Lecture 33

Question 1

What are the three ways that calcium can be added to plasma?

Answer 1

1. Absorption from the digestive tract
2. Reabsorption (mobilisation) from the bone
3. Reabsorption at the kidneys

Question 2

What are the two main ways that calcium can be removed from plasma?

Answer 2

1. Calcification of bone

2. Filtration at kidneys

Question 3

What are the main calcium sensing receptors and where are they found?

Answer 3

CaSR- found mainly in parathyroid and thyroid glands

Question 4

How many parathyroid glands do mammals have and where are they located?

Answer 4

Mammals have 4 parathyroid glands. Dogs have 2 external glands and 2 internal

Question 5

What is the primary cell of the parathyroid and what is secreted by them?

Answer 5

the chief cells that secrete PTH

Question 6

Describe the relationship between plasma calcium concentrations and para-thyroid hormone secretion:

Answer 6

the relationship is sigmoidal. The system is designed to respond more drastically to hypocalcaemia

Question 7

What are the three main renal effects of para-thyroid hormone?

Answer 7

1. Stimulation of calcium re-absorption (predominantly influencing the distal nephron)
2. Inhibition of phosphate re-absorption (the proximal tubule is quantitatively more important, maintains appropriate Ca:P in face of hypoglycemia)
3. Stimulates synthesis of calcitriol (increasing hydroxylation in proximal tubule)

Question 8

How does parathyroid hormone increase bone re-absorption?

Answer 8

PTH increases the synthesis of RANKL and decrease OPG that leads to increased action of the OC (more calcium)

Question 9

Explain how parathyroid stimulates the conversion of vitamin D3 to active calcitrol within the kidney:

Answer 9

1. PTH stimulates the conversion of vitamin D3 to active calcitrol in kidney
2. Calcitrol increases calcium uptake in GIT by synthesis of calcium binding protein and Ca2+ATPase in enterocyte

Question 10

What is the effect of calcitriol on PTH?

Answer 10

calcitriol suppresses gene transcription reducing PTH synthesis

Question 11

What is the effect of phosphate on PTH?

Answer 11

High phosphate stimulates PTH secretion

Question 12

How is calcitriol synthesised?

Answer 12

1. Inactive Vitamin D comes from the diet or is produced by the skin
2. Converted in the proximal tubule of the kidney through 1-alpha-hydroxylase (PTH is required for activation from the kidney)

Question 13

What is the effect of calcitrol on the gastrointestinal tract?

Answer 13

Increases absorption of Ca2+ and P in the GIT

Question 14

What is the effect of calcitrol on parathyroid glands?

Answer 14

Decreases PTH transcription

Question 15

What is the effect of calcitrol on bone?

Answer 15

Stimulates the production of RANKL, increasing osteoclast activity

Question 16

What is the effect of calcitrol on the kidney?

Answer 16

Increases calcium re-absoprtion within the distal tubule

Question 17

Where is calcitonin produced?

Answer 17

para-follicular (C-cells) of the thyroid

Question 18

What is the primary biological actions of calcitonin?

Answer 18

decreases re-absorption of calcium and phosphate

Question 19

What are the short term and the long-term effects of calcitonin?

Answer 19

In the short term, calcitonin decreases osteocyte osteolysis (transfer of Ca from canaliculi to ECF), leading to a decrease in Ca levels in the blood. In the long-term, calcitonin decreases bone re-absorption by inhibiting the activity of osteoclasts, causing decreased calcium and potassium.