Lecture 22 - Renal handling of calcium Flashcards
What can rickets be caused by?
a deficiency or impaired metabolism of vitamin D, calcium or phosphorus.
The predominant cause is vitamin D deficiency
What is Ca2+ homeostasis a balance between?
Kidneys, intestine and bone
What is the concentration % of Ca2+ in the Body?
(Bone/Teeth, ICF and the ECF)
Bone and Teeth (99%)
ICF = generally < 0.1 µM (1%)
ECF = 2-3 mM (0.1%)
What happens when ECF Ca2+ > 3 mM?
Hypercalcemia (High Ca2+ blood)
What happens when ECF Ca2+ < 2 mM?
Hypocalcaemia (Low Ca2+ blood)
Why is it important to maintain appropriate ICF and ECF concentrations of Ca2+?
- proper bone formation
- neurotransmission
- mitosis, cell division and growth
- muscle contraction
- blood clotting
- growth
- enzymatic reactions
- 2nd messenger function
What are the problems of low ECF Ca2+ (hypocalcaemia)? (6)
- increase excitability of:
– nerve cells
– muscle cells - ʻpins and needlesʼ
- airway obstruction
- epileptic seizures
- cardiac arrhythmias
- hypocalcemia tetany
– muscle spasms
What are the problems of high ECF Ca2+ (hypercalcemia)? (5)
- decrease excitability of:
– nerve cells
– muscle cells - disorientation
- lethargy
- 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.
C. The ECF Ca2+ concentration is between 2-3 mM.
What % of Ca2+ in the plasma can be filtered?
60%
How is Ca2+ stored in plasma?
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=)
What is the average Daily filtered load of Ca2+?
GFR x [Ca2+]plasma = Daily filtered load
180 L/day x 2.5 mmol/L = 450 mmoles/day (filtered)
What is the reabsorption of Ca2+ in the PT?
The PT Reabsorbs 50-60% of Filtered load of Ca2+ through solvent drag/bulk flow. This Ca2+ transport is via the paracellular (100%) pathway
What is the reabsorption of Ca2+ in the TAL?
The TAL Reabsorbs 15% of Filtered load the of Ca2+. This reabsorption however is regulated by Ca2+sensing receptor
monitors.
What does Claudin-16 do?
Claudin-16 plays a role in maintaining the permeability of the tight junctions that favours transport and Ca2+, Mg2+ and Na+
What % of Ca2+ reabsorption does the DCT do?
10-15%
How is Ca2+ reabsorbed in the DCT?
Ca2+ channel entry - TRPV5 and TRPV6
Exit via Ca2+-ATPase and Na+/Ca2+-exchanger
What does Claudin 8 (CLND8) do?
Claudin 8 (CLND8) is a tight junctional protein which prevents the movement of Ca2+
What claudin is found in the TAL?
Claudin-16
What claudin is found in the DCT?
Claudin 8
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. Ca2+-sensing receptors monitor the intracellular Ca2+ concentration. - Senses ECF
What is the role of calbindin (CB) in Ca2+ reabsorption?
Calbindin binds to calcium - neutralises Ca2+ so can’t be used in other reaction, carries it to the Ca2+-ATPase
What hormones are involved in Ca2+ homeostasis?
Parathyroid hormone (parathyroid gland)
Calcitriol
When is Parathyroid Hormone (PTH) stimulated?
PTH is stimulated by low plasma Ca2+ levels (hypocalcemia)
