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Growth and Development > Calcium homeostasis > Flashcards

Calcium homeostasis Flashcards

1
Q

Why do we need calcium?

A 
Intracellular
-basal level ~10^-7M (v low)
-signalling molecule
-kept low by Ca2+ATPases in mito
Vital for enzymes
High concs 'toxic'
Extracellular
-levels ~10^-3M (much higher)
-tissue mineralisation
Gradient involved in membrane excitability (nerve conduction)
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2
Q

Calcium functions

A

Communication between neurons
Muscle contraction
Exocytosis
Blood clotting

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3
Q

Calcium pools

A

Intracellular in organelles e.g. SER, mitochondria
Extracellular in blood and lymph
-controlled by intake (GI) and excretion (kidney)
Bone: dynamic, daily turnover

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4
Q

Phosphate

A 
Always considered with calcium
-co-regulated
-bone huge store of both ions
Functions
-component of DNA, RNA, ATP
-phospholipids
-acid-base buffer in 2 forms: HPO42-, H2PO4-
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5
Q

Phosphate plasma conc.

A

3.5-4mg/dL

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6
Q

Plasma conc.

A

Maintenance of plasma conc Ca2+ essential

  • 9.2-10.4 mg/dL
  • 45% as free Ca2+
  • rest bound to serum proteins e.g. albumin, not physiologically active
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7
Q

Dietary calcium

A 
Calcium found in many foods
-semame seeds 6g/kg
-milk 2g/l
-brassicas 1.5g/kg
Availability affected by
-lactose: > absorption
-certain amino acids
-phytate (inositol hexaphosphate IP6) < absorption
-oxalates < absorption
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8
Q

Diet: adult and children requirement

A

Adults: daily intake to overcome losses - GI and kidney
Children: uncontrollable losses, needed for construction of new tissues
Teenagers need most

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9
Q

G.I. tract

A

Site of absorption
Calcium
-active, transcellular absorption occurs in duodenum when low Ca intake, ehanced by carrier protein calbindin, synthesis of which dependent on Vit D
-passive, paracellular absorption occurs in jejenum and ilium & colon to < extent
-uptake prop. to need (Vit D), rarely > 80%
Phosphate: passive & active

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10
Q

Kidneys

A

Site of excretion
-50% of total Ca plasma appears in filtrate
-load of 10g/day
Site of reabsorption
-phosphate up to 100%
-calcium < 99%
Important target for control (parathyroid hormone): thick ascending limb and distal nephron

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11
Q

Summary intake/ losses calcium balance

A

Adult - obligatory loss replaced by diet

  • diet: ~0.5-1.5g ingested/ day, 0.8g/day excreted
  • GI: absorption 0.25-0.5g/day, secretion
  • kidney: 10g Ca filtered/ day, 0.15-0.3g appears in urine
  • bone: 1kg stored Ca, ~0.5g/day released by resorption or deposited during bone formation
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12
Q

Bone composition provides for strength and resilience

A

Minerals resist compression, collagen resists tension

-bone adapts to tension and compression by varying props of minerals and collagen fibres

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13
Q

Bone mineralisation

A

Crystallisation process (Ca, PO4 and others)
-ions from blood plasma deposited in bone tissue
Osteoblasts produce collagen fibres that spiral along length of osteon in alternating directions
Obs also secrete > amounts alkaline phosphatase when active

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14
Q

Ectopic ossification

A

Abnormal calcification

-may occur in lungs, brain, eyes, muscles, tendons, arteries (arteriosclerosis)

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15
Q

Demineralisation

A

Dissolving bone
Releasing minerals into blood
Ocs ‘ruffled border’
-H pumps in cell membrane secrete H+ into space between Oc and bone
-Cl- follow by electrical attraction
-HCL pH4 dissolves bone minerals
-acid phophatase (cathepsin) digests collagen

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16
Q

Most of adult skeleton replaced

A

~every 10 years

17
Q

Inadequate load and weight bearing will cause

A

bones to weaken

18
Q

No load (e.g. space travel)

A

Rapid bone loss can occur

‘use it or lose it’

19
Q

Orthodontics PDL

A

P between PDL & bone
-promotes Ocs
-breakdown bone, restores normal spacing between teeth & bone
Tension on PDL behind movement
-creates Obs
-building new bone to fill gap and restore normal spacing between teeth and bone

20
Q

Ortho time course

A

Ocs take ~72 hours to get fully activated
Obs rebuild process takes ~90 days
Stabilising result takes ~10 months

21
Q

Hormones

A

Calcitonin - thyroid
Parathyroid hormone (4 glands)
Calcitriol (Vit D) - related to bone

22
Q

Resorption pits

A

Howships lacunae

23
Q

Calcitriol

A

Intestine - stimulated Ca, PO4 and Mg absorption (calbindin)
Kidney - promotes reabsorption of Ca ions
Oc - promotes activity

24
Q

Lack of calcitriol

A

Abnormal softness of bones

  • rickets in children
  • osteomalacia in adults
25
Q

PTH

A

Parathyroid glands found on posterior surface of thyroid gland
PTH released when calcium blood level too low
Essential

26
Q

Ion imbalance

A

Changes in phosphate conc have little effect

Change in calcium can be serious –> hypocalcemia, hypercalcemia

27
Q

Hypocalcaemia

A

Causes
respiratory alkalosis (hyperventilation)
Symptoms
-excessive excitability of NS –> muscle spasms, tremors or tetany
-Ca normally binds to cell surface contributing to resting membrane potential
-with < Ca, Na channels open more easily
-laryngospasm may cause suffocation

28
Q

Carpopedal spasm

A

Hypocalcaemia

  • overexcitability of NS
  • muscle spasm of hands and feet
29
Q

Hypercalcaemia

A 
Causes: hyperparathyroidism
Symptoms
>calcium bone mobilisation
-painful softening and fracture
> excretion
-renal stones
-headaches &amp; decreased muscle tone
-Na channels less likely to open, depressing NS
-near saturation point, ectopic ossification
30
Q

Osteoporosis

A 
Severe reduction in bone mass
Risk factors: 
-age: women >50, men >60
-gender
-size: tall, small frame
-smoking
-alcohol
31
Q

Osteopenia

A

Partial reduction in bone mass

32
Q

Those at greatest risk of osteoporosis

A

Postmenopausal white women

< oestrogen > number of Oc progenitors, life span of mature osteoclasts

33
Q

Other hormones involved in osteoporosis

A

Inadequate levels of vit D
Thyroid hormone
Cortisol
Gonadal steroids - reduced oestrogen and testosterone promote osteoclastogenesis

34
Q

Osteoporosis: treatment

A

Best treatment is prevention
-exercise and calcium intake
-1000mg/day between 25-40
HRT slows bone reabsorption
Bisphosphonates related to pyrophosphate
-inhibiting Oc activity and inducing Oc apoptosis
SERM (selective oestrogen receptor modulator)
Calcitonin administered by injection or as nasal spray
Teriparatide stimulates bone deposition

Growth and Development (23 decks)

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