Large Intes-ne. A major func-on of the colon is to recover water that has entered the alimentary canal. Feces

Transcription

1 Large Intes-ne A major func-on of the colon is to recover water that has entered the alimentary canal Feces Wastes of the diges-ve tract Become more solid as they move through the colon Pass through the rectum and exit via the anus Colon The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins Vitamin K Rectum Feces are stored in the un-l they can be eliminated Two sphincters between the rectum and anus control bowel movements Internal/external anal sphincter 1

2 Evolu-onary adapta-ons Diges-ve systems of vertebrates are varia-ons on a common plan However, there are intriguing adapta-ons, ohen related to diet Size and type of teeth Length of intes-nes Number of stomachs Den--on Some Dental Adapta-ons Animal s assortment of teeth Mammals have varying den--on that is adapted to their usual diet The teeth of poisonous snakes are modified as fangs for injec-ng venom All snakes can unhinge their jaws to swallow prey whole Fig Incisors Canines Molars Premolars (a) Carnivore (b) Herbivore (c) Omnivore 2

3 Herbivores Stomach and Intes-nal Adapta-ons Generally have longer alimentary canals than carnivores Indica-ve of the longer -me needed to digest vegeta-on Small intestine Stomach Small intestine Cecum Colon (large intestine) Carnivore Herbivore Mutualis-c Adapta-ons Many herbivores have fermenta-on chambers Where symbio-c microorganisms digest cellulose Crop, cecum, rumen Ruminants Coprophagy?! The most elaborate adapta-ons for an herbivorous diet Deer, sheep, caule 3

4 1 Rumen 2 Reticulum Intestine Esophagus 4 Abomasum 3 Omasum Energy Sources and Stores Nearly all of an animal s ATP genera-on is based on oxida-on of energy rich molecules: carbohydrates, proteins, and fats Animals store excess calories primarily as glycogen in the liver and muscles Energy is secondarily stored as adipose, or fat, cells When fewer calories are taken in than are expended, fuel is taken from storage and oxidized Homeostasis: 90 mg glucose/ 100 ml blood Stimulus: Blood glucose level rises after eating. Stimulus: Blood glucose level drops below set point. 4

5 Overnourishment Causes obesity Overnourishment and Obesity Results from excessive intake of food energy with the excess stored as fat Obesity Contributes to diabetes (type 2) Cancer of the colon and breasts Heart auacks, and strokes 100 µm Overnourishment and Obesity Researchers have discovered several of the mechanisms that help regulate body weight Homeosta-c mechanisms are feedback circuits that control the body s storage and metabolism of fat over the long term Hormones regulate long term and short term appe-te by affec-ng a sa-ety center in the brain 5

6 Leptin PYY Insulin Ghrelin Overnourishment and Obesity Lep-n Produced by fat cells Appe-te suppresant Mice that inherit a defect in the gene for lep-n become very obese EXPERIMENT Obese mouse with mutant ob gene (left) next to wild-type mouse. RESULTS 6

7 Obesity and Evolu-on The problem of maintaining weight partly stems from our evolu-onary past fat hoarding was a means of survival Petrels become obese as chicks In order to consume enough protein from highfat food, chicks need to consume more calories than they burn You should now be able to: 1. Name the three nutri-onal needs that must be met by an animal s diet 2. Describe the four classes of essen-al nutrients 3. Dis-nguish among undernourishment, overnourishment, and malnourishment 4. Describe the four main stages of food processing 5. Dis-nguish between a complete diges-ve tract and a gastrovascular cavity 6. Follow a meal through the mammalian diges-ve system: List important enzymes and describe their roles Compare where and how the major types of macromolecules are digested and absorbed 7. Relate varia-ons in den--on with different diets 8. Explain where and in what form energy rich molecules may be stored in the human body 7