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MEH * > 11.1 - Parathyroid And Ca And P Regulation > Flashcards

11.1 - Parathyroid And Ca And P Regulation Flashcards

1
Q

What does the skeleton provide?

A
  • structural support
  • major reserves of calcium (stored as calcium phosphate)
  • help buffer serum levels
  • releasing calcium phosphate into interstitium
  • up taking calcium phosphate

Nb: only free calcium ca2+ is biologically active

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2
Q

What does ca2+ do?

A
  • assists in clotting
  • maintain nerve and muscle function
  • essential for kidney function
  • Reduced blood cholesterol levels
  • needed for enzymes and hormone receptor binding
  • intracellular signalling pathways
  • builds and maintains bones and teeth
  • regulates heart rhythm
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3
Q

What happens in chronic hypercalcaemia?

A
  • renal calculi
  • kidney damage
  • constipation
  • dehydration
  • tiredness
  • depression
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4
Q

What happens in hypocalcaemia?

A 
Low serum calcium 
Get hyper excitability of neuromuscular junction
- pins and needles
- tetany (muscle spasms)
- paralysis
- convulsions
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5
Q

Where is the parathyroid gland located?

A

Lobes attached to the back of the thyroid

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6
Q

What cells make up the parathyroid gland?

A

Chief cells (produce parathyroid hormone), oxyphil cells and adipose tissue.

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7
Q

What hormones regulate calcium and phosphate levels?

A
  • parathyroid hormone
  • calcitriol (active vitamin D metabolite)
  • calcitonin (lowers serum calcium levels)
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8
Q

How is PTH synthesised?

A
  • Straight chained polypeptide hormone
  • low serum calcium up regulates gene transcription
  • high serum calcium down regulate
  • low serum calcium prolongs survival of mRNA
  • chief cells degrade hormone as well as synthesis it
  • cleavage of PTH is accelerated by high serum calcium levels
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9
Q

How does dietary calcium get to the bone?

A

In GI tract, is absorbed with help of calcitriol

Then deposition by osteoblasts in bone with help of calcitonin

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10
Q

How is calcium from bones lost in urine?

A

Resorption into blood stream by osteoclasts done with hep of calcitriol and PTH

Then filtered by kidneys = lost as urine

NB: may go from kidneys back to blood stream = uses PTH and calcitriol

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11
Q

What are the target organs for PTH and what are its physiological effects?

A

Kidney
- decreases calcium loss to urine, particularly in the ascending loop of Henley

Gut
- activates vitamin D and hence increases transcellular uptake of Ca from GI tract

Bone
- increases reabsorption of Ca from bone by activating osteoclasts.

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12
Q

Where is the majority of calcium reabsorbed in the kidney??

A

Proximal convoluted tubule

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13
Q

How do osteoblasts produce bone?

A

Make a collagen matrix which is mineralised by hydroxyapatite

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14
Q

How do osteoclasts facilitate bone reabsorption?

A

Produce acid microenvironment hydroxyapatite dissolve.

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15
Q

What are the actions of PTH on bone?

A
  • induces osteoblastic cells to synthesise and secrete cytokines on cell surface
  • cytokines activate osteoclasts and protect them from apoptosis
  • PTH decreases osteoblasts activity = exposes bony surfaces to osteoclasts
  • reabsorption of mineralised bone and release of Pi and Ca2+ into extracellular fluid
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16
Q

Sources of vitamin D?

A

The body makes vitamin D itself when exposed to sunlight

Cheese, butter, margarine, fish and fortified cereals are food sourced of vit D.

17
Q

How is calcitriol made?

A

7- dehydrocholesterol

Becomes

Vit D3

Goes to liver

Vit d3 is hydroxylate on C25

Goes to kidney

With PTH and hydroxylation to make di hydroxy vit D3 = calcitriol

18
Q

What happens when plasma calcium is increased (negative feedback)?

A

PTH secretion decreases

  • decreases Ca reabsorption in kidney
  • less calcitriol so less ca taken from gut
  • more bone building than breaking down

As a result plasma Ca decreases

19
Q

What role does calcium play in the clotting cascade?

A

It’s factor IV in the clotting cascade

20
Q

How can you get hypercalcemia?

A
  • malignant osteolytic bone metastasis
  • multiple myeloma

Common sites of metastasis
- Vertebrae, pelvis, femur (proximal) , ribs, humerus (proximal), skull (raindrop)

21
Q

What’s primary hyperparathyroidism?

A

Primary
One of 4 parathyroid glands develops an adenoma and secretes excessive parathyroid hormone = ultimately serum calcium falls

22
Q

What’s second hyperparathyroidism?

A

Secondary
All four glands become hyper plastic. Seen in patients with vit D deficiency. Can be seen in renal failure as cant hydroxylate vit d3 in kidney. Get low serum calcium levels which then causes PTH levels to rise.

Main problem = bone pain due to osteomalacia in vit D deficiency and in chronic renal failure due to renal osteodystrophy.

23
Q

What are the symptoms of primary hyperparathyroidism?

A

Moans - tired, exhausted, depressed

Groans - constipation, peptic ulcers, pancreatitis

Stones - kidney stones. Also, polyuria due to impaired sodium and water reabsorption

Bones - bone and muscle aches

24
Q

How does calcium affect neuronal activity?

A

Calcium raises the threshold for nerve membrane depolarisation and therefore the development of an action potential.
So,
Hypercalcemia = suppression of neuronal activity (lethargy, confusion, coma)

Hypocalcemia = excitable nerves (tingling, muscle tetany and epilepsy)

25
Q

What are the symptoms of severe hypercalcemia???

A

Polyuria can lead to dehydration.

  • lethargy
  • weakness
  • confusion
  • coma
  • renal failure

Rehydration is mainstay of treatment

26
Q

What are the motor symptoms of hypocalcemia?

A

Carpopedal spasm

27
Q

What’s the sensory symptom of hypocalcemia?

A

Tingling around mouth and in fingers

28
Q

What’s Chvosteks sign?

A

Twitching of the facial muscles in response to tapping over the area of the facial nerve

29
Q

What’s osteomalacia?

A

The ratio of mineral to matrix decreases (not enough mineral in bone) so bone building is effected = rickets in children or bone mineralisation in adults. As a result, get soft bones that are prone to bending.

30
Q

What’s is osteoporosis?

A

Decreased bone density with a normal mineral to matrix ratio

Involves degeneration of already constructed bone = get brittle bones which are prone to fracture

31
Q

What are the risk factors of osteoporosis?

A 
Post menopausal women
Low BMI
Long term oral steroid use
Heavy drinking
Smoking 
Low BMI
Prolonged inactivity e.g bed rest

MEH * (21 decks)

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