Chapter 2_ Skeletal System _ Top Hat

Chapter 2: Skeletal System

General Overview

  • Introduces the skeletal system, covering osseous tissue histology and individual bones.

  • Bones are complex organs made of:

    • Osseous tissue

    • Bone marrow (red and yellow)

    • Blood vessels and blood

    • Nerves

    • Connective tissue

    • Adipose tissue

  • The skeleton is divided into:

    • Axial Skeleton: bones along the body's midline, including the skull, vertebral column, and thorax.

    • Appendicular Skeleton: bones of the upper and lower limbs, always paired.

Section 2.1: Osseous Tissue Histology & Physiology

Histology

  • Shapes of Bones: Long, flat, short, and irregular shapes have functional and developmental implications.

  • Compact vs. Spongy Bone:

    • Compact bone: dense, forms the outer layer of bones.

    • Spongy bone: less organized, contains trabeculae and spicules.

  • Osteon: The basic unit of osseous tissue; more numerous in compact bone than spongy.

  • Lamellae Types:

    • Concentric Lamellae: circular layers surrounding a central canal.

    • Interstitial Lamellae: fills spaces between osteons.

    • Circumferential Lamellae: runs along the circumference of the bone.

  • Osteocytes: mature bone cells located in lacunae, communicate via canaliculi.

  • Bone Cells:

    • Osteoblasts: bone-building cells.

    • Osteoclasts: bone-resorbing cells.

Histological Organization of Long Bones

  • Diaphysis: the long shaft containing the medullary cavity, lined by endosteum.

  • Epiphyses: ends of long bones that contain spongy bone and red bone marrow.

  • Periosteum: connective tissue covering the outer surface, important for bone attachment.

Histological Organization of Flat Bone

  • Lacks medullary cavity; structured like a sandwich with periosteum, compact bone, and spongy bone (diploë) layers.

Physiology of Osseous Tissue

Bone Maintenance & Remodeling

  • Dynamic tissue that adapts to mechanical stress via Wolff’s Law.

  • Bone heterogeneity aids both maintenance and strength.

Calcium Homeostasis

  • Key roles in calcium storage and release controlled by:

    • Parathyroid Hormone (PTH): promotes bone resorption and raises blood calcium levels.

    • Calcitriol: also encourages bone resorption.

    • Calcitonin: facilitates bone deposition, lowering blood calcium levels.

Skeletal System Overview

  • Composed of bones, cartilage, and joints.

  • Divisions:

    • Axial Skeleton: cranial, facial bones, vertebral column, hyoid, auditory ossicles, and thoracic structures (sternum and ribs).

    • Appendicular Skeleton: upper and lower limbs, pectoral girdle, and pelvic girdle.

Anatomical Terms of Orientation

  • Familiarity with terms such as:

    • Superior vs. Inferior

    • Anterior vs. Posterior

    • Medial vs. Lateral

    • Proximal vs. Distal

    • Sagittal Orientation (Midsagittal vs. Parasagittal)

Section 2.4: Remainder of the Axial Skeleton

Components of the Axial Skeleton

  • The axial skeleton comprises the skull, vertebral column, and thoracic cage, providing support and protection for vital organs.

Skull

  • Cranial Bones: Enclose and safeguard the brain, consisting of eight bones.

    • Includes: Frontal, Parietal, Temporal, Occipital, Sphenoid, and Ethmoid bones.

  • Facial Bones: Form the structure of the face with fourteen bones, such as the mandible and maxilla.

Vertebral Column

  • Composed of 33 vertebrae divided into different regions:

    • Cervical Vertebrae (7): Support the neck.

    • Thoracic Vertebrae (12): Articulate with ribs.

    • Lumbar Vertebrae (5): Bear most body weight and provide support for the lower back.

    • Sacrum (5 fused): Forms the posterior portion of the pelvis.

    • Coccyx (4 fused): Often referred to as the tailbone.

  • Functions include protecting the spinal cord, providing structural support, and enabling flexibility.

Thoracic Cage

  • Composed of the sternum and twelve pairs of ribs, protecting the heart, lungs, and great vessels.

  • Ribs Structure:

    • True Ribs (1-7): Directly attach to the sternum.

    • False Ribs (8-12): Indirectly attach or do not attach to the sternum.

    • Floating Ribs (11-12): Do not attach to the sternum at all, providing flexibility and protection.

Summary

  • The axial skeleton is crucial for stability and protection of the body's central structures, playing a supportive role in overall posture and balance. It works synergistically with the appendicular skeleton to allow movement and flexibility while maintaining the structural integrity of the body.