Skeletal System

Skeletal System

Function of Skeletal System

Function of the Skeletal System Protection Movement Support Blood cell formation (hematopoiesis) Storage (fat and minerals) I. Function of Skeleton A. Protection – encases most internal organs B. Movement – muscle attachment C. Support – body positions (examples – legs support truck; ribs support thoracic wall) II. Function of Bones The above 3, plus: D. Forming blood cells E. Storage (minerals – calcium, phosphorus, etc; and fat) – constantly exchanging with the body as needed

Structure of the Skeletal System Axial Appendicular Skeletal System http://www.zoology.ubc.ca/~biomania/tutorial/bonesk/outline.htm Without the skeletal system you would be a shapeless bag of soft organs collapsed on the floor. You would be helpless. You would not be able to perform movements such as walking or grasping. The slightest bump to your head or chest could damage the brain or heart. It would even be impossible to chew food. There are 206 bones in the human body. Axial Skeleton: supports head neck thorax; protects brain, spinal cord, organs skull vertebrae rib cage 2. Appendicular Skeleton A. Pectoral Girdle: anchors upper limbs Weak attachment at clavicle/sternum but flexible – FREEDOM OF MOVEMENT B. Upper Limb C. Pelvic Girdle: Attaches lower limbs Very strong attachment at sacrum – BALANCE, WEIGHT TRANSMISSION D. Lower Limb http://www.zoology.ubc.ca/~biomania/tutorial/bonesk/outline.htm

The Structure of Bone: Compact Bone & Spongy Bone Forms outer part of bones Bears weight Spongy bone Made of trabeculae (latticework) Located inside bones Reduces weight of bone C. Bone Tissue Types There are two types of bone tissue based on how cells/matrix are arranged: Compact - one that looks more dense, more compact. It makes the outer part of bones and forms the shaft of long bones. It BEARS WEIGHT. Spongy - one that looks like swiss cheese or like a sponge. The cells and matrix are laid down irregularly. The lattice work is called trabeculae. Spongy bone is located inside bones. (knobs, flat) It REDUCES THE WEIGHT OF BONE. Also, can change arrangement of trabeculae in response to weight.

Spongy or Compact?

4 Types of Bone Shapes Long bones Short bones Flat bones Irregular bones Long – like the femur. Usually have shaft with two “heads”. Made up mostly of compact. Short – more cube-shaped. Made up mostly of spongy bone Flat bone – skull, ribs. Made up of two thin layers of compact bone with spongy bone inbetween. Irregular bone – vertebrae, hips.

Anatomy of a Long Bone epiphysis (head) diaphysis (shaft) epiphysis Long bones have two heads – epiphyses, and a shaft – diaphysis. The epiphyses are mostly spongy bone. RED MARROW is found here. The diaphysis is hollow. The outside is compact bone. Yellow marrow inside. Membranes Both external and internal bone surfaces are covered with membranes. The membranes cover and protect the surface of the bones. They have blood and nerve tissue. The periosteum (outer membrane) is subject to a lot of pulling: it is connected to tendons (b – m) and ligaments (b – b). epiphysis

Bone is a Living Tissue!!!

Bone is a Living Tissue!!! It is made of living cells embedded in a non-living matrix. It grows, remodels and repairs. It responds to hormonal stimulation.

Made of Living Cells Osteon Lacunae Canniculi A. Made of living cells embedded in a non-living matrix. Note the osteon: mature bone cells arranged in rings around a central canal. These canals have blood vessels and nerves. The cells are surrounded by a hard substance – the matrix – here composed mostly of calcium salts. The “hard stuff”. Since the cells lie far apart from each other, connective tissue. Cells exchange information with each other via canniculi.

Matrix minerals proteins **strength and flexibility The Matrix This is the extracellular space. * filled will mineral salts (1* Ca) – 2/3 of matrix, these salts give bone its hardness – different from other tissue. * also 20% protein (rest is water)- bone is hard, but flexible: it would be brittle if just minerals, so it is embedded with proteins & collagen fibers. Bone soaked in acid – leaches salt out (rubbery) Bone baked in oven – destroys protein (brittle)

Bone Cells Types Osteoblast – bone builders – form matrix Osteocyte – bone maintainers – maintain matrix Osteoclast – bone dissolvers – destroy matrix Bone Cells – form and maintain the matrix You can see why the matrix is important – this is what we think of when we think of bone. So what role do the cells play in bone? Osteoblasts – “bone builders” – secrete the matrix Osteocytes – “bone maintainers” - embedded in and maintain matrix (does not secrete) Osteoclasts – “bone dissolvers” – destroy the matrix

Bone is a Living Tissue!!! It is made of living cells embedded in a non-living matrix. It grows, remodels and repairs. It responds to hormonal stimulation.

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Bone Formation Figure: 05-04-1-3 Title: Bone formation in an embryo. Caption: Steps 1-3.

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Bone Repair Figure: 05-04-1-3 Title: Bone formation in an embryo. Caption: Steps 1-3.

Bone is a Living Tissue! It is made of living cells embedded in a non-living matrix. It grows, remodels and repairs. It responds to hormonal stimulation. Hormones regulate bone growth. Growth effected by various hormones - GH during childhood – testosterone and estrogen surges at puberty – which cause an incredible surge in cell division at growth plates. In adulthood, growth plates replaced by bone. Bones also respond to PTH (parathyroid hormone). When blood calcium levels are too low, PTH activates osteoclasts to break down bone (releasing calcium to blood stream).

Bone - Review: Bone cells Matrix Membranes Ligaments Cartilage Bone cells form/maintain the matrix – “hard stuff” – mostly calcium salts. The form that the matrix takes determines whether it is spongy or compact bone. Membranes cover inner and outer surfaces of bones. Ligaments – attach bone to bone (dense, confer strength) Cartilage – lends support – discs in between vertebrae, nose (between bones, reduces friction, tough but flexible)