Digestive systemDigestive system

RolesRoles

DigestionDigestion Break down food into particles that can be used by the cellsBreak down food into particles that can be used by the cells Absorb these particles and bring them into the bodyAbsorb these particles and bring them into the body Eliminate wastes Eliminate wastes

Maintain blood homeostasisMaintain blood homeostasis Deal with toxinsDeal with toxins Synthesize blood proteinsSynthesize blood proteins Regulate blood componentsRegulate blood components

The GI tractThe GI tract

It is the tube that starts at It is the tube that starts at the mouth and ends at the the mouth and ends at the anusanus

The food is processed along The food is processed along this tubethis tube

This tube is formed by 3 This tube is formed by 3 layers. The layer layers. The layer components vary with the components vary with the location of the tracklocation of the track

GI accessory organsGI accessory organs

Liver and pancreas Liver and pancreas

These organs secrete These organs secrete enzymes and juices that enzymes and juices that help digestionhelp digestion

Food particles do not Food particles do not enter these organsenter these organs

GI tract structureGI tract structure Four basic layers:Four basic layers:

Mucosa (secretion) – include also Mucosa (secretion) – include also a small ring of muscles a small ring of muscles (muscularis mucosae) with a (muscularis mucosae) with a nervous plexus (submucosal nervous plexus (submucosal plexus = Meissner’s plexus)plexus = Meissner’s plexus)

Muscular layers (movement) – Muscular layers (movement) – circular and longitudinal fibers circular and longitudinal fibers with a plexus, the myenteric with a plexus, the myenteric plexus (Auerbach plexus) plexus (Auerbach plexus) responsible for peristalsisresponsible for peristalsis

Serosa (protection), connective Serosa (protection), connective tissue, for protection is just an tissue, for protection is just an extension of the visceral extension of the visceral peritoneumperitoneum

PeristalsisPeristalsis

Contraction of circular muscle behind the bolus

Contraction of longitudinal muscle IN FRONT of the bolus

Peristalsis: coordinated contraction of both circular and longitudinal muscle layers of the G.I. musculature as controlled by the enteric nervous system

InvoluntaryInvoluntary

PeristalsisPeristalsisInvoluntaryInvoluntary

Enteric Nervous SystemEnteric Nervous System

Myenteric plexus: control

peristalsis

Submucosal plexus: control

secretion

Unique FeaturesUnique Features

Epithelia of the G.I. tract has a very high Epithelia of the G.I. tract has a very high turnover/production rate.turnover/production rate. Surface epithelia will renew itself every 2-6 days Surface epithelia will renew itself every 2-6 days

depending on the region of the intestinal tract.depending on the region of the intestinal tract. Anti-cancer therapies (targeting rapidly dividing Anti-cancer therapies (targeting rapidly dividing

cells) often have the side-effect of targeting the cells) often have the side-effect of targeting the gut as well.gut as well.

OverviewOverview

Mouth = Oral CavityMouth = Oral Cavity Mouth = oral cavityMouth = oral cavity

Cheek, lips, hard & soft Cheek, lips, hard & soft palatepalate

Lips attached to gums via Lips attached to gums via labial frenulumlabial frenulum

Palate = roof of oral cavityPalate = roof of oral cavity Hard palate = maxillae & palatine Hard palate = maxillae & palatine

bonesbones Soft palate = muscle-reinforced Soft palate = muscle-reinforced

region dorsal to the hard palate region dorsal to the hard palate palatine uvula palatine uvula

Tongue: Tongue: move food around & move food around & helps for masticationhelps for mastication

Lingual tonsils can be found at the Lingual tonsils can be found at the base of the tonguebase of the tongue

Salivary glandsSalivary glands Saliva from 3 paired glands:Saliva from 3 paired glands:

Parotid glandParotid gland (between ear & (between ear & masseter, largest gland) – masseter, largest gland) – innervated by glosspharyngeal innervated by glosspharyngeal (parasympathetic) + (parasympathetic) + T1-T3 of the cervical ganglia of the sympathetic

SubmandibularSubmandibular (under middle (under middle of mandible) - of mandible) - innervated by facial (VII) nerve (parasympathetic) & T1-T3 of the sympathetic

SublingualSublingual (posterior to (posterior to submandibular) - submandibular) - innervated by facial (VII) nerve (parasympathetic) & T1-T3 of the sympathetic

•Parasympathetic = mucus rich secretion, sympathetic = watery

Mastication (chewing)Mastication (chewing) Muscles involved in Muscles involved in

mastication:mastication: MasseterMasseter TemporalisTemporalis Medial Medial && lateral pterygoid lateral pterygoid

ALL innervated by ALL innervated by mandibular branch ofmandibular branch of Trigeminal (V) Trigeminal (V) nerve…Vnerve…V33

CN (V) palsy = inability to CN (V) palsy = inability to perform masticationperform mastication

VoluntaryVoluntary

TeethTeeth Humans have “heterodont” Humans have “heterodont”

dentition (various types of dentition (various types of teeth)teeth) Incisors, canines, premolars Incisors, canines, premolars

& molars& molars Incisors & canines = single Incisors & canines = single

root teethroot teeth Premolars & molars = Premolars & molars =

multiple rootsmultiple roots Mapped using “dental Mapped using “dental

formula” = # incisors, formula” = # incisors, canines, premolars/molars in canines, premolars/molars in maxillary portion (assumes maxillary portion (assumes everything is equal) = (I 2/2, everything is equal) = (I 2/2, C 1/1, M 3/3) X 2C 1/1, M 3/3) X 2

TeethTeeth Humans are also Humans are also

“diphyodont”: 2 sets of “diphyodont”: 2 sets of teeth during their lifespanteeth during their lifespan Deciduous teeth (milk teeth) Deciduous teeth (milk teeth)

begin eruption at 6 monthsbegin eruption at 6 months Full set by 2.5 years (full set Full set by 2.5 years (full set

= 20 teeth)= 20 teeth) (2/2, 1/1, 2/2) X 2 = 20 (2/2, 1/1, 2/2) X 2 = 20

teethteeth Permanent teeth replace Permanent teeth replace

deciduous teeth (all the way deciduous teeth (all the way through late teens)through late teens)

Final formula = (I 2/2, C 1/1, Final formula = (I 2/2, C 1/1, PM2/2, M 3/3) X 2 = 32 PM2/2, M 3/3) X 2 = 32 teethteeth

Teeth - structureTeeth - structure Crown:Crown: above the gum above the gum Neck:Neck: at the gum (gingiva) level at the gum (gingiva) level Root:Root: within the bone within the bone

Outer layer: Outer layer: EnamelEnamel the the hardest substance in the body, hardest substance in the body, protects tooth. Subject to decay, protects tooth. Subject to decay, on the crown only on the crown only

Dentin:Dentin: softer, throughout the softer, throughout the entire toothentire tooth

Cementum:Cementum: in the root, outer in the root, outer layerlayer

Pulp:Pulp: made of blood vessels and made of blood vessels and nerves, present in the pulp cavitynerves, present in the pulp cavity

Periondontal ligament:Periondontal ligament: attaches attaches the tooth to the bonethe tooth to the bone

EsophagusEsophagus Stratified squamous

epithelium (not a “simple” epithelium)

Combination of skeletal & smooth muscle (combination of voluntary & involuntary control)

EsophagusEsophagus

StomachStomach Several regions: from Several regions: from

lower esophageal lower esophageal sphinctersphincter Cardia – Cardia – fundus – body – antrumfundus – body – antrum

Several layers of muscles: Several layers of muscles: longitudinal, oblique and longitudinal, oblique and circularcircular

Epithelium folded and Epithelium folded and forming forming rugaerugae

3 muscle layers

longitudinal, circular,

transverse/oblique

Pylorus

(resistance) Antrum

(acid control & mixing)

Body/corpus

(acid & pepsin secretion, storage)

Fundus (storage)

Cardia

Lower esophageal sphincter

Gastric epitheliumGastric epithelium

Chief cells: Chief cells: secrete pepsinogen (inactive precursor to pepsin; protein hydrolase) & prochymosin (precursor to chymosin; coagulates milk)

Parietal cells in body/corpus & antrum secrete HCl & intrinsic factor

G-cells in the antrum secrete gastrin (endocrine hormone) that triggers both parietal cells & Chief cells

Enterochromaffin-like cells (ECL) secrete histamine (works in to magnify gastrin response)

Goblet cells secrete mucus

Epithelium folds and forms pitsEpithelium folds and forms pitsAlong the pits, several types of cellsAlong the pits, several types of cells

Three sections:Three sections: DuodenumDuodenum JejunumJejunum IleumIleum

Total length: about 25 Total length: about 25 feetfeet

Surface area: Surface area: 100-200 100-200 mm22 ( ( tennis court) – 25 tennis court) – 25 feet longfeet long greater area for nutrient greater area for nutrient

absorptionabsorption cells)cells)

Epithelial surface area is Epithelial surface area is amplified by a number of amplified by a number of structures:structures: Plica muscularis/circularisPlica muscularis/circularis (2-5X (2-5X

increase in surface area)increase in surface area)

VilliVilli (10-30X increase in surface (10-30X increase in surface area)area)

MicrovilliMicrovilli of each absorptive of each absorptive enterocyte (200-400X increase in enterocyte (200-400X increase in surface area).surface area). Folds of the apical plasma membrane)Folds of the apical plasma membrane)

Small intestine

Plica Villi

Microvilli

From stomach to jejunumFrom stomach to jejunum Shortest section, about 20 cm Shortest section, about 20 cm

long. long. Secretions from the pancreas Secretions from the pancreas

and liver (bile) enter duodenum and liver (bile) enter duodenum viavia Sphincter of OddiSphincter of Oddi located in located in thethe ampulla of Vater (=hepato-ampulla of Vater (=hepato-pancreatic duct)pancreatic duct)

Region of the intestine where Region of the intestine where most of food breakdown occursmost of food breakdown occurs

Jejunum

Important for nutrient Important for nutrient absorptionabsorption

Mucosa has many fold, the Mucosa has many fold, the villi and microvilli villi and microvilli increase increase surface for reabsorptionsurface for reabsorption

Epithelium is columnar Epithelium is columnar epitheliumepithelium

Within each villus: blood Within each villus: blood capillaries and 1 lymphatic capillaries and 1 lymphatic capillary, the lacteal capillary, the lacteal nutrient reabsorptionnutrient reabsorption

Last section of the small Last section of the small intestineintestine

2-4 m long2-4 m long End at the cecal valve, End at the cecal valve,

point of entry into the point of entry into the large intestinelarge intestine

Site of absorption of Site of absorption of remnants from jejunum, remnants from jejunum, bile saltsbile salts

Interface between ileum Interface between ileum (terminal small intestine) & large (terminal small intestine) & large bowelbowel Acts to limit amount/rate of Acts to limit amount/rate of

nutrient entry into the large nutrient entry into the large bowelbowel

Initial “entrance” into large Initial “entrance” into large bowel = cecumbowel = cecum Enlarged region of the proximal large Enlarged region of the proximal large

bowelbowel AppendixAppendix is located in the cecum is located in the cecum

Dense collection of lymph nodes to allow Dense collection of lymph nodes to allow immune system to sample/measure colonic immune system to sample/measure colonic microfloramicroflora

Colon (ascending, transverse, Colon (ascending, transverse, descending & sigmoid) serves to descending & sigmoid) serves to absorb electrolytes, and absorb electrolytes, and remaining water from the chymeremaining water from the chyme

As water is reabsorbed, the As water is reabsorbed, the leftover material becomes leftover material becomes thicker in consistency thicker in consistency stool stool formationformation

Colonic epithelia is generally Colonic epithelia is generally crypt-like;crypt-like; large capacity to absorb water and large capacity to absorb water and

electrolytes through surface epitheliaelectrolytes through surface epithelia crypt-like architecture also provides crypt-like architecture also provides

enormous secretory capacityenormous secretory capacity

InvoluntaryInvoluntary

Colonic musculature is Colonic musculature is unique:unique: longitudinal muscle layer longitudinal muscle layer

is “banded” into 2-3is “banded” into 2-3 tanea colitanea coli

circular muscle contracts circular muscle contracts in “rings”in “rings” haustrahaustra or or haustrationshaustrations

Musculature mixes colonic Musculature mixes colonic contents very wellcontents very well

For fecal eliminatrion For fecal eliminatrion defecationdefecation

Presence of 2 sphincters Presence of 2 sphincters near the anus:near the anus: Anal smooth muscle Anal smooth muscle

sphincter (involuntary)sphincter (involuntary) Anal striated muscle Anal striated muscle

sphincter (voluntary)sphincter (voluntary)

Pelvic diaphragm: support Pelvic diaphragm: support intestinesintestines Levator ani Levator ani

pubococcygeuspubococcygeus (anal (anal sphincter), sphincter), puborectalispuborectalis, and , and iliococcygeusiliococcygeus..

CoccygeusCoccygeus

Urogenital diaphragm Urogenital diaphragm (perineum)(perineum) Sphincter urethrea Sphincter urethrea

(external sphinter)(external sphinter) Deep transverse perineusDeep transverse perineus

Largest internal organLargest internal organ 4 lobes4 lobes

RightRight && left lobesleft lobes separated byseparated by falciform ligamentfalciform ligament ““round ligament/ligamentum teresround ligament/ligamentum teres” attached to falciform ligament = ” attached to falciform ligament =

remnant of umbilical veinremnant of umbilical vein Caudate lobeCaudate lobe closest to the IVCclosest to the IVC Quadrate lobeQuadrate lobe adjacent to gall bladderadjacent to gall bladder

Receives blood from the portal Receives blood from the portal vein, from the intestinesvein, from the intestines

Blood is too rich in nutrient Blood is too rich in nutrient and need to be dealt by the and need to be dealt by the liverliver Storage of nutrientStorage of nutrient Synthesisis of various compactSynthesisis of various compact DetoxificationDetoxification

Blood in homeostatic Blood in homeostatic equilibrium then return to the equilibrium then return to the circulation via the central vein circulation via the central vein hepatic vein hepatic vein inf. vena inf. vena cavacava

Hepatic artery brings oxygen Hepatic artery brings oxygen to the liver to the liver

The histological/functional The histological/functional units of the liverunits of the liver

Composed of rays of cells with Composed of rays of cells with sinusoidal capillariessinusoidal capillaries

Cells = Cells = hepatocyteshepatocytes (liver cells) (liver cells) Interspersed with “Interspersed with “Kupffer cellsKupffer cells” ”

= resident macrophages= resident macrophages The hepatocytes draw nutrients The hepatocytes draw nutrients

from the portal vein and from the portal vein and store/modify themstore/modify them

They detoxify toxins They detoxify toxins They synthesize bile which is They synthesize bile which is

collected by the bile ductscollected by the bile ducts

The small bile ducts fuse and form the The small bile ducts fuse and form the left and right hepatic ductsleft and right hepatic ducts

The hepatic ducts fuse to become the The hepatic ducts fuse to become the common hepatic ductcommon hepatic duct

The bile, passing into the cystic duct, The bile, passing into the cystic duct, will be store in the will be store in the gallbladdergallbladder

When needed (after a meal, the When needed (after a meal, the gallbladder will contract and empty gallbladder will contract and empty the bile into the the bile into the common bile ductcommon bile duct

The common bile duct passes around The common bile duct passes around the duodenum, enters the pancreas and the duodenum, enters the pancreas and fuses with the pancreatic duct to form fuses with the pancreatic duct to form the the hepatopancreatic duct (ampul of hepatopancreatic duct (ampul of vater)vater)

The short duct empties into the The short duct empties into the duodenum through a sphincter, the duodenum through a sphincter, the sphincter of Oddisphincter of Oddi

Liver and bile ducts

Stores & concentrates Stores & concentrates bilebile Lined by smooth muscle Lined by smooth muscle

to aid in contraction to aid in contraction during bile mobilizationduring bile mobilization

Can be afflicted by the Can be afflicted by the formation of stonesformation of stones

Diagnostic Tests: Diagnostic Tests: ERCPERCP (Endoscopic Retrograde (Endoscopic Retrograde CholangioPancreatography)CholangioPancreatography)

To remove gallbladder stonesTo remove gallbladder stones

ERCP are done to remove ERCP are done to remove gallbladder stonesgallbladder stones

Mixed gland (endocrine & Mixed gland (endocrine & exocrine)exocrine) Islets of LangerhansIslets of Langerhans = =

endocrine portionendocrine portion Pancreatic aciniPancreatic acini = exocrine = exocrine

portionportion Head is peritonealHead is peritoneal

Body & tail are secondary Body & tail are secondary retroperitonealretroperitoneal (similar to (similar to duodenum)duodenum)

VERY rich in blood supplyVERY rich in blood supply Pancreatic arteryPancreatic artery & &

pancreaduodenal branch of the pancreaduodenal branch of the SMASMA

Exocrine secretions = Exocrine secretions = proteases, carbohydrases, proteases, carbohydrases, lipases, bicarbonatelipases, bicarbonate

Two layer membrane surrounding Two layer membrane surrounding most organs in the abdomenmost organs in the abdomen

Outer layer= Outer layer= parietal peritoneumparietal peritoneum, , located against the abdominal walllocated against the abdominal wall

Inner layer: Inner layer: visceral peritoneumvisceral peritoneum, , surrounding the intestinessurrounding the intestines

The space between the 2 layers is The space between the 2 layers is the the peritoneal spaceperitoneal space has a thin has a thin layer of fluid which prevents bowel layer of fluid which prevents bowel frictionfriction

Some abdominal organs are external Some abdominal organs are external to the peritoneum (kidneys)to the peritoneum (kidneys)

Peritoneum

Formed by a double layer of Formed by a double layer of visceral peritoneumvisceral peritoneum

Binds bowel loopBinds bowel loop These layers contain blod These layers contain blod

and lymphatic capillaries as and lymphatic capillaries as well as nerves going to the well as nerves going to the intestinal wallintestinal wall

The The greater omemtumgreater omemtum: : Large fold over the abdomenLarge fold over the abdomen

The The lesser omentumlesser omentum: fold : fold between stomach lesser between stomach lesser curvature and livercurvature and liver

Mesentery

ColostomyColostomy Sometimes, fecal matter Sometimes, fecal matter

needs to be diverted into needs to be diverted into a bag because of a bag because of diseased bowels diseased bowels ileostomy – colostomyileostomy – colostomy

Crohn’s diseaseCrohn’s disease

Chronic inflammation Chronic inflammation of the intestine, most of the intestine, most commonly the ileum commonly the ileum and cecum areasand cecum areas

No known causeNo known cause

Hirschsprung diseaseHirschsprung disease

Congenital defect where Congenital defect where the nerve plexuses the nerve plexuses within the intestinal within the intestinal wall are missing wall are missing no no peristalsis peristalsis fecal fecal matter is blocked and matter is blocked and accumulates accumulates the the colon enlargescolon enlarges