Lecture 14: Bone Physiology 2 Flashcards
What are the two main purposes of bone tissue?
- Mechanical support and protection
- Store and maintain mineral homeostasis
What are the processes bones are closely linked to?
-Calcium, Phosphate
-Formation of bone and teeth
-Regulation of Vitamin D, Parathyroid Hormone (PTH) and Calcitonin
Calcium levels are controlled between _____ and ______.
extracellular fluid and three organs
What is the process of bone remodeling?
breaking down hydroxyapatite by osteoclasts
Slide 4
Slide 5
What are 3 hormones that control calcium?
Vitamin D, Parathyroid hormone (PTH), and Calcitonin
Where is vitamin D produced?
skin, kidneys
Where does vitamin D act?
intestines
What is the structure of vitamin D?
Cholestrol
Is vitamin D lipid or water soluble?
Lipid-soluble
What are the major actions of vitamin D?
- Promotes intestinal absorption of calcium and phosphate
- Increases renal reabsorption of calcium and phosphate (minor)
*Enhances bone calcification (by increasing calcium transport,
activating osteoblasts?)
What do chief cells secrete?
Parathyroid hormone (PTH)
What are the major actions of PTH?
*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
What does PTH stimulate the release of?
Calcium
True/False: Parathyroid Hormone (PTH) stimulates Osteoclast activity and bone resorption indirectly
True
Do osteoclasts have PTH receptors?
no
What happens as a result of Osteoclasts not having PTH receptors?
Osteoblasts (build bone)
signal Osteoclast precursors to form mature Osteoclasts (chew bone)
RANKL
What is osteoprotegerin (OPG) and how is it produced?
A cytokine that inhibits bone resorption and is formed by osteoblasts
What is the role of OPG?
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)
What opposes the bone resorptive activity of PTH?
OPG
The balance of ___ and ____ plays a major role in determining Osteoclast activity and bone resorption
OPG and RANKL
What maintains calcium and phosphorous homeostasis?
by the parathyroid gland
How is calcium and phosphate homeostasis maintained?
- 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
True/False: The body can’t make Calcium, but obtains it from food
True
Calcium and Phosphate are absorbed by the __________.
small intestines
Since cations are normally poorly digested name some adaptations that help the absorption of calcium.
Vitamin D promotes Calcium absorption by Intestines
True/False: Phosphate is absorbed easily
True
How much of calcium is excreted vs absorbed?
About 35% of ingested Calcium is usually absorbed; rest
is excreted
Where is calcium absorbed?
the kidneys
Normally ______ absorb 99% of filtered calcium)
renal tubules
What controls the rate of calcium absorption?
PTH
How is renal phosphate excretion controlled?
by an overflow mechanism (when phosphate concentration is < 1 mmol/L, all phosphate is resorbed)
_____ can greatly increase phosphate excretion by kidneys.
PTH
True/False: The body can’t produce its own vitamin C.
False
How is Vitamin D3 produced?
Formed in skin due to irradiation of 7-dehydrocholesterol (substance normally found in skin) by ultraviolet rays from the sun
You need exposure to ___ (or Vitamin D from ____, ______)
Sun, food, supplements
What is Calcitriol?
synthetic vitamin D
What is Calcitriol used to treat?
hypocalcemia and osteoporosis
What is known as the sunshine vitamin?
Vitamin D3
What is the most active for a vitamin D?
vitamin D3
How does vitamin D3 help the body?
by increasing calcium
absorption from intestines
to form hardened bones
What happens when plasma concentration of calcium rises?
- PTH is supressed
- 1,25-dihydroxycholecalciferol is
also depressed, which decreases
absorption of calcium from
Intestines, Bones and Kidney
(renal tubules)
How much calcium do adults need a day?
1,000-1,200 milligrams/day
Give examples of foods that are calcium-rich.
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
Where is Calcitonin produced?
Thyroid (Parafollicular cells)
Where does Calcitonin act?
Bone
What is the structure of Calcitonin?
Peptide
Is Calcitonin Lipid or Water soluble?
Water
What does Calcitonin do?
- Opposes effect of PTH (e.g. it decreases plasma calcium)
- Decreases Osteoclast activity and osteolysis
- Decreases Osteoclast formation (and subsequent osteoblast)
How is calcitonin stimulated?
by increased plasma calcium
True/False: Calcitonin only has a transient effect on plasma calcium
True
