Bisc221-baudry Lecture22

Animal Nutrition Chapter 41 Nutritional Requirements Food types and Feeding Mechanisms Food Processing Mammalian Digestive System Evolutionary Adaptation of Vertebrate Digestive Systems

Nutritional Requirements Diet has to satisfy three needs: -fuel for all cellular work -Organic raw materials for biosynthesis -Essential nutrients

Essential role of ATP: -Powers basal metabolism, activity and temperature regulation (endotherms) -Derived from organic fuel molecules: -Carbohydrates -Proteins -Fats

Homeostatic mechanisms manage animal’ s fuel: -glucose regulation -Caloric imbalance -Obesity (role of leptin)

Figure 41.1 Homeostatic regulation of cellular fuel

Insulin stimulates glucose transport inside cells

Glucagon promotes breakdown of glycogen and release of glucose in blood

Figure 41.2 A ravenous rodent

Nutritional Requirements Diet has to satisfy three needs: -fuel for all cellular work -Organic raw materials for biosynthesis -Essential nutrients

Essential role of ATP: -powers basal metabolism, activity and temperature regulation (endotherms) -Derived from organic fuel molecules: -Carbohydrates -Proteins -Fats

Homeostatic mechanisms manage animal’ s fuel: -glucose regulation -Caloric imbalance -Obesity

Essential Nutrients: -Amino acids -Essential Fatty Acids, or Vitamins -Minerals

Figure 41.3 Obtaining essential nutrients

Essential Amino Acids -Animals require 20 amino acids -They can synthesize about 10 -Remaining 10 are “essential” and must be obtained from food -Diet insufficient in amino acids causes malnutrition and protein deficiency -Most reliable source of essential amino acids is meat -Most plant proteins are incomplete, i.e., lack essential amino acids; vegetarians need combination of plants “Essential” fatty acids: animals can synthesize most fatty acids; the few essential fatty acids are abundant in most diets (linoleic acid)

Figure 41.4 Essential amino acids from a vegetarian diet

Table 41.1 Vitamin Requirements of Humans: Water-Soluble Vitamins

Table 41.1 Vitamin Requirements of Humans: Fat-Soluble Vitamins

Table 41.2 Mineral Requirements of Humans

Food types and Feeding Mechanisms - Most animals are opportunistic feeders -Three diet categories: - Herbivores (gorillas, cows, snails) - Carnivores (sharks, hawks, spiders, snakes) - Omnivores (humans, crows, bears)

Diverse feeding adaptations: -Suspension feeders (clams, oysters, whales) -Substrate feeders (maggots, leaf miners, earthworms-deposit feeders) -Fluid feeders (mosquitoes, leech) -Bulk feeders (most animals)

Figure 41.6 Suspension-feeding: a baleen whale

Figure 41.7 Substrate-feeding: a leaf miner

Figure 41.8 Fluid-feeding: a mosquito

Figure 41.9 Bulk-feeding: a python

Food Processing Four main stages of food processing: -Ingestion: the act of eating -Digestion: breaking down food into small molecules by enzymatic hydrolysis -Absorption: transport of small molecules into cells -Elimination: elimination of undigested material Digestion takes place in specialized compartments: -Intracellular Digestion: food vacuoles fuse with lysosomes -Extracellular Digestion: - Gastrovascular cavities -Complete digestive tracts or alimentary canals (unidirectional)

Figure 41.10 Intracellular digestion in Paramecium

1: Food intake

2: Formation of food vacuoles

4 1 3: Transport 3

4: Digestion

5: Elimination

2

5

Figure 41.11 Extracellular digestion in a gastrovascular cavity

Figure 41.12 Alimentary canals

Mammalian Digestive System -Consists of alimentary canal plus various accessory glands -Peristalsis, or rhythmic waves of contraction, pushes the food -Junctions between specialized segments are called sphincters and regulate movement between segments -Glands are: -3 pairs of salivary glands -Pancreas -Liver -Gallblader

Figure 41.13 The human digestive system

Mammalian Digestive System -Consists of alimentary canal plus various accessory glands -Peristalsis, or rhythmic waves of contraction, pushes the food -Junctions between specialized segments are called sphincters and regulate movement between segments -Glands are: -3 pairs of salivary glands -Pancreas -Liver -Gallblader Initiation of food processing: -Oral cavity: chewing, grinding, secretion of saliva: -Saliva contains a glycoprotein, mucin, which serves as lubricant, plus buffers and antibacterial agents - It also contains amylase, an enzyme that hydrolyzes starch and glycogen -Tong manipulates food and shape the food into a ball called bolus -Pharynx: junction that opens to both esophagus and the trachea; swallowing reflex uses the epiglottis to close the glottis - Esophagus conducts food to the stomach by peristalsis

Figure 41.14 From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 1)

Figure 41.14 From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 2)

Figure 41.14 From mouth to stomach: the swallowing reflex and esophageal peristalsis (Layer 3)

The Stomach Stomach stores food and performs preliminary digestion: -Can stretch to store about 2 liters of food and fluid -Secretes gastric juice and mixes with food with smooth muscles -Gastric juice consists of: -HCl (pH 2.0), secreted by parietal cells -Pepsin (protease), secreted as pepsinogen by chief cells located in gastric pits -Stomach also secretes mucus to protect against self-digestion -Mitosis renews stomach lining every 3 days -Gastric ulcers are caused by an acid-tolerant bacterium

-As a result of mixing, the mixture becomes a broth called acid chyme -Most of the time, stomach is closed at both ends (backflow in esophagus is heartburn) -Pyloric sphincter regulates flow into the intestine

Figure 41.15 Secretion of gastric juice

The Small Intestine -Longest section of alimentary canal (6 m in humans) -First 25 cm is called duodenum: acid chyme is mixed with digestive juices from pancreas, liver, gallblader and gland cells in intestinal wall Enzymatic action in the small intestine: -Carbohydrate digestion: pancreatic amylases, disaccharidases (maltase, sucrase, lactase) -Protein digestion: proteases (trypsin, chymotrypsin), also dipeptidases, carboxypeptidases and aminopeptidases (many secreted in inactive form and require activation) -Nucleic acid digestion: nucleases -Fat digestion: fat insoluble in water, emulsification by bile salts from gallblader, then lipases -Absorption of small molecules in jejunum and ileum Absorption of nutrients: -Trough the epithelium of small intestine (huge surface area, 300 m2) and specific structures, called villi and microvilli -Each villus is irrigated by a net of microvessels (capillaries) and vessels of lymphatic system, called lacteal -Transport of some nutrients is passive (diffusion down concentration gradient) -Other nutrients are actively transported against concentration gradient -Fats are absorbed by epithelial cells, mixed with cholesterol, and coated with proteins to form chylomicrons, and transported in lacteal, before reaching blood veins. - Capillaries converge into the hepatic portal vessel ----> liver Very efficient system: 80-90% of the organic matter is absorbed, the rest eliminated

Figure 41.16 The duodenum

Figure 41.17 Enzymatic digestion in the human digestive system

Figure 41.18 Activation of protein-digesting enzymes in the small intestine

Figure 41.19 The structure of the small intestine

Figure 41.x1 Large intestine

Hormones regulate digestion -Gastrin: secreted by stomach wall into circulation and stimulates secretion of gastric juice -Enterogastrones: secreted by wall of duodenum: -Secretin: stimulates release of bicarbonate from pancreas (neutralizes HCl) -Cholecystokinin (CCK): stimulates bile release from gallblader Large intestine (colon) reclaims water: -T-shaped junction between small and large intestines: one arm is the cecum with a finger-like extension, the appendix, the other branch the colon (1.5 m) -Water is reabsorbed in small and large intestine -Waste (feces) move in 12-24 hrs -Rich flora of harmless bacteria lives in large intestine: they produce gases and vitamins

Terminal portion is the rectum

Evolutionary Adaptation of Vertebrate Digestive Systems

-Structural adaptations are associated with diet -Dentition in mammals (compare teeth from carnivores, herbivores and omnivores) -Large expendable stomachs in carnivores (rare meals) -Length of digestive system (carnivores vs herbivores/omnivores) -Symbiotic microorganisms in herbivores -Specific adaptations in ruminants

Figure 41.20 Dentition and diet

Figure 41.21 The digestive tracts of a carnivore (coyote) and a herbivore (koala) compared

Figure 41.22 Ruminant digestion