Skeletal System and Bone Tissue: Functions

Introduction to Bone Tissue and the Skeletal System

• The chapter explores the anatomy and physiology of bone tissue.
• Bone is a solid connective tissue that provides protection.

Functions of the Skeletal System (Section 7.1)

• Bones and cartilage make up skeletal system.
• The skeletal system provides a rigid support framework to the human body.
• Movement is facilitated as muscles pull on bones.
• Soft internal organs are protected by the skeletal system.
• Minerals are stored in the bone extracellular matrix.
• Adipose is stored in the yellow bone marrow.
• Blood cells are produced in the skeletal system.
• Attachment sites for muscles.
• Storage of calcium and other minerals
• Storage of adipose tissue
• Calcium is important for muscle contraction and nerve impulses.
• Red bone marrow is the site of blood cell generation.
• Yellow bone marrow is for energy storage.
• Cartilage contributes to the skeletal system.
• Elastic cartilage isn't in the skeletal system.
• Hyaline cartilage is found where bones ends to form joints.
  • Hyaline helps bones glide past each other.
  • Loss of hyaline cartilage results to osteoarthritis.
• Fibrocartilage is between vertebrae, inside the knee, and the pubic symphysis.
• Ligaments attach bones to one another.

Anatomy of a Typical Bone

• Periosteum covers the bone's surface.
• Compact bone's outer shell protects the entire bone.
• Spongy bone contains red bone marrow.
• Yellow bone marrow is located in the medullary cavity.
• Hyaline cartilage is found at the joints.

Think-Pair-Share Activity 1

• Bones protect common organs, including the brain, heart, and lungs.
• Hard bone shields these organs, providing protection.

Professions Requiring Knowledge of Bones

• Radiologists, orthopedic surgeons, and chiropractors are examples of professions that require knowledge of bones.

Bone Classification (Section 7.2)

• Bones are classified according to their shape, such as long, short, flat, irregular, and sesamoid bones.

Classes of Bones

• Long bones: Cylinder-like shape, longer than it is wide; act as levers (e.g., femur, tibia, fibula, humerus, ulna, radius).
• Short bones: Cube-like shape, approximately equal in length, width and thickness; offer stability and support for some motion (e.g., carpals, tarsals).
• Flat bones: Thin and curved, serving as points of attachment for muscles and protectors of internal organs (e.g., sternum, ribs, scapulae, cranial bones).
• Irregular bones: Complex shape, protect internal organs (e.g., vertebrae, facial bones).
• Sesamoid bones: Small and round bones embedded in tendons; protect tendons from compressive forces (e.g., patella).

Long Bones

• They function as levers (examples: humerus, femur, ulna, tibia).
• The epiphysis is the end of long bone.
• The diaphysis is the shaft of a long bone.
• The Metaphysis is located between the epiphysis and diaphysis; contains the epiphyseal plate/line.
• The Medullary cavity refers to the space in the diaphysis that houses the yellow bone marrow and can become available for bone growth.
• Articular cartilage layer of hyaline cartilage that reduces friction in joints.
• The epiphyseal plate (the growth plate) is found in children; contains growing cartilage that allows bones to elongate; and osseifies to become the epiphyseal line in adults

Common Bone Structures

• The periosteum is a dense, irregular connective tissue lining the surface; contains blood vessels, nerves, and lymphatic vessels.
  • Tendons and ligaments attach to periosteum via perforating fibers.
• Endosteum is a dense, irregular connective tissue lining the medullary cavity.
• Both Periosteum and endosteum contain cells that allow bone growth.
• The Periosteum is attachment site for ligaments and tendons.
• Collagen fibers anchor muscle to bones.

Cartilage

• Articular cartilage is hyaline cartilage at the ends of long bones where they form joints; reduces friction and acts as a shock absorber.

Short and Flat Bones

• Compared to long bones, short bones are cube-like in shape, provide stability and support (examples: carpal bones of the wrist and tarsal bones of the ankle).
• Flat Bones: Protect internal organs are usually thin but curve (examples: cranial bones (skull), sternum, ribs, scapula).

Flat Bone Composition

• A layer of spongy bone is between two layers of compact bone.

Bone Classification: Irregular and Sesamoid Bones

• Irregular bones don't fit any classification scheme, complex shapes (examples: Vertebrae, facial bones).
• Sesamoid bones are small, round bones suspended in a tendon or ligament; protect tendons from compressive force (example: patella, and only common sesamoid bone).

Bone Markings

• Bone markings are the surface feature of bones: articulating surfaces, depressions, projections, holes, and spaces.
• Articulating surfaces are where bones meet.
• Depressions are sunken portions of bone.
• Projections project above the bone surface.
• Holes and spaces are openings/grooves in bone.

The 4 Classes of Bone Markings

• Articulating surfaces: Condyle (rounded surface e.g., occipital condyles) facet (flat surface e.g., vertebrae) head (prominent rounded surface), trochlea (rounded articulating surface).
• Depressions: Fossa (elongated basin e.g., mandibular fossa), Sulcus (groove e.g., sigmoid sulcus of the temporal bones).
• Projections: Crest (ridge e.g., iliac crest), epicondyle (projection off a condyle e.g., lateral and medial epicondyles of humerus), line (slight, elongated ridge e.g., temporal lines of the parietal bones), process (prominent feature e.g., transverse process of vertebra), ramus long projection, sharp process and rough round.
• Openings: Foramen (opening in bone e.g., foramen magnum in the occipital bone), meatus (opening into canal e.g., external auditory meatus), sinus (air-filled space in bone e.g., nasal sinus).
• Ridge bone markings are crests.
• Projection off a condyle is an example of bone markings known as epicondyle.
• A hole in the bone is best know as formamen.

Think-Pair-Share Activity

• The structure of compact bone resembles the trunk of a tree, while spongy bone resembles its branches.

The Microscopic Structure of Cartilage and Bone (Section 7.3)

• Hyaline, elastic and fibrocartilage are the 3 types of cartilage
• Cartilage tissue is semi-solid connective tissue; it's avascular, while dense irregular connective tissue covered by perichondrium provides blood vessels and nutrients to cartilage.
• Chondroblasts are cells of cartilage that secrete matrix, while chondrocytes are cells surrounded by the matrix.
• Lacunae contain chondrocytes.
• Spongy bone provides bone strength.
• Red bone marrow fills spaces within spongy bone.

Bone Cells

• Osteogenic cells or stem cells replicate, develop into osteoblasts, and communicate via canaliculi.
• Osteoblasts form new bone matrix.
• Osteocytes are mature osteoblasts that are completely surrounded by matrix; located in lacunae.
• Osteoclasts breakdown bone and aid in bone remodeling.
• Differentiated into osteoclasts, osteogenic cells, osteoblasts, and osteocytes.
• The bone matrix is concentric lamellae for compact bone.
• Blood vessels penetrate and nutrients and wastes move through canaliculi.

Breakout Group Activity

• The diagram for endochondral ossification should resemble Figure 7.15.
• The steps are: forms most long bones, cells in cartilage differentiate into osteoblasts, minerals are deposited on collagen fibers starting at diaphysisPerichondrium becomes periosteum, blood vessels penetrate periosteum forming primary ossification center: mineralization increases, and cartilage remains at epiphyseal plate to allow bone to grow in length.
• The diagram for intramembranous ossification should resemble Figure 7.14.
• The steps are: Forms flat bones of cranium and face, mesenchymal cells group together and differentiate into osteoblasts forming ossification center, osteoblasts begin to secret osteoid, trabeculae and periosteum form, and compact bone surrounds trabecular bone.

Formation and Growth of Bone and Cartilage (Section 7.4)

• New blood vessel growth is necessary for the ossification of bone regardless of the model used to supply nutrients needed for bone development because cartilage and membranous models are poorly vascularized.
• Ossification is the process of forming bone, requiring a cartilage or membranous model upon which the new bone is built using either intramembranous or endochondral ossification.
• Interstitial cartilage growth occurs as cartilage grows longer by the mitotic replication of chondrocytes, whereas appositional cartilage growth occurs as cartilage grows wider when cells in perichondrium become chondroblasts that secrete matrix.
• Epiphyseal plate is how bones grows in length.

Remodeling

• Osteoblasts form new matrix bone in place of osteoclasts lining the medullary cavity, for appositional growth.
• The changes to bones is on a daily basis.
• When homeostasis takes place minerals are made available.
• Bones increasing strength happens on the line of resistance.
• Osteolcasts are activated by parathyroid as bone is removed and calcium enters the blood stream.

Blood Calcium Regulation

• Bones store calcium to help maintain blood calcium.
• Bones take calcium from thyroid glands: calcitonin, but when it is taken from parathyroid glands: blood calcium levels increase and PTH is secreted.

Bone and Nutrition

• Calcium is stored in extracellular matrices of bones.
• Hypocalcemia results when blood calcium levels are low but when hypercalcemia result when calcium is way too high.
• Small intestines needs vitamin D to take Calcium and absorption will follow.
• Cheese, milk, leafy greens are some of the many sources of calcium.

Other Factors

• Sunlight facilitates calcium absorption where synthesis of D vitamins exist.
• When the hormone estradiol declines, there isn't as much calcium where as bones are weakening.
• Exercise is vital! So physical activities strengthen bones, but some effects, such as osteoporosis, come in play when there are bone damages due to the lack of calcium levels or over production where it is no longer in need, leading to the removal from the body.
• Possible reasons: low bone density comes from bad diet, or smoking habits, or from poor calcium levels.
• What can help it: well balanced calcium diet, quit bad habits, weight bear and physical activities.