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Endocrine System
Chapter 17 - A & P Lecture
| Question | Answer |
|---|---|
| The endocrine system is a network of glands that: | Secrete hormones (chemical messengers) Into the bloodstream To act on distant target tissues |
| Relationship to the Nervous System | Both systems maintain homeostasis, but they differ fundamentally. |
| Similarities of Nervous System & Endocrine System | Share the hypothalamus (major integration center) Can use the same chemicals Example: epinephrine = neurotransmitter and hormone Both act via receptors (often G protein-coupled) Work together to regulate body processes |
| Differences of Nervous System & Endocrine System | NS ES Transport: Axons Blood Speed: millisec sec-dy Duration: short long Signal strength: Frequency modulated Amplitude mudulated |
| Signal strength in Endocrine is modulatied by _________ and depends on ________ ___________ so more hormone means ______ _____. | amplitude, hormone concentration, stronger response |
| Major regulated processes: | Growth & development Metabolism Blood composition Reproduction |
| Growth & development | Bone growth, muscle enlargement, synapse formation |
| Metabolism | Glucose regulation, enzyme production, cardiovascular effects |
| Blood composition | Ion balance, pH, blood cells, water balance |
| Reproduction | Gamete production, pregnancy support |
| Classes of Chemical Messengers: | 1. Autocrine 2. Paracrine 3. Neurotransmitters 4. Endocrine (Hormones) |
| Autocrine | Acts on same cell that released it Example: eicosanoids |
| Paracrine | Acts on nearby cells NOT transported in blood Example: histamine |
| Neurotransmitters | Released into synapse Travel short distance Example: acetylcholine |
| Endocrine (Hormones) | Travel through blood Act on distant targets Example: insulin, thyroid hormone |
| what is the difference in the classes chemical messengers? | distance + transport mechanism |
| Hormones only affect cells with the correct _______. | receptor |
| Explain Hormone Specificity: | Binding = response Receptors are structurally specific No receptor → no effect |
| Control of Hormone Secretion: | 1. Humoral Stimuli 2. Neural Stimuli 3. Hormonal Stimuli |
| Humoral Stimuli | Triggered by blood chemistry changes Example: ↓ Ca²⁺ → ↑ parathyroid hormone |
| Neural Stimuli | Triggered by nervous system Example: Sympathetic stimulation → adrenal medulla → epinephrine |
| Hormonal Stimuli | Triggered by other hormones Example: Hypothalamus → pituitary → other glands 👉 These are tropic hormones |
| Patterns of Hormone Secretion: | Chronic, Acute, Episodic |
| Chronic | Constant levels Example: thyroid hormone |
| Acute | Sudden, irregular spikes Example: epinephrine |
| Episodic | Predictable cycles Example: reproductive hormones |
| Classes of Hormones: | Lipid-Soluble Hormones & Water-Soluble Hormones |
| Lipid-Soluble Hormones Properties: | Nonpolar Can cross cell membrane Bind intracellular (nuclear) receptors |
| Lipid-Soluble Hormones Types: | Steroids (testosterone, aldosterone) Thyroid hormone Prostaglandins |
| Water-Soluble Hormones Properties: | Polar Cannot cross membrane Bind membrane receptors |
| Water-Soluble Hormones Types: | Proteins (GH, TSH) Peptides (insulin) Some amino acid derivatives (epinephrine) |
| Binding Proteins Used By _____-______ ______. | lipid-soluble hormones |
| Binding Proteins forms: | Bound hormone & Free hormone |
| Bound hormone | Attached to protein Stable, long-lasting Acts as reservoir |
| Free hormone | Active form Can bind receptors |
| Only _____ ______ can produce a biological effect | free hormone |
| How are hormones transported in blood? | with binding proteins |
| how are hormones levels regulated? | Negative Feedback |
| Negative Feedback | Hormone inhibits its own production |
| Negative Feedback Example Sequence: | 1. Pituitary releases tropic hormone 2. Target gland releases hormone 3. That hormone inhibits pituitary + hypothalamus |
| Positive Feedback | Hormone enhances its own production 👉 Less common, self-amplifying |
| Hormone Half-Life: | Time for 50% of hormone to be removed Larger hormones → longer half-life |
| Hormone Elimination: | Lipid-Soluble & Water-Soluble |
| Lipid-Soluble: | Modified in liver (conjugation) Excreted in bile/urine |
| Water-Soluble: | Broken down by proteases Excreted by kidneys |
| Lipid-Soluble Hormone Mechanism: | Intracellular / Nuclear Receptors Process: Hormone enters cell Binds receptor (cytoplasm or nucleus) Complex binds DNA (hormone-response element) Acts as transcription factor mRNA produced → proteins synthesized Proteins cause response |
| Water-Soluble Hormone Mechanism | Membrane-Bound Receptors Types: Ligand-gated ion channels G protein-coupled receptors (GPCRs) Enzymatic receptors |
| G Protein-Coupled Receptors Structure: | α, β, γ subunits GDP (inactive) → GTP (active) |
| G Protein-Coupled Receptors Activation: | 1. Hormone binds receptor 2. GDP → GTP on α subunit 3. α separates → activates pathways |
| Second Messengers | Major ones: cAMP cGMP Ca²⁺ IP₃ DAG |
| Three Major Pathways: | ↑ cAMP Pathway ↓ cAMP Pathway Ca²⁺ / IP₃ / DAG Pathway |
| ↑ cAMP Pathway | Activates adenylate cyclase ATP → cAMP Activates protein kinases |
| ↓ cAMP Pathway | Inhibits adenylate cyclase Less signaling |
| Ca²⁺ / IP₃ / DAG Pathway | Activates phospholipase C PIP₂ → IP₃ + DAG |
| Ca²⁺ / IP₃ / DAG Pathway Effects: | IP₃ → releases Ca²⁺ DAG → enzyme activation |
| Enzymatic Receptors: | Guanylate Cyclase & Receptor Tyrosine Kinase (INSULIN) |
| Guanylate Cyclase | GTP → cGMP Activates enzymes |
| Receptor Tyrosine Kinase (INSULIN) | Binding → phosphorylation cascade Direct enzyme activation |
| Signal Amplification | One hormone → MANY intracellular effects - Nuclear = slower, less amplified - Second messenger = rapid, highly amplified |
| Receptor Regulation: | Down-Regulation & Up-Regulation |
| Down-Regulation | Fewer receptors Reduced sensitivity |
| Up-Regulation | More receptors Increased sensitivity Example: FSH → ↑ LH receptors → ovulation |
| Hormone Interactions: | Permissive, Synergistic, Antagonistic |
| Permissive | One hormone enhances another Example: Thyroid hormone ↑ epinephrine receptors |
| Synergistic | Combined effect > sum |
| Antagonistic | Oppose each other Examples: Insulin vs glucagon Calcitonin vs PTH |
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