Endocrine System Notes (MRD515) PDF

ENDOCRINE SYSTEM MRD515 LEARNING OUTCOME Describe the anatomic components and function of the endocrine system. Identify and explain the various imaging modalities used in diagnosing and treating endocrine disorders. Specify the disorders, signs and symptoms, and prognosis of the endoc...

ENDOCRINE SYSTEM MRD515 LEARNING OUTCOME Describe the anatomic components and function of the endocrine system. Identify and explain the various imaging modalities used in diagnosing and treating endocrine disorders. Specify the disorders, signs and symptoms, and prognosis of the endocrine pathologies discussed in this chapter. ANATOMY AND PHYSIOLOGY The endocrine system controls cell metabolism by releasing hormones into the bloodstream. These hormones affect different body processes. Major endocrine glands are the pituitary, pineal, adrenal, thyroid, parathyroid, and thymus glands. The pancreas, gonads (ovaries and testes), and hypothalamus also produce hormones. Hormones are released due to three types of triggers: blood chemistry changes, nervous system signals, and responses to other hormones.  The pituitary gland has three parts: anterior, intermediate, and posterior. It's known as the "master endocrine gland" and is controlled by the hypothalamus. Each part releases specific hormones.  The pineal gland in the brain manages daily rhythms with melatonin and plays a role in puberty through gonadotropin-releasing hormone (GnRH). The adrenal glands on top of the kidneys have two parts: the adrenal medulla (produces epinephrine and norepinephrine) and the adrenal cortex (produces corticosteroids). These hormones are linked to stress, electrolytes, and metabolism. The thyroid gland in the neck releases thyroid hormones (T3 and T4) for metabolism and calcitonin to control blood calcium levels. It needs iodine for production. Parathyroid Glands, found behind the thyroid, produce parathyroid hormone (PTH) to regulate blood calcium by increasing osteoclasts and calcium absorption. The pancreas serves as both an endocrine (releases hormones into the blood) and exocrine organ (releases substances to organs or surfaces). It produces insulin (reduces blood sugar) and glucagon (increases blood sugar) using islets of Langerhans. These hormones help maintain blood glucose levels in balance.  Regulation: Many of these glands and hormones are controlled by feedback mechanisms, either through direct neural signals or hormonal regulation. IMAGING CONSIDERATION Radiography is useful for diagnosing metabolic diseases affecting the skeletal system and endocrine disorders like Cushing's disease. However, it has limited utility in evaluating pituitary gland disorders, and other advanced imaging techniques like MRI, CT, or PET are increasingly preferred for definitive diagnoses in such cases.  DXA, also known as bone mineral densitometry, is crucial for assessing osteoporosis. Bone Mineral It measures bone density at specific sites like the radius, femoral neck, and Densitometry lumbar spine. Results are compared to norms, with a "T-score" reflecting standard deviations (DXA) from a 30-year-old reference population. T-scores help classify bone health as normal, osteopenia, or osteoporosis. The "Z- score" compares an individual's bone density with a population matched for age, gender, weight, and ethnicity. Magnetic Resonance Imaging (MRI) MRI is preferred over CT for imaging neuroendocrine disorders. It can reliably show pathologies in the hypothalamus and helps diagnose conditions like empty sella syndrome and pituitary adenomas, including microadenomas. Gadolinium contrast-enhanced MRI is commonly used for pituitary adenoma visualization and monitoring. Computed Tomography (CT) High-resolution brain CT with contrast is an alternative when MRI is unavailable or contraindicated for pituitary disorders. It is also useful for evaluating the pineal gland. Neck CT scans assist in assessing thyroid and parathyroid neoplastic diseases. Abdominal CT is employed for identifying adrenal neoplasms, often guided by CT for biopsy procedures. It helps evaluate adrenal gland enlargement in Cushing's disease patients.  Nuclear Medicine Procedures Iodine-123 (123I) uptake tests are valuable for diagnosing thyroid gland function and detecting nonpalpable nodules. It is used post-surgery or after ablation to assess remaining thyroid tissue. Nuclear medicine imaging using iodine-131 (131I)- metaiodobenzylguanidine (MIBG) is becoming popular for localizing medullary tumors in adrenal glands. This technique involves scanning over several days to identify increased uptake, indicating the presence of pheochromocytoma. 131I-MIBG can also be used for treating medullary adrenal gland tumors. SKELETAL DISORDERS  Osteoporosis Osteoporosis is a common metabolic bone disorder characterized by decreased bone density, leading to a weakened bone structure. It is more prevalent in postmenopausal women and can result in fractures, particularly in the hip, spine, and wrist. Radiography can detect advanced cases, but early-stage evaluation is best done through bone mineral densitometry using DXA. Secondary Osteoporosis is associated with other diseases, medications, or hereditary factors. It can be differentiated from primary osteoporosis by examining serum enzyme levels, especially alkaline phosphatase. Treatment involves dietary adjustments, vitamin supplements, and weight-bearing exercises. Osteomalacia Osteomalacia is caused by a lack of calcium in tissues, resulting in the failure of bone tissue to calcify properly. It can lead to soft osteoid instead of rigid bone (inadequate intake and absorption of vitamin D) Osteomalacia may be associated with various conditions, including intestinal malabsorption and chronic renal failure. If osteomalacia occurs before growth plate closure, it is known as rickets Radiographically, it appears siilar to osteoporosis but may show pseudofractures or Looser zones. Diagnosis involves laboratory tests and, in severe cases, bone biopsy.  Paget Disease (Osteitis Deformans) Paget disease is a metabolic disorder that affects bones and often begins in older adults (due to genetic links/viral infection) It can affect various bones, including the pelvis, spine, skull, and long bones. The disease has two stages: osteolytic (bone destruction) and osteoblastic (replacement with soft, poorly mineralized material). Radiographically, it presents as a "cotton wool" appearance due to increased bone vascularity and destruction. Early detection can be done through radionuclide bone scans. Blood tests show high alkaline phosphatase levels. While there is no cure, medication can be administered to reduce bone reabsorption in symptomatic cases. PITUITARY GLAND DISORDERS  Acromegaly Acromegaly is an endocrine disorder primarily affecting the skeletal system, caused by excessive secretion of growth hormone (GH) in adults. It is often due to a pituitary adenoma. Symptoms include a thickening and coarsening of bones, an enlarged sella turcica, and changes in the skull. Individuals with acromegaly may have a prominent forehead, jaw, enlarged hands, and coarser facial features. Diagnosis involves MRI of the brain. Treatment typically involves surgery and radiotherapy to remove the adenoma.  Diabetes Insipidus Diabetes insipidus results from an insufficient level of antidiuretic hormone (ADH- regulate water balance), which can be neurogenic (CNS) or nephrogenic (kidney) in origin. It may be secondary to brain lesions, genetic factors, or acquired renal disorders. Symptoms include excessive urination (polyuria) and increased thirst. Diagnosis is made through imaging (CT or MRI) to identify lesions affecting ADH balance. Treatment includes hormone replacement therapy. Hypopituitarism Hypopituitarism is characterized by decreased or absent pituitary hormone production from the anterior pituitary gland. It can be caused by various factors, including genetic mutations, pituitary infarction, and other medical conditions. Symptoms depend on the hormones affected and may include hormonal imbalances. Diagnosis is confirmed through MRI of the sellar region. Treatment involves hormone replacement therapy to address the specific deficiencies. ADRENAL GLAND DISORDERS Cushing Syndrome Cushing syndrome is caused by an adrenal cortex dysfunction leading to an overproduction of glucocorticoids. Glucocorticoids regulate metabolism, immune responses, and inflammation by affecting gene expression and suppressing the immune system. It can result from various factors, including prolonged steroid therapy. Symptoms include a round face ("moon" facies), fat deposits in the neck and trunk, thin skin that doesn't heal well, and irregular menstrual cycles in females. Diagnostic tests include cortisol analysis, and MRI may be used to detect pituitary adenomas. Treatment depends on the origin of the condition and may involve surgery or radiotherapy.  Addison Disease Addison disease is a rare condition characterized by primary adrenal insufficiency. It often results from autoimmune destruction of the adrenal cortex but can have other causes like infection or neoplastic disease. Symptoms include weight loss, fatigue, weakness, nausea, low blood sugar, and low blood pressure. Diagnosis involves laboratory tests for cortisol and ACTH levels. Treatment includes hormone replacement therapy (HRT) and dietary adjustments. If left untreated, it can progress to a life-threatening adrenal crisis. Adrenal Carcinomas Adrenal carcinomas are rare but aggressive tumors that originate in the adrenal glands. Metastasis from other cancers to the adrenal glands is more common. Lung cancer is the most common source of adrenal metastases, but other cancers can also spread there. Imaging techniques like contrast-enhanced CT and MRI are used for diagnosis. Surgical removal of adrenal masses is often required, and the risk of malignancy increases with the size of the tumor. PANCREATIC DISORDERS Diabetes Mellitus Diabetes mellitus is a syndrome characterized by chronic hyperglycemia (high blood sugar levels), glucose intolerance, and metabolic alterations involving carbohydrates, fats, and proteins. Normal blood glucose levels range from 70 to 120 mg/dL, and fasting glucose levels above 126 mg/dL indicate the presence of diabetes. Type 1 Diabetes This type is often genetic and autoimmune in nature. It typically develops before the age of 30 and results from the destruction of pancreatic β cells. Individuals with type 1 diabetes require insulin therapy. Symptoms include weight loss, fluctuations in blood glucose levels, increased urination, excessive thirst, and increased appetite.  Type 2 Diabetes Primarily affecting those over 40, often related to obesity and a sedentary lifestyle. It involves insulin resistance and inadequate insulin secretion. The risk factors include age, gender (more common in women), race (higher rates among certain racial groups), genetics, and environmental factors. It is associated with metabolic syndrome, which is characterized by specific criteria including obesity, high triglycerides, low HDL cholesterol, high blood pressure, and elevated fasting plasma glucose. Complications of type 2 diabetes include vascular problems such as coronary artery disease, stroke, and peripheral vascular disease. Metabolic syndrome Metabolic syndrome is identified in individuals who exhibit three or more of the five traits: increased waist circumference, high triglycerides, low HDL cholesterol, high blood pressure, and elevated fasting plasma glucose. It is considered a precursor to type 2 diabetes and is often associated with obesity and a sedentary lifestyle. THYROID AND PARATHYROID GLAND DISORDERS  Characteristic Hypothyroidism Hyperthyroidism Hyperthyroidism & Cause Deficiency of thyroid hormones (TH) Antibodies attacking TSH receptors leading to excessive TH Hypothyroidism Common Autoimmune production Graves' disease (autoimmune), Causes thyroiditis toxic nodular goiter, thyroiditis (Hashimoto's disease), iatrogenic factors, iodine deficiency Symptoms Fatigue, cold Enlarged thyroid gland (goiter), intolerance, weight nervousness, hyperactivity, eye gain, and systemic and skin changes, potential life- effects threatening thyroid storms Diagnosis Laboratory tests to Laboratory tests (serum TSH Methods evaluate thyroid levels), nuclear medicine (123I hormone levels thyroid uptake scans), sometimes MRI Treatment Hormone replacement Antithyroid drugs, surgical thyroid Options therapy (HRT) gland removal, radioactive iodine therapy Thyroid Cancers Thyroid cancers include papillary, follicular, medullary, and undifferentiated anaplastic cancers. They are more common in younger individuals and females, with radiation exposure increasing the risk. Symptoms may involve voice changes and compression- related issues. Diagnosis relies on nuclear medicine 123I thyroid uptake scans and histologic assessment through fine-needle aspiration biopsy. Treatment often involves surgical removal of the thyroid followed by radioactive iodine therapy and medication.  Hyperparathyroidism is characterized by an excess of parathyroid hormone (PTH), affecting the skeletal system. Hyperparathyroidism Types include primary (adenoma, carcinoma, or hyperplasia), secondary (due to metabolic disorders or chronic renal disease), and ectopic. Symptoms include neuromuscular weakness, fatigue, renal stones, and radiographic findings of bone reabsorption. Diagnosis may involve imaging studies like CT, sonography, or nuclear medicine scans. Treatment varies depending on the type but often includes surgery and medications. Nephrocalcinosis Nephrocalcinosis is the deposition of calcium phosphate throughout the renal parenchyma, often related to calcium metabolism disorders. It can be seen on intravenous urograms and abdominal radiographs. Treatment involves addressing the underlying metabolic condition and lowering serum calcium levels. END OF LECTURE