1 Sylvia S Mader Immagini e concetti della

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Sylvia S. Mader Immagini e concetti della biologia 2 a ed. 2 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

C 8 - Digestive system and nutrition 3 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

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, 2019

Digestion helps homeostasis Chemical digestion involves specific enzymes in the macromolecule breakdown. 5 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

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, 2019

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, 2019

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. 8 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

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. 9 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

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, 2019

Human digestive system Our digestive system is adapted to an omnivorous diet. 11 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

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, 2019

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, 2019

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, 2019

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, 2019

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, 2019

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, 2019

Pancreas and liver are accessory digestive organs that produce pancreatic juice and bile respectively. 18 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

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, 2019

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, 2019

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, 2019

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, 2019

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, 2019

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, 2019

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, 2019

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, 2019

Minerals regulate biochemical reactions, maintain fluid balance and are incorporated into structures and compounds. 27 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

Vitamins are organic compounds that regulate metabolism and physiological development. Vitamins are classified as liposoluble (as A and D) or hydro-soluble (as C and B). 28 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

Vitamins 29 Sylvia S. Mader, Concepts of Biology © Zanichelli editore, 2019

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, 2019