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What are the main organs of the skeletal system?



Aside from osseus tissue, what are bones composed of?

1. dense irregular connective tissue.
2. dense regular connective tissue.
3. bone marrow.


What are the 6 functions of the skeletal system?

1. Protection: being the hardest substance in the body provides a strong shell for important organs such as brain, heart, and lungs.

2. Mineral storage & acid-base homeostasis: bones store calcium, phosphorus, and magnesium salts (also found in blood) are vital to maintenance of electrolyte and acid-base balance.

3. Blood cell formation: Bones house red bone marrow that performs hematopoiesis aka blood cell formation.

4. Fat storage: yellow bone marrow contains adipocytes that contain triglycerides that can be used as fuel.

5. Movement: Bone serves as attachment sites for skeletal muscles that make movement when they pull on bones.

6. Support: The skeleton supports the body and provides its structural framework.


How many bones do we have?



What are the 5 classifications of bones?

1. Long bones: classified by shape, not size. Ex: most of the arm and leg bones, bones of the hands, fingers, feet and toes.
2. Short bones: classified by shape, not size. Roughly as long as they are wide. Ex: carpals and tarsals.
3. Flat bones: Thin and broad. Ex: most skull bones, clavicles, ribs, sternum, and bones of pelvis.
4. Irregular bones: Don't fit into another shape category. Ex: vertebrae, certain skull bones.
5. Sesamoid bones: sesame shaped. Specialized bones within tendons that give mechanical advantage. Ex: patella


What is the periosteum?

is a membrane composed of dense
irregular collagenous connective tissue that forms a covering, rich with blood vessels and nerves, which surrounds the outer surface of long bones


What are perforating fibers (aka Sharpey's fibers)?

are made of collagen that anchors the periosteum firmly to the underlying bone surface by penetrating deep into the bone matrix.


The shaft of long bone is called? What is the cavity inside the shaft called?

Diaphysis. Medullary aka Marrow cavity.


The rounded ends of long bone is called? And what are these covered in?

Epiphyses. Covered in hyaline cartilage (articular)


What are the two bone textures?

1. Compact bone: hard, dense outer bone. Resists stresses, linear compression, and twisting forces.
2. Spongy bone aka cancellous bone: forms a framework of bony struts that resists force from many directions and houses bone marrow.


What is endosteum?

The membrane that covers the bony struts of spongy bone and all inner surfaces of bone.


What are epiphyseal lines?

are found separating both
proximal and distal epiphyses from the diaphysis. These are the remnants of the epiphyseal plates, or growth plates, which is a line of hyaline cartilage found in the developing bones of children.


What 5 things do short, flat, irregular, and sesamoid bones lack?

diaphyses, epiphyses, medullary cavity, epiphyseal lines, or epiphyseal plates.


What are epiphyseal plates?

growth plates: a line of hyaline cartilage from which a long bone grows in length in children.


What is the internal structure of short, flat, irregular, and sesamoid bones composition?

Its like a sandwich with 2 layers of compact bone with a layer of spongy bone (that contains the marrow) in the middle


what is the spongy layer called in flat bones?

diploe, meaning fold.


What are sinuses?

Hollow, air-filled spaces, which reduces bone weight. Found in Some flat and irregular bones of the skull.


How are the external structures of all bones similar?

They are all covered in periosteum attached by perforating fibers, and well supplied by blood vessels and nerves.


What is red bone marrow composed of?

of loose connective tissue that supports islands of blood-forming hematopoietic cells.


Where is red marrow found in adults?

in the pelvis, proximal femur, humerus, vertebrae, ribs, sternum, clavicles, and scapulae. Also in skull, but degenerates w/age.


What is yellow marrow composed of? What does it store?

blood vessels and adipocytes. It stores triglycerides.


Why do children have more red marrow vs. adults who have more yellow marrow?

Children need a constant supply of blood because of their rapid growth. By age 5, yellow marrow starts to replace red until adulthood is reached.


What is the composition of osseous tissue?

extracellular matrix with a small population of cells scattered throughout.


Concerning the ECM of osseous tissue, what is the composition of the inorganic matrix, and what is its percentage?

consists of minerals (calcium salts). It makes up 65% of the total weight of the bone.
* also found in the inorganic matrix is bicarbonate, potassium, magnesium, and sodium*


Concerning the ECM of osseous tissue, what is the composition of the organic matrix, and what is its percent?

consists of collagen fibers and the usual ECM components. It makes up 35%


Bone stores what % of calcium ions in the body? What else does it store?

85%. It store phosphorus.


Calcium and phosphorus exist as a large molecule called? What is the benefit of this molecule?

hydroxyapatite crystals. Its benefit is that its super strong and resistant to compression.


What is the organic matrix known as? What does it consist of?

Osteoid. It consists of protein fibers, proteoglycans, glycosaminoglycans, glycoproteins, and bone-specific proteins.


What is the predominant protein fiber in bone, and what is its function?

Collagen fibers. They form cross-links with one another and resist torsion and tensile force. They align with hydroxyapatite crystals to enhance bone's hardness.


What is the function of glycosaminoglycans and proteglycans in the organic matrix? What do the glycoproteins do?

They create an osmotic gradient that draws water into the osteoid, which helps the tissue resist compression. Glycoproteins act as cellular glue binging to both hydroxyapatite and bone cells.