B.1.2 Structures and Function of Connective Tissues and Joints

Adapted from class notes.

Connective Tissues

• Connective tissue referes to the tissues that connects other tissues together

• This can be bone-to-bone or bone-to-muscle, can protect organs, can have immune function, and more

Bones - Type

• Bones can come in four main shape groups

  • Long bones - Cylindrical with widened ends where they articulate

    • Examples: femur, radius, ulna, humerus

  • Short bones - often cube shaped and articulate with multiple other bones

    • Examples: Carpals and tarsals

  • Flat bones - Sometimes are curved, thick or thin, have large surface area

    • Examples: Scapula, ribs, sternum

  • Irregular bones - Don’t fall into other 3 categories, have specialized functions

    • Examples: Vertebrae, bones of the face

Bones - Function

• Support/Structure: Attachment for tendons and soft tissue

• Protection: Is hard, so sensitive structures (brain, spinal cord) are protected

• Movement: Muscles pull on bones to cause movement

• Mineral Homeostasis: Storage and release (Ca, PO4)

• Blood Cells: Larger bones contain red marrow that make RBC

• Fat Storage: Yellow marrow (in long bones) store triglycerides

Bones - Structure

• Bone structure is a mix of protein (collagen) and minerals (calcium and phosphate). Proteins provide strength while minerals make bones hard

• Distal - far; proximal - close; epiphysis refers to the end of a long bone

• Ends of the bone are spongy made of red marrow

• The long section is compact and hard (to support weight)

• Blood vessels transport nutrients through holes called foramen

Ligaments

• Ligaments are the connective tissue that holds bones together

• Flexible to allow for bending and joint movement

• Strong to prevent extra movement beyond normal range

• Not elastic like muscles - cannot be stretched, and take a long time to return to normal size if stretched (that is an injury)

Cartilage

• A network of cartilage (similar to bone without mineralization)

• No blood vessel or nerves

• Provides cushion to joints, reduces friction

Fascia

• Between and surrounding other tissues (like muscles)

• Made up of fibers, fats, and fluid

• Commonly found in muscles in three main forms:

  • Epimysium - Covers the muscle

  • Perimysium - Covers bundles of muscle fibers called fascicles

  • Endomysium - Covers individual muscle fibers (cells)

Tendons

• When the fascia continues beyond the muscle, they become the tendon (when muscle cells stop)

• Tendons connect muscle to bone

  • When muscles contract, they pull on the bone, causing movement of the body

• Can be rounded or a flat sheet (called aponeurosis)

• Multiple tendons can join together in tendon sheaths (such as in the wrist [carpal tunnel])

Joints (AKA Articulations)

• Joints are where 2 bones meet

• Main purpose is to increase mobility

• Classified by the amount of movement allowed which is determined by:

  • The shape of bones articulating

  • Area of contract of the bones

  • Flexibility of the ligaments

  • Other tissues

• Joints can be:

  • Fibrous

  • Cartilaginous

  • Synovial

Joints - Fibrous and Cartilaginous

• Fibrous joints:

  • Thin layers of fibrous tissue between joints

  • No movement

  • Example: Between sutures of skull

• Cartilaginous joint:

  • Small amount of cartilage separating bones

  • Minimal movement

  • Examples: Ribs to sternum

Joints - Synovial

• The joints between major bones (stereotypical joint)

• Articular capsule surrounds the joint. Flexible arrangement of fibers

• Cartilahge and synovial fluid (high viscosity) allow for smooth joint movement

• Meniscus are discs found in soem bones (like knee)

Types of Joints

• Gliding (plane): Low amount of sliding of bones past each other

  • Ex: Between carpals/tarsals

• Hinge: Due to shape at articulation, allows only movement in one plane

  • Ex: Elbow, knuckles, between phalanges

• Pivot: One joint pivots around another

  • Ex: Radioulnar joint

• Ball + Socket: Most range of motion, a sphere fitting into a hole

  • Ex: Shoulder

• Saddle: Two saddle-like shape allows movement in two directions

  • Ex: Sternoclavicular

• Condyloid: Like a ball + socket, but the ball is an oval

  • Ex: Wrist