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Biochemistry > Bone and calcium, phosphate and magnesium > Flashcards

Bone and calcium, phosphate and magnesium Flashcards

1
Q

What influences bone growth and turnover?

A

Calcium, phosphate and magnesium metabolism
PTH and 1,25(OH)2D
Other hormones

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2
Q

What regulates calcium in the ECF?

A

PTH: low calcium in blood causes release of PTH= calcium effluent from bone, decreased calcium loss in urine and enhanced calcium absorption from intestine
1,25(OH)2D

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3
Q

Where is parathyroid hormone released from?

Where is metabolised?

A

Decreased from the chief and oxyphil cells of the parathyroid glands
Metabolised by liver and cleared by kidneys

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4
Q

What are the parent molecules of major forms of vitamin D?

A

Vitamin D2 - ergocalciferol

Vitamin D3 - cholecalciferol

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5
Q

How are the parent compounds of vitamin D converted to active form?
What are the half lives of each?

A

Parent half life = 24 hours
Hydroxylation in liver produces 25(OH) vitamin D, half life = 3 weeks
Hydroxylation in kidney produces 1,25(OH)2 vitamin D, active, half life = 4 hours

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6
Q

Outline the interaction between vitamin D and the endocrine system

A

Parathyroid glands sense low Calcium and up PTH
PTH acts in bone to release Ca and PO4
PTH acts in kidneys to up 1,25 formation and stop Ca excretion
1,25 acts on intestine to up absorption of Ca and acts on bone to release Ca and PO4

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7
Q

Outline the action of PTH on the kidneys

A

Induces 25-OH Vit D-1alpha-hydroxylase to increase 1,25(OH) production to stimulate intertidal absorption of Ca and PO4
Increases calcium reabsorption in the DCT
Decreases reabsorption of PO4 in the PCT

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8
Q

What effects can PTH have on bone?

A

Osteolysis
Differentiation of osteoclasts
Regulation of osteoblasts - bone remodelling
Bone resorption

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9
Q

What happens in renal failure?

A 
Fall in calcium 
Fall in conversion to 1,25(OH)
Increased phosphate 
Increased PTH: continual leads to type 2 hyperparathyroidism
Hypercalcaemia: autonomous PTH secretion
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10
Q

Outline overall affects of PTH on urine and serum calcium levels

A

Serum levels of total and free calcium are increased, phosphate is decreased
Levels of phosphate and cAMP are increased in urine. Levels of calcium are also increased; as tubular reabsorption is overloaded by calcium levels increased by bone and intestine

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11
Q

How is PTH affected by PO4 and Mg levels?

A

Though PTH contour phosphate the levels of PO4 do not affect PTH secretion
Mild hypomagnasaemia stimulates PTH, while severe hypomagnasaemia reduces PTH as it is a Mg dependent process.

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12
Q

What are the 6 functions of bone?

A 
Support
Protection
Assist in movement
Mineral storage
Production of blood cells
Storage of energy
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13
Q

What are the five types of bone?

A 
Long
Short
Flat
Irregular
Sesamoid
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14
Q

What are the two types of bone tissue?

A

Compact: forms outer shell of bones and is arrange in concentric layers. 80% of bone mass

Cancellous: located beneath the compact bone. Consists of mesh work of bony trabeculae and gaps for bone marrow. Remaining 20% of mass but 10X surface area of compact bone

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15
Q

What are the three types of bone cell and their function?

A

Osteoblasts: produce matrix which mineralises to form osteoid. Become quiescent and flatten to form lining cells. Respond to hormonal control to activate osteoclasts

Osteocytes: cells which sense mechanical stress and initiate remodelling. Transport of minerals in and out of the bone

Osteoclasts: dissolve bone by solubilising mineral (resorption). Effect changes to structure

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16
Q

Outline osteoclast activation

A

Osteoblasts produce RANKL, which interacts with RANK on osteoclast precursor and stimulates c-FOS which binds to DNA activated genes for differentiation into mature osteoclast. c-FOS also activates interferon-beta which prevents further differentiation. Osteoprogerin from the osteoblasts blocks RANKL to also inhibit further differentiation.

17
Q

What makes up the bone matrix?

A

40% organic: type 1 collagen, proteoglycans, osteocalcin, growth factors
60% inorganic: hydroxypatite

18
Q

What two process occur during ossification of bone?

A

Intranmembraneous ossification: occurs during flat bone development. Mineralisation of connective tissue rather than cartridge.

Endochrondral ossification: long bones. Growth plate continues to move and mineralised at the metaphysis.

19
Q

Name some common disorders of the bone

A

Osteomalacia: inadequate mineralisation
Osteoporosis: reduced bone mineral density
Pagers disease: excessive resorption and formation leading to weak and misshapen bones
Renal osteodystrophy: kidneys fail to maintain Ca and PO4
Rheumatoid arthritis: inflammation of the bone
Malignancy

20
Q

What are the six main functions of calcium

A 
Bone growth and remodelling
Secretion 
Excitation-contraction coupling 
Stabilisation of membrane potentials 
Enzyme co-factor 
Second messenger
21
Q

Where is calcium found?

A

Majority stored in skeleton

  1. 2-2.6mmol/L in serum
  2. 1-1.3mmol/L ionised in serum: 45% free, 45% bound to protein and 10% complexed with anions
22
Q

What is adjusted calcium?

Why measure it?

A

Ionised protein bound calcium

Account for changes in albumin

23
Q

What are the most common causes of hypercalcaemia?

A

Hyperparathyroidism

Malignant disease

24
Q

What are the most common causes of hypocalcaemia?

A

Renal failure
Hypoparathyroidism
Hypomagnesaemia
Vitamin D deficiency

25
Q

What are the functions of phosphate?

A

Formation of high energy compounds and second messengers
Component of DNA/RNA, bone and membranes
Phosphorylation of enzymes
Intracellular anion

26
Q

Outline the distribution of phosphate

A

85% in bone and teeth
14% within cells
1% extracellular fluid

27
Q

What are the causes of hypophosphataemia?

A

Pseudohyperphosphataemia
Increased phosphate input
Reduced phosphate excretion

28
Q

What are the causes of hypophosphataemia?

A

Inadequate phosphate absorption
abnormal urinary phosphate loss
Shifts of phosphate from extracellular fluid into the cells

29
Q

What are the functions of Mg?

A

Enzyme Cofactor
DNA replication, transcription and translation
Maintenance of ribosomes, NAs and proteins
Interact with Ca
Affect permeability of membranes and their electrical properties

Biochemistry (10 decks)

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