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Endocrine physiology > Ca2+ homeostasis > Flashcards

Ca2+ homeostasis Flashcards

1
Q

what is the** function **of calcium phosphate salts in the bone?

A
  • provide structural integrity
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2
Q

what are examples of **important biological processes **in which Ca2+ ions are essential for?

A
  • neuromuscular excitability
  • hormonal secretion
  • cell signalling
  • blood coagulation
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3
Q

what important processes are phosphate ions essential for?

A

signal transduction

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4
Q

what can occur if the the plasma Ca2+ concentration is too low (ie hypocalcemia)?

A
  • if there is less Ca2+ in the plasma, the membrane will become more permeable to Na+
  • nerves and muscles will become** over excited **
  • involuntayr muscle spasms - ie tetany
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5
Q

what can occur if the Ca2+ concentration in the plasma is too high (ie hypercalcemia)?

symptoms ..

A
  • if there is too much Ca2+ in the plasma, there will be decreased neuromuscular excitability
  • constipation
  • fatigue
  • bone pain
  • kidney stones
  • cardiac arrthymias
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6
Q

what % of total body Ca2+ is mineralised (ie not biologically available) vs the % that IS biologically available?

A
  • 99% is mineralised
  • 1% is available - freely ionised and exchangeable with ECF/plasma
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7
Q

what can Ca2+ be bound to in plasma?

A
  • proteins - esp albumin
  • CaPO4 - calcium phosphate
  • Ca citrate (calcium salt of citric acid)
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8
Q

where is intracellular Ca2+ found?

A

smooth ER or mitochondria

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9
Q

what is osteoclastic resportion?

A

Osteoclasts break down the bone and release minerals ie Ca2+ from the tissue into the blood

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10
Q

Describe the composition of bone

A
  • contains hydroxypatite crystal
  • organic matrix - collagen and other proteins
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11
Q

what does the mineralised CAPO4 serve as in bone?

A

a reservoir for Ca2+ storage

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12
Q

what is the function of osteoblasts?

A
  • bone formation
  • bone forming cells that secrete bone matrix on which CAPO4 precipitates
  • they mature enclosed in the bone matrix and become osteocytes
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13
Q

what is the** function of osteoclasts**?

A

bone resorption
* large multinucleated cells derived from monocytes whose function is to break down (resorb) bone

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14
Q

what 3 main hormones regulate Ca2+ and PO4 levels?

A
  • parathyroid hormone - PTH
  • 1,25- dihydroxy Vitamin 3 (calcitriol)
  • calcitonin
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15
Q

what **3 parts of the body **do these hormones regulate Ca2+/PO4?

resportion/absorption/excretion

A
  • bone - osteocytic osteolysis and osteoclastic resorption
  • intestine
  • kidneys
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16
Q

what is osteocytic osteolysis?

A
  • osteoclasts can remove and remodel small amounts of their surrounding bone matrix through osteocytic osteolysis
  • dosent require a decrease in bone mass
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17
Q

what is** bone resorption?**

A
  • bone resorption is the breakdown of bone tissue by osteoclasts
  • this results in the release of minerals - ie Ca2+ and PO4 which transfer into the plasma
  • stimulated by PTH
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18
Q

what cells in the parathyroid gland are responsible for secreting PTH?

A

chief / principal cells

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19
Q

what are the 2 types of PTH receptor and where are they located?

A
  • type 1 receptor - kidney and bone
  • type 2 - CNS
20
Q

what is the PTH related peptide protein?

A
  • a protein member of the parathyroid hormone family that is secreted mainly by cancer tumor cells
  • has PTH like actions
    also secreted by oxyphil cells in the parathyroid gland
21
Q

what** stimulates the release** of PTH ?

A

hypocalcemia (ie when plasma Ca2+ levels are low)

22
Q

at what measurement does max PTH secretion occur?

units - mg/dL

A

below 3.5mg/dL

23
Q

What are the calcium sensing receptors?

& what happens if Ca2+ levels are low/high

A
  • G protein coupled receptors found on chief cells and other calcium sensitive cells
  • in conditions when Ca2+ levels are low - less will be bound to receptor and PTH will be secreted
  • when Ca2+ levels are high, more will be bound to receptor and PTH secretion will be inhibited
24
Q

what is the physiological role of PTH?

A
  • prevent/reverse hypocalcemia by **increasing free plasma Ca2+ levels **
25
Q

What effect does PTH have on the bone, kidney and intestine?

A
  1. PTH acts directly on the bone and **increases bone resorption - Ca2+ release
    2    . PTH acts directly on kidney **(distal tubule) and increases Ca2+ reabsorption but decreases PO4 reabsorption
  2. PTH acts** indirectly on the intestine** by stimulating calcitonin synthesis in the kidney
26
Q

what receptor are low Ca2+ levels sensed by on the renal epithelium & what happens when it is stimulated?

A

CaSR
* once this receptor is stimulated, Ca2+ channels are stimulated which enhances reabsorption (into blood)

27
Q

how does PTH inhibit PO4 reabsorption in the kidney?

A

inhibits the **Na Pi channel (NPT2) **and therefore reduces PO4 reabsorption

28
Q

what 2 sources is vitamin D derived from?

A
  • photodependent production in keratincytes
  • ingested in the diet
29
Q

what protein is Vit D bound to in blood?

A

Vit D binding protein

30
Q

what function does vit D have in maintaining Ca2+ homeostasis?

A

promoting intestinal Ca2+ absorption

31
Q

what** chemical is converted to vit D** in keratinocytes?

A
  • 7-dehydrocholesterol
32
Q

in the process of vit D synthesis, **where **does the 2nd hydroxylation reaction take place and what is produced as a result?

A
  • second reaction takes place in the kidney, catalysed by 1 alpha hydroxylase
  • this reaction produces 1,25(OH)2 D3
33
Q

what stimulates / promotes 1 alpha hydroylase activity?

A
  • increase PTH
  • prolactin increase
  • hypophosphetemia
34
Q

what high affinity protein is Ca2+ bound to in enterocytes?

A

calbindin 9k

35
Q

what is the role of calbindin 9k?

A
  • lowers free intracellular Ca2+
  • maintains favoravle gradient of Ca2+ across apical membrane
36
Q

what is calcetonin?

A
  • produced by thyroid C cells - parafollicular cells
  • plays a minor role in Ca2+ homeostasis
37
Q

what is the physiological role of calcitonin?
ie in the bone/kidney/intestine

A
  • inhibits osteoclastic activity in bone
  • inhibits Ca2+ reabsorption in kidney
  • inhibits Ca2+ absorption in intestine

the net effect is to reduce plasma Ca2+ levels

38
Q

what is a major stimulus for calcitonin secretion?

A

an increase in Ca2+ plasma levels

39
Q

what are the 2 main causes of primary hyperparathyroidism?

A
  • single parathyroid adenoma
  • hyperplasia - enlargement of gland
40
Q

what is the clinical presentation of primary hyperparathyroidism?

A
  • can be assymptomatic
  • elevated Ca2+ levels on routine labs
  • elevated PTH
  • possible history of kidney stones, unexpected fractures
41
Q

what is the alkaline phosphatase test used for?

A

this test is a marker of bone turnover

42
Q

what can secondary hypoparathyroidism be caused by?

A

another disease that is causing lowered Ca2+ levels in blood, along with a fall in PTH

43
Q

what are the possible causes of primary hypoparathyroidism?

A
  • trauma during thyroidectomy
  • polyendocrine autoimmune disorder
  • Digeorge syndrome - paratyroid glands dont form properly
44
Q

what are examples of symptoms of hypoparathyroidism?

A
  • fatigue
  • psychological disturbances - mood swings, anxiety
  • tetany
  • low Ca+
  • low or absent PTH
45
Q

is vitamin D considered a hormone?

A

yes - it has a key role in Ca2+ homeostasis

46
Q

when vitamin D is synthesised, where does it travel to and what does it get converted to?

A

vitamin D undergoes a conversion in the liver and gets converted to its active form - calcitoriol or 1,25-(OH)2-D3

47
Q

what is calbindin 9k?

A

a high affinity Ca2+ binding protein found in tissues like the intestine and kidney

Endocrine physiology (19 decks)

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