Skeletal System

Question 1

What do osteoprogenitor cells do?

Answer 1

Found in endosteal and periosteal membranes, differentiate into osteoblasts.

Question 2

What do osteoblasts do?

Answer 2

Modified fibroblasts that synthesize and secrete organic matrix, calcify matrix.

Question 3

What do osteocytes do?

Answer 3

Mature bone cells that transfer minerals from interior to growth surfaces.

Question 4

What do osteoclasts do?

Answer 4

Form from monocytes, act to resorp bone and release Ca+2 and phosphate

Question 5

What is bone’s organic matrix comprised of?

Answer 5

• Proteoglycans
• Glycoproteins
• Type 1 collagen

Question 6

What makes up the inorganic component of bone?

Answer 6

• calcium phosphates
• calcium fluoride
• calcium hydroxide
• calcium carbonate (secreted by osteoblasts)

Question 7

What is the functional unit of bone?

Answer 7

Osteon

Question 8

What is the makeup of an osteon?

Answer 8

-Concentric lamellae of osteocytes (which sit in lacunae filled with ECF) connected by cannaliculi

Question 9

How do nutrients and wastes get into and out of osteocytes?

Answer 9

• Cannaliculi transfer nutrients and wastes between blood vessels and osteocytes
• Haversian canals and Volkmanns canals

Question 10

What is the difference between haversian canals and volkmann’s canals?

Answer 10

• Haversian canals run the length of long bones whereas volkmann’s canals run across them.
• Volkmann’s canals join Haversian canals.

Question 11

Where is cortical bone typically found?

Answer 11

Outer surface of bone

Question 12

Where is spongey (trabeccular/canellous) bone usually found?

Answer 12

Inner bone

Question 13

What are the five steps of bone formation?

Answer 13

1) Formation of bone collar around hyaline cartilage
2) Cavitation of hyaline cartilage
3) Invasion of periosteal bud
4) Continuation of ossification
5) Ossification of epiphyseal plate

Question 14

What vitamins are needed for bone growth?

Answer 14

• C
• D
• Calcium

Question 15

What hormones are needed for bone growth?

Answer 15

• Growth Hormone (leads to IGF-1 secretion)
• Insulin
• Thyroid Hormone
• Androgens

Question 16

Where does Membranous ossification occur?

Answer 16

-Flat bones

Question 17

How does membranous ossification occur?

Answer 17

-mesenchymal cells turn right into bone: osteoprogenitors->osteoblasts->bone

Question 18

Tell the bone remodeling story

Answer 18

• Osteoclasts express RANK receptor
• Osteoblasts express the protein RANKL
• Osteoblasts also secrete osteoprotegrin, which inhibits RANKL
• Osteoblasts secrete RANKL activates Osteoclasts, and this provides a normal Blast/Clast balance.
• Up until menopause, RANKL

Question 19

How much of the body’s calcium is stored in the bones?

Answer 19

-99%

Question 20

T/F Calcium does not normally move between bone and plasma

Answer 20

FALSE. In a healthy body, calcium moves freely between plasma and bone.

Question 21

T/F Calcium is the most abundant mineral in the body

Answer 21

True. 1100gm.

Question 22

T/F Maybe 1% of calcium is free floating in plasma and blood

Answer 22

True

Question 23

How much intracellular calcium is free?

Answer 23

45-50%

Question 24

How much intracellular calcium is bound to albumin?

Answer 24

40-45%

Question 25

What does free calcium play a role in and how?

Answer 25

Acts as a second messenger important in... - Blood clotting - Muscle contraction - Nerve signal transmission

Question 26

What hormones are involved with calcium homeostasis?

Answer 26

- Parathyroid hormone - Calcitonin - Vitamin D

Question 27

What systems are involved in calcium homeostasis?

Answer 27

- The kidneys | - GI System

Question 28

How is phosphate homeostasis related to calcium homeostasis?

Answer 28

- Phosphate is important aspect of ATP. Is less regulated than calcium and fluctuates easily with diet. - Regulated by same hormones as calcium, but responds in opposite ways (i.e. calcium goes up, phosphate goes down.)

Question 29

How does parathyroid hormone regulate calcium?

Answer 29

-Calcium receptors on parathyroid gland secrete a normal concentration of parathyroid hormone when calcium levels are normal, increased levels when calcium is low, and decreased levels when calcium is high.

Question 30

What three organs does parathyroid hormone impact?

Answer 30

- Bone - Kidneys - GI Tract

Question 31

How does PTH impact bone?

Answer 31

- PTH binds to osteoblasts, causing differentiation and activity of osteoclasts. - Causes increased osteoclast activity, which breaks down bone and increased blood /plasma levels of calcium AND phosphate.

Question 32

How does PTH impact the kidneys?

Answer 32

- Increases calcium reabsorption and decreases calcium secretion - Decreased phosphate reabsorption and increased phosphate excretion

Question 33

How does PTH impact the GI Tract?

Answer 33

- The GI tract actively regulates calcium and iron absorption. - PTH does not impact the small intestine actively, but rather promotes the synthesis of ACTIVE VITAMIN D to increase calcium absorption.

Question 34

How does calcitonin impact calcium?

Answer 34

- Calcitonin is secreted by parafollicular cells of the thyroid gland - High plasma calcium concentration (indicative of bone breakdown) is the stimulus for release - Calcitonin inibits release of calcium from bone. - Reduces the reabsorption of calcium and phosphate at the kidneys. - Less impactful than PTH

Question 35

Where is vitamin D found?

Answer 35

Inactive form found in dietary sources such as fish liver oils, fatty fish, eggs, leafy greens.

Question 36

How is vitamin D activated?

Answer 36

Hydroxylation at the liver and the nat the kidneys.

Question 37

What is the action of vitamin D?

Answer 37

- Acts on epithelial cells in the cut as a steroid hormone. - Alters gene transcription in cells, stimulating the cells to produce stuff that makes cells better at absorbing calcium across GI epithelium. - Enhances reabsorption of calcium at kidneys - Needed for normal calcification of bone matrix

Question 38

What are the effects of disturbances in calcium balance?

Answer 38

-Alters smooth and skeletal muscle contractions.

Question 39

What are the effects of hypocalcemia?

Answer 39

-Increased neuronal excitement and neuromuscular excitability - Seizures - Fatigue - Anxiety. - Chronic skin problems - Paresthesia of hands and feet. - Perioral tingling - Laryngospasm, bronchospasm, wheezing. - Carpopedal spasm.

Question 40

What is chvostek's sign?

Answer 40

Result of hypocalcemia, tapping over the facial nerve anterior to the ear elicits twitch in ipsilateral face muscles.

Question 41

What is trousseaus sign?

Answer 41

-Inflation of BP Cuff elects carpal spasm.

Question 42

What are the signs of hypercalcemia?

Answer 42

- Depressed Neuronal excitability - Can be acute and cause GI problems (anorexia, nausea), renal issues (polyuria, polydipsia) , neuromuscular issues (depression, confusion/stupor, coma), or cardiac issues (bradycardia, first degree AV block)

Question 43

What are the chronic signs of hypercalcemia?

Answer 43

- Constipation, pancreatitis, - Kidney stones - Generalized weakness