L5 Flashcards
Where is calcium important
· Exocytosis
• Neurotransmitter secretion
• Hormone secretion
How does hypocalcaemia destabilise neurones
- The reason hypocalcemia causes neuron excitation (contrary to the above logic) is because a decrease in extracellular calcium concentration increases the neuron membrane’s permeability to sodium and allows sodium to easily depolarize the neuron’s membrane and cause an action potential
Physical signs of hypocalcaemia
Trousseau sign of latent tetany (aka carpopedal spasm)
Chvostek’s sign
What is a carpopedal spasm
In a patient with hypocalcemia, carpal spasm may be elicited by occluding the brachial artery.
To perform the maneuver, a blood pressure cuff is placed around the arm and inflated to a pressure greater than the systolic blood pressure and held in place for 3 minutes. If carpal spasm occurs, manifested as flexion at the wrist and metacarpophalangeal joints, extension of the distal interphalangeal and proximal interphalangeal joints, and adduction of the thumb and fingers, the sign is said to be positive and the patient likely has hypocalcemia.
How does neuromuscular inability present in hypocalcemia
Chvostek's sign Trousseau's sign Paresthesias Tetany Seizures (focal, petit mal, grand mal) Fatigue Anxiety Muscle cramps Polymyositis Laryngeal spasms Bronchial spasms
Neurological signs and symptoms associated with hypocalcemia
Extrapyramidal signs due to calcification of basal ganglia Calcification of cerebral cortex or cerebellum Personality disturbances Irritability Impaired intellectual ability Nonspecific EEG changes Increased intracranial pressure Parkinsonism Choreoathetosis Dystonic spasms
Mental status of a person with hypocalcemia
Confusion
Disorientation
Psychosis
Psychoneurosis
Ectodermal changes in a person with hypocalcemia
Dry skin Coarse hair Brittle nails Alopecia Enamel hypoplasia Shortened premolar roots Thickened lamina dura Delayed tooth eruption Increased dental caries Atopic eczema Exfoliative dermatitis Psoriasis Impetigo herpetiformis
Smooth muscle involvement in an individual with hypocalcemia
Dysphagia Abdominal pain Biliary colic Dyspnea Wheezing
Opthalmologic manifestations of hypocalcemia
- Subcapsular cataracts
- Papilledema
Cardiac effects of hypocalcemia
- Prolonged QT interval in EKG
- Congestive heart failure
- Cardiomyopathy
What is the hallmark of acute hypocalcemia
- Neuromuscular irritability
- Patients often complain of numbness and tingling in their fingertips, toes, and the perioral region. Paresthesias of the extremities may occur, along with fatigue and anxiety
How can neuromuscular irritability be demonstrated clinically
By eliciting chvostek’s or trousseau’s signs
In what percentage of normal individuals is chvostek’s sign present
- In 10% of normal individuals
How can chvostek’s sign be elicited
- Tapping the skin over the facial nerve anterior to the external auditory meatus produces this sign
What causes chvostek’s sign
Low plasma calcium increases the permeability of neuronal membranes to sodium ions, causing a progressive depolarization.
This increases the ease with which action potentials can be initiated. If the plasma Ca2+ decreases to less than 50% of the normal value action potentials may be spontaneously generated, causing contraction of peripheral skeletal muscle.
The reverse is true in hypercalcemia. High Calcium causing decreased permeability and thence muscle weakness.
What is chvostek sign a sign of
- Tetany seen in hypocalcemia
What is chvostek sign also seen in
- Respiratory alkalosis, such as that seen in hyperventilation
Acute consequences of hypercalcemia
- Thirst and polyuria
- Abdominal pain
Chronic consequences of hypercalcemia
- Constipation
- Musculoskeletal aches / weakness
- Neurobehavioral symptoms
- Renal calculi
- Osteoporosis
What is albumin
Albumin is a globular, water-soluble, un-glycosylated serum protein of approximate molecular weight of 65,000 Daltons.
Albumin (when ionized in water at pH 7.4, as found in the body) is negatively charged
Why might the corrected Ca2+ be inaccurate in a lab report
- Albumin concentration may be below 20 g/l
- In severe acute illness (in these cases measure ionised Ca2+ directly)
Effect of pH on protein binding with calcium
- An increase in pH, alkalosis, promotes increased protein binding, which decreases free calcium levels
- Acidosis, on the other hand, decreases protein binding, resulting in increased free calcium levels
Reference range of ionised calcium
1.1-1.35 mmol/L