1 Sylvia S Mader Immagini e concetti della

1

Sylvia S. Mader Immagini e concetti della biologia 2 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

C 7 - Digestive system and nutrition 3 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Digestion helps homeostasis A digestive system involves various processes: Ingestion Mechanical digestion Chemical digestion Absorption Elimination 4 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Digestion helps homeostasis Chemical digestion involves specific enzymes in the macromolecule breakdown. 5 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Digestive tract An incomplete digestive tract as in planaria (a flatworm) has a single opening through which nutrients enter and exit. 6 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Digestive tract A complete digestive tract, as in birds and worms, has a mouth, an anus and specialized parts: crop (for storage), gizzard (for first mechanical digestion) and intestine (for chemical digestion). 7 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Digestive system in mammals Carnivores have a short digestive tract, as they obtain nutrients from meat more easily. They also have a relatively small cecum. 8 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Digestive system in mammals Herbivores have a long digestive tract, as it takes a long time to digest cellulose from plants, and a large cecum with specialized enzymes. 9 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Digestive system in mammals Some herbivores called ruminants (cows, sheep) have specialized stomaches divided into: rumen (1), reticulum (2), omasum (3) and abomasum (4) hosting microbial flora. 10 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Human digestive system Our digestive system is adapted to an omnivorous diet. 11 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The mouth Both first mechanical and chemical digestion occur in the mouth. • 32 teeth divided into 4 classes chew food • 3 pairs of salivary glands contain salivary amylase for digesting starch • The tongue (skeletal muscle) forms a food bolus for swallowing 12 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The esophagus is a muscular tube that passes from the pharynx to the stomach. During swallowing, the air passage is blocked by soft palate (1) and epiglottis (2), so the food bolus enters the esophagus (3). 13 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The esophagus After swallowing, peristaltic movements push the food bolus in the esophagus to the stomach. 14 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The stomach Food storage and second chemical digestion take place in the stomach. The food is mixed with gastric acid juices containing a protein digesting enzyme called pepsin. 15 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The small intestine Chemical digestion ends and absorption of nutrients takes place in the 5 to 9 meters long small intestine. Bile and pancreatic juices prepare carbohydrates, proteins and fats for digestion by maltase, peptidase and lipase. 16 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The small intestine Intestinal enzymes complete digestion to small nutrient molecules which are absorbed by the villi on the intestinal wall. villi 17 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Pancreas and liver are accessory digestive organs that produce pancreatic juice and bile respectively. 18 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Stomach and duodenum (the upper part of the intestine) are also endocrine glands and secrete hormones. Stomach produces gastrin to help regulate food digestion. Duodenum produces secretin and cholecystokinin for stimulating the digestion of fats and proteins. 19 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Liver diseases Liver malfunctioning has effects on the whole organism. Liver disorders include: • Jaundice - yellow pigmentation of the skin caused by increased levels of bilirubin in the blood. • Hepatitis - inflammation of the liver caused by viruses. • Cirrhosis - damage of tissues leading to loss of liver functions. • Liver cancer. 20 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The large intestine absorb water, minerals and vitamins and prepare waste for elimination. Is divided into cecum, colon and rectum. The cecum controls the flux of material through the intestine and the appendix protects from infections. 21 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

The large intestine The colon is the last portion of the digestive tract and extracts water and minerals from waste before final elimination. Bacteria-aided fermentation occurs. The rectum is the final part of the large intestine and terminates in the anus. Here feces are formed and expelled. 22 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Nutrition Alimentation must provide all nutrients in balance amount. The most important nutrients are: • Carbohydrates • Lipids • Proteins • Minerals • Vitamins 23 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Carbohydrates (sugars, starch and fibers) provide immediate energy. Whole-grain carbohydrates are more nutritious while fibers are indigestible cellulose carbohydrates that stimulate intestine functions. 24 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Lipids supply long-term energy and are stored in fat cells. Foods from animals (butter, meat, cheese) is rich in saturated fats and cholesterol. 25 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Proteins supply amino acids, the building blocks for cells. 8 out of 20 amino acids are essential as they can not be synthesized by our cells. Protein-rich food include meat, fish, eggs, nuts, soybean and cheese. 26 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Minerals regulate biochemical reactions, maintain fluid balance and are incorporated into structures and compounds. 27 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Vitamins are organic compounds that regulate metabolism and physiological development. Vitamins are classified as lipo-soluble (as A and D) or hydro-soluble (as C and B). 28 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Vitamins 29 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012

Nutrition disorders Obesity is defined as weighing 30% more than ideal body weight. Obesity is often associated with Type 2 Diabetes and cardiovascular diseases. Other common nutrition disorders are anorexia nervosa (distorted body image that leads to hypo-nutrition) and bulimia nervosa (binge-eating and purging). 30 Sylvia S. Mader Concepts of Biology © Zanichelli editore, 2012