Lecture 14: Bone Physiology 2

Question 1

What are the two main purposes of bone tissue?

Answer 1

1. Mechanical support and protection
2. Store and maintain mineral homeostasis

Question 2

What are the processes bones are closely linked to?

Answer 2

-Calcium, Phosphate
-Formation of bone and teeth
-Regulation of Vitamin D, Parathyroid Hormone (PTH) and Calcitonin

Question 3

Calcium levels are controlled between _____ and ______.

Answer 3

extracellular fluid and three organs

Question 4

What is the process of bone remodeling?

Answer 4

breaking down hydroxyapatite by osteoclasts

Question 5

Slide 4

Question 6

Slide 5

Question 7

What are 3 hormones that control calcium?

Answer 7

Vitamin D, Parathyroid hormone (PTH), and Calcitonin

Question 8

Where is vitamin D produced?

Answer 8

skin, kidneys

Question 9

Where does vitamin D act?

Answer 9

intestines

Question 10

What is the structure of vitamin D?

Answer 10

Cholestrol

Question 11

Is vitamin D lipid or water soluble?

Answer 11

Lipid-soluble

Question 12

What are the major actions of vitamin D?

Answer 12

• Promotes intestinal absorption of calcium and phosphate
• Increases renal reabsorption of calcium and phosphate (minor)
  *Enhances bone calcification (by increasing calcium transport,
  activating osteoblasts?)

Question 13

What do chief cells secrete?

Answer 13

Parathyroid hormone (PTH)

Question 14

What are the major actions of PTH?

Answer 14

*Increase plasma calcium
*Increase production of 1,25 Dihydroxycholecalciferol
in the kidney
*Increase calcium/phosphate absorption from bone
-Activates osteocytes, activates osteoclast proliferation
* Inhibit calcium excretion from kidneys
* Increase phosphate excretion from kidneys
* Stimulates osteolysis (so excessive PTH weakens bone and induces high calcium levels such as with Primary Hyperparathyroidism

Question 15

What does PTH stimulate the release of?

Answer 15

Calcium

Question 16

True/False: Parathyroid Hormone (PTH) stimulates Osteoclast activity and bone resorption indirectly

Answer 16

True

Question 17

Do osteoclasts have PTH receptors?

Answer 17

no

Question 18

What happens as a result of Osteoclasts not having PTH receptors?

Answer 18

Osteoblasts (build bone)
signal Osteoclast precursors to form mature Osteoclasts (chew bone)

Question 19

RANKL

Question 20

What is osteoprotegerin (OPG) and how is it produced?

Answer 20

A cytokine that inhibits bone resorption and is formed by osteoblasts

Question 21

What is the role of OPG?

Answer 21

acts as a “decoy” and binds to RANKL, preventing interaction with its receptor; therefore,
inhibiting differentiation of Preosteoclasts into mature Osteoclasts (preventing resorption of bone)

Question 22

What opposes the bone resorptive activity of PTH?

Answer 22

OPG

Question 23

The balance of ___ and ____ plays a major role in determining Osteoclast activity and bone resorption

Answer 23

OPG and RANKL

Question 24

What maintains calcium and phosphorous homeostasis?

Answer 24

by the parathyroid gland

Question 25

How is calcium and phosphate homeostasis maintained?

Answer 25

- Parathyroid Gland secretes PTH in response to low Calcium blood levels increasing Calcium levels in serum - Then, Negative feedback signals Parathyroid Gland to stop PTH release

Question 26

True/False: The body can’t make Calcium, but obtains it from food

Answer 26

True

Question 27

Calcium and Phosphate are absorbed by the __________.

Answer 27

small intestines

Question 28

Since cations are normally poorly digested name some adaptations that help the absorption of calcium.

Answer 28

 Vitamin D promotes Calcium absorption by Intestines

Question 29

True/False: Phosphate is absorbed easily

Answer 29

True

Question 30

How much of calcium is excreted vs absorbed?

Answer 30

About 35% of ingested Calcium is usually absorbed; rest is excreted

Question 31

Where is calcium absorbed?

Answer 31

the kidneys

Question 32

Normally ______ absorb 99% of filtered calcium)

Answer 32

renal tubules

Question 33

What controls the rate of calcium absorption?

Answer 33

PTH

Question 34

How is renal phosphate excretion controlled?

Answer 34

by an overflow mechanism (when phosphate concentration is < 1 mmol/L, all phosphate is resorbed)

Question 35

_____ can greatly increase phosphate excretion by kidneys.

Answer 35

PTH

Question 36

True/False: The body can't produce its own vitamin C.

Answer 36

False

Question 37

How is Vitamin D3 produced?

Answer 37

Formed in skin due to irradiation of 7-dehydrocholesterol (substance normally found in skin) by ultraviolet rays from the sun

Question 38

You need exposure to ___ (or Vitamin D from ____, ______)

Answer 38

Sun, food, supplements

Question 39

What is Calcitriol?

Answer 39

synthetic vitamin D

Question 40

What is Calcitriol used to treat?

Answer 40

hypocalcemia and osteoporosis

Question 41

What is known as the sunshine vitamin?

Answer 41

Vitamin D3

Question 42

What is the most active for a vitamin D?

Answer 42

vitamin D3

Question 43

How does vitamin D3 help the body?

Answer 43

by increasing calcium absorption from intestines to form hardened bones

Question 44

What happens when plasma concentration of calcium rises?

Answer 44

- PTH is supressed - 1,25-dihydroxycholecalciferol is also depressed, which decreases absorption of calcium from Intestines, Bones and Kidney (renal tubules)

Question 45

How much calcium do adults need a day?

Answer 45

1,000-1,200 milligrams/day

Question 46

Give examples of foods that are calcium-rich.

Answer 46

Milk, Yogurt, Hard Cheese (Parmesan, Romano),Cottage Cheese, Ice Cream, Kefir - Broccoli (roughly double the amount when cooked) - Canned seafood (sardines, salmon, shrimp) - Oranges, Almonds, Almond Milk, Soy Milk, White Beans - Rhubarb, Canned Tomatoes - Fortified Waffles, Fortified Orange Juice - Butternut Squash, Kale, Bok Choy

Question 47

Where is Calcitonin produced?

Answer 47

Thyroid (Parafollicular cells)

Question 48

Where does Calcitonin act?

Answer 48

Bone

Question 49

What is the structure of Calcitonin?

Answer 49

Peptide

Question 50

Is Calcitonin Lipid or Water soluble?

Answer 50

Water

Question 51

What does Calcitonin do?

Answer 51

- Opposes effect of PTH (e.g. it decreases plasma calcium) - Decreases Osteoclast activity and osteolysis - Decreases Osteoclast formation (and subsequent osteoblast)

Question 52

How is calcitonin stimulated?

Answer 52

by increased plasma calcium

Question 53

True/False: Calcitonin only has a transient effect on plasma calcium

Answer 53

True