Animal Form and Function: Biology

• Form and function are correlated at all levels of biological organization.

Animal Form and Function

• Animal anatomy studies the structure of animal bodies.
• Animal physiology studies the function of animal bodies.
• Anatomy and physiology are related; function follows form.

Evolution of Animal Size and Shape

• Physical laws constrain animal size and shape.
  • Body plans must facilitate sufficient environmental exchange.
  • Increasing body dimensions necessitate thicker skeletons for support.

Exchange with the Environment

• An animal's size and shape directly impact energy and material exchange with its surroundings.
• Exchange occurs as substances in aqueous solution move across the plasma membrane of each cell.
• Single-celled organisms have sufficient membrane surface area for all necessary exchange.
• Multicellular organisms with saclike body plans have thin body walls (two cells thick) to facilitate diffusion.
• Complex organisms have highly folded internal surfaces for material exchange.
• Increased surface area allows for increased exchange.

Tissues

• Animal tissues are groups of cells with similar appearance and function.
• Four main tissue types exist: epithelial, connective, muscle, and nervous.

Epithelial Tissue

• Epithelial tissue covers the body's exterior and lines organs/cavities.
• Cells are closely joined within this tissue type.
• Epithelial cell shapes include cuboidal (dice-like), columnar (brick-like), and squamous (flat tiles).
• Epithelial cell arrangement may be simple (single layer) or stratified (multiple layers).
• Epithelial tissue acts as a barrier against injury, pathogens, and fluid loss.
• It forms active interfaces with the environment.

Connective Tissue

• Connective tissue primarily binds and supports other tissues.
• It features sparsely packed cells within an extracellular matrix.
• The matrix consists of fibers in a liquid, jellylike, or solid foundation.
• Three types of protein fibers exist within connective tissue:
  • Collagenous fibers provide strength and flexibility.
  • Elastic fibers stretch and return to their original length.
  • Reticular fibers connect connective tissue to adjacent tissues.
• Types of cells found in connective tissues:
  • Fibroblasts secrete the protein of extracellular fibers.
  • Macrophages participate in the immune system.
• Six major connective tissue types:
  • Loose connective tissue binds epithelia to underlying tissues and holds organs in place.
  • Cartilage provides strong and flexible support.
  • Fibrous connective tissue is in tendons (muscle-to-bone) and ligaments (bone-to-bone).
  • Adipose tissue stores fat for insulation and fuel
  • Blood consists of blood cells and cell fragments in blood plasma.
  • Bone is mineralized and forms the skeleton.

Muscle Tissue

• Muscle tissue facilitates nearly all types of body movement.
• Muscle cells contain actin and myosin filaments that enable contraction.
• Three types of muscle tissue:
  • Skeletal muscle (striated muscle) enables voluntary movement.
  • Smooth muscle controls involuntary body activities.
  • Cardiac muscle facilitates heart contraction.

Nervous Tissue

• Nervous tissue functions to receive, process, and transmit information.
• Nervous tissue components:
  • Neurons (nerve cells) transmit nerve impulses.
  • Glial cells (glia) nourish, insulate, and replenish neurons.

Coordination and Control

• The endocrine and nervous systems coordinate and control bodily functions.
• The endocrine system uses blood to transmit chemical signals (hormones) to receptive cells.
• Hormones can impact one or more regions throughout the body.
• Hormones act relatively slowly but can have long-lasting effects.
• The nervous system transmits information between specific locations.
• Information transmitted relies on the signal pathway.
• Nerve signal transmission is very rapid.
• Neurons, muscle cells, and endocrine cells can receive nerve signals.

Regulating the Internal Environment

• Animals manage their internal environment by regulating or conforming to it.

Regulators and Conformers

• Regulators use internal regulation to control internal change, regardless of external fluctuation.
• Conformers allow their internal conditions to vary with external changes.

Homeostasis

• Homeostasis maintains internal balance.
• Fluctuations above or below a set point act as a stimulus in homeostasis.
• Sensors detect stimuli and trigger a response.
• The response returns the variable to the set point.
• Homeostasis is achieved by maintaining variables at or near a specific set point.

Mechanisms of Homeostasis

• Homeostasis relies on negative feedback to return a variable to a normal range.
• Positive feedback amplifies a stimulus and typically does not contribute to homeostasis.
• Acclimatization is the process when homeostasis adjusts to environmental changes.

Thermoregulation

• Thermoregulation is the process by which animals maintain internal temperature within a tolerable range.
• Enzymes function optimally within a specific temperature range.

Ectotherms and Endotherms

• Endothermic animals generate heat through metabolism.
• Ectothermic animals gain heat from external sources.
• Endothermy is more energetically expensive than ectothermy.
• Ectotherms generally require less food than equally sized endotherms.
• Endothermy buffers internal temperature against external fluctuations.
• Ectotherms tolerate greater variation in internal temperature.

Variation in Body Temperature

• A poikilotherm's body temperature varies with its environment.
• A homeotherm's body temperature is relatively constant.
• These terms are not equivalent to ectotherm and endotherm.
• The distinction between ectothermy and endothermy is not strict.
• Most animals regulate body temperature through physiological means.

Modes of Heat Exchange

• Organisms exchange heat through four physical processes: radiation, evaporation, convection, and conduction.

Thermoregulatory Adaptations

• Thermoregulation relies on several adaptations:
  • Insulation: Reduces heat flow. Examples include feathers, fur, blubber, and skin.
  • Circulatory adaptations: Regulating blood flow impacts thermoregulation. Endotherms and some ectotherms alter blood flow between the body core and skin.
  • Cooling by Evaporative Heat Loss: Water evaporation removes heat. Sweating or bathing cools the animal. Panting increases cooling in birds and mammals.
  • Behavioral responses: Invertebrates use postures to minimize or maximize heat absorption.
  • Adjusting Metabolic Heat Production: Thermogenesis adjusts metabolic heat to maintain body temperature. Shivering increases thermogenesis. Nonshivering thermogenesis (NST) occurs when hormones cause mitochondria to increase metabolic activity.

Physiological Thermostats

• The hypothalamus region of the brain controls thermoregulation.
• The hypothalamus triggers heat loss or heat-generating mechanisms.
• Fever results from changing the biological thermostat's set point.

Energy Requirements

• Bioenergetics describes the overall flow and transformation of energy in an animal.
• It determines animal food needs related to size, activity, and environment.

Energy Allocation and Use

• Animals obtain chemical energy from food.
• Catabolism breaks down energy-containing food molecules.
• The energy from catabolism is used for:
  • Biosynthesis, which includes body growth and repair.
  • Activity.
  • Thermoregulation.
• Remaining molecules can be used in biosynthesis or storage after energetic survival needs are met.

Quantifying Energy Use

• Metabolic rate measures the amount of energy an animal uses per unit of time.
• Metabolic rate can be determined by:
  • Measuring an animal's heat loss.
  • Measuring oxygen consumption or carbon dioxide production.

Influences on Metabolic Rate

• Metabolic rate is affected by factors like size, activity, temperature, and nutrition.

Size and Metabolic Rate

• Metabolic rate is proportional to body mass to the power of three-quarters (m^3/4).
• Smaller animals have higher metabolic rates per gram compared to larger animals.
• Higher metabolic rates in smaller animals result in a higher:
  • Oxygen delivery rate.
  • Breathing rate.
  • Heart rate.
  • Blood volume (relative to size).

Activity and Metabolic Rate

• Activity greatly affects metabolic rate for endotherms and ectotherms.
• The maximum sustainable metabolic rate is generally inversely related to activity duration.

Torpor and Energy Conservation

• Torpor is a physiological state involving decreased activity and metabolism.
• Torpor allows animals to save energy during unfavorable conditions.

Hibernation

• Hibernation is long-term torpor adapted to winter cold and food scarcity.
• During hibernation, body temperature declines, and heart/metabolic rates slow.

Estivation

• Estivation (summer torpor) enables animals to survive high temperatures and scarce water.