Calcium and Phosphorus Flashcards by Nathaniel Miller

What is unique about Calcium valence electrons ?

2+, lost readily in solution
large effective radius
attracts H2O

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What is the calcium generally considers for in the body?

a tool or carrier (messenger)
initiates a series of processes

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Bone mineralization is a huge storage for

99% of calcium
80-90% of phosphorus

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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

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What is the purpose of IP3 (inositol triphosphate) and DAG

signal transduction and lipid signaling

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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

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How can calcium leave the cytoplasm of a cell?

Through Na+ or Mg+ pumps/ ATPase or can be sequestered into cells (ER, mito, nucleus)

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Unique characteristics of phosphorus

found in the bone as hydroxyapatite Ca10(OH)2(PO4)6
preferred ionic state is orthophosphate as HPO4 and H2PO4

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at pH 7.4

ratio is 4:1
HPO4 (basic) to H2PO4 (acidic)

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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

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How can phosphate act as a buffer?

by collecting H+ and decreasing acidity inside the cell

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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)

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How is phosphate absorbed by the body

Absorbed linearly as HPO4, similarly to Ca2+
- Diffusion
-Carrier mediated with Mg / Na

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How effective is absorption in comparison of Calcium to Phosphate

Calcium is 20-30%
Phosphate is 60-70%

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What controls PTH production and secretion

plasma Ca 2+

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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

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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