Digestive System
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Transcript of Digestive System
Digestive SystemDigestive System
Objectives:
Discuss the general functions and anatomy of the digestive tract
Describe the individual organs of the system, including a discussion of the gross and microscopic anatomy.
DigestivDigestive Systeme SystemDigestivDigestive Systeme System
Muscular, hollow tube (= “digestive tract”)+Various accessory organs
consists of:
FunctionFunctionFunctionFunction
ingestion
mechanical digestion
chemical and enzymatic digestion
secretion
absorption
compaction
excretion and elimination
The function of the system as a whole is processing food in such a
way that high energy molecules can be absorbed and residues
eliminated.
Individual parts function in:
Muscularis externa
Histological Histological OrganizationOrganizationHistological Histological OrganizationOrganization
Tube made up of four layers.
Modifications along its length as needed.
12
3
4
The 4 Layers of the GutThe 4 Layers of the Gut1) Mucosa Epithelium – usually simple columnar with goblets; may be stratified squamous
if protection needed
Lamina propria - connective tissue deep to epithelium Muscularis mucosae -produces folds - plicae (small intestine) or rugae (stomach)
2) Submucosa – made up of loose connective tissue contains submucosal plexus and blood vessels
3) Muscularis externa – smooth muscle, usually two layers (controlled by the myenteric plexus ) -
outer layer: longitudinal inner layer: circular
4) Serosa visceral layer of mesentery or adventitia depending on location
MembranesMembranesMembranesMembranesPeritoneum - generic serous membrane in abdominal cavity
Mesenteries - double sheets of peritoneum, surrounding and suspending portions of the digestive organs
Greater omentum - "fatty apron", hangs anteriorly from stomach, double layer encloses fat
Lesser omentum - between stomach and liver Mesentery proper - suspends and wraps the small intestine Mesocolon - suspends and wraps the colon, parts are
i. transverse mesocolonii. sigmoid mesocolon
Oral CavityOral Cavity
Also called buccal cavity - lined with oral mucosa (type of epithelium ?)
Hard and soft palates - form roof of mouth
Tongue - skeletal muscle
Salivary glands - three pairs
Teeth
Three pairs of Three pairs of Salivary Salivary GlandsGlandsThree pairs of Three pairs of Salivary Salivary GlandsGlands
Parotid – lateral side of face, anterior to ear, drain by parotid duct to vestibule near 2nd upper molar– mumps
Submandibular – medial surface of mandible – drain near lingual frenulum drain posterior to lower molars
Sublingual – in floor of mouth - drain near frenulum
1-1.5 l / day for digestion (?)lubrication (swallowing) moistening (tasting)
Structure of TeethStructure of Teeth
Crown - exposed surface of tooth Neck - boundary between root and crown
Enamel - outer surfaceDentin – bone-like, but noncellularPulp cavity - hollow with blood vessels and
nervesRoot canal - canal length of root gingival sulcus - where gum and tooth meet
Types and Numbers of TeethTypes and Numbers of Teeth
Dental successionDeciduous (baby, milk) teeth - 20, replaced byPermanent teeth - 32 teeth
Lesser curvature
Greater curvature
Cardia - end under the heart
Fundus - bulge above the esophageal opening
Body - largest region
Pylorus - J curve, inferior end, terminates in
Cardiac and Pyloric sphincters (importance?)
Rugae – highly extendable interior folds
Gross Anatomy of the StomachGross Anatomy of the Stomach
Histology of Histology of StomachStomach
Histology of Histology of StomachStomach
Type of epithelium lining stomach?
Gastric pits – shallow pits, external half rapidly reproduces for replacement
Gastric glands – deep in lamina propria, 3 types of cells
1. Parietal cells (produce HCl and intrinsic factor)
2. Chief cells (produce pepsinogen)
3. Enteroendocrine cells – G cells (several hormones including gastrin which stimulates both parietal and chief cells)
Regions of Small Regions of Small IntestineIntestineRegions of Small Regions of Small IntestineIntestine
SI is longest part of dig. tube
Duodenum (short, 12 inches)– fixed shape & position– Mixing bowl for chyme & ?
Jejunum (2.5 m long) – Most of digestion
Ileum (longest at 3.5 m) – Most of absorption, ends in
Ileocecal valve – slit valve into large intestine (colon)
Plicae circulares – circular pleats around the interior of the small intestine
Villi – minute finger-like projections, contain capillaries & lacteals
Microvilli – sub-microscopic size, projections on single cells Function of all three?
Intestinal glands (crypts) – intestinal juice production
– Cell regeneration
Histology in lab
Structure of Small Intestinal WallStructure of Small Intestinal Wall
Cecum Cecum –– pocket at proximal end with Appendix
ColonColonAscending colon - on right, between cecum and right colic flexure
Transverse colon - horizontal portion
Descending colon - left side, between left colic flexure and
Sigmoid colon - S bend near terminal end
Regions of Large IntestineRegions of Large Intestine
Fig 25-17
Rectum Rectum –– terminal end is anal canal - ending at the anus - which has internal involuntary sphincter and external voluntary sphincter
Rectum and AnusRectum and Anus
RectumRectum – – terminal end is anal canal - ending at the anus -
– which has internal involuntary sphincter and external voluntary sphincter
– Retroperitoneal– Mucus glands– Rectal and Anal valves
1. Mucosa - abundant goblet cells, stratified squamous epithelium near anal canal
2. No villi
3. Longitudinal muscle layer incomplete, forms three bands or taenia coli
4. Circular muscle - forms pockets or haustra between bands
Histology of Large IntestineHistology of Large Intestine
LiverLiverOn right under diaphragm, largest
organ made up of 4 lobes (left and right, caudate, and quadrate)
Hilus (porta hepatis) – underside "entry" point
Extremely versatile: Know a few functions?
Gall bladder
Blood supply to liver
Microscopic anatomy: Liver lobules and triads
LiverLiver
Located in RUQ, adjacent to the Located in RUQ, adjacent to the diaphragm, largest organ made up of diaphragm, largest organ made up of 4 lobes (left and right, caudate, and 4 lobes (left and right, caudate, and quadrate)quadrate)
Falciform ligament (remnant of fetal Falciform ligament (remnant of fetal blood supplyblood supply
Hilus (porta hepatis) – "entry" point on Hilus (porta hepatis) – "entry" point on the visceral surfacethe visceral surface
Liver, cont’dLiver, cont’d
Extremely versatile: Extremely versatile: Know a few Know a few
functions?functions?
Gall bladder-storage of bileGall bladder-storage of bile
Blood supply: hepatic artery (1/3) and Blood supply: hepatic artery (1/3) and portal vein (2/3); Return via Central V. portal vein (2/3); Return via Central V. to vena cavato vena cava
Microscopic anatomy: Liver lobules and portal triads
100,000 Lobules (the basic functional unit)
Hepatocytes are arranged like spokes in a hexagonal wheel
Bathed in blood of hepatic sinusoids
From Portal V. and Hepatic A.
Triads at each corner
Kupffer Cells are phagocytic
See Fig 22.23
Gall BladderGall Bladder
Fundus, body, neckFundus, body, neck Hepatic Duct and Cystic duct Hepatic Duct and Cystic duct
connect to form the Common connect to form the Common Bile DuctBile Duct
Enters at the proximal Enters at the proximal duodenumduodenum
Storage and Concentration Storage and Concentration of Bileof Bile
Gall Stones
PancreasPancreasPancreasPancreas Retroperitoneal
Endocrine or exocrine gland? Both!
– Only 1% is endocrine
Insulin, et al.
Simple Cuboidal Epith arranged in Acini
Digestive enzymes excreted into the pancreatic duct
Common bile duct and pancreatic duct lead to duodenal ampulla and papilla
– Controlled by hepatopancreatic sphincter
PancreasPancreasPancreasPancreas Acinar Cells
– Several types of digestive enzymes e.g., trypsin
– Used as diagnostic tools for pancreatitis
Islets of Langerhans
– AKA pancreatic islets
– Insulin
– Chapt 25