Chapter 41 Animal Nutrition

Overview: The Need to Feed Every meal reminds us that we are heterotrophs, dependent on a regular supply of food In general, animals fall into three categories: Herbivores eat mainly autotrophs (plants and algae) Carnivores eat other animals Omnivores regularly consume animals as well as plants or algal matter

An adequate diet must satisfy three needs: Fuel for all cellular work Organic raw materials for biosynthesis Essential nutrients, substances that the animal cannot make for itself Main feeding mechanisms: suspension feeding, substrate feeding, fluid feeding, bulk feeding

LE 41-2a Baleen

LE 41-2b Caterpillar Feces

Video: Lobster Mouth Parts Video: Shark Eating a Seal

Concept 41.1: Homeostatic mechanisms manage an animal’s energy budget Nearly all of an animal’s ATP generation is based on oxidation of energy-rich molecules: carbohydrates, proteins, and fats

Glucose Regulation as an Example of Homeostasis Animals store excess calories as glycogen in the liver and muscles and as fat Glucose is a major fuel for cells Hormones regulate glucose metabolism When fewer calories are taken in than are expended, fuel is taken from storage and oxidized

LE 41-3 STIMULUS: Blood glucose level rises after eating. Homeostasis: 90 mg glucose/ 100 mL blood STIMULUS: Blood glucose level drops below set point.

Caloric Imbalance Undernourishment occurs in animals when their diets are chronically deficient in calories Overnourishment, or obesity, results from excessive intake, with excess stored as fat

LE 41-4 100 µm

Obesity as a Human Health Problem The World Health Organization now recognizes obesity as a major global health problem Obesity contributes to a number of health problems, including diabetes, cardiovascular disease, and colon and breast cancer

Researchers have discovered several of the mechanisms that help regulate body weight Over the long term, homeostatic mechanisms are feedback circuits that control the body’s storage and metabolism of fat Hormones regulate long-term and short-term appetite by affecting a “satiety center” in the brain

LE 41-5 Ghrelin Insulin Leptin PYY

The complexity of weight control in humans is evident from studies of the hormone leptin Mice that inherit a defect in the gene for leptin become very obese

Obesity and Evolution The problem of maintaining weight partly stems from our evolutionary past, when fat hoarding was a means of survival A species of birds called petrels become obese as chicks due to the need to consume more calories than they burn

Concept 41.2: An animal’s diet must supply carbon skeletons and essential nutrients An animal must obtain carbon skeletons from its food to build complex molecules Besides fuel and carbon skeletons, a diet must supply essential nutrients in preassembled form A malnourished animal is missing one or more essential nutrients in its diet

Herbivores may suffer mineral deficiencies if they graze on plants in soil lacking key minerals

Malnutrition is much more common than undernutrition in human populations

Essential Amino Acids Animals require 20 amino acids and can synthesize about half from molecules in their diet The remaining amino acids, the essential amino acids, must be obtained from food in preassembled form A diet that provides insufficient essential amino acids causes malnutrition called protein deficiency

Most plant proteins are incomplete in amino acid makeup Individuals who eat only plant proteins need to eat a variety to get all essential amino acids

Essential amino acids for adults LE 41-10 Essential amino acids for adults Methionine Beans and other legumes Valine Threonine Phenylalanine Leucine Corn (maize) and other grains Isoleucine Tryptophan Lysine

Some animals have adaptations that help them through periods when their bodies demand extraordinary amounts of protein

Essential Fatty Acids Animals can synthesize most of the fatty acids they need The essential fatty acids are certain unsaturated fatty acids Deficiencies in fatty acids are rare

Vitamins Vitamins are organic molecules required in the diet in small amounts 13 vitamins essential to humans have been identified Vitamins are grouped into two categories: fat-soluble and water-soluble

Minerals Minerals are simple inorganic nutrients, usually required in small amounts

Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination Ingestion is the act of eating Digestion is the process of breaking food down into molecules small enough to absorb Absorption is uptake of nutrients by body cells Elimination is the passage of undigested material out of the digestive compartment

LE 41-12 Small molecules Pieces of food Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Mechanical digestion Food Undigested material INGESTION DIGESTION ABSORPTION ELIMINATION

Digestive Compartments Most animals process food in specialized compartments These compartments reduce risk of self-digestion

Intracellular Digestion In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles

Extracellular Digestion Extracellular digestion is the breakdown of food particles outside of cells It occurs in compartments that are continuous with the outside of the animal’s body

Video: Hydra Eating Daphnia Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Video: Hydra Eating Daphnia

LE 41-13 Mouth Tentacles Gastrovascular cavity Food Epidermis Mesoglea Gastrodermis Nutritive muscular cells Flagella Gland cells Food vacuoles Mesoglea

More complex animals have a digestive tube with two openings, a mouth and an anus This digestive tube is called a complete digestive tract or an alimentary canal It can have specialized regions that carry out digestion and absorption in a stepwise fashion

Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole LE 41-14a Crop Gizzard Esophagus Intestine Pharynx Anus Mouth Typhlosole Lumen of intestine Earthworm

Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric ceca LE 41-14b Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric ceca Grasshopper

Esophagus Stomach Mouth Crop Anus LE 41-14c Esophagus Stomach Gizzard Intestine Mouth Crop Anus Bird

Concept 41.4: Each organ of the mammalian digestive system has specialized food-processing functions The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal

LE 41-15a Cardiac orifice Tongue Oral cavity Parotid gland Salivary Sublingual gland Pharynx Esophagus Submandibular gland Pyloric sphincter Liver Stomach Ascending portion of large intestine Gall- bladder Pancreas Ileum of small intestine Duodenum of small intestine Small intestine Large intestine Rectum Anus Appendix Cecum

A schematic diagram of the human digestive system LE 41-15b Salivary glands Mouth Esophagus Gall- bladder Stomach Small intestines Liver Pancreas Large intestines Rectum Anus A schematic diagram of the human digestive system

The Oral Cavity, Pharynx, and Esophagus In the oral cavity, food is lubricated and digestion begins Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers

The region we call our throat is the pharynx, a junction that opens to both the esophagus and the windpipe (trachea) The esophagus conducts food from the pharynx down to the stomach by peristalsis

LE 41-16_3 Bolus of food Tongue Epiglottis up Epiglottis up Pharynx down and open Glottis Esophageal sphincter contracted Epiglottis down Esophageal sphincter relaxed Esophageal sphincter contracted Larynx Trachea Glottis up and closed Esophagus Relaxed muscles To lungs To stomach Contracted muscles Relaxed muscles Stomach

The Stomach The stomach stores food and secretes gastric juice, which converts a meal to acid chyme Gastric juice is made up of hydrochloric acid and the enzyme pepsin Pepsin is secreted as inactive pepsinogen; pepsin is activated when mixed with hydrochloric acid in the stomach Mucus protects the stomach lining from gastric juice

LE 41-17 5 µm Interior surface of stomach Gastric gland Mucus cells Esophagus Cardiac orifice Stomach Pyloric sphincter 5 µm Small intestine Folds of epithelial tissue Interior surface of stomach Epithelium Pepsinogen and HCl are secreted into the lumen of the stomach. Pepsinogen Pepsin (active enzyme) Gastric gland HCl HCl converts pepsinogen to pepsin. Pepsin then activates more pepsinogen, starting a chain reaction. Pepsin begins the chemical digestion of proteins. Mucus cells Chief cells Parietal cells Chief cell Parietal cell

Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Helicobacter pylori

LE 41-18 Bacteria Mucus layer of stomach 1 µm

The Small Intestine The small intestine is the longest section of the alimentary canal It is the major organ of digestion and absorption

Enzymatic Action in the Small Intestine The first portion of the small intestine is the duodenum, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself

Bile Liver Gall- bladder Stomach Acid chyme Intestinal juice Pancreatic juice Pancreas Duodenum of small intestine

The pancreas produces proteases, protein-digesting enzymes that are activated after entering the duodenum

Membrane-bound enteropeptidase LE 41-20 Pancreas Membrane-bound enteropeptidase Inactive trypsinogen Trypsin Other inactive proteases Active proteases Lumen of duodenum

The liver produces bile, which aids in digestion and absorption of fats The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine

Pancreatic carboxypeptidase LE 41-21 Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Oral cavity, pharynx, esophagus Polysaccharides Disaccharides Salivary amylase Smaller polysac- charides, maltose Stomach Proteins Pepsin Small polypeptides Lumen of small intes- tine Polysaccharides Polypeptides DNA, RNA Fat globules Pancreatic amylases Pancreatic trypsin and chymotrypsin Pancreatic nucleases Bile salts Maltose and other disaccharides Fat droplets Nucleotides Smaller polypeptides Pancreatic carboxypeptidase Pancreatic lipase Amino acids Glycerol, fatty acids, glycerides Epithelium of small intestine (brush border) Small peptides Nucleotidases Nucleosides Disaccharidases Dipeptidases, carboxy- peptidase, and aminopeptidase Nucleosidases and phosphatases Monosaccharides Amino acids Nitrogenous bases, sugars, phosphates

Hormones help coordinate the secretion of digestive juices into the alimentary canal

LE 41-22 Key Liver Stimulation Inhibition Entero- gastrone Gall- bladder Gastrin CCK Stomach Pancreas Secretin Duodenum CCK

Absorption of Nutrients The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen The enormous microvillar surface greatly increases the rate of nutrient absorption

LE 41-23 Key Nutrient absorption Vein carrying blood Microvilli to hepatic portal vessel Microvilli (brush border) Blood capillaries Epithelial cells Muscle layers Epithelial cells Large circular folds Lacteal Villi Lymph vessel Villi Intestinal wall

Each villus contains a network of blood vessels and a small lymphatic vessel called a lacteal

Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells These fats are mixed with cholesterol and coated with protein, forming molecules called chylomicrons, which are transported into lacteals

LE 41-24 Fat globule Bile salts Fat droplets coated with bile salts Micelles made up of fatty acids, monoglycerides, and bile salts Epithelium of small intestine Lacteal Epithelium of lacteal

The Large Intestine The large intestine, or colon, is connected to the small intestine Its major function is to recover water that has entered the alimentary canal Wastes of the digestive tract, the feces, become more solid as they move through the colon Feces pass through the rectum and exit via the anus

The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins

Concept 41.5: Evolutionary adaptations of vertebrate digestive systems are often associated with diet Digestive systems of vertebrates are variations on a common plan However, there are intriguing adaptations, often related to diet

Some Dental Adaptations Dentition, an animal’s assortment of teeth, is one example of structural variation reflecting diet Mammals have specialized dentition that best enables them to ingest their usual diet

LE 41-26 Incisors Canines Molars Premolars Carnivore Herbivore Omnivore

Stomach and Intestinal Adaptations Herbivores generally have longer alimentary canals than carnivores, reflecting the longer time needed to digest vegetation

LE 41-27 Small intestine Stomach Small intestine Cecum Colon (large Carnivore Herbivore

Symbiotic Adaptations Many herbivores have fermentation chambers, where symbiotic microorganisms digest cellulose The most elaborate adaptations for an herbivorous diet have evolved in the animals called ruminants

LE 41-28 Intestine Rumen Reticulum Esophagus Abomasum Omasum