Calcium

Question 1

What are the sources of calcium?

Answer 1

Milk and dairy products
Salmon, oysters, clams, sardines with bones
Turnips, greens
antacids

Question 2

What factors influence calcium absorption?

Answer 2

Fat - no problem for healthy individuals

Alcohol - decreases calcium absorption even with vit D supplements, structure of microvilli is damaged

Question 3

How is Calcium absorbed?

Answer 3

Ca2+ binds to the protein calbindin9 for absorption into intestinal cell
Binds to TRPV6 receptor on intestinal cell (active transport)

-It is vitamin d dependent

Also absorbed through passive diffusion

Question 4

What form is calcium absorbed in?

Answer 4

Ca2+ (ionized form)

Question 5

How does calcium become ionized?

Answer 5

Solubilization takes place in an hour at an acidic pH.

Question 6

What regulated Calcium homeostasis?

Answer 6

3 hormones (PTH, calcitriol, and calcitonin)
5 tissues (parathyroid, kidney, gut, bone and thyroid)

Question 7

Which hormones positively regulate calcium in the blood

Answer 7

calcitriol and parathyroid hormone

Question 8

Which hormones negatively regulate calcium in the blood

Answer 8

Calcitonin

Question 9

Actions of parathyroid hormone?

Answer 9

secreted from cheif cells
increases production of calcitriol
-increases absorption in intestine (calbindin9)
-increases reabsorption in bone (calbindin28, calcitriol and pth)
-Increases resorption from bone(interacts with osteoclasts and osteoblasts)

Increased by low plasma Ca levels - to increase calcium levels in blood

Question 10

Action of calcitonin

Answer 10

synthesized in parafollicular cells of the thyroid gland

prevents Ca mobilization from bone (stimulates osteoblasts/inhibits osteoclasts)

Inhibits production of calcitriol

Diminished renal Ca reabsorption, promotes excretion

It decreases calcium levels in blood

Question 11

What is calbindin9?

Answer 11

Binds calcium in the small intestine for absorption

Is vitamin D dependent - calcitriol binds to VDR and increases transcription of calbindin9
-PTH has no direct effect

Question 12

Osteoblasts

Answer 12

From marrow stromal cells
Cells that lay down bone - deposits and orients fibrous protein
Makes matrix capable of mineralization

Question 13

Osteocytes

Answer 13

Osteoblasts that stopped matrix synthesis and are embedded
Maintains integrity

Bones with dead osteocytes are very fragile

Question 14

Osteoclasts

Answer 14

Reabsorbs bone
Secret acid, proteases and hydrolases that dissolve the mineral and digest the matrix
- releases breakdown products into blood

They die in response to calcitonin - calcitonin = osteoblasts
Doesnt have PTH sensor

Question 15

How are bone cell regulated

Answer 15

PTH - bone resorption - no PTH receptors on osteoclasts, but do have calcitonin receptors

Osteoblasts - central position in both bone formation and remodeling (PTH receptors)

Question 16

How much calcium is found intracellularly?

Answer 16

1% - tightly regulated so does not display status

Question 17

Roles of calcium in the body

Answer 17

Blood coagulation
Bone mineralization
Muscle contraction
Membrane permeability
Hormone signaling

Question 18

How does intracellular Ca enter cells?

Answer 18

Transmembrane diffusion or Voltage dependent channels

Stored in mitochondria, endoplasmic recticulum, nucleus and vesicles

Question 19

Functions of intracellular calcium

Answer 19

Phospholipase A2
Phosphodiesterases
Protein Kinase C

Calmodulin - allows it to interact with various enzymes/proteins
-phosphorylase kinase - activated phosphorylase

Question 20

Bone mineral density

Answer 20

Inluenced by the peak bone mass achieved as a child

-women have lower

Question 21

Calcium deficiency

Answer 21

Osteoporosis - reductions in the amount of of bone

- Occurs mainly in post menopausal white women

Question 22

Types of osteoporosis

Answer 22

Postmenopausal – Type 1
Senile - Type 2 (men and women, trabecular and cortical bone)
Disuse - Type 3

Question 23

Symptoms of osteoporosis

Answer 23

Weakness
Anorexia
Pain in back and hips
Fractures in femur and hip
Loss of stature

Question 24

Nutritional factors that influence osteoporosis

Answer 24

Calcium intake - intake and absorption decreases with age
Low calcium/phosphorus ratio
Excess protein

Question 25

Hormonal factors related to osteoporosis

Answer 25

Increasing PTH - mobilization of bone
Calcitriol decreases with age 1,25-(oH)2D3
Growth hormone decreases with age

Question 26

Protective factors

Answer 26

African american
Male
High bMI
no smoking
moderate alcohol

Question 27

Protective factors

Answer 27

African ame

Question 28

Prevention

Answer 28

Diet adequate in D, Ca, protein and K

Avoid excessive intake of phosphorus, protein, sodium, alcohol, caffeine