Ch. 6 The Skeletal System

IntroductionSkeletal System

BonesStructures that make up the jointsTissues

Bone Cartilage Fibrous conn. tissue – forms ligaments that connect

bone to bone

Functions of the SkeletonSupports the bodyProtects some internal organsContains & protects red bone marrowStores excess calcium

Types of Bone TissueBone cells – osteocytesMatrix – calcium salts, collagenIn normal circumstances, calcium removed =

calcium depositedRegulated by osteocytes

Fig. 6-1 shows 2 types of bone tissueCompact (ground)Cancellous (spongy)

Types of Bone Tissue (cont.)Compact

Made of osteons (haversian systems) Microscopic cylinders of bone matrix with

osteocytes in concentric rings around central haversian canals

Microscopic channels (canaliculi) connect osteocytes with blood vessels and other osteocytes

Types of Bone Tissue (cont.)Spongy

No haversian systemContains osteocytes, matrix, blood vesselsCavities often contain red bone marrow, which

produce RBCs, platelets, WBCs

Classification of BonesLongShort

Bones of wrists, anklesFlat

Ribs, shoulder blades, hip bones, cranial bonesIrregular

Vertebrae, facial bones

Classification of Bones (cont.)Long Bones

Bones of arms, legs, hands, feetShaft (diaphysis)

Made of compact bone; hollow, forming a canal within the shaft

Marrow canal (medullary cavity) contains yellow bone marrow (adipose tissue)

Ends (epiphyses) (Fig. 6-1) Made of spongy bone covered with thin layer of

compact bone Red bone marrow replaced by yellow in adult bones

Classification of Bones (cont.)Short, flat, irregular bones made of spongy

bone covered with thin layer of compact boneRed bone marrow within spongy boneJoint surfaces covered with articular cartilagePeriosteum covers remainder of bone

Fibrous conn. tissue membrane; its collagen fibers merge with tendons & ligaments attached to bone

Anchors aforementioned structures and contains blood vessels & osteoblasts

Embryonic Growth of BoneSkeleton is first made of cartilage & fibrous

connective tissue; gradually replaced by boneBone matrix produced by osteoblasts

Process called ossificationBaby has fibrous connective tissue between

skull bones (fontanels); Fig. 6-2Permit compression during birth, growth of

brain after birthThese “soft spots” are ossified by the age of 2

Embryonic Growth of Bone (cont.)Rest of embryonic skeleton

First made of cartilage ossification begins in 3rd month of gestation in long

bonesOsteoblasts produce bone matrix in center of

diaphyses of long bones and in center of short, flat, irregular bones (Fig. 6-3)

Embryonic Growth of Bone (cont.)Long bones develop centers of ossification in

epiphysesGrowth occurs in epiphyseal discs (cartilage)

at jxn of diaphysis with epiphysisBone grows in length as more cartilage is

produced on epiphysis side (Fig. 6-3)On diaphysis side, osteoblasts produce bone

matrix to replace cartilageB/w ages 16-25, all cartilage of epiphyseal disc

is replaced by bone; bone lengthening stops

Embryonic Growth of Bone (cont.)Osteoclasts dissolve & reabsorb minerals of

bone matrix (resorption)Very active in embryonic long bonesReabsorb bone matrix in center of diaphysis to

form marrow canalBlood vessels grow into marrow canals of

embryonic long bones, establishing red bone marrow

After birth, red marrow replaced by yellowRed marrow remains in spongy bone of short,

flat, irregular bones

Factors that Affect Bone Growth & MaintenanceHeredity – polygenic inheritanceNutrition – Ca, P, protein, vitamin A, C, DHormones – growth hormone, thyroxine,

parathyroid hormone, insulin, estrogen, testosterone (Table 6-1)

Exercise or “stress” – bearing weightAs simple as everyday walking

The Skeleton2 divisions

Axial – forms body’s axis Skull, vertebral column, rib cage

Appendicular – supports appendages or limbs Bones of arms, legs, shoulder, pelvic girdles

206 bones in body (Fig. 6-4)

The SkeletonStudy Fig. 6-4 thru 6-16Study Tables 6-2 thru 6-5

Joints - ArticulationsJoint – where 2 bones meet or articulateSee Table 6-5 & Fig. 6-15Classification of joints

Synarthrosis – immovable joint (suture b/w 2 cranial bones)

Amphiarthrosis – slightly movable joint (symphysis joint b/w adjacent vertebrae)

Diarthrosis – freely movable joint; largest category Ball & socket Pivot Hinge, etc.

Synovial JointsAll diarthroses are synovial joints (Fig. 6-16)On the joint surface of each bone is articular

cartilage, providing a smooth surfaceJoint capsule of fibrous connective tissue

encloses joint in a strong sheathSynovial membrane lines joint capsule,

secreting synovial fluid into joint cavity Fluid is thick & slippery, preventing friction

Synovial JointsMany have bursae

Small sacs of synovial fluid b/w joint & tendons that cross over the joint

Permit tendons to slide easily as bones are moved

BursitisExcessive use of a joint, causing inflammation

& pain

Aging & The Skeletal SystemBone tissue loses CaBone matrix thinsBones become brittleFractures are more likely to occurErosion of articular cartilage

Knees, fingersWhat can you do?

ExerciseDiet high in Ca, Vitamin D