Final - Phosphorus

Question 1

What are the sources of phosphorus?

Answer 1

The sources are widely distributed in meat, poultry, fish, eggs and milk

Animal products are superior sources of available P

Question 2

How is Phosphorus found in plants?

Answer 2

80% of P in plants is found as phytate

This limits the bioavailability to 50%

Question 3

WHat inhibits phosphorus absorption?

Answer 3

Phytate, excessive intakes of magnesium, calcium and aluminum

Question 4

What enhances phosphorus absorption?

Answer 4

Vitamin D

Question 5

Why is phytate absorption inhibited?

Answer 5

mammalian digestive system lacks phytase

-Yeast and bacteria can hydrolyze some phytates to generate free P

Question 6

How is phosphorus usually found?

Answer 6

Both organic and inorganic forms of phosphorus are not usually found free

Question 7

How is organic P found?

Answer 7

Organic P is bound to proteins, sugars & lipids and it requires hydrolysis

Question 8

How is phosphorus absorbed?

Answer 8

Phosphorus is absorbed in its inorganic form

Question 9

What enzymes free organically bound P (that are not bound to Phytate)?

Answer 9

Phospholipase C
Alkaline phosphatase
Pepsin/Trypsin - releases protein bound P

Question 10

What are the two processes that Phosphorus is absorbed by?

Answer 10

A saturable carrier mediated active transport system that is dependent on sodium (transported in vesicles) (Na-phosphate co transporter)

A concentration dependent diffusion process

Question 11

How is most of the P found the blood?

Answer 11

Most P in blood is organic

Question 12

What biological processes is Phosphorus involved in?

Answer 12

Energy transfer/storage
Cell membrane structure
Nucleic acid formation
Intracellular second messenger
Acid-base balance
Bone mineralization

Question 13

How does P function in Energy storage and transfer?

Answer 13

It functions via high energy phosphate bonds (ATP - adenosine triphosphate)
Creatine phosphate
Uridine phosphate (UTP) - activates UDP-glucose in glycogen synthesis
Coenzymes TPP NADP

Question 14

How does P function in cell membrane structures?

Answer 14

It is an important component of DNA and RNA

The phospholipids in cell membranes

Question 15

How does P function as an intracellular second messenger?

Answer 15

It is a structural component of cAMP (activates protein kinase)
Inositol triphosphate (I3P) triggers Ca release

Question 16

How does P function in acid base balance?

Answer 16

Phosphate is the main intracellular buffer

Question 17

Role of phosphoproteins

Answer 17

Phosphorylation of different molecules regulate metabolism
Changes cellular activity of different proteins (enzymes)
Phosphorylation vs. dephosphorylation

Question 18

How is P important in skeletal tissue?

Answer 18

Amphorus calcium phosphate and crystalline forms (hydroxyapatite -the chief structural element of bone)

Question 19

What hormones influence P metabolism?

Answer 19

PTH, calcitriol and calcitonin influences P metabolism

Question 20

How does PTH effect P?

Answer 20

PTH - stimulates reabsorption of phosphate from bone and stimulates the excretion of P in urine

Question 21

How does Calcitriol effect P?

Answer 21

Calcitriol stimulates P reabsorption in the kidney and absorption of alkaline phosphatase in the gut

Question 22

How does calcitonin effect P?

Answer 22

Calcitonin promotes bone mineralization (decreases plasma P)

Question 23

how is phosphorus excreted?

Answer 23

The kidneys retain about 80% of the P filtered by the glomerulus

The PTH decreases the reabsorption by the proximal tubular cells

Question 24

What is the deficiency of phosphorus?

Answer 24

Hypophosphatemia

Question 25

Who gets hypophosphatemia?

Answer 25

Phosphate deficiency - It is rare
It is common in hospital patients who are seriously ill
-Leukemia & lymphoma
-High bilirubin
-Respiratory alkalosis, sepsis
Heat stroke, gout (uric acid)

X-linked hypophosphatemina & dents syndrome - with out total body phosphorus deficit

Question 26

What are the symptoms of Hypophosphatemia

Answer 26

It impairs growth

• early P deficiency is associated with losses of K, Mg and N
• Leads to abnormalities of cellular iron transport

Osteomalcia will occur in long standing P deficiency

Other symptoms: 
profound muscle weakness
Myopathy and cardiopathy
Respiratory insufficiency
Erythrocyte, leukocyte and platelet dysfunction
Metabolic acidosis

Question 27

What might reduce plasma P and cause hypophosphatemia other that being seriously ill?

Answer 27

Decreased intake/intestinal absorption
Vitamin D Deficiency
Malabsorption
Excessive vomiting
Phosphate binding antacids
Hyperparathyroidism
Renal tube deficits
Nervous system dysfunction