Transcript Liver

The Digestive System
Chapter 48
Mechanical Breakdown of Food
Heterotrophs are divided into three groups based on their
food sources
-Herbivores are animals that eat plants exclusively
-Carnivores are animals that eat other animals
-Omnivores are animals that eat both plants and other
animals
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Herbivore
Carnivore
Omnivore
Horse
Lion
Human
Incisors
Canines
Premolars
Molars
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“Simple” Digestive Strategies
Food
Hydra (a Cnidarian)
Mouth
Wastes
Tentacle
Body stalk
Gastrovascular
cavity
-Single-celled organisms as well as sponges
digest their food intracellularly
-Other multicellular animals digest their food
extracellularly, within a digestive cavity
-Cnidarians and flatworms, have a gastrovascular
cavity...has only one opening, and no specialized
regions
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Specialization in Digestive
Systems
-Specialization occurs when the digestive tract has a
separate mouth and anus
-Nematodes have the most primitive digestive tract
...tubular gut lined by an epithelial membrane
-More complex animals have a digestive tract specialized in
different regions
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Specialization in Digestive Systems
*Mouth and pharynx = Entry
*Esophagus = Delivers food to
stomach
*Stomach = Preliminary
digestion
*Small intestine = Absorption
*Large intestine = Concentration
of wastes
*Cloaca or rectum = Waste
storage
*Liver=Produces bile
*Gallbladder=Stores and
concentrates bile
*Pancreas=produces pancreatic
juice and bicarbonate buffer
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Four GENERAL Layers
of
Gastrointestinal
Tract
Gland outside gastrointestinal tract
Blood vessel
Lumen
Mucosa
Epithelium that lines the lumen
Submucosa
Connective tissue
Gland in submucosa
Submucosal plexus
Muscularis
Circular layer
Smooth muscles
Longitudinal layer
Serosa
Epithelial
tissue layer
Covers the external surface of the tract
Nerve
Myenteric
plexus
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Initial Digestion & Swallowing
-In the mouth, saliva contains salivary amylase,
which initiates the breakdown of starch
-Tongue moves food to the back of the mouth
-Soft palate seals off nasal cavity
-Elevation of the larynx (voice box) pushes the glottis
against the epiglottis
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-Keeps food out of respiratory tract
Swallowing
*The esophagus is a muscular tube to the stomach
*It actively moves a processed lump of food, called a bolus,
through muscular action
*Swallowing center in brain stimulates successive waves of
contraction
*Peristalsis moves the food down to the stomach
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Peristalic
movement
Esophagus
Relaxation
Contraction
Food Bolus
Relaxation
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The Stomach
*The stomach has convoluted surface for expansion
*Contains an extra layer of smooth muscles for mixing food with
gastric juice...gastric juice + food = chyme
*Has two kinds of secretory cells
-Parietal cells – Secrete HCl lowers pH for protein digestion. Also
secretes intrinsic factor (for vita. B12 absorption)
-Chief cells – Secrete pepsinogen, the inactive form of pepsin
*In Stomach, No significant digestion of carbohydrates or fats occurs
Chyme exits through
the pyloric sphincter
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The
Small
Intestine
*The small intestine is primary site for carbs and fat digestion,
and absorption into the blood stream
-Consists of duodenum, jejunum and ileum
*Epithelial wall is covered with villi, which in turn are covered by
microvilli...greatly increase surface area
*Microvilli also participate in digestion
-Many adults lack the enzyme lactase...are lactose intolerant
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The Pancreas & the Duodenum
-Langerhans islet cells secrete pancreatic fluid into the duodenu
through the pancreatic duct
-Host of enzymes: trypsin, chymotrypsin, pancreatic amylase,
and lipase
Digest proteins into smaller
polypeptides, polysaccharides
Pancreatic islet
into shorter sugars, and fats
(of Langerhans)
into free fatty acids &
 cell
monoglycerides
From liver  cell
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Common
bile duct
Pancreas
Gallbladder
Pancreatic
duct
Duodenum
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The Liver & The Duodenum
-The liver is the body’s largest internal organ
-It secretes bile into the duodenum during digestion of a
meal...bile consists of bile pigments (waste products)
and bile salts (for emulsification of fats)
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Pancreatic islet
(of Langerhans)
From liver
 cell
 cell
Common
bile duct
Pancreas
Gallbladder
Pancreatic
duct
Duodenum
-Gallbladder Stores
and concentrates bile
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Absorption
*Blood carries amino acids and monosaccharides to the liver
via the hepatic portal vein
*Fatty acids and monoglycerides, diffuse into epithelial cells,
they are assembled into triglycerides & then chylomicrons,
and then, enter the lymphatic system and then, they join the
circulatory system
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Remember the Hepatic portal vein
leads into the Liver...and then
The Liver:
-Chemically modifies the substances
absorbed from the digestive tract before
they reach the rest of the body
-Removes toxins, pesticides, &
carcinogens, converting them to less toxic
forms
-Regulates levels of steroid hormones
-Produces most proteins found in plasma
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Water Absorption in Small
Intestine
About 9 liters of fluid pass through
the small intestine per day
-Only about 50 g of solid and 100 mL
of liquid leave the body as feces
-The normal fluid absorption efficiency
of the human digestive tract is 99%
(via osmosis)
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The Large Intestine
Main function is waste material concentration
-Compacted feces are stored in the rectum,
until it can be eliminated through the anus
Most mammals have a rectum
-Most vertebrates have a common cavity,
the cloaca, where the urinary, reproductive,
and gastrointestinal tracts join
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Large intestine, or colon, is much shorter than
small intestine, but has larger diameter
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Small intestine empties directly
into the large intestine at a
junction were two vestigial
structures, cecum & appendix,
remain
Ascending portion
of large intestine
No digestion occurs
Only 4% absorption
Ileocecal valve
...water, remaining
Last portion of
electrolytes & vitamin K...
small intestine
vitamin K is made by intestinal
Cecum
bacteria in mammals and is
Appendix
involved in blood clotting
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Variations in Digestive Systems
The digestive tracts of
some animals contain
bacteria and protists
that convert cellulose
into substances the host
can absorb
Ruminants have a 4-chambered
stomach
-Rumen, reticulum, omasum, abomasum
-Rumen has cellulose-degrading microbes
-Contents can be regurgitated from the Rumen &
rechewed...called rumination
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Animals, such as horses, deer and rabbits, digest cellulose
in the cecum... such animals practice coprophagy...
eat their feces to
absorb nutrients
on the second
passage of food...
Food is past
the stomach so not
regurgitated
Protein diets are more
easily digested so have
shorter tract and few
specialized pouches.
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Digestive Tract & Hormones
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Stomach
Liver
pH
Proteins
Gastrin
(+)
(+)
( – ) Chief cells Parietal cells
GIP
Pepsin
(+)
HCl
Bile
Pancreas Enzymes
Bicarbonate
Gallbladder
(+)
Acinar
cells
(+)
CCK
Secretin
Duodenum
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Regulation of blood glucose
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Metabolism
Eating carbohydraterich meal
Fasting or
exercise
Increasing blood glucose
Decreasing blood glucose
Pancreatic Islets
Pancreatic Islets
Insulin secretion
Insulin secretion
Glucagon secretion
Glucagon secretion
Formation of
glycogen (in liver)
and fat (in adipose
tissue)
Breakdown of
glycogen (in liver)
and fat (in adipose
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tissue)
glycogenolysis
Hormones involved in the control
of feeding and energy
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Essential Nutrients
Essential nutrients...exist because animals
have lost the ability to manufacture some
nutrients but they are still necessary for
health and so must be obtained in the diet
-These include some of the:
-Vitamins
-Amino acids
-Long-chain unsaturated fatty acids
-Minerals
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