Biology Chapter: Bone and Tissue Functions

Anatomy Lecture 2: Tissues and Structures of the Body

• The lecture covered tissues and structures of the lower limbs, radiology, a summary, and a look forward to the next week's topics.
• Body organization begins with chemicals, followed by cell components (organelles), cells, tissues, organs, organ systems, and finally, the whole body.
• Structures in the body can be composed of one or multiple tissue types.
  • Bone is largely connective tissue.
  • The heart has epithelial, muscle, and connective tissue, along with nerves.
• Tissues are broadly categorized into four types:
  • Epithelial: A covering material
  • Connective: Connects structures and provides support.
  • Muscle: Contracts to cause or control movement.
  • Nervous: Enables communication between body parts through electrical impulses.

What Structures Are There in the Body?

• Bones
• Cartilage
• Ligaments
• Synovium/Bursa
• Muscles
• Tendons/Aponeurosis
• Joints
• Fascia/Adipose tissue
• Vascular structures
• Neural structures
• Skin

Bone

• Bone is a living, dynamically changing structure that adapts to stresses. (Wolff's Law)
• Functions:
  • Protection for other structures
  • Framework for other structures
  • Levers and pulleys for movement
  • Reservoir for calcium and fat
  • Formation of blood cells
• Structure:
  • Cells: Osteocytes (lay down new bone), Osteoclasts ('eat' old bone)
  • Matrix: Dense, tough connective tissue lattice containing calcium phosphate; resilient, slightly elastic, resisting compression.
  • Supplied by vascular structures and nerves.
  • Surrounded by periosteum (two layers: outer fibrous, inner highly vascular 'cambium').

Classifications of Bone

• Compact (cortical): Strong, dense, forms tubular bodies, filled with marrow.
• Cancellous (spongy): Lattice of bony spicules (trabeculae); helps redistribute stress and absorb shock.

Compact Bone: Structure

• Concentric lamellae
• Lacunae (spaces)
• Canaliculi
• Haversian canal
• Capillaries
• Osteocytes

Cancellous Bone: Structure

• Trabeculae
• Osteoid
• Active osteoblasts
• Inactive osteoblasts
• Marrow spaces
• Osteoblasts
• Osteocytes
• Osteoclasts

The Tibia

• An example of a long bone, featuring
  • Proximal epiphysis
  • Diaphysis
  • Distal epiphysis
  • Compact bone
  • Spongy bone (marrow)
  • Periosteum
  • Yellow marrow
  • Nutrient artery

Bone Classifications (Based on Shape)

• Long bones: Compact (shaft), cancellous (ends), covered with hyaline cartilage.
• Example: Femur, Tibia, Metatarsal
• Short bones: Primarily cancellous surrounded by a compact shell; cube-shaped. Joint surfaces covered in hyaline cartilage.
  • Example: Calcaneus, Talus
• Flat bones: Thin inner and outer layer of cortical bone separated by a layer of cancellous bone.
  • Example: Skull, Scapula
• Irregular bones: Thin shell of compact bone surrounding cancellous bone; odd shapes.
  • Example: Vertebrae
• Sesamoids: Bones within tendons (e.g., patella).

Bone Marrow

• Occupies cavities in long and short bones, and spaces amongst trabeculae in other cancellous bones.
• In children, primarily red (hemopoietic); red & white blood cells, platelets.
• Gradually replaced by yellow marrow (fatty) after 7 years of age; around 50% of each by adulthood.

Bone Development

• Two types:
  • Membranous: Bone develops directly from connective tissue membrane.
  • Endochondral: Cartilage model is laid down and gradually replaced by bone formation (how limbs form).

Endochondral Bone Development

• Stages of cartilage model ossification: The diagram shows stages of ossification, revealing how limbs grow and form.

Ossification Rates (for various bones)

• Diagram showing the relative timing of ossification for different bones in the lower limb.

Radiographic view of adult and child knees

• X-Ray images of typical knee anatomy for a child and adult

Bones of the Pelvis

• Diagram of pelvis bone anatomy (ilium, sacrum, anterior superior/inferior iliac spines, pubis, ischium, iliac crest, sacroiliac joint, obturator foramen, femur).

The Knee

• Features of the knee joint components (femur, tibia, fibula, anterior/posterior cruciate ligaments, medial/lateral collateral ligaments, medial/lateral meniscus).

Rear Foot & Ankle

• Diagram of ankle joint components (tibia, fibula, talus, calcaneus, cuboid, navicular, cuneiforms, metatarsals, interosseous ligament, medial/lateral ligament, talocalcaneal ligament).

Cartilage

• Connective tissue made of collagen embedded in a gel-like matrix.
  • Hyaline: Important in joint formation, protecting bone surfaces.
  • Fibrocartilage: Tough, found in weight-bearing joints (knee menisci)
  • Elastic: Springy, found in the ears.

Ligaments

• Bands of connective tissue connecting two bones.
  • Often allow motion in one direction but restrict it in others.
  • Types:
    • Inelastic: Dense bundles of collagen; e.g., ankle & knee.
    • Elastic: Elastic fibers; e.g., plantar calcaneonavicular ligament.
  • Ligaments within the joint capsule are intracapsular; those outside are extracapsular.

Synovial Membranes/Sheaths and Bursae

• Fluid-filled sacs that reduce friction and protect tendons and joints.
  • Synovial membranes: inner lining of joints; secretion helps lubricate.
  • Synovial sheathes: Similar to synovial membranes, but they surround tendons.
  • Bursae: Sacs situated under tendons to prevent friction from bony lumps

Muscles

• Muscles enable body movement.
  • Types: Cardiac, smooth, skeletal.
  • Skeletal muscle: Under conscious brain control, composed of striated fibers.
    • They work by contracting, in various shapes
      • Rhomboid
      • Quadrilateral
      • Strap
      • Strap with tendinous intersections
      • Fusiform
      • Two bellies
      • Two headed
      • Triangular
      • Unipennate
      • Bipennate
      • Multipennate
    • Have points of origin (attachment that doesn't move much) and insertion (attached to another part by a tendon).
    • Types of contraction (dynamic - eccentric/concentric; static - isometric).
    • Jobs performed by skeletal muscles
      • Prime mover (Agonist): Causes a movement.
      • Antagonist: Works against a prime mover.
      • Fixator (stabilizer): Holds a body part stable during a movement, while the other muscles perform the desired movement.
      • Synergist: Assists the prime mover.
• Muscle Structure
• Includes tendons and aponeuroses (fibrous tissue, connecting muscle to bone)

Skeletal Muscle Types

• Type 1: Slow twitch, red (myoglobin) — Marathon runner.
• Type 2a: Quite fast twitch, white — 800-meter runner.
• Type 2x (formerly 2b): Fast twitch, white — 100-meter runner, powerlifter.

Muscles & Stress

• Muscles and soft tissues grow stronger with use (Davis' Law).

Tendon/Aponeurosis

• Tendons: Long inelastic cords of connective tissue attaching muscles to bones.
  • Tendons cross over joints and may cause motion some distance from the muscle, even going around corners.
• Aponeurosis: Thin, wide sheets of connective tissue that also attach muscles to bones (e.g., ventral abdominal aponeurosis).

Joints

• Junctions where two or more bones meet.
• Types:
  • Fibrous: Negligible or no movement(skull sutures).
  • Cartilaginous: Small amount of movement (symphysis pubis).
  • Synovial: Large range of motion (hip, knee, elbow).

Fibrous Joints

• Bone margins interlock like jigsaw pieces; inherently rigid and stable.
• Sharpey's fibers strongly bind the bones.

Cartilaginous Joints

• Bones are united by a plate of fibrous cartilage, with a thin layer of hyaline cartilage on the ends of the bones.

Synovial Joints

• Highly moveable; trade-off between stability and maneuverability (depends on shape, ligament strength, and muscle control).

Joint Shapes

• Types of synovial joints (hinge, ball-and-socket, pivot, plane, saddle, condyloid, ellipsoid).

Fascia

• Membranes surrounding deep structures in the body.
  • Superficial: Surrounds everything under the skin.
  • Deep: Divides deep structures into compartments (e.g., thigh compartments).

Fascial Adaptations

• Retinacula (thickening of fascia) holds tendons, blood vessels, and nerves in place.
• Tracts (e.g., iliotibial tract) provide stability.

Cardiovascular System

• Heart and blood vessels pump blood around the body and back to the heart.
  • Pulmonary and Systemic systems.
  • Heart: Muscular bag with 4 chambers — contracts to push blood to other body parts.
  • Other vessels: Takes blood to and from the heart (arteries, arterioles, metarterioles, pre-capillary sphincters, capillaries, venules, veins)

What Does the CV System Do?

• Exchange of gases (oxygen in, carbon dioxide out).
• Delivers nutrients and hormones.
• Removes waste products.
• Protection (clotting, leukocytes).
• Temperature regulation.
• Homeostasis.

Arteries

• Muscular and elastic walls deliver blood from the heart to other places.
• Aid in heart pumping
• High pressure.

Veins

• Less muscular and elastic than arteries.
• Deliver blood back to the heart from everywhere else.
• Lower pressure system.
• One-way valves prevent backflow.

Capillaries

• Tiny vessels with walls one cell thick.
• Leaky—diffusion of oxygen, nutrients, carbon dioxide, and waste products.

Anastomosis

• Joining of blood vessels, allowing blood to pass from one vessel to another (useful if one vessel is blocked).

Lymphatics

• Parallel system with veins, carrying fluid and proteins away from tissues to blood.
• Drain into large veins.
• Lymph nodes act as filters, containing phagocytes and antibodies.

The Nervous System

• Body's communication system (processes information and controls actions).
• Types of Nervous Systems
  • Central nervous system (CNS): Brain and spinal cord
    • Integration and control center for body functions.
  • Peripheral nerves system (PNS): Cranial and spinal nerves
    • Connects the CNS to the rest of the body; communication pathway for impulses from the brain, and back to the brain, from the rest of the body
  • Somatic Nervous System: Voluntary actions
  • Automatic Nervous System: Actions not under conscious control (sympathetic & parasympathetic).

Somatic: Afferent & Efferent

• Sensory (afferent) impulses from body to the brain.
• Pain, temperature, vibration, pressure, muscle and tendon tension, and joint position.
• Motor (efferent) impulses from the brain to the muscles for body movements

Autonomic

• Functions not under conscious control.
  • Sympathetic: "revs up" body for action.
  • Parasympathetic: "slows down" body for rest, recovery. (balance eaching).

Cranial Nerves

• Nerves that originate in the brain; involved in various functions including sensory perception and motor control (diagram of each).

Spinal Nerves

• Originate from spinal cord—supply specific body parts (diagram).

Lumbar & Sacral Plexi

• Nerve networks from several spinal nerves that distribute to the lower limbs.

Main Nerves of the Lower Limbs

• Femoral (L2-L4)
• Obturator (L2-L4)
• Sciatic (L4-S3)

Skin

• Largest organ, covering 1.5 to 2 square meters and weighing about 16% of body weight.
  • Protection
  • Temperature control
  • Receptors
  • Vitamin D synthesis
  • Communication

Skin: Structure

• Layers:
  • Epidermis (outer surface, stratified, thick on palms & soles).
  • Dermis (deeper, containing blood vessels, nerves, hair roots, and glands).
  • Subcutaneous tissue (fat and connective tissue).
• Diagram of skin structure showing layers, hair follicles, sweat glands, oil glands.

Summary

• Overview of the various anatomical concepts and their connections.

Next Week

• Instructions to revise notes and textbook material; prepare for osteology of the lower limb, focusing on anterior thigh compartment and surface anatomy, as well as time and location.