Chapter 19. The musculoskeletal system
At the end of this section you can:
- Classify the different types of bones in the skeleton
- Explain the role of different cell types in bone
- Explain how bones form during development
Mineral salts mainly include hydroxyapatite, a mineral formed from calcium phosphate. calcificationIt is the deposition process of mineral salts in the matrix of collagen fibers that crystallizes and hardens the tissue. The calcification process takes place only in the presence of collagen fibers.
The bones of the human skeleton are classified according to their shape: long bones, short bones, flat bones, suture bones, sesamoid bones, and irregular bones (Fig. 19.16).
long bonesthey are longer than they are wide, and have a stalk and two ends. O Shaft, or central rod, contains bone marrow in a marrow cavity. the rounded ends, Epiphysen, are covered with articular cartilage and filled with red bone marrow, which produces blood cells (Fig. 19.17). Most limb bones are long bones - for example, the femur, tibia, ulna, and radius. Exceptions are the patella and the bones of the wrist and ankle.
short bones, or cube bones, are bones that are the same width and length, giving them a cube shape. For example, the bones of the wrist (carpal) and ankle (tarsal) are short bones (Figure 19.16).
flat bonesare thin, relatively wide bones found where extensive organ protection is required or where large surfaces are needed for muscle attachments. Examples of flat bones include the sternum (breastbone), ribs, shoulder blades (shoulder blades), and the roof of the skull (Figure 19.16).
sesamoid bonesthey are small, flat bones and shaped like a sesame seed. The kneecaps are sesamoids (Fig. 19.18). Sesame legs develop in tendons and can be found near joints in knees, hands, and feet.
Bones are considered organs because they contain different types of tissues such as blood, connective tissue, nerves, and bone tissue. Osteocytes, the living cells of bone tissue, form the mineral matrix of bones. There are two types of bone tissue: compact and spongy.
compact bone tissue
compressed bone(or cortical bone) forms the hard outer layer of all bones and surrounds the medullary cavity or bone marrow. Provides protection and strength to the bones. Compact bone tissue is made up of units called osteons or Haversian systems. Osteonenare cylindrical structures containing a mineral matrix and living osteocytes connected by tubules that carry blood. They are aligned parallel to the long axis of the bone. Each osteon consists of Slats, which are layers of a compact matrix surrounding a central canal called the Haversian canal. O Havers Canal (osteonic canal)contains the blood vessels and nerve fibers of the bone (Fig. 19.19). Osteons in compact bone tissue are oriented in the same direction along the lines of stress and help the bone resist bending or fracture. Therefore, compact bone tissue is prominent in areas of the bone where loads are applied in only a few directions.
Which of the following statements about bone tissue is incorrect?
- Compact bone tissue consists of cylindrical osteons aligned to run the length of the bone.
- Haversian canals contain only blood vessels.
- Haversian canals contain blood vessels and nerve fibers.
- There is spongy tissue on the inside of the bone and compact bone tissue on the outside.
spongy bone tissue
While compact bone tissue forms the outer layer of all bones, cancellous boneor cancellous bone forms the inner layer of all bones. Spongy bone tissue does not contain osteons, which form compact bone tissue. Instead it consists of bunch, which are lamellae that are arranged like rods or plates. There is red bone marrow between the trabuculae. Blood vessels within this tissue provide nutrients and remove waste products to osteocytes. The red bone marrow of the femur and the interior of other large bones, such as the ileum, make up the blood cells.
Cancellous bone reduces bone density and allows the ends of long bones to compress as a result of the stress placed on the bone. Cancellous bone occurs in areas of the bone that are not heavily used or where loads come from multiple directions. The epiphyses of bones such as B. the femoral neck are exposed to loads from different directions. Imagine placing a heavy framed painting on the floor. You can hold one side of the picture with a toothpick if the toothpick is perpendicular to the floor and the picture. Now drill a hole and stick the toothpick into the wall to hang the picture. In this case, the function of the toothpick is to transfer downward pressure from the painting to the wall. The force on the picture is directly on the floor, but the force on the rod is both pulling down the picture wire and pushing up the bottom of the hole in the wall. The toothpick will break straight into the wall.
The femoral neck is horizontal like the toothpick on the wall. The weight of the body pushes it down near the joint, but the vertical shaft of the femur pushes it up at the other end. The femoral neck must be strong enough to transmit the downward force of body weight horizontally to the vertical axis of the femur (Fig. 19.20).
concept in action
VisionmicrographsMusculoskeletal tissue while reviewing anatomy.
cell types in bones
Bones are made up of four types of cells: osteoblasts, osteoclasts, osteocytes, and osteoprogenitor cells. Osteoblastenare bone cells that are responsible for the formation of bones. Osteoblasts synthesize and secrete the organic and inorganic portions of the extracellular matrix of bone tissue and collagen fibers. Osteoblasts become entrapped in these secretions and differentiate into less active osteocytes. Osteoclastsare large bone cells with up to 50 cell nuclei. They remove the bone structure by releasing lysosomal enzymes and acids that dissolve the bone matrix. Released from the bones into the blood, these minerals help regulate calcium levels in body fluids. Bone can also be resorbed for remodeling when the applied loads are changed. Osteozytenthey are mature bone cells and the chief cells of bone connective tissue; these cells cannot divide. Osteocytes maintain normal bone structure by recycling mineral salts from the bone matrix. osteoprogenitor cellsare squamous stem cells that divide to produce daughter cells that differentiate into osteoblasts. Osteoprogenitor cells are important in fracture healing.
Ossification, or osteogenesis, is the process of bone formation by osteoblasts. Ossification differs from the calcification process; While calcification occurs during bone ossification, it can also occur in other tissues. Ossification begins about six weeks after fertilization in an embryo. Before this period, the embryonic skeleton consists entirely of fibrous membranes and hyaline cartilage. The development of bone from fibrous membranes is called intramembranous ossification; The development of hyaline cartilage is called endochondral ossification. Bone growth continues until about age 25. Bones can increase in thickness throughout life, but after age 25 ossification is primarily for bone remodeling and repair.
intramembranous Ossificationis the process of bone development from fibrous membranes. It is involved in the formation of the flat bones of the skull, jaw and collarbones. Ossification begins when mesenchymal cells form a blueprint for future bone. They then differentiate into osteoblasts in the ossification center. Osteoblasts secrete the extracellular matrix and deposit calcium, which hardens the matrix. The non-mineralized portion of bone or osteoid continues to form around the blood vessels, forming cancellous bone. Connective tissue in the matrix differentiates into red bone marrow in the fetus. The cancellous bone is remodeled into a thin layer of compact bone on the surface of the cancellous bone.
In long bones, chondrocytes form a cast of the diaphysis of hyaline cartilage. In response to complex developmental signals, the matrix begins to calcify. This calcification prevents the diffusion of nutrients into the matrix, leading to the death of chondrocytes and the opening of cavities in the cartilage of the diaphysis. Blood vessels invade the cavities, and osteoblasts and osteoclasts modify the calcified cartilage matrix in spongy bone. Osteoclasts then break off some of the cancellous bone to create a medullary or medullary cavity in the middle of the diaphysis. Dense, irregular connective tissue forms a sheath (periosteum) around the bones. The periosteum helps attach bones to surrounding tissues, tendons, and ligaments. The bone continues to grow and lengthen as the cartilage cells in the epiphyses divide.
In the final stage of prenatal bone development, the centers of the epiphyses begin to calcify. Secondary ossification centers form in the epiphyses when blood vessels and osteoblasts invade these areas and transform hyaline cartilage into cancellous bone. Hyaline cartilage persists until puberty Epiphysenfuge(growth plate), this is the area between the diaphysis and epiphysis that is responsible for the length growth of the long bones (Fig. 19.21).
Long bones continue to lengthen, possibly into adolescence, with the addition of bone tissue at the epiphyseal plate. They also increase in width by appositional growth.
elongation of the long bones
Chondrocytes on the epiphyseal side of the epiphyseal plate divide; one cell remains undifferentiated near the epiphysis and one cell moves toward the diaphysis. The cells pushed out of the epiphysis mature and are destroyed by calcification. This process replaces cartilage with bone on the diaphyseal side of the plate, resulting in elongation of the bone.
Long bones stop growing around age 18 in women and around age 21 in men, in a process called epiphyseal closure. During this process, the cartilage cells stop dividing and all of the cartilage is replaced with bone. The epiphyseal plate disappears, leaving a structure called the epiphyseal line or epiphyseal remnant, and the epiphysis and diaphysis fuse.
thickening of long bones
appositional growthis the increase in bone diameter by adding bone tissue to the bone surface. Osteoblasts on the bone surface secrete bone matrix and osteoclasts on the inner surface break down bone. Osteoblasts differentiate into osteocytes. A balance between these two processes allows bone to thicken without becoming too heavy.
Bone remodeling and repair
Bone turnover continues after birth into adulthood. bone reconstructionIt is the replacement of old bone tissue with new bone tissue. It involves the processes of bone deposition by osteoblasts and bone resorption by osteoclasts. Normal bone growth requires vitamins D, C and A and minerals such as calcium, phosphorus and magnesium. Hormones such as parathyroid hormone, growth hormone and calcitonin are also required for proper bone growth and maintenance.
Bone turnover rates are quite high, with five to seven percent of bone mass being recycled every week. There are differences in the rate of turnover in different areas of the skeleton and in different areas of a bone. For example, the bone at the femoral head can be completely replaced every six months, while the bone along the shaft changes much more slowly.
Bone remodeling allows bones to adapt to stress and to grow thicker and stronger when subjected to stress. Bones that are not subjected to normal loading, for example when a limb is in plaster, begin to lose mass. A broken or fractured bone is repaired in four stages:
- Blood vessels in the broken bone rupture and bleed, causing clotted blood or hematoma at the fracture site. The severed blood vessels at the broken bone ends are closed by the clotting process and the nutrient-poor bone cells begin to die.
- A few days after the rupture, capillaries grow into the hematoma and phagocytes begin removing dead cells. Although fragments of the blood clot may remain, fibroblasts and osteoblasts invade the area and begin to regenerate bone. Fibroblasts produce collagen fibers that connect the ends of broken bones, and osteoblasts begin to form spongy bone. The repair tissue between the fractured bone ends is called fibrocartilaginous callus because it is composed of hyaline and fibrocartilage.Figure 19.22🇧🇷 Some Bone Pins may also appear at this point.
- The fibrocartilaginous callus is transformed into a bony callus of cancellous bone. It takes about two months for the ends of the broken bone to be firmly connected after the fracture. This is similar to endochondral bone formation as the cartilage becomes ossified; Osteoblasts, osteoclasts and bone matrix are present.
- The bone callus is then remodeled by osteoclasts and osteoblasts, removing excess material outside the bone and inside the medullary cavity. Compact bone is added to create bony tissue similar to the original, intact bone. This remodeling can take many months and the bone can remain uneven for years.
Scientific method connection
Question:What effect does the removal of calcium and collagen have on bone structure?
Background:Conduct a literature review on the role of calcium and collagen in maintaining bone structure. Conduct bibliographical research on diseases in which bone structure is compromised.
Hypothesis:Develop a hypothesis that predicts the flexibility, strength, and mass of bones that have had their calcium and collagen components removed. Develop a hypothesis about trying to add calcium back to decalcified bones.
Test the hypothesis:Test the prediction by removing calcium from chicken bones by soaking them in a jar of vinegar for seven days. Test the hypothesis about adding calcium to the decalcified bone by placing the decalcified chicken bones in a jar of water with added calcium supplements. Test the prediction by denaturing the collagen in the bones by baking them at 250 °C for three hours.
Analyze the data:Create a table showing changes in flexibility, strength, and bone mass in the three different environments.
Report result:Under what conditions was the bone most flexible? Under what conditions was the bone strongest?
To reach a decision:Did the results support or disprove the hypothesis? How do the results observed in this experiment correlate with diseases that destroy bone tissue?
Bone, or bone tissue, is a connective tissue that contains specialized cells, mineral salts, and collagen fibers. The human skeleton can be divided into long bones, short bones, flat bones and irregular bones. Compact bone tissue consists of osteons and forms the outer layer of all bones. Spongy bone tissue consists of trabeculae and forms the inner part of all bones. Bone tissue is made up of four types of cells: osteocytes, osteoclasts, osteoprogenitor cells, and osteoblasts. Ossification is the process of bone formation by osteoblasts. Intramembranous ossification is the process of bone development from fibrous membranes. Endochondral ossification is the process of bone development from hyaline cartilage. Long bones lengthen when chondrocytes divide and secrete hyaline cartilage. Osteoblasts replace cartilage with bone. Appositional growth is the increase in bone diameter by adding bone tissue to the bone surface. Bone remodeling includes the processes of bone deposition by osteoblasts and bone resorption by osteoclasts. Bone repair occurs in four phases and can take several months.
- Or Haversian channel:
- arranged as rods or plates
- contains bone blood vessels and nerve fibers
- is responsible for the length growth of the tubular bones
- synthesize and secret matrix
- Die Epiphysenfuge:
- arranged as rods or plates
- contains bone blood vessels and nerve fibers
- is responsible for the length growth of the tubular bones
- synthesizes and secretes bone matrix
- The cells responsible for bone resorption are ________.
- Compact bone consists of ________.
- compressed collagen
- only calcium phosphate
- What are the main differences between cancellous bone and compact bone?
- What are the functions of osteoblasts, osteocytes and osteoclasts?
- Compact bone tissue forms the hard outer layer of all bones and is made up of osteons. Compact bone tissue is prominent in areas of bone where loads are applied in only a few directions. Cancellous bone forms the inner layer of all bones and consists of trabeculae. Cancellous bone occurs in areas of the bone that are not heavily used or where loads come from multiple directions.
- Osteocytes are used to exchange nutrients and waste products with the blood. They also maintain normal bone structure by recycling mineral salts in the bone matrix. Osteoclasts remove bone tissue by releasing lysosomal enzymes and acids that dissolve the bone matrix. Osteoblasts are bone cells responsible for bone formation.
- appositional growth
- Enlargement of the bone diameter through accumulation of bone tissue on the bone surface
- bone reconstruction
- Replacement of old bone tissue with new bone tissue
- (also bone tissue) Connective tissue that makes up the endoskeleton
- Process of deposition of mineral salts in the matrix of collagen fibers that crystallize and harden the tissue
- compacted bone
- forms the hard outer layer of all bones
- Central axis of the bone, contains bone marrow in a marrow cavity
- endochondral ossification
- Process of bone development from hyaline cartilage
- Area between the diaphysis and epiphysis that is responsible for the length growth of the long bones
- rounded end of the bone, covered with articular cartilage and filled with red bone marrow, which produces blood cells
- planus bone
- Thin, relatively wide bone is found where extensive organ protection is required or where large muscle attachment surfaces are required
- Havers Canal
- contains bone blood vessels and nerve fibers
- intramembranous Ossification
- Process of bone development from fibrous membranes
- jagged bone
- bones with complex shapes; Examples are vertebrae and hip bones
- Layer of compact tissue surrounding a central canal called Haversian canal
- long bone
- Bone longer than wide, with a shaft and two ends
- bone tissue
- Connective tissue that makes up the endoskeleton
- (also osteogenesis) Process of bone formation by osteoblasts
- Bone cell responsible for bone formation
- large bone cells with up to 50 nuclei that are responsible for bone remodeling
- mature bone cells and the main cell of bone tissue
- cylindrical structure aligned parallel to the long axis of the bone
- small, flat bone in the shape of a sesame seed; develops within the tendons
- short bone
- Bone that has the same width and length, giving it a cube shape
- spongy bone tissue
- forms the inner layer of all bones
- small, flat, irregularly shaped bone that forms between the flat bones of the skull
- Lamellae arranged in rods or plates