Structure and Function

Constraints on Animal Body Plans

• All animals must perform several crucial functions:

  • Find food

  • Eliminate waste

  • Retain moisture and exchange gases

  • Retain heat

  • Repel parasites

Exchange Mechanisms

• Organisms can accomplish some functions via diffusion if their cells are in direct contact with the environment.

  • Limitations in complexity are noted.

    • Example: Single-celled organisms exchange materials effectively through direct contact with their environment (0.15 mm).

    • Multi-layered organisms (~1.5 m, two cell layers) have more complex requirements for nutrient and gas exchange.

Simple Animals and Diffusion

• Simple animals, such as flatworms, utilize diffusion because they have a high surface area to volume ratio for effective gas and nutrient exchange.

• Complex animals require specialized systems to:

  • Provide oxygen and nutrients to cells (e.g., alveoli in lungs).

Functional Systems in Animal Bodies

• Key systems involved in supporting life functions include:

  • Digestive system: responsible for nutrient absorption (e.g., lining of the small intestine).

  • Circulatory system: transports oxygen (O2) and carbon dioxide (CO2).

  • Respiratory system: exchanges gases.

  • Excretory system: eliminates waste (e.g., kidneys handling nitrogenous wastes).

Physical Constraints on Body Plans

• Movement efficiency through various mediums (water, land, air) imposes physical constraints on body designs.

• Form and function are interconnected at every level of biological organization.

  • Example: Enzyme specificity to metabolic pathways and the receptor-substrate relationship exemplify this correlation.

Questions on Structure & Function

• Characteristics of main tissue types:

• Definition and mechanism of homeostasis.

• Differences between endotherms and ectotherms.

• Methods of thermoregulation in animals.

Hierarchical Organization of Animals

• Cells: Basic units of life.

• Tissues: Groups of cells sharing common structure and function; four main types in mammals:

  • Epithelial

  • Muscle

  • Connective

  • Nervous

• Organs: Multiple tissues working together.

• Systems: Several organs functioning collaboratively.

Tissue Types Overview

Epithelial Tissue

• Sheets of cells covering exterior body, lining organs and cavities;

  • Cells are tightly packed with tight junctions for barrier function.

Nervous Tissue

• Composed of highly differentiated cells (neurons and glial cells).

• Functions in information relay to other tissues.

Connective Tissue

• Features sparse cells scattered within the extracellular matrix (mostly collagen).

  • Types include:

    • Loose connective (most widespread)

    • Fibrous connective (tendons and ligaments)

    • Bone (mineralized connective tissue)

    • Cartilage (collagen fibers in a rubbery matrix)

    • Blood (cells in a liquid matrix - plasma).

Muscle Tissue

• Contains myosin and actin filaments responsible for movement.

• Types:

  • Skeletal Muscle: Voluntary movement, attached to bones.

  • Smooth Muscle: Involuntary movement, found in walls of organs.

  • Cardiac Muscle: Located in the heart, features intercalated disks for coordinated contractions.

Homeostasis

• Integration of various systems necessary to maintain a steady state of internal conditions despite external changes (e.g., blood pH, body temperature).

• Mechanisms:

  • Regulators: Use internal mechanisms;

  • Conformers: Internal conditions change with environmental shifts (less energy required).

Thermoregulation Mechanisms

Endotherms vs. Ectotherms

• Endotherms: Generate most body heat through metabolism (e.g., birds, mammals). They maintain stable internal temperatures despite environmental changes.

• Ectotherms: Depend primarily on external sources for body heat (e.g., reptiles, amphibians). They can regulate temperature behaviorally but require less food due to lower metabolism.

Feedback Mechanisms

• Homeostasis is managed by feedback control loops.

  • Sensors detect deviations from the set point.

  • Responses are enacted to restore balance.

  • Positive feedback amplifies stimulus; negative feedback dampens stimulus.

Temperature Regulation

• Insulation methods: fat, hair, or feathers.

• Thermogenesis processes: shivering and non-shivering thermogenesis (heat production via mitochondria).

Heat Exchange Processes

• Evaporative Cooling: Heat loss from liquid converting to gas.

• Convection: Heat loss due to movement of air or liquid.

• Radiation and Conduction: Direct heat transfer from sun or surface.

Counter-Current Exchange Mechanism

• Blood flow system where warm blood going to extremities is positioned adjacently to returning cooled blood for heat retention.

Energy Conservation Strategies

• During tough times, decreasing metabolic rates saves energy.

• Torpor: A state of decreased activity/metabolism.

  • Daily torpor in small birds/mammals lowers body temperature by 10-15 degrees.

  • Seasonal torpor includes hibernation and estivation.