Chapter 2 The Endocrine System PDF

CHAPTER 2 The Endocrine System Key Questions About Hormones 1.Where do hormones come from? 1. Produced by glands and secreted into the blood. 2.Where do hormones go? 1. Travel through the blood to target tissues with specific receptors. 3.What do hormones do? 1. Interact with receptors to:...

CHAPTER 2 The Endocrine System Key Questions About Hormones 1.Where do hormones come from? 1. Produced by glands and secreted into the blood. 2.Where do hormones go? 1. Travel through the blood to target tissues with specific receptors. 3.What do hormones do? 1. Interact with receptors to: 1.Trigger biochemical changes. 2.Activate genes for biological responses. How Hormones Work Genomic Effects: Hormones bind to receptors inside cells. Change gene activity to produce long-term effects. Nongenomic Effects: Hormones act on receptors outside cells. Produce faster effects on behavior. Genes are still involved, despite the name. Chemical Communication Chemical Communication in Life Chemical communication is found at all levels of life: Within cells (intracellular processes). Between cells, organs, individuals, and populations. Communication involves: Release of chemical agents. Detection through receptor activation. Types of Chemical Mediation Types of Chemical Mediation Intracrine Mediation Chemicals act within the same cell. Some evolved into hormones or pheromones. Autocrine Mediation Cells release products that act back on themselves. Example: Steroid-producing cells have receptors for their own hormones. Paracrine Mediation Chemicals affect nearby cells. Example: Neurons release neurotransmitters; embryonic cells guide tissue development. Endocrine Mediation Hormones are secreted into the bloodstream and travel to distant targets. Example:-Insulin: Secreted by the pancreas, regulates blood glucose levels body-wide. Ectocrine Mediation Substances released externally affect other individuals. Example: Pheromones. Type of Communication Definition Examples - Neurotransmitters: Dopamine released by one Paracrine Chemicals released by one cell affect nearby cells. neuron affects an adjacent neuron. - Wound Healing: Growth factors like platelet- derived growth factor (PDGF) stimulate nearby cells for tissue repair. - Embryonic Development: Sonic Hedgehog (Shh) protein guides the differentiation of nearby cells. - Pheromones in Animals: Ants release Chemicals released into the environment to affect Ectocrine pheromones to mark food trails; mice use other individuals. pheromones to attract mates. - Human Sweat: Compounds like androstenone may influence others' perceptions. - Plants: Release of methyl jasmonate warns nearby plants of herbivorous insects. Hormones are secreted into the bloodstream and - Insulin: Secreted by the pancreas, regulates Endocrine travel to distant targets. blood glucose levels body-wide. - Adrenaline (Epinephrine): Released by the adrenal glands to increase heart rate and mobilize energy during stress. - Thyroid Hormones (T3 and T4): Produced by the thyroid, regulate metabolism across the body. - Cancer Cells: Release growth factors like Cells secrete substances that act back on the Autocrine vascular endothelial growth factor (VEGF) to same cell. promote self-proliferation. - Immune Cells: T cells secrete interleukin-2 (IL-2) to enhance their own activation and proliferation. - Steroid-Producing Cells: Produce cortisol, which regulates its own production through negative feedback.  Comparison between pheromones, alomones, kairomones and synomones Feature Pheromones Alomones Kairomones Synomones Chemical signals that affect Chemical signals that affect Chemical signals that affect Chemical signals that communicate individuals of a different Definition individuals of a different species, individuals of a different species, with members of the same species. species, benefiting the benefiting the sender. benefiting both sender and receiver. receiver. Used for communication, such as Typically used for defense or Often used in predator-prey or Often used in mutualistic Function mating, alarm signaling, and social predation. host-parasite interactions. relationships like pollination. coordination. Members of a different Target Organism Members of the same species. Members of a different species. Members of a different species. species. Benefits the sender, often by Benefits the receiver, Alters behavior or physiology of the Effect deterring predators or sometimes at the sender's Benefits both sender and receiver. receiver for species coordination. competitors. expense. - Sex pheromones in moths to - Odors from prey that help - Floral scents that attract - Skunk spray to repel attract mates. - Alarm pheromones predators locate them. - pollinators (flowers and bees). - Coral Examples predators. - Plant chemicals in ants to trigger a colony-wide Human sweat chemicals that reef chemicals that help symbiotic that deter herbivores. response. attract mosquitoes. fish find shelter.  Do Humans Use Pheromones? The Myth and Origins of Human Pheromones Pheromones in Animals: First discovered in the 1950s, pheromones are chemical signals that influence behavior in animals (e.g., mating, territorial marking). The Myth in Humans: By the 1970s-80s, speculation grew that humans might also use pheromones for attraction. The VNO Debate: Early studies on the vomeronasal organ (VNO) suggested humans might lack a functional VNO, complicating claims of pheromone detection. Pop Culture Influence: The idea of pheromones in humans gained popularity through advertising and pop culture in the 1980s. eaki Inagaki et al. (2014) (from: Gaskin, Stéphane. Behavioral Neuroscience: Fundamentals and beyond 20 Do Humans Use Pheromones? Pheromone Products:Pheromone Perfumes/Colognes: Products like Pure Instinct and Athena Pheromones claim to increase sexual attraction. Pheromone Sprays & Capsules: Marketed to enhance social chemistry and desirability. Scientific Skepticism:Weak Evidence: Limited or inconclusive evidence of pheromones affecting human behavior. E.g., Menstrual synchrony: McClintock, M. K. (1971). Menstrual synchrony and its hormonal, behavioral, and environmental causes. Placebo Effect: Marketing success may be due to psychological factors rather than pheromone impact. https://www.youtube.com/watch?v=_aoWR1ZDUQc Systems of Chemical Communication Endocrine System: Hormones. Nervous System: Neurotransmitters. Immune System: Cytokines. Each system studied by different specialists: Neuroscientists study neurotransmitters. Endocrinologists focus on hormones. Immunologists examine cytokines. Integration of Systems Nervous, endocrine, and immune systems interact significantly. Examples of overlap: Immune cells have receptors for neurotransmitters and hormones. Neurons have receptors for hormones and cytokines. Similarities in communication: Receptor structures. Signal transduction mechanisms. Gene activation pathways.  Introduction to Endocrinology The term endocrine comes from Greek: Endon = “within” General Krinein = “to release.” Features of Hormone is derived from Greek hormon = “to excite” or “to set into motion.” the Endocrinology: Study of endocrine glands and their hormones. Endocrine Neurohormones: Special hormones System released into the blood by neurosecretory cells (nerve cells). Neuroendocrinology: Studies the interaction between the nervous and endocrine systems. Endocrine vs. Exocrine Glands Endocrine glands: Release hormones directly into the blood (e.g., thyroid, adrenal glands). Exocrine glands: Use ducts to release products into internal or external environments (e.g., sweat, salivary glands). Dual-function glands: Some glands, like the pancreas, have both endocrine and exocrine functions: Exocrine: Secretes digestive juices into intestines. Endocrine: Produces hormones like insulin to regulate energy use. Expanding the Definition of Endocrine Glands Adipose tissue: Produces leptin, a hormone involved in energy balance. Stomach: Produces ghrelin, a hormone regulating hunger. Brain: Acts as an endocrine organ, producing a wide variety of hormones.  Dual Function Organs (endocrine and exocrine) Organ Endocrine Function Exocrine Function Secretes insulin and glucagon into the Secretes digestive enzymes into the Pancreas bloodstream. duodenum via ducts. Produce sex hormones (estrogen, Produce gametes (eggs, sperm) and Gonads (Ovaries & Testes) testosterone). release them during reproduction. Produces bile, secreted into the Liver Produces IGF-1 and other hormones. gallbladder and duodenum. Release minor amounts of hormones Secrete sweat to the skin’s surface Sweat Glands like prolactin. through ducts. Release prolactin and oxytocin for milk Secrete milk through ducts to nourish Mammary Glands production. infants. Release small amounts of hormones like Secrete saliva into the mouth through Salivary Glands prolactin. ducts. Secrete erythropoietin and renin into Excrete urine via the ureters and out Kidneys the blood. through the urethra. Hormones: Production and Release Types of hormones: Protein/Peptide hormones (water- soluble): Stored in secretory granules (vesicles). Released through exocytosis: Vesicles fuse with the cell membrane, releasing hormones into the extracellular space, then into the bloodstream. Steroid hormones (lipid-soluble): Not stored; produced and released on demand. Derived from cholesterol, which can be stored in lipid droplets in cells. Transport of Hormones in the Blood Protein/Peptide hormones: Soluble in blood (an aqueous solution). Steroid hormones: Not water-soluble; bind to carrier proteins in the blood. Carrier proteins help regulate hormone actions. Hormone Receptors: The Lock-and-Key Mechanism Receptors are specific binding sites: Located on the cell membrane or inside the cell. Bind to particular hormones with high affinity and specificity. Hormones act like a key to the receptor’s lock. Despite low hormone concentrations in the blood, high receptor affinity ensures potent effects. Receptor Sensitivity and Hormone Effects Cross-reaction: When hormone levels are very high, receptors may bind related hormones, causing unintended biological responses. Receptor availability affects biological response: Low receptor numbers: Can cause endocrine deficiency even with normal hormone levels. Example: Androgen receptor deficiency can prevent male traits despite normal testosterone. High receptor numbers: Can lead to endocrine excess symptoms despite normal hormone levels.  Non-Steroid Steroid Aspect Hormones Hormones Solubility Water-soluble Lipid-soluble Inside the Receptor On the cell cytoplasm or Location membrane nucleus Activates second Alters gene Mechanism messengers transcription Speed of Action Fast Slow Insulin, Testosterone, Examples Epinephrine Cortisol Examples: Examples: Testosterone: Insulin: Binds to Promotes protein membrane receptors to synthesis in increase glucose muscles and uptake into cells. development of Epinephrine: male traits. Activates second Cortisol: messengers to increase Regulates heart rate and energy metabolism and mobilization during immune responses stress. during stress. Chapter 2 Part 2 The Endocrine Syatem Anatomy and Locations of Key Endocrine Organs Endocrine Organ Location Key Function Controls reproduction, metabolism, and Beneath the thalamus, at the base Hypothalamus homeostasis; releases of the brain. neurohormones that regulate the pituitary. Produces tropic hormones At the base of the skull, in the (e.g., TSH, ACTH, FSH, LH, Pituitary Gland sella turcica (bony depression). GH); regulates other endocrine glands. Produces thyroid hormones Thyroid Gland Upper trachea, near the larynx. (T3, T4) that regulate metabolism. Functions as both an Behind the stomach, within the endocrine (insulin, Pancreas curve of the duodenum. glucagon) and exocrine (digestive enzymes) organ. Secrete steroid hormones (e.g., cortisol, aldosterone) Adrenal Glands On top of the kidneys. and catecholamines (e.g., adrenaline). Produces melatonin, which In the brain, between the Pineal Gland regulates sleep-wake telencephalon and diencephalon. cycles. Produce sex hormones (e.g., testosterone, Gonads Testes: In the scrotum; Ovaries: In estrogen, progesterone) for (Testes/Ovaries) the abdomen. reproduction and secondary sex characteristics. Produces hormones (e.g., In the uterus during pregnancy hCG, progesterone) that Placenta (temporary organ). support pregnancy and fetal development. Types of Hormones (protein vs. peptides) Protein hormones: Larger in size, composed of long chains of amino acids (more than 50 amino acids). Peptide hormones: Smaller, usually consist of short chains of amino acids (fewer than 50 amino acids). Examples: Protein hormones: Insulin, growth hormone, prolactin. Peptide hormones: Oxytocin, vasopressin (ADH), glucagon. Protein hormones: Growth hormone regulates growth and metabolism; insulin regulates glucose metabolism. Peptide hormones: Oxytocin regulates childbirth and lactation; vasopressin regulates water balance. Types of Hormones Type of Hormone Examples Releasing Organ(s) Insulin, Glucagon, Growth Pituitary gland, Pancreas, Protein Hormones Hormone, Prolactin, ACTH, Hypothalamus TSH Leptin, Ghrelin, Calcitonin, Adipose tissue, Stomach, Peptide Hormones Parathyroid Hormone Parathyroid gland Cortisol, Estrogen, Adrenal glands, Gonads Steroid Hormones Progesterone, Testosterone, (ovaries/testes) Aldosterone Dopamine, Thyroid Hypothalamus, Pineal gland, Monoamine Hormones Hormones (T3, T4), Adrenal glands, Thyroid Melatonin, Epinephrine gland Various tissues, including Prostaglandins, Lipid-Based Hormones the immune system, uterus, Leukotrienes, Thromboxanes and brain  Some key Hormones and their Functions Steroid Hormones Hormone Function Everyday Life Example During stressful situations Regulates stress response, (e.g., a work deadline), Cortisol metabolism, and immune cortisol helps you manage function. the stress. Regulates female In women, estrogen reproductive system, regulates the menstrual Estrogen menstrual cycle, and cycle and affects mood, secondary sex skin, and bone health. characteristics. Regulates male reproductive Testosterone affects muscle system, muscle mass, and development, mood, and Testosterone secondary sex libido, and it’s also characteristics. important for bone density. Regulates sodium and Helps maintain normal blood Aldosterone potassium balance, affecting pressure by balancing salt blood pressure. and water in the body.  Some Key Hormones and their Functions Non-Steroid Hormones Hormone Function Everyday Life Example Steroid or Non-Steroid After eating, insulin helps cells Regulates blood sugar levels by Insulin absorb glucose from the Non-steroid (Peptide) promoting glucose uptake into cells. bloodstream, providing energy. Affects energy levels, metabolism Regulates metabolism, energy Thyroxine (T4) (how quickly you burn calories), and Non-steroid (Amino Acid Derivative) production, and growth. overall vitality. After eating, leptin signals the brain Regulates energy balance by Leptin that you're full, helping to prevent Non-steroid (Peptide) suppressing appetite. overeating. Ghrelin increases before meals, Stimulates appetite and promotes Ghrelin making you feel hungry and Non-steroid (Peptide) hunger. encouraging food intake. Released during childbirth and Stimulates uterine contractions breastfeeding, also fosters Oxytocin during labor and promotes bonding Non-steroid (Peptide) emotional bonds (e.g., hugs, behaviors. bonding with loved ones). Prepares the body for fight or flight During a sudden emergency (e.g., Adrenaline (Epinephrine) response by increasing heart rate near accident), adrenaline increases Non-steroid (Amino Acid Derivative) and blood flow. alertness and readiness to act. After giving birth, prolactin allows a Stimulates milk production in Prolactin mother to produce breast milk for Non-steroid (Peptide) women after childbirth. feeding her baby. Essential for childhood growth, and Stimulates growth, cell Growth Hormone helps repair tissues after injuries Non-steroid (Peptide) reproduction, and regeneration. during adulthood. Helps maintain healthy bones and Regulates calcium levels in the Parathyroid Hormone teeth by regulating calcium balance Non-steroid (Peptide) blood. in the body. Produced at night to help you sleep, Regulates sleep-wake cycles melatonin helps you adjust to time Hypothalamic Hormones Location: The hypothalamus is located at the base of the brain and consists of several nuclei that control essential functions, including metabolism and reproduction. Neurosecretory Cells: These are specialized neurons at the base of the hypothalamus that release neurohormones into the blood vessels of the pituitary gland. While they function like endocrine glands, they are structurally similar to neurons, having dendrites, axons, and other typical neuron features. Neurohormones: Released in response to neuronal impulses, neurohormones are released into the blood rather than a synaptic space, allowing communication between the hypothalamus and the pituitary gland. Releasing and Inhibiting Hormones: Releasing Hormones: These small peptide hormones (3 to 44 amino acids) stimulate the anterior pituitary to release specific hormones. Examples: TRH (Thyrotropin-Releasing Hormone) GHRH (Growth Hormone-Releasing Hormone) GnRH (Gonadotropin-Releasing Hormone) MRH (Melanotropin-Releasing Hormone) CRH (Corticotropin-Releasing Hormone) Inhibiting Hormones: These hormones prevent the release of specific hormones from the pituitary. Examples: Somatostatin (also called GHIH or Growth Hormone-Inhibiting Hormone) GnIH (Gonadotropin-Inhibitory Hormone) Dopamine: Acts as a neurohormone in the hypothalamus, inhibiting the release of prolactin (PIH) and melanotropin (MIH) from the anterior pituitary. Hypocretin (Orexin): Involved in regulating sleep, metabolic balance, and potentially activating the sympathetic nervous system.  FIGURE 2.6: Amino Acid Sequences of Selected Releasing Hormones The amino acid sequences of several releasing hormones, including TRH, GnRH, somatostatin (GHIH), CRH, and GHRH, have been identified. Both melanotropin inhibitory hormone (MIH) and prolactin inhibitory hormone (PIH) are believed to be dopamine. The term pGLU refers to pyroglutamyl, and NH2 indicates the amide group of the C-terminal amino acid. Hormonal Variability and Species Specificity Protein and Peptide Hormone Variability: Hormones like GnRH can vary in amino acid sequences between species, affecting how they interact with receptors in different animals. For example, injecting mammalian GnRH into a toad might not have any reproductive effect. Immune Response to Foreign Hormones: Protein hormones extracted from other species can cause immune reactions if used for prolonged treatment in a different species. The Pituitary Gland Anterior Pituitary Origin of the Term "Pituitary": Derived from Latin "mucus"; once thought to collect waste from the brain. Pituitary Gland as the "Master Gland": Historically, it was believed to control many physiological processes. Two Distinct Parts of the Pituitary: Anterior Pituitary (Adenohypophysis): Develops from Rathke’s pouch, a structure from the roof of the mouth. Posterior Pituitary (Neurohypophysis): Originates as an outgrowth from the brain. Pituitary Size & Location: Small (size of a blueberry), located beneath the hypothalamus. Structure and Communication with Hypothalamus: Portal System: Special blood circuit connecting Function hypothalamus to anterior pituitary. One-way blood flow: Ensures hormonal signals from hypothalamus reach the anterior pituitary. The hypothalamus and pituitary gland are crucial components of the endocrine system. They regulate various physiological processes through hormone secretion. This axis plays a key role in maintaining homeostasis in the body. Two Methods of Communication Neurohormones via the Portal System: Neurohormones from the hypothalamus reach the anterior pituitary through a specialized blood circuit. Direct Neural Connections: The hypothalamus also communicates with the posterior pituitary via direct neural pathways.  Anterior Pituitary Hormones Stimulus for Hormone Structure Primary Functions Additional Information Release Glycoprotein (200– Gonadotropin- Stimulates steroidogenesis in the Composed of α and β subunits; β- Luteinizing 220 amino acids, releasing hormone gonads; promotes ovulation and subunit determines specific function Hormone (LH) 10%–25% (GnRH) testosterone production and species specificity carbohydrate) Glycoprotein (200– Follicle- Gonadotropin- Composed of α and β subunits; β- 220 amino acids, Promotes development and maturation Stimulating releasing hormone subunit determines specific function 10%–25% of gametes (sperm and ova) Hormone (FSH) (GnRH) and species specificity carbohydrate) Glycoprotein (200– Thyroid- Thyrotropin- Composed of α and β subunits; β- 220 amino acids, Stimulates the thyroid gland to release Stimulating releasing hormone subunit determines specific function 10%–25% thyroid hormones (T3 and T4) Hormone (TSH) (TRH) and species specificity carbohydrate) Stimulates production of Growth hormone- Stimulates somatic growth, protein Growth Hormone Protein (190–220 somatomedins; has anti-insulin releasing hormone synthesis, and fat mobilization; (GH) amino acids) effects and indirect effects on the (GHRH) increases blood sugar levels thymus Promotes lactation in female mammals; Protein (198 amino Thyrotropin- Has many functions beyond lactation; involved in reproduction, growth, water Prolactin (PRL) acids, 3 disulfide releasing hormone conserved throughout vertebrate balance, and integumentary bonds) (TRH) evolution maintenance Adrenocorticotro Corticotropin- Derived from POMC; plays a key role Peptide (39 amino Stimulates the adrenal cortex to release pic Hormone releasing hormone in stress response and metabolism acids) cortisol and other glucocorticoids (ACTH) (CRH) regulation Melanocyte- Corticotropin- Stimulates the production and release Derived from POMC; involved in Peptide (13 amino Stimulating releasing hormone of melanin by melanocytes in the skin pigmentation and can influence acids) Hormone (MSH) (CRH) and hair appetite and sexual arousal Posterior Pituitary Hormones Primary Hormones: Oxytocin Function:Stimulates smooth muscle contractions in the uterus and mammary glands Involved in social behaviors and emotional bonding (e.g., maternal attachment) Links to PFC = decision-making, social cognition, emotional regulation, bonding and empathy. Nacc = reward, rewarding aspects of social behavior, maternal behavior, social motivation. MEA = sexual and parental behavior (oxytocin release). Effects:Uterine contraction during labor Milk ejection during breastfeeding Promotes social and emotional connections Vasopressin (anti-diuretic hormone [ADH]) Function Maintains water balance by regulating water reabsorption in kidney Controls blood pressure through vasoconstriction Links to the lateral septum (LS) and ventral pallidum may modulate social behaviour and reward. Effects: Increases water retention in kidneys (reducing urine output) Increases blood pressure Involved in social behaviors and pair bonding Gonadal Hormones Primary Hormones: Functions: Effects: Estrogen Regulate sexual differentiation, Estrogen: Development of Progesterone reproductive cycles, and female reproductive system, Testosterone secondary sexual sexual behavior, mood characteristics regulation, Promotes female Influence behavior (e.g., libido, secondary sexual aggression) characteristics (e.g., breast development, menstrual cycle), Enhances mood and cognitive function. Progesterone: Prepares the uterus for pregnancy, regulates menstrual cycle, maintenance of pregnancy. Testosterone: Development of male reproductive organs, promotes muscle mass, aggression, Stimulates the development of male secondary sexual characteristics (e.g., facial hair, deep voice), promotes spermatogenesis, Influences aggression, libido, and muscle mass Adrenal Hormones Primary Hormones: Cortisol Aldosterone Adrenaline (Epinephrine) Functions: Cortisol: Stress response, metabolism regulation Controls immune function Aldosterone: Regulates sodium and potassium balance Increases water retention to control blood pressure Adrenaline (Epinephrine): Fight-or-flight response Increases heart rate, blood pressure, and glucose availability Effects: Cortisol: Increases glucose production, suppresses immune responses Aldosterone: Regulates blood pressure and fluid balance Adrenaline: Increases heart rate and energy availability for physical exertion Gastrointestinal Hormones Primary Hormones: Functions: Effects: Gastrin Gastrin: Gastrin, CCK, Secretin: Aid Cholecystokinin (CCK) Stimulates gastric acid digestion and nutrient Secretin secretion for digestion absorption Ghrelin Cholecystokinin (CCK): Ghrelin & Leptin: Control Leptin Stimulates bile release and appetite and energy balance pancreatic enzyme secretion Inhibits gastric emptying to aid digestion Secretin: Stimulates bicarbonate release to neutralize stomach acid Ghrelin: Stimulates appetite, increases food intake Leptin: Signals satiety to regulate food intake and body weight How Hormones Are Regulated