Calcium Homeostasis and Hormonal Regulation

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Clinical Chemistry
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1

impulse transmission and muscular contraction

calcium functions for optimal excitability of neural and muscular tissue

2

blood coagulation, hormone secretion, and intracellular adhesion

calcium functions for organ systems

3

skin, liver, small intestine, skeleton, parathyroid glands, kidneys

organs calcium maintains homeostasis for

4

mineral repository

calcium skeletal function

5

hydroxyapatite salt

makes up 99% of calcium in the human body

6

extracellular fluids

makes up 1% of calcium in the human body

7

ionized

form of 50% of calcium in the blood

8

protein bound

form of 40% of calcium in the blood

9

complexed to citrate and phosphate

form of 10% of calcium in the blood

10

pH

influences calcium binding

11

vitamin D, parathyroid hormone, and calcitonin

hormones responsible for regulating bone and mineral metabolism through calcium homeostasis

12

vitmain D

metabolic product of cholesterol synthesis; skin, liver and kidneys

13

7-dehydrocholesterol -> vitamin D3 (by UV light) + hepatic 25-hydroxylase = 25-hydroxy vitamin D

de novo vitamin D synthesis

14

hepatic 25-hydroxylase

metabolizes vitamin D3 to 25-hydroxy vitamin D

15

25-hydroxy vitamin D

measured to assess vitamin D stores

16

rickets and osteomalacia

two conditions which have low levels of vitamin D

17

renal 1alpha-hydroxylase

enzyme that converts 1,25-dihydroxy vitamin D to active form

18

PTH

regulates 1alpha-hydroxylase

19

increased vitamin D, increased calcium, increased intestinal absorption

relationship between vitamin D and calcium

20

PTH

preserves blood calcium and phosphate in the normal range

21

raise blood calcium, increase bone resorption to increase blood levels, increase kidney reabsorption of renal tubular calcium, stimulates 1alpha-hydroxylation of 25-hydroxyl vitamin D, indirectly stimulates intestinal absorption, and lowers phosphate levels through excretion

functions of parathyroid hormone (6)

22

calcium sensing receptors

contained within the parathyroid to regulate PTH secretion

23

suppresses PTH

high calcium affect on PTH

24

stimulates PTH

low calcium affect on PTH

25

1,25(OD)2D levels

control calcium absorption

26

phosphate

binds calcium in the lumen forming insoluble calcium phosphate precipitate

27

normal GI function

required for maintaining calcium absorption

28

renal failure

significantly impacts calcium and phosphate metabolism and secretion of phosphate; blocks hydroxylation leading to inactive forms of vitamin D being created; increased PTH then causes calcium phosphate complexes, hypercalcemia, and potential kidney stone development

29

bone

repository for calcium, phosphate, and magnesium

30

osteoblasts

mediate bone formation

31

osteoclasts

mediate bone breakdown and resorption

32

vitamin D and PTH

act on osteoblasts

33

osteoblasts

produce hormones to regulate osteoclasts

34

bone remodeling

imbalance leads to osteoporosis and fracture risk

35

cortical

shaft of long bones

36

trabecular

axial skeleton honeycomb bones

37

8.6-10.0 mg/dL

total calcium reference range

38

4.6-5.3 mg/dL

ionized calcium reference range

39

increased or decreased with ionized calcium levels

albumin's relationship to calcium levels

40

duration of elevation

factor that determines symptoms and damage of increased calcium levels

41

CNS, GI, renal, skeletal, and cardiovascular

systems affected by hypercalcemia

42

lethargy, decreased altertness, depression, confusion, coma (extreme cases)

CNS affects of hypercalcemia

43

anorexia, constipation, nausea, vomiting

GI affects of hypercalcemia

44

impaired concentration leading to hydration since calcium acts as a diuretic

renal affects of hypercalcemia

45

increased bone resorption and bone demineralization and increased fracture risk

skeletal affects of hypercalcemia

46

hypertension

cardiovascular affects of hypercalcemia

47

parathyroid gland and CSR disorders, cancer-mediated, granulomatous diseases (TBm Crohn's), medications (vitamin A and D toxicity), miscellaneous (William's syndrome or immobilization)

5 causes of hypercalcemia

48

PHPT-primary hyperparathyroidism

autonomous overproduction of PTH caused by adenoma, hyperplasia, carcinoma, familial syndromes

49

secondary and tertiary hyperparathyroidism

sustained PTH production caused by variety of factors-renal issues hypercalcemic and hyperphosphatemic lead to PT hyperplasia

50

familial hypocalciuric hypercalemia

inactivating mutation of CSR; calcium receptor antibodies; lithium carbonate

51

adrenal insufficiency, hyperthyroidism, pheochromocytoma

endocrine disorders that can cause secondary hyperparathyroidism

52

PTHrP production by tumors

parathyroid-related protein structurally similar to PTH produced in some tumor cells (breast and lung)

53

lymphomas

increase hydroxylation of vitamin D causing hypercalcemia

54

cytokine production by tumor cells

activates bone resorption

55

primary hyperparathyroidism

most common cause of hypercalcemia; autonomous production of PTH; often asymptomatic and identified through routine bloodwork; causes increased calcium, decreased phosphate, and normal to increased PTH

56

adenoma of one parathyroid gland

most common cause of hyperparathyroidism

57

familial hypocalciuric hypercalemia

benign condition caused by mutation affecting CSRs; PTH and calcium are increased but stable with a low urine calcium output

58

hypocalcemia

can be caused by organ system dysfunction, hormone issues, acid-base disturbances; leads to tetany, numbness, tingling, irritability, seizures, impaired mental function, and contractile dysfunction

59

hypoparathyroidism

can be caused by endocrine issues, vitamin D deficiency, hypomagnesemia, or secondary factors

60

post-operative, autoimmune, congenital mutations, and pseudohypoparathyroidism

four causes of hypoparathyroidism in which there is a lack of PTH

61

hypomagnesemia

leads to lack of PTH synthesis and release

62

secondary hypoparathyroidism

compensatory mechanism of parathyroid to address low calcium levels

63

pseudohypoparathyroidism

target tissues do not respond to PTH; intracellular signaling process does not work correctly

64

rickets

bone growth abnormality due to vitamin D deficiency; skeletal deformity and bending of long bones-usually legs

65

osteomalacia

abnormal bone mineralization after skeletal maturation; increased fracture risk

66

osteoporosis

most prevalent metabolic disease in adults; silent until fracture; risk factors include hypogonadism, post-menopause, age, family history, lean body, smoking, alcoholism, glucocorticosteroid excess, hyperparathyroidism, and vitamin D metabolism disorders

67

glucocorticosteroids

inhibit osteoblasts and induce apoptosis by stimulating osteoclasts leading to bone mass loss

68

tertiary hyperparathyroidism caused by chronic kidney disease

has a significant impact in bone and mineral metabolism; impacted kidneys do not excrete phosphate resulting in calcium-phosphate precipitation; increased PTH secretion to counteract decreased calcium results in hyperplasia which then causes increased calcium