4-Calcium homeostasis

Question 1

Features of calcium

Answer 1

Comes out of solution at very low concentrations

Question 2

Feature of the skeleton

Answer 2

Living tissue that is constantly dying and regenerating

Question 3

how much calcium do we absorbed a day

Answer 3

200mg net intake

Question 4

What i the total plasma Ca levels

Answer 4

2.5mM
40% bound to macromolecular proteins
5% complexed as salts
1.2mM of free ionised calcium
You regulate the 1.2mM not the 2.5mM

Question 5

How many parathyroid glands do you have

Answer 5

4,
5% of people have more than 4
Found in a butterfly spot like shape on the thyroid gland

Question 6

What is the origin of the PT gland

Answer 6

derived from the pharyngeal pouch endoderm driven by Gcm-2
Gcm-2 also expressed in the pharyngeal pouch of the internal gill
PT glands in neck as derived from the gill

Question 7

Parathyroid hormone

Answer 7

Produced in cheif cells of the PT gland
84 alpha helix

Question 8

Relationship between extracellular Ca and PTH

Answer 8

PTH secretion is inversely proportional to serum Ca
EC50=1.2mM
Steep sigmoidal relationship
Occurs over a fifth of an order
One of the most tightly regulated relationships in the body

Question 9

Ca sensing receptor (GPCR)

Answer 9

Doesn’t desensitise like other GPCRs so continuously sensing calcium
responsive to both Ca and Mg but less sensitive to Mg
Present in parathyroid cells and the kidneys
limits Ca reabsorption in kidneys
2 GPCRs, one Gi one Gq

Question 10

Bone reabsorption

Answer 10

Daily pulsatile release of PTH secretion leads to bone formation
Chronically elevated PTH breaks bone down

Question 11

Renal Ca absorption

Answer 11

Distal convoluted tubule is the last control point
Most reabsorption happens in proximal tubule (70%)
PTH acts upon the thick ascending limb and the DCT to increase absorption

Question 12

Vitamin D

Answer 12

Does what PTH does and more
Pro-vitamin D3 converted to preVitamin D3 by UVB (sun)
Increases net intestinal Ca uptake (no PTH receptors in gut but there are VD3 ones)
Increases bone resorption (demineralisation)
Increases renal reabsorption

Question 13

Intestinal Ca absorption

Answer 13

Active absorption through TRPV5&6 but mainly 5
Passive absorption occurs too
Binds to CalD inside
Moved to blood through PMCA and NCX
VD3 increases expression of CalD and TRPV6

Question 14

Ca and cell death

Answer 14

Ca drives apoptosis
Make less ATP with age so can’t pump Ca out
Cells die with age

Question 15

Calbindins

Answer 15

CaB -D28k mainly expressed in the kidneys
D9K in the gut
Provide (re)absorptive epithelia with protection from Ca mM
Expression dependent on VD3

Question 16

Calcitonin

Answer 16

Secreted from parafollicular thyroidal C cells
Antagonises action of everything but PHT and VD3
Opposite action than PTH
Leads to bone deposition
More important in fish as sea has 10 times mire Ca than our blood

Question 17

Diseases

Answer 17

Primary hyperparathyroidism-too much PTH from thyroid
Secondary hyperparathyroidism-renal failure
Osteoporosis and rickets
Calcium stones