Healthy bones and metabolism Flashcards
How much calcium does the body contain?
~ 1kg (25mol)
What is the percentage of calcuim in our body that is in our bones?
99%
How much calcium travels in the body and from and to where?
approximately 500mmo1/240 moves between bone and ECF
What forms are calcium in the body
Diffusible (ion complexed to lots of proteins, slows it and able to diffuse as it is bigger)- which can be spilt into
‘Free’ calcium- physiologically active(ionised calcium)
Complexed to proteins
Protein bound
Which form of calcium is homeostatically managed?
‘Free’ calcium
How is calcium used around the body? Describe calcium cycle in body
From bone to ECF- Bone resorption and exchange From ECF to bone- Bone formation and exchange Formation and resorption in balance Kidney to ECF - Reabsorption Plasma to kidney- Glomellular filtration Gut to Plasma- Absorption Plasma to Gut - Secretion Food to gut gut to faeces Plasma to skin thorugh sweating
What is bone resorption?
Bone broken down and calcium and phosphate taken back into ECF
Otherwise known as reuptake
What is reabsorption?
Not breaking down anything but taking up ions
What regulates calcium ? 3
Parathyroid hormone
Vitamin D
Calcitonin
Where is Parathyroid hormone secreted from? Where is that?
Parathyroid glands which sit on four corners of the thyroid gland on the neck
The process of secreting Parathyroid hormone-Size of each form
First- Pre pro PTH- 115 amino acids
- > Pro PTH- 90 amino acids
- > Mature PTH- 84 amino acids
What does PTH do and where?
In Kidney:
Increases calcium resorption/ reuptake in distal tubules
Increases phosphate excretion
Increases formation of active vitamin D
In Bone:
Stimulates bone resorption
How does PTH regulate calcium when it is at a low level?
Hypocalcemia- stimulus detected
Trigger Calcium Sensing Receptor in Parathyroid gland (CaSR)
Increases PTH
What is hypocalcemia
Low calcium
What does increasing bone resorption do?
Increases calcium and phosphate
What does Increasing calcium resorption
Increasing formation of active vitamin D do?
Decreases phosphate resorption
How would you describe results of measurements that are abnormal? why?
NOT abnormal
SAY Appropiate
Because if someone has a low level of calcuim, it would be expected to see high levels of PTH therefore better to say appropiate than high or low
What are the common forms of Vitamin D?
Most common are Vitamin D2 and Vitamin D3
What is Vitamin D derived from? How can you tell from the structures?
Cholesterol
Steroid backbone
Where is most Vitamin D derived from?
UV light on skin
What is Vitamin D2 used as?
Food additive
What food source contains Vitamin D?
Oily fish
How is vitamin D overally sythesised
dehydrocholesterol in skin turned into Vitamin D3 Cholecalciferol by UV light
Is Vitamin D3 (cholecalciferol) biologically active?
No
Activation of Vitamin D? Where?
In liver
Vitamin D3 (Cholecalciferol) undergoes hydroxylation so becomes Calcidol/ 25(OH)D / 25-hydroxycholecalciferol
Reaction is dependent upon availability of substrate (Vitamin D)
In kidney
25(OH)D undergoes enzymatic reaction
Enzyme- 1α hydroxylase
Which changes 25(OH)D into 1,25-dihydroxycholecaIciferol
Is Calcidol/ 25(OH)D / 25-hyclroxycholecalciferol biologically active?
No
How is the activation of Vitamin D in kidney regulated?
decreased phosphate
decreased 1,25-OHD
increased PTH
Is 1,25(OH)D biologically active?
yes
What does activated Vitamin D do?
In bone-
Stimulates bone resorption
In Intestine-
Stimulates calcium absorption
Stimulates phosphate absorption
When do we look at abonormal Vitamin D Levels and PTH levels?
Calcium and ohosphate levels
If in same direction- Vitamin D
If in different directions- PTH
What is Vitamin Deficiency called in adults
Osteomalacia
What is Vitamin Deficiency called in chilldren
Rickets
What is calcitonin?
32 amino acids protein
What secretes calcitonin and from where?
parafollicular cells of the parathyroid gland
What does calcitonin do?
Opposes the effect of PTH
What happens if there are high levels of calcium
Thyroid gland releases calcitonin ->
Inhibit osteoclast activity and Calcium reabsorption on the kidney decreased-> calcium levels dropped
What is bone density?
A measure of the amount of mineral present in the bone
Why is bone density measured
Used to diagnose osteoporosis
What is it a factor for?
A contributing factor to the fracture risk
What is a DEXA scan?
Scans for bone density
What can affect bone density- 8
Calcium intake
Calcium absorption — Vitamin D (sun exposure and dietary factors)
Functionality of PTH — Magnesium deficiency
Weight bearing exercise
Smoking — affects bone turnover
BMI
Healthy diet — oily fish, whole grains, cut down on fat and sugar
Hormones
Steroid hormones, oestrogen, thyroid hormones
What is osteopaenia?
Lower bone density
What do vegans eat to supplement calcium
need leafy green vegetables, almonds, sesame seeds.Pulses, tofu
What do people with lactose intolerance eat to supplement calcium
- pilchards, curly kale, watercress, sesame seeds
Factors that contributes to fracture risk? 6
Age Previous fracture Alcohol intake Smoking status Medication (steroids) Bone density
What happens to bone density in women over time? Why?
Bone density in women decreases after the menopause
decreasing oestrogen levels
