Physiology
Endocrine
The chromaffin cells of the adrenal medulla secrete catecholamines, stimulated by which of the following:
Answer:
The chromaffin cells of the medulla secrete noradrenaline (20%) and adrenaline (80%), stimulated by sympathetic preganglionic neurones located in the spinal cord which directly innervate the adrenal medulla. These catecholamines act on alpha- and beta- G-protein coupled receptors , having the same effect in tissues as the stimulation of sympathetic nerves. Catecholamines are broken down extracellularly and in the liver by catechol-O-methyltransferase (COMT) and intracellularly by monoamine oxidase (MAO).Catecholamines
Physiology / Endocrine / Adrenal Function
Last Updated: 21st April 2019
The chromaffin cells of the medulla secrete noradrenaline (20%) and adrenaline (80%), stimulated by sympathetic preganglionic neurones located in the spinal cord.
Derivation and Degradation
These catecholamine hormones are derived from tyrosine by a series of steps catalysed by specific enzymes. The production of the rate-limited enzyme, phenylethanolamine-N-methyltransferase, is stimulated by cortisol, providing a direct link between the functioning of the adrenal medulla and cortex.
Catecholamines are broken down extracellularly and in the liver by catechol-O-methyltransferase (COMT) and intracellularly by monoamine oxidase (MAO).
Effects of Adrenaline
These catecholamines act on alpha- and beta- G-protein coupled receptors , having the same effect in tissues as the stimulation of sympathetic nerves. Noradrenaline has equal potency at all adrenoceptors, but adrenaline at normal plasma concentrations will only activate beta-receptors (higher levels do stimulate alpha-receptors).
Actions of adrenaline:
- Cardiovascular system
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- Increased rate and force of cardiac contraction
- Vasoconstriction of vessels in skin, mucous membranes and splanchnic bed
- Vasodilation of skeletal muscle vessels
- Increased cardiac output and blood pressure
- Respiratory system
- Bronchodilation
- Increased ventilation rate
- Gastrointestinal system
- Smooth muscle relaxation
- Contraction of sphincters
- Metabolism
- Decreased insulin release
- Increased glucagon release
- Increased thermogenesis
- Increased glycolysis
- Increased lipolysis
- Eye
- Pupillary dilation
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
