Calcium Metabolism

Question 1

Identify where most of the Ca and PO4 is stored in the body

Answer 1

Bone

Question 2

List and describe the major sites of regulation for blood calcium

Answer 2

Kidney- Out: renal excretion
Gut- In: intestinal absorption, Out: fecal excretion
Bone- In: bone resorption, Out: bone formation (Ca incorporation into bone)

Question 3

Describe the major pathway for loss of Ca++ in the body

Answer 3

Sites of calcium loss are in the gut (fecal excretion), kidneys (urine output), and in the bones (Ca incorporation into bone)

Question 4

List hormones that are significant in Ca homeostasis

Answer 4

Parathyroid hormone, Calcitonin

Question 5

Describe general effects of PTH on calcium and phosphate in blood, urine, and bone

Answer 5

Calcium:
Blood- increases
Urine- decrease
Bone- decrease

Phosphate:
Blood- decrease
Urine- increase
Bone- decrease

Question 6

Describe the general effects of PTH on vitamin D synthesis

Answer 6

activates vitamin D in kidneys to calcitrol

Question 7

Describe the source and effects of calcitonin.

Answer 7

Source: Perifollicular “C” cells of the thyroid produce calcitonin
inhibits bone resorption, decreases tubular calcium reabsorption

Question 8

Describe, without using structure, the sites of synthesis of active vitamin D3 and the role of PTH

Answer 8

skin, liver, kidney (PTH)

Question 9

Describe effects of vitamin D3 on the gut, bone and kidney

Answer 9

209
Gut: stimulate transepithelial transport of calcium and phosphate in the small intestine
Bone: stimulates terminal differentiation of osteoclasts, stimulate osteoblasts to stimulate osteoclasts to mobilize calcium
Kidney: synthesizes vitamin D to calcitrol , induced by PTH

Question 10

Describe effects of PTH on bone, gut, and kidney.

Answer 10

Gut- calcitrol increases intestinal absorption of calcium
Bone- increases bone resorption, moves calcium and phosphate from bones into extracellular fluid
Kidney- stimulates activation of Vitamin D, converts 25(OH)vitamin D to calcitrol; increases tubular calcium reabsorption, decreases tubular phosphate reabsorption

Question 11

Describe effect of varying Ca and PO4 levels in the serum on parathormone secretion and calcitonin secretion.

Answer 11

CaxPO4 = K
K> 60-70, Ca salts are deposited
K< 30, bone resorption occurs
Calcitonin acts to lower serum levels of Ca/PO4
PTH acts when Ca gets too low/decreases PO4

Question 12

Distinguish primary from secondary hyperparathyroidism

Answer 12

Primary: high PTH and high Ca; not feedback sensitive
Secondary: high PTH, low to normal Ca

Question 13

Name one cause of secondary hyperparathyroidism

Answer 13

Chronic renal failure

Poor nutrition

Question 14

Describe how you would differentiate hypervitaminosis D from primary hyperparathyroidism

Answer 14

primary hyperparathyroidism- high PTH, high Ca

hypervitaminosis D- high Ca, low PTH

Question 15

Describe what typically triggers soft tissue mineralization, and organs affected.

Answer 15

commonly triggered by hypercalcemia; when product of CaxPO4 > 60-70, CaPO4 is deposited in the skin as a salt in a variety of soft tissues
kidney, skin, GI tract, cardiac and skeletal muscle, tendons and ligaments are common sites of deposition
structural and functional abnormalities result
basically irreversible

Question 16

Define: Hypocalcemia

Answer 16

can be seen in postparturient paresis (milk fever) and c-cell carcinoma

Question 17

Define: Hypercalcemia

Answer 17

high level of calcium in the blood, can be caused by Primary Hyperparathyroidism

Question 18

Define: calcitonin

Answer 18

small protein, functions to lower serum levels of Ca and PO4 by inhibiting bone resorption, decreases tubular calcium reabsorption, may not be physiologically significant

Question 19

Functions of phosphorus

Answer 19

ATP, buffer, enzyme activation, DNA/RNA, membrane structure, second messengers; loss is primarily seen through the kidneys

Question 20

Define: calcitrol, 1,25 -dihydroxyvitamin D

Answer 20

form of vitamin D that increases intestinal absorption of calcium

Question 21

Define: milk fever

Answer 21

hypocalcemic disorder associated with initiation of lactation in dairy cows: loss of calcium in milk

Question 22

Define: hyperparathyroidism

Answer 22

Primary common in dogs, seen in cats
Usually do to adenoma, not feedback sensitive
high PTH, high Ca, low PO4; extensive bone loss
no treatment except surgery
Secondary chronic renal disease cases, nutritional: occurs do to hypocalcemia, overstimulation of PTH and bone loss (high PTH, low to normal Ca)

Question 23

Define: hypoparathyroidism

Answer 23

rare
can be of autoimmune origin or caused by surgery for hyperthyroidism
young adults, 1-4 years old
symptoms- neuromuscular problems, focal muscle twitching, rear limb cramping, generalized muscle spasms, convulsions
emergency treatment: IV injection of Ca
oral treatment (maintenance): calcium lactate/carbonate and dihydrotachysterol

Question 24

Define: hypervitaminosis D

Answer 24

causes hypercalcemia and PTH suppression; high Ca and PO4 levels due to increased GI absorption and bone breakdown

Question 25

Define: malignancy

Answer 25

presence of tumor can cause hypercalcemia and low PTH levels; cannot be distinguished from hypervitaminosis D by just measuring PTH and Ca; some tumors produce a protein with effects similar to PTH,

Question 26

Define: cholecalciferol

Answer 26

in skin it is Vitamin D3, can also be provided in diet; sometimes used in rodenticides because it can cause hypervitaminosis D