Calcium Disorders in Small Animals Flashcards
What processes does calcium play a pivotal role in?
Nerve conduction and neuromuscular transmission
Muscle contraction
Intracellular messenger involved in any number of cell signalling pathways
Coagulation
What are the two main pools of calcium?
Bone
Extracellular fluid
In what form is the calcium in bone present in?
Calcium hydroxyapatite
In what form is the calcium in extracellular fluid in?
Calcium bound to albumin
Calcium chelated to various compounds
Ionised calcium
Describe the uptake, storage and excretion of calcium..
Uptake = GIT
Required normal GIT function
Calcium actively absorbed from diet
Stored in skeleton
Mobilised by osteocalasts - Ca and PO4 released (precipitates as CaPO4)
Urinary excretion
Phosphate also excreted
What is calcium strictly controlled by?
Parathyroid hormone
Metabolites of Vit D (calcitriol)
Calcitonin
Describe how PTH controls calcium levels…
Increased in calcium via kidney:
- Increased Ca resorption
- Converstion of 25D3 to 1,25D3 (more biologically active)
Increases calcium via bones:
Activation of osteoclast activity
Increases calcium via GIT:
Enchanced absorbtion
Increases urinary phosphate excretion
What would happen to calcium and phosphate if you had too much PTH?
Calcium increases
Phosphate decreases
What are the actions of calcitriol?
Increases serum calcium: Increases GI absorption Facilitates renal resorption Mobilising Ca and PO4 from bone -ve feedback on own secretion Maintaining immune function
What would happen to calcium and phosphate if you had too much calcitriol?
Both calcium and phosphate would increase
How can you measure serum calcium?
Interested in ionised Ca
When you look at Ca always look at albumin
Ionised Ca prone to collection artefacts –> increased pH increases protein binding
Because CaPO4 is insoluble what needs to happen for an increase in ionised Ca when it is mobilised from bone?
PO4 has to be readily removed - otherwise will precipitate.
What needs to happen for disturbances in calcium balance to occur?
Disruption in:
- Hormonal control of calcium
- Organs involved in absorption, storage or excretion of calcium
What may disruption in calcium metabolism lead to?
Hyper/hypocalcaemia is problem with hormones/excretion/resorption
Altered bone metabolism without changes to serum calcium if nutritional secondary hyperparathyroidism
How can all raw meat diets be an issue for calcium?
Calcium to phosporus ration 1:50 in raw meat diet
Desired ration 1.2:1
Chronic resorption of bone to keep Ca normal
PTH very high
Why is calcium phosphate important?
High calcium phosphate = precipitation and deposition in tissues, esp kidneys
DEATH
What are the clinical signs of hypercalcaemia?
PUPD Weakness, lethargy, depression Inappetence, vomiting, diarrhoea, constipation Facial pruritis and oral discomfort Muscle twitching and fasciculations Cardiac tachydysrhythmias Sudden death
OR NO CLINICAL SIGNS
What may you see on clinical pathology with hypercalcaemia?
Hypercalcaemia
With or without disruption to serum phosphate
With or without disruption to renal function
What effects on renal function does hypercalcaemia have?
Interferes with tubular function = trouble concentrating urine
- Dog USG <1.035
- Cat USG <1.040
- Stops absorption of Na in thin ascending limb and reduces tissues sensitivity (medullary hypertonicity)
Vasoconstriction of afferent glomerular arteriole
Azotemia
Structural renal disease
CaPO4 precipitate
Is hypercalcaemia due to renal function if:
a. Low or normal phosphate
b. High phosphate
a. Cannot be due to renal dysfunction
b. Either renal dysfunction or structural renal disease due to CaPO4
What are the reasons for hypercalaemia?
Non-pathological
Rapidly growing dogs
Lab error
Transient
Haemoconcentration (dehydration)
Hyperalbuminaemia
Pathological
Increased PTH/PTH-like activity
Unrelated to increased PTH activity
What can cause hypercalcaemia due to increase PTH activity?
Primary hyperparathryoidism
What can cause hypercalcaemia due to increased PTH-like activity?
Paraneoplastic effect
Lymphoma, anal sac adenocarcinoma, pultiple myelomas
If you have high calcium, should PTH be high or low?
LOW
If you have hypercalcaemia and PTH is normal, the PTH is too high.
