Animal Nutrition

Chapter 33 - Animal Nutrition

Overview: The Need to Feed

  • Animal Nutrition Process:

    • Food is taken in, taken apart, and taken up.

    • Animals categorized into three groups based on diet:

    • Herbivores: Primarily consume plants and algae.

    • Carnivores: Mainly eat other animals.

    • Omnivores: Regularly consume both animals and plants or algae.

    • Most animals are opportunistic feeders.

Concept 33.1: Dietary Requirements

  • An animal's diet must provide essential resources:

    • Chemical Energy: Converted into ATP to power cellular processes.

    • Organic Molecules:

    • Organic carbon and nitrogen are needed to synthesize various organic molecules.

    • Essential Nutrients: Required by cells, must be obtained from food sources.

Essential Nutrients

  • Definition: Essential nutrients are those that an animal cannot synthesize and must be obtained through diet.

  • Four classes of essential nutrients:

    1. Essential Amino Acids

    2. Essential Fatty Acids

    3. Vitamins

    4. Minerals

Essential Fatty Acids and Amino Acids

  • Animals require 20 amino acids, synthesizing about half from dietary molecules. The rest, known as essential amino acids, must be obtained from food.

  • Fatty acids play vital roles in cellular components:

    • Membrane phospholipids, signaling molecules, storage fats.

  • Essential fatty acids cannot be synthesized by animals but can be produced by plants.

  • Animals usually obtain sufficient essential fatty acids through their diet.

Vitamins

  • Definition: Organic molecules needed in small quantities.

  • Essential Vitamins for Humans:

    • Total: 13 essential vitamins.

  • Vitamins categorized into two types:

    • Fat-soluble: Stored in the body (A, D, E, K).

    • Water-soluble: Not stored and need regular replenishment (C, B-complex).

Minerals

  • Definition: Simple inorganic nutrients required in small amounts.

  • Health Concerns: Excessive ingestion of some minerals can impair health.

Dietary Deficiencies

  • Malnutrition: Resulting from long-term absence of essential nutrients from diet.

  • Consequences of Deficiency:

    • Can cause deformities, diseases, and death.

    • Animals may consume salt, minerals, shells, or stones to prevent deficiencies.

  • Common malnutrition type among humans due to insufficient amino acids.

    • Example: Individuals consuming simple rice diets may lack vitamin A.

    • Solution: Genetic engineering to produce strains of rice that synthesize beta-carotene, which converts to vitamin A.

Undernourishment

  • Arises when diet lacks sufficient chemical energy, leading to:

    • Usage of stored fat and carbohydrates.

    • Breakdown of proteins, loss of muscle mass.

    • Possible brain protein deficiency.

    • Can result in death or irreversible damage.

Concept 33.2: Food Processing

  • Four stages involved in food processing:

    1. Ingestion

    2. Digestion

    3. Absorption

    4. Elimination

Ingestion

  • The act of eating or feeding.

  • Strategies for resource extraction from food vary widely among animals.

Digestion

  • Definition: Breaking down food into absorbable molecules.

  • Mechanical Digestion: Includes chewing; increases surface area for digestion.

  • Chemical Digestion: Splits food into smaller molecules via enzymatic hydrolysis.

Absorption

  • Uptake of nutrients by body cells.

Elimination

  • The process of expelling undigested material from the digestive system.

Digestive Compartments

  • Specialized compartments in most animals help in food processing and prevent the digestion of own cells and tissues.

Intracellular Digestion

  • Involves engulfing food particles through phagocytosis.

  • Food vacuoles that contain food fuse with lysosomes containing hydrolytic enzymes to break down the particles.

Extracellular Digestion

  • Definition: Breakdown of food particles outside the cells, occurring in compartments that are continuous with the external environment.

  • Simple animals possess a gastrovascular cavity for digestion and nutrient distribution.

  • Complex animals have a complete digestive tract (alimentary canal) with distinct mouth and anus.

  • The alimentary canal may include specialized regions for digestion and absorption in sequential order.

Concept 33.3: The Mammalian Digestive System

  • Composed of an alimentary canal and accessory glands that secrete digestive juices via ducts.

  • Accessory Glands:

    • Salivary glands

    • Pancreas

    • Liver

    • Gallbladder

The Oral Cavity, Pharynx, and Esophagus

  • Mechanical Digestion: Begins in the oral cavity with the help of salivary glands that deliver saliva.

  • Teeth: Chew food and expose it to salivary amylase to initiate glucose polymer breakdown.

  • Components of Saliva: Mucus (water, salts, glycoproteins, cells) allows easy swallowing.

  • Tongue: Shapes food into a bolus.

  • Throat (Pharynx): Junction opening to both esophagus and trachea.

  • Esophagus: Connects to the stomach; moves food through peristalsis (rhythmic muscle contractions).

  • Sphincters: Valves managing the movement of materials between compartments.

Digestion in the Stomach

  • Stores food and secretes gastric juice.

  • Chyme: Mixture of food and digestive juice from digestion.

Chemical Digestion in the Stomach

  • Gastric juice pH = 2; denatures proteins and kills bacteria.

  • Key Components:

    • Hydrochloric acid (HCl)

    • Pepsin: A protease enzyme that cleaves proteins into smaller peptides.

  • Mucus: Protects stomach lining from damage by gastric juice.

  • New epithelial cells are regenerated every three days.

  • Gastric Ulcers: Caused primarily by the bacterium Helicobacter pylori.

Stomach Dynamics

  • Coordinated muscle contractions mix stomach contents.

  • Sphincters control chyme release into the small intestine after 2–6 hours post-meal.

Digestion in the Small Intestine

  • Structure: Longest section of the alimentary canal, primary organ for digestion and absorption.

  • Duodenum: First segment where chyme from the stomach mixes with digestive juices from pancreas, liver, gallbladder, and intestinal wall.

Pancreas Functions

  • Produces proteases (e.g., trypsin, chymotrypsin) activated in the duodenum.

  • Secretes alkaline solutions that neutralize acidic chyme.

Bile and Fat Digestion

  • Bile: Produced by the liver; stored in the gallbladder to aid in fat digestion and absorption by emulsifying fat droplets.

Absorption in the Small Intestine

  • Large surface area due to villi and microvilli enhances nutrient absorption.

  • Transport can be passive or active depending on nutrient type.

Hepatic Portal Vein

  • Transports nutrient-rich blood from the villi capillaries to the liver, which regulates nutrient distribution and detoxifies substances.

Absorption of Fats

  • Bile salts emulsify dietary fats allowing lipase enzymes to convert triglycerides into fatty acids and monoglycerides.

  • Epithelial cells reassemble fatty acids and monoglycerides into triglycerides, packaged into chylomicrons for transport in the lymphatic system.

Processing in the Large Intestine

  • Cecum: Aids in plant material fermentation; includes appendix (minor role in immunity).

  • Major Function of Colon: Recovery of water from the alimentary canal; harbors bacteria (e.g., Escherichia coli) for organic material fermentation and vitamin production.

  • Feces consist of undigested materials and bacteria.

  • Stored in the rectum until eliminated through the anus.

Overview of the Mammalian Digestive System

  • Blood and lymphatic vessels transport absorbed nutrients, maintaining the body's metabolic needs.

Concept 33.4: Evolutionary Adaptations of Vertebrate Digestive Systems

  • Digestive systems have evolved structural adaptations related to varying diets.

Dental Adaptations

  • Dentition: Refers to the variety of teeth in animals reflecting their dietary needs.

  • Mammal Success: Due to specialized dentition; nonmammalian vertebrates generally have less specialized teeth, with exceptions.

Stomach and Intestinal Adaptations

  • Carnivores often possess large, expandable stomachs; herbivores/omnivores feature longer alimentary canals due to the need for prolonged digestion.

Mutualistic Adaptations

  • Herbivores often possess fermentation chambers in their digestive tracts with bacteria and protists that digest cellulose.

  • Human Microbiome: Collective bacteria in the digestive system; imbalance can lead to infections (e.g., elimination by H. pylori).

Concept 33.5: Feedback Circuits Regulating Digestion and Energy Allocation

  • Digestion and nutrient intake are closely regulated to meet physiological needs.

Regulation of Digestion

  • Digestive steps activate based on necessity.

  • Enteric nervous system aids in digestion regulation, along with hormones.

Energy Allocation

  • Bioenergetics: Flow and transformation of energy determine nutritional needs.

  • Metabolic Rate: Energy use per time, assessable by heat loss, O2 consumption, or CO2 production.

Minimum Metabolic Rate

  • Essential to maintain basic cellular functions.

  • Basal Metabolic Rate (BMR): Minimum rate for resting, nongrowing endotherms with an empty stomach.

  • Standard Metabolic Rate (SMR): For fasting ectotherms at a specific temperature.

Energy Storage Regulation

  • Excess energy intake is stored, initially in liver/muscle cells as glycogen, followed by fat in adipose cells as glycogen stores deplete during energy deficit.

Regulation of Blood Glucose

  • Coordination of insulin and glucagon secretion manages blood sugar levels to maintain homeostasis.

Diabetes Mellitus

  • Condition resulting from insulin deficiency or insensitivity leading to inadequate glucose uptake and reliance on fat as an energy source.

  • Type 1 diabetes: Autoimmune destruction of pancreatic beta cells.

  • Type 2 diabetes: Insulin resistance characteristic, influenced by genetics, body weight, and lifestyle factors.

Regulation of Appetite and Consumption

  • Overnourishment: Leads to obesity, associated with health issues (e.g., type 2 diabetes, certain cancers, cardiovascular diseases).

  • Key hormones influencing appetite include:

    • Ghrelin: Hunger signal from the stomach.

    • Insulin and PYY: Suppress appetite post-meal.

    • Leptin: Produced by adipose tissue; regulates appetite and body fat levels.