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 1. Hypothalamus 2. Pituitary: anterior and posterior 3. Thyroid 4. Parathyroid 5. Pancreas 6. Ovaries 7. Testes 8. Adrenals: medulla and cortex

Hypothalamus O 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

HYPOTHALAMUS HormoneFunction ADHIncreases water reabsorption by kidney Oxytocin Stimulates contraction of pregnant uterus, milk ejection from breasts after childbirth

Pituitary gland (hypophysis) O Also known as ‘the master gland’ O Located in the skull beneath the hypothalamus of the brain O Divided into the anterior and posterior glands O 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)

HYPOTHALAMUS LH Female: stimulates OVULATION and development of corpus luteum to produce estrogen and progesterone Male: stimulates secretion of testosterone, development of interstitial tissue of testes

ANTERIOR PITUITARY HormoneFunction GH Stimulates growth of bone and muscle, promotes protein synthesis and fat metabolism, decreases carbohydrate metabolism prolactin stimulates the production of breast milk. ACTH Stimulates synthesis and secretion of adrenal cortical hormones TSH Stimulates synthesis and secretion of thyroid hormones FSH Female: stimulates growth of ovarian follicle, ovulation Male: stimulates sperm production

Adrenal cortex Mineralocorticoids e.g. Aldosterone Increases sodium absorption, potassium loss by kidney Glucocorticoids e.g. Cortisol Affects metabolism of all nutrients; regulates blood glucose levels, affects growth, has anti-inflammatory action, and decreases effects of stress Androgens e.g. testosterone Have minimal intrinsic androgenic activity

Adrenal medulla Epinephrine Norepinephrine Function: Serve as neurotransmitters for the sympathetic nervous system

Thyroid gland HormoneFunction T3 & T4Increase metabolic rate; increase protein and bone turnover; increase responsiveness to catecholamines; necessary for foetal and infant growth and development. CalcitoninReduces the concentration of calcium and phosphate in the blood by aiding the absorption of calcium into the matrix of bones

Parathyroid gland Parathyroid hormone Function: Regulates serum calcium by stimulating oesteoclasts to break down the calcium containing matrix to release free calcium ions into the bloodstream.

pancreas InsulinLowers blood glucose by facilitating glucose transport across cell membranes of muscle, liver, and adipose tissue GlucagonIncreases blood glucose concentration by stimulation of glycogenolysis and glyconeogenesis SomatostatinDelays intestinal absorption of glucose

gonads Testes ( testosterone ) development of male sex organs and secondary sex characteristics; aids in sperm production Ovaries (oestrogen & progesteron e) Affects development of female sex organs and secondary sex characteristics. Influences menstrual cycle; stimulates growth of uterine wall; maintains pregnancy

Disorders of the posterior pituitary ADH and oxytocin are 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 O 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. O Hyposecretion Grow hormone: dwarfism ADH: diabetes insipidus:

causes O 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 O 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 to 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 O 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.