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CC 2 LEC > Calcium HORMONES > Flashcards

Calcium HORMONES Flashcards

1
Q

Parathyroid Hormone
s Secreted by the____ of the____

A

chief cells

parathyroid glands

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2
Q

• Rapid response to reduced calcium (in minutes)

A

PTH

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3
Q

PTH

Polypeptide:

Operates in tissues via cAMP
secondary messenger

A

84 amino acid residues

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4
Q

Effects of PTH
Bone

First phase:_______
Second phase:______

A

osteolysis mediated by osteoblasts and osteocytes (calcium pump)

activation and formation of osteoclasts for bone resorption

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5
Q

EFFECTS OF PTH

Kidney

A

Increased reabsorption of calcium in the thick ascending nephron loop and distal convoluted tubule

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6
Q

EFFECTS of PTH

INTESTINE

A

Increased calcium absorption aided by 1, 25-dihydroxycholecalciferol (active metabolite of vitamin D)

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7
Q

Regulation of PTH
Calcium-Sensing Receptor

High plasma calcium level
• Activation of______

Increased levels of______ and _____ as secondary messengers

Release of calcium from intracellular stores

Decreased release of PTH

A

Phospholipase C

DIACYLGLYCEROL (DG) and
INOSITOL TRISPHOSPHATE (IP3)

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8
Q

Monitors blood calcium levels

Adjusts PTH secretion

Found in PT gland

A

Calcium-Sensing Receptors

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9
Q

secondary messengers

A

DIACYLGLYCEROL (DG)

INOSITOL TRISPHOSPHATE (IP3)

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10
Q

PTH Lab Methods

A

Measurement of bio-intact PTH

PTH-related peptide

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11
Q

Measurement of bio-intact PTH (using 2 antibodies that measure the____ and ____)

A

Amino terminus

caroboxylic acid terminus

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12
Q

Measurement of bio-intact PTH (using 2 antibodies that measure the N-terminal and C-terminal)

ASSAY?

A

Two-site chemiluminescent assay

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13
Q

PTH-related peptide
• produced by….

A

tumors (hypercalcemia of malignancy)

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14
Q

• 141 AA (shares the same homology with PTH in the first 13 AA and can activate PTH receptor)
• its normal physiological role is not clear

A

PTH-related peptide

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15
Q

PTH related peptide

•____AA (shares the same homology with PTH in the first____ AA and can activate PTH receptor)
• its normal physiological role is not clear

A

141 AA

13 AA

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16
Q

Vitamin D…

is NOT a CLASSIC

is NOT a TRUE

is TRUE

A

NOT A CLASSIC HORMONE

NOT A TURE VITAMIN

A TRUE HORMONE

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17
Q

WHY???

• NOT A CLASSIC HORMONE:

• NOT A TRUE VITAMIN:

• A TRUE HORMONE:

A

it is not produced and secreted by an endocrine “gland”.

it can be synthesized de novo

it can act on distant target cells to evoke responses after binding to high affinity receptors

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18
Q

Vitamin D

______-soluble hormone
• binds to a typical intracellular receptor

CARRIER PROTEIN:______

A

Lipid

hydroxylated a-globulin

19
Q

Sources of Vitamin D

Skin Synthesis:
When exposed to UVB light,_________ in the skin is converted to______

Dietary Intake:
Cholecalciferol (Vitamin D3) is obtained from_______

Ergocalciferol (Vitamin D2) is obtained from______

A

7-dehydrocholesterol; cholecalciferol (Vitamin D3)

animal sources, like fatty fish and fortified foods

plant sources and supplements.

20
Q

What converts 7-dehydrocholesterol to Cholecalciferol (Vitamin D3)

A

Ultraviolet light

21
Q

Transport to the Liver

Cholecalciferol (Vitamin D3) and ergocalciferol (Vitamin D2) are transported to the____ via the bloodstream, bound to the Vitamin D-binding protein (DBP).

A

liver

22
Q

Liver Hydroxylation (First Activation Step)

In the liver, Vitamin D3/D2 undergoes hydroxylation by the enzyme______ to form________.

A

25-hydroxylase; calcidiol (25-hydroxyvitamin D)

23
Q

• This is the main circulating form of Vitamin D in the blood.
• It is inactive but serves as a marker for Vitamin D status due to its long half-life.

A

Calcidiol

24
Q

Transport to the Kidneys

Calcidiol (25-hydroxyvitamin D) is transported to the kidneys for further activation.

This transport still relies on the Vitamin D-binding protein (DBP).

Kidney Hydroxylation (Second Activation Step)

In the kidneys, calcidiol (25-OH Vitamin D) is converted to the active form,_______ by the enzyme _______

A

calcitriol (1,25-dihydroxyvitamin D)

1-α-hydroxylase

25
Q

Regulation of 1-α-hydroxylase:

What stimulates the activity of 1-α-hydroxylase during low calcium levels?

•	Calcium and Phosphate Levels: High levels inhibit the enzyme to prevent excessive production of calcitriol.
A

Parathyroid Hormone (PTH)

26
Q

Biological Actions of Calcitriol (Active Vitamin D)

A

Intestinal Absorption of Calcium:
• Calcitriol increases the production of calcium-binding proteins (e.g., calbindin) in intestinal cells, enhancing calcium absorption from food.

Bone Resorption:
• Calcitriol works with PTH to mobilize calcium and phosphate from bone during times of deficiency.

Renal Reabsorption:
• It reduces calcium and phosphate excretion in the kidneys, maintaining blood levels.

27
Q

Inactivation Pathway

Excess calcidiol (25-OH Vitamin D) and calcitriol (1,25-dihydroxyvitamin D) are converted to inactive metabolites by the enzyme______

Inactive Metabolites:
• Examples______, which is excreted to prevent toxicity

A

24-hydroxylase

include 24,25-dihydroxyvitamin D

28
Q

: Converts Vitamin D into calcidiol (25-OH Vitamin D).

: Converts calcidiol into the active form, calcitriol (1,25(OH)₂D).

: Converts excess calcitriol or calcidiol into inactive forms.

A

25-Hydroxylase (Liver)

1-α-Hydroxylase (Kidneys)

24-Hydroxylase (Kidneys)

29
Q

Vitamin D3 Lab Methods

Better marker:
• half life???

A

25-HYDROXY VITAMIN D (longer half-
life)

2-3 weeks versus 5-8 hours

30
Q

Vitamin D3 Lab Methods

Reference method:
Values are influenced by_____

A

DUAL MASS SPECTROMETRY

sunlight exposure

31
Q

Calcitonin

Acts to decrease plasma______

PTH and Vitamin D3 regulation dominate (more powerful secretion than calcitonin).

Secreted by the _______of the thyroid gland

Target cell:_____

A

Calcium levels

parafollicular cells or C cells

osteoclast

32
Q

Major effect of calcitonin

A

• rapid fall in Ca + caused by inhibition of bone resorption

33
Q

LABORATORY METHODS: CALCITONIN

A

Serum Calcitonin

Pentagastrin (Pg) Stimulation Test

Calcium Stimulation Test

34
Q

• As tumor marker for detecting residual thyroid tissue or metastasis in patients with Medullary Thyroid Carcinoma (MTC)

• It should be measured_______

A

Serum Calcitonin

before and 6 months after surgery

35
Q

• IV administration (0.5 ug / kg body weight) over 5 seconds

• Blood samples: baseline, 1, 2, 5, and 10 minutes after the start of infusion

A

Pentagastrin (Pg) Stimulation Test

36
Q

Pentagastrin (Pg) Stimulation Test

• IV administration (________) over 5 seconds
• Blood samples: baseline,________ after the start of infusion

A

0.5 ug / kg body weight

1, 2, 5, and 10 minutes

37
Q

• IV administration of calcium gluconate (2.5 mg/ kg body weight) over 30-60 seconds

• Blood samples: baseline, 1, 2, and 5 minutes after the start of infusion

• Less sensitive than Pg Test, but if combined with Pg Test, it enhances the sensitivity of the Pg Test to diagnose medullary thyroid carcinoma

A

Calcium Stimulation Test

38
Q

Calcium Stimulation Test

• IV administration of______(_____) over 30-60 seconds

• Blood samples: baseline, _____minutes after the start of infusion

• Less sensitive than Pg Test, but if combined with Pg Test, it enhances the sensitivity of the Pg Test to diagnose medullary thyroid carcinoma

A

calcium gluconate ; 2.5 mg
/ kg body weight

1, 2, and 5

39
Q

calcium stimulation test

of plasma calcitonin = C Cell Hyperplasia

A

> 100 ng/L

40
Q

Pg test

Normal (80% of adults)

A

<10 ng/L

41
Q

Pg test

5% of normal adults

A

> 30 but <50 ng/ L

42
Q

Pg test

Possible MTC or other thyroid pathology

A

> 50 but <100 ng/L

43
Q

Pg test

Probable MTC

A

> 100 ng/L

44
Q

Pg test

Basal or post-Pg CT value____

C cell pathology or residual tissue in MEN 2 patients and MTC patients after surgery

A

> 10 pg/mL

CC 2 LEC (13 decks)

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