Bones and skeletal tissues

What does it mean "bone remodeling"? What are the cells responsible of this process? What are the hormones that regulates this process? What is another factor regulating bone remodeling?

bone remodeling is the process of depositing bone and removed at the endosteal surface. This process occurs at the endosteum lining the central canals of osteons. Osteoblasts and osteoclasts are responsible for this. Hematopoietic stem cells and parathyroid hormones are integral to this process. Zero gravity can hamper bone growth.

Describe the postnatal growth of long bones. How do bones lengthen? How do they widen? Describe the microscopic anatomy of the epiphyseal plate.

Bone growth is stimulated by the pituitary gland at the epiphyseal plates. The thyroid makes sure that the bone is growing within the proper parameters. Since growth in both directions happens at the same time. As the bone grows out, the epiphyseal plate grows out as well and when closure of this plate occurs, the growing stops and the growing of the bone stops because the mitotically active cartilage cells stop being produced. to grow in width, the osteogenic layer have osteoblasts that that add bone tissue in the cuneiform lamalle. while the osteoclasts remove bone from the surface of the diaphysis wall. Layers of the epiphyseal plate resting 1- Proliferation zone- cartilage cells undergo mitosis 2- Hypertrophic zone- older cartilage cells enlarge 3- Calcification zone- matrix becomes calcified, cartilage cells die, matrix begins deteriorating 4- Ossification Zone- new bone is forming

Why are bones considered an organ?

Bones are considered organs because they contain several different types of tissues such as nerves, blood tissue, cartilage and others besides bone.

What is the endochondral ossification? List and describe the 5 phases of this process.

Bones that are formed in hyaline cartilage, and get replaced by bone tissue, growth is not completed until early adulthood. 1. Perichondrium surrounding the diaphysis is invaded by blood vessels and becomes a bone forming periosteum. Osteoblasts lay down a new layer of collar bone around the diaphysis. 2. The cartilage in the center calcifies and becomes impermeable to diffusing nutrients. The inside starts to deteriorate and cavities begin to form. Elsewhere the cartilage is healthy and grows causing the bont to become long. 3. The periosteal bud goes into the diaphysis and further erodes it. Bone covered trabeculae is formed and this is the first sign of spongy bone. Bone tissue continues to form around the diaphysis and this makes up the primary ossification center. 4. The bone continues to lengthen due to calcifying and replacement of trabeculae. Osteocytes break down the ends to form cavities. A bud comes in and bone trabecular forms. These become secondary ossification centers. Epiphysis ossify, and cartilaginous epiphyseal plates separate diaphysis and epiphysis. these plates are also areas of bone growth.

Describe differences between compact bone tissue and spongy bone tissue.

Compact Bone- Forms the outer layer, made out of osteons Spongy Bone- Inside the outer compact bone layer, made up of trabeculae and has red marrow found between trabeculae

What is a compound fracture? And a simple fracture?

Compound- when broken ends protrude through the skin Simple- Bone breaks cleanly, does not break skin

Name the six more common types of fracture. Describe the 4 phases of bone repair.

Fractures 1. Comminuted- fragments into 3 or more pieces 2. Compression- bone is crushed 3. Spiral- ragged break from excessive twisting 4. Epiphyseal- separates from diaphysis along epiphyseal plate 5. Depressed- broken bone portion is pressed inward 6. Greenstick- partial breakage, bends other part 4 phases of bone repair 1. Hematoma formation- Vessels break and given some time clot, inflammation. 2. Fibrocartilage and callus formation- New blood vessels grow near the clot and bone forming cells appear. they invade the clot and deposit repair tissue, soft callus. This layers and becomes dense ct. It can then be called fibrocartilage. 3. Bony callus formation- Trabeculae span both of the two fragments and unite the fragments, now becomes hard callus. Trabeculae grows thicker and firm. 4. Bone remodeling- Over months, bone is remodeled and excess is removed and compact bone is laid down.

Describe in detail the gross anatomy of a long bone. Describe the gross anatomy of flat, short and irregular bones.

Long Bone: Long and wide with two distinct ends Flat Bone: Thin, flattened and somewhat curved Short Bone: Cube like shaped Irregular Bone: Various shapes that do not fit into the others, can have holes in them

Name 6 functions of bones.

Support- Provides hard framework that supports the body Movement- skeletal muscles attach to bones through tendons and act as hinges. Protection- Bones like the skull and rib cage surround organs and provide them with protection. Mineral Storage- They serve as a reservoir especially for organs like the brain. Blood cell formation and energy storage- bones contain red and yellow bone marrow which store fat and helps produce red blood cells. Energy Metabolism- Secretes a hormone that influences blood sugar regulation and energy metabolism.

Describe the chemical composition of bone and distinguish between its organic and inorganic components.

The organic compounds are made up of cells and osteoids which make up roughly a third of the matrix, this contributes to bone flexibility. The inorganic is largely calcium and phosphate.

What is the intramembranous ossification? List and describe the 4 phases of this process.

This includes bones of the skull and the clavicle. this has to do with the modeling of bones without being molded in cartilage. 1) Mesenchyme cells begin to group in the connective tissue and become osteoblasts. 2) These start to secrete the organic part of the bone matrix, osteoid, which will then mineralize. 3) When surrounded by matrix osteoblasts can be reidentified as osteocytes. Bone tissue forms in the embryonic blood vessels and are woven randomly. The result is woven bone tissue that has trabeculae but it lacks lamalle. At the same time, mesenchyme thickens on the outer parts and becomes periosteum. 4) Trabeculae at periphery grows thicker and that form compact bone on the ends. In side, spongy bone is formed because trabeculae remains distinct, this becomes a flat bone.

What is osteoporosis and how is it treated?

This is characterized by low bone mass and deterioration of the microscopic architecture of the bony skeleton. It is treated with supplemental calcium and vitamin D. Newer treatments suppress osteoclast activity and slow down bone loss. Also a parathyroid hormone allows for uptake of more calcium. These are not cures but they allow avoidance of fractures.