Calcium & Phosphate Regulation

High parathyroid hormone because kidney disease reduces the dogs ability to excrete phosphate, thus the dog has high phosphate. Phosphate will bind to free Ca++, lowing Ca++ ECF levels. Low Ca++ lvls stimulate the release of parathyroid hormone.

A dog had severe kidney disease. Would you expect his parathyroid levels to be high or low?

inhibits

Active vitamin D [stimulates/inhibits] the secretion of parathyroid hormone.

parafollicular cells of thyroid

Calcitonin is secreted from _______________

Ca+ increase in blood Phosphate will decrease in blood While PTH brings Ca++ and P+ out of bone, PTH's effect on kidney is so strong at causing phosphate excretion that phosphate levels drop.

If a patient recieves an injection of parathyroid hormone, Ca++ levels will {increase/decrease] and Phosphate levels will [increase/decrease]

Bone (removes Ca+ from bone and into ECF) Kidney (Ca+ reabsorbed) *remember, PTH has an indirect effect on the GI not a direct!!

In order to increase Ca++ lvls, parathyroid hormone directly acts on which of the following: -Bone -Kidney -GI intestines -Liver

1alpha-hydroxlase

Once Vitamin D is first hydroxylated into 25-hydroxycholecalciferol, _____________________ enzyme forms the active version of vitamin D, 1,25-dihydroxycholecalciferol.

24-hydroxylase

Once Vitamin D is first hydroxylated into 25-hydroxycholecalciferol, _____________________ enzyme forms the deactived version of vitamin D, 24,25-dihydroxycholecalciferol.

protein hormone

Parathyroid hormone is a _____________ hormone: -protein -steroid -AA derived

N-terminus

Parathyroid hormone is composed of a C-terminus and N-terminus. Which is the active portion, ie. which part binds to the receptor?

low calcium

Parathyroid hormone is released whenever calcium levels are [high/low] in ECF.

1. osteoblast-osteocyte pump (Parathyroid hormone binds to PTH receptor or Osteoblasts/cytes, causing osteoblasta to pump Ca++/Phosphorus from bone into ECF.) 2. More slowely, PTH activates osteoclasts to dissolve actual bone mineral. (This is indirect action, as PTH is actually activating osteoblast to secrete signals to activate osteoclasts)

Through what mechanisms does parathyroid hormone effect bone?

True excess meat would deliver excess phosphorus. Excess P binds to free Ca++ in blood, lowering ECF Ca++ lvls and causing excess secretion of PTH

True or False An animal fed an all meat diet risks developing hyperparathroidism.

True Total removal of the thyroid has little effect on calcium balance in adults, as long as adult gets proper dietary nutrition.

True or False Calcitonin's function is not neccessary for life in adult mammals.

True Vitamin D allows PTH to effect bones. Exaggerated effects would remove to much calcium from bones, causing demineralization

True or False Excess vitamin D can lead bone mineral to dissolve.

True

True or False In blood, calcium can either be bound to proteins or traveling freely

False PTH and Vit D have opposite effects on phosphate. PTH inhibits phosphate reabsorption, causing more phosphate to be excreted. Vit D promotes phosphate reabsorption, causing less phosphate to be excreted. PTH and Vit D are important in maintaining phosphate balance in bones.

True or False PTH and Vitamin D have synergistic effects on phosphate, as both lead to increased phosphate excretion.

True PTH blocks phosphate reabsorpotion, causing more phosphate to be excreted in urine.

True or False Parathyroid hormone blocks phosphate reabsorption in the kidneys.

False PTH indirectly acts on the gut to increase Ca++ absorption. Specifically, PTH directly acts on the kidney, kidney releases Vitamin D. Vitamin D increase Ca++ absorption within gut.

True or False Parathyroid hormone directly act on the GI system in order to increase Ca++ absorption within the gut.

False PTH directly effects osteoblasts. However, osteoclasts do NOT have a PTH receptor.

True or False Parathyroid hormone directly acts on osteoclasts and osteoblasts via a PTH receptor.

false pth indirecty acts on osteoclasts

True or False Parathyroid hormone directly acts on osteoclasts and osteoblasts via a PTH receptor.

True Phosphate binds to ECF calcium, lowing the concentration of free calcium. Low free calcium stimulates the release of parathyroid hormone from chief cells.

True or False Phosphate indirectly stimulates the secretion of parathyroid hormone.

True Vitamin D must undergo hydroxylations to become biologically active

True or False Vitamin D has very little biological activity.

True

True or False Vitamin D is produced in response to exposure of UV light.

Feces (majority) and urine

What are the 2 primary ways humans loose calcium from the body?

Urine (majority) and feces

What are the 2 primary ways the body gets rid of phospahte?

1. Increases Ca++ reabsorption (less Ca+ secreted in urine) 2. Increases phosphate secreation (more P in urine) 3. Increases formation of active vitamin D

What are the 3 effects parathyroid hormone has on the kidneys?

allows PTH to effect bone osteoblasts/osteocyte pump

What effects does active vitamin D (1,25Dihydroxycholecalciferol) have on bone?

increases Ca++ absorption increases phosphate absorption

What effects does active vitamin D (1,25Dihydroxycholecalciferol) have on the intestinal tract?

increases calcium reabsorption increases phosphate reabsorption

What effects does active vitamin D (1,25Dihydroxycholecalciferol) have on the kidneys?

Increased PTH secretion would cause high levels of Ca+ and normal/high lvls of Phosphate

What effects would you see with a dog who has primary hyperparathyroidism?

parathyroid hormone low calcium low phosphate low vitamin D

What factors increase the activity of 1-alpha hydroxylase enzyme?

high calcium high phosphate high active Vitamin D lvls

What factors increase the activity of 24-hydroxylase enzyme?

bone loss occurs because Ca++ is constantly being removed from the bone.

What happens if parathyroid hormone is chronically elevated?

form mature bone by secreting osteoid

What is the function of Osteoblasts?

Osteoclasts are derivatives of monocytes and function to dissolve bone.

What is the function of osteoclasts?

Osteocytes are osteoblasts that have become strapped within osteoid. They function to maintain communication with osteoblasts.

What is the function of osteocytes?

Tonic inhibition There are Ca++ sensory receptors on chief cell membranes. When Ca++ is bound to these receptors, PTH synthesis and releases is INHIBITED. If no Ca++ is bound the the receptors, the PTH is synthesized and released.

What is the mechanism behind how Ca++ levels are sensed by parathyroid chief cells?

Renal disease would cause kidneys not to excrete phosphate as well. Excess phosphate would bind with free calcium, lowering ECF Ca++ levels. This would cause high PTH.

What is the physiology behind renal secondary hyperparathyroism?

cholecalciferol

What is the scientific name for inactive Vitamin D?

calcium

Which is more abundant in blood- calcium or phosphate?

parathyroid hormone

Which of the following increase the activity of 1-alpha hydroxylase? -calcium excess -phosphate excess -high vitamin D -parathyroid hormone

1,25-Dihydroxycholecalciferol cholecalciferol is hydroxylated to form 25-hydroxycholecalciferol. 25-hydroxycholecalciferol is hydroxylated by 1alpha-hydroxylase to form 1,25-dihydroxycholecalciferol.

Which of the following is biologically active: -cholecalciferol -24,25-Dihydroxycholecalciferol -1,25 Dihydroxycholecalciferol -3beta cholecalciferol

chief cells

_____________ cells are found within the parathyroid glands.

calcitonin

_______________ enzyme is secreted from parafollicular cells in response to high ECF calcium levels.

calcitonin Calcitonin is released in response to HIGH Ca+ and act to lower Ca+ lvls. PTH is released in response to LOW Ca+ lvls and acts to raise Ca+ lvls.

__________________ enzyme is said to oppose the actions of parathyroid hormone.

7-Dehydrocholesterol

_______________________ is produced by the liver and travels in capillaries to the skin. Once exposed to Sunlight, it is converted into Vitamin D3.

decreased Na+ channels are harder to open. Thus, Na+ does not rush into cells so cells remain more negative.

hypercalcemia causes [increased/decreased] neuronal excitability.

increased Na+ channels are influenced by Ca++. Low Ca++ makes it easier for Na++ to open. Thus, more Na+ rushes into cell, making them more positive and easier to excite.

hypocalcemia causes [increased/decreased] neuronal excitability.

true The kidneys are extremely important when considering phosphate removal. Damage to them will decreases the amount of phosphate that is secreted.

true or false In kidney disease patients, it is common to see increased phosphate levels.