Physiology
Endocrine
Regarding the position of the pituitary gland, which of the following statements is CORRECT:
Answer:
The pituitary gland lies immediately beneath the hypothalamus in a bony hollow of the sphenoid bone (the sella turcica), and it is covered by the fibrous diaphragma sellae of the dura mater. The optic chiasm lies directly superior to the anterior pituitary. The posterior pituitary is connected to the median eminence of the hypothalamus by the pituitary stalk (also known as the infundibulum). The cavernous sinuses (including cranial nerves III - VI) lie lateral to the pituitary gland.Pituitary Gland
Physiology / Endocrine / Pituitary Function
Last Updated: 26th July 2024
Anatomical Location
The pituitary gland lies immediately beneath the hypothalamus in a bony hollow of the sphenoid bone (the sella turcica), and it is covered by the fibrous diaphragma sellae of the dura mater. The optic chiasm lies directly superior to the anterior pituitary. The posterior pituitary is connected to the median eminence of the hypothalamus by the pituitary stalk (also known as the infundibulum). The cavernous sinuses (including cranial nerves III - VI) lie lateral to the pituitary gland. The pituitary gland is primarily divided into two sub glands, the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).
Anatomical Location of the Pituitary Gland. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
Anterior Pituitary Gland
Anterior pituitary hormones are released under the control of hypothalamic releasing or inhibiting hormones originating from small neurons with their cell bodies in the hypothalamus and released into the blood at the median eminence. These hypothalamic hormones are transported directly to the anterior pituitary via hypophyseal portal vessels and act to stimulate or inhibit release of anterior pituitary hormones by the activation of receptors on specific groups of pituitary cells.
The anterior pituitary hormones (and the hormones released by their target organs) inhibit further release of hypothalamic and anterior pituitary hormones by negative feedback mechanisms.
The following hormones are secreted from the anterior pituitary gland:
- Follicle-stimulating hormone (FSH)
- Prolactin
- Thyroid-stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Luteinising hormone (LH)
- Growth hormone (GH)
This can be remembered using the mnemonic: Fresh Pituitary Tastes Almost Like Guinness.
Function of the Anterior Pituitary Gland. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
Posterior Pituitary Gland
The posterior pituitary gland secretes two peptide hormones:
- Oxytocin
- Antidiuretic hormone (ADH)
The posterior pituitary is really a direct extension of the hypothalamus. Oxytocin and ADH are manufactured in the cell bodies of large neurons in the hypothalamus and are transported down the axons of these cells to their terminals on capillaries originating from the inferior hypophyseal artery within the posterior pituitary gland. When these neurons are activated, they release oxytocin or ADH into the general circulation from whence they can reach the relevant target tissues to produce the required effect.
ADH release is controlled by negative feedback mechanisms based on plasma osmolality and blood volume, oxytocin however is involved in positive feedback mechanisms.
Function of the Posterior Pituitary Gland. (Image by OpenStax College [CC BY 3.0 , via Wikimedia Commons)
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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 |
