine pancreasSepta

• Connective tissue

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Microscopic structures to be identified

Identify the organ and its layers:Mucosa, submucosa, muscularis

externa, adventitia or serosa Esophagus

Stratified squamous epitheliumGastroesophageal junction

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Microscopic structures to be identified Stomach

Simple columnar epitheliumGastric pit

DuodenumVilli

• Brush border• Goblet cells

Intestinal criptsBrunner’s glands

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Microscopic structures to be identified Jejunum

Leafy villi, cryptsBrush borderGoblet cells

IleumVilli with goblet cells and brush

border, cryptsPeyer’s Patch

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Large intestineCripts, abundant goblet cells

Salivary glandsSerous acini (demilunes)Mucous aciniDucts

PancreasAcinar exocrine vs. endocrine

pancreatic islets

Microscopic structures to be identified

71

Microscopic structures to be identified Liver

Hexagonal lobulesTriad

• Hepatic portal vein• Hepatic artery• Bile duct

Central veinSinusoids vs. plates of hepatocytes

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Cat structures to be identified

Esophagus Stomach

Lesser and greater curvaturesLesser and greater omentum

Small intestineMesentery properIleocecal valve

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Cat structures to be identified

Large intestineMesocolonRectumAnus

Liver Gall bladder Pancreas

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Exercise 41 Digestive System 1. Digestion and absorption It is the physical and chemical break down...

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