The Digestive System Chapter 22

Figure 41.6 Exploring: Four Main Feeding Mechanisms of Animals

Four stages of food processing

The Mouth Ingestion of food – Food ball = bolus Salivary glands Mechanical digestion with teeth Chemical digestion with saliva Salivary glands Secrete enzyme amylase Starch breakdown starts here Muscular tongue Tasting Helps with swallowing

The Pharynx Connects mouth to esophagus Opens windpipe which leads to lungs Epiglottis controls whether the pharynx is open to lungs or stomach

The Esophagus Muscular tube that connects pharynx to stomach Moves food via peristalsis, waves of muscular contraction

The Stomach Large organ and functions as storage tank Cells lining the stomach secrete gastric juice a fluid made up of Hydrochloric acid Digestive enzyme - pepsin for breaking down proteins into amino acids Mucus – protects stomach New product of stomach juices and food is now called chyme

Figure 41.11 The stomach and its secretions.

Stomach  Small Intestine Through the duodenum First 10 inches of small intestine Where most digestion occurs Connected to Liver Gallbladder Pancreas

Stomach  Small Intestine Pancreas Pancreatic juices Neutralize stomach acid Contain enzymes that aid in digestion

Stomach  Small Intestine Liver and gall bladder Gall bladder stores bile produced by liver Bile has salts that Break up fats Contains dark pigments Can crystallize into gall stones

Nutrient Absorption The Small Intestine Without nutrient absorption we would eat and still starve. The structure of the intestinal lining, or epithelium, is specialized for nutrient absorption Lots of surface area!! (20 ft. long) Villi Microvilli

Figure 41.13 Nutrient absorption in the small intestine.

The Large Intestine Twice as wide as small intestine – but shorter (5 ft. long) At the junction of the small and large intestine is a small extension called the appendix. The appendix contains white blood cells that make minor contributions to the immune system. Appendicitis is a bacterial infection of the appendix

The Large Intestine – The colon forms the main portion of the large intestine absorbs water from the alimentary canal produces feces, consisting of undigested material About one-third of the dry weight of feces consists of bacteria from the colon

The Large Intestine – The rectum The rectum, the last 15 cm (6 inches) of the large intestine, stores feces until they can be eliminated. Two rectal sphincters regulate the opening of the anus one voluntary one involuntary Relaxing the voluntary sphincter expels feces

Helpful review videos https://www.youtube.com/watch?v=s06XzaKqELk https://www.youtube.com/watch?v=Og5xAdC8EUI