endocrine physiology lectures 10-20 lol Flashcards
To learn the very basics
5 roles of calcium in the body
1) important part of the blood clotting cascade
2) important part of cell signalling
3) role in apoptosis
4) skeletal strength- 99% of calcium in the body is wrapped up in bone, to give strength to the skeleton
5) membrane excitability
Is there a role of calcium in muscle contraction?
yes
Calcium distribution throughout the body?
99% in the body
Intracellular 0.9%
only 0.1% is in the extracellular fluid.
Out of the 0.1% of calcium in the extracellular fluid, how much is actually free vs bound to protein?
0.05% is bound to protein, and then 0.05% physiologically active.
Where is calcium stored intracelluarly?
mitochondria and sarcoplasmic reticulum
What are the three hormones involved in endocrine control of calcium homeostasis?
1) Parathyroid hormone
2) Calcitriol (from inactive Vit D, now turned steroid hormone by liver and kidneys)
3) calcitonin- peptide hormone
Which two hormones act to increase calcium levels in the blood/serum?
PTH
Calcitriol (from inactive vit D, made into steroid hormone by liver and kidneys).
What type of a hormone is calcitonin, and where is it released from
peptide hormones, released from parafollicular (clear) cells of the thyroid gland
When is PTH released?
in response to decrease in free calcium plasma
How does PTH act to increase calcium in the plasma?
1) Bind to osteoclasts to increase release of calcium and phosphate in bones
2) Inhibit osteoblasts from reabsorbing calcium
3) Increasing reabsorption of calcium from kidney tubules, to therefore decreasing its excretion in the urine
4) Increasing renal excretion of phosphate.
5) Stimulate kidney to synthesise calcitriol from Vit D
so basically: control calcium at bone level, stop it from leaving the body, (controlling phosphate will stop bones level) and bring in another helper
Why does PTH, increasing renal excretion of phosphate, help elevate calcium serum levels?
In order to put calcium back into bone, phosphate is required.
What does hypocalcaemia lead to?
Increases hyperexcitation of neurons (imagine calcium controls the neurons)
Increases permeability of sodium
So more calcium = less sodium
What symptoms of hypocalcaemia in extreme?
tetany, and if spreads to larynx and respiratory muscles, asphyxiation
What does hypercalcaemia lead to?
reduces exciteability of neurons, so reduce neuromuscular activity
Extreme cases of hyper-calcaemic can lead to what symptom?
cardiac arrhythmias
Plasma proteins have a high or low affinity for calcium?
high
Calcium in bones is stored in the form of what?
hydroxyapatite (in the extra-cellular matrix).
Why is phosphate homeostasis important?
Phosphate needed for packing calcium into hydroxyapatite
No phosphate has what affect on bones
weak
How much of the 0.1% of plasma calcium, being bound to proteins like albumin, or being free, is determined by what?
pH
If body more alkaline, what does this so to Ca plasma levels? and why
lowers because binding is increased
What happens to calcium levels if you hyperventilate?
pH rises because you blow off more CO2, therefore decrease H ions, so up pH (less acidic)
so more binding
therefore hypo calcaemic tetany
acidosis affect on calcium levels
decrease in binding capacity, therefore plasma calcium rises
Why does pH affect calcium levels?
Because H ions compete with calcium for the binding sites on the plasma proteins.
Total body calcium equation
= calcium in - calcium out
What happens to your bones when it’s put under a sustained amount of stress?
The denser your bone becomes (bone ends up be constantly remodelled)
Osteoblasts become what in established bone?
osteocytes
How to osteoclasts work? (2)
Secrete H+ ions to dissolve calcium salts
Provide enzymes to digest ECM
Why would PTH ever stop being secreted?
It’s a negative feedback mechanism
Part of the ways that PTH increases the level of calcium in the serum, is to stimulate production of calcitriol at kidney level. What is calcitriol?
An active form of vitamin D
What does calcitriol do?
Increase absorption of calcitriol from the gut
Where is calcitriol derived from?
cholesterol. but also like vitamin D3 so i don’t even know
The formation of which hormone is enhanced by prolactin in lactating women? (That help’s with calcium levels in serum).
calitriol
What level of vitamin D is deficient at ng/ml
20
When vitamin D deficient, and the body makes up for lack of calcitriol (getting calcium from diet), PTH starts removing Ca from bone. What does this mean for the bones?
You can get easily fractured bones
What happens to calcium absorbency from the gut with age?
Decreases with age
Vitamin D deficiency affects bone development in children. What disease could this lead to?
Rickets
Thyroid cancer could lead to the release of lots of calcitonin (which decreases levels of calcium in the blood). What happens to the levels of calcium in the blood?
Normal
What is calcitonin produced by? And what type of hormone is it
It’s produced by the thyroid gland, and it’s a peptide hormone.
What are the main actions of calcitonin? Like actual actions
Bind to osteoclasts, and inhibit bone resorption, and increase renal excretion of phosphate
State the hormones produced by the adrenal gland, in order from outside in
aldosterone,
cortisol,
testosterone,
norepinephrine and epinephrine (of medulla)
what’s that rhyme to remember hormones produced by different layers of adrenal gland
salt sugar sex stress
How does cortisol affect glucose levels
releases stored glucose
If all steroid hormones are derived from cholesterol, how are different hormones produced from different zones?
different enzymes are found in different adrenal zones, resulting in different end products
How does insulin alter Ca balance
increases bone formation, and antagonises action of cortisol.
Oestrogen does what to Ca levels
Promotes bone formation via oestrogen receptors on osteoblasts. Post-menopausal osteoporosis is major problem
Growth hormone affects Ca levels how?
constant stimulus for bone formation
Prolactin affects Ca levels in the blood how
Promotes calcium absorption from the gut by stimulating synthesis of calcitriol.
Most common reason for adrenal gland hypofunction?
where adrenal gland has been destroyed by some pathological process
meaning of adrenal insufficiency, and how serious is it
where adrenal glands do not produce enough steroid hormones, particularly cortisol and aldosterone.
Addison’s disease vs adrenal insufficiency
Addison’s disease is specifically when the adrenal glands have been damaged
Hyposecretion of which two hormones in Addison’s disease?
Cortisol and aldosterone
Most common cause of Addison’s disease
autoimmune
Secondary adrenal insufficiency results from what?
Lack of adrenocorticotropic hormone (ACTH), therefore adrenal glands aren’t stimulated, so no cortisol.
Because of damage to pituitary gland.
Describe the process of being stressed, leading to release of cortisol i.e the hypothalamo-hypopituitary adrenal axis…..
stress
brain sends stimulus to hypothalamus (acts as neural integrator)
hypothalamus releases CRH,
which acts on the anterior pituitary,
which then secretes ACTH
which acts on the adrenal gland
therefore cortisol is released.
Symptoms of adrenal insufficiency?
Fatigue, dizziness, and fainting
Muscle weakness and muscle cramps
Thirst and craving salt
Weight loss
Abdominal pain
Depression
Reduced libido
Rhyme for remembering adrenal insufficiency
Feeling tired, dizzy, and faint,
Muscles weak, cramps like a complaint.
Thirsty for salt, weight on a slide,
Abdominal pain, in yourself you hide.
Depression looms, libido takes flight,
These are the signs, don’t let them alight.
Two important signs of adrenal insufficiency? remembering that its a drop in aldosterone (and cortisol) and rise in ACTH
bronze hyperpigmentation of the skin
hypotension especially when standing up
What causes the bronze hyperpigmentation of the skin in hypo/ insufficiency of the adrenal glands/ addison’s?
ACTH builds up, which starts to interact with melanocytes, which then produce melatonin
Most important investigation for adrenal insufficiency? that could be only one
hyponatraemia (low sodium)
Biochemical findings of calcium, potassium and glucose in adrenal insufficiency
High potassium
Low glucose
High calcium
What is the test of choice for diagnosing adrenal insufficiency?
The short Synacthen test
When do you perform the short synacthen test?
early in the morning
What does the short synacthen test involve?
The test involves giving a dose of Synacthen, which is synthetic ACTH. The blood cortisol is checked before and 30 and 60 minutes after the dose. The synthetic ACTH will stimulate healthy adrenal glands to produce cortisol. The cortisol level should at least double
What is synacthen?
Synthetic ACTH, given for the short synacthen test IM or IV
How to manage adrenal insufficiency?
Replacement steroids
How to replace cortisol
hydrocortisone (a glucocorticoid)
How to replace aldosterone
fludrocortisone
What’s a steroid card?
Card, given alongside ID tag and emergency letter, to alert emergency services that they depend on steroids for life.
In adrenal crises, patients present with: (4)
Reduced consciousness
Hypotension
Hypoglycaemia
Hyponatraemia and hyperkalaemia
Management of adrenal crises?
ABCDE
Hydrocortisone IM or IV
Intravenous fluids
Correct hypoglycaemia (IV dextrose)
Careful monitoring of electrolytes and fluid balance
Plasma ACTH: meaning of if it’s suppressed vs elevated in adrenal insufficiency?
Elevated = primary
Suppressed = secondary
Meaning of secondary adrenal insufficiency? (Knowing primary = damage to actual adrenal gland).
damage to pituitary gland, because the pituitary gland releases the ACTH
Why does the pituitary gland release ACTH?
Because it acted upon by CRH, which was released by the hypothalamus
What glucocorticoid replacement when you have addisons
hydrocortisone 20-30mg daily, given in two separate doses to mimic normal bodily functions.
What synthetic hormone to replace aldosterone?
Fludrocortisone
People with adrenal gland insufficiency, what do you do to steroid dose during periods of illness like the flu?
double the dose
Commonest symptom of hyperfunction of the adrenal gland?
hypertension
Why hypertension with hyperfunction of the adrenal gland?
Hypersecretion of aldosterone