Keef: Parathyroid Gland Flashcards
Total body content of Ca+
1,300g
Total body content of Phosphorus
600g
Where is most calcium (99%) and phosphate (86%) located?
in bones and teeth
Is there more calcium INSIDE cells or OUTSIDE cells?
More inside cells (0.9%)
Is there more phosphorus INSIDE cells or OUTSIDE cells?
More inside cells (14%)
Calcium variation in plasma is about (blank)% per day. Most calcium is in what form?
1-2%; ionized form
Phosphorus variation in plasma is about (blank)% per day. Most phosphorus is in what form?
50-150%; HPO4(2-)
We ingest about 1000mg of calcium per day. How much of this is reabsorbed? How much of this is excreted in urine?
30% absorbed
1% excreted
We ingest about 900mg of phosphate per day. How much of this is reabsorbed? How much of this is excreted in urine?
60% reabsorbed
10% excreted
Calcium enters epithelial cells of duodenum and jejunum down its electrochemical gradient. It requires (blank) channels.
TRP Ca+ channels
Once inside the intestinal cells, calcium is bound by (blank) so that intracellular [Ca+] does not increase too much.
calbindin
To get out of the intestinal cells and into the interstitial space, calcium undergoes primary active transport via a (blank) or secondary active transport via a (blank).
Ca+/ATPase; Ca+/Na+ exchanger
In the duodenum and jejunum, is calcium absorbed actively or passively?
In the ileum, is absorption active or passive?
active; passive
In the duodenum, jejunum, and ileum, Pi gets into intestinal cells via ACTIVE transport. What does it require? Once inside the intestinal cells, it can travel down its gradient into the interstitial space.
Na+
In the kidney, 70% of Ca+ is reabsorbed in the proximal tubule. Is this paracellular or transcellular? Throughout the rest of the nephron, is reabsorption paracellular or transcellular?
paracellular; transcellular
How much of Ca+ is excreted from nephron?
1%
What effect does PTH have on calcium reabsorption?
PTH stimulates Ca+ reabsorption via the G-protein GS, which stimulates cAMP, activates PKA, and enhances transcellular movement of Ca+ by increasing TRP channels
Ca+ enters cells in the distal nephron by moving down its gradient through TRP channels and carrier proteins. Once in the cell, it binds to (blank). To get out of the cell and into the blood, it can exit through Ca+/ATPase or Ca+/Na+ exchanger.
Calbindin
In the proximal tubule, about 80% of phosphate is reabsorbed. Is this paracellular or transcellular?
transcellular
How much of phosphate is excreted from the nephron?
10%
What effect does PTH have on phosphate reabsorption in the nephron?
It inhibits phosphate reabsorption
Phosphate is reabsorbed into intestinal cells along with (blank). It exits out into the interstitial space/blood stream via anion exchange.
Na+
What two things make up mature compact bones?
- osteoid (collagen)
2. hydroxyapatite crystals
Bone remodeling is an adaptive process.
Growth > resorption until what age?
Resorption > growth after what age?
20-30 years
40+
Bone disorder: increased osteoid + mineral
osteopetrosis
Bone disorder: “soft bones,” demineralization, rickets in children
osteomalacia
Bone disorder: decreased osteoid + mineral
osteoporosis
Drugs used for treatment of osteoporosis:
3 drugs decrease osteoclast bone resorption
1 drug activates bone formation
bisphosphates, calcitonin, estrogen
PTH
Rapid, non-hormonal regulation of plasma calcium occurs in these two ways
- protein bound calcium
2. exchange with bone
Long term, hormonal regulation of plasma calcium occurs via these three ways
- PTH
- calcitriol (active Vit D)
- calcitonin
Cells within the parathyroid gland with Ca+ sensing receptors that release parathyroid hormone
chief cells
When extracellular Ca+ is high, what happens to PTH release?
decreased PTH release
When extracellular Ca+ is low, what happens to PTH release?
increased PTH release
Released from C cells of the thyroid gland in response to increased serum Ca+ levels. Released in opposition to PTH.
calcitonin
Is calcitonin essential for regulation of serum calcium levels?
No; PTH much more important
Calcitonin and parathyroid hormone have (blank) effects on bone resorption
opposing
If [Ca+]o is above normal, thyroid releases (blank). What does this do to osteoclast activity?
calcitonin; decreases osteoclast activity
If [Ca+]o is below normal, thyroid releases (blank). What does this do to osteoclast activity?
PTH; increases osteoclast activity
In the kidney, 25-hydroxycholecalcigerol is converted to (blank), which is the active form of Vitamin D. This is why patients with kidney failure must supplement with Vit D.
calcitriol
What is the enzyme that takes Vit D to its active form? What two things can stimulate this enzymatic step?
25-hydroxyvitamin D3 1 alpha-hydroxylase;
- release of PTH
- decreased plasma [Pi]
What is the DIRECT effect of PTH on Pi excretion, which overrides the effect of Vit D on Pi excretion?
PTH INCREASES Pi EXCRETION
What effect does calcitriol (Vit D) have on Ca+ and Pi in bone? In the kidneys? In the intestines?
In bone: increases Ca+ and Pi mobilization
In kidneys: decreases Ca+ and Pi excretion
In intestines: increases Ca+ and Pi absorption
(blank) is essential for life. Death by hypocalcemic tetany can occur if [Ca]o falls below 2.1 mM/L. What are some of the symptoms of hypocalcemic tetany?
PTH; CATS go numb - convulsions, arrhythmias, tetany, and numbness
What does hypoparathyroidism do to the following? Calcium Phosphate PTH Alkaline phosphate
Calcium: decreased
Phosphate: increased
PTH: decreased
Alkaline phosphate: no change
What does pseudohypoparathyroidism do to the following? Calcium Phosphate PTH Alkaline phosphate
Calcium: decrease
Phosphate: increase
PTH: increase
Alkaline phosphate: no change
What does osteomalacia/rickets do to the following? Calcium Phosphate PTH Alkaline phosphate
Calcium: decrease
Phosphate: decrease
PTH: increase
Alkaline phosphate: increase
What does chronic renal failure do to the following? Calcium Phosphate PTH Alkaline phosphate
Calcium: decrease
Phosphate: increase
PTH: increase
Alkaline phosphate: increase
What does Vit D intoxication do to the following? Calcium Phosphate PTH Calcium in urine
Calcium: increase
Phosphate: increase
PTH: decrease
Calcium in urine: INCREASE
What does primary hyperparathyroidism do to the following? Calcium Phosphate PTH Calcium in urine
Calcium: increase
Phosphate: decrease
PTH: increase
Calcium in urine: increase
Most common cause of hypoparathyroidism? Treatment?
injury during head and neck surgery
restore/maintain Ca+ levels, Vit D supplements
In hypoparathyroidism, there is LESS release of PTH from parathyroid glands. Main effect?
[Ca+] decreased
[Pi] increased
Lack of response to PTH; most commonly due to a genetic defect in the PTH pathway.
pseudohypoparathyroidism
Main effect of pseudohypoparathyroidism?
[Ca+] decreased
[Pi] increased
[PTH] high, but not being “sensed”
Softening of the bone because of a loss of calcium in the bone material; can be caused by
inadequate vitamin D intake and/or disorders that interfere with the absorption of Ca+ from intestine
osteomalacia/Rickets
PTH stimulates osteoblast alkaline phosphatase activity in blood and is therefore an indicator of enhanced (blank)
bone remodeling
Main effect of osteomalacia/rickets?
[Ca+] and [Pi] are low because there is impaired reabsorption or not enough Vit D to stimulate reabsorption. [AP] levels will be high, because osteoclasts are stimulated to retrieve Ca+ from bone
Loss of kidney function and 1alpha-hydroxylase (forms active Vit D) activity
chronic renal failure
Main effect of renal failure?
No Vit D –> minimal Ca+ reabsorption.
Plasma phosphate will increase, because you can’t excrete it effectively.
Metabolic acidosis as a result of kidney failure and increased PTH will both increase bone breakdown in an attempt to increase plasma Ca+. So [AP] high.
JUST AWFUL.
Too much Vitamin D
Too much Ca+ reabsorption, so PTH will decrease.
This will lead to higher plasma phosphate levels. Calcium in urine!!!
Primary hyperparathyroidism
Too much PTH, causes too much Ca+ reabsorption. Increased Pi excretion. Loss of Ca+ in urine.
Ca+ sensing receptor in chief cells of parathyroid gland work mainly by what mechanism?
Ca+ sensing receptors in the kidney work mainly by what mechanism?
Inhibit PTH secretion
Inhibit reabsorption of Ca+
