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Semester 2: Advanced Endocrinology
Hormones: classification, chemical properties, hormonal effects and regulation
Hormones: classification, chemical properties, hormonal effects and regulation
Classification of Hormones
Hormones can be classified based on several criteria including chemistry and function. The primary classifications include: 1. Peptide Hormones - composed of amino acids, including insulin and glucagon. 2. Steroid Hormones - derived from cholesterol, including cortisol and sex hormones. 3. Amino Acid Derivatives - derived from single amino acids, including thyroid hormones and catecholamines.
Chemical Properties of Hormones
Hormones exhibit diverse chemical properties based on their structure. Peptide hormones are usually water-soluble and circulate freely in the blood. Steroid hormones are lipid-soluble and require carrier proteins to travel in the bloodstream. This affects their mechanism of action and half-life in circulation.
Hormonal Effects
Hormones exert a wide range of effects on target tissues. Examples include: 1. Metabolic regulation - insulin lowers blood glucose while glucagon raises it. 2. Growth and development - growth hormone stimulates growth processes. 3. Stress response - cortisol regulates metabolism and immune response during stress.
Regulation of Hormone Secretion
Hormonal regulation involves complex feedback mechanisms. 1. Negative feedback - a high level of a hormone inhibits its further secretion, e.g., thyroid hormones suppress TSH production. 2. Positive feedback - a hormone promotes its own secretion, e.g., oxytocin during childbirth. 3. Neuroendocrine regulation - the nervous system influences hormone release under stress or other stimuli.
Receptors: cell surface and intracellular receptors including G-protein coupled and pharmacological receptors
Receptors: cell surface and intracellular receptors including G-protein coupled and pharmacological receptors
Introduction to Receptors
Receptors are proteins that detect and respond to external signals. They play a crucial role in cellular communication and signal transduction.
Types of Receptors
Receptors are broadly classified into two categories: cell surface receptors and intracellular receptors.
Cell Surface Receptors
These receptors are located on the plasma membrane of cells. They bind to extracellular ligands and initiate signal transduction pathways.
Intracellular Receptors
These receptors are located within the cell, usually in the cytoplasm or nucleus. They bind to ligands that can cross the plasma membrane, such as steroid hormones.
G-Protein Coupled Receptors (GPCRs)
GPCRs are a large family of cell surface receptors that play a crucial role in transducing extracellular signals. They activate intracellular G-proteins, leading to various physiological responses.
Pharmacological Receptors
These receptors interact with drugs and other pharmacological agents. Understanding their function is key in drug design and therapeutic interventions.
Signaling Pathways
Different receptors activate various signaling pathways, impacting cellular responses like growth, metabolism, and apoptosis.
Conclusion
Receptors are vital for cell communication. Their types and mechanisms greatly influence pharmacology and biochemistry.
Second messenger systems: Ca2+, cAMP, cGMP, DAG, IP3
Second messenger systems in endocrinology
Introduction to second messengers
Second messengers are intracellular signaling molecules that mediate cellular responses to hormones and other extracellular signals. They play a critical role in signal transduction pathways.
Calcium ions (Ca2+)
Calcium ions serve as a vital second messenger in various signaling pathways. They are involved in muscle contraction, neurotransmitter release, and other cellular processes. The increase in intracellular Ca2+ levels often results from the activation of phospholipase C or specific ion channels.
Cyclic AMP (cAMP)
cAMP is a key second messenger generated from ATP by the action of adenylyl cyclase. It activates protein kinase A (PKA), which phosphorylates various target proteins, leading to diverse physiological effects, such as glucose metabolism regulation and gene expression.
Cyclic GMP (cGMP)
cGMP is synthesized from GTP by guanylyl cyclase and functions in smooth muscle relaxation, platelet aggregation, and neuronal signaling. It activates protein kinase G (PKG) and modulates ion channels.
Diacylglycerol (DAG)
DAG is produced by the hydrolysis of phospholipids and works alongside IP3 to activate protein kinase C (PKC). It plays a role in regulating cellular processes like proliferation and differentiation.
Inositol trisphosphate (IP3)
IP3 is produced from phosphatidylinositol 4,5-bisphosphate (PIP2) by phospholipase C. It facilitates the release of Ca2+ from the endoplasmic reticulum, linking membrane receptors to intracellular responses.
Integration and cross-talk of second messenger systems
Second messenger systems can interact and influence each other, leading to complex signaling networks. Understanding these interactions is crucial for unraveling the mechanisms of various hormonal responses.
Steroid hormones and glycoprotein hormones: chemical nature, mechanism of action
Steroid hormones and glycoprotein hormones: chemical nature, mechanism of action
Chemical Nature of Steroid Hormones
Steroid hormones are lipophilic molecules derived from cholesterol. They include hormones such as cortisol, aldosterone, testosterone, and estrogen. Their structure consists of four fused carbon rings, and they can easily pass through cell membranes due to their lipid solubility.
Chemical Nature of Glycoprotein Hormones
Glycoprotein hormones are composed of proteins that have carbohydrate moieties. Examples include luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone. These hormones typically have complex structures that influence their stability and receptor interaction.
Mechanism of Action of Steroid Hormones
Steroid hormones exert their effects by passing through the cell membrane and binding to specific intracellular receptors. This hormone-receptor complex then translocates to the nucleus, where it binds to DNA and regulates gene expression, leading to changes in protein synthesis.
Mechanism of Action of Glycoprotein Hormones
Glycoprotein hormones act through membrane-bound receptors, which are linked to intracellular signaling pathways. Upon hormone binding, these receptors often activate second messenger systems, such as cyclic AMP, leading to a cascade of intracellular events that result in physiological responses.
Endocrine glands: hypothalamus, pituitary, thyroid, parathyroid, adrenal, pineal, pancreas, gastrointestinal hormones, sex hormones
Endocrine Glands
Hypothalamus
The hypothalamus is a small region located at the base of the brain that plays a crucial role in the endocrine system. It regulates various bodily functions through hormone secretion and controls the pituitary gland. It produces releasing and inhibiting hormones that affect anterior pituitary hormone release.
Pituitary Gland
Often referred to as the master gland, the pituitary gland is divided into anterior and posterior sections. The anterior pituitary secretes hormones such as growth hormone, prolactin, and adrenocorticotropic hormone. The posterior pituitary stores and releases oxytocin and vasopressin, produced by the hypothalamus.
Thyroid Gland
The thyroid gland, located in the neck, produces thyroid hormones including thyroxine (T4) and triiodothyronine (T3) which regulate metabolism, energy generation, and overall growth. It is crucial for proper development and function of many bodily systems.
Parathyroid Glands
These small glands are situated behind the thyroid and are responsible for regulating calcium levels in the blood through the secretion of parathyroid hormone (PTH). PTH increases calcium levels by promoting calcium release from bones and increasing intestinal absorption.
Adrenal Glands
The adrenal glands are located on top of each kidney and consist of the cortex and medulla. The adrenal cortex produces corticosteroids such as cortisol and aldosterone, while the adrenal medulla secretes catecholamines like adrenaline, which are involved in the stress response.
Pineal Gland
The pineal gland, situated deep in the brain, is primarily responsible for the secretion of melatonin, which regulates sleep and circadian rhythms. It is sensitive to light and dark cycles, influencing reproductive hormones and seasonal biological rhythms.
Pancreas
The pancreas has both endocrine and exocrine functions. Its endocrine component produces insulin and glucagon, which are vital for glucose metabolism and maintaining blood sugar levels. Insulin lowers blood sugar, while glucagon raises it.
Gastrointestinal Hormones
Gastrointestinal hormones include gastrin, secretin, and cholecystokinin. They regulate digestive processes by stimulating digestive juices, regulating appetite, and enhancing gut motility.
Sex Hormones
Sex hormones, including estrogens, progesterone, and testosterone, are produced in the gonads and play key roles in sexual development and reproduction. They regulate reproductive cycles, secondary sexual characteristics, and influence various physiological processes.
Dysfunction and pathophysiology of endocrine glands, laboratory diagnosis, ELISA and PCR techniques
Dysfunction and Pathophysiology of Endocrine Glands, Laboratory Diagnosis, ELISA and PCR Techniques
Dysfunction of Endocrine Glands
Endocrine glands can become dysfunctional due to various factors including inflammation, infection, genetic mutations, and neoplasia. Common dysfunctions include hypersecretion and hyposecretion of hormones, which can lead to conditions like hyperthyroidism, hypothyroidism, Cushing's syndrome, and Addison's disease.
Pathophysiology of Endocrine Disorders
The pathophysiology of endocrine disorders often involves dysfunction in hormone signaling pathways, receptor sensitivities, or feedback mechanisms. For instance, in diabetes mellitus, the pancreas fails to produce adequate insulin or cells become resistant to insulin action, disrupting glucose homeostasis.
Laboratory Diagnosis of Endocrine Disorders
Laboratory diagnosis involves measuring hormone levels through blood, urine, or tissue samples. Imbalances can indicate dysfunction of specific glands. Tests might include serum hormone assays, stimulation tests, and suppression tests to confirm diagnoses.
ELISA Technique
Enzyme-Linked Immunosorbent Assay (ELISA) is a commonly used laboratory technique to detect and quantify proteins, hormones, or antibodies in biological samples. In endocrine studies, it assists in measuring hormone levels with high specificity and sensitivity.
PCR Technique
Polymerase Chain Reaction (PCR) is a molecular biology technique used to amplify DNA sequences. In endocrinology, PCR can detect genetic mutations associated with endocrine disorders, allowing for precise diagnosis and monitoring of conditions.
