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203: The endocrine system > Calcium homeostasis > Flashcards

Flashcards in Calcium homeostasis Deck (22)
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1

Function of calcium

Exocytosis in cells.

Build and maintenance of bone.

Blood clotting.

Many biochemical processes.

2

Serum calcium
- How it is transported [3]

Mostly found as free ions [50%]
- These are biologically active

Bound to proteins [40%]:
- Albumin (90%)
- Globulin (10%)

Bound to cations [10%]
- Phosphate
- Citrate

3

Physiological range of serum calcium

2.15-2.55 mmol/L

4

Hypocalcaemia
- Definition
- Physiology
- Physical signs

Serum calcium <2.15 mmol/L

Physiology
- Low calcium, makes neurones a lot more permeable to Na+ (Ca2+ competes with Na+)

Signs
- Trousseau's sign
- Chvostek's sign

5

Consequences of hypocalcaemia
- Acute [3]
- Chronic [6]

Acute
- Thirst
- Polyuria
- Abdominal pain

Chronic
- MSK pain/ weakness
- Constipation
- Neurobehavioral changes
- Kidney stones
- Osteoporosis

6

Parathyroid hormone
- Structure
- Synthesis
- Secretion

Peptide hormone

Made by chief cells of the parathyroid gland.

Secreted in response to low Ca2+ levels.
- Chief cell contains receptors that are Ca2+ sensing

7

PTH release

Ca2+ sensing receptors on chief cells recognise low Ca2+ levels
- Changes shape of the receptor
- Chief cells processes modified to release PTH in the presence of Mg2+

8

PTH action on receptors

PTH acts on PTH-1 receptors on bone and kidneys
- Changes the shape of the receptor.

Bone
- Calcium release

Kidneys
- More absorption of Ca2+ in loop of Henle, DT, CD.
- Less Phosphate reabsorption in PT [prevents calcium phosphate precipitation]

9

PTH action on bone

PTH activates osteoblasts
- Causes release of rank ligand

Rank ligand activates osteoclasts
- Break down of bone using H+ and enzymes (CATK, TRAP).
- Ca2+ release into the blood.

10

Corrected calcium

Calculation of serum Ca2+ based on the amount bound the albumin.

Not accurate if album is <20g/L.

11

Mg2+ and PTH
- Causes of hypomagnesaemia

Mg2+ is a co-factor required for the release of PTH.
- Low Mg2+ = no PTH release= hypocalcaemia.

Causes of hypomagnesaemia
- GI problems
- PPIs

12

Sources of Vit.D

- UV from the sun causes the skin to make cholecalciferol [Vit D3]

Diet
- Cod liver oil
- Wild oily fish
- Fortified foods
- Irradiated mushrooms

13

Vit D metabolism

In liver
- Vit.D3 Converted to 25-OH, Vit.D

In kidneys
- PTH acts to convert 25-OH, Vit D into 1,25-OH-Vit.D

In bowel
- 1,25-OH, Vit.D stimulates the insertion of Ca2+ transporters and calbindin
- Allows more absorption of Ca2+

14

Feedback of PTH and vitamin D

1,25-OH, Vit.D negatively feedbacks to PTH release.

1,25-OH, Vit.D also feedbacks to osteocytes---> Increases FGF-23
- FGF-23 inhibits 1,25-OH production

15

Hypercalcaemia
- Definitions
- Causes

Serum calcium >2.55mmol/L

Causes
- Primary hyperparathyroidism
- Malignancy (of PT)

16

Primary hyperparathyroidism
- Definition
- Presentation
- Complications

Overactivity of the PT= high PTH levels


Presents as:
- High Ca2+ levels
- Low Phosphate levels
- High PTH levels

Complications
- Bone cysts
- Osteoporosis
- Kidney stones

17

Causes of primary hyperparathyroidism

Parathyroid adenoma

Primary hyperplasia of parathyroid.

PT carcinoma

18

Imagining of PT adenoma

Sestamibi PT scan
- Measure gamma rays from radioactive decay of technetium sestamibi
- Adenoma absorbs radioactive substance very fast so can be spotted in scan.


Neck ultrasound

19

Hypoparathyroidism
- Definition
- Causes

Under-active parathyroid

Defined by
- Low calcium
- Low/ normal PTH
- High phosphate levels

Causes:
- Iatrogenic [70%]
- Autoimmune
- Hypomagnesemia--> Mg required for PTH secretion
- Genetic

20

Secondary hyperparathyroidism
- Definition
- Causes

High PT levels not directly caused by the PT gland.
- Problem elsewhere leads to PT hyperplasia.
- Low Ca2+, high PTH.

Causes:
- Chronic kidney failure [inability metabolise vit.D anf excrete phosphate]
- Malabsorption of vit.D
- Lack of sun exposure
- Extensive bowel surgery

21

Iatrogenic causes of hypoparathyroidism

Thyroidectomy
- Removal of thyroid could include removing PT gland.

Radial neck surgery

22

Complications of Vit.D deficiency

Osteoporosis/ osteomalacia in adults

Rickets in children