Thyroid and Pancreas Notes PDF

**The Thyroid Gland and Pancreas: Anatomy, Physiology, and Disorders** This unit will cover the anatomy, physiology, and functions of the thyroid gland and pancreas, as well as common disorders associated with these endocrine glands. The thyroid gland plays a crucial role in metabolism, growth, and...

**The Thyroid Gland and Pancreas: Anatomy, Physiology, and Disorders** This unit will cover the anatomy, physiology, and functions of the thyroid gland and pancreas, as well as common disorders associated with these endocrine glands. The thyroid gland plays a crucial role in metabolism, growth, and calcium homeostasis, while the pancreas is essential in digestion and the regulation of blood glucose levels. **1. The Thyroid Gland** **Role of the Thyroid Gland:** - The thyroid gland is located in the neck and produces key hormones that regulate metabolism and calcium levels in the body. - **Thyroxine (T4):** A hormone consisting of four iodine atoms and one molecule of tyrosine. It is the precursor to T3 and is crucial for metabolism. - **Triiodothyronine (T3):** Similar to thyroxine but with three iodine atoms. It is the active form of thyroid hormone, produced in smaller amounts directly by the thyroid gland but also converted from T4 in tissues. - **Calcitonin:** Produced by the parafollicular (C) cells of the thyroid, this hormone helps regulate calcium levels by reducing calcium concentrations in the blood, opposing the effects of parathyroid hormone (PTH). **Effects of T3 and T4 in Adults:** - **Basal Metabolic Rate (BMR):** T3 and T4 increase BMR by 60-100% above normal levels, accelerating metabolic processes. - **Upregulation of Beta Receptors:** These hormones increase the sensitivity of tissues to catecholamines (e.g., adrenaline), enhancing the effects of the sympathetic nervous system. - **Growth and Development:** They promote body growth, particularly in the nervous system, skeletal muscles, and organs. - **Thermoregulation:** T3 and T4 maintain normal body temperature by increasing heat production through metabolism. - **Cardiovascular Effects:** They increase cardiac output and cause peripheral vasodilation, leading to skin flushing. - **Digestive System:** T3 and T4 increase motility, leading to increased appetite and, in some cases, diarrhoea. - **Cerebral Activity:** These hormones increase mental activity but can also cause nervousness, anxiety, and even psychoneurotic tendencies when in excess. - **Glucose Metabolism:** T3 and T4 enhance glucose uptake, glycolysis, and gluconeogenesis. - **Cholesterol Metabolism:** They help the liver process and remove excess cholesterol from the body. **Effects of T3 and T4 in Children:** - **Nervous System Development:** Essential for the development and growth of the nervous tissue and brain in the foetus and neonate. - **Skeletal and Muscle Growth:** T3 and T4 promote the growth of bones, muscles, and organs. A deficiency can lead to short stature, cognitive impairments, and developmental delays. **Formation of T1, T2, T3, and T4:** - **Iodine Intake:** Approximately 1 mg of iodine per week is required in the diet. Iodine is absorbed as iodide in the gut. - **Iodide Transport:** The iodide pump in the thyroid gland transports iodides from the blood into the thyroid epithelial cells and follicles. - **Iodine Oxidation:** Thyroid peroxidase oxidises iodide ions to form iodine atoms. - **Thyroglobulin and Tyrosine:** Iodine binds to thyroglobulin, a protein that contains tyrosine, forming monoiodothyronine (T1). Further iodine additions lead to the formation of diiodothyronine (T2), triiodothyronine (T3), and thyroxine (T4). **Regulation of T3 and T4 Secretion:** - **Stimuli:** Low levels of T3 and T4 or a drop in body temperature trigger the hypothalamus to release thyrotropin-releasing hormone (TRH). - **TRH and TSH:** TRH signals the anterior pituitary gland to release thyroid-stimulating hormone (TSH). - **Thyroid Response:** TSH stimulates the thyroid gland to increase production of T3 and T4. - **Negative Feedback:** Elevated levels of T3 and T4 in the bloodstream inhibit the release of TRH and TSH, forming a negative feedback loop. **2. Thyroid Disorders** **Hypothyroidism:** - **Causes:** - **Iodine Deficiency:** Common in areas with iodine-deficient soil, leading to reduced thyroid hormone production. - **Hashimoto\'s Thyroiditis:** An autoimmune condition where the immune system attacks the thyroid, causing swelling and dysfunction. - **Trauma:** Surgical, radiation, or drug-induced damage to the thyroid. - **Symptoms:** - Extreme sleepiness (somnolence) for 14-16 hours a day. - Muscular sluggishness, slowed heart rate, and reduced blood pressure. - Weight gain, constipation, mental slowness, hair loss, dry skin, and myxoedema (widespread swelling). **Hyperthyroidism:** - **Causes:** - **Graves\' Disease:** An autoimmune disorder that produces antibodies stimulating TSH receptors, leading to excess T3 and T4 production. - **Thyroiditis:** Inflammation of the thyroid gland. - **Other Causes:** Trauma, radiation, infection, or rarely, ingestion of thyroid hormone (hamburger thyrotoxicosis). - **Symptoms:** - Heat intolerance, increased sweating, skin flushing, weight loss, diarrhoea, tachycardia, and elevated blood pressure. - Nervousness, fine tremor, and exophthalmos (protruding eyeballs). **Thyroid Cancer:** - **Types:** Papillary carcinoma is the most common type of thyroid cancer. It is generally slow-growing but can lead to hyperthyroidism. - **Symptoms:** An increase in the size of the thyroid gland, hyperthyroidism, and potential metastasis. **Goitre:** - **Cause:** Lack of iodine leading to thyroid enlargement. - **Presentation:** Visible swelling in the neck due to the enlarged thyroid gland, which can occur in hypo-, hyper-, or euthyroid states. **Hashimoto\'s Disease:** - **Description:** An autoimmune condition where antibodies destroy thyroid epithelial cells, leading to gland atrophy and reduced T3 and T4 output. - **Prevalence:** More common in females, particularly between the ages of 40-60. **The Parathyroid Gland:** - **Function:** Regulates calcium, magnesium, and phosphate levels in the body through parathyroid hormone (PTH). - **PTH:** Increases osteoclast activity in bones, enhances calcium reabsorption in the kidneys, and stimulates calcium absorption in the gut via calcitriol. **3. The Pancreas** **Exocrine Function of the Pancreas:** - **Role in Digestion:** The pancreas produces digestive enzymes that break down proteins, fats, and carbohydrates. - **Proteases:** Break down proteins. - **Lipases:** Break down fats (including phospholipase A2, lysophospholipase, and cholesterol esterase). - **Amylase:** Breaks down starch and other carbohydrates. - **Secretion:** These enzymes are produced in the acinar cells and released into the duodenum via the pancreatic duct. **Endocrine Function of the Pancreas:** - **Insulin:** - **Production:** Released by beta cells in response to high blood glucose levels. - **Function:** Promotes glucose uptake by cells, glycogenesis (glucose storage as glycogen), and lipogenesis (fat storage). It also inhibits the breakdown of fats (lipolysis) and proteins, thereby reducing blood glucose levels. - **Glucagon:** - **Production:** Released by alpha cells when blood glucose levels are low. - **Function:** Stimulates glycogenolysis (breakdown of glycogen to glucose), gluconeogenesis (formation of glucose from non-carbohydrate sources), and lipolysis, increasing blood glucose levels. - **Somatostatin:** - **Function:** Inhibits the release of insulin and glucagon, regulating the endocrine function of the pancreas and affecting neurotransmission and cell proliferation. - **Pancreatic Polypeptide (PP):** - **Function:** Regulates pancreatic secretion activities, influences hepatic glycogen levels, and affects gastrointestinal secretions. **4. Disorders of the Pancreas** **Diabetes Mellitus:** - **Type 1 Diabetes:** - **Description:** An autoimmune condition leading to the destruction of beta cells in the pancreas, resulting in insufficient insulin production. - **Symptoms:** Excessive thirst (polydipsia), frequent urination (polyuria), excessive hunger (polyphagia), weight loss, fatigue, and the presence of ketones in blood and urine. - **Management:** Requires insulin administration to maintain blood glucose levels and prevent complications such as diabetic ketoacidosis. - **Type 2 Diabetes:** - **Description:** Characterised by insulin resistance or reduced insulin sensitivity, often associated with obesity. - **Symptoms:** Similar to type 1 diabetes, but typically occurs in older adults and is managed with lifestyle changes, oral medications, and sometimes insulin. - **Prevalence:** Much more common than type 1, with a ratio of approximately 10:1. - **Other Types:** - **Gestational Diabetes:** Occurs during pregnancy and can increase the risk of developing type 2 diabetes later in life. - **Latent Autoimmune Diabetes in Adults (LADA):** Also known as type 1.5 diabetes, it shares characteristics with both type 1 and type 2 diabetes. - **Maturity-Onset Diabetes of the Young (MODY):** A hereditary form of diabetes due to a single gene mutation. - **Other Varieties:** Steroid-induced diabetes, brittle diabetes, secondary diabetes, diabetes insipidus, and juvenile diabetes. **Diagnosis of Diabetes:** - **Fasting Blood Glucose:** Normal levels are between 4.0 to 5.4 mmol/L (72 to 99 mg/dL). - **Glucose Tolerance Test:** Involves ingesting a glucose solution and measuring blood glucose levels over time to assess insulin function. **Multiple Choice Questions (MCQs)** 1. **Which hormone is primarily responsible for reducing blood calcium levels?** - a\) Parathyroid hormone (PTH) - b\) Calcitonin - c\) Thyroxine (T4) - d\) Insulin 2. **What triggers the release of thyroid-stimulating hormone (TSH)?** - a\) High levels of T3 and T4 - b\) Low body temperature - c\) Elevated calcium levels - d\) High blood glucose levels 3. **Which of the following is a symptom of hyperthyroidism?** - a\) Weight gain - b\) Cold intolerance - c\) Tachycardia - d\) Depression 4. **What is the primary function of insulin?** - a\) Increase blood glucose levels - b\) Decrease blood glucose levels - c\) Stimulate lipolysis - d\) Inhibit protein synthesis 5. **Which condition is characterised by the destruction of beta cells in the pancreas?** - a\) Type 2 diabetes - b\) Gestational diabetes - c\) Type 1 diabetes - d\) Maturity-Onset Diabetes of the Young (MODY) **Clinical Cases** **Case 1: Hashimoto's Thyroiditis** **Presentation:**\ A 50-year-old woman presents with fatigue, weight gain, cold intolerance, and dry skin. Physical examination reveals a goitre, and blood tests show elevated TSH and low T3 and T4 levels. **Discussion:** - **Question:** Explain the pathophysiology of Hashimoto's Thyroiditis and the role of autoimmunity in this condition. Discuss the treatment options available. - **Answer:** Hashimoto's Thyroiditis is an autoimmune disorder where antibodies attack and destroy the thyroid gland's epithelial cells, leading to hypothyroidism. Treatment typically involves hormone replacement therapy with levothyroxine. **Case 2: Type 2 Diabetes Mellitus** **Presentation:**\ A 60-year-old man with a BMI of 32 presents with polyuria, polydipsia, and blurred vision. Blood tests reveal elevated fasting glucose levels and HbA1c. **Discussion:** - **Question:** Discuss the role of insulin resistance in type 2 diabetes and the impact of obesity on this condition. What are the primary treatment strategies? - **Answer:** Type 2 diabetes is characterised by insulin resistance, where the body's cells do not respond effectively to insulin, leading to elevated blood glucose levels. Obesity contributes to insulin resistance by altering the metabolism of fats and glucose. Treatment includes lifestyle changes, oral hypoglycaemic agents, and sometimes insulin.