Skeletal System. Overview and General Anatomy

Transcription

1 Skeletal System Overview and General Anatomy 1

2 Bone Functions Support Protection Movement Storage Fat, calcium, phosphorus Hemopoiesis While we usually think of the skeleton as just our support framework, the skeleton actually has several functions: some obvious, and some not-so-obvious. Support: Our bones act as places to anchor our organs so they always stay in more-or-less the same orientation and relationship to one another. You wouldn t want your intestines and other organs just flopping around inside your cavities, would you? Because the bones are so rigid and strong, they form several protective vaults around some of our most delicate organs. The bones of the skull completely surround and protect the brain. The vertebrae enclose and protect the spinal cord. The rib cage protects the heart and lungs. The pelvic bones partially surround the reproductive organs, including the uterus, which offers some protection to a developing fetus. The skeleton works together with the muscles to afford voluntary movement. Almost all voluntary movement involves muscles levering the ends of two bones closer together or further apart across a joint. We don t think about the bones storage function often, but it s very important. In adults, the yellow bone marrow is mostly fat storage, which gives us quick access to backup energy reserves. In addition, the matrix of the bone is mostly calcium salts. Since calcium ions are required for muscle contraction and nerve communication, we need to keep our blood calcium levels in homeostasis. Excess calcium (that is not excreted) is stored in the bone matrix. If more blood calcium is needed, bone matrix is catabolized to release the calcium into the blood. The red bone marrow is the only place in the body where new blood cells are formed. This is a process called hemopoiesis. 2

3 Axial vs. Appendicular Skeleton Axial Skull, vertebrae, ribs, sacrum, sternum Appendicular Girdles and limbs We can categorize all of the skeleton s bones into two categories: The axial skeleton includes the main part of the skeleton: the bones around the body s longitudinal axis. The axial skeleton includes the bones of the skull, the vertebrae, the ribs, the sacrum (butt-bone) and the coccyx (tailbone). The appendicular skeleton includes the appendages attached to the axial skeleton. It includes the upper and lower limbs, as well as the girdles that attach the limbs to the axial skeleton. The upper limbs are attached to the axial skeleton with the pectoral girdle, which consists of the clavicles (collar bones) and the scapulae (shoulder blades). The lower limbs are attached to the axial skeleton with the pelvic girdle, which consists of the pelvic bones. 3

4 Axial vs. Appendicular Skeleton Note that the pectoral and pelvic girdles are considered part of the appendicular skeleton. 4

5 Bone Types Long bones femur, humerus, etc. Short bones carpals, tarsals, etc. The human body has at least 206 bones in most people. We can anatomically distinguish 5 different types. Long bones are the largest and heaviest, but they have adaptations that keep them as light as possible. For example, long bones are hollow and have a lot of empty space inside of them. Examples of long bones include the femur, tibia and fibula (lower limb) as well as the humerus, radius and ulna (upper limb). Short bones are more-or-less round and are much smaller than long bones. Anatomically they are a shell of compact bone surrounding a medulla of spongy bone. The short bones include the carpals (wrist bones) and tarsals (ankle bones). 5

6 Bone Types Flat bones scapulae, sternum, ribs, etc. Irregular bones vertebrae, teeth, etc. Flat bones are, as the name implies, flat. They are larger than short bones, but like short bones, their centers consist of spongy bone. Much of the red bone marrow of adults is found in flat bones. Some examples include the ribs, the scapulae, the sternum, and most of the bones of the skull. Irregular bones have various shapes, but most of them have processes extending from them. Usually, these processes are either articulating processes (which fit into fossae to form joints) or act as anchor points for tendons and/or ligaments. Examples include the vertebrae, the mandible, the teeth, and the coxae. 6

7 Bone types Sesamoid bones patella, hallux sesamoid Sesamoid bones are so-called because most of them are about the size and shape of sesame seeds. Different people have sesamoid bones in different locations, but the knuckles of the hand and foot are common places. The most noteworthy sesamoid bones are the patellae (knee caps). Sesamoid bones grow entirely inside of ligaments or tendons and serve to hold a ligament out of a joint. The knee cap for example, is large enough that it blocks the patellar tendon from slipping into the knee joint. 7

8 Long Bone Anatomy Epiphyses External: Diaphysis Epiphyses Periosteum Diaphysis Long bones have anatomical features not found in other types of bones. The long bone shaft is a diaphysis. The bulbous ends are called epiphyses. They are anatomically different on the inside. The periosteum is a dense connective tissue capsule surrounding each bone. In addition to supplying blood to the bone s cells it contains many osteoblasts which lay down new layers of matrix as a bone grows in width. 8

9 Long Bone Anatomy Internal: Spongy bone Compact bone Epiphyseal lines Medullary cavity. Endosteum Marrow Long bones are hollow. This helps reduce their weight without sacraficing strength. It also gives a chamber for bone marrow storage. The medullary cavity is lined by a dense connective tissue membrane called endosteum. Anatomically, the outer wall of the entire long bone is compact bone. The compact bone layer is thickest around the diaphysis (necessary because of the hollow medullary cavity). The epiphyses are not hollow. They consist of wall-to-wall spongy bone. With lots of marrow-filled spaces between trabeculae. In the epiphyses, we can see epiphyseal lines. These are the calcified remains of growth plates, the sites of bone lengthening during development. Both the meduallary cavity and the spaces in the spongy bone are filled with bone marrow. 9

10 Long Bone Anatomy Internal: Spongy bone Compact bone Epiphyseal lines Medullary cavity. Endosteum Marrow The epiphyseal lines are hard to see in this drawing, but you should be able to make out two lines of compact bone in this proximal femoral epiphysis. When this femur was growing, these were the cartilaginous growth plates. 10

11 Long Bone Anatomy Bone marrow Red bone marrow Hemopoiesis Yellow bone marrow Fat Two types of bone marrow: red marrow produces new blood cells; yellow marrow is mostly fat and does not produce new blood cells. Most marrow in children is red but in adults, only the axial skeleton, the girdles, and the proximal tips of the femurs and humeri have red bone marrow. 11

12 Bone Features Every bump, lump, hole, canal, and indentation on every bone has a name, but the names are usually descriptive. We can break the features down into two broad categories: projections (raised areas of bone) and depressions (lowered areas of bone or holes through a bone). Projections can appear either rounded and smooth or somewhat rougher. We found the rounded, smooth projections at articulating ends of bones, where they fit into depressions (fossae, usually) in other bones to form a moveable joint. The rougher ones are the sites of tendon and/or ligament attachment. Some of the more common projections include: Tuberosities, which are very large projections that usually act as anchoring points for tendons and ligaments. The ball of the hip is sometimes also called a tuberosity. Trochanters are also very large projections where large tendons attach. We only find trochanters at the distal end of the femur. Tubercles are somewhat smaller than tuberosities and trochanters, but they serve as attachment points as well. Processes are large, usually long, projections that stick out from a bone. Condyles (on the next slide) are smooth, rounded projections that articulate with other bones. 12

13 Bone Features Some of the more common depressions (and holes) include: Fossae, which are shallow and rounded. They usually articulate with a condyle of another bone at a moveable joint. Sinuses, which are empty, air-filled spaces, such as the sinuses in the skull. Foramina, which are more-or-less circular openings in a bone, such as the large foramen magnum in the inferior aspect of the skull, through which the medulla oblongata and spinal cord extend. Fissures, which are basically elongated foramina, such as the orbital fissures, through which the optic nerve as well as the eye s blood vessels extend. Meati, which are more tunnel-like, such as the external auditory meatus, through which the auditory nerve passes. 13

14 Bone Features Memorize Tuberosity Tubercle Trochanter Process Condyle Meatus Sinus Fossa Fissure Be able to identify each of these in figures and on models. 14

15 Bone Features We ll be looking at the skull in some detail because it shows almost all of the bone features you should know. In this figure, try to identify a meatus, a foramen, a few processes, a condyle (and the fossa in which it sits), and a tubercle. (The tubercle is hard to see in this figure because it s at the back of the skull). 15

16 Bone Features In these figures of a femur, a tibia, and a coxa, see how many features you can identify. Can you find condyles, trochanters, and fossae? 16