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Regulation Of Ca And Pi Metabolism Flashcards

1
Q

How is the calcium distributed in the body?

A

ECF - 0.1%

Plasma - <0.5 %

ICF - 1%

Bones/Teeth = 99%

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2
Q

What is the biologically active form of Calcium?

A

Free, ionized Ca

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3
Q

What forms of calcium are found in the blood?

A

Protein bound (40%)

Ultrafilterable (60%)
A. Complexed to anions
B. Ionized (most)

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4
Q

What happens to calcium w/ age?

What does this cause?

A

Decrease in amt. of Ca absorbed from diet
Decrease in amt of Ca in diet

Can cause resorption of bone —> osteopenia Or osteoporosis

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5
Q

What is hypocalcemia?

A

Decrease in plasma [ca]

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6
Q

What are the symptoms of HYPOcalcemia?

A 
!!!!!◦ Hyperreflexia 
◦ Spontaneous twitching
◦ Muscle cramp
◦ Tingling
◦ Numbness
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7
Q

What are some tests for HYPOcalcemia?

A

Chvostek sign

Trousseau sign

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8
Q

What is Chvostek sign?

A

‣ Twitching of facial muscle when facial n. Is tapped

Tests for HYPOcalcemia

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9
Q

What is Trousseau sign?

A

‣ Carpopedal spasm when blood pressure cuff is inflated

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10
Q

what is HYPERcalcemia?

A

Increase in plasma [Ca]

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11
Q

What are the symptoms of Hypercalcemia?

A 
◦ Decreased Qt interval
◦ Constipation
◦ Lack of appetite
◦ Polyuria
◦ Polydipsia
!!!!!◦ Muscle weakness
!!!!!◦ Hyporeflexia
◦ Lethargy
◦ Coma
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12
Q

What can change the forms of Calcium present in the plasma? (Protein bound, vs anion complexed, vs ionized)

A
  1. Change in plasma protein concen.
  2. Change in anion conc.
  3. Acid base abnormalities
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13
Q

What will increased plasma protein concentration due to ca in plasma?

A

Increase total ca concentration

W/ no change in ionized Ca

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14
Q

What will an increase in Anion concentration do?

I.e. increase in phosphate concentration

A

Change fraction of Ca:anions&raquo_space; Ca:ionized

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15
Q

How do acid base abnormalities affect fraction of Ionized Ca?

Acidemia?
Alkemia?

A

Changes fraction bound to albumin

Acidemia: increases ionized Ca bc less bound to anions

Alkemia: decreases ionized Ca bc more bound to albumen

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16
Q

What usually accompanies alkemia?

A

HYPOcalcemia (bc not much ionized active Ca now - more bound to albumin)

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17
Q

How does low plasma calcium concentration influence membrane excitability?

A

Low extracellular [Ca] —> reduced activation threshold for Na

Action potential easier to evoke

= increase in membrane excitability
(Spontaneous APs)

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18
Q

What is the physical basis for HYPOcalcemic tetany?

A

Spontaneous muscle contraction due to low extracellular calcium that allows APs to be more easily reached

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19
Q

How does HIGH plasma [Ca] influence membrane excitability?

A

Increases activation threshold for Na

Makes it harder to have AP

DECREASES membrane excitability

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20
Q

What is the physiological basis for the HYPOreflexia seen in HYPERcalcemia?

A

High extracellular ca decreases membrane excitability

Depresses nervous system —> reflex responses slowed

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21
Q

How do kidneys help maintain Calcium balance?

A

Excrete same amt. of Ca that is absorbed by GI tract

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22
Q

How does Vitamin D regulate Calcium homeostasis?

A

Helps Ca absorption from GI tract

helps with bone resorption

(Will increase Ca)

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23
Q

How does PTH regulate calcium homeostasis?

A

‣ Helps with bone resorption
‣ Helps with reabsorption of Ca from kidneys

(Increases Ca)

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24
Q

How does Calcitonin regulate calcium homeostasis?

A

Inhibits bone resorption

Decreases Ca

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25
How does bone remodeling affect Ca levels?
No net gain or loss of calcium
26
What is the relationship between phosphate and calcium?
Pi = inverse extracellular [ ] to Ca | I.e. high pi = low ca
27
What regulates phosphate?
Same hormones as ca | Vitamin D, calcitonin, PTH
28
What is the distribution of Pi in the body?
``` ‣ Bone = 85% ‣ Plasma = 1% • 84% ionized • 10% protein bound • 6% complexed (to various cations, K+na+) ‣ ICF = 15% ```
29
How is Ca and Pi metabolism regulated by Gonadal hormones
Estradiol-17B —> increases Ca absorption from GI and renal tubal calcium reabsorption
30
What does estradiol-17B regulate? What will it favor?
osteoblast and osteoclast function ◦ Promotes survival of osteoblasts ◦ Promotes apoptosis of osteoclasts ‣ Favors bone formation over resorption
31
How is Ca and Pi metabolism regulated by Adrenal glucocorticoids?
Cortisol will promote bone resorption And renal ca wasting Inhibits intestinal absorption of Ca =lowers Ca
32
What can patients treated w/ high levels of a glucocorticoid develop?
Glucocorticoid induced osteoporosis
33
What is osteoporosis? Who does it affect more?
Change in bone mass Women
34
What is the treatment for osteoporosis?
Low doses of PTH | Antiresorptive therapy Estrogen, RANKL inhibits, calcitonin
35
When will PTH be secreted? Function?
When calcium is low or Pi high to stimulate bone resorption and thus lead to increase of calcium
36
Where is PTH synthesized and secreted from?
From chief cells in parathyroid glands
37
What kind of hormone is PTH?
Peptide hormone composed of a single chain w/ 84 AAs Was synthesized as preproPTH, cleaved to proPTH, cleaved to PTh and packed into secretory granules
38
What will inhibit PTH secretion? How/
Chronic HYPERcalcium High Ca will increase breakdown of stored PTH and release inactive PTH fragments into circulation
39
What can cause hyperplasia of the parathyroid glands?
Chronic HYPO-calcemia Will cause increased synthesis and storage of PTH
40
What does HYPOmagnesemia cause? What is this seen in?
Inhibition of PTH synthesis and storage and secretion Alcoholism
41
What does PTH function thru?
Thru GPCR connected to adenylyl Cyclase, cAMP
42
What are the actions of PTH on bone?
Bone resorption Thru promotion of osteoblasts growth and survival that will secrete cytokines and affect OSTEOCLASTS Regulates M-CSF, RANKL, and OPG production
43
What will sustained elevated levels of PTH do?
Shifts balance from osteoblasts to Osteoclasts activity thru cytokines Increases bone turnover Reduces bone density
44
What is the action of PTH on the kidneys
Decrease pi Reabsorption Increase Ca reabsorption Increase urinary cAMP Stimulate 1a-hydroxylase activity —> increase vitamin D
45
How does PTH decrease pi reabsorption in the kidneys?
Represses NPT2a expression, inhibiting entrance of Pi Causing urinary excretion of Pi
46
What is the effect of PTH on intestines?
Increases Ca absorption indirectly via Vitamin D
47
What does PTH do at the proximal tubule of kidneys?
Binds to R. —> activates Gs Gs—> increases cAMP cAMP excreted in urine as Urinary cAMP ``` Inhibits NPT (sodium dep. phosphate co-transporter) Decreases Pi reabsorption —> Phosphaturia ```
48
What are the actions of PTH at the distal convoluted tubule?
Second renal action of PTH Complements increase in plasma Ca that resulted from combo of bone resorption and phosphaturia
49
What does vitamin d act to increase? To accomplish what?
Increases both Ca and Pi to promote mineralization of new bone
50
What is the inactive form of vitamin D?
Cholecalciferol (pro-hormone)
51
How is Vit. D transformed into an active metabolite?
Thru hydroxylation
52
What are the actions of VItamin D at the small intestine?
Increases absorption of Ca and Pi Calcium: synthesizes proteins - TRPV6: allows passage of calcium from intestinal lumen into epithelial cell - Calbindin: binds calcium in epithelial cell and helps take it to transporters - Pumps; help move Ca to interstitial space so it can go into blood Pi: helps synthesize pumps for Pi that helps take it out of intestinal lumen
53
What are the actions of Vitamin D on bone?
Sensitized Osteoblasts to PTH (PTH will then increase their growth and thru constant stimulation activate osteoclasts) Regulates osteonecrosis and calcification and mineralization
54
How does Vitamin D act on the kidneys?
Stimulates the expression of NPT2a and promotes Pi reabsorption (opposite of PTH) Minimal actions on Ca
55
How does Vitamin D act on parathyroid glands?
Inhibits PTH gene expression Stimulates expression of CaSR gene
56
What is CaSR?
Calcium sensitive receptor Activates Gq/Gi Inhibits CYP1-a gene Thus no 1-alpha hydroxylase Thus no vitamin D active made
57
How is 1,25 dihydroxycholecalciferol synthesis regulated?
Low ca, high pth, high pi will stimulate 1alpha-hydroxylase to convert Vit. D to active form Inhibited by increased CaSR receptors Active vitamin d will inhibit synthesis thru increasing CaSR gene expression
58
What is the function of 1-alpha-hydroxylase?
Hydroxylates Vit. D into active form (1,25-dihydorxycholecacilferol)
59
What transcribe 1-alpha-hydroxylase?
CYP1-alpha gene
60
What will inhibit expression of CYP1-gene? Activates?
High Ca (no need to vitamin d) Active form of Vit. D (negative feedback system) Activated by cAMP/PKA thru actions of PTH
61
How do PTH and Vitamin D work together on bone formation and resorption?
Vit. D and PTH work together to stimulate osteoclasts activity and bone resorption Thus increasing Ca
62
Where are PTH receptors found for bone?
On osteoblasts
63
What are the short term actions provided by PTH on bone?
* Bone formation via direct action on osteoblasts | * (Can even use intermittent synthetic PTH administration in osteoporosis treatment)
64
What are the long term actions of PTH on bone?
• Increase bone resorption ◦ Via indirect action on osteoclasts mediated by cytokine released from osteoblasts
65
What are 4 factors that are involved in bone formation and resorption?
M-CSF RANLK RANK OPG
66
What is M-CSF?
Macrophage colony stimulating factor Induces stem cells to make OSTEOCLASTS
67
What is RANKL?
Cell surface protein (Receptor Activator for NF-Kappa b Ligand) Primary mediator of osteoclast formation
68
What produces RANKL?
Osteoblasts Bone lining cells Apoptotic osteocytes
69
What is RANK?
Receptor on osteoclasts and osteoclasts precursors
70
What is OPG?
Osteoprotegerin - a soluble protein receptors produced by osteoblasts Tricks RANKL to bind Inhibits RANKL/RANK interaction Thus NO BONE BREAK DOWN
71
How does PTH act on bone formation factors?
Increases RANKL Decreases OPG Allows for Bone breakdown = increased Ca
72
How does Vitamin D act on bone formation factors?
Increases RANKL | Increasing Bone breakdown, increased ca
73
What is the action of Cacitonin on bone resorption?
Stimulates deposition of Ca in bones Reduces Ca uptake in kidney = decreases ca
74
When is calcitonin secreted? From where?
When Ca levels are high Acts to decrease levels From thyroid gland
75
What is primary HYPER parathyroidism?
Defect @ parathyroid gland (adenoma) Increases secretion of PTH
76
What are the results of Primary Hyperparathyroidism?
Increased resorption of bone CYP1-alpha gene activation -> increased VIt. D Increased Pi excretion from kidneys Increased Ca excretion form kidneys
77
What are the Sxs of Primary HYPERparathyroidism?
Excessive urinary excretion of pi, cAMP, and Ca Stones, bones and groans • Hypercalciuria - stones • Increased bone resorption = bones • Constipation = groans Hypercalcemia (slow reflexes, constipation, lethargy) Hypophosphatemia
78
What is the treatment for primary HYPERparathyroidism?
Parathyroidectomy
79
``` How will levels of PTH Ca Pi Vit. D ``` Change in PRIMARY hyperparathyroidism ?
PTH: increased Ca: increased Pi: decreased Vit. D.: increased
80
Wha is secondary HYPERparathyroidism?
Increase in PTH levels SECONDARY TO LOW BLOOD [Ca] | !!!!
81
What can cause low blood [Ca] in secondary HYPERparathyroidism?
Renal failure (cannot reabsorb Ca) Vitamin D deficiency (cannot help with bone resorption etc.)
82
``` How will levels of PTH Ca Pi Vit. D ``` Change in SECONDARY hyperparathyroidism caused by RENAL FAILURE?
PTH: high Ca: low (primary cause) Pi: HIGH bc kidney cannot excrete it Vit. D: low
83
``` How will levels of PTH Ca Pi Vit. D ``` Change in SECONDARY hyperparathyroidism caused by VITAMIN D DEFICIENCY?
PTH: high Ca: low (bc no vitamin d) Pi: low Pi (bc vitamin d also assists in Pi) Vit. D: low
84
What can cause HYPO-parathyroidism?
Thyroid surgery Parathyroid surgery Autoimmune or congenital condition
85
What are the SXs of hypoparathyroidsim?
``` ‣ Associated with low calcium • Bc PTH cannot act to increase ‣ muscle spasm, cramping ‣ Numbness, tingling, burning, • Especially around mouth and fingers ‣ seizures ‣ Kids: • Poor teeth development • Mental deficits ```
86
What are the treatments for Hypoparathyroidism?
Oral Ca supplement Active form of Vit. D supplement
87
``` How will levels of PTH Ca Pi Vit. D ``` Change in HYPOparathyroidism?
PTH: low Ca: low Pi: High Vit. D: low
88
What is Pseudohypoparathyroidism type1a also called?
Albright Hereditary Osteodystrophy
89
What causes Albright HEreditary Osteodystrophy? What will develop because of it?
Inherited autosomal dominant disorder That causes defective Gs for PTH in bone and kidney = no cAMP produced but PTH keeps stimulating HYPOcalcemia HYPERphosphatemia
90
How do you test for Psuedohypoparathyroidsim type 1a?
Exogenous increase of PTH levels Will see no response in phosphaturia and urinary cAMP levels
91
What are the symptoms of Albright hereditary Osteodystrophy?
``` ‣ Short stature ‣ Short neck ‣ Obesity ‣ Subcutaneous calcification ‣ Shortened metatarsals ‣ Shortened metacarpals ```
92
``` How will levels of PTH Ca Pi Vit. D ``` Change in PsuedoHYPOparathyroidism (Albright hereditary Osteodystrophy)?
PTH: High (but not sense by receptors bc Gs is defective) Ca: Low Pi: HIGH (bc PTH cannot act to get rid of it) Vit. D: low
93
What is the pathophysiology behind humoral hypercalcemia of malignancy?
PTH related peptide is produced by TUMORS PTH related peptides will bind same receptors as PTH and increase Ca (pseudo increase!!)
94
What are the symptoms of HUmoral HYPERcalcemia of Malignancy?
``` ‣ Increase in urinary Ca ‣ Increase urinary Pi ‣ Increase cAMP ‣ Increase in blood Ca (hypercalcemia) ‣ Decrease blood Pi (hypophosphatemia) ```
95
``` How will levels of PTH Ca Pi Vit. D ``` Change in Humoral HYPERcalcemia of Malginancy?
PTH: low (bc of Vit. D feedback) Ca: high (bc of exogenous pseudo PTH being produced by TUMOR) Pi: low Vit. D: low (bc no PTH to synthesize it)
96
What is Familial HYPOcalciuric HYPERcalcemia (FHH)?
Autosomal dominant disorder that causes a mutation that will INACTIVATE CaSR in parathyroid glands and Ca receptors in ascending limb of kidneys If CaSR inactive cannot inhibit PTH gene
97
How does FHH present?
‣ Decrease in urinary ca excretion (hypocalciuria) ‣ Increase in serum [Ca] (hypercalcemia) (Bc CaSR not inhibiting PTH, PTH increased, increased reabsorption of Ca from kidneys)
98
``` How will levels of PTH Serum Ca Urinary ca Pi Vit. D ``` Change in Familial Hypocalciuric HYPERcalcemia?
PTH: high (or no change) Serum Ca: HIGH Urinary ca: low Pi: no change Vit. D: no change
99
What can impaired vitamin d metabolism?
``` ◦ Dietary deficiency ◦ Deficit in synthesis ‣ Absence of 1-alpha-hydroxylase ◦ vitamin D resistance ‣ Mutation affecting vitamin D receptor ```
100
What could changes in the metabolism be due to?
Gi disorders Chronic renal failure Pi Depletion
101
What would vitamin D deficiency result in during childhood?
Rickets
102
What would vitamin d deficiency result in during adulthood?
Osteomalacia
103
``` How will levels of PTH Ca Pi Urinary output of pi and cAMP Vit. D ``` Change in Vitamin D deficiency?
PTH: increase (bc no Vit. D to feedback) Ca: no change/ lower Pi: LOW (bc Vit. D big reabsrober of it from kidneys) urine: increase pi, increase cAMP Vit D: low
104
What is rickets caused by?
Congential disorder caused by ‣ Pseudo vitamin D -deficient rickets or Vitamin D dependent rickets type 1 • Low 1 alpha-hydroxylase ‣ Pseudovitamin D-deficient rickets or vitamin D dependent rickets type 2 • Decreased vitamin D receptors
105
What does RIckets result in? Characteristics?
Cannot mineralized growing bone Characterized by growth failure and skeletal deformities In kids
106
What can cause osteomalacia in adults?
Nutritional osteomalacia from vitamin D deficiency Caused by GI disorder, suboptimal nutrition, inadequate sun exposure, malabsorption of Ca due to gastric bypass surgery
107
What does osteomalacia result in? Characteristics? Sxs?
New bone fails to mineralized Characterized by bending and softening of weight-bearing bones ``` ‣ Bone pain ‣ Muscle weakness ‣ Bone tenderness ‣ Fracture ‣ Muscle spams, cramps, positive Chvostek’s sign, tingling/numbness ```
108
What is suspected inc ashes of bone pain associated w/ malabsorption?
Osteomalacia

..3 (16 decks)

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