AAMC Biology Test Bank #70-120
Parathyroid Hormone - ✅✅ -- actos on bone tissue to encourage
formation and activity of osteoclasts
- impairs new bone formation
Osteoclasts -✅✅-- breakdown bone cells
Vitamin D - ✅✅-- in activated form, functions like a hormone
- nonpolar; acts on small intestine to stimulate absorption of calcium and
bone tissue
- enhances effect of parathyroid hormone
- obtained from diet or action of UV light on skin
Calcitonin -✅✅-- decreases bone resorption
- small effect
Vitamin C - ✅✅ -- required for synthesis of bone matrix
- needed for bone formation
Rickets -✅✅ -- causes inadequate mineralization of new bone matrix
- low mineral:organic matter ratio
- abnormality causes distortion of bones (bowed legs)
- caused by insufficient vitamin D activity (no absorption of calcium to
strengthen bones)
Osteoperosis - ✅✅ -- affects mostly postmenopausal women
- more bone resorption than bone formation
- reduction of bone mass BUT normal ratio of mineral:organic matter
= probably due to lack of activity
Which could produce rickets?
I. metabolic deficiency of parathyroid hormone
✅✅
II. impairment of conversion of vitamin D to its active form
III. inability of active form of vitamin D to act on target tissue - -II and
III: rickets is caused by insufficient vitamin D activity
- this reduces ability of body to absorb calcium from the small intestine
- to maintain calcium in blood plasma, parathyroid hormone would promote
breakdown of bone tissue and cause bones to weaken
- if there were a metabolic deficiency of PTH hormone, the body wouldn't
break down bone tissue (so not option I) -> causes higher than normal ratio
of mineral to organic matter in bones
- if body couldn't convert Vitamin D to its active form, or if vitamin D were
unable to act on its target tissue, vitamin D activity would be impaired
(option II and III)
Why do calcium supplements often include vitamin D?
, a. vitamin D is needed to prevent rickets
b. activated form of vitamin D stimulates absorption of calcium into blood
c. activated form of vitamin D enhances action of calcitonin
✅✅
d. activated form of vitamin D enhances uptake of calcium by bone tissue -
-B: activated form of vitamin D stimulates absorption of calcium into
blood
- vitamin D acts on small intestine to stimulate calcium reabsorption
- inclusion of vitamin D in calcium supplements ensures vitamin D is
present in the body to promote the absorption of calcium
A low level of calcium in the plasma will trigger an increase of
I. osteoclast activity
✅✅
II. parathyroid hormone
III. vitamin C - -I and II
- if calcium in blood plasma is low, body mobilizes stores of calcium from
the bones via parathyroid hormone
- parathyroid hormone increases number of osteoclasts, which break down
bone cells
- increase in both PTH hormone and osteoclast activity would increase
level of calcium in the blood
- NOT option III because vitamin C promotes bone formation, a process
that lowers calcium level in the plasma
Under what condition would the level of calcitonin tend to increase?
a. when there's a dietary deficiency of calcium
b. when there's a dietary deficiency of vitamin D
✅✅
c. when the level of calcium in the plasma is high
d. when the level of parathyroid hormone is too low - -C: calcitonin
prevents bone resorption, which occurs when the level of calcium in the
plasma is low (more Ca2+ needed to be released!)
- resorption is not needed when calcium levels are high
- resorption would be reduced by calcitonin if there's high calcium levels in
the plasma
What would be the result of complete removal of parathyroid glands?
a. severe neural and muscular problems due to deficiency of calcium in the
plasma
b. increase in calcitonin production to compensate for calcium deficiency in
the plasma
c. drastic change in the ratio of mineral to matrix tissue in bones
✅✅
d. calcification of some organs due to accumulation of calcium in the
plasma - -a: removing PTH gland would lead to hypocalcemia (low
blood calcium) due to now PTH hormone
- this would cause increased neuromuscular excitability because the
change in membrane potential is kept in balance with extracellular calcium
- person would eventually die from severe respiratory muscle spasms
Parathyroid Hormone - ✅✅ -- actos on bone tissue to encourage
formation and activity of osteoclasts
- impairs new bone formation
Osteoclasts -✅✅-- breakdown bone cells
Vitamin D - ✅✅-- in activated form, functions like a hormone
- nonpolar; acts on small intestine to stimulate absorption of calcium and
bone tissue
- enhances effect of parathyroid hormone
- obtained from diet or action of UV light on skin
Calcitonin -✅✅-- decreases bone resorption
- small effect
Vitamin C - ✅✅ -- required for synthesis of bone matrix
- needed for bone formation
Rickets -✅✅ -- causes inadequate mineralization of new bone matrix
- low mineral:organic matter ratio
- abnormality causes distortion of bones (bowed legs)
- caused by insufficient vitamin D activity (no absorption of calcium to
strengthen bones)
Osteoperosis - ✅✅ -- affects mostly postmenopausal women
- more bone resorption than bone formation
- reduction of bone mass BUT normal ratio of mineral:organic matter
= probably due to lack of activity
Which could produce rickets?
I. metabolic deficiency of parathyroid hormone
✅✅
II. impairment of conversion of vitamin D to its active form
III. inability of active form of vitamin D to act on target tissue - -II and
III: rickets is caused by insufficient vitamin D activity
- this reduces ability of body to absorb calcium from the small intestine
- to maintain calcium in blood plasma, parathyroid hormone would promote
breakdown of bone tissue and cause bones to weaken
- if there were a metabolic deficiency of PTH hormone, the body wouldn't
break down bone tissue (so not option I) -> causes higher than normal ratio
of mineral to organic matter in bones
- if body couldn't convert Vitamin D to its active form, or if vitamin D were
unable to act on its target tissue, vitamin D activity would be impaired
(option II and III)
Why do calcium supplements often include vitamin D?
, a. vitamin D is needed to prevent rickets
b. activated form of vitamin D stimulates absorption of calcium into blood
c. activated form of vitamin D enhances action of calcitonin
✅✅
d. activated form of vitamin D enhances uptake of calcium by bone tissue -
-B: activated form of vitamin D stimulates absorption of calcium into
blood
- vitamin D acts on small intestine to stimulate calcium reabsorption
- inclusion of vitamin D in calcium supplements ensures vitamin D is
present in the body to promote the absorption of calcium
A low level of calcium in the plasma will trigger an increase of
I. osteoclast activity
✅✅
II. parathyroid hormone
III. vitamin C - -I and II
- if calcium in blood plasma is low, body mobilizes stores of calcium from
the bones via parathyroid hormone
- parathyroid hormone increases number of osteoclasts, which break down
bone cells
- increase in both PTH hormone and osteoclast activity would increase
level of calcium in the blood
- NOT option III because vitamin C promotes bone formation, a process
that lowers calcium level in the plasma
Under what condition would the level of calcitonin tend to increase?
a. when there's a dietary deficiency of calcium
b. when there's a dietary deficiency of vitamin D
✅✅
c. when the level of calcium in the plasma is high
d. when the level of parathyroid hormone is too low - -C: calcitonin
prevents bone resorption, which occurs when the level of calcium in the
plasma is low (more Ca2+ needed to be released!)
- resorption is not needed when calcium levels are high
- resorption would be reduced by calcitonin if there's high calcium levels in
the plasma
What would be the result of complete removal of parathyroid glands?
a. severe neural and muscular problems due to deficiency of calcium in the
plasma
b. increase in calcitonin production to compensate for calcium deficiency in
the plasma
c. drastic change in the ratio of mineral to matrix tissue in bones
✅✅
d. calcification of some organs due to accumulation of calcium in the
plasma - -a: removing PTH gland would lead to hypocalcemia (low
blood calcium) due to now PTH hormone
- this would cause increased neuromuscular excitability because the
change in membrane potential is kept in balance with extracellular calcium
- person would eventually die from severe respiratory muscle spasms
