05a: Calcium and Parathyroid Flashcards by Nuna H

List the three hormones primarily involved in Ca metabolism regulation

PTH
1,25-DHCC (Dihydroxycholecalciferol)
Calcitonin

How well did you know this?

Not at all

Perfectly

T/F: 1,25-DHCC is a steroid hormone.

True

How well did you know this?

Not at all

Perfectly

1,25-DHCC is derived from (X) that primarily functions to (increase/decrease):

X = vitamin D
Increase;
Ca absorption from intestine

How well did you know this?

Not at all

Perfectly

A (high/low) Ca concentration increases (X) cell excitability. This leads to the condition (Y) tetany.

Low;
X = nerve and muscle
Y = hypocalcemic

How well did you know this?

Not at all

Perfectly

A (high/low) Ca concentration can cause cardiac arrhythmia and (over-excites/depresses) neuromuscular excitability

High;

Depresses

How well did you know this?

Not at all

Perfectly

(X)% of Ca is in the skeleton. Normal plasma calcium concentration is:

X = 99

10 mg/dL

How well did you know this?

Not at all

Perfectly

(X)%, of plasma Ca is bound to plasma proteins. The rest is ultrafiltrable, which means it’s either (Y) or (Z).

X = 40
Y = complexed with anions (PO4)
Z = free, ionized

How well did you know this?

Not at all

Perfectly

T/F: Ca that’s complexed with anions (such as PO4) is the biologically active form.

False - free, ionized Ca is

How well did you know this?

Not at all

Perfectly

T/F: Person taking in 1.0 g Ca means that 0.9 g of it will be absorbed by gut.

False - only 0.5 g

How well did you know this?

Not at all

Perfectly

T/F: Person taking in 1.0 g Ca means that net gain is about 0.2 g.

True - 0.175 g

How well did you know this?

Not at all

Perfectly

Net gain of Ca in body is offset by (gain/loss) of (X) in (Y) organ/system. This maintains Ca balance.

(Equal) loss;
X = Ca
Y = kidney

How well did you know this?

Not at all

Perfectly

List the main sites of important Ca regulation.

Bones
Kidney
GI

How well did you know this?

Not at all

Perfectly

T/F: Most of the Ca in bones is in a rapidly exchangeable pool.

False - only 500 of 25,000 mmol are

How well did you know this?

Not at all

Perfectly

(X)% of Ca is reabosrbed in kidney.

X = 98

How well did you know this?

Not at all

Perfectly

Ca reabsorption in GI tract is via (X) channel/transporter/ATPas.

X = Ca-dependent ATPase

How well did you know this?

Not at all

Perfectly

Bone is a(n) (X) matrix, impregnated with (Y).

X = collagenous
Y = hydroxyapatites (Ca phosphates)

How well did you know this?

Not at all

Perfectly

Bone is both (cellular/acellular) and (well/poorly)-vascularized.

Cellular; well-vascularized

How well did you know this?

Not at all

Perfectly

The outer layer of (X) bone is (more/less) metabolically active than the inner layer of (Y) bone.

X = compact
Less
Y = spongy/trabecular

How well did you know this?

Not at all

Perfectly

(X) cells form bone by secreting (Y).

X = osteoblasts
Y = collagen

How well did you know this?

Not at all

Perfectly

(X) cells are surrounded by bone matrix and send long processes that ramify throughout bone. They formed from (Y) cells.

X = osteocytes;
Y = osteoblasts (differentiation)

How well did you know this?

Not at all

Perfectly

The “bone membrane” separates (X) and (Y) compartments.

X = mineralized bone matrix
Y = ECF (and rest of body)

How well did you know this?

Not at all

Perfectly

Bone membrane: what are the components?

Endosteum
Periosteum
Osteocytes

How well did you know this?

Not at all

Perfectly

Bone resorption is carried out by (X) cells, derived from (Y) cells.

X = osteoclasts
Y = monocyte precursors

How well did you know this?

Not at all

Perfectly

Osteoclasts secrete (X) that dissolve (Y) from underlying bone.

X = acids and proteases
Y = mineral crystals and protein matrix

How well did you know this?

Not at all

Perfectly

T/F: Osteoclasts and osteoblasts continually communicate with each other via endocrine factors/hormones.

False - paracrine factors

Bone: The cytoplasmic processes of (X) cells extend deep into bone and connect to those of (Y) cells via (gap/tight) junctions.

``` X = osteoblasts; Y = osteocytes ``` Gap

UV light acts on (X) compound in skin to produce vitamin D3. Where is vitamin D3 taken?

X = 7-dehydrocholesterol Liver

Vit D synthesis: liver modifies vitamin D3 via (X), forming (Y).

``` X = hydroxylation Y = 25OH-D3 ```

The major biologically active form of vitamin D is (X). The final step in its formation occurs in (Y).

``` X = 1,25-(OH)2-D3 Y = kidney (proximal tubule) ```

Vit D synthesis: Instead of (X) modification, the kidney could modify 25OH-D3 via (Y), to promote degradation.

``` X = hydroxylation at 1-position Y = hydroxylation at 24-position ```

List the overall, general goals/functions of 1,25-(OH)2-D3.

Provide Ca and phosphate to ECF for bone mineralization

Vit D deficiency in children causes (X), and in adults causes (Y).

``` X = rickets Y = osteomalacia ```

1,25-(OH)2-D3 acts primarily by binding (X) receptor, which (increases/decreases) production of (Y).

X = nuclear (VDR, Vitamin D Receptor) Increases; Y = CaBP; and Ca and P transporters

T/F: Vitamin D Receptor is only present in Ca-regulating tissues.

False - wide variety of other tissues as well

One method in treating psoriasis uses the mechanism of 1,25-(OH)2-D3 (stimulation/inhibition) of (X) process in cells containing (Y).

Inhibition X = cell proliferation Y = VDR

1,25-(OH)2-D3 (increases/decreases) Ca absorption in GI tract by inducing (increase/decrease):

``` Increases; Increase; 1. ECaC (epithelial channels) 2. Calbindin 3. Ca/Na exchangers; Ca pumps ```

T/F: 1,25-(OH)2-D3 directly promotes Ca deposition in bone.

False - acts indirectly by increasing plasma Ca and P absorption (their supersaturating levels will promote mineralization)

T/F: 1,25-(OH)2-D3 acts indirectly to promote osteoclastic activity and bone resorption.

True

1,25-(OH)2-D3 acts in synergy with (X), either one being far less effective in (Y) function in absence of the other.

``` X = PTH Y = mobilizing Ca stores ```

1,25-(OH)2-D3 acts on proximal nephron to (increase/decrease) (X).

Increase; | X = Na-dependent phosphate transporter (thus, increases phosphate reuptake)

1,25-(OH)2-D3 acts on distal nephron to (increase/decrease) (X).

Increase; | X = ECaC and Calbindin (thus, Ca reabsorption)

High plasma concentrations of (X) inhibit 1,25-(OH)2-D3 synthesis (neg-feedback). Specifically, they inhibit (Y).

``` X = Ca and P; and 1,25-(OH)2-D3 Y = 1a-hydroxylase ```

Synthesis of 1a-hydroxylase enzyme is prompted by (high/low) levels of PTH and (high/low) levels of P.

High; low

1,25-(OH)2-D3 feedback/regulation: (X) stimulates (Y) enzyme to produce (Z), leading to degradative pathway.

``` X = 1,25-(OH)2-D3 Y = 24-hydroxylase Z = 24,25-(OH)2-D3 ```

(X) cells in the parathyroid make PTH. The hormone is synthesized as (Y) and undergoes (Z) modification to become "mature" PTH.

``` X = chief/principal Y = pre-pro-hormone Z = cleavage ```

T/F: Half-life of intact PTH is about 30 min.

False - 5 min

T/F: PTH is rapidly cleaved/degraded in peripheral tissues.

False - in Kupfer cells in liver

Primary signal that stimulates PTH secretion is (X).

X = low circulating Ca levels

Ca Sensing Receptor (CaSR) is found in (X) cells. It functions to:

X = parathyroid chief Monitor extracellular Ca levels

By default, PTH is (secreted/stored) in/from (X) cells until (Y).

Secreted; X = chief Y = high Ca levels bind CaSR, which activates pathway to inhibit PTH secretion

T/F: Like 1,25-(OH)2-D3, PTH acts to increase serum Ca and PO4.

False - increase serum Ca, but decrease serum PO4

PTH acts by activating (X) receptor, leading to (production/cleavage) of (Y).

X = G-protein Production X = cAMP and IP3

List the 5 general actions of PTH.

1. Increase bone resoprtion/Ca mobilization 2. Increase Ca reabsorption (kidney) 3. Decrease plasma PO4 4. Increase 1,25-(OH)2-D3 production 5. Increase osteoclast and osteoblast formation

PTH will (increase/decrease) serum PO4 via which mechanism?

Decrease; Increase urine PO4 excretion (decreases proximal tubule reabsorption)

T/F: PTH acts directly on intestine to increase Ca reabsorption.

False - indirect by stimulating 1,25-(OH)2-D3 formation

Bone: (X) compounds stimulate the expression of RANKL on surface of (Y) cells. This interacts with (Z).

``` X = PTH and 1,25-(OH)2-D3 Y = osteoblasts Z = RANK (receptor) on (pre)osteoclasts ```

T/F: Increasing RANKL expression on osteoblasts will decrease bone resorption.

False - RANKL activates osteoclasts (via binding RANK receptor)

(X) hormones are important regulators of bone resorption. They enhance (Y) production, which acts as decoy by binding/blocking (RANK/RANKL).

``` X = estrogens Y = Osteoprotegerin (OPG) ``` RANKL (prevents RANK activation)

T/F: PTH has a short-term anabolic effect, by increasing osteoblast activity.

True (but limited)

Pulsatile injections of (X) is used clinically to treat osteoporosis. The pulsatile nature functions to sidestep (Y).

``` X = PTH Y = osteoblast apoptosis (via prolonged PTH stimulation) ```

Specific action of PTH on proximal nephron: (increase/decrease) (X) activity, which (increases/decreases) (Y) formation and excretion.

Increase; X = AC Increases; Y = cAMP (thus, phosphate)

(High/low) urinary levels of (X) is often used as an index of excess PTH secretion.

High; | X = cAMP

Severe (increases/decreases) in Mg levels inhibit PTH production.

Both!

PTH regulation: (X) acts directly on parathyroid to decrease PTH secretion.

X = Ca

PTH regulation: (X) acts directly on parathyroid to decrease PTH precursor production.

X = 1,25-(OH)2-D3

Chronic kidney disease likely leads to (hyper/hypo)-parathyroidism. Why?

Hyperparathyroidism (due to low 1,25-(OH)2-D3 formation and low Ca reabsorption)

Parathyroidectomy will lead to (increase/decrease) in plasma concentrations of (X).

Increase (X = PO4); Decrease (X = Ca)

T/F: PTH is essential for life.

True

You'd expect to see Ca-containing stones in PTH (deficiency/excess).

Excess

PTH-related peptide (PTHrP) is found in plasma of some patients. What are its actions? Serum PTH levels would (increase/decrease) in presence PTHrP.

All same physiological actions of PTH; Decrease (result of hypercalcemia)

Calcitonin is produced by (X) cells in presence of (high/low) levels of (Y).

X = parafollicular cells (in thyroid) High; Y = Ca

Calcitonin (increases/decreases) Ca permeability in osteoclasts/osteoblasts, thus (increasing/decreasing) plasma Ca and PO4.

Decreases; | decreasing

The biological activity of PTH is dictated mainly by the (X) portion of the molecule.

X = N-terminal

The main circulating form of vitamin D3 is (X). And most is (bound/unbound).

X = 25-hydroxyvitamin D3 Bound (to Vit DBP)

T/F: High PTH levels may lead to osteomalacia.

False - PTH stimulates 1a-hydroxylase

High plasma FGF23 would (stimulate/inhibit) 1a-hydroxylase and (increases/decreases) chance of osteomalacia.

Inhibit; | increases