Topic 12: Bones Flashcards
Describe the functions of bones
- Enable movement
- Provide form and structure
- Protect internal organs
- Store essential minerals
- House the bone marrow (where red blood cells and immune cells are produced)
- Site of energy metabolism
- Endocrine functions
Describe different bone types
- Cortical (compact) bone: very dense, only 10% porous
+ make up 80% of bones in the body
+ external layers of all bones
+ responsible for strength and mechanical functions
+ in long limb bones, cortical surrounds medullary cavity which contains bone marrow inside - Cancellous (spongy/trabecular) bone: 50-90% porous
+ mainly in axial skeleton
+ large bone surface, 4x times more metabolically active than cortical bone –> easier to abosrb minerals and be broken down
Describe the components and overall structure/formation of bone matrix
Collagen and hydroxyapatite form bone matrix.
Osteoblasts produce osteoid - the organic framework where alkaline phosphatase can be deposited. ALP increases the concentration of inorganic phosphate in osteoid, causing the calcium and phosphate product to increase and produce crystals of hydroxyapatite.
Hydroxyapatite will combine with collagen secreted by osteoblasts to form bone matrix, the foundation for further bone formation.
What happens to bones if there is too much calcium or collagen?
If there is too much calcium, the bones become brittle.
If there is too much collagen, the bones become bendy.
Describe how and why bone remodelling happens
Bone remodelling happens to:
- renew bones strength and minerals
- repair damage
- prevent damaged bone to accummulate
In bone remodelling, bone resorption occurs first when some stimulus trigger osteoclasts to break down the bone, then osteoblasts come in to lay down the collagen matrix, followed by mineralisation, which is bone formation.
Describe how bone remodelling change bones throughout our lives
Bone mass changes with age. As we get old, resorption rate exceeds formation rate, leading to more bone and strength loss.
During bone modelling, bone resorption happens faster than bone formation so there will be time when bone is weeker than usual.
Describe different types of bone cells
- Osteoblasts: bone-forming cells
+ Produce organic collagen matrix, osteoid and then mineralizes it.
+ Can differentiate into osteocytes or return resting lining cell - Osteocytes: bone cells
+ Form a canalicular network between each other
+ releases factors which can bind to receptors of osteoclast precursors and increase/decrease osteoclast formation and activity
+ sense changes at matrix level like microcracks and send signals to osteoclasts - Osteoclasts: bone-resorping cells
+ Secrete acid to demineralize and breakdown collagen matrix
+ Liberate minerals into the circulation
Describe different methods of bone growth
- Intramembranous ossification (flat bones): a transformation of a membrane of connective tissues into bony structure
- Endochondral ossification (others): mesenchymal cells differentiate into chondrocytes (cartilage cells) which then die, leaving spcaes for osteoblasts to fill in. Bones replace cartilage at the ends of diaphysis, leading to longtitudinal bone growth.
Describe osteoporosis
Osteoporosis is when there is micro-structural deterioration of bone tissues, resulting in low bone strength and increased bone fragility. This is caused by a decoupling of bone resorption and formation.
Explain some factors affecting the probability of having osteoporosis
- Menopause: oestrogen deficiency leads to an increase in osteoclasts/bone resorption and a decrease in osteoblasts/bone formation.
- Senile osteoporosis: declined supply of osteoblasts in proportion to demand
- Genetic factors
- Diseases
- Endorcine changes
- Inflammation
- Medications
- Lifestyle
- Nutrition
Describe factors contributing to bone strength
- Collagenous proteins provides tensile strength (flexibility)
- Mineralized osteoid provides compressive strength
