Animal Nutrition Human Digestion

Human digestive system Click here for video http://health.howstuffworks.com/adam-200086.htm Human digestive system After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested. Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours. In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

What do animals need to live? Animals make energy using: food oxygen food ATP O2 mitochondria

Animals build bodies using: food for raw materials amino acids, sugars, fats, nucleotides ATP energy for synthesis

Mouth Functions mechanical digestion teeth break up food chemical digestion (saliva) amylase enzyme digests starch All that in spit!

Swallowing (& not choking) ESOPHAGUS Peristalsis involuntary muscle contractions to move food along

Stomach Functions disinfect food hydrochloric acid = pH 2 But the stomach is made out of protein! What stops the stomach from digesting itself? Functions disinfect food hydrochloric acid = pH 2 kills bacteria food storage can stretch to fit ~2L food digests protein pepsin enzyme mucus secreted by stomach cells protects stomach lining Still, the epithelium is continually eroded, and the epithelium is completely replaced by mitosis every three days. Gastric ulcers, lesions in the stomach lining, are caused by the acid-tolerant bacterium Heliobacter pylori. Ulcers are often treated with antibiotics. Pepsin is secreted in an inactive form, called pepsinogen by specialized chief cells in gastric pits. Parietal cells, also in the pits, secrete hydrochloric acid which converts pepsinogen to the active pepsin only when both reach the lumen of the stomach, minimizing self-digestion. Also, in a positive-feedback system, activated pepsin can activate more pepsinogen molecules.

Small intestine Functions digestion absorption nutrients move into body cells by: diffusion active transport About every 20 seconds, the stomach contents are mixed by the churning action of smooth muscles. As a result of mixing and enzyme action, what begins in the stomach as a recently swallowed meal becomes a nutrient-rich broth known as acid chyme. At the opening from the stomach to the small intestine is the pyloric sphincter, which helps regulate the passage of chyme into the intestine. A squirt at a time, it takes about 2 to 6 hours after a meal for the stomach to empty.

Absorption in Small Intestines Absorption through villi & microvilli finger-like projections increases surface area for absorption SMALL INTESTINES 6 meters long, but can stretch to cover a tennis court

Pancreas Produces digestive enzymes Buffers neutralizes acid from stomach pancreas small intestine

Balancing Blood Sugar levels Homeostasis Balancing Blood Sugar levels insulin body cells take up sugar from blood liver stores sugar reduces appetite pancreas liver high blood sugar level low liver releases sugar triggers hunger pancreas liver Feedback glucagon

Liver & Gall Bladder Produces bile breaks up fats gallbladder only stores bile (that’s why you can have your gall bladder removed) bile contains colors from old red blood cells collected in liver = iron in RBC rusts & makes feces brown

Large intestines (colon) Function re-absorbs water use ~9 liters of water every day in digestive juices if don’t reabsorb water would die of dehydration > 90% of water re-absorbed not enough water re-absorbed diarrhea can be fatal! too much water re-absorbed constipation

Appendix Vestigial organ

So don’t forget to wash your hands! Rectum Last section of large intestines eliminate feces what’s left over? undigested materials mainly cellulose from plants called roughage or fiber keeps everything moving & cleans out intestines masses of bacteria So don’t forget to wash your hands!

DIGESTIVE HOMEOSTATIC DISORDERS 1. Ulcer: open sores in the lining of the stomach. Used to think ulcers were caused by stress tried to control with antacids Now know ulcers caused by bacterial infection of stomach H. pylori bacteria now cure with antibiotics

2. Gallstones: small hard stones made of cholesterol that collect in the gallbladder. 3. Constipation: too much water taken out of the feces resulting in difficulty evacuating the feces.

4. Diarrhea: too little water taken out of feces; prolonged diarrhea can cause dehydration of body tissues. 5. Appendicitis: infection and inflammation of the appendix.