the digestive system guts, teeth and glands! images from:
TRANSCRIPT
The Digestive System
Guts, teeth and glands!
Images from: http://www.whfreeman.com/life/update/
Why Guts?
• Multicellular animals must have specialized structures for obtaining and breaking down their food.
• There are two processes: feeding and digestion.
• Animals are heterotrophs, they must absorb nutrients or ingest food sources.
How to dine...
• Ingestive eaters (us).
• Absorptive feeders (tapeworm)
• Filter feeders (clam)
• Substrate feeders (earthworms)
• Fluid feeders (mosquito)
Vertebrate Digestion
• The digestive system uses mechanical and chemical digestion to breakdown food.
Tube in a tube• Vertebrates have a tube-within-a-tube system.
• digestion occurs in the lumen with the nutrient molecules being transferred to the blood.
Stages of digestion
• Movement of food
• Secretion of digestive juices
• Digestion of food into molecules
• Absorption of molecules
• Elimination of undigested food and wastes
The Digestive System
• Mouth, pharynx,• esophagus, stomach• small intestine• large intestine• anus• salivary glands• pancreas• liver and gall bladder
The Start• In the mouth, teeth, jaws and the tongue begin
the mechanical breakdown of food.
• Chemical breakdown of starch by amylase
• Mucus moistens food and lubricates the esophagus.
• The chewed food and saliva is then pushed into the pharynx and esophagus.
• The esophagus uses peristalsis to send the food to the stomach.
Move the food
• Food is chewed and passed to the stomach through the esophagus. The name of the movement is peristalsis. (see video)
The Stomach
• Holds 1 to 2L (folds)
• The stomach secretes mucus, hydrochloric acid and pepsin. HCl lowers pH of the stomach to activate pepsin.
• Pepsin hydrolysis of proteins into peptides.
• The stomach also mechanically churns the food. Chyme, leaves the stomach and enters the small intestine.
• Ulcers occur when mucus lining is reduced.
The Small Intestine
• 3 m long tube with coils and folding plus villi. Very large surface area!
• Final digestion of all food and absorbtion.
• Villi produce enzymes which complete the digestion of peptides and sugars.
• The absorption process in the villi.
Villi
• Sugars and amino acids go into the bloodstream via capillaries in each villus.
• Glycerol and fatty acids go into the lymphatic system. Absorption is an active transport, requiring cellular energy.
Duodenum - busy place
• Secretions from the liver and pancreas are used for digestion in the duodenum.
• The pancreas secretes digestive enzymes and stomach acid-neutralizing bicarbonate.
• The liver produces bile, which is stored in the gall bladder before entering the bile duct into the duodenum.
Small intestine - more
• Digestion of carbohydrates, proteins, and fats continues in the small intestine. See table in text - page 166.
• Bile emulsifies fats so that lipases can completely digested lipids.
• Most absorption occurs in the ileum and jejeunum (second third of the small intestine).
Liver and Gall Bladder
• The liver produces bile and helps to detoxify of blood
• synthesis of blood proteins
• destruction of old erythrocytes
• storage of glucose as glycogen
• De-amination amino groups and ammonia. (this produces urea, less toxic)
Glycogen-Glucose
• Low glucose levels in the blood cause glucagon to stimulate breakdown of glycogen into glucose.
• Insulin helps store glucose and glycogen in the liver (see page 929)
• When no glucose or glycogen is available, amino acids are converted into glucose in the liver.
The Large Intestine what to do with left overs!
• The large intestine produces an alkaline mucus that neutralizes acids produced by bacterial metabolism.
• Water, salts, and vitamins are absorbed, the remaining contents in the lumen form feces (mostly cellulose, bacteria, bilirubin).
• Bacteria in the large intestine, such as E. coli, produce vitamins (including vitamin K) that are absorbed.
Nutrition
• See the basics of nutrition in your text.
• Have a hand out!