Parathyroid Hormone and Calcitonin

Question 1

Calcium and calcium ions (Ca2+) are important for many body functions such as:

Answer 1

• Growth and maintenance of skeletal system, neurotransmitter release, muscle contraction, hormone secretion, blood clotting, intracellular Ca2+ signalling, apoptosis.
• Bone and tooth formation
• Cell division and growth
• Neuronal activity
• Skeletal and smooth muscle activity
• Cardiac activity and blood coagulation
• Secretory activity of glands

Question 2

Calcium homeostasis is governed by:

Answer 2

a careful balancing of Ca2+ absorption, excretion and storage.

Question 3

The regulation of calcium homeostasis involves two key hormones:

Answer 3

calcitonin and parathyroid hormone.

Other important factors include vitamin D and extracellular Ca2+ concentration

Question 4

Gut absorption of Ca2+ from the diet is responsible for net intake of ___mg Ca2+ per day

Answer 4

200mg

Question 5

Total plasma Ca2+ levels are:

Answer 5

2.5mM (10mg/dl)

Question 6

How much stored Ca2+ does the bone account for?

Answer 6

1kg

Question 7

The kidneys excrete around ___mg Ca2+ per day.

Answer 7

200mg

Question 8

Osteoclats and osteoblasts:

Answer 8

clasts crumble + blasts build

Question 9

Diseases of Ca2+ homeostasis

Answer 9

• Primary hyperparathyroidism
• Secondary hyperparathyroidism (renal failure)
• Osteoporosis
• Rickets (vitamin D deficiency or mutation affecting vitamin D synthesis)
• Calcium stones
• Receptor mutations (PTH receptor, extracellular Ca2+ sensing receptor)

Question 10

Name of protein produced by thyroid gland contains non follicular cells.

Answer 10

Calcitonin

Question 11

What is the name of the cells that product the calcitonin:

Answer 11

Parafollicular (clear or C) cells

- Those specialised cells are fewer in number than thyroid follicular cells and are found in between the follicles.

Question 12

Main function of calcitonin?

Answer 12

reduce blood calcium ion (Ca2+) concentration (abbreviated to [Ca2+])

• It also opposes the effects of parathyroid hormone (PTH) which is made by cells in the parathyroid gland .

Question 13

How many parathyroid glands do most people have?

Answer 13

Most people have four parathyroid glands and these are located on posterior surface of thyroid gland. 5% of the population have fewer parathyroid glands.

Question 14

Parathyroid glands have 2 types of cells:

Answer 14

• Chief cells (few in number) plus many oxyphil cells (unknown function)

Question 15

What do chief cells do?

Answer 15

produce parathyroid hormone (PTH) a small helical protein hormone of 84 aa (t1/2 <20 minutes)

Question 16

Function of PTH?

Answer 16

• Function of PTH is to increase blood [Ca2+] when it gets too low.
• Low [Ca2+] is detected by the G protein coupled Ca2+ sensing receptors, CaSR.

Question 17

How does PTH work?

Answer 17

PTH raises blood Ca2+ concentrations by:
1) Indirectly stimulation osteoclasts to release more Ca2+ from (bone resorption)

2) Increasing renal Ca2+ reabsorption (i.e reducing Ca2+ excretion via filtration)
3) Increasing production of vitamin D, which stimulates the uptake of Ca2+ from the intestine, as well as increasing bone resorption and renal Ca2+ reabsorption.

(Has opposite effect to calcitonin, which lowers [Ca2+])

Regulation by negative feedback:

• Increase in blood [Ca2+] decreases PTH secretion
• Increase in blood [Ca2+] also increases bone formation

Question 18

How does calcitonin work?

Answer 18

Calcitonin reduced blood [Ca2+] by:
1) Reducing osteoclast activity to reduce bone resorption and allows rapid bone deposition by osteoblasts

(has opposite effect to PTH, which increases Ca2+ concs)

Question 19

Effects of calcitonin?

Answer 19

Effects of calcitonin are minor consequence in humans!

High or low calcitonin levels do not cause disease.

Question 20

Diseases of Ca2+ homeostasis examples:

Answer 20

• Primary hyperparathyroidism
• Secondary hyperparathyroidism (renal failure)
• Osteoporosis
• Rickets (vit D deficiency)
• Calcium stones
• Paget’s disease

Question 21

Causes of rickets:

Answer 21

1. Vitamin D deficiency
2. Phosphate and calcium deficiency – less commonly, osteomalacia/rickets can be caused by phosphate or calcium deficiency. In certain rare conditions, some of which are inherited, the kidneys are not able to retain phosphate, which then leads to phosphate deficiency.

Question 22

Consequences of rickets?

Answer 22

Symptoms of osteomalacia can be vague with the person complaining of not feeling well with general aches and pains. Widespread bone pain, especially in the hips and lower back, can occur. The bones can be unnaturally tender even with moderate pressure. In later stages, the person may develop muscle weakness, particularly of the thighs, which causes difficulty in getting up from a sitting position and walking up stairs.
In children, rickets can cause:
•	bowing of the legs
•	the chest wall appearing to stick out
•	soft skull bones
•	curvature of the spine
•	short stature.

Question 23

Rickets: drug treatments:

Answer 23

As the majority of cases are due to vitamin D deficiency, treatment is with vitamin D replacement. This can be in the form of tablets or liquid medication.

However, if the patient is severely deficient in vitamin D or has very severe symptoms, larger doses of vitamin D may be given. This can be taken either orally every few weeks or through an injection given into the muscle every few months. Injections may also be considered for people who have a problem with absorbing the medication.

Question 24

Which tissues play a key role maintaining calcium homeostasis?

Answer 24

Intestines, kidneys, blood and bone

Question 25

Chief cells are located in which gland?

Answer 25

Parathyroid gland

Question 26

C cells are located in which gland?

Answer 26

Thyroid

Question 27

C cells are responsible for the production of which hormone?

Answer 27

Calcitoin

Question 28

Chief cells are responsible for the production of which hormone?

Answer 28

Parathyroid hormone

Question 29

What effect does calcitonin have on tissues involved with Ca2+ homeostasis?

Answer 29

Reduced osteoclast activity to reduce bone resorption and allow bone deposition by osteoblasts

Question 30

What effect does PTH have on tissues involved with Ca2+ homeostasis?

Answer 30

PTH raises blood Ca2+ concentrations by:

1) Indirectly stimulation osteoclasts to release more Ca2+ from (bone resorption)
2) Increasing renal Ca2+ reabsorption (i.e reducing Ca2+ excretion via filtration)
3) Increasing production of vitamin D, which stimulates the uptake of Ca2+ from the intestine, as well as increasing bone resorption and renal Ca2+ reabsorption.