THE ENDOCRINE SYSTEM FELIX K. NYANDE
The endocrine system • A collection of glands that secrete hormones. • Hormones are released into circulation to arrive at a target organ. • The target organ has cells that possess the appropriate receptor(s) • The system use cycles and negative feedback to regulate physiological functions
Major endocrine Glands • Hypothalamus • Pituitary: anterior and posterior • Thyroid • Parathyroid • Pancreas • Ovaries • Testes • Adrenals: medulla and cortex
Hypothalamus • Releasing and inhibiting hormones that control the release of pituitary hormones. • Corticotropin-releasing hormone (CRH) • Thyrotropin-releasing hormone (TRH) • Growth hormone-releasing hormone • (GHRH) • Gonadotropin-releasing hormone • (GnRH) • Vasopressin and oxytocin
Pituitary gland (hypophysis) • Also known as ‘the master gland’ • Located in the skull beneath the hypothalamus of the brain • Divided into the anterior and posterior glands • Posterior gland stores hormones from the hypothalamus
Anterior pituitary • Growth hormone (GH) • Adrenocorticotropic hormone (ACTH) • Thyroid-stimulating hormone (TSH) • Follicle-stimulating hormone (FSH) • Luteinizing hormone (LH)
Adrenal medulla • Epinephrine • Norepinephrine • Function: Serve as neurotransmitters for the sympathetic nervous system
Parathyroid gland • Parathyroid hormone • Function: • Regulates serumcalcium by stimulating oesteoclasts to break down the calcium containing matrix to release free calcium ions into the bloodstream.
Disorders of the posterior pituitary • ADH and oxytocinare synthesized in the hypothalamus and stored in the posterior pituitary. • Vasopressin controls the excretion of water by the kidney; its secretion is stimulated by an increase in the osmolality of the blood or by a decrease in blood pressure. • Oxytocin facilitates milk ejection during lactation and increases the force of uterine contractions during labor and delivery. Oxytocin secretion is stimulated during pregnancy and at childbirth.
Disorders of the anterior pituitary • Hypersecretion: • ACTH: Cushing’s syndrome • growth hormone: acromegaly. Acromegaly, an excess of growth hormone in adults, results in bone and soft tissue deformities and enlargement of the viscera without an increase in height. • In children:gigantism, with a person reaching 7 or 8 feet tall. • Hyposecretion • Grow hormone: dwarfism • ADH: diabetes insipidus:
causes • Hypopitutarism: • disease of the pituitary gland itself or of the hypothalamus, • destruction of the anterior lobe of the pituitary gland • Panhypopituitarism • (Simmonds’ disease): total absence of all pituitary secretions and is rare. • Postpartum pituitary necrosis (Sheehan’s syndrome) • radiation therapy to the head and neck area. • Total destruction of the pituitary gland by trauma, tumor, or vascular lesion
General manifestations • extreme weight loss, emaciation, • Atrophy of all endocrine glands and organs, • hair loss, • impotence, • amenorrhea, • hypometabolism, and • hypoglycemia. • Coma and death occur if the missing hormones are not replaced.
Diabetes insipidus • Diabetes insipidus is a disorder of the posterior lobe of the pituitary gland caused by a deficiency of antidiuretic hormone (ADH), or vasopressin and characterised by polydipsia and large volumes of dilute urine
causes • head trauma, • brain tumor, • surgical ablation or irradiation of the pituitary gland. • Infections of the central nervous system (meningitis, encephalitis, tuberculosis) • Other tumours(eg, metastatic disease, lymphoma of the • breast or lung). • failure of the renal tubules to respond to ADH; this nephrogenic form may be related to hypokalemia, hypercalcemia, and a variety of medications • (eg, lithium, demeclocycline
Clinical manifestations • very dilute, water-like urine with a specific gravity of 1.001 to 1.005 • The urine contains no abnormal substances such as glucose and albumin. • patient tends to drink 2 to 20 liters of fluid daily • hypernatremia • severe dehydration.
Diagnostic investigations • Fluid deprivation test: carried out by withholding fluids for 8 to 12 hours or until 3% to 5% of the body weight is lost. The patient is weighed frequently during the test. Plasma and urine osmolality studies are performed at the beginning and end of the test. The inability to increase the specific gravity and osmolality of the urine is characteristic of diabetes insipidus. • Measurements of plasma levels of ADH (vasopressin) and plasma and urine osmolality, trial of desmopressin (synthetic vasopressin) therapy • intravenous infusion of hypertonic saline solution.
management • The objectives of therapy are to • replace ADH • ensure adequate fluid replacement, • identify and correct the underlying intracranial or Nephrogenic pathology.
management • PHARMACOLOGIC THERAPY • Desmopressin (intranasal or IM)
management • inform the patient and family about follow-up care and emergency measures. • provide specific verbal and written instructions, • show the patient how to administer the medications • advise the patient to wear a medical identification bracelet and to carry medication and information about this disorder at all times.