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Cadaver dissection videos

• http://anatomy.med.umich.edu/courseinfo/video_index.html– Gastrointestinal:

http://anatomy.med.umich.edu/gastrointestinal_system/peritoneum_vid.html

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The Digestive System

• Mouth---bite, chew, swallow

• Pharynx and esophagus----transport

• Stomach----mechanical disruption; absorption of water & alcohol

• Small intestine--chemical & mechanical digestion & absorption

• Large intestine----absorb electrolytes & vitamins (B and K)

• Rectum and anus---defecation

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Layers of the GI Tract

1. Mucosal layer

2. Submucosal layer

3. Muscularis layer

4. Serosa layer

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Mucosa• Epithelium

– stratified squamous (in mouth, esophagus & anus) = tough

– simple columnar in the rest

• secretes enzymes and absorbs nutrients

• specialized cells (goblet) secrete mucous onto cell surfaces

• enteroendocrine cells---secrete hormones controlling organ function

• Lamina propria

– thin layer of loose connective tissue

– contains BV and lymphatic tissue

• Muscularis mucosae---thin layer of smooth muscle

– causes folds to form in mucosal layer

– increases local movements

– movements increase absorption

with exposure to “new” nutrients

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Submucosa

• Loose connective tissue– containing BV, glands and lymphatic tissue

• Meissner’s plexus– parasympathetic

– innervation• vasoconstriction

• local movement by muscularis mucosa smooth muscle

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Muscularis

• Skeletal muscle = voluntary control– in mouth, pharynx, upper esophagus and anus

– control over swallowing and defecation

• Smooth muscle = involuntary control– inner circular fibers & outer longitudinal fibers

– mixes, crushes & propels food along by peristalsis

• Auerbach’s plexus (myenteric)– both parasympathetic & sympathetic innervation of circular and

longitudinal smooth muscle layers

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Serosa

• An example of a serous membrane• Covers all organs and walls of cavities not open to

the outside of the body• Secretes a serous fluid• Consists of connective tissue covered with simple

squamous epithelium

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Peritoneum• Peritoneal cavity

– potential space containing a bit of serous fluid

– Contains most of the digestive organs

• A sheet of serosa forms the peritoneal cavity

• Serosa is known as the Peritoneum– Cavity within the abdomen that

contains the viscera

– Formed by a parietal layer

– visceral layer covers organs

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• Serosa also forms connections from the parietal peritoneum to several organs in the cavity = Mesenteries

• 4 kinds:

• Mesentery – parietal peritoneum to small intestines

• Mesocolon – parietal peritoneum to large intestine (colon)

• Lesser omentum

• Greater omentum

The 4 Mesenteries

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The path of food:oral cavity/teeth/salivary glands

oropharynx/epiglottis

esophagus

stomach

small intestine: duodenum

small intestine: ileum

small intestine: jejunum

large intestine: ascending colon

large intestine: transverse colon

large intestine: descending colon

sigmoid colon rectum anus

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Mouth

• Oral cavity proper---the roof = hard, soft palate and uvula– floor – geniohyoid, mylohyoid – contains the tongue– lips and cheeks-----contains buccinator muscle that keeps food between upper &

lower teeth– Vestibule---area between cheeks and teeth

• Lined with an oral mucosa (stratified squamous epithelium & lamina propria)– Lining of the cheeks = buccal mucosa– Lining of the maxilla and mandible = alveolar mucosa (gingiva)

• Landmarks: lingual frenulum, labial frenulum, uvula– Shortened lingual frenulum can impede movement of the tongue within the mouth

Tubal tonsil

Geniohyoid

Mylohyoid

Epiglottis

Vocal cords

Lingual tonsil

Larynx

Oropharynx

Nasopharynx

Laryngopharynx

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Pharyngeal Arches• Two arches skeletal muscles that

elevate the soft palate when we swallow– Closes off the nasopharynx and directs

food into the oropharynx

• First arch = Palatoglossal muscle– extends from palate down to tongue– uvula dangles from the middle of this

arch– forms the boundary between the oral

cavity and oropharnyx

• Second arch = Palatopharyngeal muscle– extends from palate to pharyngeal

wall– part of the oropharynx– found behind the palatine tonsil

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Structure and Function of the Tongue• Muscular structure covered

with an oral mucosa• Muscle of tongue is attached to

hyoid, mandible, hard palate and styloid process

• Two groups of muscles• 1. Intrinsic muscles

– Change the shape of the tongue

– Organized as transverse muscles, longitudinal and vertical muscles

• 2. Extrinsic muscles– move the tongue in the oral

cavity– Styloglossus, palatoglossus &

hyoglossus– Geniohyoid & genioglossus

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Salivary Glands • Parotid below your ear and over the masseter

• Submandibular is under lower edge of mandible

• Sublingual is deep to the tongue in floor of mouth

• All have ducts that empty into the oral cavity (exocrine glands)

• Classified either as: serous or mixed

• Wet food for easier swallowing

• Dissolves food for tasting

• Bicarbonate ions buffer acidic foods

• Helps build stronger enamel

• Chemical digestion begins with enzyme salivary

amylase & lingual lipase

• Also contains lysozyme ---helps destroy bacteria

• Protects mouth from infection with its rinsing action

• Serous glands - cells secrete a watery fluid – e.g. parotid

• Mixed glands secrete both mucus and a serous fluid – e.g. submandibular & sublingual

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Parotid

Submandibular

Sublingual

• Parotid glandsecretes the

enzyme Salivary amylase

• Submucosalayer of the tongue

secretesLingual lipase

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Salivation

• Parasympathetic nerves - Increase salivation– sight, smell, sounds, memory of food, tongue

stimulation---rock in mouth– cerebral cortex signals the salivatory nuclei in

brainstem– carried by parasympathetic nerves = CN 7 & 9

• Sympathetic nerves - Stop salivation – dry mouth when you are afraid– sympathetic nerves

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Teeth:-grinding, tearing and shearing of food

-two main divisions: crown and root-crown: above gumline/gingiva

-covered with a layer of enamel-root: below the gumline, embedded in the alveolar socket of the jaw

-entry of nerves and blood vessels via the apical foramen-root is secured in the jaw by two tissues: cementum & periodontal

membrane/ligament-neck – where crown and root meet

-gingiva should form a tight a seal at this area-inside of the tooth = pulp (nerves/blood vessels)

-nerves and BVs enter the root via apical foramen and travel through root canals to enter the pulp cavity

-tooth is formed of a calcified connective tissue called dentin-dentin, enamel and cementum – made of calcium phosphate very similar to bone

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Primary and Secondary Dentition

-primary: 20 teeth starting at 6 months-secondary/adult: between 6 and 12 years = 32 teeth 8 incisors 4 canines (cuspids) 8 premolars (bicuspids) 12 molars (tricupids)

** third pair of molars (wisdom teeth) may not erupt -impacted

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Pharynx• Funnel-shaped tube extending from internal

nares to the esophagus (posteriorly) and larynx (anteriorly)

• Skeletal muscle lined by mucous membrane• Deglutition or swallowing is facilitated by saliva

and mucus– starts when bolus is pushed into the oropharynx– sensory nerves send signals to deglutition center in

brainstem

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Esophagus• Collapsed muscular tube

• In front of vertebrae

• Posterior to trachea

• Posterior to the heart

• Pierces the diaphragm at hiatus– hiatal hernia or diaphragmatic

hernia

• Mucosa = stratified squamous

• Submucosa = large mucous glands

• Muscularis = upper 1/3 is skeletal, middle is mixed, lower 1/3 is smooth– upper & lower esophageal

sphincters are prominent circular muscle

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Esophagus

ThoracicAorta

Diaphragm

Liver

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Physiology of the Esophagus - Swallowing

• Voluntary phase---tongue pushes food to back of oral cavity

• Involuntary phase----pharyngeal stage– breathing stops & airways are closed– soft palate & uvula are lifted to close off

nasopharynx– vocal cords close– epiglottis is bent over airway as larynx is

lifted– controlled by autonomic nervous system

• Peristalsis pushes food down– circular fibers behind bolus

– longitudinal fibers in front of bolus shorten the distance of travel

• Travel time is 4-8 seconds for solids and 1 sec for liquids

• Lower sphincter relaxes as food approaches

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Gastroesophageal Reflex Disease• If lower esophageal sphincter fails to open

– distension of esophagus feels like chest pain or heart attack

• If lower esophageal sphincter fails to close– stomach acids enter esophagus & cause heartburn (GERD)

– for a weak sphincter---don't eat a large meal and lay down in front of TV

– smoking and alcohol make the sphincter relax worsening the situation

• Control the symptoms by avoiding– coffee, chocolate, tomatoes, fatty foods, onions & mint

– take Tagamet HB or Pepcid AC 60 minutes before eating

– neutralize existing stomach acids with Tums

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Anatomy of Stomach• Size when empty

– large sausage– stretches due to rugae (folds in the mucosa caused by contraction of the m. mucosae)

• Muscularis – three layers of smooth muscle– longitudinal– circular– oblique

• Parts of stomach– Cardiac region– Fundus– Dody– Pyloric region---starts to narrow as

approaches pyloric sphincter- Greater curvature- Lesser curvature

• Bolus of food enters and mixes with gastric juice Chyme• Stomach empties as small squirts of chyme leave the stomach through the pyloric

valve/sphincter

FUNDUS

BODY

DUODENUM

PYLORIC REGION

PANCREAS GREATER CURVATURELESS

ER

CU

RV

ATU

RE

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Mucosa of the Stomach

• simple columnar epithelium with embedded mucus cells

• Mucosa forms columns of secretory cells = gastric glands that open into the stomach lumen through gastric pits

• Chief cells secrete pepsinogen (inactive) into the stomach which will become pepsin (active) – for protein digestion

• Parietal cells secrete H+ and Cl- ions into the stomach – become Hydrochloric acid

• HCl converts pepsinogen into pepsin = protein digestion

• Intrinsic factor (parietal cells)

– absorption of vitamin B12 for RBC production

• Gastrin hormone (G cells)

• Increases gastric juice production, gastric motility and increase gastric emptying

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Anatomy of the Small Intestine

• 20 feet long----1 inch in diameter

• Large surface area for majority of absorption

• 3 parts– duodenum---10 inches– jejunum---8 feet– ileum---12 feet

• ends at ileocecal valve

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SmallIntestine

AscendingColon

Liver

Gallbladder

Stomach

DescendingColon

Mesentery ofSmall Intestine

Lesser Omentum

TransverseColon

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Small Intestine

• Structures that increase surface area– plica circularis

• permanent ½ inch tall folds in the mucosa

• not found in lower ileum

• cannot stretch out like rugae in stomach

– villi• 1 Millimeter tall• Core is lamina propria

of mucosal layer• Contains vascular

capillaries and lacteals (lymphatic capillaries)

– microvilli• Found on the apical

surface of absorptive cells

• Gives the villus the appearance of a brush border

Small intestine - Mucosa

• Absorptive cells-project their microvilli into the

lumen of the SI-absorb amino acids and

saccharides from food• Epithelial cells at the bottom

of the villus form a gland = Intestinal gland – production of intestinal juice or brush-border enzymes

• Goblet cells – mucus production

• Enteroendocrine cells– Found within the intestinal

glands – Secrete three hormones– secretin– cholecystokinin– gastric inhibitory peptide

• Paneth cells– secretes lysozyme– kills bacteria• Submucosal layer has duodenal glands

secretes alkaline mucus

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Anatomy of Large Intestine

• 5 feet long by 2½ inches in diameter• Ascending & descending colon are retroperitoneal (not in the peritoneal cavity)• Cecum & appendix

• Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx• Anal canal = last 1 inch of GI tract

– internal sphincter----smooth muscle & involuntary – external sphincter----skeletal muscle & voluntary control

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Histology of Large Intestine

• Muscular layer– internal circular layer is normal

– outer longitudinal muscle can be seen from the outside

• taeniae coli = shorter bands

• Permanent contractions of these bands puckers the LI into pouches called haustra (also called diverticula)

• epiploic appendages

• Serosa = visceral peritoneum

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Histology of Large Intestine

• Mucosa– smooth tube -----no villi – intestinal glands found in the mucosa

– simple columnar cells absorb water & goblet cells secrete mucus

• Submucosal & mucosa contain lymphatic nodules

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Defecation

• Reflex moves feces into rectum

• Stretch receptors signal to the sacral spinal cord

• Parasympathetic nerves contract muscles of rectum & relax internal anal sphincter

• External sphincter is voluntarily controlled

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Anatomy of the Pancreas

• 5" long by 1" thick• Head close to curve in

C-shaped duodenum• pancreatic duct joins

common bile duct from liver

• Opens 4" below pyloric sphincter

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Pancreatic Juice

• 1 + 1/2 Quarts/day at pH of 7.1 to 8.2

• Contains water, enzymes & sodium bicarbonate

• Digestive enzymes:– pancreatic amylase, pancreatic lipase, proteases

(protein degradation)– Ribonuclease & deoxyribonuclease - digest nucleic

acids

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– trypsinogen---activated by enterokinase (a brush border enzyme)

– chymotrypsinogen----activated by trypsin

– procarboxypeptidase-activated by trypsin

– proelastase---activated by trypsin

Trypsinogen TrypsinEnterokinase (intestines)

Chymotrypsinogen ChymotrypsinTrypsin

Proelastase ElastaseTrypsin

Procarboxypeptidase CarboxypeptidaseTrypsin

The 4 Proteases

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Anatomy of the Liver and Gallbladder

• Liver– weighs 3 lbs.

– below diaphragm

– right lobe larger

– gallbladder on right lobe

– size causes right kidney to be lower than left

• Gallbladder– fundus, body & neck

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Gallbladder

Common Bile Duct

PancreaticDuct

Right & LeftHepatic Ducts

Cystic Duct Ampulla of Vater

CommonHepaticDuct

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Blood Supply to the Liver• Hepatic portal vein

– nutrient rich blood from stomach, spleen & intestines

– splenic vein + superior mesenteric vein + inferior mesenteric vein

• Hepatic artery branches off the Common hepatic artery (from the celiac trunk)

SplenicVein

SuperiorMesentericVein

HepaticPortal Vein

CommonBileDuct

InferiorMesentericVein

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Histology of the Liver

• Hepatocytes arranged in lobules • Sinusoids in between hepatocytes

are blood-filled spaces • Kupffer cells phagocytize microbes

& foreign matter

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Gallbladder• Lined with simple columnar epithelium

• No submucosa

• Three layers of smooth muscle

• For the production of Bile• role in the absorption of fats

• Stimulated by the presence of fat in the duodenum

• Fat stimulates CCK production by SI which stimulates contraction of the gallbladder and the release of bile

Flow of Bile

• Bile capillaries

• Hepatic ducts connect to form common hepatic duct

• Cystic duct from gallbladder & common hepatic duct join to form common bile duct

• Common bile duct & pancreatic duct empty into duodenum

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Types of Digestion

• Mechanical – mouth, stomach, SI, LI

• Chemical – mouth, stomach, SI

Chemical Digestion in GI tract

Digestion of Carbohydrates

• Mouth---salivary amylase• Esophagus & stomach---nothing

happens• Duodenum----pancreatic

amylase• Brush border enzymes (maltase,

sucrase & lactase) act on disaccharides– these enzymes produce the

monosaccharides fructose, glucose & galactose

– lactose intolerance (no enzyme; bacteria ferment sugar)--gas & diarrhea

Digestion of Proteins

• Stomach

– HCl denatures or unfolds proteins

– pepsin turns proteins into peptides

• Pancreas

– Proteases --split peptides into smaller peptides and dipeptides

• Intestines

– brush border enzymes-----aminopeptidase or dipeptidase------split off amino acid at amino end of a peptide (aminopeptidase) or split dipeptides into individual amino acids (dipeptidase)

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Digestion of Lipids

• Mouth----lingual lipase

• Small intestine

– emulsification by bile

– pancreatic lipase---splits into fatty acids & monoglyceride

– no enzymes in brush border

Digestion of Nucleic Acids

• Pancreatic juice contains 2 nucleases– ribonuclease which digests RNA

– deoxyribonuclease which digests DNA

• Nucleotides produced are further digested by brush border enzymes (nucleosidease and phosphatase)– pentose, phosphate & nitrogenous bases

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Digestion in the Mouth• Mechanical digestion (mastication or chewing)

• breaks into pieces• mixes with saliva so it forms a bolus

• Chemical digestion– salivary amylase

• begins starch digestion at pH of 6.5 or 7.0 found in mouth• when bolus & enzyme hit the pH 2.5 gastric juices hydrolysis

ceases

– lingual lipase• secreted by glands in tongue – Ebner’s glands• begins breakdown of triglycerides into fatty acids and glycerol

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Stomach--Mechanical Digestion

• Gentle mixing waves – every 15 to 25 seconds– mixes bolus with 2 quarts/day of gastric juice to

turn it into chyme (a thin liquid)

• More vigorous waves – travel from body of stomach to pyloric region

• Intense waves near the pylorus – open it and squirt out 1-2 teaspoons full with

each wave

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Stomach--Chemical Digestion

• Protein digestion begins– HCl denatures (unfolds) protein molecules– HCl transforms pepsinogen into pepsin that breaks

peptides bonds between certain amino acids

• Fat digestion continues– gastric lipase splits the triglycerides in milk fat

• most effective at pH 5 to 6 (infant stomach)

• HCl kills microbes in food• Mucous cells protect stomach walls from being

digested with 1-3mm thick layer of mucous

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Absorption of Nutrients by the Stomach

• Water especially if it is cold• Electrolytes• Some drugs (especially aspirin) & alcohol• Fat content in the stomach slows the passage of alcohol to the

intestine where absorption is more rapid • Gastric mucosal cells contain alcohol dehydrogenase that converts

some alcohol to acetaldehyde-----more of this enzyme found in males than females

• Females have less total body fluid that same size male so end up with higher blood alcohol levels with same intake of alcohol

Mechanical Digestion in the Small Intestine

• 1. Weak peristalsis in comparison to the stomach---chyme remains in SI for 3 to 5 hours– starts at the lower portion of the

stomach and pushes the chyme forward– reaches the end of the ileum after 90 –

120 minutes– then another wave starts in the stomach

• 2. Segmentation---local mixing of chyme over the surface of the absorptive cells in the SI– does NOT push the food through the SI– moves chyme back and forth within a

segment of the SI– done in specific segments – most rapid in the duodenum and slows

at it reaches the ileum

- Mucosal layer forms Intestinal glands = Crypts of Lieberkuhn- Glands secretes intestinal juice or brush border enzymes

-sucrase, maltase, lactase, dextrinase – dissacharides

-aminopeptidase or dipeptidase – peptides-phosphatase - nucleic acids-enterokinase – trypsin activation

Small Intestine-Chemical Digestion

-duodenum is also the site for secretion of the Pancreatic juice:

-trypsin, chymotrypsin, elastase, carboxypeptidase-1-2 qt./day------ at pH 7.6-enzymes are made in the pancreas as inactive forms

eg. trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase

-trypsin synthesized as trypsinogen - converted to trypsin by the enzyme enterokinase (brush border enzyme)

-activated trypsin then converts others into their active forms

Small Intestine-Chemical Digestion

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Mechanical Digestion in Large Intestine

• Done by the smooth muscle • Peristaltic waves (3 to 12 contractions/minute)

– haustral churning----relaxed pouches are filled from below by muscular contractions (elevator)

– gastroilial reflex = when stomach is full, gastrin hormone relaxes ileocecal sphincter so small intestine will empty and make room

– gastrocolic reflex = when stomach fills, a strong peristaltic wave moves contents of transverse colon into rectum

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Chemical Digestion in Large Intestine• No human digestive enzymes are secreted by the LI• only mucous – by the Goblet cells in the intestinal glands• Chyme that leaves the SI is acted upon by the action of

bacteria (E.coli)• Bacteria actions:

– ferment undigested carbohydrates carbon dioxide & methane gas

– breakdown undigested proteins - simpler substances (indoles, skatoles, hydrogen sulfide)----odor

– turn bilirubin into simpler substances that produce color

• Bacteria produce vitamin K and B in colon

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Absorption & Feces Formation in the Large Intestine

• food has now been in the GI tract for 3 to 10 hours• solid or semisolid due to water reaborption = feces• feces – water, salts, sloughed-off epithelial cells, bacteria, products of bacterial

decomposition, unabsorbed and undigested materials• 90% of all water absorption takes place in the SI – 10% in the LI• but the LI is very important in maintaining water balance• also absorbs some electrolytes---Na+ and Cl- and vitamins• dietary fiber = indigestible plant carbohydrates (cellulose, lignin and pectin)• soluble fiber – dissolves in water (beans, barley, broccoli, prunes, apples and

citrus)– forms a gel that slows the passage of materials through the colon– also helps to lower blood cholesterol – binds to bile salts to prevent their

reabsorption– liver must make more cholesterol to make more bile salts – takes this cholesterol

from the blood• insoluble fiber – woody or structural parts of the plant (skins of fruits and

vegetables, coatings around bran and corn)– passes though the colon relatively unchanged

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Where will the absorbed nutrients go?

24-58

Absorption of Water

• 9 liters of fluid dumped into GI tract each day

• Small intestine reabsorbs 8 liters

• Large intestine reabsorbs 90% of that last liter

• Absorption is by osmosis through cell walls into vascular capillaries inside villi

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Liver Functions--Carbohydrate Metabolism

• Turn proteins into glucose

• Turn triglycerides into glucose

• Turn excess glucose into glycogen & store

in the liver

• Turn glycogen back into glucose as needed

Liver Functions --Lipid Metabolism

• Synthesize cholesterol

• Synthesize lipoproteins----HDL and LDL (used to transport fatty acids in bloodstream)

• Stores some fat

• Breaks down some fatty acids

Liver Functions--Protein Metabolism

• Deamination = removes NH2 (amine group) from amino acids

• Converts resulting toxic ammonia (NH3) into urea for excretion by the kidney

• Synthesizes plasma proteins utilized in the clotting mechanism and immune system

• Convert one amino acid into another

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Other Liver Functions

• Detoxifies the blood by removing or altering drugs & hormones (thyroid & estrogen)

• Releases bile salts help digestion by emulsification• Stores fat soluble vitamins-----A, B12, D, E, K• Stores iron and copper• Phagocytizes worn out blood cells & bacteria• Activates vitamin D (the skin can also do this with 1 hr

of sunlight a week)

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Gallbladder• Simple columnar epithelium

• No submucosa

• Three layers of smooth muscle

• Serosa or visceral peritoneum

Bile Production

• One quart of bile/day is secreted by the liver– yellow-green in color & pH 7.6 to 8.6

• Components– water & cholesterol

– bile salts = Na & K salts of bile acids

– bile pigments (bilirubin) from hemoglobin molecule

Flow of Bile

• Bile capillaries

• Hepatic ducts connect to form common hepatic duct

• Cystic duct from gallbladder & common hepatic duct join to form common bile duct

• Common bile duct & pancreatic duct empty into duodenum