BI1002: Structure and Function – Support and Movement Study Notes

BI1002: Structure and Function – Introduction to Support and Movement

• Course Metadata:     * Module: BI1002 (Structure and Function).     * Topic: Support and Movement.     * Institution: Cardiff University (Wales Centre for Anatomical Education).     * Lecturer: Dr. Hannah Shaw.

• Lecture Series Overview:     * Lecture 1: Introduction to support systems.     * Lecture 2: Structure and function of the human skeletal system.     * Lecture 3 (Spring): Skeletal muscles.     * Related Topics: Neurological control of movement (delivered by Dr. Emma Ynell).     * Integration: Students are encouraged to relate this information to other modules for a holistic understanding.

Fundamental Engineering Principles of Support: Hollow Tubes

• The Hollow Tube Concept: A central engineering principle mentioned is that hollow tubes are structurally stronger than solid tubes of the same mass.

• Biological Application: This efficiency in strength-to-weight ratio is a recurring theme in both plant (xylem) and animal (long bones) support systems.

Support Mechanisms in Plants

• Multi-level Support: Support in plants is provided hierarchically at cellular, tissue, and gross structural levels.

• Cellular Components Involved in Support and Metabolism:     * Plasma Membrane.     * Peroxisome.     * Golgi Apparatus.     * Mitochondria.     * Chloroplast.     * Vacuole.     * Ribosomes.     * Smooth Endoplasmic Reticulum.     * Cytoplasm.     * Rough Endoplasmic Reticulum.     * Nucleus (containing the Nucleolus and surrounded by the Nuclear Envelope).     * Cell Wall (the primary rigid structure).

• Cellular Support via Turgor Pressure:     * Mechanism: Support is maintained by the interaction between the cell wall and the cell vacuole.     * Wilting/Plasmolysis: When the vacuole loses water, the cell becomes plasmolysed, leading to loss of turgor and gross wilting of the plant.

Plant Tissue Morphology and Stem Structure

• Tissue Layers of the Stem:     * Epidermis: The outermost protective layer.     * Cortex (Collenchyma):         * Characterized by primary cell walls with specific thickening, often at the corners.         * Properties: Flexible, allowing the plant to bend without breaking.     * Pith (Parenchyma):         * Characterized by thin cell walls.         * Function: Increasing the volume of the vacuole within these cells increases the overall size and internal pressure.     * Vascular Bundles: Combined structures of Xylem and Phloem.

• The "Pneumatic Tire" Analogy: The relationship between the pith and cortex provides support. The parenchyma (pith) presses outward against the collenchyma (cortex), creating a pressurized, rigid structure similar to a pneumatic tire (Load Range A).

• Vascular Bundle Specialization:     * Xylem: Functions as hollow tubes for water transport. These structures undergo apoptosis (programmed cell death), leaving behind reinforced cell walls.     * Lignin: A complex polymer that reinforces cell walls.     * Sclerenchyma: Tissue that surrounds vascular bundles. It features a thick secondary cell wall and provides both rigidity and elasticity (the ability to return to the original shape after deformation).     * Reinforced Concrete Analogy: The combination of flexible and rigid components in plant stems is compared to reinforced concrete.

• Comparative Morphology (Monocotyledonous vs. Dicotyledonous):     * Dicotyledonous stem: Vascular bundles are arranged in a organized ring.     * Monocotyledonous stem: Vascular bundles are scattered throughout the ground tissue.     * Bending Resistance: Dicotyledonous plants are generally harder to bend due to their organized vascular arrangement.

Gross Plant Anatomy: Shoot and Root Systems

• The Shoot System:     * Terminal bud: The primary growing point at the top of the stem.     * Axillary bud: Bud growing from the axil of a leaf.     * Node: The part of a plant stem whence one or more leaves emerge.     * Internode: The segment of a stem between two nodes.     * Petiole: The stalk that joins a leaf to a stem.     * Leaf components: Blade/margin, midvein, and veins.     * Cotyledon: Embryonic leaf in seed-bearing plants.

• The Root System:     * Primary Root ("Tap Root"): The central, largest root.     * Lateral Roots (Secondary Roots): Branch off from the primary root.     * Root Cap: Protects the growing tip of the root.     * Vascular Cylinder: Central portion of the root containing transport tissues.     * Functions of Roots:         1. Absorption of water and dissolved minerals.         2. Anchorage and stability for the entire plant.

Animal Skeletal Systems: Hydrostatic Skeletons

• Definition: A skeleton formed by a fluid-filled compartment (capsule) within the body, under hydrostatic pressure.

• Example: The Earthworm:     * Structure: A capsule of fluid surrounded by two layers of muscle: circular and longitudinal.     * Septae/Bristles: Internal walls (septae) and external hair-like structures (bristles/setae) aid in movement and stability.

• Mechanism of Movement:     * The fluid-filled cavity acts as a rigid column for muscle action.     * Circular Muscle Contraction: Elongates and narrows the body segments, pushing them forward.     * Longitudinal Muscle Contraction: Shortens and thickens the body segments, pulling trailing segments forward.     * Anchorage: Bristles anchor specific segments to the ground to prevent backward sliding during contraction.     * Result: Segmental contraction and anchorage drive the body forward for burrowing.

Animal Skeletal Systems: Exoskeletons

• Definition: A hard outer surface that protects soft tissues (armor) and provides structural support.

• Phyla Examples:     * Mollusks: Clams, mussels.     * Arthropods: Insects, crabs, lobsters.

• Etymology: "Arthro" = joint; "podia" = foot.

• Functions:     * Provides strength and mobility.     * Acts as a site for muscle attachment to facilitate movement.

• Hierarchical Structure (e.g., Lobster Exoskeleton):     * Composed of Chitin (a polysaccharide).     * Layers:         1. Epicuticle: Approximately $70\,mm$ (noting scale markers: $1\,mm$, $10\,\mu m$, $10\,\text{Å}$, $3\,nm$).         2. Exocuticle: Approximately $100\,nm$.         3. Endocuticle: Approximately $200\,nm$.     * Properties: Strong and light. Mineralization provides hardness/protection, while joints remain thin and flexible.

• Limitations of Exoskeletons:     * Internal tissues can be crushed if the shell is breached.     * They do not grow with the body; animals must undergo molting (ecdysis).     * Vulnerability: The animal is soft and vulnerable until the new exoskeleton hardens.     * Exoskeletons are size-limiting; they become too heavy for very large land-dwelling animals.

Animal Skeletal Systems: Endoskeletons

• Definition: A rigid internal framework found in vertebrates.

• Primary Functions:     * Rigid system for muscle contraction.     * Protection of vital internal organs.     * Rigid support against gravity.

• Types of Endoskeletons:     1. Cartilaginous (Chondrichthyes):         * Found in sharks and rays.         * Composition: Cartilage (which may be calcified).         * Benefits: Light, efficient, and flexible. However, the tissue must be thin.     2. Bony:         * Found in most vertebrates, supporting weight for large land animals.         * Development: Initially develops from a cartilaginous skeleton.         * Mechanics: Act as levers moved by muscles.         * Dynamic Nature: Bone is living tissue that responds to physiological loading.

Bone Anatomy and Microstructure

• Gross Structure:     * Bones are not solid; they contain a central (medullary) cavity.     * Function of Cavity: Reduces total weight while maintaining strength to resist compression and tension.

• Microscopic Structure (The Bone Matrix):     * Consists of living cells embedded in a mineralized extracellular matrix.     * Osteon: The functional unit of compact bone. Columns arranged around an artery.

• Detailed Histological Components:     * Central Canal (Haversian Canal): Contains blood vessels (arteries, veins) and nerves.     * Concentric Lamellae: Circular layers of bone matrix.     * Collagen Fibers: Specific orientation for structural integrity.     * Endosteum: Membrane lining the inner cavity.     * Osteocytes: Living bone cells.     * Circumferential Lamellae: Layers that go around the entire bone circumference.     * Perforating Fibers (Sharpey's Fibers): Secure periosteum to bone.     * Perforating Canal (Volkmann's Canal): Channels for blood vessels (arterioles, venules, capillaries) connecting central canals.     * Interstitial Lamellae: Fill spaces between osteons.     * Trabeculae of Spongy Bone: Lattice-like structure found in the ends of long bones.

Summary Take-Home Messages

• Support systems vary based on the size of the organism to provide efficient and effective support.

• The use of hollow tubes is a universal mechanism of support found in both plants and animals.