Physiology
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This was previously featured in an exam
Endocrine
Question 75 of 180
A 15 year old is brought into ED with persistent diarrhoea and vomiting. She is severely dehydrated. Which of the following hormones is released in response to dehydration:
Answer:
Antidiuretic hormone (ADH) is released in response to raised plasma osmolality seen in dehydration. ADH acts on the kidneys to promote water retention and on the vascular system to cause vasoconstriction.Pituitary Hormone Dysfunction
Physiology / Endocrine / Pituitary Function
Last Updated: 8th December 2020
| Hormone | Stimulation | Inhibition | Action | Clinical Excess | Clinical Deficiency |
|---|---|---|---|---|---|
| ACTH | CRH | Cortisol | Acts on adrenal cortex to stimulate release of glucocorticoids which regulate metabolism and stress response | Cushing's disease | Secondary adrenal insufficiency |
| TSH | TRH | Thyroxine | Acts on thyroid gland to stimulate release of thyroid hormones which regulate metabolism | Secondary hyperthyroidism | Secondary hypothyroidism |
| FSH/LH | GnRH | Prolactin, oestrogen/testosterone | Acts on gonads to stimulate production of oestrogen/testosterone and production of eggs/sperm | Infertility | Gonadal insufficiency |
| GH | GHRH | Somatostatin | Acts on liver, bone and muscles to stimulate production of IGFs which stimulate body growth and a higher metabolic rate | Acromegaly in adults or gigantism in children | Adult GH deficiency syndrome in adults or dwarfism in children |
| Prolactin | PRH, TRH | Dopamine | Acts on mammary glands to promote milk production | Hyperprolactinemia | Failure of postpartum lactation |
| ADH | Raised plasma osmolality | Low plasma osmolality, alcohol, caffeine, glucocorticoids and atrial natriuretic peptide (ANP) | Acts on kidneys to promote water retention and on vascular system to cause vasoconstriction | SIADH | Central diabetes insipidus |
| Oxytocin | Stretch receptors in nipple and cervix | Stress | Acts on female reproductive system to trigger uterine contractions during childbirth and milk ejection during suckling | / | / |
Anterior Pituitary Hormones
ACTH
- Adrenocorticotropic hormone (ACTH) acts on the adrenal cortex to stimulate glucocorticoid and androgen release.
- ACTH secretion is stimulated by corticotropin-releasing hormone (CRH) from the hypothalamus.
- ACTH secretion is inhibited by cortisol.
- ACTH deficiency results in secondary adrenal insufficiency.
- Excess levels of ACTH due to a functioning pituitary adenoma results in Cushing's disease.
TSH
- Thyroid-stimulating hormone (TSH) acts on the thyroid gland to stimulate thyroid hormone (T3 and T4) release.
- TSH secretion is stimulated by thyrotropin-releasing hormone (TRH) from the hypothalamus.
- TSH secretion is inhibited by raised serum levels of T3 or T4, somatostatin, dopamine, glucocorticoids, acute non-thyroidal illness and increased human chorionic gonadotropin (e.g. in early pregnancy).
- TSH deficiency results in secondary hypothyroidism.
- Excess TSH (extremely rare) results in secondary hyperthyroidism.
FSH/LH
- The gonadotropins, luteinising hormone (LH) and follicle stimulating hormone (FSH) act via G-protein coupled receptors on the gonads. In the male, LH acts to stimulate production of testosterone, which acts in concert with FSH to support spermatogenesis. In the female, LH and FSH are essential for normal menstruation and reproduction.
- LH/FSH secretion is stimulated by gonadotropin-releasing hormone (GnRH) from the hypothalamus. GnRH is released in a pulsatile fashion, which is essential for normal reproductive activity.
- LH/FSH secretion is inhibited by prolactin (via GnRH) and sex steroids.
- LH/FSH deficiency results in gonadal insufficiency (decreased sex steroids).
- Excess levels of FSH/LH (extremely rare) results in infertility.
Growth Hormone
- Growth hormone (GH) acts on the liver to stimulate insulin-like growth factor (IGF) production to promote skeletal and muscular growth and protein synthesis.
- GH secretion is stimulated by growth hormone-releasing hormone (GHRH) from the hypothalamus.
- GH secretion is inhibited by growth hormone-inhibiting hormone (somatostatin) and IGF-1.
- Excess levels of GH results in acromegaly in adults and gigantism in children (if excess GH occurs prior to epiphyseal fusion).
- GH deficiency results in dwarfism in children or adult GH deficiency syndrome in adults.
Prolactin
- Prolactin acts on the mammary glands and reproductive organs to promote growth of these organs and initiate lactation.
- Prolactin secretion is stimulated by prolactin-releasing factor (PRF) and thyrotropin-releasing hormone (TRH) from the hypothalamus.
- Prolactin secretion is inhibited by dopamine secreted by the hypothalamus.
- Prolactin levels rise physiologically in pregnancy, puerperium, and breast stimulation.
- Excess levels of prolactin may be caused by a prolactinoma (prolactin-secreting pituitary adenoma); compression of the pituitary stalk by a pituitary or hypothalamic tumour preventing normal dopaminergic inhibition of prolactin release; PCOS; severe hypothyroidism (due to increased synthesis of TRH); drugs e.g. dopamine antagonists, antipsychotics
- Hyperprolactinaemia causes symptoms such as oligomenorrhoea/amenorrhoea, galactorrhoea, loss of libido, erectile dysfunction and infertility (via inhibition of the release of GnRH from the hypothalamus).
- Prolactin deficiency results in failure of postpartum lactation.
Posterior Pituitary Hormones
ADH
- Antidiuretic hormone (ADH) acts on the kidneys to increase water permeability in the distal nephron allowing greater water reabsorption and concentration of urine. ADH also acts on vascular smooth muscle, causing vasoconstriction.
- ADH release is stimulated mainly by raised plasma osmolality detected by osmoreceptors in the anterior hypothalamus. Other stimuli to ADH release include volume depletion, angiotensin II, hypoxia, hypercapnia, adrenaline, cortisol, sex steroids, pain, trauma, temperature and psychogenic stimuli.
- ADH release is inhibited by low plasma osmolality, alcohol, caffeine, glucocorticoids and atrial natriuretic peptide (ANP).
- ADH deficiency results in central diabetes insipidus.
- Excess levels of ADH results in syndrome of inappropriate ADH secretion (SIADH).
Oxytocin
- Oxytocin acts on the mammary glands to stimulate milk ejection, and the uterus to stimulate uterine contraction in childbirth.
- Oxytocin release is stimulated by stretch receptors in the nipple and the cervix and by oestrogen.
- Oxytocin release is inhibited by stress.
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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 |
