Digestive System
Chapter 23
QUIZ PICTURE
Absorption of Nutrients

The passage of digested molecules of food,
water, minerals, and vitamins from the
lumen of the GI tract into the mucosal cells
by active or passive transport into blood
or lymph
Upper esophageal
Tonic contractions are shown by
sphincters; most are smooth muscle,
some are skeletal.
Lower esophageal
Oddi
Pyloric
Ileocecal
Internal anal
External anal
Fig. 22-9, pg: 691
Slide 11
Quiz Picture
Homeostatic Imbalance
Peritonitis
 Inflammation of peritoneum
 Puncture wound of abdomen
Salivary Glands
Parotid Glands- located anterior to ear
 Sublingual Glands- located in floor of mouth
 Submandibular Glands- located under jaw
 Function: produce saliva- mostly water, salivary
amylase, antimicrobials
Saliva moistens food, starts starch breakdown,
dissolves food chemicals for taste

Homeostatic Imbalance
Mumps
 Inflammation of parotid gland
 Passed by saliva
 In males can lead to testes infection
Homeostatic Imbalance
Halitosis
 Inhibited saliva production
 No saliva=no washing of mouth
 Cavities, anaerobic bacteria make hydrgen
sulfide, methyl mercaptan and cadaverine
which smell like rotten eggs, feces and
corpes
Mouth, Pharynx, Esophagus
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Mouth- place where mechanical breakdown of
food begins with chewing
Pharynx- has 2 skeletal muscle layers whose
contractions propel food into esophagus
Esophagus- long tube to stomach posterior to
trachea; conduit for food; peristalsis (alternate
waves of contraction/relaxation of muscle that
propels food to stomach)
Swallowing uses contraction of tongue, upper pharynx constrictors, and
laryngeal muscles.
Is voluntarily initiated, but medullary swallowing center coordinates muscles.
Fig. 22-10, pg: 692
Slide 29
Stomach
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Chemical breakdown of proteins begins
here
food becomes chyme
upper end to esophagus is cardiac portion;
fundus is top
middle is body and end is pylorus
Quiz Picture
Stomach Histology
Epithelium- simple columnar
1.
Gastric pits- primarily goblet cells
2.
Gastric glands- below gastric pits
Neck Cells- produce acidic mucous
Parietal Cells- secrete HCl and Intrinsic Factor
Chief Cells- produce pepsinogen to digest protein
Enteroendocrine Cells- release hormones; gastrin,
histamine, endorphins, serotonin, cholecystekinin,
somatostatin
Stomach Mucosal Barrier
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Bicarbonate rich mucous on stomach wall
Epithelial cells connected by tight junctions
Gastric Gland cells impermeable to HCl
Damaged epithelial cells replaced quickly;
lining shed every 3-6 days
Functions of Stomach

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Protein digestion- only enzymatic type that
occurs here
Secretion of IF- essential for intestinal
absorption of B12; B12 deficiency causes
Pernicious Anemia
Control of Gastric Secretion
Neural Control- CN X (Vagus)- stimulation
causes increase of all gland secretion
 Gut Brain local reflexes
Hormonal Control- Gastrin- stimulates
secretion of enzymes and HCl and
hormones of small intestine

Homeostatic Imbalances
Gastroesophageal reflux disease (GERD)
 Heartburn
 Stomach acid travels back up esophagus
 Hiatal hernia
 Damage to esophagus if prolonged
Homeostatic Imbalances
Gastric Ulcers
 Erosion of stomach wall
 Breach mucosal barrier
 Stress, medicines, bacteria (helicobacter
pylori
Small Intestine
Three Sections
1. Duodenum
2. Jejunem
3. Ilium
Peritoneum

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Serous membrane- double membrane
Mesentery is a sheet of 2 serous
membranes fused back to back; holds part
of the GI tract together; extends from body
wall to digestive organs; provides route for
blood/lymphatic vessels and nerves
Quiz Picture
Quiz Picture
Sm Int
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2) villi
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fingerlike
projections on
mucosa
Surface cells
for absorption
Contains
capillary bed
and lacteal
(lymph
capillary)
Made of cells

3) microvilli
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tiny plasma
membrane
projections of
absorptive cells of
mucosa
Fuzzy appearance
called brush
border
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Brush border
enzymes located
here
On a single cell
Histology of Small Intestine

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Epithelium- simple columnar with goblet cells;
enteroendocrine cells that secrete intestinal
Gastrin, Secretin, Cholecystikinin (CCK), GIP,
VIP
Intestinal Pits located above intestinal glands that
are called Crypts of Leiberkuhn- secrete
intestinal juice, lysozyme
Brunner’s Glands- duodenum only; alkaline
mucous
Liver
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Digestive function- produce bile for
transport to small intestine
Other functions include storage of Vit. A, D,
E, and K and production of proteins
including albumin, clotting factors and
production of cholesterol
Gross anatomy of Liver
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About 3 pounds
Divided into right and left lobes
Bile produced in the liver leaves through
the common hepatic duct which joins the
Cystic Duct of the gall bladder to form the
Common Bile Duct
Under R costal margin from 5th to 10th rib
Histology of Liver

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Functional Unit- Liver Lobule consisting of
hepatocytes (liver cells) and vessels; hexagonal
with each corner being a portal triad (artery, vein,
bile duct); center is the central vein
Sinusoids- leaky capillaries between liver cells;
also Kupffer cells (macrophages
Bile Canaliculi- canals between liver cells that
take bile to bile ducts
Homeostatic Imbalances
Cirrhosis
 Chronic inflammation of the liver
 Obstructed blood flow through liver, portal
hypertension
 Chronic alcoholism or hepatitis
Bile
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Bile Salts- cholesterol derivatives; emulsify
fats
Phospholipids
Fats
Electrolytes
Bile Pigments
Gall Bladder

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Green muscular sac; about 4 inches long;
stores bile until needed during digestion
Major Stimulus for releaseCholecystekinin (CCK)
Pancreas
Retroperitoneal organ under stomach
 Endocrine and exocrine functions
 Digestive function is exocrine in nature;
secretes pancreatic juice containing water,
bicarbonate ions and enzymes
 Neural and hormonal control
Secretin- release bicarb; CCK- release
enzymes – pancreatic juice - on list
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Large Intestine

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About 4-5 feet long
Function: absorb water from undigested
food products and deliver waste to be
eliminated
Gross Anatomy
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Teniae Coli- Longitudinal muscle of
muscularis is tightened up to form a line
through the outside of the LI
Haustra- pocket-like sacs formed due to
tone of teniae
Epiploic Appendages- fat filled pouches of
visceral peritoneum on surface
Quiz Picture
Microscopic Anatomy
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Simple columnar Epithelium up to anal
canal which is stratified squamous
epithelium
Deep crypts containing an enormous
number of goblet cells; no digestive
enzymes
Homeostatic Imbalances
Appendicitis
 Infection of appendix
 Blocked by feces, swells and cut of venous
flow so appendix dies
 adolescence
Homeostatic Imbalances
Diarrhea/Constipation
 Watery stools/Hard stools
 Food rushed through large intestine
 Irritation of colon
 Bad diet
Chemical Digestion/Absorption
Chemical Digestion/Absorption
Carbohydrates
 broken down into sugars
 Starts with salivary amylase in mouth and
progresses to pancreatic amylase in small
intestine and brush border enzymes in the
microvilli
Chemical Digestion/Absorption
Proteins
 starts in stomach when pepsinogen is
converted to pepsin by HCl environment of
stomach
 Brush border enzymes and pancreatic
enzymes (Trypsin/Chymotrypsin) digest
proteins all the way to amino acids
Chemical Digestion/Absorption
Nucleic Acids
 broken down by pancreatic nucleases and
by brush border enzymes in the small
intestine
Chemical Digestion/Absorption
Lipids
 Small intestine is the only place that this
occurs
 needs to be emulsified by bile into fat
droplets
 some lipases secreted by pancreas
 as emulsifications get smaller they become
micelles
Chemical Digestion/Absorption
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Vitamins- A, D, E, and K are fat soluble and
follow the absorption of fat; water soluble
vitamins are absorbed by diffusion; B12
can only be absorbed if attached to IF;
absorbed by endocytosis
Electrolytes- absorbed by active and
passive transport along entire small
intestine
Chemical Digestion/Absorption
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Water- directly coupled to solute intake;
water chases particles and is absorbed by
osmosis along the intestines
Carbohydrates- facilitated diffusion and
secondary active transport
Proteins- coupled to the active transport of
sodium ion
Lipids- micelles by simple diffusion (into
Lymph)