bone lexture 1

Bone tissue is removed by

osteoclasts

biochemical investigations of calcium levels

99% of calcium is found in bobes and the rest circulates in the blood free ionised calcium-50% of calcium in body -active within the body bound calcium-40% of calcium in body-is attached to protein/other compounds and is inactive within the body complexed calcium- 10% of calcium in body - with free calcium constitute the diffusible fraction of calcium most commonly, doctors mesure the total amount of calcium in the blood called (total calcium) mesuring both active and inactive forms urine tells us how much calcium is beith excreated by the kidneys

bone remodeling

Bone remodeling (or bone metabolism) is a lifelong process where mature bone tissue is removed from the skeleton (a process called bone resorption) and new bone tissue is formed (a process called ossification or new bone formation). These processes also control the reshaping or replacement of bone following injuries like fractures but also micro-damage, which occurs during normal activity. Remodeling responds also to functional demands of the mechanical loading. In the first year of life, almost 100% of the skeleton is replaced. In adults, remodeling proceeds at about 10% per year.[1] An imbalance in the regulation of bone remodeling's two sub-processes, bone resorption and bone formation, results in many metabolic bone diseases, such as osteoporosis Bone homeostasis involves multiple but coordinated cellular and molecular events.[3] Two main types of cells are responsible for bone metabolism: osteoblasts (which secrete new bone), and osteoclasts (which break bone down). The structure of bones as well as adequate supply of calcium requires close cooperation between these two cell types and other cell populations present at the bone remodeling sites (eg. immune cells).[4] Bone metabolism relies on complex signaling pathways and control mechanisms to achieve proper rates of growth and differentiation. These controls include the action of several hormones, including parathyroid hormone (PTH), vitamin D, growth hormone, steroids, and calcitonin, as well as several bone marrow-derived membrane and soluble cytokines and growth factors (ex. M-CSF, RANKL, VEGF, IL-6 family...). It is in this way that the body is able to maintain proper levels of calcium required for physiological processes. Thus bone remodeling is not just occasional "repair of bone damage" but rather an active, continual process that is always happening in a healthy body. Subsequent to appropriate signaling, osteoclasts move to resorb the surface of the bone, followed by deposition of bone by osteoblasts. Together, the cells that are responsible for bone remodeling are known as the basic multicellular unit (BMU), and the temporal duration (i.e. lifespan) of the BMU is referred to as the bone remodeling period.[5]

hormonal regulation of bone growth

Growth hormone stimulates epiphyseal plate formation in infancy and childhood Thyroid hormone modulates activity of growth hormone Testosterone and estrogens (at puberty) Promote adolescent growth spurts End growth by inducing epiphyseal plate closure excess of deficits of any of these cause abnormal skeletol growth

biochemical investigations of calcium levels

blood calcium is tested to help diagnose and to monitor a range of rare conditions releating to the bones, heart, nerves and kidneys better understanding of your health by comparing your calcium result and your phosphate result at the same time when paraphoid hormone (PTH) from the parathyroid gland is released - calcium goes up and phosphate goes down in kidney disease - low calcium and high phosphate are often seen depending on the levels you have, these two tests can help your doctor discover whether you have a parathyroid disorder or other conditions

summary

bone cells do may things for the skeletal system, including development of new bones and continuel remodeling five main types of bone cell involved in development/remodeling -osteoclasts -osteoprogenitor cells -osteoblasts -osteocytes -bone lining cells bones are made up of both -organic components- bone cells and osteoid -inorganic componants-hydroxyapatites bone remodeling is controlled by several hormones and vitamins including parathyroid hormone, calcitonin and vitamin D screening of calcium, phosphate, alkaline phosphotase and parathyroid hormone are the most common tests undertaken to look at diseases of the bone

Bone Homeostasis

bone remodeling is controlled by several hormones and vitamins including Parathyroid hormone PTH- released by the parathyroid gland calcitonin-released by they thyroin gland vitamin D- produced within the body by exposure to sunlight, food and supliments

chemical componants of bones

bone structure is made up of both organic and inorganic componants organic componants cells -osteoclasts, osteoprogenitor cells, osteoblast, osteocytes. and bone lineing cells osteoid -unmineralized matrix produced by osteoblasts to for a framework upon which to build new bone -accounts fot 50 percent bone voleume and 40 percent bone weight -composed of fibres(predominantly type 1 collegen) -sacrificial bonds in and between collegen provides structure and tensile strengh to prevent fracture Remander is made up of ground substances (proglycans and glycoproteins)

intial biochemical investigations in calcium disorders and bone disease osteomalacia and rickets

calcium low! phosphate low! alkaline phosphytase elevated! parathyroid hormone elevated! soft bones caused by vitamin D defficiency

intial biochemical investigations in calcium disorders and bone disease pagents disease

calcium normal phosphate normal alkaline phosphytase elevated! parathyroid hormone normal abnormal bone structure

intial biochemical investigations in calcium disorders and bone disease osteoporosis

calcium normal phosphate normal alkaline phosphytase normal parathyroid hormone normal bone density/mass

several features in the structure of the bone give it mechanical strengh and ability to absorb impact

collegen fillaments running in diifferent directions variation substructure of bone give subchondral tissue -smooth tissue at the end of each bone compact tissue (also known as cortical bone) -forms the hard cortex of the bone - each osteon consists of concentric layers. of conpact bone tissue that soouroounds a central canal with the haversian canal containing the bones blood supplies. cancellous tissue -the spongey tissue inside of the compact cortex bone cells work together inside the bones to support the skeletal system

bone lining cells

derived from older osteoblast that have filled in previous bone cavaties and become flattened so they can cover bone mainly found in adult bones however some are seen in children bone lineing cells are active cells and comunicate with neighbouring cells through gap junctions responsible for imediate release of calcium in the bone if calcium is low otherwise relativly inactive protective role by preventing chemicals within the body from destroying the bone

bone homeostasis video from slide

https://www.youtube.com/watch?v=qDmjNtf5VsE

biochemical investegations of phosphate low levels assotiated with

hypercalcemia(especially when due to elevated PTH) overused of diuretics severe burns diabetic ketoacidosis fter treatment hypothyroidism hypokalemia(low potassium) rickets and osteomalacia( due to vitaminn D deficiency)

high calcium levels coud sugest

hyperparathydroism cancer saroidosis excess vitamin d intake certain drugs milk alkali syndrome

chemical componants of bone

inorganic componants Hydroxyapatites -50% by volume -70% by weight _ of humone bone is a modified form of hydroxyapatite(bone mineral) -naturally occuring mineral form of calcium pgosphate crystals that crystalize in a hexagonal system around collegen fibres - responsible for hardness and resiliance to compression

biochemical investegations of phosphate elevated phispate assotiates=d with

kidney failure hypoparathyroidism hypocalcaaemia diabetic ketoacidosis when first seen phosphate supplimentation

calcium can be used as a diagnostiv test if tou go to your doctor with symptoms that sugest

kidney stones bone disease neurologic(nerve related) disorders

Osteclasts

large cells breac down bone derived from haematopoietic cells that become macropharges NOT! osteoprogenitor cells osteoclasts are usully found in small pits on bones called resorptive pits and cause bone breackdown i) latching onto bone at site of reabsorbtion ii) releases enzymes which breack down bone tissue leading to release of calcium and phosphate iii) this reabsorption prosess can sometimes take up to weeks for osteoclasts to complete tightly controlled by hormones prduced by thyroid and parathyroid gland

low calcium levels are sugestive of

low protein levels inderactive parathyroid gland(hypoparathyroidism) decreased dietry intake of calcium decreased levels of vit d magnesium deficiency to much phosphate acute inflamation of the pancreas chronic kidney disease calcium ions becoming bound to protein (alkalosis) bone disease malnutrition alcholism

biochemical investigations of other follow up tests

magnesium urine calcum excreation 25 hydroxychloecalciferol- vitamin D urine hydroxyproline excreation osteocalin

Osteocytes

once a osteoblast creates the new bone around itself it is trapped and can no longer move or form bone, now call a osteocyte Transformation into osteocyte causes them to loose the majority of there organiles and gain microfilaments which allow them to contact the bone lineing cells through gap junctions osteocytes are suggested to be involved in i) additional remodeling of bone ii) secreation of growth factors which activate lining cells or stimulate osteoblast iii) though interaction with otherr osteocytes may help prevent to much strain on the bone by providing support and structure

and then new bone tissue is formed by

osteoblasts

re-modeking of bone structure osteoblasts

osteoblasts are important because they allow bones to be produced, remodelled and repaired Derived from differentiation of osteogenic cells in the tissue that covers the outside of the bone from the bone marrow the osteoblast creates and repairs new bone by i) releaseing collegen ii) the ostersoid act as a frannework upon which calciun phosphate is deposited and which is then hardened by hydroxide and bicarbonate ions iii) once the osteoblast is finished working it is traped inside the bone once it hardens(becoming known as a osteocyte) iiii) other osteoblasts remain on top of the new bone lining cells that protect the underlying bone

five main types of cells involved in bone development/re-modeling which are specialised forms of similar cells

osteoclasts osteoprogenitor cells osteoblasts osteocytes bone lineing cells

osteoprogenitior cells

osteoprogenitor cells are also known as osteogenic cells mitotically active stem cells which when stimulated differentiates into osteoblast or bone lineing cells(with some persisting as osteoprogenitors) osteogenic cell (develops into osteoblast) osteoblast (forms bone matrix) osteocyte (maintains bone tissue)

structure of bones mechanical vs immunological

our bones are made up of diffrent tissues composed of bone cells and a central bone marrow involved in generating componants of blood system

bichemical investigations parathyroid hormone

parathyroid hormone(PTH) is produced by parathyroid glands When calcium levels drop, pathyroid hormone is released calcium levels the increase go back to notmal range once calcium levels raise negative feedback helps maintain normal levels mesuring PTH can help explain the reasons for abnormal calcium levels and wherther this is due to alterations in parathyroid function

biochemical investigations of phosphate levels

phosphates are vital for energy production, muscle, nerve function and bone growth serum phosphate test measure the amount of inorganic phoshate on your blood plasma -70-80% of phosphates combine with calcium to form bones and teeth -10% are found in muscles -1% is in nerve cells The rest is found within cells throughout the body, where id is mainly used to store energy, about 1% of total body phospate is within plasma dietry soursed of phosphatates- beans nuts, cereals, dairy products, eggs, beef, chicken and fish. the body maintains phosphate levels in the blood by regulating how much it absorbs from the intestine and excretes/conserves in the kidneys.

learning objectives

structure of the bones remodeling of bone structure role of diifferent cells in bone remodelinf including -osteoclasts -osteoprogenator cells -osteoblasts -osteocytes -bone lineing cells hormonal growth of bone bone homostasis biochemical investigations in calcium/bone disorders including calcium, phosphotate, alkaline phosphotase and other mesures

re-modeling of bone structure

the bones do many things for the skeletal system, such as the development of new bones and continuel bone remodeling

Both osteoclast and osteoblast processes utilize cytokine

transforming growth factor beta and insulin growth factors

hormonal regulation og bone homeostasis

we recycle 5-7% of bone mass/week spongey bone replaced - every 3-4 years compact bone replaced - every 10 years older bones become more brittle as calcium salts crystalize and can fracture more easily mechanisms have been developed to ensure bone homeostasis bone remodeling occours continuously but it is controlled by genetic factors and hormonal control loops( which regulate calcium levels rather than bone density itself)

biochemical investigations of calcium levels

your doctor may also request a calcium test if -you have kidney disease symptoms to much calcium -tiredness -weekness -loss of appertite -nausea -abdominal pain -increased urinary frequency symptoms low calcium -cramps in your abdomen -muscle cramps -fingers tingling diseases that can br assotiated with abnormail levels of calcium such as thyroid disease, interstinal disease, cancer or poor nutrition