OMG calcium
What are the major sites of calcium regulation
Occurs via transfer of calcium between the blood and 3 major target organs - bone, intestine, kidney
What are the types of cells in the parathyroid glands
Chief cells - sources of PTH, most numerous
Oxyphil cells - unknown function, appear at puberty, increase in number with age
What is the function of calcitonin
Is to inhibit bone resorption by inhibiting osteoclasts
- stimulates osteoblasts to form bone taking calcium out of circulation
- inhibits the mobilization of bone by osteroclasts
- End result is a decrease in the level of calcium in the blood thus helping to maintain proper blood calcium levels
What is the difference between resporption and reabsorption
Resorption - the process of breaking down and assimilating
Reabsorption - the process of re-absorbing
How is parathyroid hormone secretion controlled
PTH is released in response to low extracellular concentration of free calcium
Calcium concentrations fall below the normal range, there is a steep increase in secretion of parathyroid hormone
Low levels of the hormone are secreted even when blood calcium levels are high
What is hyperparathyroidism
Primary hyperthyroidism (To much PTH released) - due to a parathyroid tumour = Affects parathyroid directly
Secondary - occurs when a disease outside of the parathyroid gland leads to excessive secretion of PTH
What are the major sites of calcium regulation
Bone - stimulating resportion of bone mineral releases calcium and phosphate into blood
Small intestine - site where dietary calcium is actively transported across mucosa
Kidney - calcium that enters the glomerular filtrate is reabsorbed from the tubular system back into blood, which preserves blood
What are calcium sensing receptors
Expressed in a broad range of cells including parathyroid cells and C cells in the thyroid gland
What is milk fever
A severe drop in blood calcium
What hormones regulate calcium homeostasis
Parathyroid hormone - increased circulating calcium
1,25-DHC or vitamin D3 - increased circulating calcium
Calcitonin - decrease circulating calcium
What is Vitamin D/1,25-DHC? what does it do
Cholecalciferol
acts to increase blood calcium
generated through the activity of PTH within the kidney
Most important effect of VitD is to facilitate absorption of Calcium from the SI
What are the signs and consequences of milk fever
Signs = impaired nerve and muscle function leads to the downer cow situation
Sub clinical = muscles of GI, uterus and teat end can be impaired
Cows are more likely to develop mastitis, having calving difficulties, experience retained placentas, have a displaced abomasum
What do the parathyroid glands do
generally two pairs
about 2-5% of the human population has supernumerary parathyroids
Evolved from gills which also regulate calcium and ionic balance in fishes
Parathyroid glands are not associated with thyroid in birds, reptiles, and amphibians
What is calcitonin
Considered a hypocalcemic hormone
a 32 AA polypeptide hormone synthesized by parafollicular C cells of the thyroid gland
release is stimulated by elevated blood calcium levels
How do you prevent and treat milk fever
Prevent - DCAD diet, calcium deficient diet, higher magnesium (reduces blood pH)
Treatment - supplement blood calcium, IV injection of calcium salts or calcium and phosphorus supplements around parturition