Regents Biology

36.1 – The Skeletal System

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The Skeleton

  All organisms need structural support.   cytoskeleton (unicellular)   exoskeleton (arthropods) or an endoskeleton

(vertebrates)

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The Skeleton

  Functions of the skeleton:   support   protects internal organs   movement   stores mineral reserves   provides site for blood cell

formation

  Bones and other connective tissues (cartilage and ligaments) form the skeletal system.

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Appendicular Skeleton •  The bones of the arms

and legs, along with the bones of the pelvis and shoulder area form the appendicular skeleton (grey).

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Structure of Bones

Bone marrow

Periosteum

Spongy bone

Compact bone

Haversian canal Compact bone

Spongy bone

Periosteum

Osteocyte Artery

Vein

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Structure of Bones   a network of living

cells and protein fibers surrounded by deposits of calcium salts

  surrounded by a tough layer of connective tissue called the periosteum

  Blood vessels in the periosteum carry oxygen and nutrients to the bone.

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  Osteocytes (mature bone cells) are embedded in the bone matrix.

  Other bone cells (osteoclasts and osteoblasts) line the Haversian canals and the surfaces of compact and spongy bone.   Osteoclasts break down bone.   Osteoblasts produce bone.

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Bone Marrow   a soft tissue inside

the cavities within bones

  two types:   Yellow marrow –

made up of fat cells.

  Red marrow produces red blood cells, some kinds of white blood cells, and platelets.

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Bone Marrow

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Development of Bones

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Development of Bones   The skeleton of an embryo is composed of cartilage

(strong connective tissue, softer and more flexible than bone).

  Cartilage is replaced by bone ossification.   Bone tissue forms as osteoblasts secrete mineral

deposits.   When the osteoblasts become surrounded by bone

tissue, they mature into osteocytes.

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  Many long bones have growth plates at either end.

  Growth of cartilage at these plates causes bones to lengthen. Gradually, this cartilage is replaced by bone tissue.

  By early adulthood, cartilage in the growth plates is replaced by bone, the bones become ossified, and growth stops.

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Bone Growth

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Joints   where one bone attaches to

another bone is called a joint

  Joints permit bones to move without damaging each other.

  3 types: immovable, slightly movable, or freely movable

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Immovable Joints   “fixed joints”

allow no movement

  bones are interlocked and held together by connective tissue, or they are fused together

  Ex: skull bones

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Slightly Movable Joints

  permit a small amount of restricted movement

  Ex: joints between adjacent vertebrae

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Freely Movable Joints   permit movement in one

or more directions

  4 common types

 ball-and-socket joints (many directions)

 hinge joints (back-and-forth)

 pivot joints (one bone rotates around the other)

  saddle joints

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Structure of Joints   Ligaments hold bones

together in joints and are attached to membranes that surround bones.

  Synovial fluid lubricates surface of joint, enabling the bones to slide past each other more smoothly.

  Bursae act as shock absorbers.