Skeletal System

• The skeletal system is a fundamental component of the human body, providing both structure and support.
• Comprising 206 bones in the adult human, 80 from the axial and 126 from the appendicular skeleton, the skeletal system not only forms the body's framework but also plays a crucial role in protecting vital organs, facilitating movement, and storing essential minerals
• Each bone is intricately connected by joints, enabling a range of motion while maintaining stability. Additionally, the skeletal system houses the bone marrow, which is responsible for producing blood cells
• Through its complex interactions with muscles, tendons, and ligaments, the skeletal system is integral to both our physical form and overall health.
• Functions of the bone and the skeletal system

  1. Support
  2. Protection
  3. Assistance in movement
  4. Mineral Homeostasis
  5. Blood cell production
  6. Triglyceride storage
• 1. Support - the skeletal system provides the body with a structural framework
• 2. Protection - the skeleton gives protection for the vital organs of the body from injury.
• 3. Assistance in movement - The skeletal system supports movement by providing a framework for muscles to attach. Bones act as levers, and joints function as pivot points. When muscles contract, they pull on bones, allowing various body movements like walking, running, and lifting.
• Mineral Homeostasis - Bone tissue makes up about 18% of the weight of the human body. On demand, bone releases minerals into the blood to maintain critical mineral balances (homeostasis) and to distribute the minerals to other parts of the body.
• 5. Blood cell production - the bones house the red bone marrow, which is responsible for the production of red blood cells, white blood cells, and platelets
• Triglyceride storage - The skeletal system helps in triglyceride storage through the yellow bone marrow, which is primarily found in the medullary cavity of long bones. Yellow bone marrow consists mostly of adipocytes (fat cells), which store triglycerides as an energy reserve. These triglycerides can be mobilized when the body needs energy during periods of fasting or increased energy demand
• Long- have greater length than width, consist of a diaphyses (body) and a variable number of extremities or epiphyses (ends), and are slightly curved for strength. Most appropriate example is the humerus.
• Short- somewhat cube-shaped and are nearly equal in length and width. Consists of spongy bone tissue except at the surface, which has a thin layer of compact bone tissue. Examples of short bones are most carpal (wrist) bones and most tarsal (ankle) bones.
• Flat- are generally thin and composed of two nearly parallel plates of compact bone tissue enclosing a layer of spongy bone tissue. Flat bones include the cranial cavity bones (which protect the brain) and the sternum and ribs (which protect organs in the thorax).
• Irregular- have complex shapes and cannot be grouped into any of the previous categories. Such bones include the vertebrae (backbones), hip bones, certain facial bones, and the calcaneus (heel bone).
• Sesamoid- shaped like a sesame seed. Developed in certain tendons where there is considerable friction, tension, and physical strain, such as the kneecaps.
• Diaphysis- also called body or shaft, is the long, cylindrical, main portion of the bone.
• 2. Epiphyses- the ends of the bone. The singular term is epiphysis.
• 3. Metaphyses- the regions between the diaphysis and the epiphyses. (hyaline cartilage)
• 4. Articular Cartilage - reduces friction and absorbs shocks at freely movable joints
• 5. Periosteum - Surrounds the bone surface if it is not covered by articular cartilage
• Medullary Cavity - Is a hollow, cylindrical space within the diaphysis that contains fatty yellow bone marrow and numerous blood vessels.
• Endosteum - a thin membrane that lines the internal surfaces of all cavities within bones. It contains a single layer of a small amount of connective tissue and consists of osteoblasts, osteoclasts, and osteoprogenitor cells.
• Histology of bone tissue

  1. Extracellular Matrix
  2. Calcium Phosphate
  3. Calcification
• EXTRACELLULAR MATRIX

  15% Water - 30% Collagen fibers - 55% crystallized mineral salts
• ● CALCIUM PHOSPHATE (Ca3PO4)2

  Most abundant mineral salt in the bone. - Binds with other mineral salts to form hydroxyapatite.
• CALCIFICATION - Initiated by osteoblasts
• Osteoprogenitor cells - Unspecialized bone stem cells derived from mesenchyme. These cells are located along the inner osteogenic layer of the periosteum, in the endosteum, and in the canals within bone that contain blood vessels
• Osteoprogenitor cells - These cells are the only type of bone cell that undergo cell division to develop into osteoblasts.
• Osteoblasts - These cells are bone-building cells. These cells have an extensive endoplasmic reticulum and numerous ribosomes
• Osteoblasts - They make and produce organic components needed to build the extracellular matrix of bone tissues, a process called bone deposition. They initiate calcification and turn into osteocytes
• Osteocytes - They are the mature bone cells. Osteocytes are the main cells in bone tissues.
• Osteocytes - Maintain daily metabolism such as the exchange of nutrients and wastes with the blood.
• Osteoclasts - These cells are huge cells derived from the fusion of as many as 50 monocytes — a type of white blood cell. They are concentrated in the endosteum.
• Osteoclasts - The cell releases powerful lysosomal enzymes and acids that digest the protein and mineral components of the underlying extracellular bone matrix in a process called bone resorption
• Compact- the strongest type of bone, it is dense and primarily supports and resists stress.
• Spongy- consists of open spaces called trabeculae and contains the bone marrow.
• Intramembranous Ossification - Intra (within) Mesenchymal cells (membrane)\
• Bone tissue is a type of replacement tissue. It eventually ends up replacing embryonic cartilage
• Mesenchymal cells - a precursor cell for connective tissues