L22 Flashcards
what is rickets
Rickets – due to a deficiency or impaired
metabolism of vitamin D, calcium or phosphorus.
The predominant cause is vitamin D deficiency.
what activates metabilisum of vitamin D
The kidney activates metabilisum of vitamin D
describe the difference between healthy bones and bones of those with rickets
Normal individual has a thick bone and quite ossified (little openings)
In rickets the bones are think an the bones are porous, they get bone softening and troubles with their teeth, they also have muscle weakness
what is osteoporosis
Osteoporosis is when the bone mass and density is reduced. They have very weak bones and have a high incidence of hip replacement as they fall over and break the bones which then need to be replaced. They also have lots of knee replacement
what % of new zealanders are lactose intolerant
10%
Ca homeostasis is a balance between what organs
kidney, intestine and bone
daily intake of Ca = daily Ca excreted
what % of Ca is excreted in feces and urine
feces = 80% (800mg ish)
urine 20% (200mg ish)
what is the concentration of Ca in the body
bone/teeth, ICF and ECF
bone/teeth = 99% of the bosies Ca
- ICF = generally < 0.1 µM (1%)
- ECF = 2-3 mM (0.1%)
what Ca concentrations define hyper and hypocalcemia
–ECF > 3 mM = hypercalcemia (High Ca2+ blood)
–ECF < 2 mM = hypocalcemia (Low Ca2+ blood)
Why is it important to maintain appropriate ICF and ECF concentrations of Ca2+?
theres 8
- proper bone formation
- neurotransmission (release of vesical)
- mitosis, cell division and growth
- muscle contraction
- blood clotting
- growth
- enzymatic reactions
- 2nd messenger function
what does hypocalcemia (low ECF Ca) cause
• increase excitability of:
– nerve cells
– muscle cells
• pins and needles • airway obstruction (increase in mucus) • epileptic seizures • cardiac arrhythmias • hypocalcemia tetany – muscle spasms
what does hypercalcemia (high ECF Ca) cause
• decrease excitability of:
– nerve cells
– muscle cells
- disorientation
- lethargy (lack of energy)
- cardiac arrhythmias
- death
Which of the following statements is TRUE?
A. The bulk of Ca 2+ in the body is located within the ICF.
B. Low ECF Ca2+ causes decreased excitability of nerve cells.
C. The ECF Ca2+ concentration is between 2-3 mM.
D. Osteoporosis causes and increase in bone mass
A. bulk in bone/teeth
B. causes increased excitability. decreased outside = increased inside as things are relative (I think)
D. decrease in bone mas
C is correct
how is Ca found in the plasma
3 ways
• 50% of the Ca2+ is ionized
• 40% of the Ca2+ is bound to protein
(normally albumin), thus not filtered
• 10% of the Ca2+ is complexed with anions (HCO3, citrate, phosphate, SO4=)
So, only 60% of the plasma Ca2+ can be filtered!
what % of Ca in the plasma can be filtered
60%
what % of Ca in the plasma can be filtered
60%
as the 40% bound to albumin is not filtered (proteins can’t get through the filtration barrier)
what is the equation for dailey filtered load of an ion
eg Ca
GFR x [Ca2+]plasma = Daily filtered load
180 L/day x 2.5 mmol/L = 450 mmoles/day
(filtered)
what % of Ca does the PT reabsorb
50-60% of the filtered load of Ca
how does the PT reabsorb Ca
Ca transport is 100% via the paracellular pathway
occurs via solvent drag
what % of Ca does the thick ascending limb reabsorb
15% of daily filtered load of Ca
how does Ca get reabsorbed in the thick ascending limb
paracellular pathway
what controls the permeability of the tight junctions of the thick ascending limb
- Claudin-16 plays a role in maintaining the permeability of the tight junctions that favours transport and Ca2+, Mg2+ and Na +
where is the Ca sensor receptor located
on the basolateral membrane of the thick ascending limb
what is the role of the CaSR
it monitors the ECF concentration of Ca
If you are in hypERcalcenia it will be detected by the Ca sensor receptor which will alter the function (downregulate) NKCC and the K channel (ROMK)
Under hyPOclacemic conditions it will not down regulate
what % of the dailey filtered load of Ca does the distal convoluted tubule reabsorb
10-15%
what are the primary transporters of Ca in the distal convoluted tubule
TRPV5 and TRPV6
these are Ca channels in the apical membrane which move Ca down its concentration gradient
once Ca enters the distal convoluted tubule cell how does it get from the apical to the basolateral membrane
calbindin
this is a Ca binding protein which helps shuttle Ca across the cell
what are the Ca membrane proteins in the basolateral membrane (to get Ca out of the cell)
Ca ATPase (PMCa1b)
Na/Ca exchanger (NCX1)
how many Na and Ca are transported via the Na/Ca exchanger (NCX1)
3Na into the cell and 1Ca out of the cell
in the distal convoluted tubule Ca does NOT move through the paracellular pathway. why is this
Claudin 8 (CLND8) is a tight junctional protein which prevents the movement of Ca2+
this is located in DCT
Which of the following statements is FALSE?
A. 50% of the Ca2+ in plasma is ionized.
B. 60% of the blood Ca2+ can be filtered at the glomerulus.
C. The proximal tubule reabsorbs 50-60% of the filtered Ca2+.
D. Ca2+-sensing receptors monitor the intracellular Ca2+
concentration.
D is false because it should say extracellular concentration of Ca
what hormones are involved in Ca homeostasis
- Parathyroid hormone
* Calcitriol
when and where (which cells) is parathyroid hormone (PTH) secreted from in Ca homeostasis
• Parathyroid hormone is secreted from the parathyroid gland
– the calcium sensing receptor on the membrane of the chief cells monitors ECF Ca2+ levels and when it detects hypocalcemia PTH is released
PTH causes 3 things to happen to try and increase extracellular Ca concentrations. what are these
PTH stimulates bone resorption (break down) which releases Ca2+ into the plasma
PTH also stimulates reabsorption of Ca2+ by the TAL and DT
PTH increases the release of calcitriol which results in increased Ca2+ absorption by the intestine
what is PTH effect on the bones
PTH stimulates bone resorption (break down) which releases Ca2+ into the plasma
therefore increase in Pi and Ca release
what is PTH effect on the nephron
PTH also stimulates reabsorption of Ca2+ by the TAL and DT
how does PTH effect the intestine
PTH increases the release of calcitriol which results in increased Ca2+ absorption by the intestine
PTH has 2 effectors what are these
bone and the kidneys
what is PTH overall effect on the kidneys
3 things
increases Pi excretion
decreases Ca excretion
increases calcitriol production (which goes on to cause the intestines to increase Ca and Pi absorption)
what is calcitriol
metabolite of vitamin D3
what secretes calcitriol
- activated in the kidney – proximal tubule (PT)
• Calcitriol is released by the influence of PTH due to low calcium
what are the effects of calcitriol
theres 4
- stimulates resorption (breakdown) of bone and releases Ca2+ into the plasma
- stimulates reabsorption of Ca2+ by the DT
- stimulates Ca2+ absorption by the intestine
- negative feedback on the parathyroid gland to regulate the release of PTH
what is calcitriols effect on the bone
• stimulates resorption (breakdown) of bone and releases Ca2+ into the plasma
what is calcitriols effect on the nephron
• stimulates reabsorption of Ca2+ by the DT
what is calcitriols effect on the intestine
• stimulates Ca2+ absorption by the intestine
what role does calcitriol play in negative feedback on PTH
• negative feedback on the parathyroid gland to regulate the release of PTH
Which of the following statements is FALSE?
A. The kidneys, bone and intestine all play roles in Ca2+ homeostasis.
B. The parathyroid hormone is released by high plasma Ca2+.
C. Calcitriol is activated vitamin D3.
D. Parathyroid hormone stimulates resorption of bone
B is false as PTH is released in low conc of Ca
