Physiology of Calcium-Regulating Hormones (Toribio) Flashcards
What is the most important calcium regulating hormone?
PTH
List the Functions of PTH:
- Increases Blood calcium
- Reduces blood Phosphorus
- Activates vitamin D
- Promotes bone remodeling
Mammals have ______ parathyroid glands
- Parathyroids III (caudal, internal, lower)
- Parathyroids IV (external, cranial, upper)
4
What are the 3 cell types of the Parathyroid glands?
- Chief cells
- Clear cells
- Oxyphil cells
Fill in the blanks:
______________ produce PTH in response to hypocalcemia (Main cells)
_______________ are less active cells but secrete PTH
_______________ are inactive cells
(PTH = 84 aa, 1-34 is the active domain)
- Chief cells
- Clear cells
- Oxyphil cells
(T/F) PTH receptor is present in renal tubular cells and osteoblasts
True
What controls PTH secretion?
- Ca2+ concentrations
- Calcium-sensing receptor
- Vitamin D (1,25- dihydroxyvitamin D)
- Phosphate (PO4, Pi) concentrations
- Mg2+ concentrations
(T/F) Hypercalcemia increases PTH release
False, Hypocalcemia
(T/F) Stimulation by Ca2+ inhibits PTH secretion
True
(T/F) Vitamin D inhibits PTH synthesis and secretion, decreases parathyroid chief cell proliferation
True
(T/F) Hypophosphatemia stimulates PTH secretion
False, Hyperphospatemia
(T/F) Mag2+ facilitates Ca2+ homeostasis (PTH secretion and action)
True
PTH targets the:
- Kidneys
- Increases calcium reabsorption (and Mg reabsorption ThickAL)
- Inhibits phosphate reabsorption (PCT) = increase excretion
- Increases 1,25(OH)2D synthesis (tubular cells) - Bones
- Increases bone resorption during hypocalcemia
- PTH interacts with PTH receptors on osteoblasts to secrete factors that activate osteoclasts
PTH actions on bone resorption are indirect via ___________________
osteoblasts
Is a decoy receptor for RANKL to balance resorption and avoid excessive bone loss
OPG
________________ DO NOT have receptors for PTH but have receptors for calcitonin
Osteoclasts
The following is Hyperparathyroidism or Hypoparathyroidism?
Secondary
1. Sepsis (critically ill patients)
2. Hypomagnesemia
Hypoparathyroidism
The following is Hyperparathyroidism or Hypoparathyroidism:
Secondary
1. Renal
2. Nutritional
Hyperparathyroidism
Produced by the parafollicular cells (C Cells) of the thyroid gland in response to hypercalcemia
Calcitonin (CT)
- 32 aa
- decreases blood calcium
- decreases bone loss/resorption
What controls calcitonin secretion?
- Ca2+ concentrations
- Stimulation by Ca2+ increases CT secretion
- Gastrin
(T/F) Hypocalcemia increases CT release
False, Hypercalcemia
What is a strong stimulator of CT release?
Gastrin
List the functions of vitamin D:
- Increases calcium and phosphorus absorption and reabsorption
- Modulates bone remodeling
- Inhibits parathyroid cell function / PTH secretion
- Regulates the immune function
(T/F) Vitamin D is important for intestinal absorption and renal reabsorption of calcium
False, calcium AND phosphorus
(T/F) There is active vitamin D in milk
False, it would be a bad idea
(T/F) Vitamin D inhibits parathyroid chief cell proliferation, activity, and PTH secretion
True
Why do animals with chronic kidney disease have increased PTH concentrations?
The activation of vitamin D takes place in the Kidneys (the kidney suppresses PTH)
(T/F) PTHrP is not important for development of animals
False
Low calcium stimulates ________________ secretion
PTH
Vitamin D is activated in the ____________ by ___________________
kidney, 1alpha-hydroxylase
Osteoclast activation requires PTH binding to _________________
osteoblast
Vitamin D stimulates renal reabsorption of ________________
Calcium and phosphorus
Vitamin D stimulates intestinal absorption of ________________
Calcium and Phosphate
PTH increases paracellular calcium reabsorption by _________________
binding to its receptor in the renal tubular cell, specifically in the TAL, by making the lumen more positive
If serum PTH concentrations are elevated, what is expected?
Increased renal excretion of phosphorus and increased reabsorption of calcium
What are some important things about magnesium?
- It is important for the synthesis and action of PTH
- PTH increases its renal reabsorption
- Contributes to energy homeostasis
(T/F) Unlike calcium, magnesium is minimally stored in bone
False
(T/F) In the lactating animal, parathyroid hormone-related protein (PTHrP) is produced by the mammary gland to reduce/stop bone resorption
False
What makes renal tubules electropositive?
PTH
What binds receptors on osteoclasts?
Calcitonin
What promotes the absorption of phosphorus?
Vitamin D
Where is PTHrP secreted?
It is secreted by multiple tissues
