1/3 Parathyroid gland - Calcium Regulation COMPLETE***

Question 1

Where is most calcium found?
- Where is the rest?
- Of blood calcium, how much of it is in an ionised form (active)?

Answer 1

stored within bone as the extracellular matrix

in the blood

half

Question 2

Calcium: What can Ionised calcium do?
- What monitors ionised calcium concentration?
- Ionised Calcium must be tightly regulated between which values?

Answer 2

interact with tissues

the parathyroid gland

1-1.25mmol/l

Question 3

Calcium: State the 2 broad ways ionised calcium concentration is controlled

Answer 3

hormonal control
buffering with exchangeable calcium in bone salts and calcium in mitochondria

Question 4

Calcium: Hormonal Control
- Which hormones regulates blood calcium levels? 3

Answer 4

parathyroid hormone
calcitonin
active vitamin d3

Question 5

Calcium: Parathyroid Hormone
- What synthesises it?
- Where is this gland located?
- How does parathyroid hormone release work? 2

Answer 5

the chief cells in the parathyroid gland

posterior to the thyroid gland

low ionised calcium concentrations are detected by G protein coupled calcium receptors
this stimulates the release of parathyroid hormone

Question 6

Calcium: How is PTH release regulated?

Answer 6

ionised calcium has negative feedback on PTH secretion

Question 7

Calcium: Describe the synthesis of Parathyroid hormone (PTH) by chief cells 3

Answer 7

a long preprohormone polypeptide consisting of 110 amino acids is cleaved to form a pro hormone of 90 amino acids
the pro hormone is cleaved to form PTH
PTH is then packaged into secretory vesicles

Question 8

Calcium: Which amino acids in PTH mediate the action of this hormone?
- How long is the half life?
- Where is the hormone eventually degraded?

Answer 8

the first 34

10 minutes

in the liver

Question 9

Calcium: Describe the pattern of PTH secretion 3

Answer 9

it is continuously secreted
secretion increases as the
PTH secretion increases when ionised calcium concentration falls below 1mmol/l
PTH secretion decreases when ionised calcium concentration increases about 1.25mmol/l

Question 10

Calcium: Which organs does Parathyroid hormone have an effect on?

Answer 10

bone
kidney
intestine

Question 11

Calcium: PTH effect on Bone
- What is the function of osteoclasts?
- Where are osteoblasts and osteocytes found?
- Where does bone fluid lie?

Answer 11

to erode bone and incorporate calcium into the extracellular fluid

covering the bone surface

between the osteocyte-osteoblast membrane and the bone

Question 12

Calcium: PTH effect on Bone
- Which 2 phases are initiated by PTH release and what is their purpose?

Answer 12

a fast phase to obtain calcium from bone fluid
a slow phase to obtain calcium from bone

Question 13

Calcium: PTH effect on Bone
- How long does the fast phase take to obtain calcium?
- Describe the events of the fast phase 5

Answer 13

minutes

PTH interacts with membrane receptors on osteocytes and osteoblasts
this increases the permeability of the the bone-fluid side of the membrane to calcium
calcium uptake from bone fluid increases
bone fluid calcium concentration falls
nearby calcium phosphate crystals replace calcium in the bone fluid

Question 14

Calcium: PTH effect on Bone
- How is the slow phase activated?
- Describe the events of the slow phase 7

Answer 14

by the activation of osteocytes and osteoblasts in the fast phase

existing osteoclasts are activated
new osteoclasts are formed
the multinucleate osteoclasts attach to bone
they form a reaction chamber at attachment
osteoclasts release organic acids and proteolytic enzymes
bone is resorbed
calcium and phosphate and transported across the osteoclast into the blood

Question 15

Calcium: PTH effect on Kidney
- Describe the effect of PTH on the kidney 4

Answer 15

PTH increases calcium reabsorption in the distal convoluted tubules and collecting costs
this helps retain calcium and magnesium
PTH decreases phosphorus reabsorption in the proximal convoluted tubule to facilitate this
so there is rapid loss of phosphorus

Question 16

Calcium: PTH effect on Bone
- How long does the slow phase take to obtain calcium?

Answer 16

48 hours

Question 17

Calcium: Where does Calcitonin come from?
- What is another name for Active Vitamin D3?
- Where does Calcitriol act?

Answer 17

the parafollicular cells within the thyroid gland

calcitriol

on the intestines
on the kidney

Question 18

Where can vitamin D be obtained from for cats and dogs?
- What happens to vitamin D that is absorbed through the intestines? 4

Answer 18

diet

it is converted into 25-hydroxyvitamin D in the liver
25 -hydroxyvitamin D is converted to calcitriol in the renal tubules
this is catalysed by 1-alpha-hydroxylase
this enzyme is activated by PTH

Question 19

Calcium: PTH effect on Intestines 2

Answer 19

PTH activates the enzyme needed to convert inactive vitamin D into calcitriol
calcitriol increases calcium absorption from the intestine by entering intestinal epithelial cells and increasing the synthesis of calcium transport proteins

Question 20

Calcium: How does Calcitriol affect the kidney?

Answer 20

it acts on renal tubular epithelial cells to increase the reabsorption of calcium and phosphorus from urine

Question 21

Calcium: What can excess Calcitriol cause?

Answer 21

calcium deposition