THE PITUITARY GLAND
The Pituitary Gland is divided into 2 areas.
The Anterior Pituitary:
- Under the regulation of the hypothalamus, the anterior pituitary makes and releases a hormone.
- Growth Hormone (GH).
- Thyroid-stimulating Hormone (TSH).
- Adrenocorticotropin (ACTH).
- Follicle-stimulating Hormone (FSH).
- Leutinizing Hormone (LH).
The Posterior Pituitary:
- Stores and secretes hormones that are made in the hypothalamus.
- Oxytocin and anti-diuretic hormone (ADH).
ANTERIOR PITUITARY HORMONES
- GHRH (Growth Hormone Releasing Hormone) released from the hypothalamus in regulating the secretion of Growth hormone (GH).
- GH secretion is high in newborns, till 4 yr of age.
- Growth of brain and eye independent of growth hormone.
- Insulin-like growth factor 1 (IGF-1) released from the liver inhibits GH secretion by stimulating somatostatin secretion from the hypothalamus.
- Sermorelin – a synthetic analog of GHRH. Which is used as a diagnostic agent for testing childhood short stature.
- Promotes retention of nitrogen and other tissue constituents.
- Induces lipolysis especially in adipose tissue.
- Increases hepatic glucose output.
- Glycogenolysis in the liver.
- Is protein anabolic hormone.
Growth Hormone Deficiency:
- It occurs as a result of damage to the pituitary or hypothalamus by a tumor, infection, surgery, or radiation therapy.
- In childhood: short stature and adiposity, hypoglycemia.
- Adults: Generalized obesity, reduced muscle mass.
- Lack of GH can cause dwarfism.
Growth Hormone Excess:
- It leading to a benign pituitary tumor.
- In adults causes acromegaly.
- If this occurred before the long bone epiphyses close, it leads to the rare condition, gigantism.
Treatment of Excess GH Disorders:
- Synthetic Somatostatin (Octreotide).
- DA agonists (Bromocriptine).
- Surgical removal / Radiotherapy of the tumor.
- GH Antagonists (Pegvisomant).
- Hypothyroidism, Pancreatitis, Gynecomastia.
- It is a growth hormone release-inhibiting hormone (GHRIH).
- It is inhibiting the secretion of GH. Also inhibiting the secretion of TSH, insulin, and gastrin.
- Because of the short half-life and lack of specificity use of somatostatin is very limited.
- Octreotide, Lanreotide, Seglitide are somatostatin analogs.
Thyroid-stimulating Hormone (TSH) / Thyrotrophin
- TSH stimulates the secretion of thyroxine (T4) and triiodothyronine (T3).
- Synthesis and release of TSH by the pituitary are controlled by the hypothalamus.
- Inappropriate TSH secretion results in hypo or hyperthyroidism.
- Promoting steroidogenesis and stimulates cortisol secretion by the adrenal cortex.
- Promotes growth of adrenal cortex.
- Cushing’s syndrome – due to excess production of ACTH from basophil pituitary tumors.
Follicle – Stimulating Hormone (FSH)
- Females: Stimulates growth and development of ovarian follicles, promotes secretion of estrogen by ovaries.
- Males: Essential for sperm production.
- Preparations are available for clinical use:
- Urofollitropin (a purified form of the urine of postmenopausal women).
- 2 recombinant forms: follitropin alpha and follitropin beta.
Leutinizing Hormone (LH)
- Females: Mainly triggers the ovulation, formation of corpus luteum in the ovary, and regulation of ovarian secretion of female sex hormones.
- Males: Stimulates the testes to secrete testosterone.
- Lutropin alfa, approved for use in combination with follitropin alfa for stimulation of follicular development in infertile women with profound LH deficiency.
- Lactotroph cells are responsible for the secretion of prolactin.
- Its secretion is stimulated by estrogen.
- Females: stimulates breast development and milk production.
- Males: involved in testicular function.
- Prolactin secretion is inhibited by dopamine agonists, which act in the pituitary to inhibit prolactin release, used in the treatment of hyperprolactinemia.
- It is an ergot derivative and a potent dopamine agonist.
- Act on D2 receptor.
- Inhibit prolactin release.
- Increases growth hormone release in normal individuals.
POSTERIOR PITUITARY HORMONES
- It is synthesized in the hypothalamus and transported to the posterior pituitary.
- It is an effective uterine stimulant that produces contraction and is used intravenously to induce or reinforce labor.
- Induces the release of milk.
- Suckling sends a message to the hypothalamus via the nervous system to release oxytocin, which further stimulates the milk glands.
Clinical uses of Oxytocin:
- Induction of labor.
- Control of postpartum bleeding.
- Fetal distress, placental abruption or uterine rupture, excessive fluid retention.
Vasopressin (Antidiuretic Hormone ADH):
- Synthesized in the hypothalamus and transported to the posterior pituitary.
- ADH is to increase water conservation by the kidney.
- A high level of ADH secretion leads to the reabsorption of water by the kidney.
- ADH causes peripheral blood vessel constriction to help elevate blood pressure.
- Diabetes insipidus.
- Nocturnal enuresis (by decreasing nocturnal urine production).
• Hyponatremia and seizures.
Synthetic ADH Drugs:
- Vasopressin, Desmopressin.
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