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Digestive Systems
Digestive Systems Overviews
Objectives
•Describe the structures and functions of
the digestive system of ruminant animals
•Draw the structures of the digestive
system of ruminant animals
•Label the structures of the digestive
system of ruminant animals
Digestion
• Digestion: Breaking down large, nutrient
macromolecules into simpler molecules for use by
an organism.
• Food enters the mouth and goes through
mechanical and chemical changes as it passes
through the alimentary canal.
Types of Stomachs
• Simple Stomach
– Man, Pig
• Complex Stomach
– Cattle, Sheep, Goats
• Simple Stomach with enlarged ceacum
– Horses, Rabbits, Guinea Pigs
Parts of Digestive Tract
• Mouth: initial opening of alimentary canal
– Salivary Glands
• secrete juices that contain enzymes to help break up
the food
– Mastication
• chewing, crushing, preparing food for swallowing
Parts of Digestive Tract
• Pharynx: funnel shaped muscle between
mouth and esophagus
– part of digestive and respiratory tracts
• Esophagus: muscular tube connecting
pharnyx to stomach
– muscle contractions move food down to
stomach
Parts of Digestive Tract
• Stomach: located between esophagus and
small intestine
– Two basics types
• Simple
• Ruminant
Parts of Digestive Tract
Simple Stomach
• Humans, swine, rabbits and horses
– Divided into three regions
• cardiac
• fundus
• pylorus
Simple Stomach
• Digestion:
– is mechanical, muscle contractions
– is chemical, enzymes soften and break down
macromolecules of food
• enzymes are catalysts, they start the chemical
reactions
Simple Stomach
• Enzymes that break down food
– Gastric-break down proteins in stomach
– Liver and pancreatic-break down fats in small
intestine
– Intestinal-break down carbohydrates and
proteins in small intestine
Parts of Digestion Tract
Ruminant Stomach
• Sheep, Cows and Goats
• Occupies 3/4 of the abdominal cavity
Four Components of Ruminant
Stomach
• Rumen
– composes 80% of ruminant stomach in mature
bovine animals and 30% in young animals
• Reticulum
– composes about 5% of bovine stomach
– prevents indigestible objects from entering the
stomach
Four Components of Ruminant
Stomach
• Omasum
– composes 7-8% of bovine stomach
– absorbs mostly water
• Abomasum
– the “true” stomach
– composes 7-8% of stomach in mature animals
and 70% in young animals
Digestion in the Ruminant
Stomach
• Rumination: The process of regurgitation,
re-mastication, re-salivation and reswallowing of food.
• Purpose: To smash and break up food which
provides more surface area bacteria to break
down
Parts of Digestive Tract
• Small Intestine: long, coiled tube
connecting the stomach with the large
intestine.
– Is covered by villi which increases surface area
to increase absorption
– Food moves through by muscle contractions
called peristaltic movement
– Final breakdown and absorption of nutrients
occurs here
Parts of the Digestive Tract
• Large Intestine
– Includes cecum, colon and rectum
– Absorbs water
– Very little nutrient absorption takes place here
Parts of the Digestive Tract
Accessory Organs
• Pancreas
– secretes enzymes which breakdown fat and
starches
• Liver
– secrets bile which digest fats
The Digestion Process
The Digestion Process
• Food is broken down
• Animals have digestive systems adapted to
the foods that they consume
• Four types of digestive systems
–
–
–
–
Ruminant(polygstric)
Simple Stomach(monogastric)
Avian
Equine-modified simple stomach
Ruminant Digestive System
Modified to handle the breakdown of
large amounts of fiber
Ruminant Digestive System
• Mouth
– no upper incisors, hard palate
– molars for grinding coarse vegetation
– saliva does not contain enzymes
• Esophagus
– muscular tube connecting the mouth to the
stomach
Ruminant Digestive Systems
•
•
•
•
The Four Compartmented Stomach
Rumen: storage area and fermentation vat
Reticulum: nails and wire may be found
here-hardware stomach
Omasum: eliminates excess water from feed
Abomasum: true stomach, gastric juices
and enzymes are secreted
Ruminant Digestive Systems
Stomach (cont.)
• Regurgitation: first step in rumination
– large quantities of roughage are consumed and
are chewed just enough to swallow
– after swallowing, regurgitation (“cud chewing”)
takes place, food is re-chewed
Ruminant Digestive System
• Small Intestine
–
–
–
–
connects stomach to large intestine
food nutrients absorbed into blood
contains bile and pancreatic juices
pushes food through by muscle contractions
Ruminant Digestive System
• Large Intestine
– Contains Cecum, Colon and Rectum
• Cecum: sac at junction of small intestine and large
intestine
• Colon and rectum: at end of system
– not as long as small intestine, but larger in
diameter
– water and some nutrient absorption occurs here
– where residue solidifies before excretion
Monogastric Digestive System
Characterized by inability to digest
roughage efficiently
Objectives
• Describe the structures and functions of the
digestive system of non-ruminant animas
• Draw the structures of the digestive system
of non-ruminant animals
• Label the structure of the digestive system
of non-ruminant animals
Monogastric Digestive System
• Mouth
– has upper and lower incisors
– digestive enzymes secreted which breaks down
nutrients
• Esophagus
– connects mouth to stomach
Monogastric Digestive System
• Stomach
– secretes Hydrochloric Acid to break down
nutrients
– enzymes such as pepsin also secreted here
– churning action mixes food
– small and large intestine
• function just as in ruminant systems
Avian Digestive Systems
Characterized by several organs not
found in other species that are
adapted for grinding hard or encased
food
Avian Digestive Systems
• Mouth
– no teeth which leads to the saying “scarce as a
hen’s teeth!!”
– Salivation excretion moistens food
• Esophagus
– has a modification called the “crop” which
stores and moistens food
– connects mouth and stomach
Avian Digestive Systems
• Stomach
– Contains two parts
• Proventriculus: same as monogastric stomach and
provides digestive excretions
• Gizzard: located after proventriculus, very muscular,
used to grind food
Avian Digestive Systems
• Small Intestine
– similar functions as in ruminants and
monogastric systems
• Large Intestine
– similar functions as in ruminants and
monogastric systems
– “cloaca”: chamber into which urinary and
genital canals open
– “ceca”: aids in fiber digestion and absorption
Equine Digestive Systems
Characterized by non-ruminant
animals that consume and digest
feeds high in fiber
Equine Digestive Systems
• Mouth
– intact top and bottom incisors
– molars adapted to chewing fibrous feeds
– no digestive enzymes in saliva
• Esophagus
– not well adapted for regurgitation
– connects mouth and stomach
Equine Digestive System
• Stomach
– similar to monogastric system
• Small intestine
– similar to monogastric and ruminant systems
– no gall bladder to store bile
– enlarged cecum to aid in fiber breakdown
Equine Digestive System
• Large Intestine
– similar to monogastric systems
– cecum (at junction of small and large intestines)
and colon take up most of the volume of the
equine digestive system
Accessory Organs
Organs that aid in the digestive
process without actually being part of
the digestive system
Accessory Organs
• Pancreas
– produces and secretes digestive enzymes
– produces insulin which regulates carbohydrate
metabolism
• Liver
– produces bile-breaks down fatty acids
– stores iron, handles fats and carbohydrates in
the blood
The End!!