Fluid & Electrolyte Balance

Question 1

What factors can be observed via measurements of Na+/K+/Cl-/HCO3-?

Answer 1

Fluid, electrolyte status and urine function

Question 2

How is water secretion by the kidneys controlled?

Answer 2

It is controlled by ADH (anti-diuretic hormone), which is secreted from the posterior pituitary glands depending on the osmolarity of the body.

• Increased salt conc. in blood (high osmolality) = ADH secreted (increasing water reabsorption)
• Low osmolality (blood being more diluted) = ADH switched off

Question 3

What are normal Na+ levels in the blood?

Answer 3

135-145 mmol/L

Question 4

How can Na+ be excreted?

Answer 4

Via kidneys, sweat, gut and vomiting

Question 5

Which 2 substances regulate urinary Na+ output?

Answer 5

• Aldosterone - causing Na+/H2O retention

- Atrial natriuretic peptide (ANP) - secreted by the heart to increase Na+ urinary excretion

Question 6

Describe the RAAS process and the end result of this system.

Answer 6

1. Liver produces angiotensin & kidneys produce the enzyme renin
2. This produces angiotensin I
3. Lungs produce angiotensin converting enzyme (ACE), which converts angiotensin I into angiotensin II
4. Angiotensin II binds to the adrenal glands of the kidneys to stimulate aldosterone production
5. Aldosterone works on:
   - The heart
   - The kidneys (increase Na+/H2O retention and K+ excretion)
   - Blood vessels (vasoconstriction)

Question 7

What is hyponatremia, and what causes it?

Answer 7

It is low Na+ levels in the body caused by vomiting, burns, diarrhoea, Addison’s disease (low aldosterone levels so Na+ not retained), or inappropriate ADH secretions

Question 8

What happens to cells during hyponatremia?

Answer 8

Water moves from extracellular fluid (ECF) to intracellular fluid (ICF) to restore osmotic pressure of the cells

Question 9

What are the symptoms of hyponatremia?

Answer 9

1. Nausea
2. Lethargy
3. Reduced consciousness
4. Headaches

Question 10

What are the clinical signs of hyponatremia?

Answer 10

1. Decreased urinary output
2. Hypotension
3. Increased pulse
4. Decreased skin turgor

Question 11

Which 2 drugs are associated with hyponatremia?

Answer 11

Lithium and SSRIs

Question 12

What is hypernatremia, and what causes it?

Answer 12

It is high Na+ levels in the body caused by low water intake, excess water loss, diabetes insipidus (no ADH), sweating, over-infusion of saline/salts

Question 13

How does hypernatremia form concentrated urine?

Answer 13

High Na+ levels induces a higher osmotic pressure.

This increases urea in the ECF of cells, which forms concentrated urine. ADH is then released.

Question 14

What are the symptoms of hypernatremia?

Answer 14

1. Thirst
2. Dry mouth
3. Weakness
4. Loss of skin turgor

Question 15

What are normal K+ levels in the blood?

Answer 15

3.5-5mmol/L

Question 16

What type of electrolyte is K+?

Answer 16

It is an excitation electrolyte so used for e.g. muscle health

Question 17

Which protein stimulates the uptake of K+ in cells?

Answer 17

Insulin

Question 18

What occurs in acidosis in relation to K+ & H+?

Answer 18

During acidosis, K+ is displaced by H+ and increases, causing hyperkalaemia

Question 19

What can cause hyperkalaemia?

Answer 19

1. Renal failure
2. Addisons disease
3. Hormonal effects - e.g. low insulin
4. Excess K+ supplements
5. Excess of K+ sparing diuretics

Question 20

How can hyperkalaemia be treated?

Answer 20

1. Bicarbonate infusion
2. Insulin - to increase K+ cellular uptake
3. Salbutamol

Question 21

Why is hyperkalaemia known as an medical emergency?

Answer 21

Because it can effect cardiac/skeletal muscles

Question 22

What causes hypokalaemia?

Answer 22

1. GI losses
2. Renal failure
3. Alkalosis
4. High aldosterone levels - Conn’s syndrome
5. Drug induced - e.g. diuretics, corticosteroids

Question 23

Which specific drug increases in toxicity during hypokalaemia?

Answer 23

Digoxin.

Question 24

Which protein can affect Ca2+ levels in the body?

Answer 24

Albumin, because it carries Ca2+

Question 25

What 2 substances control Ca2+ homeostasis in the body?

Answer 25

1. Vitamin D | 2. Parathyroid hormone (PTH) - secreted from parathyroid glands in response to low unbound Ca2+ levels

Question 26

What is the difference between osteoclasts and osteoblasts?

Answer 26

1. Osteoclasts - shed Ca2+ from the bone to provide for the body 2. Osteoblasts - puts Ca2+ into the bone

Question 27

What is the effect of PTH in terms of Ca2+ in the body?

Answer 27

It increases osteoclastic reabsorption and increases renal reabsorption of Ca2+ - this all increases Ca2+ levels in the body

Question 28

This equation is used for which types of patients specifically? Corrected calcium (mmol/L) = total measured calcium + 0.02 (40-albumin)

Answer 28

Patients with low albumin levels

Question 29

What can cause hypocalcaemia?

Answer 29

1. Renal disease 2. Vitamin D deficiency 3. Hypoparathyroidism

Question 30

What are the early symptoms of hypocalcaemia?

Answer 30

Numbing/tingling sensation of fingers, due to muscular disturbances.

Question 31

How is hypocalcaemia managed?

Answer 31

Ca2+ supplements.

Question 32

What can cause hypercalcaemia?

Answer 32

1. Vitamin D overdose 2. Bone diseases 3. Hyperparathyroidism

Question 33

Which drug class is used to treat hypercalcaemia?

Answer 33

Bisphosphonates - they bind to Ca2+ in the bone to retain it