Unifying Concepts of Animal Structure and Function (Chapter 20) – General Biology Study Notes

Animals: Form and Function

Introduction

This chapter explores the relationship between animal structure and function, emphasizing how evolutionary processes shape anatomy and physiology. It covers the hierarchical organization of animal bodies, the major tissue types, organ systems, and mechanisms of internal regulation.

Structure and Function in Animal Tissues

Gecko Adhesive System: An Example of Structure-Function Relationship

• Gecko feet possess specialized structures called setae that allow them to adhere to surfaces.

• Adhesion is due to van der Waals forces—weak attractions between molecules on the spatulae (tips of setae) and the surface.

• A single seta can support the weight of an ant, demonstrating the efficiency of this adaptation.

• Increasing shear load increases contact area, enhancing adhesion; decreasing shear load makes release easier.

• Application: The design of robots such as Stanford's StickyBot is inspired by gecko adhesion mechanisms.

20.1 Evolution Connection: Imperfect Design in Animal Form

• Evolution does not always produce perfect designs; structures may reflect historical constraints.

• Example: The laryngeal nerve in giraffes takes a long, circuitous route from the brain to the throat due to evolutionary changes in neck length, not optimal design.

20.2 Structure Fits Function at All Levels of Organization

• Anatomy: Study of structure.

• Physiology: Study of function.

• Animals are organized hierarchically:

  • Tissues: Groups of similar cells performing a common function.

  • Organs: Structures composed of two or more tissues performing specific tasks.

  • Organ systems: Groups of organs working together for vital functions.

• Example: Muscle cell (cellular level) → Muscle tissue (tissue level) → Heart (organ level) → Circulatory system (organ system level) → Giraffe (organism level).

20.3 Animal Tissues: Categories and Functions

• Four main tissue types:

  1. Epithelial tissue (上皮組織)

  2. Connective tissue (結締組織)

  3. Muscle tissue (肌肉組織)

  4. Nervous tissue (神經組織)

20.4 Epithelial Tissue

Structure and Function

• Epithelial tissues are sheets of closely packed cells covering body surfaces and lining organs/cavities.

• Cell shapes:

  1. Squamous: Flat, like fried eggs.

  2. Cuboidal: As tall as wide.

  3. Columnar: Taller than wide.

• Named by:

  • Number of layers: Simple (one layer) or Stratified (multiple layers).

  • Shape of apical surface cells: squamous, cuboidal, or columnar.

• Example: Simple squamous epithelium lines blood vessels; stratified squamous epithelium forms the skin's surface.

20.5 Connective Tissue

Types and Functions

• Connective tissue supports and binds other tissues. Six major types:

Type	Main Features	Function
Loose connective tissue	Ropelike collagen and elastic fibers	Joins skin to underlying tissues
Fibrous connective tissue	Densely packed collagen fibers	Forms tendons (attach muscle to bone)
Adipose tissue	Fat-storing cells in fiber matrix	Stores energy, insulates, cushions
Cartilage	Strong, flexible matrix	Supports, cushions joints
Bone	Collagen matrix, mineralized (Ca, Mg, phosphate)	Structural support, protection
Blood	Cells in plasma	Transports substances

• Example: Adipose tissue stores fat; bone contains osteocytes in a mineral matrix.

20.6 Muscle Tissue

Types and Functions

• Muscle tissue is the most abundant tissue in animals, responsible for movement.

• Three types in vertebrates:

  1. Skeletal muscle: Voluntary movement.

  2. Cardiac muscle: Pumps blood (involuntary).

  3. Smooth muscle: Moves walls of internal organs (involuntary).

• Example: Cardiac muscle controls heartbeats without conscious effort.

20.7 Nervous Tissue

Structure and Function

• Nervous tissue senses stimuli and transmits information rapidly.

• Neurons conduct electrical impulses.

• Other cells (neuroglia) insulate axons, nourish neurons, and regulate fluid environment.

• Example: Astrocytes, oligodendrocytes, microglia, and ependymal cells are types of neuroglia.

Organs and Organ Systems

Organization and Integration

• Organs are composed of multiple tissue types, each contributing to the organ's function.

• Organ systems consist of multiple organs working together for vital functions.

• Example: The small intestine contains epithelial, connective, muscle, and nervous tissues.

20.10 Organ Systems: Functions and Interactions

• Skeletal and muscular systems: Support and movement.

• Digestive and respiratory systems: Obtain food and oxygen.

• Circulatory system: Transports materials.

• Urinary system: Disposes of wastes.

• Integumentary system: Covers and protects the body.

20.11 The Integumentary System

Structure and Functions of Skin

• Skin has two layers:

  1. Epidermis: Stratified squamous epithelium; forms surface.

  2. Dermis: Dense connective tissue with elastic and collagen fibers; contains hair follicles, glands, nerves, and blood vessels.

• Functions:

  • Epidermis: Resists damage, prevents water loss, blocks microbes.

  • Dermis: Sensory information, vitamin D synthesis, temperature regulation.

• Exposure to UV light triggers melanin production (tanning) and can damage DNA, leading to aging, cataracts, and skin cancer.

• Hair: Insulates body; made of keratin-filled dead cells.

• Oil glands: Lubricate hair, condition skin, inhibit bacteria.

External Exchange and Internal Regulation

Homeostasis and Regulation

• Homeostasis: Active maintenance of a stable internal environment despite external fluctuations.

• Homeostatic mechanisms regulate temperature, pH, and other variables.

• Negative feedback: Control systems detect changes and initiate responses to keep variables near set points.

• Example: Body temperature regulation via sweating or shivering.

Endothermy and Ectothermy

• Endotherms (birds, mammals): Generate heat metabolically.

• Ectotherms (most invertebrates, fishes, amphibians, reptiles): Gain heat from environment.

• Poikilotherms: Body temperature varies with environment.

• Homeotherms: Body temperature remains relatively constant.

Thermoregulation Mechanisms

• Countercurrent heat exchangers: Arteries and veins arranged to conserve heat (e.g., whale flippers, mammal legs).

• Nonshivering thermogenesis: Brown fat generates heat without muscle activity.

Alterations in Homeostasis

• Set points and normal ranges can change with age or show cyclic variation (circadian rhythms).

• Acclimatization: Adjustment of homeostasis to external changes.

• Torpor: Temporary drop in metabolic rate and body temperature.

• Hibernation: Extended period of reduced metabolic rate and body temperature.

• Example: Arctic ground squirrels use torpor and hibernation to survive cold climates.