Animal Body Plans: Symmetry & Metabolism

Animal Body Plans

• Three key aspects of animal body plans include symmetry, bioenergetics/thermoregulation, and tissues.

Evolution of Symmetry

• Sponges lack definite symmetry.
• All other animals exhibit symmetry described as Eumetozoa.
• Eumetazoa symmetry is defined along an imaginary axis through the body.
• Radial and bilateral symmetry are the two main types of symmetry present.

Symmetry Descriptions

• Radial symmetry arranges body parts around a central axis and can be bisected into two equal halves in any 2-D plane.
• Bilateral symmetry features right and left halves as mirror images, and only the sagittal plane bisects the animal into two equal halves.

Body Shapes, Sizes, and Metabolism

• Small, unicellular organisms acquire nutrients through diffusion.
• Cell size is limited by the surface area-to-volume ratio.
• As cell size increases, the surface area-to-volume ratio decreases, which is not good.
• Larger organisms compensate by having more (multicellular) smaller cells rather than larger cells.
• Providing nutrients and oxygen to all cells necessitates specialized cells, organs, and organ systems.

Evolution of Tissues

• Parazoa (sponges) lack defined tissues and organs, but they can disaggregate and aggregate their cells.
• Eumetazoa has distinct and well-defined tissues with mostly irreversible cell type differentiation.

Bioenergetics

• Energy from nutrients fuels anabolic reactions.
• Basal Metabolic Rate (BMR) is the average amount of energy used in a non-active state.
• Excess energy is released as heat.
• Smaller endothermic organisms have a higher BMR than larger ones to compensate for the heat lost from their surface area.
• Active animals exhibit a higher BMR than less active ones.

Body Planes and Cavities

• The sagittal plane divides the body into right and left portions.
• The midsagittal plane divides the body into two equal right and left halves.
• The frontal (coronal) plane separates the front from the back.
• The transverse (horizontal) plane divides the animal into upper and lower portions, sometimes called a cross-section.
• An oblique plane is a transverse cut at an angle.

Multicellular Animal Tissues Types

• There are four main types of animal tissues: epithelia, connective, muscles, and neurons.
• Epithelia line cavities, open spaces, and surfaces.
• Connective tissues connect tissues and provides support.
• Muscles generate movement.
• Neurons generate and transmit electrical signals.

Epithelial Types

• Squamous epithelium can be simple or stratified.
• Cuboidal epithelium can also be simple.

Muscle Tissues Types and Properties

• Three muscle tissue types exist: skeletal, smooth, and cardiac.
• Skeletal muscle is voluntary and striated.
• Smooth muscle is involuntary with no striations.
• Cardiac muscle is involuntary, striated, and contains intercalated discs.

Nervous Tissue

• Nervous tissue consists of neurons and neuroglia.
• Nervous tissue will generate and transmit electrical impulses

Homeostasis and Thermoregulation

• Homeostasis maintains stable internal conditions around a set point.
• If conditions deviate from the set point, homeostatic mechanisms activate.
• A set point can change over time, however homeostasis will still respond to that point.
• Acclimatization occurs when changes in one organ system help maintain a set point in another.

Negative Feedback Loops

• These loops counteract internal changes, reversing the direction of change.
• Most biological systems operate on negative feedback, for example temperature, glucose, pH, and blood calcium.

Positive Feedback Loops

• These loops maintain and potentially strengthen the response to a stimulus.
• Not many biological systems are based on positive feedback.
• Oxytocin production is an example of positive feedback, and the birth of a human infant is a result of this.

Thermoregulation

• Animals must maintain a constant internal temperature for efficient enzyme function and to avoid denaturation.
• Thermoregulatory control is managed by the hypothalamus.
• Animals can be either Endotherms or Ectotherms
• Temperature is maintained through radiation, convection, conduction, and/or evaporation.