11. Osteoporosis- No FQ! Flashcards
O. Describe the normal histology of bone.
There are 4 types of bone cell
1. Osteoblasts- these are the cells that form the bone matrix. It secretes osteoid (collagen- protein mix)
2. Osteocytes- these cells maintain bone tissue [also produce FGF23- which is a phosphate conc regulator.]
3. Osteoclasts- these cells reabsorb bone differentiate from monocytes—
4. Osteogenetic- these are the stem cells
Bone matrix consists of organic and inorganic components. It is these components that give bone its hardness and resistance.
functions of bone
- structural to provide an attachment framework
- protection of internal organs
- storage for hydroxyapatite (calcium and phosphate)
- allow movement by forming joints
different types of bone.
There is the axial and appendicular skeleton.
Then there is long, short, irregular, flat and sesmoid bone
Then woven and compact
Woven bone is the immature form with randomly arrranfed collagen fibres in the osteoid
Lamella bone is composted of regular parallel bands of collagen. It Is formed by remoudled woven bone
And microscopically trabecular bone and corticol bone
Cortical bone forms the walls and is dense which cancellous bone consists of the irregular plates called trabecular.
O.
Explain the role of bone cells in the process of producing, remodelling and mineralising bone.
Bones are constantly being remoudled. Which is required to keep them healthy and also allow trapped minerals to be released. The ongoing turnover of bone is a process of reabsorption followed by replacement, the key cells are the osteoclasts and osteoblasts. The remoudling can be split in to 3 phases
1. Reabsorption- this is where the osteoclasts reabsorb the bone
2. Reversal-this is where cells prepare the surface for new bone to be laid down
3. Formation- osteoblasts lay down new compact bone.
Mineralizing of bone-
This is the process of laying down minerals on matrix of the bone the main are calcium and phosphorus. This is done by the osteocytes. The process is controlled by systemic hormone PTH, VIT D, the bone cells and also cell products
O. Understand the mechanism by which the human body regulates calcium and phosphate levels, in particular the function of vitamin D and parathyroid hormone.
control of calcium reg. is via the Gi tract, kidneys and bone. dihydroxyvitaminD
The 2 main controllers of an increase in plasma calcium are parathyroid and vit D. a decease in plasma ca 2+ stimulates the parathyroid glands by directly acting on a Ca2+ plasma membrane receptor to secrete the protein parathyroid hormone. This does the following;
- Increase calcium reabsorption from bone by activating the osteoclasts. Which causes both Ca2+ and PO3- release, into the extracellular fluid. Although it is the osteoblasts that show the parathyroid receptor and stimulate the osteoclast via paracrine factors.
- Stimulates the formation in the kidneys of 1,25-dihydroxy vitamin which then in turn up regulates the absorption of calcium in the intestines.
- Directly increases calcium reabsorption in the kidney and decreases phosphate reabsorption to stop an increase of phosphate as it is being increased due to bone secretion
1,25- dihydroxyvitamin D The major function of this hormone is to stimulate the reabsorbing of calcium in the intestines. The major control point in the second hydrolalation in the kidney which requires parathyroid hormone.
Hormons involved in Ca and phosphate reg + facts about storage
Bone contains 99% of the bodies calcium stores.
Hormones for bone formation: Insulin, GH/ IGH-1, Eostrogen and Toesterone Calcitonin.
Hormones- bone reabsorpt.
Parathyroid, Cortisol, T3, [not a hormone] 1.25-
O. Define osteoporosis,
a medical condition where the bone becomes brittle and fragile due to loss of tissue. It is usually a result of hormonal changes or a calcium/ vit D deficiency a dexor score of more than 2.5. is a problem with bone density and all blood tests would be normal. It is loss of osteoid. Risk factors include; sedentary lifestyle, use of coricosteriods, smoking, increase in age, women,
O. Define, osteopenia
Osteopenia- a condition where the protein and mineral content of bone tissue is reduced. Less severe that osteoporosis. A dexor score of 1-2.5
O. Define Osteomalacia
this is softening of the bones due to a calcium/ vit D deficiency.it is the adult version of rickets and us a mineral difficency.
O. Describe the microscopic differences between normal and osteoporotic bone.
The word osteoporosis means porous bone. The bone becomes fragile and therefore can break with trivial trauma. There are 2 forms of normal bone
1. cortical bone which is dense and compact. It runs the length of the long bones forming hallow cylinders
2. trabecular bone occurs at the heads of long bone it has a honeycomb structure. This type of bone takes the stresses of the weight.
In osteoporic bone the spongy/ honey comb structure is lost this is due to the osteoclasts reabsorbing more bone than is manufactured
O. Describe the steps involved in bone fracture healing.
The definition of a fracture is a break in the continuity of a bone.
First the fracture must be reduced in to the anatomical position to stop deformity and therefore loss in function. the process of fracture healing is mainly determined by the periosteum (the connective tissue covering the bone) as it contains precursors which develop into the osteoblasts and chondroblasts that are essential for healing. Bone marrow is also another source
Boys cant pee during erections Bone collar formation Cavitation Periosteal bud invasion Diaspheses bud elongation epiphyseal ossification
process is as follows;
- Reactive phase
i. Fracture and inflammatory phase p
ii. Granulation tissue formation - Reparative
i. Cartilage callus formation
ii. Lamellar bone deposition - Remodelling phase
i. To form the original contour of the bone.
? Reactive phase
i. Fracture and inflammatory phase p
ii. Granulation tissue formation
After a fracture, blood cells fill the site until the blood vessels constrict to stop bleeding. The blood forms a clot known as a hematoma. These cells release cytokines which in turn increase capillary permeability causing fibroblasts to surround the site. These form an aggregation known as a granulation tissue. Osteoclasts also move in to reabsorb broken/dead bone.
?. Reparative phase
i. Cartilage callus formation
ii. Lamellar bone deposition
Days after the fracture the cells of the periosteum replicate and then differentiate into the chondroblasts which form hyaline cartilage(promimal cells to fracture) the more distal cells develop in to osteoblasts which change the cartilage into bone. The granulosa cells aslo become chondroblasts. When the 2 meet the new tissue is called a fracture callus.
The next phase is the replacement if the hyaline cartilage and woven bone by endochondral ossification (cartilage) and bony substitution (woven) in to lamellar bone.
? Remodelling phase
i. To form the original contour of the bone.
Remodelong process subsitutes the trabecular bone with compact bone. The trabecular bone is reabsorbed by osteoclasts forming a pit wherer osteoblasts deposit compact bone this forms the same shape and strength of the original bone.
