Download Powerpoint 23 Digestion

The Digestive System
A. Digestive processes
B. Organization
1. General histology of the GI tract
a. Mucosa
b. Submucosa
c. Muscularis
d. Serosa
2. Peritoneum
C. Mouth (oral cavity)
1. Tongue
2. Salivary glands
a. Composition of saliva
b. Secretion of saliva
3. Physiology of digestion in the mouth
a. Mechanical digestion
b. Chemical digestion
4. Physiology of deglutition
D. Esophagus
1. Histology
2. Physiology
E. Stomach
1. Anatomy and Histology
2. Physiology of digestion in the stomach
a. Mechanical digestion
b. Chemical digestion
3. Regulation of gastric secretion and motility
a. Cephalic phase
b. Gastric phase
c. Intestinal phase
4. Regulation of gastric emptying
5. Absorption
F. Pancreas
1. Anatomy and Histology
2. Pancreatic juice
3. Regulation of pancreatic secretions
G. Liver
1. Anatomy and Histology
2. Blood supply
3. Bile
4. Regulation of bile secretion
5. Physiology of the liver
H. Gallbladder
1. Histology
2. Physiology
I. Small intestine
1. Anatomy and Histology
2. Intestinal juice and brush border enzymes
3. Physiology of digestion in the small intestine
a. Mechanical digestion
b. Chemical digestion
4. Regulation of intestinal secretion and motility
5. Physiology of absorption
J. Large intestine
1. Anatomy and Histology
2. Physiology of digestion in the large intestine
a. Mechanical digestion
b. Chemical digestion
3. Absorption and feces formation
4. Physiology of defecation
Food is vital to life because
1. provides energy
2. provides building blocks
Why do we have a digestive system?
Five Basic Digestive Processes
1.
2.
3.
4.
5.
ingestion
movement of food (peristalsis)
digestion
absorption
defecation
Two Types of Digestion
1. mechanical
2. chemical
Digestive System Overview
Organization
1. gastrointestinal tract
mouth
pharynx
esophagus
stomach
small intestine
large intestine
2. accessory organs
Teeth
Tongue
Salivary glands
Liver
gallbladder
pancreas
General Histology
1. mucosa
a. epithelium
b. lamina propria
c. muscularis mucosae
2. submucosa
(submucosal plexus)
3. muscularis
a. inner circular
b. outer longitudinal
c. myenteric plexus
4. serosa
(visceral peritoneum)
Peritoneum
1.
2.
3.
4.
parietal vs visceral
peritoneal cavity
mesentery
mesocolon
Mouth (oral cavity)
1.
2.
3.
4.
5.
6.
7.
boundaries
hard palate vs soft palate
palatoglossal arches
palatopharyngeal arches
epithelium
vestibule
fauces
fauces
Tongue
1.
2.
3.
4.
5.
intrinsic muscles
extrinsic muscles
frenulum
bolus
hypoglossal nerve
Salivary Glands
1. buccal, lingual, labial
2. paired glands
a. parotid
b. submandibular
c. sublingual
Saliva is composed of 99.5% water, used to
dissolve foods, and 0.5% solutes, including:
1.
2.
3.
4.
salivary amylase
ions (Na, K, Cl, HCO3, HPO4)
mucous
lysozyme
Salivation is controlled by the
parasympathetic nervous system
(cranial nerves VII and IX).
Three types of stimuli may initiate
salivation:
1. psychic
2. chemical
3. tactile
Physiology of Digestion in Mouth
1. mechanical = mastication
2. chemical
salivary amylase
starch -----------------------> maltose
(glu+glu)
Swallowing (Deglutition)
1. voluntary (buccal) stage
(cranial nerves V, VII, XII)
2. pharyngeal-stage
(deglutition reflex)
(cranial nerves IX, X, XI)
3. esophageal stage
Esophagus
1.
2.
3.
4.
5.
gross anatomy
esophageal hiatus
mucosa
muscularis
sphincters
a. upper
b. lower (gastroesophageal)
lumen
stratified
squamous
epithelium
mucosa
submucosa
IC
muscularis externa
OL
adventitia
Stomach Anatomy
1.
2.
3.
4.
5.
location
divisions
pyloric sphincter
curvatures
rugae
Stomach Histology
1. simple columnar epithelium
2. gastric glands
a. chief cells
(pepsinogen, gastric lipase)
b. parietal cells
(HCl, intrinsic factor)
c. mucous neck cells (mucous)
d. G cells (gastrin)
3. muscularis
inner oblique fibers
outer longitudinal
fibers
middle circular fibers
serosa has been
removed
Mechanical Digestion in the
Stomach
1. regular gentle peristaltic waves
2. mixing waves producing chyme
Chemical Digestion in the Stomach
1. pepsinogen
HCl
pepsin (pH 1 - 3)
proteins
2. gastric lipase
3. rennin (infant only)
peptides
Mode of Hydrochloric Acid
Secretion
Pepsid AC
Zantac
Three Phases of Stomach Control
Cephalic Phase
Gastric Phase
Intestinal Phase
Stomach Regulation-First Phase
1. cephalic phase
a. psychic stimuli
b. vagus nerve
c. increased motility and secretion
Stomach Regulation-Cephalic Phase
Cephalic phase
PSYCHIC STIMULI
thought and anticipation of food
sight, taste, smell of food
sound of food preparation
parasympathetic output via the vagus nerve (X)
stimulation of stomach’s enteric nervous system
increased gastric secretion + increased gastric motility
Stomach Regulation-Second Phase
2. gastric phase
a. stretch receptors and
chemoreceptors
b. local parasympathetic response
c. gastrin
Stomach Regulation-Gastric Phase
food enters the stomach
increased stretch of stomach wall
increased pH stimulates chemoreceptors
input to brainstem
direct stimulation of stomach’s
enteric nervous system
parasympathetic output via
the vagus nerve (X)
increased gastrin secretion
increased gastric secretion + increased gastric motility
Positive Feedback Control of
Gastric Secretion
Negative Feedback of the Gastric Phase
CONTROLLED CONDITION
Food entering stomach disrupts
homeostasis by causing an increase in
gastric juice pH AND stretch (distention) of
stomach wall
RETURN TO HOMEOSTASIS
RECEPTOR
In response, there is increased acidity in
stomach chyme and the mixing waves
begin emptying the stomach. An empty
stomach is a return to homeostasis.
Chemoreceptors and stretch receptors
increased pH and stretch of stomach wall,
and generate nerve impulses that pass to
the control centers
EFFECTORS
CONTROL CENTER
Enteric nervous system and medullary
neurons generate parasympathetic
impulses that pass to the effectors
Parietal cells of the gastric mucosa
secrete HCl and the muscularis contracts
more vigorously (increased frequency and
strength of mixing waves)
Stomach Regulation-Third Phase
3. intestinal phase
a. stretch receptors and
chemoreceptors
b. enterogastric reflex
c. hormones
(1) gastrin (+)
(2) cholecystokinin (CCK) (-)
(3) secretin (-)
(4) gastric inhibitory peptide
(GIP) (-)
Stomach Regulation-Intestinal Phase
chyme enters the duodenum
increased stretch of duodenal wall
increased enteric endocrine cell activity
enterogastric
reflex
direct stimulation of
duodenum’s enteric
nervous system
secretion of
cholecystokinin
secretin
input to brainstem
enteric gastrin
decreased parasympathetic
output from the vagus nerve (X)
to stomach
increased sympathetic
output to stomach
inhibits
inhibits
inhibits
decreased stomach activity
increased stomach activity
NET EFFECT
gastric inhibition
Gastric Emptying
STIMULATION OF GASTRIC EMPTYING
INHIBITION OF GASTRIC EMPTYING
distention of stomach
partially digested proteins
alcohol
caffeine
distention of duodenum
increased gastrin secretion
increased vagal activity
enterogastric reflex
partially digested
proteins, fatty acids,
glucose in duodenum
secretion of cholecystokinin
and secretin
contraction of gastroesophageal sphincter
relaxation of pyloric sphincter
increased rate of mixing waves
increased gastric secretion
contraction of pyloric sphincter
decreased rate of mixing waves
decreased gastric secretion
increased rate of emptying
decreased rate of emptying
Stomach Absorption
Accomplishments of digestion to this point in the GI tract
starch  maltose by salivary amylase (action stops in stomach)
proteins  partially digested proteins (action of pepsin)
lipids  partially digested fats (action of lingual and gastric lipase)
creation of chyme from food, drink, saliva, and gastric juice
Stomach Absorption
1.
2.
3.
4.
water
electrolytes
certain drugs (aspirin)
alcohol
Accessory Organs of Digestion
Pancreas
Liver
Gallbladder
Pancreas
1.
2.
3.
4.
5.
6.
gross anatomy
main pancreatic duct
hepatopancreatic ampulla
accessory pancreatic duct
99% exocrine
1% endocrine
Pancreatic Juice
1.
2.
3.
4.
5.
sodium bicarbonate (NaHCO3)
pancreatic amylase
pancreatic lipase and cholesterol esterase
nucleases -- DNAse and RNAse
protein-digesting enzymes
a. trypsinogen (inactive)
b. chymotrypsinogen (inactive)
c. procarboxypeptidase (inactive)
Pancreatic Regulation-Neural
Control and Endocrine Control
1. vagus nerve
2. CCK = enzymes
3. secretin = NaHCO3
Pancreatic Regulation
NEURAL CONTROL
psychic stimuli
stretch of stomach
increased parasympathetic
impulses via vagus nerve
increased pancreatic secretion
ENDOCRINE CONTROL
acid chyme in duodenum
enteroendocrine cells stimulated
increased secretin
increased cholecystokinin
increased secretion
of bicarbonate ions
increased secretion
of enzymes
Liver Anatomy
1.
2.
3.
4.
5.
6.
location
lobes
falciform ligament
bile
bile canaliculi
ducts
Liver Histology
1.
2.
3.
4.
5.
6.
7.
lobule
hepatocytes
central vein
sinusoids
flow of bile
blood flow
portal triad
Bile
1. is a detergent
2. emulsification of fats
Produced continuously at slow rate
Secretion increased in response to:
vagus nerve – psychic and gastric phases
secretin – from the duodenum during
intestinal phase
Physiology of the Liver
1. carbohydrate metabolism
a. glycogenesis
b. glycogenolysis
c. gluconeogenesis
2. lipid metabolism
3. protein metabolism
a. deamination (-NH2)
b. urea formation
c. plasma protein production
4. detoxification
5. synthesis and
excretion of bile
6. storage
7. phagocytosis of
RBCs
8. activation of vitamin D
Gallbladder
1.
2.
3.
4.
5.
6.
anatomy
rugae
cystic duct
stores/concentrates bile
sphincter of Oddi
CCK
Biliary Tract
common hepatic duct +
cystic duct =
common bile duct +
main pancreatic duct =
ampulla of Vater
sphincter of Oddi
Regulation of Bile Secretion
REGULATION OF BILE
SECRETION
acid chyme in
duodenum
enteroendocrine cells
stimulated
cholecystokinin
secretion
gallbladder
contraction
relaxation of
sphincter of Oddi
release of bile into
duodenum
Small Intestine Anatomy
1. 21 ft. x 1 in.
2. duodenum (10 in.)
-- retroperitoneal
3. jejunum (8 ft.)
-- mesentery
4. ileum (12 ft.)
-- mesentery
5. ileocecal sphincter
Small Intestine Histology
1.
2.
3.
4.
5.
intestinal glands
plicae circulares
villi
microvilli
Peyer's patches
Intestinal Juice and Brush
Border Enzymes
Maltase
Lactase
Peptidases
Dextrinases
Nucleosidases
Phosphatases
Small Intestine-Mechanical
Digestion
1. segmentation
2. peristalsis
Review of Chemical Digestion of Carbohydrates
STARCH
mouth
SUCROSE
LACTOSE
SUCROSE
LACTOSE
salivary
amylase
stomach
small intestine
pancreatic
amylase
MALTOSE
brush border
maltase
brush border
sucrase
brush border
lactase
glucose + glucose
glucose + fructose
glucose + galactose
(absorbed into blood of villus)
(absorbed into blood of villus)
(absorbed into blood of villus)
Review the Chemical Digestion of Proteins
Review the Chemical Digestion of Lipids
Regulation of small intestinal
secretion and motility
1. local reflexes
2. parasympathetic reflexes
(vagus nerve)
3. gastrin
Regulation of the Small Intestine
GASTRIC PHASE
psychic stimuli
stretch of stomach
chemoreceptors in stomach
stretch of small intestine
gastroileal reflex
increased parasympathetic
impulses via vagus nerve
increased gastrin secretion
increased small intestinal
motility secretion
+
relaxation of ileocecal sphincter
increased enteric nervous
system activity
Small Intestine Absorption
1. monosaccharides
2. amino acids
hepatic portal blood 
liver  inferior vena cava 
general circulation
monosaccharides
amino acids
thoracic
duct
inferior
vena cava
lacteal
with
chylomicrons
hepatic
portal vein
superior
mesenteric vein
3. fats
triglycerides
chylomicrons
lymph  lacteals 
intestinal trunk  thoracic duct
 general circulation
4. water
blood
capillary
lymphatic vessel
Water absorption
GI tract fluids/24 hours
Ingested or secreted
into GI tract
saliva = 1 L
ingested liquids = 2L
gastric juice = 2 L
bile = 1L
pancreatic juice = 2 L
intestinal juice = 1L
total = 9 L
Absorbed into blood
small intestine =
8L
large intestine =
0.9 L
Excreted
in feces
0.1 L
Large Intestine Anatomy
1. 5 ft. x 2.5 in.
2. cecum with appendix
3. colon
a. ascending
b. transverse
c. descending
d. sigmoid
4. rectum
Large Intestine Anatomy Con’t
5. haustra
6. taenia coli
7. epiploic appendages
8. anal canal
9. anus
10. internal anal sphincter
11. external anal sphincter
Large Intestine Histology
no villi
lumen
1. no plicae circulares
2. no villi
3. goblet cells
goblet
cells
intestinal
gland
muscularis mucosae
submucosa
Mechanical Digestion in the
Large Intestine
1. haustral churning
2. mass peristalsis
(gastrocolic reflex)
3. peristalsis
Chemical digestion in the
large intestine
1. bacteria fermentation
2. bacteria secrete vitamin K and some
B complex vitamins
Large Intestine Absorption
1. simple molecules and vitamins
2. most remaining water (~900 ml/day)
Feces consists of:
1. water (about 100 ml/day)
2. undigested foodstuffs (plant fibers = cellulose)
3. bacteria
4. products of bacterial decomposition
5. sloughed epithelial cells
Defecation Reflex in the Adult
1. distention of the rectum
stimulates stretch receptors
2. sacral parasympathetic area output,
causing:
a. contraction of the descending colon,
sigmoid colon, and rectum; and
b. reflex relaxation of the
internal anal sphincter
3. voluntary relaxation of the
external anal sphincter
(in the infant, this is also reflexive)
4. expulsion of feces