Bone Structure PDF

2/16/25, 6:42 PM 6.1.2: Bone Structure Bone Structure 1. What are dense regular and dense irregular collagenous connective tissues? (Module 4.3.1) 2. What are collagen fibers? (Module 4.1.2) 3. What is hyaline cartilage? (...

2/16/25, 6:42 PM 6.1.2: Bone Structure Bone Structure 1. What are dense regular and dense irregular collagenous connective tissues? (Module 4.3.1) 2. What are collagen fibers? (Module 4.1.2) 3. What is hyaline cartilage? (Module 4.3.2) Looking at all the bones in a skeleton, you can see that they show great diversity in appearance. However, even with all this variation, we can define five structural bone classes, and each of our 206 bones fits into one of these OT DISTR classes. The criterion used to categorize a bone is its general shape. In this section we examine bone shapes, then N discuss their structure in more detail. O I B Classification of Bones by Shape D UT - © P E A RS O N E The five general bone shapes, shown in Figure 6.2, are long, short, flat, irregular, and sesamoid. Let’s take a IGUEZ... closer look at what defines each shape. Long bones. Long bones are named for the fact that they are longer than they are wide (Figure 6.2a). Examples of long bones include most bones of the arms and legs (including the humerus, or arm bone), as well as bones of the hands, feet, fingers, and toes. Note that long bones are not named for their size—in fact, some long bones are quite small. ODR Short bones. Short bones are about as long as they are wide, or roughly cube-shaped (Figure 6.2b). Examples of short bones include the carpals (bones of the wrist) and tarsals (bones of the ankle). Like long AR FO bones, short bones are named for their shape rather than their size. N Flat bones. As implied by their name, flat bones are thin and broad (Figure 6.2c). Examples of flat bones R TA include most bones of the skull,Hthe ribs, the sternum, and the bones of the pelvis. T Irregular bones. The irregular bones R S ANdue to their irregular shapes (Figure E P do not fit into the other classes IVA T 6.2d). Examples of irregular bones include the T E U S E OFcertain skull bones. vertebrae and Sesamoid bones. Sesamoid bones (SEH-suh-moyd; “sesame-shaped”) are small, relatively flat, and oval- shaped bones located within tendons (​Figure 6.2e​). They give the tendon a mechanical advantage, providing better leverage for muscles, and also reduce wear and tear on the tendon. An example of a sesamoid bone is the patella (kneecap). Figure 6.2 Classification of bones by shape. https://plus.pearson.com/courses/ediger74207/products/e465533c-0856-4464-ba3f-21fa655407d3/pages/urn:pearson:entity:5e772fd8-d4b5-47ba-82af-3d5eddfca1b8?… 1/6 2/16/25, 6:42 PM 6.1.2: Bone Structure N OT DISTR IB DO The five classifications are detailed as follows. UT - Diagram A, long bone, shows the humerus. A long bone is longer than it is wide. © P E A RS O N E Diagram B, short bone, shows the trapezium, a carpal bone. A short bone is about as long as it is wide. IGUEZ... Diagram C, flat bone, shows the sternum. A flat bone is broad, flat, and thin. Diagram D, irregular bone, shows a vertebra. An irregular bone’s shape does not fit into other classes. Diagram E, sesamoid bone, shows the patella. A sesamoid bone is a round, flat bone found within a ODR tendon. AR FO Structure of a Long Bone N R TA HEyou’ll see that most of its surfacesNare covered with a membrane, the T When you look at a long bone’s surface, periosteum (pehr′-ee-AHS-tee-um; peri- =PR SA 6.3a). The periosteum is “around,” oste- = “bone”)T(Figure IVATtissue composed of dense irregular collagenous connective EO E USthat F supplied with blood vessels and nerves. is richly As Figure 6.3a shows, the periosteum is firmly attached to the underlying bone by collagen fibers called perforating fibers. These fibers penetrate deeply into the bone matrix, securing the periosteum in place. The innermost surface of the periosteum contains different types of bone cells, as we’ll see in the next module. Figure 6.3 Structure of long bones. https://plus.pearson.com/courses/ediger74207/products/e465533c-0856-4464-ba3f-21fa655407d3/pages/urn:pearson:entity:5e772fd8-d4b5-47ba-82af-3d5eddfca1b8?… 2/6 2/16/25, 6:42 PM 6.1.2: Bone Structure N OT DISTR O I B D UT - © P E A RS O N E IGUEZ... ODR AR FO N R TA HE T N PR IVAT T SA E USE OF https://plus.pearson.com/courses/ediger74207/products/e465533c-0856-4464-ba3f-21fa655407d3/pages/urn:pearson:entity:5e772fd8-d4b5-47ba-82af-3d5eddfca1b8?… 3/6 2/16/25, 6:42 PM 6.1.2: Bone Structure The two diagrams read as follows. Diagram A shows the external structure of a long bone, and Diagram B shows a sectioned long bone. In A, hyaline, or articular, cartilage caps the ball of the hip in the epiphysis, and the nutrient foramen runs through the cavity of the diaphysis. Perforating fibers attach the periosteum to the diaphysis. Diagram B, red bone marrow fills three cavities in the spongy bone of the epiphysis that are separated by the epiphyseal lines. The endosteum surrounds the medullary cavity, which perforates compact bone in the diaphysis, and the nutrient artery runs through the medullary cavity. Yellow bone marrow fills the cavity above the nutrient artery. Each long bone has a middle shaft and two rounded ends, features unique to long bones. The shaft of a long bone is called its diaphysis (dy-AF-uh-sis; dia- = “across”). At the ends of the bones we find the enlarged, rounded N OT DISTR epiphyses (eh-PIF-uh-seez; singular, epiphysis; epi- = “upon”). Notice in Figure 6.3a that the epiphyses are covered with a thin layer of hyaline cartilage, also known as articular cartilage, which allows bones to rub together with reduced friction at joints. O I B D UT - Inside a long bone (Figure 6.3b) the diaphysis surrounds a hollow cavity called the medullary cavity (MED-yoo- © P E A RS O N lehr-ee), also known as the marrow cavity (medullary = “marrow”). As its name implies, this is where much of E the marrow of a long bone is housed. The marrow can be either yellow or red, depending on the bone and the IGUEZ... person’s age. As you can see in Figure 6.3b, bone has two obviously different textures. The hard, dense outer bone is compact bone. The structure of compact bone enables it to resist the majority of stresses placed on it, which are linear compression and twisting forces. The inner, honeycomb-like bone is spongy bone, or cancellous bone (KAN-sel- ODR us). Spongy bone forms a framework of bony struts that allows it to resist forces in many directions and provides a place for the bone marrow to reside. The diaphyses of long bones consist of a very thick layer of compact bone AR with only scant inner spongy bone surrounding the medullary cavity. As with the diaphysis, the outer parts of the FO epiphyses are compact bone; however, the interior of the epiphyses consists of abundant spongy bone. Both N R compact and spongy bone will be discussed further in Module 6.2. TA HE T N A lined with a membrane called the PRall inner surfaces of bone,TSare The bony struts of spongy bone, and indeed IVALike endosteum (en-DAHS-tee-um; endo- = “within”). TE theU S E OF the endosteum contains different types of periosteum, bone cells that help maintain bone homeostasis. However, the endosteum is thinner and lacks the fibrous outer layer that we see with the periosteum. One final thing to note in Figure 6.3b is the presence of lines running across the proximal and distal ends of the bone between the epiphysis and the diaphysis. These lines, called epiphyseal lines (eh-PIF-ih-see-uhl), are remnants of a structure termed the epiphyseal plate. The epiphyseal plate, also known as the growth plate, is a line of hyaline cartilage from which a long bone grows in length in children and adolescents. Bone growth and the role of the epiphyseal plate are discussed in Module 6.4. Structure of Short, Flat, Irregular, and Sesamoid Bones Short, flat, irregular, and sesamoid bones do not have diaphyses or epiphyses. As a result, they contain no medullary cavity, epiphyseal lines, or epiphyseal plates. But as you can see in Figure 6.4, they do share some similarities with long bones. Externally these bones are covered with a periosteum attached by perforating fibers and well supplied with blood vessels and nerves. In addition, they have an outer layer of compact bone that surrounds the inner spongy bone. https://plus.pearson.com/courses/ediger74207/products/e465533c-0856-4464-ba3f-21fa655407d3/pages/urn:pearson:entity:5e772fd8-d4b5-47ba-82af-3d5eddfca1b8?… 4/6 2/16/25, 6:42 PM 6.1.2: Bone Structure Figure 6.4 Structure of short, flat, irregular, and sesamoid bones. N OT DISTR Notice that their internal structure is fairly simple. A section through one of these bones resembles a “sandwich” made up of two thin layers of compact bone and a middle layer of spongy bone housing bone marrow. In flat O I B D bones, the spongy bone is called the diploë (dip-LOH-ee; diploë = “fold”). The interior of some flat and irregular bones of the skull contains hollow, air-filled spaces called sinuses that make the bones lighter. UT - © P E A RS O N E Blood and Nerve Supply to Bone IGUEZ... Bones are well supplied with blood vessels (look again at Figures 6.3 and 6.4), as evidenced by the extensive bleeding that occurs whenever a bone is injured. Bones are also supplied with many sensory fibers, which is why such an injury hurts so acutely. The blood supply to short, flat, irregular, and sesamoid bones comes largely from vessels in the periosteum that penetrate the bone. Long bones also get a significant portion (about one-third) of their blood supply from the periosteum, which supplies primarily the compact bone. However, their greatest ODR source of blood comes from one or two nutrient arteries that enter the bone via a small hole in the diaphysis AR called the nutrient foramen (fohr-AY-men; see Figure 6.3b). The nutrient artery passes through compact bone FO into the inner medullary cavity, where it supplies the internal structures of the long bone. The epiphyses receive N some of their blood supply from the nutrient artery, but most of it comes from small blood vessels that enter and R TA exit via numerous small holes in their H T compact E bone. N PR IVAT T SA Red and Yellow Bone Marrow E USE OF As we discussed earlier, there are two types of bone marrow with different functions. Red bone marrow consists of a network of reticular fibers supporting islands of blood-forming, or hematopoietic, cells. Yellow bone marrow, which stores triglycerides, consists mostly of blood vessels and adipocytes. In infants and young children, most bone marrow is red because their rapid rate of growth requires a constant supply of new blood cells. At about age 5, yellow bone marrow begins to replace some of the red bone marrow. By the time we reach adulthood, most bone marrow in the body is yellow. Red marrow remains only in the bones of the pelvis, the proximal femur and humerus (thigh and arm bones), the vertebrae, the ribs, the sternum, the clavicles, and the scapulae (shoulder blades). A small amount of red marrow is also found in certain bones of the skull, but this degenerates as we age. Adults have limited red bone marrow because we are not actively growing and do not need hematopoiesis to occur as rapidly as it does in young children. However, some yellow marrow can be replaced with red marrow if increased blood cell production is needed. Bone marrow can also be transplanted to treat some diseases of the blood—see A&P in the Real World: Bone Marrow Transplantation. A&P in the Real World https://plus.pearson.com/courses/ediger74207/products/e465533c-0856-4464-ba3f-21fa655407d3/pages/urn:pearson:entity:5e772fd8-d4b5-47ba-82af-3d5eddfca1b8?… 5/6 2/16/25, 6:42 PM 6.1.2: Bone Structure Bone Marrow Transplantation Diseases of the blood such as leukemia, sickle-cell anemia, and aplastic anemia feature improperly functioning hematopoietic cells. One potential treatment for such diseases is bone marrow transplantation, in which hematopoietic cells from red bone marrow are removed from a matching donor and given to a recipient. Bone marrow is removed from a donor by a procedure called a bone marrow harvest, during which a needle is inserted into the pelvic bone of an anesthetized donor and red bone marrow is withdrawn. This is generally repeated several times until one to two quarts of red bone marrow—about 2% of the total—has been removed. Before the recipient can receive the donor’s marrow, the recipient’s own marrow is destroyed with chemotherapy and/or radiation. At this point, the bone marrow from the donor is given to the recipient intravenously, and the cells travel to the recipient’s spongy bone. If all goes well, in about 2–4 weeks the hematopoietic tissue will begin producing blood cells. Recipients typically experience flu-like symptoms during this period, and they run the risk of complications, including infection and transplant rejection. However, if the transplant “takes,” or is accepted, many recipients can return to a healthy life. Quick Check N OT DISTR O I B D 1. ​3. Look at Figure 6.2 and classify the following bones as long, short, flat, or irregular. UT - 1. a. Phalanges (fingers) © P E A RS O N 2. b. Ribs E 3. c. Carpals IGUEZ... 4. d. Pelvis 5. e. Humerus 2. 4. Where are compact bone and spongy bone located, and what are their functions? 3. 5. What are the two types of bone marrow, and what are their functions? ODR Apply What You Learned AR FO 1. 1. Predict how the characteristics of a person’s bones would change if compact bone were located on the N inside and spongy bone on the outside. R TA HEthe epiphyseal plate. Predict the long-term T 2. 2. Sometimes a bone is injured at A N effect this might have on the injured bone. PR S Tartery 3. 3. Predict the potential consequences of Idamaging VATE theSE U O F nutrient in a bone injury. How would this affect the ability of the bone to heal? See answers in Appendix A. https://plus.pearson.com/courses/ediger74207/products/e465533c-0856-4464-ba3f-21fa655407d3/pages/urn:pearson:entity:5e772fd8-d4b5-47ba-82af-3d5eddfca1b8?… 6/6