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Digestive system
Body has a structural organization
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Body is an open system
Why?
Respiratory, digestive and excretory systems
allow for exchange with external environment
Circulatory system
in charge of transport within the body
Blood exchanges materials with each cell
via interstitial fluid
Since the body is an open system
it is sensitive
to changes in the surrounding environment
Body needs to maintain constant conditions inside
“Homeostasis”
What needs to be maintain constant?
•Concentration of oxygen and carbon dioxide
•Concentration of nutrients and waste products
•Temperature
•Water
Systems function together to maintain homeostasis
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Organ’s form fits Organ’s function
As product of natural selection
Structure of a body part (aka anatomy)
Corresponds
With the task it must perform (aka physiology)
What is the purpose of Food?
Source chemical energy
That can be extracted by cellular respiration
This process requires participation of
Digestive,
Respiratory and
Circulatory Systems
Source of building materials
Some need to be consumed already fabricated
 essential nutrients
8 amino acids
13 Vitamins
12 Minerals
Essential fatty acids
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Why does food need to be broken down?
Food processing occurs in four stages
Digestive system consists of an
alimentary canal and accessory glands
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Small intestine: example of form fits function
Function: Absorption of nutrients
Form:
Your small intestine is about 4 times your body length
Diameter, folds, villi, microvilli
Increase the surface area of absorption
Digestive Systems in Animals
No digestive system: Sponges why?
Gastrovascular cavity: Cnidarians and Flatworms
(absent in Tape worm)
One opening, two way movement of food
How is the gastrovascular cavity of flatworms
different from that of the cnidarians?
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Digestive Systems in Animals
Digestive tract: two openings, one way movement, advantage?
Pharynx: muscular pouch
For mechanical digestion
Esophagus
Crop: moistens and stores
food
Gizzard: churns food and
Usually has grit or gravel
Intestine:
Earthworm is crescent shape
Accessory organs:
Pancreas and liver
Adaptations
In mouth:
In intestine
the cecum stores food
where bacteria are able to break down the cellulose
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A bear and not a bear
Pandas spend up to 14 hours eating
Koalas spend about 4.7 h eating
0.3 lbs food/lb body (6x)
0.05 lbs food/lb body
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