the physiology of the bone Flashcards
osteocytes
Osteocytes are mature bone cells derived from osteoblasts. .
They are embedded within the bone matrix and are responsible for maintaining bone tissue by regulating mineral homeostasis and responding to mechanical stress
osteoblasts
Osteoblasts are bone-forming cells responsible for synthesizing and depositing new bone tissue during bone formation and repair
They secrete collagen and other proteins that form the organic matrix of bone, which is then mineralized to create new bone tissue.
osteoclasts
Osteoclasts are large multinucleated cells responsible for bone resorption, which is the process of breaking down bone tissue
They play a crucial role in bone remodeling and repair by removing old or damaged bone tissue.
ossification
Ossification is the process by which bone tissue is formed, involving the deposition of mineralized matrix by osteoblasts and subsequent remodeling of this matrix into mature bone tissue.
state some functions of the skeleton
Structural support for heart, lungs and marrow
Protection for brain, uterus and other internal organs
Attachment sites for muscles allowing limb movement
Mineral reservoir for calcium and phosphorus
Defence against acidosis
Trap for some dangerous minerals such as lead
briefly describe how the skeletob protects the body against acidosis
The skeleton helps regulate pH by acting as a buffer, absorbing excess acid and releasing alkaline compounds, thereby maintaining the body’s acid-base balance.
the three main components of the bone
cortical bone(compact bone)
trabecular bone(cancellous/spongy bone)
bone marrow cavity
name some properties of the cortical and trabecular bone respectively
Strong, dense, regular structure
Lightweight, irregular lattice, porous/permeable
lamellar bone
a type of bone tissue characterized by its organized arrangement of collagen fibers into layers or lamellae. These layers provide strength and resilience to bone.
note that it is a component of both the cortical and trabecular bones
a brief description of the harvesian systems
cylindrical units found primarily in compact bone. Each Haversian system comprises concentric layers of lamellar bone encircling a central canal housing blood vessels and nerves.
some functions of harvesian systems
play a pivotal role in bone remodeling and repair processes.
They facilitate the exchange of nutrients and waste products, contributing to bone metabolism and homeostasis.
provides structural support to the bone
does the bone have a fixed or static structure
no
the main or primary mineral of the bone is?
hydroxyapatite
(Ca10(PO4)6(OH)2)
what percentage of the bone is;
organic
minerals
30% organic
70% minerals
osteoblasts are derived from?
mesenchym stem cell line
main functions of osteoblasts
bone formation
mineralisation of the matrix
secretion of proteinous organic matrix
osteoblasts are low in mitochondria and golgi content, true or false
false, they are high in mitochondria and golgi content
to provide energy in the form of ATP (adenosine triphosphate) to support the metabolic processes required for osteoblast activity, including the synthesis and secretion of the organic components of the bone matrix, such as collagen.
factor secreted by the osteoblasts to activate osteoclasts
RANK- Ligand
aka (Receptor Activator of Nuclear Factor κB Ligand)
osteoblasts possess some hormone receptors. Name three of the hormones for which they have these receptors?
PTH
Vitamin D
Oestrogen
what happens to osteoblasts in each of these contexts respectively…
when trapped by a new bone?
when they remain on the surface of a new bone ?
they differentiate into osteocytes
they differentiate into lining cells
note that the cells that do not undergo any of these processes undergo apoptosis
osteoclasts are derived from?
hematopoietic stem cells
precurser cells of osteoclasts
macrophages or monocytes
osteoclasts are formed on fusion of it’s precursor cells. which factors on the precursor cells stimulate this fusion?
RANK receptors on the precursor cells stimulate the fusion of the precursor cells
bone resorption is mediated by which type of bone cells
osteoclasts
purposes of bone resorption
Radial growth
Bone remodelling Maintaining vascularity
Liberating ions
osteogenesis
Process whereby calcium phosphate crystals precipitate and attach to a collagenous lattice support
the two main mechanisms of bone ossification
endochondral ossification and intramembranous ossification
intramembranous ossfication
bone formation that primarily occurs in long bones like the femur, and involves the replacement of cartillage with bone tissue
endochondral ossification
bone formation that primarily occurs in flat and some irregularly shaped bones. it involved the differentiation of mesenchymal cells (embryonic connective tissue cells) into osteoblasts within a fibrous membrane
the two main requirements for osteogenesis to occur
matrix formation
mineralisation (involves the deposition of calcium phosphate crystals onto the collagen fibers within the organic matrix)
what causes the following;
growth in length of a bone
growth in diameter of a bone
by proliferation of chondrocytes at the epiphyseal plates and at the primary ossification front
deposition of new bone under the periosteal collar
calcium functions in bone
play a crucial role in bone mineralization, providing strength and rigidity to the bone structure.
They also participate in various cellular signaling processes within bone cells.
phosphorus function in bone
combine with calcium ions to form hydroxyapatite crystals, the primary mineral component of bone.
primary phosphate regulation occurs in which organ
the kidneys
what influence does an increase in PTH have on phosphate levels in the blood
it decreases phosphate levels as PTH enhances phosphate secretion
it is a vitamin as well
which hormone decreases PTH production
vitamin D
inhibition of PTH production means an increase in phosphate levels
two main hormones that regulate calcium levels and their effects on calcium in the body
vitamin d and PTH
they both increase calcium levels in the body
how many mechanisms does PTH use to regulate calcium levels in body
state these mechanisms
3
activation of osteoclasts
Enhancement of Renal Calcium Reabsorption
stimulation of vitamin D activation
how many main mechanisms does vitamin D use to regulate calcium levels in the body
state them
2
Renal Reabsorption
Intestinal Absorption
PTH does not increase phosphate excretion in urine, true or false
false
an increase in vitamin d increases calcium and phosphate absorption from the intestine, true or false
true
osteoclasts express PTH receptors on their surfaces, true or false
false, they do not
prolonged PTH receptor activation causes?
bone resorption
intermittant= irregular
intermittant PTH receptor activation causes?
bone formation
hypercalcaemia and hyperphospataemia increase vitamin D activity, true or false
no they decrease it
hypocalcaemia and…. increase it rather
name the enzymes involved in vitamin D synthesis and their functions
7-dehydrocholesterol reductase: Converts 7-dehydrocholesterol to cholesterol in the skin upon exposure to UVB radiation.
25-hydroxylase: Converts vitamin D into its active form, calcitriol, in the liver.
1-alpha-hydroxylase: Converts calcidiol to calcitriol in the kidneys, the active form of vitamin D.
24-hydroxylase: Converts calcitriol into its inactive form, calcitroic acid, for regulation of vitamin D levels.
transcalciferin function in vitamin d synthesis
Its main role is to transport vitamin D from where it is synthesized (skin or obtained from diet) to target tissues where it is needed for various physiological processes.
what are some actions (functions ) of vitamin D
increase absorption of Ca2+
Indirectly stimulate osteoclast activity (as PTH)
Inhibit PTH synthesis (feedback inhibition)
difference between osteomalacia and rickets
Softening of bones in adults due to vitamin D deficiency or metabolic issues while
Rickets is a similar condition occurring in children during growth periods, leading to bone deformities
both affect the bone’s mineralisation process, thereby causing soft and weak bones
respectively name some disorders of;
bone mineralisation
bone density
osteomalacia
rickets
Hypophosphatasia
osteoporosis
Paget’s disease of bone
Osteopenia
name some risk factors of osteoporosis
Age
Smoking
Sex
Alcohol
Ethnicity
Exercise
Familial
Diet
what disease is considered a precursor to osteoporosis
osteopenia
