Parathyroid Hormone and Calcitonin Flashcards
Calcium and calcium ions (Ca2+) are important for many body functions such as:
- 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
Calcium homeostasis is governed by:
a careful balancing of Ca2+ absorption, excretion and storage.
The regulation of calcium homeostasis involves two key hormones:
calcitonin and parathyroid hormone.
Other important factors include vitamin D and extracellular Ca2+ concentration
Gut absorption of Ca2+ from the diet is responsible for net intake of ___mg Ca2+ per day
200mg
Total plasma Ca2+ levels are:
2.5mM (10mg/dl)
How much stored Ca2+ does the bone account for?
1kg
The kidneys excrete around ___mg Ca2+ per day.
200mg
Osteoclats and osteoblasts:
clasts crumble + blasts build
Diseases of Ca2+ homeostasis
- 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)
Name of protein produced by thyroid gland contains non follicular cells.
Calcitonin
What is the name of the cells that product the calcitonin:
Parafollicular (clear or C) cells
- Those specialised cells are fewer in number than thyroid follicular cells and are found in between the follicles.
Main function of calcitonin?
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 .
How many parathyroid glands do most people have?
Most people have four parathyroid glands and these are located on posterior surface of thyroid gland. 5% of the population have fewer parathyroid glands.
Parathyroid glands have 2 types of cells:
- Chief cells (few in number) plus many oxyphil cells (unknown function)
What do chief cells do?
produce parathyroid hormone (PTH) a small helical protein hormone of 84 aa (t1/2 <20 minutes)
Function of PTH?
- 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.
How does PTH work?
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
How does calcitonin work?
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)
Effects of calcitonin?
Effects of calcitonin are minor consequence in humans!
High or low calcitonin levels do not cause disease.
Diseases of Ca2+ homeostasis examples:
- Primary hyperparathyroidism
- Secondary hyperparathyroidism (renal failure)
- Osteoporosis
- Rickets (vit D deficiency)
- Calcium stones
- Paget’s disease
Causes of rickets:
- Vitamin D deficiency
- 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.
Consequences of rickets?
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.
Rickets: drug treatments:
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.
Which tissues play a key role maintaining calcium homeostasis?
Intestines, kidneys, blood and bone
Chief cells are located in which gland?
Parathyroid gland
C cells are located in which gland?
Thyroid
C cells are responsible for the production of which hormone?
Calcitoin
Chief cells are responsible for the production of which hormone?
Parathyroid hormone
What effect does calcitonin have on tissues involved with Ca2+ homeostasis?
Reduced osteoclast activity to reduce bone resorption and allow bone deposition by osteoblasts
What effect does PTH have on tissues involved with Ca2+ homeostasis?
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.
