Wk 1 - Bone as a Tissue and Endocrine Control Flashcards
What are the organic and inorganic materials of bone matrix?
ORGANIC:
•Collagen (fibres)
•Proteoglycan - Glycosaminoglycan (Gels)
INORGANIC: the minerals
•Calcium and Phosphate
•Found as hydroxyapatite crystals [Ca10(PO4)OH)2]
What is the functional unit of mature cortical bone?
The osteon
What are the cells of bone tissue?
- Osteocytes (mature osteoblasts)
- Osteoblasts (building)
- Osteoclasts (crushing)
- Osteoprogenitor (creating - stem cells)
What are osteocytes responsible for?
•Bone maintenance
What are osteoblasts responsible for?
- Bone deposition
- Secretes osteoid (unmineralised matrix)
- Responsible for the mineralisation of osteoid by releasing alkaline phosphatase
What are osteoclasts responsible for?
- Dissolving bone matrix
* Bone resorption (by releasing protons and therefore decreasing pH)
What are osteoprogenitor cells responsible for?
•Precursors to osteoblasts
Where is calcitonin secreted from?
The parafollicular cells of the thyroid gland
What stimulates a secretion of calcitonin?
A high concentration of Ca2+ in the blood
What is the function of calcitonin
- Inhibits osteoclast activity
- Lengthens lifespan of osteoblasts
- Decreases blood Ca2+ concentration
Where is parathyroid hormone secreted from?
The parathyroid gland
What stimulates the secretion of parathyroid hormone
A low concentration of Ca2+ in the blood
What is the function of parathyroid hormone?
- Increase bone resorption
- Increases kidney absorption of Ca2+ (from filtrate)
- Increases tubular excretion of PO4 3-
- Increases enzymatic conversion of vitamin D to its active form
- Increases number (osteoclastogenesis) and activity of osteoclasts
Where is oestrogen secreted?
Ovaries
What is the function of oestrogen?
- Increases bone density
* Closes epiphyseal plates (physes)
Where is testosterone secreted?
The testis
What is the function of testosterone?
•Increase bone density
What happens to osteoclastogenesis in the presence of oestrogen?
Osteoclastogenesis is inhibited
Where is growth hormone secreted?
The anterior pituitary
What is the function of growth hormone?
To stimulate longitudinal bone growth (both directly and indirectly)
Where are glucocorticoids secreted from?
The adrenal cortex
What is the most important glucocorticoid?
Cortisol
What are the function of GC (cortisol)?
- Important in stress responses
- Inhibit bone matrix mineralisation
- Induce apoptosis of osteoblasts
- Inhibits osteoprotegerin (will increase number and activity of osteoclasts)
What is the function of Vitamin D?
•Increase availability of Ca2+ and PO4 3- through increased intestinal absorption
What is the purpose of both the central and perforating canals?
To carry neurovascular structures
What is the functions of canaliculi?
- the exchange of nutrients between lamallae
* house dendritic processes from osteoctyes (for communication between adjacent osteocytes)
