lecture day 5 skeletal system

Skeletal System

Functions of the skeletal system:

• Support – structural framework (muscle attachments and maintaining the shape of body movements)

• Protection – protects brain and other organs

• Movement – muscle attachment

• Mineral storage and release – calcium and phosphate

• Blood cell production – erythrocytes (red blood cells), thrombocytes (platelets), leukocytes (white blood cells)

• Triglyceride (lipid) storage – happens in yellow bone marrow

Bone histology:

• Matrix is dense and contains calcium salts and collagen

• Collagen is a really strong fiber

• Calcium salts prevent bones from being bendy

• collagen provides strength and calcium salts provide rigidity

Bone Anatomy:

-        Epiphysis: proximal end and distal,

-        Diaphysis: runs along length of bone, medullary cavity (makes bone not dense and heavy)

-        Metaphysis: area between epiphysis and diaphysis

-        Epiphyseal plate: found in child, epiphyseal line = adult, found between epiphysis and diaphysis, location where bone growth occur

-        Compact bone: solid bone alongside the dialysis

-        Spongy bone: seen more in the epiphysis area

Bone cells:  

Osteo – “bone whatever”

• Osteoprogenitor cells – (osteogenic cells) stem cells, job to make new bone cells

• Osteoblasts – making new bone matrix, blast = making something, deposit calcium phosphate and make collagen fibers

• Osteocytes – maintain bone, makes sure matrix stays strong and in good condition

• Osteoclasts – clasts = breakdown something, osteolysis, breakdown bone using digestive enzymes

Structure of compact bone: found in external layers of bone and in the diaphysis  

·        Osteon – ring-like appearance, goes all the way down the bone

o   osteocytes in their lacunae – tan oval cells in the osteons

o   central canal or Haversian canal – found in the middle of osteons, location for blood to flow along the length of the osteons

o   perforating canals – what brings blood inside of the bones and then between those central canals, between the central canals in the bone

o   concentric lamellae – in the rings (osteons), areas that the canaliculi form in

o   canaliculi – provides communication between cells, allows a way for nutrients to get to cells and waste to be removed

o   interstitial lamellae – matrix that’s found between osteons, used to be osteons but as bones grow the blood supply gets cut off and becomes interstitial lamellae

o   circumferential lamellae – rings that go around the outer shafts of the dialysis of the bone

Structure of spongy bone:

·        no osteons

·        trabeculae (groovy bone)

·        have little pore openings that allow for nutrient exchange to occur within the tissue

·        lightens the weight of bone, still gives some strength

·        protects bone marrow

·        yellow bone marrow – stores triglycerides

·        red bone marrow – where blood cells develop

Periosteum  

Functions:

·        durable membrane that goes around the bone, has fibrous layer and cellular layer inside

Endosteum

            Function:

·        layer that lines the inside of the medullary cavity

·        contains osteoblasts, osteogenic cells, and osteoclasts

BONE PHYSIOLOGY

Ossification: process of turning tissue into bone (cartilage into bone is the main process)

·        Fibrodysplasia ossificans progressive (muscle tissue turns into bone)

Calcification: depositing calcium into tissue

o   Ectopic calcification – when calcium is deposited into anything that isn’t bone

o   Can also occur in any type of tissue

Endochondral ossification – how bones develop from fetal to puberty

Steps:

• Epiphyseal plate – cartilage continues to grow on one side with the bone continues to turn cartilage into bone on the other side

Intramembranous ossification – how flat bones develop (skull, pelvis)

Appositional growth: bone increases in diameter (occurs in adulthood too, bones get thicker and wider to combat stress)

Blood and nerve supply (in a typical bone like the humerus)  

Bone remodeling: remodels bones to help fix damage from stress

Physiology of Osseous Tissue

• Hormones that regulate calcium/phosphate homeostasis

• NEGATIVE FEEDBACK

• TOO LOW – hypocalcemia

  • Parathyroid hormone (PTH)  

• TOO HIGH – hypercalcemia

  • Calcitonin (thyroid gland)

Importance:

-        Muscle contraction

-        Blood clotting

-        Enzyme cofactor

-        Cell signaling

-        Exocytosis

Ways to change calcium levels:

-        Bone response (stores calcium)

-        Intestinal response (absorb calcium)

-        Kidney response (eliminates calcium in urine)

Osteopenia (Fig 6.17)

-        More likely to happen in females