Endocrine Glands and Hormones Lecture 2023 PDF

ENDOCRINE GLANDS AND HORMONES Dr. Kelly Roballo With Thanks to Selen Olgun, MD, PhD 1 2 3 4 5 6 Describe the difference between endocrine and exocrine glands. List the different types of endocrine glands Explain the concept of feedback control to include both positive and negative feedbac...

ENDOCRINE GLANDS AND HORMONES Dr. Kelly Roballo With Thanks to Selen Olgun, MD, PhD 1 2 3 4 5 6 Describe the difference between endocrine and exocrine glands. List the different types of endocrine glands Explain the concept of feedback control to include both positive and negative feedback. Describe the neoplastic production of hormones and the related clinical relevance. Compare and contrast steroid, peptide and amino-acid hormones. Explain the significance of Dr. Percy L. Julian’s contributions to the fields of chemistry and medicine. LEARNING OBJECTIVES • Hormone • A chemical substance that is secreted into the internal body fluids by one cell (or a group of related cells) and has a physiological effect on other cells in the body. • Can be steroids/non-steroids • Mechanisms of release: DEFINITIONS • Endocrine • Product secreted directly into the blood. (Thyroid gland) • Exocrine • Product secreted into a duct and then onto a body surface. (Salivary glands) ENDOCRINE GLANDS • Pituitary Gland • Thyroid Gland • Parathyroid glands • Testes • Ovaries • Adrenals • Endocrine pancreas TYPES OF HORMONES STEROID HORMONE FAMILY • Steroid hormones are small, lipid-soluble molecules derived from cholesterol • Not stored, synthesized de novo on demand • Circulate in the blood bound to globulins and other plasma proteins • Bind intracellular receptors (cytosolic & nuclear) • Effects are slow (hours), depend on gene transcription, protein synthesis, etc. SYNTHESIS OF STEROID HORMONES DR. PERCY LAVON JULIAN • American Chemist • First African-American Chemist inducted into the National Academy of the Sciences • Notable works: • First to synthesize Physostigmine used to treat Glaucoma • Found a cheap and effective way to massproduce cortisone, hydrocortisone, testosterone and progesterone • These discoveries increased the availability and decreased the price of these drugs. Increasing access to people worldwide. • Without Dr. Julian’s work, we would not have many of the common and vital treatments we have today. PEPTIDE/PROTEIN HORMONES • 3 to 200 amino acids long • synthesized and stored in specific cells (insulin = pancreatic beta cells), released in bursts • • generally circulate unbound in plasma, but there are exceptions bind extracellular receptors, and depend on 2nd messengers for signal transduction (Insulin à Insulin Receptor à growth, glucose metabolism, etc) • effects are very rapid (minutes), and initial effects do not depend on new protein synthesis PEPTIDE HORMONE SYNTHESIS SECRETION OF PROTEIN HORMONES AMINO ACID HORMONES - Synthesized from TYROSINE - Stored and secreted in bursts 1)Thyroid Hormone • circulates >99%bound, very long half-life (days) • Binds to intracellular receptors (but plasma membrane transporter) • Effects through gene transcription, slow 2) Epinephrine, Norepinephrine • • • • circulates unbound very short half-life (2-3 minutes) binds to extracellular receptors effects through 2nd messengers, very rapid HORMONE RELEASE CELL-TO-CELL COMMUNIC ATION • Direct contact • Synaptic • Chemical Signaling • Endocrine Signaling • Paracrine Signaling • Autocrine • Extracellular vesicles In addition to their direct main effects, hormones can have other effects: (1) Synergistic effects, so that the effect of the two synergistic hormones is greater than that of either hormone alone (example is thyroid hormone and epinephrine on heart rate, since in addition to its direct effects of increasing heart rate, thyroid hormone increases the number of adrenergic receptors which can then respond to epinephrine). (2) Permissive e.g., thyroid hormone (TH) presence is necessary for aldosterone to stimulate Na+/K+ pumps, although TH has no stimulatory effect on these pumps by itself. (3) Antagonistic e.g., insulin vs. glucagon/epinephrine effects on glycogen synthesis FEEDBACK CONTROL Updated slide in “Supplemental” PPT • It is essential for our endocrine system to increase or decrease its activity in response to different stimuli and conditions. • This is accomplished via feedback loops • Negative feedback • Signals from target cells cause inhibitory response at glandular level. • Positive feedback • Signals amplify physiological processes to increase signal strength or prolong duration. • Ex: Oxytocin and Childbirth Feedback of Hormones HORMONAL RHYTHMS • The release of hormones are pulsatile and episodic (Frequency and amplitude) can vary daily (e.g. cortisol) or monthly (estradiol) or remain fairly constant (Thyroid hormone) • GH peaks at night • Cortisol peaks in the morning CIRCADIAN RHYTHM A clock with an intrinsic 24-25hour cycle is located in the suprachiasmatic nucleus (SCN) of the hypothalamus. This free running clock is entrained by environmental light signals to the external 24-hour day. The pineal gland with its hormone, melatonin, is both an agent and regulator of the SCN HORMONES ARE REMOVED FROM THE BLOOD AND TISSUES BY 6 BASIC METHODS 1. Enzymatic degradation in blood and extracellular fluids 2. Endocytosis of hormone-receptor complex by target cell with subsequent intracellular enzymatic processing and return of "cleared" receptor to plasma membrane 3. Liver enzymatic degradation and/or excretion in bile 4. Liver re-synthesis (example: aromatization of testosterone into estrogen) 5. Kidney excretion into urine 6. Hormonal binding to target sites NEUROENDOCRINE (NE) CELLS / TUMORS Neuroendocrine (NE) cells are like nerve cells, but they make hormones like cells of the endocrine system. They receive signals from the nervous system and respond by making and releasing hormones, which control many body functions. Neuroendocrine tumors (NET) or neuroendocrine neoplasms (NEN) are cancers that begin in neuroendocrine cells. Pancreatic NETs are a common example. Occurrence of the most common types of neuroendocrine neoplasms. The occurrence of the main types of neuroendocrine tumors presented as the percentage of all NENs. GINENs represent the largest subgroup of NENs, followed by lung and pancreatic NENs. Subtypes not listed in this figure include NENs from the thyroid, kidney, adrenal gland, breast, prostate and skin NEOPLASTIC HORMONE PRODUCTION • Condition where non-endocrine tissue secretes hormones. • Paraneoplastic syndromes • Release of physiologically active substances by a tumor. • Small-cell Lung cancer- anti-diuretic hormone secretion leading to hyponatremia (SIADH) • Peptide hormones most often released. THANK YOU