Lecture 1 Flashcards
What is Bone made up of
Type 1 Collagen
What is Bone filled with
Hydroxyapatite
Calcium management
Skeleton acts as a reservoir for Ca
Types of hormones which offer skeletal management
Sex Steroid, thyroxine, corticosteroids and insulin
4 cell types relevant to bone formation and metabolism
Osteoblasts, Osteoclasts, Osteocytes, Osteoprogenitor
Osteoblasts position
Bone Surface
Osteoblasts Feature
Responsible for laying down bone
Osteoclasts Position
Bone surface but low numbers
Osteoclasts Features
Move across bone surface reabsorbing bone, multinucleated and contain many mitochondria
Osteocytes Position
Cannot divide, most abundant cell in bone, networked by canaliculi
Osteocytes Features
Cannot divide, most abundant cell in bone. Networked by canaliculi
Three Hormones that play vital roles
Calcitrol, Parathyroid Hormone, Calcitonin
Calcitrol
Active form of Vitamin D
Role of Calcitrol
Increases blood Ca2+
How does Calcitriol increase Ca2+
Increase calcium and phosphate absorption from Intestines
Increasing calcium resorption from bone via indirect osteoclast and direct osteoblast stimulation, decreasing urinary excretion of calcium, by increasing calcium reabsorption by kidneys.
How does calcitriol act
Bids to nuclear receptor protein on target tissue and regulate gene expression
Parathyroid Hormone role
Increase calcium resorption from bone via indirect osteoclast stimulation
Decreasing urinary excretion of calcium, by increasing calcium resorption by kidneys
Increasing urinary excretion of inorganic phosphate, by decreasing Pi reabsorption by kidneys
Stimulating calcitriol production in the kidneys
Role of Calcitonin
Decreases blood Ca2+
How does Calcitonin decrease Ca2+
Inhibiting calcium resorption from bone via direct osteoblast stimulation
Increasing urinary excretion of calcium and inorganic phosphate by decreasing resorption by kidneys.
Bone Mineral Density
g bone mineral per cm^2
Peak Bone Mass
The amount of bony tissue present at the end of the skeletal maturation
Lower BMD=
Greater chance/ severity of fracture
Bone Density decreases Over time
Oestrogen inhibits bone resorption by reducing osteoblast numbers and activity. A lack if oestrogen allows osteoclast to be more active allowing bone resorption to occur.
Osteoporosis
BMD lies 2.5 standard deviations or more below the average value for young healthy person (T- score)
Osteopenia
T- Score between -1 to -2.5
Typical stress points
Spine, Hip and wrist
Why are women more at risk
Menopausal effect (Oestrogen) Affected by previous pregnancies Women tend to live longer
Osteomalacia
softening of the bones, typically through a deficiency of vitamin D or calcium.
Mothers at risk due to
- Low Ca intake
- Low sun exposure
- Long periods of lactation
Role of Vitamin D3
Bone growth, Cells of the immune system, pancreas, skin
Causes in VD deficiency
Poor diet, inability to absorb/ metabolise vitamin D3, low sunlight exposure
Vitamin D3 Formation
- Sunlight (UV), shining on the skin
- Inactive form of VD travels to the liver and then the kidneys in a 2 step activation pathway.
- Active VD can then enter cells and stimulate receptor protein to bind to DNA in the nucleus, acting as a regulator for hundreds of genes.
How is VD3 deficiency a risk factor
Risk factor for osteoporosis and osteomalacia
Why is sufficient Calcium vital for achieving a high peak bone mass
Peak total body BMD and BMC is attained by the age of 22 yrs and 26 yrs
During adolescence around 50 % of peak bone mass is laid down
