Phys of Ca-Regulating Hormones (Fan)

Question 1

physiologic roles of Ca

Answer 1

Bonne growth/remodeling
Secretion (excitation coupled)
Contraction 
Action Potentials
Cofactors for Enzymes
Secondary messangers

Question 2

What age does out total body calcium peak? Significance?

Answer 2

25; risk of osteoporosis increases with age

Question 3

Describe the distribution of Ca in the body

Answer 3

99% in bone
1& Intracellular
.1% extracell (inc plasma)

Question 4

Describe the distribution of Ca in the blood

Answer 4

Free > proteins bound&raquo_space; anion bound

Question 5

What is the normal mM/L for Ca in the blood

Answer 5

10 mg/dl or 2.5 mM/L

Question 6

hypocalcemia is defined as …

hypercalcemia is defined as …

Answer 6

10/5 mg/dl

Question 7

When ECF [Ca++] falls below normal, the nervous system becomes (less or more excitable)
How far below normal does Ca have to fall for this to happen

Answer 7

more

<50% of nml

Question 8

What happens when [Ca++] falls below 50% of nml

Answer 8

muscle spontaneously discharge impulses → tetanic muscle contraction

TETANY

Question 9

WHat effect does severe hypocalcemia have on cardiac muscle?

Answer 9

long QT and arrhythmias

Question 10

How is Ca excreted

Answer 10

feces&raquo_space; urine

*but kidneys do have a large capacity to excrete urine by reducing tubular reabs (55% filtered and ~90% reabs)

Question 11

PTH is secreted by …

Answer 11

chief cells of the parathyroid gland

Question 12

WHat produces calcitonin

Answer 12

C cells in thyroid gland

Question 13

structual diff of PTH and calcitonin

Answer 13

PTH = 84 aa and Calcitonin = 32 aa

Question 14

PTH (↓ or ↑) Ca in blood by…

Answer 14

↑ Ca by …
↑ release from bone
↑ reabs/↓secretion from kidney

Question 15

PTH (↓ or ↑) PO4 in blood by…

Answer 15

↓PO4 by ↑excretion/↓reabs via kidneys

Question 16

How long after PTH infusion will Ca/PO4 levels change

Answer 16

immediately

Question 17

Describe how PTH effects Ca and PO4 is exchange between the bone fluid and ECF

Answer 17

1. ↑formation and activity of ostoclast →↑bone reabs → ↑Ca and ↑PO4 released into bone fluid
2. ↑ activity of Ca pump on osteocyte and blast membranes and ↑ permeability of their membranes → movement of Ca from bone fluid into ECF

Question 18

Describe the effect of PTH on osteoclasts

Answer 18

PTH bind PTHR1 on osteoblasts → ↑RANKL and ↓OPG on osteoblasts → RANKL bind RANK in osteoclast precursor → activation of osteoclasts gene trcpt and diff → mature osteoclast → ↑bone reabs → ↑Ca in plasma

Question 19

OPG is secreted by ____ and its effect is to _____

Answer 19

secreted by osteoblasts to inhibit osteoclast formation/bone reabsoption

Question 20

effect of PTH on OPG production

Answer 20

↓

Question 21

What stimulates OPG production

Answer 21

estrogen

Question 22

effect of LOW dose PTH on osteoclasrs

Answer 22

↑ osteoblast prolif/differentiation and ↓ apoptosis of osteoblasts → ↑bone formation

(via PTHR on osteoblasts)

Question 23

Describe effect of PTH on renal kidney

Answer 23

inc reabs of Ca by 10-15% → 99% of Ca that is filtered is reabsorbed and only 1% is excreted

Question 24

How much Ca is filtered at the glomerulus? Why is some not freely filtered?

Answer 24

55% bc the other 40% is bound to plasma proteins and is not filterable

Question 25

T or F: it take a big inc or dec in Ca levels to see an response in PTH or calcitonin levels

Answer 25

F: small change!!!

Question 26

Changes in ECF [Ca] are sensed by...

Answer 26

GPCR on parathyroid chief cells to ↑or↑ PTH secretion ↑Ca are sensed by Ca sensing receptor ↓Ca are sensed by Relaxed Ca sensor

Question 27

Effect of ↑PTH on vit D

Answer 27

PTH is needed to convert 25-vit D to 1,25-vit D

Question 28

Calcitonin ↑ or ↓ Ca levels? PO4 levels? | How

Answer 28

↓Ca and ↓PO4 inhibit osteoclasts → ↓bone reabs inhibits reabs of Ca in kidney

Question 29

Function of Calcitonin

Answer 29

protects against Ca loss from skeleton during periods of Ca mobilization (pregnancy, lactation, being a child)

Question 30

Calcitonin is used pharmacologically to treat

Answer 30

osteoporosis

Question 31

Describe Vit D synthesis

Answer 31

Cholecalciferol (UV rxn) or Ergocalciferol (diet) go to liver → liver makes 25(OH)vitD → kidney converts it to 1,25(OH)2vitD (if PTH is there/low Ca)

Question 32

Describe the effects of vit D in the body

Answer 32

↑ Ca absorption in GI ↓ Ca reabs in kidney ↑ bone resorption ↓ PTH synthesis (feedback)

Question 33

Where does the control of vit D synthesis occur? Explain

Answer 33

kidney: - if high Ca, 24alpha-hydroxylase is active and converts 25(OH)vitD to inactive 24,25(OH2)vitD * also active by 1,25vitD (feedback), FGF23 -if Ca low + PTH, 1alpha-hydroxylase is active and converts 25(OH)vitD to 1, 25(OH)2vitD

Question 34

______ in skin is converted to Cholecalciferol via UV light

Answer 34

7-dehydrocholesterol (provitamin D)

Question 35

A slight dec in [Ca] below normal, causes increased formation of _____

Answer 35

1,25(OH2)D

Question 36

complex precipitate of Ca and PO4

Answer 36

hydroxyapatite

Question 37

What determines whether Ca or PO4 are laid down or resorbed from bone?

Answer 37

product of their concentrations **NOT on their individual concs***

Question 38

Ca x PO4 > solubility product →

Answer 38

bone deposition

Question 39

Ca x PO4 < solubility product →

Answer 39

bone reaorption

Question 40

inc in Ca or PO4 in the ECF would ...

Answer 40

inc bone mineralization/deposition

Question 41

normal levels of PO4 in blood

Answer 41

4 mg/dl or 1.3 mM

Question 42

levels of PO4 in children are (lower or higher). why?>

Answer 42

higher, due to active bone growth!!

Question 43

Describe the distribution of PO4 in the body

Answer 43

Bone (85%) > ICF (14%) > ECF <(0.1%)

Question 44

Describe the distribution of PO4 in the blood

Answer 44

Free (55%) > CATION bound (35%) > PROTEIN bound (10%) **the ppt slide was wrong!!

Question 45

How is PO4 excreted

Answer 45

Urine > feces *kidney clearance more imp for maintaining PO4 balance

Question 46

Describe the changes in PO4 metabolism with renal failure

Answer 46

↓renal Cx → ↑ Sr PO4 (→ ↑bone mineralization → ↓Ca → ↑PTH → ↑ VitD ??) → ↑bone resorption + deposition of Ca in vasculature

Question 47

FGF23 is produced in ____

Answer 47

bone

Question 48

FGF 23 is secreted into blood in response to ...

Answer 48

↑PO4 ↑ Vit D ↑ PTH

Question 49

FGF23 acts in kidneys to...

Answer 49

↓ expression of Na-PO4 co-transporter (↓reabs) and dec vitD synthesis → ↓PO4 (→ ↑bone resorption and ↑Ca)