Calcium and Parathyroid Flashcards
How many parathyroid glands are ususally present?
4
however this is variable
Where are parathyroid glands usually located?
posterior to the thyroid glands
can also be locate in the mediastinum?
Blood supply to the parathyroid glands mirror the thyroid glands. True or false
True
What pharyngeal pouch do the inferior parathyroid glands originate from?
pharyngeal pouch III
What pharyngeal pouch do the superior parathyroid glands originate from?
pharyngeal pouch IV
What are the main cell types in the parathyroid glands and their functions?
- chief cells - produces PTH (parathyroid hormone)
- Oxyphil cells- unknown function
Chief cells in stomach produce pepsinogen
What is the speculated function of the oxyphil cells?
may secrete excess PTH in cancer of the parathyroid gland
What is the main function of the parathyroid gland?
calcium homeostasis
Outline reasons why calcium homeostasis is important
- coagulation- factors II, VII, IX, X are dependent on calcium as they are negatively charged
- nerve depolarisation
- skeletal/smooth/cardiac muscle contraction
- enzyme co-factors
- cardiac stability
- bone and teeth
- regulation of hormone secretion
Why is calcium important for cardiac stability ?
- myocyte action potential/cardiac repolarisation cycle
- phase 2 involves a calcium influx which slows down the rate of repolarisation (mediation of repolarisation)
- also allows contraction of the the myocytes to carry on occuring
Calcium is the most abundant mineral in the body. True or false
True
body contains around 1kg of calcium
How is calcium homeostasis achieved?
- bones
- intestines
- kidneys
Bones store 99% of the bodies calcium. How are bones involved in calcium homeostasis?
- bone remodelling under control of PTH/calcitonin
- osteoclasts resorb bone (release calcium into blood)
- osteoblasts synthesise bone
osteoblasts send signals to osteoclasts before bone resorption occurs
When is parathyroid hormone released?
released when plasma/serum calcium levels are too low
When is calcitonin released?
released when plasma/serum calcium levels are too high
released from parafollicular cells
How are the intestines involved in calcium homeostasis?
they are involved in the absorption of calcium ions from the diet
How are the kidneys involved in calcium homeostasis?
majority of filtered calcium is reabsorbed in the kidneys
kidneys also convert inactive vitamin D into active vitamin D (calcitrol)
What is the function of parathyroid hormone?
- increase serum calcium levels
- stimulate osteoclast activity (bone resorbtion)
- increases calcium reabsorption at the kidneys
- increases phosphate excretion at the kidneys (less reabsorption of phosphate)
- promotes kidneys to convert inactive vitamin D into calcitrol
What is the function of calcitonin?
- decreases serum levels of calcium
- inhibits osteoclast activity- reduced bone resorption
- increased calcium secretion at kidneys (less reabsorption)
- decreases phosphate excretion at kidneys- increased phosphate retention; more phosphate moved into bones and bone fluid
What is the function of calcitrol?
- increased serum calcium levels
- increased intestinal absorption of calcium
- stimulates bone resorption (calcium mobilisation in bone)
- increases calcium reabsorption at kidneys
similar action to PTH except PTH does not affect intestine
What is the active form of vitamin D?
calcitrol
1,25 dihydroxyvitamin D
How is the active form of vitamin D produced?
- 7-dehydrocholesterol on the skin converted into cholecalciferol (vitamin D3)
- Vitamin D3 (fish, meat), vitamin D2 (supplements) are obtained via dietary intake
- vitamin D3 (cholecalciferol)/D2 are then 25 hydroxylated in the liver to produce 25-hydroxycalciferol
- additional hydroxylation then takes place in the kidney to produce 1,25 hydroxycholecalciferol
Vitamin D deficiency causes ________ in children
rickets
soft bone which spreads under pressure
pelvic, femural, tibial abnormalities
What is the main function of vitamin D (aside from its role in calcium homeostasis)?
augment immune function
What are the symptoms of a vitamin D deficiency?
- excessive sweating
- high blood pressure
- tiredness and fatigue
- digestive problems
- mood swings
- impaire immunity
- psoriasis
- overweight/obese
- pain
What patients are at risk of vitamin D deficiency?
- infants and children aged under 4
- pregnant and breastfeeding women, particularly teenages and young women
- people over 65
- people who have low or no exposure to the sun e.g. those who cover the skin for cultural reasons, who are housebound or confined indoors for long periods
- people with darker skin, for example people of african, afro-carribean or south asian family origin
What is hypercalcaemia?
this is when serum calcium levels >2.6mmol/L
What are the causes of hypercalcaemia?
primary hyperparathyroidism- overproduction of PTH (adenoma, adenocarcinoma, hyperplasia)
cancer >90% of cases
What is the classic presentation of hypercalcaemia?
Stones
Bones
Groans
Psychiatric moans
- renal stones (calcium oxalate); submandibular stones, lower prevalence in parotid
- bone pain due to osteoporosis
- abdominal pain, constipation and myalgia- pancreatitis, stomach ulcers
- poor sleep, fatigue, depression, psychosis
Polydipsia and polyuria also observed in hypercalcaemia in a similar way to glycosuria; calcium and glucose drag water out when not reabsorbed; leads to dehydration of cells hence polydipsia and resulting polyuria
What is the cause of primary hyperparathyroidism?
- overproduction of PTH by parathyroid
- male >female
- > 80% of cases due to a single adenoma
- elevated calcium with normal or elevated PTH
What is the cause of secondary hyperparathyroidism?
- excessive PTH production in response to chronically low Ca2+ ions; usually as a result of chronic renal failure - kidney failing to reabsorb calcium ions
- decreased calcium levels with elevated PTH
What is the cause of tertiary hyperparathyroidism?
- parathyroid gland is chronically overstimulated, continues to produce excessive PTH despite normalisation of calcium
- elevated calcium and elevated PTH
*[resolution of kidney problems by parathyroid gland now programmed to overproduce PTH]
What investigations can be carried out for a diagnosis of hyperparathyroidism ?
- serum calcium, PTH and vitamin D
- DEXA scan- bone density scan for osteoporosis
- CT neck for surgical plannin- adenomas/lumps
How can primary hyperparathyroidism be managed?
- parathyroidectomy (adenoma)
- monitor calcium levels annually
- avoid medication that increases calcium levels (thiazide diuretics, lithium)
- +/- vitamin D supplementation
- +/- bisphosphonates
What is hypocalcaemia ?
serum calcium levels of <2.1mmol/L
What are the causes of hypocalcaemia?
most commonly hypoparathyroidism (autoimmne or iatrogenic)
* vitamin D deficiency
* alcoholism
* eating disorders
* CRF- chronic renal failure- failure to reabsorb
* osteoporosis treatment
* vomiting
What are the clinical signs of hypocalcaemia?
[CATS go numb]
- convulsions
- arrhythmias (prolonged QT interval on ECG)
- Tetany, chvosteks sign, trousseaus sign
- parasthesia in hands, feet and mouth (go numb)
What is Chvostek sign?
facial nerve spasm/twicth
tap cheek; a twitch of facial muscle is observed
Tetany Vs tetanus
Tetanus is an infection
Tetany- hypocalcaemic hyper-reactive nerves
What investigations are required for hypoparathyroidism?
- ECG
- vitamin D
- thyroid function
- renal ultrasound
80% of hypoparathyroidism have a ___________ cause.
post-surgical
What is the management of hypoparathyroidism?
- severe: IV calcium with ECG monitoring
- mild/moderate: oral Ca2+, PTH, thiazide diuretic
What are the dental considerations for hyperparathyroidism?
- osteoporosis
- in children- tooth development defect and alteration in dental eruption
- in adults- drifting of teeth, complaint of jaw pain, sensitive teeth when chewing and soft tissue calcifications
- malocclusion due to drifting teeth, spacing of teeth may be the first signs of the disease
- prone to developing cystic lesions around the mandible
- brown tumours- filled with giant osteoclastic cells driven to increase calcium levels; granulomatous tissue
- no lamina dura lining the socket; due to mobilisation of calcium from bone
What are the dental considerations for hypoparathyroidism
- enamel hypoplasia-not enough crown
- delayed eruption
- poorly calcified dentin
- pulp calcifications
- malformed roots
- parasthesia in mouth [CATs go NUMB]
- Facial muscle abnormalities- hyperactive nerves- due to hypocalcaemia
