Exam 6: Bone Development and Calcium Homeostasis Flashcards
Describe the ectoderm
It is on the surface and will form the skin and neural tisuses
Describe the mesoderm
The middle layer and it will form the bones, muscles, and connective tissues
What is programmed to initiate limb formation?
Lateral body wall of mesoderm
What does the mesoderm of each side of the developing lateral body wall form?
A cylindrical thickening (Wolff’s crest)
What develops over Wolff’s crest? Where?
Focal ectodermal thickenings
At the sites where individual limbs will develop
Describe how long bone develops
Condensation of mesenchyme forms cartilage model of bone
Formation of perichondrium and invasion of nutrient artery
Degeneration of chondrocytes forms medulary cavity
Transformation of perichondrium to periosteum
Periosteum form concentric layers of cortical bone in the diaphysis
Vessels at joint capsule insertion invade epiphyseal areas
Epiphyseal and metaphyseal form
Understand the anatomy of a long bone and the terms given to each specific region of the bone in growing and mature animals.
Understand the anatomy of a long bone and the terms given to each specific region of the bone in growing and mature animals.
What is cancellous bone?
Epiphyseal and metaphyseal bone that appears spongy and trabecular
What absorbs concussion in bone?
Tiny trabecular plates
What is compact bone?
Cortical bone of the diaphysis, which is dense and strong
What forms osteons?
Concentric bone lamellae that were formed during development of the diaphysis are remodeled along lines of stress by cutting and filling cones to form osteons
What do osteons do?
Strengthen bone cortex
What is the metaphyseal physis responsible for?
Growth in length of a long bone by proliferation of chondrocytes followed by enchondral ossification to form cancellous bone of metaphysis
What is epiphyseal physis responsible for?
3D growth of epiphysis by proliferation of chondrocytes followed by encohndral ossification to form epiphyseal cancellous and subchondral bones
What is the final shape of the ends of a bone at maturity determined by
Interstitial growth of cartilage in growing epiphyseal physes
Describe enchondral ossification
Chondrocytes proliferate in inner and outer mitotic layers beneath articular surface
Chondrocytes from inner mitotic layer become collagen and proteoglycan matrix
Mature chondrocytes hypertrophy, hypretrophic chondrocytes form matrix vessicles and die
Hydroxyappetite crystal form at matrix vesicle sites calcifiying cartilage
Capillary loops with osteogenic mesenchyme invade tunnels formed by dying hypertrophic chondrocytes only after cartilage calcifies
Osteoblasts layer bone on spicules of calcified cartilage to form bony trabeculae
Osteoclasts remodel calcified spicules and bone trabeculae to produce cancellous bone
Look at the anatomy of a growth plate
Look at the anatomy of a growth plate
What is calcium essential for?
Bone development and maintenance
Muscle contraction
Nerve conduction
Blood
What can decreased Ca cause in bone development and maintenance?
Limb deformity during growth
Osteomalacia with potential limb fractures
Bran disease
What can decreased Ca cause in nerve conduction?
Nerve cell hyperexcitability with tetany in most species
Paralysis in cows
What does decreased Ca cause in blood clotting?
Inadequate clot formation
What happens with inadequate Ca during growth?
Faulty enchondral ossification
What does faulty enchondral ossification cause?
Poor calcification of cartilage in physis
Delayed bone formation
Wide unstable cartilage zone in physis
Limb deviation
What does inadequate Ca in diet of mature horses (bran disease) cause?
Osteoclasts reabsorb bone to maintain serum Ca levels
What does Osteoclasts reabsorbing bone to maintain serum Ca levels cause?
Osteoblasts produce much osteoid to replace lost bone
Osteoid fails to mineralize
Bone fibrous and thickened
What does Ca losses due to pregnancy and lactation cause?
Eclampsia Parturient paresis (milk fever)
What does eclampsia cause?
Nerve hyperexcitability
Tonic muscle contraction leading to seizures
Stiffness, limb pain, increase temperature, ataxia
Describe nerve hyperexcitability
Lack of Ca to stabilize voltage gated Na channels-spontaneous depolarization
Describe parturient paresis (milk fever)
Ach release at motor end plate depends on adequate Ca
Need for adequate Ca at motor end plate more pronounced in cows that other species
Causes paralysis and death if not treated
What is the normal Ca level maintained at in most species?
8.5 to 11 mg/dl
What is the level of Ca with tetany?
Below 6 mg/dl
What is the Ca level that can cause death?
Below 4 mg/dl
What is the nerve axon the basis for?
Action potential and nerve transmission
What is action potential and nerve transmission established by?
NaK pump
Selective permeability
Is K high on the inside or outside?
Inside
Describe the propagation of the action potential
Depolarization in one area triggers a wave of depolarization that spreads in each direction
Membrane voltage change opens adjacent voltage-gated Na channels
What does increased Ca do to nerves?
Makes it less excitable
What does a nerve require when there is increased Ca?
Greater change in voltage to trigger action potential
What does decreased Ca do to nerves?
Makes nerve more excitable
Tremors, muscle spasms, tetany
Nerve may spontaneously depolarize if Ca is low enough
What does depolarization trigger at the motor end plate?
Release of Ach from synaptic vesicles
What does Ach trigger once release from the motor end plate?
Muscle contraction
What happens with hypercalcemia?
Depresses nervous system and muscle activity
Decreased appetite
Constipation
Describe the 3 forms of Ca found in plasma
50% ionized form (active): diffusible through membranes, 4.6 mg/dl
41% protein-bound: nondiffusible, 3.9 mg/dl
9% complexed to negative ions and nonionized, 0.9 mg/dl
What is the total amount of Ca in plasma?
9.4 mg/dl
What is the Ca bank?
Bone
How can Ca level in ECF be altered?
By Ca pumps in cell membranes of the bone lining cells
What are the mechanisms of controlling Ca?
Increase or decrease GI absorption
Increase or decrease renal losses
Move Ca into or out of bone
What are the control systems of Ca from most powerful to least?
Parathyroid hormone (chief cells of parathyroid gland) Vitamin D (diet or skin) Calcitonin (C cells of the thyroid)
What is the last thing for vitamin D3 to go through to be come activated?
Kidney
Look at overview of vitamin D chart
Look at overview of vitamin D chart
What must be done to D3 in order to have an effect on Ca levels?
It must be activated
What does active vitamin D act to do?
Increase intestinal absorption of Ca
What is necessary for PTH to work on bone?
Active vitamin D
Describe parathyroid hormone
Most powerful mechanism for controlling extracellular Ca and phosphate
Acts to increase Ca
What happens as PTH increases Ca?
Increases intestinal absorption
Increases reabsorption of Ca and P from bone
Decreases renal losses of Ca, increases excretion of P
What happens if you remove 2 parathyroid glands?
No problem
What happens if you remove 3 parathyroid glands?
Transient hypocalcemia
What happens if you remove 4 parathyroid glands?
Bad news
What stimulates calcitonin secretion?
Increased plasma Ca
What does calcitonin act to do?
Decrease Ca (opposite of PTH)
What does calcitonin do to osteoclasts?
Decreases absorptive action of osteoclasts
Decreases formation of new osteoclasts
Describe hypoparathyroidism
Inadequate PTH secretion
Decreased osteocyte and osteoclast bone resorption
Ca level in ECF drops
Bone stays strong
Describe what happens if the parathyroids are suddenly removed in hypoparathyroidism
Blood Ca falls from normal of 9.4 mg/dl to 6-7 mg/dl in 2-3 days
Tetany occurs
Laryngeal muscles particularly susceptible to low Ca
Describe the primary form of hyperparathyroidism
Excess PTH secretion
Usually due to tumor
Extreme osteoclastic reabsorption of bone
Extremely weak bone with consequent fractures
Usually causes high Ca levels and low P levels in ECF
What is the secondary form of hyperparathyroidism most commonly cause by?
Poor nutrition and decreased Ca intake
Also seen when kidney damage causes inadequate activation of vitamin D
What does the nutritional or renal form of hyperthyroidism (secondary form) cause?
Low serum Ca secondarily stimulates PTH in attempt to maintain blood Ca levels
What does increased PTH lead to in the secondary form of hyperparathyroidism?
Ca reabsorption from bone to maintain ECF levels
What does Ca reabsorption from bone to maintain ECF levels cause?
Weakened bone, tiny or larger fractures, bone pain, lameness
Increased deposition of osteoid that fails to calcify thus bones thicken and become fibrotic
What is rickets?
Inadequate vitamin D
What does rickets cause?
Mildly low Ca in ECF but pronounced decrease in phosphate
What is a sign of rickets?
Weak bones due to increased PTH
What can late stages of rickets cause?
Tetany as bone stores depleted and ECF Ca drops
What can excessively rapid administration of Ca containing solutions cause?
Slow heart and death
What is the most common problem of excessively rapid administration of Ca depleting solutions?
Rapid IV tetracycline antibiotic administration
