Parathyroid hormone, calcitonin and cholecalciferol in Calcium homeostasis Flashcards by Iseoluwa Ojo

Forms of Calcium
-The average young adult contains __g of calcium in their body, ___% of which is stored in bone, ____% in blood and ____% inside cells.

1200

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Calcium in the blood exists in___ forms:

three

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Forms of calcium in the blood

List them

____
____
_____

Free-ionised

Bound to anions
Bound to proteins

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Forms of calcium in the blood

Free-ionised– (diffusible or not?) , (biologically active or not?)
*Bound to anionse.g. ____ – (diffusible or not?), (biologically active or not?)
*Bound to proteins(mainly ____) – ( diffusible or not?) ,( biologically active or not?)

Diffusible; active

phosphate; diffusible; not active

albumin;not diffusible; not active

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Calcium Homeostasis

Calcium homeostasis is a complex process involving the following 4 key components:
serum ___, serum ____,______, and _____ hormone (PTH).

calcium

phosphate

1,25-dihydroxyvitamin D-3

parathyroid

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More than 99% of the total body calcium is stored in ____ in the form of _____ and ______, predominantly as ______.

-Normally, a very (small or large?) portion of this calcium is available for exchange in the serum.

bone

phosphate; hydroxide salts

hydroxyapatite

Small

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Parathyroid hormone (PTH)
-Parathyroid hormone (PTH) is a \_\_\_peptide containing \_\_ amino acids that is secreted by the parathyroid glands after cleavage from \_\_\_parathyroid hormone (\_\_\_amino acids) to \_\_\_parathyroid hormone (\_\_\_amino acids) to the mature hormone.

poly; 84

prepro; 115

pro; 90

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The major target end organs for parathyroid hormone (PTH) action are the ____, ____ system (___), and ____.

kidneys

skeletal; bones

intestine

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Alternative names for parathyroid hormone;___;_____;____.

PTH

parathormone

parathyrin

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Parathyroid hormone is secreted from four parathyroid glands, which are small glands in the neck, located ____ the thyroid gland.

behind

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Feedback inhibition of parathyroid hormone (PTH) release occurs primarily by (direct or indirect ?) effect of ____ at the level of the____

Direct

calcium

parathyroid gland.

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Major target organs of the PTH
Kidneys
-The primary response to parathyroid hormone (PTH) by the kidney is to______
-Parathyroid hormone also stimulates the production of _____in the kidneys.
-In the kidney, parathyroid hormone (PTH)____ reabsorption of phosphate in the____
-while ___ calcium reabsorption in the_____,____, and______.

increase renal calcium resorption

activevitamin D

blocks; proximal tubule

promoting; ascending loop of Henle; distal tubule; collecting tubule

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PTH converts____ to its most active metabolite,______ , by activation of the enzyme _____in the _______ of the kidney.

25-hydroxyvitamin D

1,25-dihydroxyvitamin D-3

1-hydroxylase

proximal tubules

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Major target organs of the PTH

Bones
-parathyroid hormone stimulates the ____ of calcium from large calcium stores in the bones into the _____.
-This increases bone ____ and (increases or decreases?) the formation of new bone.
-Parathyroid hormone (PTH) promotes absorption of calcium from the bone in 2 ways.
______ and ______

release

bloodstream

destruction

Decreases

Rapid phase and slow phase

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The rapid phase of promotion of absorption of calcium from bone:
-brings about a rise in serum calcium within ____ and appears to occur at the level of the ____ and ______

minutes

osteoblasts and osteocytes.

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Although it may seem counterintuitive that the cells that promote deposition of bone are involved in resorption,these cells form an interconnected network known as the_____ overlying the ____, but with a small layer of____ termed ____.
-When parathyroid hormone (PTH) binds to receptors on these cells, the ______ membrane pumps calcium ions from the ____ into the ______.

osteocytic membrane

bone matrix

interposed fluid

bone fluid

osteocytic ; bone fluid

extracellular fluid

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The slow phase of promotion of absorption of calcium from bone:

occurs over ____ and has 2 components.
First, _____ are activated to ____ formed bone
Second, ____ of osteoclasts occurs.

several days

osteoclasts; digest

proliferation

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mature and immature osteoclasts lack parathyroid hormone (PTH) membrane receptors
T/F

Only mature ones lack it

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activation and proliferation of osteoclasts appear to be stimulated by _____ released by activated _____and _____ or by differentiation of (mature or immature?) osteoclast precursors that possess parathyroid hormone (PTH) and vitamin D receptors

cytokines

osteoblasts and osteocytes

Immature

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Major target organs of the PTH

Intestine
-parathyroid hormone (directly or indirectly?) increases calcium absorption from food in the intestine, via its effects on ____ metabolism

Indirectly

vitamin D

Facilitating calcium absorption from the small intestine would serve to _____ blood levels of calcium.

elevate

Vitamin D induces synthesis of a_____ protein in____ cells that facilitates efficient absorption of calcium into blood.

calcium-binding

intestinal epithelial

Although not well elucidated, 1,25-(OH)2D3 appears to exert a mild _____ effect on the parathyroid gland

inhibitory

VITAMIN D

In concert with _____ hormone, vitamin D also enhances ____ of calcium out of bone.
it can either be made in the ____ from a ___-like precursor (______) by exposure to____ or can be provided ____ in the diet.

parathyroid

Absorption

skin; cholesterol

7-dehydrocholesterol; sunlight

pre-formed

The version of vitamin D made in the skin is referred to as _____whereas the dietary form can be vitamin D3 (_____) or a closely related molecule of ___ origin known as vitamin D2 (_____).

vitamin D3 cholecalciferol plant; ergocalciferol

The two forms of vitamin D(2 and 3) are metabolised (exact the same, differently or similarly?) in humans, are (equal or not?) in potency, and can be considered ____.

Similarly Equal equivalent

It is now firmly established that vitamin D_ is metabolised first in the __ to ____(25-OH-D or ____) and subsequently in the _____ to _____to produce a biologically active hormone.

3 liver; 25-hydroxyvitamin-D ; calcidiol kidneys; 1,25-(OH)2D (3)

The 1,25-(OH)2D, like all vitamin D metabolites, is present in the blood complexed to vitamin D binding protein, a specific ____ -The 1,25-(OH)2D is believed to act on target cells similarly to the way a ____ hormone would act.

a-globulin. steroid

Free calcitriol hormone crosses the plasma membrane and interacts with a specific nuclear receptor known as the ____, a ___-binding, ____ protein with a molecular weight of _____. -This ligand-receptor complex binds to a specific ____ and, with associated transcription factors (e.g.,_____), enhances transcription of mRNAs which code for _____ proteins,_____ proteins, or ____ proteins.

vitamin D receptor DNA zinc-finger 55,000 vitamin D-responsive element retinoid X receptor calcium-transporting ; bone matrix ; cell cycle-regulating

1,25-(OH)2D stimulates intestinal absorption of ____ and ___ and mobilises them by stimulating bone ____. -These functions serve the common purpose of restoring blood levels of ____ and ____to normal when concentrations of the two ions are low.

calcium and phosphate resorption calcium and phosphate

-after normal calcium levels is reached , The further secretion of PTH is turned off not only by the ____, but also by a ____ feedback loop involving ____ (directly or indirectly?) suppressing PTH synthesis in the parathyroid gland.

feedback action of calcium short; 1,25-(OH)2D Directly

Which is largely circulating and which is tightly regulated between 25-OH-D-1-aa-hydroxylase And 25-OH-D.

25-OH-D-1-aa-hydroxylase is tightly regulated 25-OH-D is largely circulating

CONTROL OF parathyroid hormone -The parathyroid cell monitors extracellular free calcium concentration via an____ protein that functions as a calcium sensing receptor

integral membrane

Primary Hyperparathyroidism - is the result of _____ disease - most commonly due to a ___(____) which secretes the hormone without proper regulation. - Common manifestations of this disorder are chronic elevations of blood calcium concentration (____),____ and_____ of bone

parathyroid gland parathyroid tumor ; adenoma hypercalcemia; kidney stones decalcification

Secondary Hyperparathyroidism - is the situation where disease _____leads to excessive secretion of parathyroid hormone. - A common cause of this disorder is ___ disease - if the kidneys are unable to reabsorb calcium, blood calcium levels will___, stimulating continual secretion of _____ hormone to maintain normal calcium levels in blood.

outside of the parathyroid gland kidney fall parathyroid

Secondary hyperparathyroidism result from inadequate nutrition T/F

diets that are deficient in calcium or vitamin D, or which contain excessive___ (e.g. all meat diets for ____). -A prominent effect of secondary hyperparathyroidism is _____ of bone, leading to pathologic fractures or " ____ bones".

phosphorus carnivore decalcification rubber

Tertiary hyperparathyroidism is rare or common??

Rare

Tertiary hyperparathyroidism causes hypercalcaemia due to excess parathyroid hormone production as a result of ______

all four glands being overactive.

Inadequate production of parathyroid hormone - hypoparathyroidism - typically results in decreased concentrations of ____ and increased concentrations of ____ in blood. - Common causes of this disorder include _____ and ____ that lead to destruction of parathyroid glands. - The resulting hypocalcemia often leads to ____and ____, and can be acutely life-threatening. - Treatment focuses on restoring normal blood calcium concentrations by calcium____,_____ and _____ therapy.

calcium phosphorus surgical removal of the parathyroid glands diseases tetany and convulsions infusions; oral calcium supplements; vitamin D

CALCITONIN | -is a hormone that functions to (elevate or reduce?) blood calcium levels.

reduce

When the amount of calcium in blood rises above the normal range, ____cells in the ____gland secrete ____.

parafollicular thyroid calcitonin

Calcitonin is secreted in response to hypercalcemia and has at least two effects: * (enhancement or Suppression?) of renal tubular reabsorption of calcium * (activation or Inhibition?) of bone resorption

Suppression Inhibition

calcitonin enhances excretion of calcium into urine. T/F

Calcitonin maximizes fluxes of calcium from bone into blood. T/F

F It minimizes it

calcitonin has significant calcium-lowing effects in humans. T/F

F It has minimal influence on blood calcium levels in humans.

During calcium deprivation Renal excretion of phosphate is _____ by ______ During calcium loading Renal excretion of phosphate is _____ due to______

Strongly stimulated by PTH Decreased due to hypoparathyroidism

Long-term deprivation of calcium leads to bone thinning T/F

High intestinal absorption and enhanced renal excretion , guards against hypercalcemia T/F

F Low intestinal absorption *