Physiology
Endocrine
Regarding the adrenal medulla, which of the following statements is INCORRECT:
Answer:
The adrenal medulla produces catecholamines, and is controlled by and functions in concert with the sympathetic nervous system. The chromaffin cells of the medulla secrete noradrenaline (20%) and adrenaline (80%), stimulated by sympathetic preganglionic neurones located in the spinal cord. In response to stress, catecholamines are released from the adrenal medulla to produce a rapid increase in cardiac output and the mobilisation of metabolic fuels. These catecholamines act on alpha- and beta- G-protein coupled receptors , having the same effect in tissues as the stimulation of sympathetic nerves.Adrenal Function
Physiology / Endocrine / Adrenal Function
Last Updated: 26th July 2024
The adrenal glands are located on the superior pole of each kidney. The glands are retroperitoneal, covered in perinephric fat and enclosed in renal fascia. The adrenal gland is divided into two functionally distinct regions; the larger outer region (comprising about 90% of the gland) called the adrenal cortex and the inner, much smaller region called the adrenal medulla.
Adrenal Gland. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
Adrenal Cortex
The adrenal cortex is functionally and anatomically divided into three zones of tissue which each secrete different steroid hormones:
- The outer zona glomerulosa secretes mineralocorticoid (aldosterone) which regulates salt and water homeostasis.
- The zona fasciculata secretes glucocorticoid (cortisol and its analogues) which regulates carbohydrate metabolism and the response to stress.
- The inner zona reticularis secretes the androgen dehydroepiandrosterone (DHEA) which has effects on the maintenance of secondary sexual characteristics.
The release of cortisol and DHEA is stimulated by adrenocorticotropic (ACTH) hormone from the anterior pituitary, which in turn is released in response to corticotropin-releasing hormone (CRH) from the hypothalamus.
The secretion of aldosterone, in contrast, is mainly regulated by the renin-angiotensin system, in response to low circulating blood volume, hyponatraemia or hyperkalemia.
Adrenal Medulla
The adrenal medulla produces catecholamines, and is controlled by and functions in concert with the sympathetic nervous system.
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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 |
