Endocrine System PDF

Endocrine System Hypothalamus and its components very important Controls pituitary gland paraventricular nuclei suparaoptic nuclei T3 & T4 Levels Matter 1. Elevated TSH (Thyroid Stimulating Hormone) levels typically indicate that the thyroid gland is not producing enough T3 (triiodothyronine) and T4...

Endocrine System Hypothalamus and its components very important Controls pituitary gland paraventricular nuclei suparaoptic nuclei T3 & T4 Levels Matter 1. Elevated TSH (Thyroid Stimulating Hormone) levels typically indicate that the thyroid gland is not producing enough T3 (triiodothyronine) and T4 (thyroxine) hormones. TSH stimulates the thyroid gland to release T3 and T4, and high TSH levels suggest the body is trying to boost thyroid hormone production due to insufficient levels in the bloodstream. 2. Low T3 and T4 levels, known as hypothyroidism, can lead to symptoms such as fatigue, weight gain, and sensitivity to cold. Monitoring TSH, T3, and T4 levels helps in diagnosing and managing thyroid disorders. Prolactin Prolactin is a hormone produced by the pituitary gland, and its primary function is to stimulate milk production in the mammary glands of the breasts. It plays a crucial role in lactation during pregnancy and after childbirth. Prolactin is composed of a single polypeptide chain and is regulated by factors such as suckling, stress, and certain medications. Elevated levels of prolactin outside of pregnancy and lactation can be associated with conditions like hyperprolactinemia, which may have various causes. Endocrinology (specific study of hormones and endocrine organs) Hormones are chemical messengers secreted by cells into the extra cellular fluids. These hormones travels through the blood and regulate metabolic function of the other cells in the body. Binding of hormones to cellular components Function of endocrine hormones Reproduction Growth and development Maintenance of electrolyte, water, and nutrient balance of the blood Regulation of cellular metabolism and energy balance Mobilization of body defenses Endocrine glands (ductless glands that produce hormones) include the pituitary, thyroid, adrenal, parathyroid, and pineal glands; the hypothalamus also produces and releases hormones 3 types of hormones 1) Amino Acid Based which are produced from amino acids ( water soluble) 2) steroid hormones which are synthesized from cholesterol (lipid soluble) 3) eicosanoids which are synthesized from polyunsaturated fatty acids known as arachidonic acid Describe the two major mechanism by which hormones bring about their effects on their target tissues. 1. **Genomic Mechanism:** - **Receptor Binding:** Hormones, such as steroid hormones (e.g., estrogen, cortisol), bind to specific nuclear receptors within the target cell. - **Formation of Hormone-Receptor Complex:** The hormone-receptor complex enters the nucleus and binds to specific DNA sequences known as hormone response elements (HREs). - **Gene Transcription and mRNA Synthesis:** This binding initiates or inhibits gene transcription, leading to the synthesis of messenger RNA (mRNA). - **Protein Synthesis:** The mRNA directs the synthesis of new proteins, which mediate the ultimate physiological response within the target cell. 2. **Non-genomic Mechanism:** - **Cell Surface Receptors:** Hormones like peptide hormones (e.g., insulin, adrenaline) interact with receptors located on the cell membrane. - **Activation of Second Messengers:** Binding of hormones triggers the activation of second messenger molecules (e.g., cAMP, calcium ions) inside the cell. - **Cellular Response:** Second messengers initiate a cascade of intracellular events, leading to rapid physiological responses such as enzyme activation, ion channel opening, or other cellular processes. - **No Gene Expression Alteration:** Unlike genomic mechanisms, nongenomic actions do not involve changes in gene expression; instead, they modulate existing cellular functions swiftly. In summary, genomic actions involve altering gene expression and protein synthesis, while non-genomic actions rapidly affect cellular functions through second messenger systems at the cell membrane. These mechanisms contribute to the diverse and precise regulation of physiological processes by hormones. A hormone typically produces one or more of the following changes: alters plasma membrane permeability or or membrane potential, or both, by opening or closing ion channels Stimulate synthesis of enzymes and other protein within the cell Activates or deactivates enzymes Induced secretory activity Stimulates mitosis Hormones act at receptors in one of 2 ways 1. Water-soluble hormones act on receptors in the plasma membrane. These receptors are usually coupled via regulatory molecules called called G proteins to one or more intercellular second messengers which mediate the target cell’s response 2. Lipid soluble hormones (steroid and thyroid) act in receptors inside the cell which directly activates genes MSH Melanocyte-Stimulating Hormone (MSH) is a protein hormone that regulates the production and release of melanin, the pigment responsible for the color of skin, hair, and eyes. MSH is produced by the pituitary gland, and its primary function is to stimulate melanocytes, the cells responsible for melanin synthesis. MSH levels can be influenced by factors such as exposure to sunlight, stress, and certain diseases. Additionally, MSH plays a role in various physiological processes, including appetite and energy homeostasis. Cyclic amp signaling mechanism 1. Receptor Activation -Protein-Coupled Receptors (GPCRs): Many hormones, neurotransmitters, and other signaling molecules bind to GPCRs on the cell membrane. Hormone Binding: Binding of the ligand (e.g., adrenaline, glucagon) to the GPCR activates the receptor. 2. G-Protein Activation - G-Protein Coupling: Activated receptors stimulate a G-protein (GTP-binding protein) associated with the inner side of the cell membrane. - GTP Exchange: The G-protein exchanges its bound GDP for GTP, becoming activated. 3. Adenylyl Cyclase Activation - Activation of Adenylyl Cyclase: The activated G-protein stimulates adenylyl cyclase, an enzyme embedded in the cell membrane. - cAMP Synthesis: Adenylyl cyclase converts ATP (adenosine triphosphate) into cyclic AMP (cAMP). 4. cAMP as a Second Messenger - cAMP Diffusion: cAMP freely diffuses into the cell cytoplasm, acting as a second messenger. - Protein Kinase A (PKA) Activation: cAMP activates protein kinase A (PKA) by binding to its regulatory subunits, leading to the release and activation of the catalytic subunits. 5. Phosphorylation of Target Proteins - PKA Phosphorylation: Active PKA phosphorylates various target proteins, including enzymes and transcription factors, modifying their activity. - Cellular Responses: Phosphorylation events mediated by cAMP/PKA can lead to a variety of cellular responses, such as changes in metabolism, gene expression, and cell function. 6. Termination of cAMP Signaling - cAMP Degradation: cAMP is short-lived due to the action of phosphodiesterases, which degrade it to AMP (adenosine monophosphate). - G-Protein Inactivation: The G-protein is inactivated when it hydrolyzes GTP to GDP, turning off the adenylyl cyclase. The cyclic AMP signaling pathway is involved in the regulation of diverse cellular processes, including metabolism, gene expression, and neurotransmission. Its tight control allows for precise and rapid cellular responses to extracellular signals. Hypothyroidism: Definition: Insufficient thyroid hormone production. Symptoms: Fatigue, weight gain, cold sensitivity, dry skin, constipation, mood changes. Causes: Autoimmune disorders, iodine deficiency, certain medications. Diagnosis: Blood tests measuring TSH, T3, and T4 levels. Treatment: Lifelong replacement therapy with synthetic thyroid hormones. Hyperthyroidism: Definition: Excessive thyroid hormone production. Symptoms: Weight loss, increased appetite, heat intolerance, rapid heart rate, anxiety. Causes: Autoimmune conditions (Graves' disease), thyroid nodules, excess iodine. Diagnosis: Blood tests, imaging studies (scan, ultrasound). Treatment: Medications to control hormone levels, radioactive iodine therapy, or surgery in severe cases. Goiter: A goiter is an enlarged thyroid gland, resulting in swelling at the front of the neck. This condition can occur due to various factors, with the most common causes being iodine deficiency, autoimmune diseases (like Hashimoto’s thyroiditis), or excessive stimulation of the thyroid gland (Graves’ disease). When the thyroid doesn’t produce enough thyroid hormones (hypothyroidism) due to iodine deficiency or other factors, the pituitary gland releases more Thyroid-Stimulating Hormone (TSH) to stimulate thyroid activity, leading to goiter. In some cases, goiter may not cause noticeable symptoms, but it can result in difficulties swallowing or breathing. Calcitonin: Calcitonin is a hormone produced by the thyroid gland, specifically by the parafollicular or C cells. Its primary function is to regulate calcium and phosphate levels in the blood. Calcitonin works in opposition to parathyroid hormone (PTH), which is released by the parathyroid glands. When blood calcium levels are elevated, calcitonin is released and acts to reduce calcium levels by promoting its storage in the bones and inhibiting its absorption in the intestines and kidneys. While calcitonin’s role in normal calcium regulation is relatively minor compared to PTH, it is essential for maintaining overall calcium homeostasis in the body. ACTH Adrenocorticotropic Hormone (ACTH) is a peptide hormone that plays a crucial role in the regulation of the adrenal cortex. Here's an overview: Structure: ACTH is a polypeptide hormone and is part of the proopiomelanocortin (POMC) family of peptides. POMC is a precursor molecule that is enzymatically cleaved to yield various bioactive peptides, including ACTH. Functions: 1. Stimulation of Cortisol Production:ACTH primarily stimulates the adrenal cortex to produce and release cortisol, a glucocorticoid hormone involved in various physiological processes such as metabolism, immune response, and stress regulation. Regulation and Production: 1. Hypothalamus-Pituitary-Adrenal (HPA) Axis: ACTH is regulated by the hypothalamuspituitary-adrenal axis. The hypothalamus releases corticotropin-releasing hormone (CRH), which stimulates the pituitary gland to release ACT 2. Negative Feedback: Cortisol, the end product of ACTH action, exerts negative feedback on the HPA axis. Elevated cortisol levels signal the hypothalamus and pituitary to reduce the release of CRH and ACTH, respectively, maintaining a delicate balance. 3. Circadian Rhythm and Stress: ACTH secretion follows a circadian rhythm, peaking in the early morning. Additionally, stress can trigger an increased release of ACTH and cortisol. Understanding ACTH's regulation is essential for comprehending its role in responding to stress, maintaining homeostasis, and contributing to the body's adaptation to various physiological challenges. TSH Thyroid Stimulating Hormone (TSH) is produced by the pituitary gland and stimulates the thyroid gland to release thyroid hormones. T4 (thyroxine) and T3 (triiodothyronine) are the main thyroid hormones. T4 has four iodine atoms, while T3 has three. They regulate metabolism, energy production, and growth. Iodine is crucial for thyroid hormone synthesis, and their levels are regulated by a feedback loop involving the hypothalamus, pituitary gland, and thyroid gland. Follicle-Stimulating Hormone (FSH): Function: FSH plays a pivotal role in reproduction. In females, it stimulates the growth of ovarian follicles, leading to the maturation of eggs. In males, FSH stimulates the production of sperm in the testes. Feedback Loop: Negative feedback regulates FSH. Rising levels of sex hormones (estrogen in females, testosterone in males) inhibit further FSH release to maintain hormonal balance. Luteinizing Hormone (LH): Function: LH is crucial for reproductive processes. In females, it triggers ovulation, the release of an egg from the ovary. In males, LH stimulates the production of testosterone in the testes. Feedback Loop: Similar to FSH, LH is regulated by negative feedback involving sex hormones. Hypothalamic-Pituitary Feedback Loops: Example: In the hypothalamic-pituitary-gonadal axis, the hypothalamus releases gonadotropin-releasing hormone (GnRH), stimulating the pituitary to release FSH and LH. Rising sex hormone levels then inhibit GnRH release, forming a negative feedback loop. Hypothalamic Pathways: Production: The hypothalamus synthesizes releasing hormones (e.g., GnRH) that travel to the pituitary, stimulating or inhibiting the release of hormones. Example: GnRH stimulates the release of FSH and LH in the gonadal axis. Oxytocin: Function: Oxytocin plays a key role in uterine contractions during labor, facilitating milk ejection during breastfeeding, and promoting social bonding. Birthing Process: During childbirth, oxytocin promotes rhythmic contractions of the uterus, aiding in the delivery of the baby. Antidiuretic Hormone (Vasopressin): Function: Vasopressin regulates water balance by promoting water reabsorption in the kidneys, reducing urine output. Release Triggers: Factors like increased blood osmolality (higher concentration of solutes) or decreased blood volume stimulate ADH release. Inhibition: Alcohol inhibits ADH release, leading to increased urine production and potential dehydration. Circadian Rhythm: Definition: Circadian rhythm is the body’s internal clock regulating the sleep-wake cycle and other physiological processes. Regulation: Governed by the suprachiasmatic nucleus in the hypothalamus, influenced by external cues like light. Example: Melatonin, produced by the pineal gland, helps regulate the sleep-wake cycle and is influenced by circadian rhythms. Thyroid Gland: Location and Production: The thyroid gland is situated in the neck. It produces thyroid hormones (T3 and T4). Synthesis: Thyroid hormones are synthesized from the amino acid tyrosine and iodine. Iodine is crucial for the formation of these hormones. Role of Iodine: Iodine deficiency can lead to decreased thyroid hormone production, resulting in conditions like goiter and hypothyroidism. Adequate iodine intake is essential for thyroid function. The hypothalamus is a crucial region in the brain responsible for regulating various physiological processes and maintaining homeostasis. Its main components include: 1. Hormones: The hypothalamus produces and releases hormones that control the secretion of hormones from the pituitary gland, influencing various bodily functions. 2. Neural Pathways: It integrates and processes information from different parts of the brain, linking the nervous and endocrine systems. 3. Autonomic Nervous System Control: The hypothalamus regulates the autonomic nervous system, influencing functions like heart rate, blood pressure, and digestive processes. 4. Body Temperature Regulation: It helps maintain a stable body temperature through mechanisms like sweating or shivering. 5. Thirst and Hunger Regulation: The hypothalamus plays a role in controlling appetite, thirst, and satiety, influencing eating and drinking behaviors. 6. Circadian Rhythms: It is involved in regulating the body's internal clock and sleep-wake cycles. The hypothalamus is vital for overall physiological balance and orchestrates responses to internal and external stimuli. Growth Hormone (GH): GH is produced by the pituitary gland and plays a crucial role in growth, cell repair, and metabolism. It stimulates the growth of bones and tissues, particularly during childhood and adolescence. Growth Hormone Feedback Loop: 1. Hypothalamus: Releases Growth Hormone-Releasing Hormone (GHRH). 2. Anterior Pituitary Gland: Responds to GHRH by releasing GH. 3. Liver and Other Tissues: GH stimulates the liver to produce Insulinlike Growth Factor-1 (IGF-1), which mediates most of GH’s effects on growth and development. 4. Negative Feedback: Elevated IGF-1 levels inhibit further GH release, helping to maintain a balance. Abnormal GH Secretion: 1. Hyposecretion (Dwarfism): Insufficient GH during childhood can lead to stunted growth and proportionally small stature. 2. Hypersecretion (Acromegaly and Gigantism): Acromegaly: Excessive GH secretion after growth plates close in adulthood, resulting in enlargement of hands, feet, and facial features. Gigantism: Excessive GH secretion during childhood and adolescence, causing abnormal height and bone growth. Monitoring GH levels and understanding these conditions helps diagnose and manage abnormalities in growth hormone secretion. The production of thyroid hormones (T3 and T4) involves a series of steps and is regulated by a feedback loop. Here’s an overview: 1. Thyroid-Stimulating Hormone (TSH) Release: Hypothalamus releases Thyrotropin-Releasing Hormone (TRH). TRH signals the anterior pituitary gland to release Thyroid-Stimulating Hormone (TSH). 2. Stimulation of Thyroid Gland: TSH stimulates the thyroid gland to produce and release thyroid hormones T3 (triiodothyronine) and T4 (thyroxine). 3. Thyroid Hormone Synthesis: The thyroid gland contains follicular cells that take up iodine from the bloodstream. Iodine is incorporated into tyrosine molecules to form T3 and T4. 4. Release into Bloodstream: T3 and T4 are released into the bloodstream, where they circulate and exert their effects on various tissues. 5. Negative Feedback Loop: Elevated levels of T3 and T4 inhibit the release of TRH and TSH through a negative feedback loop involving the hypothalamus and pituitary gland. Low levels of T3 and T4 stimulate the release of TRH and TSH to increase thyroid hormone production. This regulated feedback loop ensures that thyroid hormone levels are maintained within a narrow range, contributing to overall metabolic balance in the body. Posterior Pituitary Hormones: 1. Oxytocin: Function: Stimulates uterine contractions during labor and childbirth. Also involved in milk ejection during breastfeeding. Additionally, it has roles in social bonding and emotional behaviors. Release Trigger: Triggered by stretching of the cervix and uterus during labor, as well as sensory stimuli from breastfeeding. 2. Vasopressin (Antidiuretic Hormone - ADH): Function: Regulates water balance and blood pressure by controlling water reabsorption in the kidneys, reducing urine volume and preventing dehydration. Release Trigger: Triggered by increased blood osmolarity (concentration) and low blood volume, signaling dehydration. Anterior Pituitary Hormones: 1. Growth Hormone (GH): Function: Stimulates growth, cell reproduction, and regeneration. It plays a crucial role in childhood growth and maintaining tissues and organs throughout life. 2. Thyroid-Stimulating Hormone (TSH): Function: Stimulates the thyroid gland to produce and release thyroid hormones (T3 and T4), regulating metabolism and energy levels. 3. Adrenocorticotropic Hormone (ACTH): Function: Stimulates the adrenal glands to release cortisol, which plays a role in stress response and metabolism. 4. Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH): Function: Regulate the reproductive system. LH triggers ovulation in females and testosterone production in males, while FSH stimulates egg maturation in females and sperm production in males. 5. Prolactin: Function: Stimulates milk production in mammary glands during lactation. 6. Melanocyte-Stimulating Hormone (MSH): Function: Regulates skin pigmentation by influencing melanocytes. Understanding the roles of these hormones is crucial for comprehending how the endocrine system controls various physiological processes in the body.