Parathyroid Disoders - Exam 3 Flashcards
Where are the parathyroid glands located? How many? Describe their appearance.
posterior thyroid gland
4 glands located on the posterior thyroid gland
Size -grain of rice to pea-sized
Shape - smooth surface, oval or bean-shaped
Normally not visible or palpable on neck exam
Parathyroid Hormone (PTH), which plays a key role in regulating _____ level. ____: synthesize and release PTH. ______ are less abundant, larger, acidophilic, nonfunctional
extracellular calcium
Principal (chief) cells
Oxyphil cells
Amounts of _____ and ____ increases with age
adipocyte deposits
oxyphil cells
Describe the textures of the thyroid and parathyroid glands
thryoid is bumpy
parathyroid is smooth
What is the net effect of PTH? ______ in the serum interacts with _____ on the surface of cells in the parathyroid glands and kidney
increase serum calcium
Ionized Calcium (aka free calcium, NOT bound to albumin)
calcium-sensing receptors (CaSR)
What do high calcium levels stimulate? What about low calcium levels?
stimulates CaSR receptors → PTH suppression
CaSR receptors are not stimulated → PTH release
What is PTH’s response to low calcium? minutes? hours? days?
minutes: release of preformed PTH
hours: PTH mRNA expression → increased PTH synthesis
days: parathyroid cell replication → increased parathyroid gland mass
What are the 4 functions of calcium?
-maintain skeletal strength
-regulates contraction of muscle
-cellular signaling (especially neurons)
-secretion of hormones and enzymes
Where are the 3 areas that calcium is stored?
1: bone as hydroxyapatite
#2: intracellular fluid
#3: Extracellular fluid
Bone: majority (99%) of the calcium in bone is stored as _____
hydroxyapatite
What is the job of calcium that is stored in the intracellular fluid?
Intracellularsignaling (second messengers), enzyme activation, muscle contraction
What is important to note about the calcium that is stored in extracellular fluid?
50% of the calcium is bound to proteins and only has minimal fluctuation
50% is unbound and fluctuates freely
______ is serum calcium that is not bound to proteins. How is serum calcium balance maintained?
Ionized calcium
by release of calcium from intracellular storage or influx from extracellular fluid
What 3 organs are responsible for maintaining the narrow balance of EXTRAcellular calcium and phosphorus? What are the responsibilities of each?
intestines: absorb dietary Ca
kidneys: reabsorb or excrete Ca as needed
skeletal system: reservoir for Ca, releases and reserving as needed
What is the function of phosphorus?
Helps form several major body components: skeleton (its part of hydroxyapatite), cell membranes, DNA/RNA and ATP
balance of several vitamins and minerals
pH regulation and enzyme activation
Most phosphorus in the body is as the ______. Name 3 places phosphorus is stored?
phosphate ion, PO4
Bone - majority (85%) in bone as hydroxyapatite
Intracellular/Soft Tissues - (14%) of overall body phosphorus. Phosphate ion, several parts of cellular structures and enzymes.
Extracellular Fluid - Blood, extracellular matrix
1% of overall body phosphorus, mainly as the ion PO4
_____ enhances the intestines ability to absorb calcium and phosphorus
vitamin D
In a normal healthy person, how are calcium and phosphorus related? What 3 major hormones maintain this balance?
inverse relationship, when calcium increases phosphorus decreases
PTH
Vit D (Calcitriol)
Calcitonin
What are the effects of PTH on bone? on kidney?
Bone:
Stimulates release of Ca2+
Stimulates release of PO4-
Kidney:
Increased Ca2+ reabsorption
Increased PO4- excretion
Stimulates production of calcitriol (1,25 Vitamin D)
How does PTH effect calcitriol?
Converted from inactive 25-OH Vitamin D by kidneys under the influence of PTH to its metabolically active form
What are the effects of calcitriol on the intestines?
Increased calcium absorption
Increased phosphorus absorption
What are the effects of calcitriol on bone?
Enhances effects of PTH on bone to promote more calcium release
Where does calcitonin originate? When is it released? What is the effect of calcitonin on the body?
calcitonin-secreting cells (C cells) in the thyroid
Calcitonin is released by the thyroid when C-cells become overstimulated by elevated calcium levels
Works in opposition to PTH
Suppresses renal reabsorption of Ca2+ → increased Ca2+ excretion
Inhibits osteoclasts in bone → decreased release and increased storage of Ca2+
What does the total serum calcium measure? What is normal? Which is the metabolically active form?
protein bound Ca plus free Ca
8.5-10.5
40-50% is protein bound to albumin
ionized calcium is free and considered metabolically active 4.4-5.4