Animal Nutri1on. Overview: The Need to Feed 24/04/12 BIOL212 NSCC

Transcription

1 Animal Nutri1on BIOL212 NSCC Overview: The Need to Feed Food is taken in, taken apart, and taken up in the process of animal nutri&on In general, animals fall into three categories: Herbivores eat mainly plants and algae Carnivores eat other animals Omnivores regularly consume animals as well as plants or algae Most animals are also opportunis1c feeders Figure 41.1 Video: Lobster Mouth Parts Video: Shark Ea1ng a Seal 1

2 Concept 41.1: An animal s diet must supply chemical energy, organic molecules, and essen1al nutrients An animal s diet provides: Chemical energy, which is converted into ATP to power cellular processes Organic building blocks, such as organic carbon and organic nitrogen, to synthesize a variety of organic molecules Essen&al nutrients, which are required by cells and must be obtained from dietary sources Essen1al Nutrients There are four classes of essen1al nutrients: Essen1al amino acids Essen1al faqy acids Vitamins Minerals Essen%al Amino Acids Animals require 20 amino acids and can synthesize about half from molecules in their diet The remaining amino acids, the essen&al amino acids, must be obtained from food in preassembled form Meat, eggs, and cheese provide all the essen1al amino acids and are thus complete proteins Most plant proteins are incomplete in amino acid composi1on Individuals who eat only plant proteins need to eat specific plant combina1ons to get all the essen1al amino acids Some animals have adapta1ons that help them through periods when their bodies demand extraordinary amounts of protein 2

3 Figure 41.2 Essen%al Fa0y Acids Animals can synthesize most of the faqy acids they need The essen&al fa7y acids must be obtained from the diet and include certain unsaturated faqy acids (i.e., faqy acids with one or more double bonds) Deficiencies in faqy acids are rare Vitamins Table 41.1 Vitamins are organic molecules required in the diet in small amounts Thirteen vitamins are essen1al for humans Vitamins are grouped into two categories: fat- soluble and water- soluble 3

4 Minerals Table 41.2 Minerals are simple inorganic nutrients, usually required in small amounts Inges1ng large amounts of some minerals can upset homeosta1c balance Dietary Deficiencies Malnourishment is the long- term absence from the diet of one or more essen1al nutrients Deficiencies in Essen%al Nutrients Deficiencies in essen1al nutrients can cause deformi1es, disease, and death Golden Rice is an engineered strain of rice with beta- carotene, which is converted to vitamin A in the body 4

5 Figure 41.3 Undernutri%on Undernutri1on results when a diet does not provide enough chemical energy An undernourished individual will Use up stored fat and carbohydrates Break down its own proteins Lose muscle mass Suffer protein deficiency of the brain Die or suffer irreversible damage Figure 41.4 Assessing Nutri1onal Needs Gene1c defects that disrupt food uptake provide informa1on about human nutri1on For example, hemochromatosis causes iron buildup without excessive iron intake Insights into human nutri1on have come from epidemiology, the study of human health and disease in popula1ons Neural tube defects were found to be the result of a deficiency in folic acid in pregnant mothers RESULTS Group Vitamin supplements (experimental group) No vitamin supplements (control group) Number of infants/fetuses studied Infants/fetuses with a neural tube defect 1 (0.7%) 12 (5.9%) 5

6 Figure 41.5 Concept 41.2: The main stages of food processing are inges1on, diges1on, absorp1on, and elimina1on Inges&on is the act of ea1ng Mechanical digestion Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Undigested material 1 Ingestion 2 Digestion 3 Absorption 4 Elimination Figure 41.5a Suspension Feeders Many aqua1c animals are suspension feeders, which si_ small food par1cles from the water 6

7 Figure 41.6 Suspension Feeders and Filter Feeders Baleen Substrate Feeders Fluid Feeders Substrate Feeders Substrate feeders are animals that live in or on their food source Bulk Feeders Caterpillar Feces Fluid Feeders Fluid feeders suck nutrient- rich fluid from a living host Bulk Feeders Bulk feeders eat rela1vely large pieces of food 7

8 Diges&on is the process of breaking food down into molecules small enough to absorb Mechanical diges1on, including chewing, increases the surface area of food Chemical diges1on splits food into small molecules that can pass through membranes; these are used to build larger molecules In chemical diges1on, the process of enzyma&c hydrolysis splits bonds in molecules with the addi1on of water Absorp&on is uptake of nutrients by body cells Elimina&on is the passage of undigested material out of the diges1ve system Diges1ve Compartments Most animals process food in specialized compartments These compartments reduce the risk of an animal diges1ng its own cells and 1ssues Intracellular Diges%on In intracellular diges&on, food par1cles are engulfed by phagocytosis Food vacuoles, containing food, fuse with lysosomes containing hydroly1c enzymes 8

9 Figure 41.7 Extracellular Diges%on Mouth Extracellular diges&on is the breakdown of food par1cles outside of cells It occurs in compartments that are con1nuous with the outside of the animal s body Animals with simple body plans have a gastrovascular cavity that func1ons in both diges1on and distribu1on of nutrients Food Tentacles 1 Digestive enzymes released 2 Food particles broken down Video: Hydra Ea1ng Daphnia Epidermis 3 Food particles engulfed and digested Gastrodermis Figure 41.8 Esophagus Pharynx Crop Gizzard Intestine More complex animals have a diges1ve tube with two openings, a mouth and an anus This diges1ve tube is called a complete diges&ve tract or an alimentary canal It can have specialized regions that carry out diges1on and absorp1on in a stepwise fashion Mouth (a) Earthworm Foregut Midgut Hindgut Esophagus Rectum Anus Crop Mouth Gastric cecae (b) Grasshopper Anus Esophagus Crop Stomach Gizzard Intestine Mouth (c) Bird Anus 9

10 Concept 41.3: Organs specialized for sequen1al stages of food processing form the mammalian diges1ve system The mammalian diges1ve system consists of an alimentary canal and accessory glands that secrete diges1ve juices through ducts Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder Food is pushed along by peristalsis, rhythmic contrac1ons of muscles in the wall of the canal Valves called sphincters (muscles) regulate the movement of material between compartments Tongue Salivary glands Gallbladder Pancreas Small intestine Large intestine Rectum Anus Figure 41.9 Liver Oral cavity Pharynx Esophagus Sphincter Sphincter Stomach Duodenum of small intestine Mouth Esophagus Gallbladder Liver Pancreas Salivary glands Stomach Small intestine Large intestine Rectum Anus Schematic diagram The Oral Cavity, Pharynx, and Esophagus The first stage of diges1on is mechanical and takes place in the oral cavity Salivary glands deliver saliva to lubricate food Teeth chew food into smaller par1cles that are exposed to salivary amylase, ini1a1ng breakdown of glucose polymers Saliva also contains mucus, a viscous mixture of water, salts, cells, and glycoproteins 10

11 The tongue shapes food into a bolus and provides help with swallowing The throat, or pharynx, is the junc1on that opens to both the esophagus and the trachea The esophagus connects to the stomach The trachea (windpipe) leads to the lungs The esophagus conducts food from the pharynx down to the stomach by peristalsis Swallowing causes the epiglogs to block entry to the trachea, and the bolus is guided by the larynx, the upper part of the respiratory tract Coughing occurs when the swallowing reflex fails and food or liquids reach the windpipe Tongue Pharynx Glottis Larynx Figure Trachea Bolus of food Epiglottis up Esophageal sphincter contracted Esophagus To lungs To stomach Relaxed muscles Contracted muscles Diges1on in the Stomach The stomach stores food and secretes gastric juice, which converts a meal to acid chyme Sphincter relaxed Stomach 11

12 Chemical Diges%on in the Stomach Gastric juice has a low ph of about 2, which kills bacteria and denatures proteins Gastric juice is made up of hydrochloric acid (HCl) and pepsin Pepsin is a protease, or protein- diges1ng enzyme, that cleaves proteins into smaller pep1des Parietal cells secrete hydrogen and chloride ions separately into the lumen (cavity) of the stomach Chief cells secrete inac1ve pepsinogen, which is ac1vated to pepsin when mixed with hydrochloric acid in the stomach Mucus protects the stomach lining from gastric juice Figure Esophagus Sphincter Stomach 10 µm Gastric pits on interior surface of stomach Gastric gland Mucous cell Chief cell Sphincter Small intestine Epithelium Pepsinogen Pepsin 2 HCl Chief cell 1 Cl - H + 3 Folds of epithelial tissue Parietal cell Gastric ulcers, lesions in the lining, are caused mainly by the bacterium Heliobacter pylori Parietal cell 12

13 Stomach Dynamics Coordinated contrac1on and relaxa1on of stomach muscle churn the stomach s contents Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intes1ne Diges1on in the Small Intes1ne The small intes&ne is the longest sec1on of the alimentary canal It is the major organ of diges1on and absorp1on Oral cavity, pharynx, esophagus Figure Carbohydrate digestion Polysaccharides Disaccharides Salivary amylase Stomach Small intestine (enzymes from pancreas) Smaller Maltose polysaccharides Pancreatic amylases Disaccharides Protein digestion Proteins Pepsin Small polypeptides Pancreatic trypsin and chymotrypsin Smaller polypeptides Nucleic acid digestion DNA, RNA Pancreatic nucleases Nucleotides Fat digestion Fat (triglycerides) Pancreatic lipase The first por1on of the small intes1ne is the duodenum, where chyme from the stomach mixes with diges1ve juices from the pancreas, liver, gallbladder, and the small intes1ne itself Pancreatic carboxypeptidase Small peptides Glycerol, fatty acids, monoglycerides Small intestine (enzymes from epithelium) Disaccharidases Dipeptidases, carboxypeptidase, and aminopeptidase Nucleotidases Nucleosides Nucleosidases and phosphatases Monosaccharides Amino acids Nitrogenous bases, sugars, phosphates 13

14 Pancrea%c Secre%ons The pancreas produces proteases, trypsin and chymotrypsin, that are ac1vated in the lumen of the duodenum Its solu1on is alkaline and neutralizes the acidic chyme. Bile Produc%on by the Liver In the small intes1ne, bile aids in diges1on and absorp1on of fats Bile is made in the liver and stored in the gallbladder Bile also destroys nonfunc1onal red blood cells Secre%ons of the Small Intes%ne The epithelial lining of the duodenum produces several diges1ve enzymes Enzyma1c diges1on is completed as peristalsis moves the chyme and diges1ve juices along the small intes1ne Most diges1on occurs in the duodenum; the jejunum and ileum func1on mainly in absorp1on of nutrients and water Absorp1on in the Small Intes1ne The small intes1ne has a huge surface area, due to villi and microvilli that are exposed to the intes1nal lumen The enormous microvillar surface creates a brush border that greatly increases the rate of nutrient absorp1on Transport across the epithelial cells can be passive or ac1ve depending on the nutrient 14

15 Figure 41.13a Vein carrying blood to liver Figure 41.13b Villi Microvilli (brush border) at apical (lumenal) surface Lumen Blood capillaries Epithelial cells Muscle layers Intestinal wall Key Nutrient absorption Villi Large circular folds Epithelial cells Basal surface Lymph vessel Lacteal Key Nutrient absorption The hepa&c portal vein carries nutrient- rich blood from the capillaries of the villi to the liver, then to the heart The liver regulates nutrient distribu1on, interconverts many organic molecules, and detoxifies many organic molecules Epithelial cells absorb faqy acids and monoglycerides and recombine them into triglycerides These fats are coated with phospholipids, cholesterol, and proteins to form water- soluble chylomicrons Chylomicrons are transported into a lacteal, a lympha1c vessel in each villus Lympha1c vessels deliver chylomicron- containing lymph to large veins that return blood to the heart 15

16 Figure 41.14a Figure 41.14b LUMEN Triglycerides OF SMALL INTESTINE Epithelial cell Fatty acids Monoglycerides Phospholipids, cholesterol, and proteins Triglycerides Chylomicron Triglycerides Lacteal Absorp1on in the Large Intes1ne Figure The colon of the large intes&ne is connected to the small intes1ne The cecum aids in the fermenta1on of plant material and connects where the small and large intes1nes meet The human cecum has an extension called the appendix, which plays a very minor role in immunity Ascending portion of colon Small intestine Cecum Appendix 16

17 A major func1on of the colon is to recover water that has entered the alimentary canal The colon houses bacteria (e.g., Escherichia coli) which live on unabsorbed organic material; some produce vitamins Feces, including undigested material and bacteria, become more solid as they move through the colon Feces are stored in the rectum un1l they can be eliminated through the anus Two sphincters between the rectum and anus control bowel movements Concept 41.4: Evolu1onary adapta1ons of vertebrate diges1ve systems correlate with diet Diges1ve systems of vertebrates are varia1ons on a common plan However, there are intriguing adapta1ons, o_en related to diet Dental Adapta1ons Den11on, an animal s assortment of teeth, is one example of structural varia1on reflec1ng diet The success of mammals is due in part to their den11on, which is specialized for different diets Nonmammalian vertebrates have less specialized teeth, though excep1ons exist For example, the teeth of poisonous snakes are modified as fangs for injec1ng venom 17

18 Figure Carnivore Stomach and Intes1nal Adapta1ons Herbivore Omnivore Many carnivores have large, expandable stomachs Herbivores and omnivores generally have longer alimentary canals than carnivores, reflec1ng the longer 1me needed to digest vegeta1on Key Incisors Canines Premolars Molars Figure Mutualis1c Adapta1ons Small intestine Stomach Small intestine Many herbivores have fermenta1on chambers, where mutualis1c microorganisms digest cellulose The most elaborate adapta1ons for an herbivorous diet have evolved in the animals called ruminants Cecum Carnivore Colon (large intestine) Herbivore 18

19 Figure Rumen 2 Intestine Reticulum Esophagus Concept 41.5: Feedback circuits regulate diges1on, energy storage, and appe1te The intake of food and the use of nutrients varies with an animal s diet and environment 4 Abomasum 3 Omasum Regula1on of Diges1on Each step in the diges1ve system is ac1vated as needed The enteric division of the nervous system helps to regulate the diges1ve process The endocrine system also regulates diges1on through the release and transport of hormones Figure 41.19a 1 Liver Gallbladder Duodenum of small intestine Key + Stimulation - Inhibition Food Stomach Gastric juices Gastrin + Pancreas 19

20 Figure 41.19b Figure 41.19c 2 Bile 3 CCK + Chyme HCO 3 -, enzymes Secretin and CCK - Gastric juices Key + - Stimulation Inhibition Secretin + CCK + Key + Stimulation - Inhibition Regula1on of Energy Storage The body stores energy- rich molecules that are not needed right away for metabolism In humans, energy is stored first in the liver and muscle cells in the polymer glycogen Excess energy is stored in adipose 1ssue, the most space- efficient storage 1ssue Glucose Homeostasis Oxida1on of glucose generates ATP to fuel cellular processes The hormones insulin and glucagon regulate the breakdown of glycogen into glucose The liver is the site for glucose homeostasis A carbohydrate- rich meal raises insulin levels, which triggers the synthesis of glycogen Low blood sugar causes glucagon to s1mulate the breakdown of glycogen and release glucose 20

21 Figure Transport of glucose into body cells and storage of glucose as glycogen Breakdown of glycogen and release of glucose into blood Homeostasis: mg glucose/ 100 ml blood Stimulus: Blood glucose level rises after eating. Stimulus: Blood glucose level drops below set point. Pancreas secretes insulin. Pancreas secretes glucagon. Regula1on of Appe1te and Consump1on Overnourishment causes obesity, which results from excessive intake of food energy with the excess stored as fat Obesity contributes to diabetes (type 2), cancer of the colon and breasts, heart aqacks, and strokes Researchers have discovered several of the mechanisms that help regulate body weight Figure Satiety center Leptin - PYY - Insulin - Ghrelin + Hormones regulate long- term and short- term appe1te by affec1ng a sa1ety center in the brain Studies on mice revealed that the hormone lep&n plays an important role in regula1ng obesity Lep1n is produced by adipose 1ssue and can help to suppress appe1te 21

22 Figure Figure 41.22a EXPERIMENT Obese mouse with mutant ob gene (left) next to wild-type mouse RESULTS Genotype pairing (red type indicates mutant genes) Subject Paired with ob + ob +, db + db + ob + ob +, db + db + Average change in body mass (g) of subject 8.3 Obese mouse with mutant ob gene (left) next to wild-type mouse ob ob, db + db + ob ob, db + db ob ob, db + db + ob + ob +, db + db ob ob, db + db + ob + ob +, db db * *Due to pronounced weight loss and weakening, subjects in this pairing were reweighed after less than eight weeks. Figure 41.22b RESULTS Genotype pairing (red type indicates mutant genes) Subject Paired with ob + ob +, db + db + ob + ob +, db + db + ob ob, db + db + ob ob, db + db + ob ob, db + db + ob + ob +, db + db + ob ob, db + db + ob + ob +, db db Average change in body mass (g) of subject * Obesity and Evolu1on A species of birds called petrels become obese as chicks; in order to consume enough protein from high- fat food, chicks need to consume more calories than they burn *Due to pronounced weight loss and weakening, subjects in this pairing were reweighed after less than eight weeks. 22

23 Figure The problem of maintaining weight partly stems from our evolu1onary past, when fat hoarding was a means of survival Individuals who were more likely to eat faqy food and store energy as adipose 1ssue may have been more likely to survive famines Figure 41.UN01 Veins to heart Hepatic portal vein Lymphatic system Liver Mouth Stomach Esophagus Absorbed food (except lipids) Lipids Absorbed water Secretions from salivary glands Secretions from gastric glands Small intestine Secretions from liver Secretions from pancreas Anus Large Rectum intestine 23