Calcium Flashcards
1
Q
Normal Serum Ca
A
Normal = 9.5 mg/dl (8.5-10)
- 45% bound to albumin
- 10% in complexes w/ phosphate or carbonate
- 45% free or ionized
2
Q
Ca Sources and Absorption
A
- Intake = 1000 mg but only 150-200 absorbed (proximal SI - duodenum and jejunem)
- Dark green leafy vegetables, dairy, almonds, soy, fortified foods (cereal, OJ, etc)
- Supplements - most common is Ca carbonate (w/ food need acid) OR Ca citrate (do NOT need food)
- Aided by activated Vit D (1,25 dihydroxyvitamin D) but also some passive absorption
- 1st Hydroxylation - in liver @ 25
- 2nd Hydroxylation - in kidney @ 1 (regulated by PTH and FGF-23)
3
Q
PTH Regulation and 5 Roles
A
- PTH - cleaved into PTH 1-34 (main effects)
- Mainly regulated by serum Ca conc - Ca-sensing receptor on parathyroids sense free Ca++ (dec serum Ca++ - secrete PTH v. inc serum Ca++ - binds receptors - inhibits PTH secretion and dec levels of PTH mRNA)
- Actions
1- Stim 1,25 Vit D production in kidney
2- Stim Ca reabsorption in tubules
3- Block phosphate reabsorption in tubules
4- Activates osteoclasts for resorption ACUTELY and osteoblasts SUBACUTE/CHRONICALLY
5- Activate Ca transport indirectly in intestine via 1,25 Vit D
4
Q
FHH and ADHH
A
- Familial Hypocalciuric Hypercalcemia (FHH) - inactivating mutation of Ca sensing receptor - higher set point
- Auto Dom Hypocalcemic Hypercalciuria (ADHH) - lower set pt
5
Q
Kidney Ca Control
A
- 65% reabsorbed in proximal tubule (not tightly regulated) - coupled to Na and water transport
- 35% delivered to cortical TAL and distal tubules - reabsorbed there under regulation of PTH (very tightly regulated)
6
Q
Hypocalcemia Value + Signs/Symptoms
A
<2 SD below mean in lab (usually 8.5) - must check albumin and Mg
ALL SIGNS DUE TO HYPEREXCITABILITY (dec mem threshold)
- Neuro - fatigue, seizures, peri-oral numbness/tingling, basal ganglia or intra-cerebral calcifications
- Cardio - prolonged QT –> arrhythmias
- MSK - twitches, cramping, tetani
- GI - cramping
- Pulm - bronchospasm
- Eyes - cataracts
7
Q
Chvostek and Trousseau’s Signs
A
Chvostek’s Sign - twitch facial muscles when tap facial nerve w/ reflex hammer (only helpful if no sign at baseline)
Trousseau’s Sign - spasms of forearm w/ BP cuff > systolic
8
Q
How does the body respond to hypocalcemia acutely and chronically?
A
- Acute - parathyroids sense dec free Ca –> inc PTH (min) –> 2 acute effects
- 1- Inc Ca reabsorption / dec Ca excretion in kidney
- 2- Stimulate osteoclasts (net release of Ca into serum)
- In few days … elevated PTH –> inc 1,25 Vit D synthesis (takes few days) which inc Ca absorption in gut
- If not corrected … chronic elevated PTH –> delayed activation of osteoblasts too so restore Ca balance from bone; maintain Ca by dec excretion and hyper-absorption
9
Q
Hypoparathyroidism
A
- Low free Ca w/ low PTH, often high phosphorous, low 1,25 Vit D –> lower absorption, low bone turnover (no net losses or gains), PTH not stimulating kidneys so “open faucet” - more Ca given - more Ca in urine
- Causes - surgery, autoimmune, infiltration
(hemochromatosis, Wilson’s), congenital - Tx - Ca supplement and 1,25 Vit D (calcitrol), monitor urinary Ca
10
Q
Vit D Def
A
- Diagnosed by low 25 OH Vit D
- Results from malabsorption, inadequate skin exposure, dec activation (liver or renal disease), genetics (mutations in hydroxylases or Vit D receptors)
- Reduced levels –> mineralization defects in bone
- Rickets in kids
- Osteomalacia in adults
- Lab Patterns = low Vit D, low absorption, high PTH secondary to low Ca –> inc bone resorption and will try to inc 1,25 Vit D (not successful b/c substrate to low) and max reabsorption of Ca in kidneys
- Tx - Vit D supplements; use 1,25 Vit D if end-stage renal disease OR hypoparathyroidism (cannot activate on own)
11
Q
Magnesium Def
A
- More common in hospitalized patients (malabsorption or inc losses of Mg in urine from diuretics and IV fluids, can also be due to alcoholism or cisplatinin for chemo)
- Co-factor for PTH; low Mg –> inhibition of PTH secretion and dec PTH effects on target organs (kidney and bone)
- Tx - oral Mg replacement (some GI upset)
12
Q
Pancreatitis
A
- Causes - duct obstruction, alcohol, meds, trauma
- Mild to severe hypocalcemia is a poor prognostic factor
- Mechanism - pancreatic lipase released into peritoneal space –> digests triglycerides –> free FAs (neg charge) which bind Ca (pos charge) –> insoluble FA-Ca salts (soaps)
- Chronically causes malabsorption of Ca and Vit D
- Tx
- Ca replacement by IV if acute
- Resolves w/ resolution of pancreatitis
- Ca and Vit D replacement if chronic
13
Q
Hypercalcemia Value (+ correction)
A
- Definition - > 2 SD above normal of lab; about 10.2-10.5; no grading criteria
- Generally, 12-14 mild; > 14 severe
- Correct for albumin
- Corrected Total Ca = Meas Ca + .8 (4- meas albumin)
14
Q
How does the body respond to hypercalcemia acutely and chronically?
A
- Acute - parathyroids sense inc Ca –> no PTH –> dec Ca reabsorption in kidneys ands dec bone resorption
- Chronic - body adapts by re-coupling bone resorption and formation; fall in 1,25 Vit D –> dec absorption in gut and still excreting more Ca in urine
15
Q
Hypercalcemia Signs and Symptoms
A
(all related to inc depolarization threshold across cell - dec response to chemical and neural stimuli)
- Neuro - fatigue, obtunded, comatose (influenced by rate of onset, age, baseline mental status)
- Renal - polyuria and inc thirst/dehydration; Ca inhibits water reabsorption by osmotic diuresis; Ca inhibits ADH effect on distal nephron –> nephrogenic DI + Ca-phos deposits in interstitium or Ca stones
- Cardio - Shorter Q-T intervals, Ca-phos deposits in conduction system, vasoconstrict in response to diuresis
- MSK - weakness b/c dec contractility
- GI - constipation, ileus (hypoactive smooth muscle), deposits in pancreas –> pancreatitis
