Chapter 5 : The Skeletal System
Cells are classified according to their internal organisation
Skeletal System : consists of 3 types of connective tissue: BONES // LIGAMENTS // CARTILAGE
Bones are the HARD ELEMENTS of the skeleton
Most of its mass = non-living extracellular crystals of calcium minerals (i.e. anorganic matrix) BUT bones are LIVING
tissue (nerves, vessels). 5 important functions :
Support /Protection/Movement (same as skeleton overall)
Blood cell formation : cells in certain bones are the only source of new RBCs, WBCs & platelets !
LT Mineral storage (Calcium & Phosphate) if need high BUT paid with strength !
Bones CONTAIN LIVING CELLS
Typical long bone (longer than wide) : DIATHESIS + EPIPHYSIS (knob) at each eand.
Dense Compact bone Forms shaft & covers ends :
Central cavity in shaft is filled with ‘YELLOW BONE MARROW’ (=fat to be used for energy)
Outer surface is covered by ERIOSTEMON (tough layer of connective tissue, containing bone-forming cells)
If epiphysis forms joint => covered by layer of CARTILAGE to reduce friction.
Extracellular deposits of calcium & phosphate around living cells ‘OSTEOCYTES’, that are arranged in rings in
cylindrical structures called ‘OSTEONS’. Osteocytes near an osteon center receive nutrients by diffusion from
vessels that pass thru a CENTRAL CANAL.
As bone gets hard, osteocytes get trapped in hollow chambers ‘LACUNAE’ but stay in contact via CANICULI
channels. Within caniculi, extensions of the cytoplasm of adjactent osteocytes are joint by GAP JUNCTIONS =>
Allows exchange of nutrients => All osteocytes can be supplied.
Spongy bone inside each epiphysis :
Less dense than compact bone, latticework of hard TRABECULAE (=calcium + living cells).
In long bones of upper arms & legs : spaces between trabeculae are filled with RED BONE MARROW
OSTEOCYTES do not need central channels => trabeculae give each osteocyte access to vessels in redbonemarrow.
LIGAMENTS hold bones together
Attach bone to bone. Consist of DENSE FIBROUS connective tissue (packed collagen fibers in same direction, with a
few fibroblasts in between) => Strenght AND flexibility !
Cells are classified according to their internal organisation
Skeletal System : consists of 3 types of connective tissue: BONES // LIGAMENTS // CARTILAGE
Bones are the HARD ELEMENTS of the skeleton
Most of its mass = non-living extracellular crystals of calcium minerals (i.e. anorganic matrix) BUT bones are LIVING
tissue (nerves, vessels). 5 important functions :
Support /Protection/Movement (same as skeleton overall)
Blood cell formation : cells in certain bones are the only source of new RBCs, WBCs & platelets !
LT Mineral storage (Calcium & Phosphate) if need high BUT paid with strength !
Bones CONTAIN LIVING CELLS
Typical long bone (longer than wide) : DIATHESIS + EPIPHYSIS (knob) at each eand.
Dense Compact bone Forms shaft & covers ends :
Central cavity in shaft is filled with ‘YELLOW BONE MARROW’ (=fat to be used for energy)
Outer surface is covered by ERIOSTEMON (tough layer of connective tissue, containing bone-forming cells)
If epiphysis forms joint => covered by layer of CARTILAGE to reduce friction.
Extracellular deposits of calcium & phosphate around living cells ‘OSTEOCYTES’, that are arranged in rings in
cylindrical structures called ‘OSTEONS’. Osteocytes near an osteon center receive nutrients by diffusion from
vessels that pass thru a CENTRAL CANAL.
As bone gets hard, osteocytes get trapped in hollow chambers ‘LACUNAE’ but stay in contact via CANICULI
channels. Within caniculi, extensions of the cytoplasm of adjactent osteocytes are joint by GAP JUNCTIONS =>
Allows exchange of nutrients => All osteocytes can be supplied.
Spongy bone inside each epiphysis :
Less dense than compact bone, latticework of hard TRABECULAE (=calcium + living cells).
In long bones of upper arms & legs : spaces between trabeculae are filled with RED BONE MARROW
OSTEOCYTES do not need central channels => trabeculae give each osteocyte access to vessels in redbonemarrow.
LIGAMENTS hold bones together
Attach bone to bone. Consist of DENSE FIBROUS connective tissue (packed collagen fibers in same direction, with a
few fibroblasts in between) => Strenght AND flexibility !
