The Digestive System

The Digestive System Breaks down food into smaller particles so cells can use it Built around alimentary canal (one-way tube passing through body) Digestive system includes: mouth, pharynx, esophagus, stomach, small intestine, and large intestine Accessory structures include: salivary glands, pancreas, and liver

The Digestive System ACCESSORY ORGANS ALIMENTARY CANAL Figure 22.5 The Digestive System ACCESSORY ORGANS ALIMENTARY CANAL Oral cavity (mouth) Tongue Pharynx Salivary glands Esophagus Liver Gallbladder Stomach Pancreas Small intestine Colon of large intestine Appendix Rectum Anus

The Mouth Chewing (mastication) begins process of mechanical digestion = physical break down of large pieces of food into smaller pieces Saliva, a digestive enzyme, begins breaking down food molecules (starches like crackers) into different molecules = chemical digestion Saliva also moistens food and makes it easier to chew/swallow and helps fight infections by killing some bacteria on food The muscular tongue tastes, shapes food into a ball, and pushes the food to the back of the mouth for swallowing.

The Pharynx The pharynx During swallowing, a reflex connects the mouth to the esophagus and opens to the trachea, which leads to the lungs. During swallowing, a reflex moves the opening of the trachea upward and tips the epiglottis to close the trachea entrance

The Pharynx BREATHING SWALLOWING Epiglottis Epiglottis down up Pharynx Figure 22.7 The Pharynx BREATHING SWALLOWING Epiglottis up Epiglottis down Pharynx Adam’s apple Trachea closed Air flowing into open trachea (windpipe) Esophagus closed Food flowing into open esophagus

The Esophagus Clump of food (bolus) goes down throat and into esophagus Bolus moves through esophagus by peristalsis – contractions of smooth muscle surround esophagus squeeze food down esophagus “Heartburn” is caused by stomach acid entering the esophagus and irritating the lining of the esophagus

Swallowing

The Stomach Bolus empties into the stomach from the esophagus Stomach continues mechanical and chemical digestion of food Chemical digestion – some glands in the stomach produce mucus to protect the wall of stomach and other glands produce hydrochloric acid (HCl). The acid activates an enzyme called pepsin (made by another set of glands). Pepsin and HCl together chemically break down food molecules Mechanical digestion – stomach muscles contract and churn to mix food with stomach juices (mixture now called chyme). After an hour or two, chyme moves into the small intestine

The Small Intestine, Pancreas, and Liver Chyme enters first part of small intestine called duodenum Location where most chemical digestion takes place (small intestine) Small intestine is 6.5m long and 2.5cm wide Enzyme from pancreas and liver enter duodenum Pancreas releases two enzymes – one to help chemically digest food and the other to neutralize the stomach acid Liver releases bile to help break down fats from food

The Liver and Pancreas Bile Liver Stomach Bile Gallbladder Chyme Figure 22.11 The Liver and Pancreas Bile Liver Stomach Bile Gallbladder Chyme Intestinal enzymes Pancreatic juice Duodenum of small intestine Pancreas

The Small Intestine, Pancreas, and Liver (continued) After duodenum, most chemical digestion is completed and the rest of the small intestine absorbs nutrients Projections called villi create and enormous surface area for absorption of nutrients Contractions of smooth muscle move chyme along

Epithelial cells and blood capillary Figure 22.13 The Small Intestine Blood vessels Muscle layers Interior of intestine Intestinal wall Nutrient absorption Villi Interior of intestine Nutrient absorption Nutrient absorption Microvilli Epithelial cells Blood capillaries Lymphatic vessel Blood Epithelial cells and blood capillary Villi

The Large Intestine (Colon) Large intestine is 2m long and 7cm wide Removes water from undigested material left over from small intestine Bacteria in large intestine helps digestion Concentrated waste material remaining after water removal is eliminated from body What is the condition called when too much water is reabsorbed in the large intestine? Constipation What is the condition called when not enough water is reabsorbed in the large intestine? Diarrhea

The Large Intestine (Colon) Figure 22.14 The Large Intestine (Colon) Colon of large intestine Small intestine Sphincter End of small intestine Rectum Anus Nutrient flow Appendix

Path of Digestion = mouth – esophagus, stomach, small intestine, large intestine, anus