Lecture 13 Outline (Ch. 41) I.Animal Nutrition Overview II.Food Intake III.Digestive Compartments IV.Adaptations V.Energy sources and stores VI. Summary

What is/are the overall function(s) digestion?

3 Overview: The Need to Feed Food is taken in, taken apart, and taken up in the process of animal nutrition In general, animals fall into three categories: – Herbivores eat mainly autotrophs (plants, algae) – Carnivores eat other animals – Omnivores regularly consume animals as well as plants or algal matter

4 Meat, eggs, cheese - provide all nine essential amino acids ( “complete” proteins) Individuals eating only plant proteins need specific plant combinations for all essential amino acids Essential Parts of Diet Beans and other legumes Corn (maize) and other grains Lysine Essential amino acids for adults Tryptophan Isoleucine Leucine Phenylalanine Threonine Valine Methionine

5 Animals can synthesize most fatty acids they need The essential fatty acids are certain unsaturated fatty acids that must be obtained from the diet Essential Parts of Diet Vitamins: organic molecules needed in small amounts 13 essential vitamins for humans Fat-soluble & water-soluble B-complex Biotin/B 7 Vitamin C (ascorbic acid) Vitamin A Vitamin D Vitamin E Vitamin K

6 Minerals Minerals: inorganic nutrients, small amounts needed Calcium Phosphorus Potassium Sulfur Chlorine Sodium Magnesium Iron A diet missing a certain essential part or not enough calories overall leads to malnourishment or undernourishment

If a person is following a vegan diet, why is it recommended to eat a variety of plant sources? Remember, these are the parts of diet: Chemical energy (converted to ATP) Organic carbon and nitrogen Essential nutrients must be obtained

8 Ingestion: the act of eating Suspension feeders - many aquatic animals, which sift small food particles from the water Substrate feeders are animals that live in or on their food source Fluid feeders suck nutrient-rich fluid from a living host Bulk feeders eat relatively large pieces of food Food Intake

9 Humpback whale, a suspension feeder Baleen Leaf miner caterpillar, substrate feeder Caterpillar Feces Mosquito, a fluid feeder Rock python, a bulk feeder

Label each region of the digestive tract below: What are the function(s) of each region?

IngestionDigestion Absorption Elimination Undigested material Chemical digestion (enzymatic hydrolysis) Nutrient molecules enter body cells Small molecules Mechanical digestion Food Pieces of food Food Intake Digestion: process of breaking food down into molecules small enough to absorb. In chemical digestion, enzymatic hydrolysis splits bonds in molecules Absorption is uptake of nutrients by body cells Elimination is the passage of undigested material out of the digestive compartment

12 Digestive Compartments Most animals process food (i.e. hydrolysis) in specialized compartments Reduces risk animal digesting its own cells/ tissues Gastrovascular cavity Food Epidermis Mouth Tentacles Gastrodermis Gastrovascular Cavity: For both digestion and distribution of nutrients Cells secrete digestive enzymes

13 More complex animals: digestive tube with two openings (mouth, anus) “Tube within a tube” Called alimentary canal Specialized regions, carry out digestion and absorption stepwise Digestive Compartments Esophagus Mouth Pharynx CropGizzard Typhlosole Intestine Lumen of intestine Anus (b) Grasshopper Foregut (c) Bird (a) Earthworm MidgutHindgut Esophagus Rectum Anus Mouth Crop Gastric cecae Esophagus Mouth Crop Anus Stomach Gizzard Intestine

14 Cecum Anus Ascending portion of large intestine Gall- bladder Small intestine Large intestine Small intestine Rectum Pancreas Liver Salivary glands Tongue Oral cavity Pharynx Esophagus Sphincter Stomach Sphincter Duodenum of small intestine Appendix Liver Pancreas Small intestine Large intestine Rectum Stomach Gall- bladder A schematic diagram of the human digestive system Esophagus Salivary glands Mouth Digestive Compartments Mammalian alimentary canal and accessory glands that secrete digestive juices through ducts Food moves by peristalsis

15 Larynx Trachea Pharynx Tongue Esophagus Food To stomach To lungs Epiglottis down Esophageal sphincter relaxed Epiglottis up Sphincter relaxed Relaxed muscles Contracted muscles Relaxed muscles Stomach Oral Cavity, Pharynx, Esophagus Food  bolus, saliva added, digestion begins with amylase and mucus Pharynx, junction opens to both the esophagus and the trachea (windpipe) Esophagus conducts food pharynx to stomach by peristalsis Epiglottis blocks entry to the trachea, and larynx.

16 Digestion in the Stomach The stomach stores food and secretes gastric juice, which converts a meal to acid chyme Highly folded Gastric juice - hydrochloric acid (parietal cells) and the enzyme pepsin (chief cells) Pepsin initially secreted as pepsinogen Mucus protects the stomach lining from gastric juice Esophagus Small intestine Epithelium Stomach Sphincter Parietal cell Chief cell Folds of epithelial tissue Pepsin Sphincter Pepsinogen HCl H+H+ Cl – Mucus cells Gastric gland µm

17 Digestion in the Small Intestine The small intestine: longest section of alimentary canal Major organ of enzymatic digestion and absorption 1 st : duodenum -acid chyme from stomach mixes with digestive juices from pancreas, liver, gallbladder, and the small intestine itself. -2 nd : jejunum -3 rd : ileum

18 Digestion in the Small Intestine liver/gallbladder bile aids digestion and absorption of fats small intestine lining of duodenum (brush border) produces several digestive enzymes jejunum and ileum mainly absorb water & nutrients pancreas proteases trypsin & chymotrypsin amylase & lipase bicarbonate neutralizes the acidic chyme

19 Fat digestionNucleic acid digestion Protein digestion Fat (triglycerides) DNA, RNA Nucleotides Pancreatic nucleases Pancreatic lipase Glycerol, fatty acids, monoglycerides Nucleotidases Nucleosides Nucleosidases and phosphatases Nitrogenous bases, sugars, phosphates Amino acids Dipeptidases, carboxy- peptidase, and aminopeptidase Small peptides Pancreatic carboxypeptidase Smaller polypeptides Pancreatic trypsin and chymotrypsin Small polypeptides Proteins Pepsin Carbohydrate digestion PolysaccharidesDisaccharides Salivary amylase Smaller polysaccharides Maltose Pancreatic amylases Disaccharides Disaccharidases Monosaccharides Small intestine (enzymes from epithelium) Small intestine (enzymes from pancreas) Stomach Oral cavity, pharynx, esophagus

20 Absorption in the Large Intestine The colon of the large intestine is connected to the small intestine Feces stored in rectum until eliminated The cecum aids in fermentation of plant material, - connects where the small and large intestines meet Human cecum extension (appendix), -minor role in immunity

Here’s our generalized digestive tract again: What are the secretions and purpose from each region listed below: Mouth & teeth Esophagus Stomach Small intestine Large intestine

22 The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins Two sphincters between the rectum and anus control bowel movements –Internal smooth muscle sphincter (involuntary) –External striated muscle sphincter (voluntary) Absorption in the Large Intestine

23 Mutualistic Adaptations Many herbivores have symbiotic microorganisms that digest cellulose The most elaborate adaptations in ruminants Esophagus Omasum Abomasum Intestine Rumen Reticulum

24 Herbivores generally longer alimentary canals than carnivores; longer time needed to digest vegetation Coprophagy – method to recover more nutrients by ingesting feces Cecum Small intestine HerbivoreCarnivore Colon (large intestine) Stomach Small intestine Adaptations Enzymes for digesting plant matter

Homeostasis: 90 mg glucose/ 100 mL blood Stimulus: Blood glucose level rises after eating. Stimulus: Blood glucose level drops below set point. Energy Sources and Stores Pancreas releases insulin – cells uptake sugars Pancreas releases glucagon – liver releases sugars

If you eat a meal high in sugar, what happens? Describe the steps including changes in blood sugar and changes in hormones.

27 Energy Sources and Stores Animals store excess calories as glycogen in the liver and muscles Energy secondarily stored as adipose, or fat, cells Fewer calories taken in than expended  fuel is taken from storage and oxidized 100 µm Fat cells Excessive intake of food energy, excess stored as fat Obesity contributes to diabetes (type 2), colon and breast cancer, heart attacks, and strokes

28 Leptin PYY Insulin Ghrelin Energy Sources and Stores The complexity of weight control in humans is well- studied Mice that inherit a defect in the gene for leptin become very obese Ghrelin – secreted by stomach, stimulates appetite Insulin – secreted by pancreas, suppresses appetite Leptin – released by fat cells, suppresses appetite PYY – secreted by Sm. Intestine, suppresses appetite hypothalamus

29 Obese mouse with mutant ob gene (left) – mutant for leptin production – next to wild-type sibling mouse.

The gene db codes for the leptin receptor. If mice are mutant for the db gene what happens? 1.They fail to make leptin – increased appetite 2.They fail to detect leptin – decreased appetite 3.They fail to detect leptin – increased appetite 4.They fail to make leptin – decreased appetite