Download Ch. 23 Digestion

Digestive System
Chapter 23
Two major parts
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Alimentary canal
GI tract- long hollow
canal from mouth to
anal canal; continuous
with outside of body
Oral cavity, pharynx,
esophagus, stomach,
small intestine, large
intestine, anal canal
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Accessory organs
Teeth, tongue, salivary
glands, liver, pancreas
Functions of Digestive System
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Mechanical and chemical breakdown of
food
absorption of nutrients
elimination of waste products
QUIZ PICTURE
Mechanical Breakdown of Food
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Physical preparation of food for breakdown
by enzymes
Includes chewing, mixing of food with
saliva, food churning in stomach,
segmentation of food in small intestine
Chemical Breakdown of Food
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Series of steps which breaks down large
food molecules with enzymes secreted into
the alimentary canal
Begins in the mouth and is completed in
the small intestine
Absorption of Nutrients
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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
Elimination of Waste
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Ridding the body of indigestible by products
of digestion
Upper esophageal
Lower esophageal
Oddi
Pyloric
Ileocecal
Internal anal
External anal
Fig. 22-9, pg: 691
Slide 11
Histology of GI Tract
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1.
2.
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4 Basic Layers
Mucosa
Submucosa
Muscularis Externa
Serosa
Quiz Picture
Mucosa
Functions:
1. Secretion of mucous, hormones, enzymes
2. Absorption of nutrients
3. Protection against infection
Simple columnar epithelium atop loose areolar
connective tissue and lymphatic tissue with a
base of smooth muscle that controls movement
of this layer
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Submucosa
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Dense CT layer with blood and lymph
vessels, lymph follicles, nerve fibers
Muscularis Externa
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Layer responsible for segmentation and
peristalsis
Inner circular and outer longitudinal layers
of smooth muscle; thickened areas can
form sphincters that act as valves
Serosa
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This is also the visceral peritoneum; formed
of areolar CT and covered by simple
squamous epithelium
The esophagus doesn’t have a serosa
because it is in the thorax; it has an
adventitia (fibrous CT) that connects it to
surrounding structures in chest
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
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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
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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
Small Intestine
1. Duodenum- 10 inches; receives bile from
the bile duct and pancreatic juice from the
pancreatic duct; 2 ducts join together and
secretion regulated by sphincter of Oddi
Small Intestine (con’t)
2. Jejunum- about 8 feet long
3. Ilium- about 12 feet long; joins the large
intestine at the ileocecal valve
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
Modifications for Absorption
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Plicae Circularis- deep permanent folds of
mucosa/submucosa
Villi- fingerlike projections of mucosa; act like the loops
of terry cloth to increase absorptive surface area;
contains the lacteals of the lymph system for fat
absorption
Microvilli- fingerlike projections of plasma membrane of
each individual cell of the simple columnar epithelium
containing brush border enzymes
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
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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
Subdivisions of Large Intestine
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Cecum
Appendix
Colon
Rectum
Anal Canal
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)
Nutrition
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Process by which an organism obtains
substances to promote growth,
maintenance and repair
Major Nutrients
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Carbohydrates
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Lipids
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Proteins
Vitamins
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Most used as coenzymes to accomplish
some particular task
Minerals
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Seven required in large amounts: calcium,
phosphorus, potassium, sulfur, sodium,
chlorine, magnesium
Trace amounts of several others: F, Co, Cr,
Cu, I, Fe, Mn, Se, Zn
Function: added to other molecules for
strength and better function eg. Fe in
hemoglobin
Adipose Tissue Metabolism
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Stored fat in adipose tissue
Most calories per gram compared to CHO
and proteins
Body will metabolize fat if glucose is not
available
Energy Balance
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Energy Intake = Energy Output
If we consume more calories than we need
to perform essential functions we store the
excess as adipose
If we consume fewer calories than we need
to perform essential functions we lose
adipose fat stores and can starve