Parathyroid Gland : Calcium And Phosphate Regulation Flashcards
How many grams of calcium do adult humans contain ?
1000g
Around how many mg of calcium is exchanged between bone and ECF each day ?
300-600mg
What is normal serum concentration ?
2.2-2.6 mM
In the ECF , what percentage of calcium is ionised , protein bound and complexed ?
47% is ionised ( active form )
47% is protein bound ( inactive form )
6% is complexed ( eg with Pi , citrate , carbonate )
Where is most calcium stored ?
In the skeleton
Why is calcium important ?
- Builds and maintains bones and teeth
- Regulates heart rhythm
- Eases insomnia
- Helps regulate the passage of nutrients in and out of cell walls
- Assists in normal clotting of blood ( factor 4 )
- Helps maintain proper nerve and muscle function
- Lowers blood pressure
- Reduced blood cholesterol levels
- Reduces chances of colon cancer
What is EDTA ?
When taking a blood sample , you add EDTA which prevents blood from clotting as it removes calcium by chelating it. This is because calcium is an important clotting factor ( factor 4). This helps to preserve the blood for longer
Why do we need to giv IV calcium in blood transfusions?
Because when blood donors donate their blood - the blood is put into a bag which contains citrate. Citrate chelates calcium ions. And so when giving blood transfusions to patients - blood will have low calcium levels.
And so we need to give massive transfusions of IV calcium.
What are the three hormones involved in regulation of calcium and phosphate ?
- Parathyroid hormone
- Calcitriol
- Calcitonin
Normally , how many parathyroid glands do we have ?
4
What cells secrete the parathyroid hormone ?
Chief cells - stained darker than oxyphil cells
Why is parathyroid hormone known as an acute hormone in calcium regulation ?
Because the effects it takes are very quick - it has Avery short half life of 4.5 minutes. And after that is cleaved by the liver.
Does PTH move freely in the blood or is it bound to a protein ?
Has no serum binding protein
What type of hormone is PTH ?
Polypeptide hormone
What is the f7nction of oxyphil cells ?
No function known
Synthesis of PTH is regulated both at transcriptional and post transcriptional levels , what occurs at low serum and high serum calcium levels ?
Low serum calcium up regulates gene transcription
High serum calcium down regulates gene transcription
Low serum calcium prolongs survival of mRNA.
What are PTH target organs and physiological effects ?
- PTH will bind to receptors on the bone which would increase the activity of osteoclasts and decreases activity of osetoblasts. which would degrade bone releasing calcium into the bloodstream
- The intestine : PTH activates the inactive form of vitamin D into Calcitriol which is the active form of vitamin D. Vitamin D is required for the resorption of dietary calcium from GI tract.
- the kidney : decreases loss of calcium to urine by increasing calcium reabsorption by the kidneys and and increases phosphate loss into the urine.
Outline the process by which the activated form of vitamin D is synthesised ?
- Vitamin D3 ( cholecalciferol) is synthesised by sunlight and cholesterol. This is hydroxylated in the liver into 25(OH)D
- 25(OH)Dis the pre hormone substrate. It is produced in the liver from D3 ( cholecalciferol). In the kidneys , 25(OH)D is activated by the PTH and hydroxylated again.
- 1,25( OH ) 2D also known as calcitriol is the activated version of vitamin D. It is produced in the kidney.
What is the difference between D3 to hormones ?
Vitamin D38# not secreted by classical endocrine glands
Vitamin D3 is formed in the skin or from the diet.
What are the effects of Calcitriol ( 1,25(OH)2D ?
- Plays an essential role in the gut , it aids with the reabsorption of dietary calcium.
- Bone : increases Ca2+ removal
- Kidney : signals for calcium to be rebabsorbed by the kidney and stimulates phosphate excretion .
Where is calcitonin secreted from and what is its main function ?
Secreted from the C cells in the thyroid gland ( lay around the thyroid follicle ).
Their main function is to decrease calcium serum levels by retaining calcium in the skeleton by preventing bone breakdown , increasing bone building, decreases ca2++ reabsorption by the gut , decreases calcitriol levels which all dcereases plasma Ca2+ Levels.
What is hypercalcaemia? And what are associated consequences?
- This is when serum calcium levels rise above 3 mmol/L
The high calcium levels leads to polyuria which leads to dehydration.
‘ STONES , MOANS , GROANS AND ACHES ‘
STONES = renal calculi ( renal stones ) GROANS = severe constipation which leads to abdominal pain MOANS = depression / tiredness / lethargy BONES = muscle aches
Main treatment for hypercalcaemia?
Rehydration eases symptoms
What are the two main causes of severe hypercalcaemia?
- Malignant osetolytic bone metastasis which increases bone degradation due to increase activity of osetoclasts. The common cancers that metastasise to bone is : breast , lung , renal , thyroid cancers.
- Squamous tumours in the head , neck and lungs. This tumour secretes parathyroid hormone receptor peptide. This acts on parathyroid hormone receptors which increases serum calcium levels.
What are common sites for bone metastasis?
1. Vertebrae Pelvis Proximal parts of the femur Ribs Proximal parts of the humerus Skull,
What are the two causes of hyperparathyroidism?
- Primary cause : one of the 4 parathyroid glands develop an adenoma and secretes excessive parathyroid hormone. This causes calcium to rise and serum phosphate to fall.
- Secondary causes : All 4 parathyroid glands become hyper plastic. This is seen in vitamin D deficiency patients. Vitamin D deficiency means that their calcium absorption is low resulting in low serum calcium levels which then causes PTH levels to rise.
What are symptoms of hyperparathyroidism?
STONES = kidney stones , also polyuria due to impaired sodium and water rebaosptiom
- MOANS = depressed , tired , exhausted
- GROANS : constipation , peptic ulcers and pancreatitis
- BONES= bone and muscle aches
What is the difference between osteomalacia and osteoporosis?
- Osteomalacia results in defective mineralistion of bones this is due to vitamin D deficiency which results in less calcium being absorbed by the gut etc. NO amount of dietary calcium can improve this. Only vitamin D supplements. This is the adult version of ‘ rickets ‘ in children. This leads to soft bones.
- Whereas osteoporosis is due to old age etc - the bone is fully mineralised but it is structurally degraded
