Physiology Study Guide

📖 Core Concepts Physiology – scientific study of how living systems function and the mechanisms behind those functions. Levels of organization – from molecules → cells → tissues → organs → whole organisms → populations. Physiological vs. pathological state – normal functioning vs. disease‑related dysfunction. Homeostasis – the body’s ability to keep internal conditions stable through regulated processes. Signal integration – coordination of organ systems via electrical (nervous) and chemical (endocrine) signals. Comparative physiology – examines functional differences among species and how evolution & environment shape them. 📌 Must Remember Claude Bernard → coined milieu intérieur (internal environment). Sliding filament theory (Huxley & Huxley, 1954) → basis of muscle contraction. Major human organ systems – nervous, endocrine, cardiovascular, respiratory, digestive, urinary. Plant core processes – photosynthesis (light → chemical energy) and respiration (sugar → ATP). Stomatal function – controls gas exchange & water loss; key to transpiration and photosynthetic efficiency. 🔄 Key Processes Cell Division Replication of DNA → segregation of chromosomes → cytokinesis → two daughter cells. Cell Signaling Signal molecule (ligand) → receptor activation → intracellular cascade → cellular response. Cell Metabolism (simplified) Nutrient uptake → catabolic pathways (e.g., glycolysis) → ATP production → anabolic pathways (biosynthesis). Photosynthesis Light absorption → water splitting → O₂ release → CO₂ fixation → sugar (glucose) synthesis. Respiration (plants & animals) Glucose oxidation → CO₂ + H₂O + ATP (energy for cellular work). 🔍 Key Comparisons Nervous vs. Endocrine System Speed: nervous → milliseconds; endocrine → seconds‑to‑hours. Signal type: electrical impulses vs. hormones (chemical). Range: localized synapses vs. bloodstream (systemic). Physiological vs. Pathological State Normal vs. disease; homeostatic balance vs. disrupted regulation. Plant vs. Animal Respiration Plants can perform both aerobic respiration and photo‑respiration; animals rely solely on aerobic pathways. ⚠️ Common Misunderstandings “Physiology = anatomy” – anatomy describes structure; physiology explains function. “All hormones act fast” – many hormones have long‑lasting effects; speed depends on hormone type and target tissue. “Photosynthesis only occurs in leaves” – any green tissue with chloroplasts can photosynthesize. 🧠 Mental Models / Intuition “Homeostatic thermostat” – imagine a thermostat that detects a variable (e.g., temperature) and activates heating or cooling to keep it at set point. “Cell as a factory” – inputs (nutrients) → production lines (metabolic pathways) → outputs (ATP, building blocks) + waste. 🚩 Exceptions & Edge Cases Stomatal regulation – while generally closed under drought, some desert plants keep stomata open at night (CAM photosynthesis) to minimize water loss. Evolutionary physiology – traits that appear “inefficient” today may be vestiges of past adaptive pressures. 📍 When to Use Which Choose anatomy vs. physiology focus – if the question asks where something occurs, think anatomy; if it asks how it works, think physiology. Signal pathway identification – if a problem mentions rapid response → nervous system; if prolonged, hormonal/endocrine. Metabolic pathway selection – for short‑term energy demand → glycolysis; for sustained energy → oxidative phosphorylation. 👀 Patterns to Recognize Feedback loops – negative feedback → restores set point (common in homeostasis); positive feedback → amplifies change (e.g., childbirth). Structure‑function pairing – thick-walled vessels → high pressure; thin‑walled alveoli → gas exchange. Energy flow – light energy → chemical energy (photosynthesis) → ATP (respiration) → mechanical work. 🗂️ Exam Traps Distractor: “Hormones act faster than nerves” – false; nerves transmit faster. Misleading choice: “Photosynthesis occurs in mitochondria” – photosynthesis takes place in chloroplasts. Near‑miss: “Cell division only produces identical cells” – meiotic division creates genetically distinct gametes; mitosis produces identical somatic cells. Trap: “Stomata open only during the day” – CAM plants open stomata at night; answer must consider plant type.