Biological Functions of Calcium, Magnesium, and Phosphorus (Toribio)

Question 1

Use correct terminology
Match the following with the appropriate organ:
1. Absorption -
2. Reabsorption -
3. Resorption -

Answer 1

1. Intestine
2. Kidney
3. Bone

Question 2

A mare with a foal may show signs of?

Answer 2

hypocalcemia

Question 3

Which two elements have similar behaviors in the biological system?

Answer 3

Magnesium & Calcium

Question 4

Is a naturally occurring mineral (calcium phosphate mineral) form of calcium apatite that shows good biocompatibility and is an excellent candidate for bone repair and substitution

Answer 4

Hydroxyapatite

Question 5

(T/F) The skeleton contains approximately 99% of the total body calcium as hydroxyapatite crystals [(Ca10(PO4)6(OH)2

Answer 5

True

Question 6

(T/F) Phosphorus (or phosphate) represents ~1% of the body weight, with most (85%) located in the bone matrix (hydroxyapatite), 15% in blood and soft tissues, and less than 0.1% in the extracellular fluid

Answer 6

True

Question 7

• Alkaline Metal
• 5th most abundant element in the body
• about 1.5% of the body weight is calcium
• Is found in 3 main compartments:
  - Skeleton (99%)
  - Soft tissue/cell organelles (0.9%)
  - Extracellular fluid/ Plasma (0.1%)
  What element was that describing?

Answer 7

Calcium

Question 8

Which of the following is correct?
A. Oxygen > Calcium > Carbon > Nitrogen > Hydrogen
B. Oxygen > Nitrogen > Carbon > Hydrogen > Calcium
C. Oxygen > Carbon > Hydrogen > Nitrogen > Calcium

Answer 8

C. Oxygen > Carbon > Hydrogen > Nitrogen > Calcium

Question 9

The free or the ionized calcium is going to make up about ______% of the total calcium in the blood

Answer 9

55

Question 10

What are the 3 forms that plasma total calcium exists?

Answer 10

• Bound to proteins such as albumin (40-45%)
• Ionized = free, active Ca2+ (50-55%)
• Complexed to anions: lactate, bicarbonate, and phosphate (5%)

Question 11

________ blocks Na+ from getting into cells = Blocks depolarization

Answer 11

Ca2+ (Na+ channel antagonist)

Question 12

Striated muscle = needs ____________ Ca2+

Answer 12

intracellular

Question 13

Neurons and smooth muscle = need ______________ Ca2+

Answer 13

extracellular

Question 14

Calcium binding to proteins is pH-dependent
(T/F) In acidosis there is increased binding = increased plasma Ca2+

Answer 14

False, decreased binding

Question 15

Calcium binding to proteins is pH-dependent
(T/F) In alkalosis there is increased binding = decreased plasma Ca2+

Answer 15

True

Question 16

In acidosis, the hydrogens will displace Mg2+ and Ca2+ from albumin, then when you measure the total calcium, it is the same. But what would not be the same?

Answer 16

Active calcium (you have more free calcium)

Question 17

(T/F) Most Ca absorption occurs in the large intestine

Answer 17

False, small intestine

Question 18

(T/F) ~40-70% of the calcium in the diet is absorbed

Answer 18

True

Question 19

• Phytate
• Oxalate
• Phosphate (chelation)
  What do these elements do?

Answer 19

Reduce calcium absorption

Question 20

Absorption is:
Passive, non-saturable, concentration-dependent, voltage-dependent

Answer 20

Paracellular

Question 21

Absorption is:
Active, saturable, concentration-independent, needs energy, more regulated

Answer 21

Transcellular

Question 22

What are the 3 steps of Transcellular?

Answer 22

1- Apical entry
* Epithelial calcium channels – (ECaC = TRPV)
2- Cytoplasmic diffusion:
* Calbindin D9k and D28k
3- Basolateral extrusion:
* Plasma membrane calcium ATPase (PMCA)
* Sodium/Calcium exchanger (NCX)

Question 23

Renal Handling of Calcium
(T/F) ~70% of calcium is reabsorbed in distal tubules

Answer 23

False, proximal tubules

Question 24

Renal Handling of Calcium
(T/F) ~20% of calcium is reabsorbed in the ascending loop of Henle

Answer 24

True

Question 25

Renal Handling of Calcium (T/F) ~5-10% of calcium is reabsorbed in the distal tubules and it is paracellular

Answer 25

False, Transcellular

Question 26

(T/F) Most calcium reabsorption is Transcellular

Answer 26

False, Paracellular

Question 27

- Non-metal, anion - 6th most abundant element in the body - about 1% of body weight - Concentrations are higher in growing animals and alkaline phosphatase is also higher in young animals - Found in 3 main compartment - Skeleton (85%) - Soft tissues (15%) - Extracellular fluid (0.1%) What element was that describing?

Answer 27

Phosphorus

Question 28

What form of phosphorus is the one measured clinically in blood samples?

Answer 28

Inorganic (30%) *The other 70% part is bound to the cells

Question 29

Phosphorus Functions *As part of phospholipids is essential for cell membrane stability *As part of ATP/GTP/energy – muscle contraction, hormone secretion, enzyme activation, energy, and electrolyte regulation *As part of cAMP is essential for cell signaling *It is part of nucleic acids (DNA, RNA) *In oxygen transport (2,3-diphosphoglycerate)

Answer 29

Non-structural (phosphorus as a regulatory ion) - the 15%

Question 30

Phosphorus Absorption (T/F) ~20-60% of phosphorus in the diet is absorbed depending on species, requirements, and age

Answer 30

True

Question 31

Phosphorus Absorption (T/F) Most phosphorus absorption occurs in the proximal small intestine and large intestine

Answer 31

False, distal small intestine

Question 32

Phosphorus Absorption is: cotransporter-dependent, requiring sodium

Answer 32

Transcellular

Question 33

(T/F) Multiple factors influence intestinal phosphorus reabsorption including requirements, age, diet composition, factors in the diet, and hormones*

Answer 33

False, absorption

Question 34

(T/F) Multiple factors influence renal reabsorption of phosphorus including requirements, age, and hormones (PTH, FGF-23, vitamin D*)

Answer 34

True

Question 35

Phosphorus reabsorption is ___________________

Answer 35

Na-dependent

Question 36

Most (80%) phosphorus reabsorbed in ____________ tubules - Transcellular 3 steps: apical entry, cytoplasmic diffusion, basolateral extrusion

Answer 36

proximal

Question 37

- Divalent cation, alkaline metal - 11th most abundant element in the body - ~0.05% of the body weight - It is found in 3 main compartments: - Skeleton (60%) - Soft tissues (38%) - Extracellular fluid (2%) What element was this describing?

Answer 37

Magnesium

Question 38

(T/F) In blood, most magnesium is in plasma

Answer 38

True

Question 39

Total magnesium exists in 3 forms:

Answer 39

1- Bound to protein such as albumin (30%) 2- Ionized = free, active (60%) 3- Complexed to anions: lactate, bicarbonate, and phosphate (10%)

Question 40

Magnesium Functions * Cofactor for >300 enzymes/enzymatic reactions * Important for energy metabolism * Important for cell membrane stability * Essential for transmembrane ion transport (e.g. Na+/K+ ATPase) * Any process that requires ATP/energy also requires Mg2+ * Nucleic acid synthesis requires Mg2+ * Essential for calcium homeostasis ** PTH synthesis and PTH receptor activation require Mg2+**

Answer 40

Non-structural (magnesium as a regulatory ion) - the 40%

Question 41

Magnesium Absorption (T/F) ~30-50% of magnesium in the diet is absorbed

Answer 41

True

Question 42

Magnesium Absorption Most magnesium absorption occurs in the small intestine, except in:

Answer 42

ruminants where most magnesium absorption occurs in the rumen

Question 43

What are the elements in the diet that reduce magnesium absorption?

Answer 43

- Excessive phosphates - Oxalates - Fatty acids

Question 44

Renal Handling of Magnesium (T/F) ~20% of Mg is reabsorbed in proximal tubules

Answer 44

True

Question 45

Renal Handling of Magnesium (T/F) ~60% of Mg is reabsorbed in the ascending loop of Henle

Answer 45

True

Question 46

Renal Handling of Magnesium (T/F) ~5% of Mg is reabsorbed in the proximal tubules

Answer 46

False, distal tubules (Transcellular)

Question 47

What are the factors that influence magnesium concentrations?

Answer 47

* Electrolytes (calcium, phosphorus) * Acid-base status (acidosis/alkalosis) similar to Ca2+ * Hormones (PTH, insulin) * Plasma proteins (albumin in particular)

Question 48

Most in the skeleton; ionized calcium (Ca2+) is active form; most absorption in small intestine; most reabsorption in PCT; multitude of functions; affected by pH

Answer 48

Calcium

Question 49

Most in the skeleton; organic/inorganic; inorganic is measured clinically; most absorption in distal SI and large intestine; most reabsorption in PCT; a multitude of functions; higher in young animals

Answer 49

Phosphorus

Question 50

Most in the skeleton; ionized magnesium (Mg2+) is active form; most absorbed in the small intestine (and rumen); most reabsorption in DCT; a multitude of functions; Mg2+ affected by pH; important for calcium homeostasis

Answer 50

Magnesium

Question 51

Of the different forms of calcium in circulation, which one is influenced by albumin concentrations?

Answer 51

Total calcium

Question 52

(T/F) A high pH increased the binding of calcium to albumin

Answer 52

True

Question 53

(T/F) Acidosis increases binding of calcium to plasma proteins

Answer 53

False

Question 54

(T/F) Phosphorus is important in energy generation and electrolyte transport

Answer 54

True

Question 55

(T/F) Processes that require ATP also require magnesium

Answer 55

True

Question 56

What is an explanation as to why animals with hypocalcemia may become hyperexcitable?

Answer 56

Low extracellular calcium promotes Na+ entry into excitable cells