Physiology of Calcium-Regulating Hormones (Toribio)

Question 1

What is the most important calcium regulating hormone?

Answer 1

PTH

Question 2

List the Functions of PTH:

Answer 2

• Increases Blood calcium
• Reduces blood Phosphorus
• Activates vitamin D
• Promotes bone remodeling

Question 3

Mammals have ______ parathyroid glands
- Parathyroids III (caudal, internal, lower)
- Parathyroids IV (external, cranial, upper)

Answer 3

4

Question 4

What are the 3 cell types of the Parathyroid glands?

Answer 4

• Chief cells
• Clear cells
• Oxyphil cells

Question 5

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)

Answer 5

• Chief cells
• Clear cells
• Oxyphil cells

Question 6

(T/F) PTH receptor is present in renal tubular cells and osteoblasts

Answer 6

True

Question 7

What controls PTH secretion?

Answer 7

• Ca2+ concentrations
• Calcium-sensing receptor
• Vitamin D (1,25- dihydroxyvitamin D)
• Phosphate (PO4, Pi) concentrations
• Mg2+ concentrations

Question 8

(T/F) Hypercalcemia increases PTH release

Answer 8

False, Hypocalcemia

Question 9

(T/F) Stimulation by Ca2+ inhibits PTH secretion

Answer 9

True

Question 10

(T/F) Vitamin D inhibits PTH synthesis and secretion, decreases parathyroid chief cell proliferation

Answer 10

True

Question 11

(T/F) Hypophosphatemia stimulates PTH secretion

Answer 11

False, Hyperphospatemia

Question 12

(T/F) Mag2+ facilitates Ca2+ homeostasis (PTH secretion and action)

Answer 12

True

Question 13

PTH targets the:

Answer 13

• 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

Question 14

PTH actions on bone resorption are indirect via ___________________

Answer 14

osteoblasts

Question 15

Is a decoy receptor for RANKL to balance resorption and avoid excessive bone loss

Answer 15

OPG

Question 16

________________ DO NOT have receptors for PTH but have receptors for calcitonin

Answer 16

Osteoclasts

Question 17

The following is Hyperparathyroidism or Hypoparathyroidism?

Secondary
1. Sepsis (critically ill patients)
2. Hypomagnesemia

Answer 17

Hypoparathyroidism

Question 18

The following is Hyperparathyroidism or Hypoparathyroidism:

Secondary
1. Renal
2. Nutritional

Answer 18

Hyperparathyroidism

Question 19

Produced by the parafollicular cells (C Cells) of the thyroid gland in response to hypercalcemia

Answer 19

Calcitonin (CT)
- 32 aa
- decreases blood calcium
- decreases bone loss/resorption

Question 20

What controls calcitonin secretion?

Answer 20

• Ca2+ concentrations
• Stimulation by Ca2+ increases CT secretion
• Gastrin

Question 21

(T/F) Hypocalcemia increases CT release

Answer 21

False, Hypercalcemia

Question 22

What is a strong stimulator of CT release?

Answer 22

Gastrin

Question 23

List the functions of vitamin D:

Answer 23

• Increases calcium and phosphorus absorption and reabsorption
• Modulates bone remodeling
• Inhibits parathyroid cell function / PTH secretion
• Regulates the immune function

Question 24

(T/F) Vitamin D is important for intestinal absorption and renal reabsorption of calcium

Answer 24

False, calcium AND phosphorus

Question 25

(T/F) There is active vitamin D in milk

Answer 25

False, it would be a bad idea

Question 26

(T/F) Vitamin D inhibits parathyroid chief cell proliferation, activity, and PTH secretion

Answer 26

True

Question 27

Why do animals with chronic kidney disease have increased PTH concentrations?

Answer 27

The activation of vitamin D takes place in the Kidneys (the kidney suppresses PTH)

Question 28

(T/F) PTHrP is not important for development of animals

Answer 28

False

Question 29

Low calcium stimulates ________________ secretion

Answer 29

PTH

Question 30

Vitamin D is activated in the ____________ by ___________________

Answer 30

kidney, 1alpha-hydroxylase

Question 31

Osteoclast activation requires PTH binding to _________________

Answer 31

osteoblast

Question 32

Vitamin D stimulates renal reabsorption of ________________

Answer 32

Calcium and phosphorus

Question 33

Vitamin D stimulates intestinal absorption of ________________

Answer 33

Calcium and Phosphate

Question 34

PTH increases paracellular calcium reabsorption by _________________

Answer 34

binding to its receptor in the renal tubular cell, specifically in the TAL, by making the lumen more positive

Question 35

If serum PTH concentrations are elevated, what is expected?

Answer 35

Increased renal excretion of phosphorus and increased reabsorption of calcium

Question 36

What are some important things about magnesium?

Answer 36

- It is important for the synthesis and action of PTH - PTH increases its renal reabsorption - Contributes to energy homeostasis

Question 37

(T/F) Unlike calcium, magnesium is minimally stored in bone

Answer 37

False

Question 38

(T/F) In the lactating animal, parathyroid hormone-related protein (PTHrP) is produced by the mammary gland to reduce/stop bone resorption

Answer 38

False

Question 39

What makes renal tubules electropositive?

Answer 39

PTH

Question 40

What binds receptors on osteoclasts?

Answer 40

Calcitonin

Question 41

What promotes the absorption of phosphorus?

Answer 41

Vitamin D

Question 42

Where is PTHrP secreted?

Answer 42

It is secreted by multiple tissues