Animal Nutrition and Physiology

Animal Nutrition

  • Need to Feed
    • An animal's diet must supply three key components:
    • Chemical energy: converted into ATP to power processes in the body
    • Organic molecules: required for constructing organic compounds
    • Essential nutrients: specific nutrients necessary for cellular function that must be obtained from dietary sources

Classification of Animals Based on Diet

  • Herbivores:
    • Primarily consume autotrophs (plants, algae).
  • Carnivores:
    • Primarily consume other animals.
  • Omnivores:
    • Consume both plants and animals.

Essential Nutrients

  • Essential nutrients are classified into four categories:
    • Amino Acids:
    • Animals require 20 amino acids, can synthesize about half from dietary molecules.
    • The remainder, known as essential amino acids, must be ingested in preassembled form.
    • Inadequate intake leads to malnutrition termed protein deficiency.
    • Complete proteins (e.g., meat, eggs, cheese) contain all essential amino acids; most plant proteins are incomplete.
    • Fatty Acids:
    • Animals can synthesize most fatty acids but must ingest certain unsaturated fatty acids (essential fatty acids) from their diet.
    • Deficiency in fatty acids is rare.
    • Vitamins:
    • Organic molecules required in small amounts for various functions, often acting as cofactors or coenzymes in enzymatic reactions.
    • There are 13 essential vitamins grouped into fat-soluble and water-soluble categories.
    • Minerals:
    • Simple inorganic nutrients required in small amounts for various physiological functions, including structural roles and enzyme activity.

Dietary Deficiencies

  • Undernourishment:
    • Results from consistently insufficient chemical energy intake.
    • Effects include the use of stored fat and carbohydrates, breakdown of proteins, muscle mass loss, and potential irreversible damage to critical organs.
  • Malnourishment:
    • Long-term absence of one or more essential nutrients can lead to deformities, disease, or death; improvement requires dietary adjustment.

Food Processing Stages

  1. Ingestion:
    • Act of eating.
  2. Digestion:
    • Breaking down food into absorbable molecules via mechanical (chewing) and chemical (enzymatic) processes.
  3. Absorption:
    • Uptake of nutrients into body cells.
  4. Elimination:
    • Removal of undigested material.

Digestive Compartments

  • Animals utilize specialized compartments to process food, mitigating risks of self-digestion.
  • Intracellular Digestion:
    • Engulfing food particles through phagocytosis, utilizing food vacuoles and lysosomal enzymes.
  • Extracellular Digestion:
    • Breakdown of food externally before absorption, occurring in compartments like alimentary canals.

Mammalian Digestive System Composition

  • Alimentary Canal:
    • Continuous with the exterior, includes various organs for digestion.
  • Accessory Glands:
    • Salivary glands, pancreas, liver, and gallbladder, each secreting digestive juices into the alimentary canal.

Stages of Digestion

Oral Cavity, Pharynx, and Esophagus

  • Mechanical Digestion:
    • Teeth chew food, mixed with saliva containing salivary amylase that initiates carbohydrate breakdown.
  • Swallowing Mechanism:
    • Tongue forms food into a bolus; pharynx leads to esophagus (for food) and trachea (for air).

Stomach

  • Storage and Digestion:
    • Stores food, and gastric juice is secreted, converting food to chyme.
    • Gastric juice (pH 2) comprises hydrochloric acid and pepsin (a protease).
    • Epiglottis Function:
    • Blocks trachea during swallowing.

Small Intestine

  • Major Site for Digestive Activity:
    • Chyme mixes with bile and pancreatic juices primarily in the duodenum.
    • Absorption:
    • Nutrient absorption occurs through villi and microvilli significantly increasing surface area for nutrient uptake.

Pancreatic and Bile Secretions

  • Enzyme Activation:
    • Pancreas produces digestive enzymes (e.g., proteases) activated in the lumen of the small intestine; alkaline solution neutralizes chyme.
  • Bile:
    • Aids in fat digestion; produced by the liver and stored in gallbladder.

Absorption Process

Absorption in the Small and Large Intestine

  • Villi and Microvilli:
    • Enhance absorption due to increased surface area.
  • Capillary Networks:
    • Nutrient-rich blood travels through the hepatic portal vein to the liver.
  • Functions of Large Intestine:
    • Water recovery and housing of bacteria.
    • Formation and storage of feces until elimination.

Comparative Anatomy of Digestive Systems

  • Vertebrate Adaptations:
    • Various digestive systems reflect dietary habits, including differences in dentition.
    • Herbivores possess longer alimentary canals for digesting plant material.
  • Dentition Adaptations:
    • Carnivorous species possess sharp teeth, while herbivores have flat molars for grinding.

Mutualistic Relationships in Digestion

  • Animals host billions of bacteria, aiding in digestion and nutrient absorption.
    • Changes in gut microbiome can influence overall health and nutrient metabolism.

Excretion of Nitrogenous Waste

Types of Nitrogenous Wastes

  • Ammonia:
    • Very toxic, requires large amounts of water for excretion.
  • Urea:
    • Less toxic form; most terrestrial mammals excrete urea due to limited water availability.
  • Uric Acid:
    • Relatively non-toxic; requires even less water for excretion, common in birds and reptiles.

Excretory Processes Overview

  • Functionality:
    • Nitrogenous waste processing involves filtration, reabsorption, and secretion.
  • Kidneys:
    • Specialized systems that regulate excretion and osmoregulation through nephron units.

Urine Formation Steps

  1. Filtration at the Glomerulus:
    • Blood filtrate formation through Bowman's Capsule.
  2. Reabsorption and Secretion:
    • In proximal tubules, ions and molecules are transport actively/passively into capillaries.
  3. Collecting Duct Action:
    • Further concentration of urine occurs before excretion.

Regulation of Circulation and Gas Exchange

Circulatory Systems Overview

  • Exchange Surfaces:
    • Circulatory systems link environmental exchange (gases, nutrients) to cellular function.
    • Simplistic organisms may rely on diffusion; complex animals utilize specialized systems for efficient transport.

Closed vs Open Circulatory Systems

  • Closed Circulatory Systems:
    • Blood confined to vessels; more efficient for active animals.
  • Open Circulatory Systems:
    • Blood mixes with interstitial fluid (hemolymph); lower pressure, less efficient.

Evolutionary Adaptations of Circulatory Systems

  • Single Circulation:
    • Bony fishes with two-chambered hearts aim for efficient oxygen delivery post-gill.
  • Double Circulation:
    • Birds and mammals possess four-chambered hearts, separating oxygenated and deoxygenated blood pathways.

Gas Exchange Mechanisms

  • Respiratory Surfaces:
    • Large, moist surfaces like gills or lungs facilitate gas exchange through diffusion.

Gills in Aquatic Animals

  • Gills utilize countercurrent exchange systems for optimal oxygen uptake.

Lungs in Terrestrial Animals

  • Lungs are extensive infoldings of the body surface; air is delivered via respiratory pathways.

Regulation of Breathing

  • Control Centers:
    • Medulla oblongata regulates breathing rate sensitive to CO2 and pH levels.

Hormones and Endocrine System

Intercellular Communication

  • Hormones act as regulators, reaching target cells through bloodstream, only affecting those with specific receptors.

Endocrine Signaling Types

  • Endocrine Signaling: Long-distance communication through hormones.
  • Paracrine and Autocrine Signaling: Local actions where target cells are near the secreting cell.
  • Synaptic Signaling: Neurons transmit signals via neurotransmitters at synapses.

Endocrine Tissues and Organs

  • Specialized endocrine glands, such as the thyroid, pituitary, and adrenal appropriate physiological responses through hormones.

Feedback Regulation within Endocrine Pathways

  • Negative Feedback: Reduces system's output, maintaining homeostasis.
  • Positive Feedback: Enhances responses for rapid changes in hormone levels.

Hormones and Biological Rhythms

  • Melatonin release from the pineal gland regulates circadian rhythms in response to light cycles.

Neuron and Synapse Communication

Neuron Structure and Function

  • Neurons communicate using electrical (action potentials) and chemical (neurotransmitters) signals.

Action Potentials Overview

  • Triggered by depolarization at the axon hillock; propagate signals in one direction along the axon.

Synaptic Transmission Process

  1. Presynaptic neuron releases neurotransmitters into synaptic cleft.
  2. Binding alters postsynaptic cell membrane potential, generating EPSPs or IPSPs.

Integration of Signals

  • Summation of EPSPs and IPSPs determines whether an action potential is generated (temporal and spatial summation).

Neurotransmitter Types

  • Categories include amino acids, biogenic amines, neuropeptides, and gases.

Neurotransmitter Functions

  • Facilitate communication across synapses; involved in various physiological processes including pain perception and arousal.

The Structure of the Nervous System

Central Nervous System (CNS) vs Peripheral Nervous System (PNS)

  • CNS comprises brain and spinal cord; PNS is composed of nerves and ganglia, transmitting signals between CNS and body.

Vertebrate Brain Structure

  • The vertebrate brain is regionally specialized with forebrain, midbrain, and hindbrain.

Learning and Memory

  • Involves neural plasticity, where changes in synaptic connections underlie the formation and consolidation of memory.

Evolution of Cognition

  • Neuronal organization in the vertebrate brain supports the sophisticated processing of information, relevant for survival and social interaction.