Flashcards in Physiology of Bone & Calcium Homeostasis Deck (37):
3 main hormonal controllers of Ca+2
Parathyroid Hormone (PTH)
Vitamin D3 (calcitrol)
main hormones involved in growth
Growth Hormone and IGFs
Thyroid hormone (permissive role in growth, direct contribution for nervous system development)
main histological constituents of bone
Cells (osteoclasts, osteoblasts, osteocytes, osteoprogenitor cells)
Extracellular Matrix (Collagen, Calcium Phosphate)
[most common Hydroxyapatite]
main constituents of bone macroscopically
Main cell type on which bone growth depends
main product of the osteoblast
Enzymes + Osteoid [collagen+protein mix]
main site of bone growth
3 main divisions of bone
where in the bone are the chondrocytes localised
once they have laid down the osteoid osteoblasts become
large, mobile, multinucleate cells
osteoclasts and osteoblast are derived from the same cell lineage
osteoclasts are derived from Haematopoietic Stem Cells
osteoblasts mesenchymal stem cells
what are the main products of osteoclasts
acid and proteases
name some of the functions of calcium
structural functions (cement of the tight junction)
cofactor in blood coagulation
normal excitability of neurone and muscle
what are the main 3 pools of calcium within the body
bone matrix (99%)
what are the main target sites for calcium regulation
how much of Daily calcium intake is absorbed by the intestine?
main regulators of calcium uptake from the intestine
how is most calcium lost in the body
what is the main signal for the release of parathyroid hormone PTH? what type of hormone is it?
low plasma (extracellular) calcium
peptic hormone, little stored
main results after the release of PTH?
increasing plasma calcium and decreasing plasma phosphate levels
actions of PTH on bone are by directly stimulating osteoclasts
osteoclast do not have receptors for PTH. PTH actions are mediated by binding to osteoblasts and inhibiting the production of osteoprotegin (OPG) and increasing RANKL
where is the parathyroid?
4 small glands that sit behind the thyroid
in order of time, what are the main results PTH at different targets?
what is the main function of PTH on the intestine?
indirectly increases ca+2 absorption by increasing the synthesis of calcitrol
what is the main function of PTH on the kidneys?
increase reabsorption of calcium and decrease reabsorption of phosphate
where is the main site for calcitonin secretion?
C cells of the thyroid
what is the main stimulus for the release of calcitonin?
high Ca+2 levels
actions of calcitonin
lowering plasma calcium and phosphate
just as PTH calcitonin has a homeostatic role
F, only secreted in extreme hypercalcaemia
may have a role protecting the bone during lactation and pregnancy
main target sites and functions of calcitonin?
kidney increase excretion of both calcium and phosphate
increase bone deposition
what is the main vitamin D precursor obtained from the diet and also produced in the body when exposed to direct sunlight?
Vitamin D3 (17-dehydrocholesterol)
in order to obtain the active form of vitamin D, calcitrol, adding of 2 hydroxyl groups are required this is done sequentially in ---1---- and ---2--- being the site of action of PTH
Vitamin D travels bound to plasma proteins? and what is the name of the main active form?
1.25-Dihydroxycholecalciferol --> Vitamin D3 ---> calcitriol
what are the main outcomes of vitamin D deficiency?
Children --> rickets
Adults --> osteomalacia
main function of oestrogen in bone?
increases deposition of bone and