Calcium and Phosphorus Flashcards
What is unique about Calcium valence electrons ?
2+, lost readily in solution
large effective radius
attracts H2O
What is the calcium generally considers for in the body?
a tool or carrier (messenger)
initiates a series of processes
Bone mineralization is a huge storage for
99% of calcium
80-90% of phosphorus
Only 1% of Calcium is ionized and is responsible for?
Blood clotting - Platelets
Enzyme regulation - calmodulin
Blood clotting, nerves, muscles,
membrane permeability - bind membranes and change conformation
What is the purpose of IP3 (inositol triphosphate) and DAG
signal transduction and lipid signaling
How is IP3 made, what does it do?
Through phosphorylation of PI and hydrolysis of PIP2 (cofactor magnesium)
Allows more intracellular calcium by binding the channel
How can calcium leave the cytoplasm of a cell?
Through Na+ or Mg+ pumps/ ATPase or can be sequestered into cells (ER, mito, nucleus)
Unique characteristics of phosphorus
found in the bone as hydroxyapatite Ca10(OH)2(PO4)6
preferred ionic state is orthophosphate as HPO4 and H2PO4
at pH 7.4
ratio is 4:1
HPO4 (basic) to H2PO4 (acidic)
Biological fxn of Phosphate
Bone mineralization
Electrolyte homeostasis
Structural role (phosphates, DNA/RNA - alt with pentose sugars)
Secondary messenger - kinase, phosphates, cAMP
Vit B metabolism
How can phosphate act as a buffer?
by collecting H+ and decreasing acidity inside the cell
3 ways calcium can be absorbed small I
Duodenum - Transcellular (major route) - Rq, energy + channel+ BPcalbindin — stim by low Calcium and calcitriol (Vit D)
illenum/jejunum - paracellular - energy independent (passive), depends on concentration
Colonic fermentation - fibers release Ca2+ (4-10% can be absorbed this way)
How is phosphate absorbed by the body
Absorbed linearly as HPO4, similarly to Ca2+
- Diffusion
-Carrier mediated with Mg / Na
How effective is absorption in comparison of Calcium to Phosphate
Calcium is 20-30%
Phosphate is 60-70%
What controls PTH production and secretion
plasma Ca 2+
What are the actions of PTH
Stimulates bone osteoblast – trigger breakdown
Stimulates kidney tubular cells to increase Ca2+ absorb
Stims kidneys to increase conversion to in kidneys to Active Vit D
Increase in intestine + bloodstream absorb
- Actions are indirectly done via second messenger
How is phosphate affected with increase PTH to kidney tubular cells?
There is a decrease in re-absorption = increase in urine
What is calcitonin, where it is released? Function?
Secreted from the thyroid glad (front of neck)
Releases when Ca2+ is HIGH
Increase Ca2+ storage/mineralization
reduce kidney/intestine/ bloodstream absorption
Vit D inhibited
What is the purpose of bone remodeling 10% of the bone ever year?
Allow support of the body/ done defects
Incubate developing immune cells
Act as a reserve inorganic minerals
maintains optimal level of calcium in the blood
Osteroclast vs Osteoblast
Clast = Clash of Clans = destroy and resorb old bone
B = Build = deposit new bone
“Coupled” but with bias on Clast
Bone remodeling cycle has two phases describe each
Activation phase: conversion of osteoclast precursor to active (40days) rq calciotropic factors (Vit D, PTH, prolactin, RANKL)
Reversal phase: Bone resorption to formation (145 days) rq anabolic factors (estrogen, calcitonin, calcium, Osteoprotegrin)
- Osteoprotegrin enzyme inhibits bone breakdown
Where does must reabsorption of phosphorus take place vs calcium
P: proximal tubule by activated sodium-phosphate cotransporter - linear relationship with excretion
C: Paracellular (b/c bound to albumin its harder)
List all factors that decrease calcium absorption and excretion
Ab: fibre, phytate, oxalate, cations (Zn,Mg), excess unab fats
Ex: increase plasma phosphate = decrease in ionic Ca2+ = increase in PTH (increase absorption)
Excess calcium can interrupt absorption of
iron and fatty acids
List all factors that decrease phosphate absorption and excretion
Ab: phytate (legumes), excess Ca, Mg, Al
Ex: depletion, parathyroidectomy, calcitriol
List all factors that increased calcium absorption and excretion
Absrob: PTH, Estrogen, Calcitriol (Active Vit D), Sugars , proteins
Excrete: sodium, Sulfur AA , caffeine
List all factors that increase phosphate absorption and excretion
Ab: Calcitriol
Ex: PTH, Excess, estrogen, Thyroid hormones, phosphatonins
How do phosphatonins like FGF-23 affect phosphorus excretion
secreted from osteocytes in bone and suppress sodium-phosphate cotransporters
Also suppresses CYP27B which makes calcitriol
why are formula fed infants a concern in regards to calcium
reduced bioavailability and they need Ca2+ retention to support bone growth peak
RDA / AI for calcium
Infants — 200-260mg (AI)
Teens — 1300 mg
Adults - 1000mg
Adult F >50 - 1200mg
RDA for Phosphorus
Infants — 100-275mg (AI)
Teens - 1250mg
Adults - 700mg
Food sources of Phosphorus
Almost everywhere: dairy product, meat, fish, eggs = 70% of intake
also processed foods & soda
Chrons disease
Intestinal disorder, fat malabsorption
Why does an inverse relationship exist between calcium and hypertension
They have reciprocal effects on hormone system and BP
Preeclampsia
Decreased turnover of calcium metabolism = increased intracellular Ca2+, decreases ATP activity
Describe causes of Hypocalcemia & consequences
Causes: Inadequate Vit D production, PTH resistance, Vitamin D resistance
Consequences: Fatigue, Neuromuscular irritability
Describe causes and consequences of Hypercalcemia
Causes: Hyperabsorption of Ca due to high PT, Decreased urinary excretion, Increased bone resorption due to high PTH, Severe dehydration
Consequences: Fatigue, nausea, kidney stones
What is the difference b/w Osteoporosis Type I vs Type II
Type I: Primarily menopausal women, 50-70, wrist and spine, Women 6:1
Type II (Senile): 70 >, Hip, Women 2:1
Where would you likely see a Phosphorus deficiency or excess
Pre-term babies, low P diet + supplements
Excess: Concern in pop with compromised kidney fxn
Phosphorus deficiency would occur where?
Re-feeding syndrome: catabolism = increase plasma phosphate, eat = Cells uptake P for use of energy during depletion = rapid depletion of P from plasma
Hyperventilation + respiratory alkalosis
Alcoholic: decrease P intake + poor absorption + disorganization of muscle
Describe causes and consequences of Hypophosphatemia
Causes: Vit D deficiency or resistance, Increased urinary loss, Intracellular shifts of P from serum into cells
Consequences: CNS irritability, Muscle myopathy, Metabolic abnormalities
Describe causes and consequences of hyperphosphatemia
Causes: Decreased urinary excretion, Acute P load
Consequences: Hypocalcemia - By binding to calcium which is then excreted. If secondary to renal disorders - hyperparathyroidism
