Flashcards in Skeletal System Deck (43):
What do osteoprogenitor cells do?
Found in endosteal and periosteal membranes, differentiate into osteoblasts.
What do osteoblasts do?
Modified fibroblasts that synthesize and secrete organic matrix, calcify matrix.
What do osteocytes do?
Mature bone cells that transfer minerals from interior to growth surfaces.
What do osteoclasts do?
Form from monocytes, act to resorp bone and release Ca+2 and phosphate
What is bone's organic matrix comprised of?
-Type 1 collagen
What makes up the inorganic component of bone?
-calcium carbonate (secreted by osteoblasts)
What is the functional unit of bone?
What is the makeup of an osteon?
-Concentric lamellae of osteocytes (which sit in lacunae filled with ECF) connected by cannaliculi
How do nutrients and wastes get into and out of osteocytes?
-Cannaliculi transfer nutrients and wastes between blood vessels and osteocytes
-Haversian canals and Volkmanns canals
What is the difference between haversian canals and volkmann's canals?
-Haversian canals run the length of long bones whereas volkmann's canals run across them.
-Volkmann's canals join Haversian canals.
Where is cortical bone typically found?
Outer surface of bone
Where is spongey (trabeccular/canellous) bone usually found?
What are the five steps of bone formation?
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
What vitamins are needed for bone growth?
What hormones are needed for bone growth?
-Growth Hormone (leads to IGF-1 secretion)
Where does Membranous ossification occur?
How does membranous ossification occur?
-mesenchymal cells turn right into bone: osteoprogenitors->osteoblasts->bone
Tell the bone remodeling story
-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
How much of the body's calcium is stored in the bones?
T/F Calcium does not normally move between bone and plasma
FALSE. In a healthy body, calcium moves freely between plasma and bone.
T/F Calcium is the most abundant mineral in the body
T/F Maybe 1% of calcium is free floating in plasma and blood
How much intracellular calcium is free?
How much intracellular calcium is bound to albumin?
What does free calcium play a role in and how?
Acts as a second messenger important in...
-Nerve signal transmission
What hormones are involved with calcium homeostasis?
What systems are involved in calcium homeostasis?
How is phosphate homeostasis related to calcium homeostasis?
-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.)
How does parathyroid hormone regulate calcium?
-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.
What three organs does parathyroid hormone impact?
How does PTH impact bone?
-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.
How does PTH impact the kidneys?
-Increases calcium reabsorption and decreases calcium secretion
-Decreased phosphate reabsorption and increased phosphate excretion
How does PTH impact the GI Tract?
-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.
How does calcitonin impact calcium?
-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
Where is vitamin D found?
Inactive form found in dietary sources such as fish liver oils, fatty fish, eggs, leafy greens.
How is vitamin D activated?
Hydroxylation at the liver and the nat the kidneys.
What is the action of vitamin D?
-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
What are the effects of disturbances in calcium balance?
-Alters smooth and skeletal muscle contractions.
What are the effects of hypocalcemia?
-Increased neuronal excitement and neuromuscular excitability
-Chronic skin problems
-Paresthesia of hands and feet.
-Laryngospasm, bronchospasm, wheezing.
What is chvostek's sign?
Result of hypocalcemia, tapping over the facial nerve anterior to the ear elicits twitch in ipsilateral face muscles.
What is trousseaus sign?
-Inflation of BP Cuff elects carpal spasm.
What are the signs of hypercalcemia?
-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)