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Animal Nutrition/Digestion
IB Topic 6.1 (page 164)
Introduction Physiology: how and why the parts of the
body function the way they do Anatomy: the study of the structure.
Structure and function Physiology is an experimental science
Cells of organisms function best in a constant internal environment
Digestion The body needs to get essential nutrients An essential step because the bulk of food
taken in consists of insoluble molecules Too large to cross the gut wall and enter the
blood stream The bulk of our diet consists of:
carbohydrates, lipids, and proteins Must be hydrolyzed Food cannot be said to have truly entered the
body until it has been digested and absorbed
The five steps of nutrition 1. Ingestion 2. Digestion 3. Absorption 4. Assimilation 5. Egestion/elimination
Ingestion Food is taken into the mouth for
processing in the gut
Digestion Process of breaking food down into
molecules small enough for the body to absorb
Mechanical digestion Teeth (mastication) and muscular walls of the
gut (peristalsis: waves of contraction and relaxation
Increases surface area Chemical digestion
Enzymes (mainly in the stomach and intestine)
Absorption Soluble products of digestion are absorbed
into blood circulation system
Assimilation Products of digestion absorbed from blood
into body cells (such as liver and muscle cells) and used or stored
Egestion or elimination Undigested food and dead cells from the
lining of the gut, together with bacteria from the gut flora, expelled from the body as feces
Enzymes (remember … ) Huge contributor in chemical digestion Digestion enzymes are protein catalysts
produced in specialized cells in glands associated with the gut
Enzymes speed up the breakdown of insoluble food substances
Remember pH and temperature Think homeostasis
What you need to know: Enzyme Source Substrate Product Optimum
pH
Amylase Salivary glands
Starch Maltose 6.5-7.5
Pepsin Gastric glands
Protein Polypeptides and amino
acids
2.0
Lipase Pancreas Triglyceride Fatty acids and
glycerol
7.0
Lets take a trip down the alimentary canal … 1. The oral cavity 2. The stomach 3. The small intestine 4. The large intestine
Also reference Figure6.2 in your text
The oral cavity Mechanical and chemical manipulation of food Saliva moistens food and helps prevent tooth
decay by buffering/neutralizing acids Also contains antibacterial agents
The pharynx Opens both to the windpipe (trachea) and esophagus When we swallow, the windpipe moves up and the
glottis is covered by the epiglottis The esophagus
Food travels down the esophagus to the stomach Peristalsis
The stomach J-shaped, pouch-like organ that hangs
inferior to the diaphragm in the upper left portion of the abdominal cavity
1-2 L capacity The wall of the stomach is elastic, so large
meals can be swallowed quickly, stored, and then gradually released into the small intestine
The wall of the stomach is muscular and contracts rhythmically to squeeze the food, mixing it and breaking it into smaller lumps
Functions of the stomach Gastric glands secrete gastric juices
(includes HCL) HCL has a pH of 1.5-2.0 Good for protein digestion (protease)
Goblet cells secrete mucus Prevents autolysis
Chyme Semi-liquid
A typical meal may spend up to 4 hours in the stomach
The small intestine Completion of digestion of carbohydrates,
lipids, and proteins Useful products are absorbed In humans, about 5 meters long The inner-most layer contains finger-like
projections called villi
Digestion in the small intestine Food enters the first part (duodenum) a
little at a time The chyme meets bile from the bile duct
and the pancreatic juice from the pancreas Bile neutralizes the acidity of the chyme Bile lowers the surface tension of large fat
globules (emulsification) Pancreatic juice contains several enzymes:
amylase, lipase, and protease
Absorption in the small intestine The products of digestion (monomers,
minerals, vitamins) are absorbed as they make contact with the villi
Efficient because the villi drastically increase the surface area of the small intestine
Active transport Products of digestion are taken into cells Protein pump molecules
Assimilation follows absorption The fate of absorbed nutrients is called
assimilation In the villi:
Sugars are passed into the capillary network, then to the liver
Amino acids are passed into the capillary network, then to the liver (make new proteins)
Lipids are absorbed as fatty acids and glycerol into the lacteal vessels lymphatic system blood circulation
The large intestine No villi; surface area is increased by numerous
folds At this point, most of the useful nutrients have
been absorbed What remains:
Undigested matter (plant fiber), mucus, dead intestinal cells, bacteria, mineral ions, and water
In the colon, water and mineral salts (Na+, Cl-) are absorbed
What remains is now called feces Bacteria compose about 50% of feces (so wash your
hands!) Bile pigments color the feces
Animations http://www.pennhealth.com/health_info/an
imationplayer/ Digestion Peristalsis Heartburn Ulcers
Lets Model A Trip Down the Alimentary Canal … Students will be assigned a portion of the
digestive system Arrange yourselves in the proper order Pink Koosh ball will represent a piece of food As the “food” passes from person to person down
the digestive system, the student who is holding the ball will state the function of their body part in processing the food. In some cases, the food may not reach you – you are a
vital, accessory organ
Small Group Discussion What would be the consequences if a person’s stomach was
surgically removed, or did not function properly? What about:
Small intestine Large intestine Pancreas Gall bladder Liver Teeth and/or tongue Salivary glands
Which of these digestive organs could you live without? What accommodations would you need to make to maintain good nutrition and digestive function? Which of these organs are absolutely impossible to live without?
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