Animal Nutrition/Digestion Chapter 41 & IB Topic 6.1

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

You need to know at least one of these: EnzymeSourceSubstrateProductOptimum pH AmylaseSalivary glands StarchMaltose PepsinGastric glands Protein Polypeptides 2.0 LipasePancreasTriglycerideFatty 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 Figure 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 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  nimationplayer/ nimationplayer/ Digestion Peristalsis Heartburn Ulcers