Nutrition and Digestion Chapter 21 Nutrition and Digestion

OBTAINING AND PROCESSING FOOD 21.1 Animals ingest their food in a variety of ways Animal diets are highly varied, and include Herbivores, plant-eaters Carnivores, meat-eaters Omnivores, eating both plants and other animals

Animal feeding mechanisms include Animal feeding mechanisms include Suspension, substrate, fluid, and bulk feeding Caterpillar Feces Figure 21.1C Figure 21.1B Figure 21.1A Figure 21.1D

21.2 Overview: Food processing occurs in four stages 21.2 Overview: Food processing occurs in four stages Small molecules Pieces of food Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Mechanical digestion Food Undigested material 1 Ingestion 2 Digestion 3 Absorption 4 Elimination Figure 21.2A

Ingestion-taking food into the body Digestion-chemical and mechanical breakdown of food. Nutrient macromolecules are digested to monomers before absorption Absorption-absorbing nutrients into the body Elimination-removes undigested material from the body

21.3 Digestion occurs in specialized compartments 21.3 Digestion occurs in specialized compartments Food is digested in compartments Which house hydrolytic enzymes Sponges digest their food Entirely in food vacuoles

In cnidarians, like hydra In cnidarians, like hydra The digestive compartment is a gastrovascular cavity with a single opening, the mouth Mouth Tentacle 1 Digestive enzymes released from a gland cell 2 Soft tissues digested Food (Daphnia, a water flea) 3 Food particle engulfed Gastrovascular cavity 4 Food particle digested in food vacuole Figure 21.3A

Alimentary canal-tube- shaped digestive compartment that has two Most animals have an alimentary canal, running from mouth to anus, with specialized regions Alimentary canal-tube- shaped digestive compartment that has two openings and through which food moves in one direction. Mo uth Pharynx Esophagus Crop Gizzard Anus Intestine Dorsal fold Earthworm Interior of intestine Wall of intestine Esophagus Stomach Anus Mouth Crop Grasshopper Gastric pouches Intestine Stomach Gizzard Mouth Intestine Esophagus Crop Anus Figure 21.3B Bird

Bird digestive system: Esophagus, crop, stomach, gizzard, intestine, anus   Gizzard-grinds food Intestines-absorb water and compact wastes.

HUMAN DIGESTIVE SYSTEM 21.4 The human digestive system consists of an alimentary canal and accessory glands The rhythmic muscle contractions of peristalsis -squeeze food toward the stomach along the alimentary canal Human alimentary canal: oral cavity, pharynx, esophagus, stomach, small intestine, large intestine  

Regulates the passage of food from the stomach to the small intestine The pyloric sphincter Regulates the passage of food from the stomach to the small intestine Oral cavity Tongue Mouth Salivary glands Pharynx Esophagus Liver Esophagus Constriction Stomach Pyloric sphincter Gall- bladder Pancreas Small intestine Large intestine Small intestine Rectum Figure 21.4 Anus

21.5 Digestion begins in the oral cavity 21.5 Digestion begins in the oral cavity The teeth break up food, saliva moistens it and salivary enzymes begin the hydrolysis of starch Functions of saliva: lubricating food.   neutralizing food acids.   controlling bacterial populations.   hydrolyzing starch. Teeth Incisors Canine Premolars Molars Tongue Salivary glands Opening of a salivary gland duct Figure 21.5

The tongue pushes the bolus of food into the pharynx The tongue: taste food.   manipulate food.   shape food into a bolus.   push food into the pharynx.  

21.6 The food and breathing passages both open into the pharynx 21.6 The food and breathing passages both open into the pharynx The esophagus and trachea both open into the pharynx.   Epiglottis-a flap of cartilage that flips down to cover the entry to the trachea during swallowing Tongue Bolus of food Pharynx Epiglottis up Epiglottis down Epiglottis up Esophageal sphincter Larynx up Larynx Larynx down Trachea (windpipe) Esophagus Esophagus Sphincter contracted Sphincter relaxed Sphincter contracted Figure 21.6

21.8 The esophagus squeezes food along to the stomach by peristalsis 21.8 The esophagus squeezes food along to the stomach by peristalsis Peristalsis in the esophagus Moves the bolus into the stomach Muscles contract Muscles contract, constricting passageway and pushing bolus down Muscles relax Bolus of food Muscles relax, allowing passageway to open Muscles contract Muscles relax Stomach Figure 21.8

21.9 The stomach stores food and breaks it down with acid and enzymes 21.9 The stomach stores food and breaks it down with acid and enzymes Pepsin in the gastric juice Begins the hydrolysis of protein Mixes with food to produce acid chyme Colorized SEM 2,500 Lumen (cavity) of stomach Interior surface of stomach Pits Release of juice (mucus, HCl, and pepsinogen) 3 Food particle Pepsinogen Pepsin (active enzyme) Release of gastric juice Epithelium 2 Mucous cells HCl Stomach 1 Gastric gland Pyloric sphincter Chief cells Figure 21.9 Parietal cells

21.11 The small intestine is the major organ of chemical digestion and nutrient absorption Alkaline pancreatic juice neutralizes the acid chyme & its enzymes digest food polymers The pancreas produces digestive enzymes and a solution rich in bicarbonate Liver Bile Gall- bladder Stomach Bile Acid chyme Pancreas Intestinal enzymes Pancreatic juice Duodenum of small intestine Figure 21.11A

Bile, made in the liver and stored in the gall bladder Emulsifies fat for attack by pancreatic enzymes

The epithelial cells lining the intestine have surface projections, called microvilli, that increase the area for absorption Vein with blood en route to the liver Lumen Muscle layers Large circular folds Villi Nutrient absorption Figure 21.11B, Part 1 Intestinal wall

Nutrients pass across the epithelium and into the blood Nutrients pass across the epithelium and into the blood Which flows to the liver where nutrients are processed and stored Lumen of intestine Nutrient absorption Nutrient absorption into epithelial cells Microvilli Epithelial cells Amino acids and sugars Fatty acids and glycerol Fats Blood capillaries Blood Lymph vessel Lymph Epithelial cells Figure 21.11B, Part 2 Villi

21.12 The large intestine reclaims water and compacts the feces 21.12 The large intestine reclaims water and compacts the feces The large intestine, or colon Reabsorbs water from undigested material Feces are stored in the rectum Large intestine (colon) Small intestine Sphincter End of small intestine Rectum Anus Nutrient flow Appendix Cecum Figure 21.12

DIETS AND DIGESTIVE ADAPTATIONS 21.13 Adaptations of vertebrate digestive systems reflect diet Dietary adaptations of herbivores include Longer alimentary canals Cellulose-digesting microbes housed in special chambers

Alimentary canals of herbivores Alimentary canals of herbivores Are usually longer than those found in carnivores Small intestine Small intestine Stomach Cecum Colon (large intestine) Figure 21.13A Carnivore Herbivore

Process food with the aid of microbes in four chambers Ruminants such as cows Process food with the aid of microbes in four chambers 3 Omasum 1 Rumen Intestine Esophagus Rumen 4 Abomasum 2 Reticulum Figure 21.13B