Download Lecture 1

Cadaver dissection videos
• http://anatomy.med.umich.edu/courseinfo/vi
deo_index.html
– Gastrointestinal:
http://anatomy.med.umich.edu/gastrointestinal_
system/peritoneum_vid.html
24-1
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
24-2
Layers of the GI Tract
1. Mucosal layer
2. Submucosal
layer
3. Muscularis layer
4. Serosa layer
24-3
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
24-4
Submucosa
• Loose connective tissue
– containing BV, glands and lymphatic tissue
• Meissner’s plexus
– parasympathetic
– innervation
• vasoconstriction
• local movement by
muscularis mucosa
smooth muscle
24-5
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
24-6
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
24-7
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
24-8
The 4 Mesenteries
• 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
24-9
The path of food:
oral cavity/teeth/salivary glands
oropharynx/epiglottis
esophagus
stomach
small intestine: duodenum
small intestine: jejunum
small intestine: ileum
large intestine: ascending colon
large intestine: transverse colon
large intestine: descending colon
sigmoid colon
rectum
anus
24-10
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
24-11
– Shortened lingual frenulum can impede movement of the tongue within the mouth
Tubal tonsil
Nasopharynx
Geniohyoid
Oropharynx
Mylohyoid
Laryngopharynx
Larynx
Lingual tonsil
Epiglottis
Vocal cords
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
24-13
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
24-14
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
24-15
• Parotid gland
secretes the
enzyme Salivary
amylase
• Submucosa
layer of the tongue
secretes
Lingual lipase
Parotid
Sublingual
Submandibular
24-16
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
24-17
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
24-18
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
24-19
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
24-20
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
24-21
Thoracic
Aorta
Esophagus
Diaphragm
Liver
24-22
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
24-23
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
24-24
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
24-25
FUNDUS
BODY
PYLORIC REGION
PANCREAS
DUODENUM
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
24-27
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
24-28
Lesser
Omentum
Liver
Stomach
Gallbladder
Transverse
Colon
Ascending
Colon
Descending
Colon
Mesentery of
Small Intestine
Small
Intestine
24-29
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
24-30
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
• Submucosal layer has duodenal glands
secretes alkaline mucus
• 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
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
24-32
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
24-33
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
24-34
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
24-35
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
24-36
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
24-37
The 4 Proteases
Enterokinase (intestines)
– trypsinogen--Trypsinogen
Trypsin
activated by
enterokinase (a brush
border enzyme)
Trypsin
– chymotrypsinogen---- Chymotrypsinogen
Chymotrypsin
activated by trypsin
– procarboxypeptidaseactivated by trypsin
– proelastase--Trypsin
Proelastase
Elastase
activated by trypsin
Procarboxypeptidase
Trypsin
Carboxypeptidase
24-38
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
24-39
Right & Left
Hepatic Ducts
Common
Hepatic
Duct
Pancreatic
Duct
Gallbladder
Cystic Duct
Ampulla of Vater
Common Bile Duct
24-40
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)
Hepatic
Portal
Vein
Common
Bile
Duct
Splenic
Vein
Superior
Mesenteric
Vein
Inferior
Mesenteric
Vein
24-41
Histology of the Liver
• Hepatocytes arranged in lobules
• Sinusoids in between hepatocytes
are blood-filled spaces
• Kupffer cells phagocytize microbes
& foreign matter
24-42
•
•
•
•
Lined with simple columnar epithelium
No submucosa
Three layers of smooth muscle
For the production of Bile
•
Gallbladder
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
24-43
Types of Digestion
• Mechanical – mouth, stomach, SI, LI
• Chemical – mouth, stomach, SI
24-44
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)
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
24-46
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
24-47
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
24-48
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
24-49
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
24-50
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
Small Intestine-Chemical Digestion
- 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
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
24-54
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
24-55
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
24-56
Where will the absorbed nutrients go?
24-57
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
24-58
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
24-59
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)
24-60
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
24-61