Overview
This lecture reviews the four main themes in physiology: energy use, cell communication, structure/function relationships, and control systems that maintain homeostasis.
Equilibrium vs. Dynamic Steady State
- Equilibrium means both concentration and rate are the same inside and outside a system.
- Dynamic steady state has equal rates in and out, but maintains concentration differences using energy.
- Dynamic steady state models homeostasis in the body.
Four Main Themes in Physiology
1. Energy Use
- Cells capture energy from breaking down molecules (like sugars) through aerobic respiration.
- ATP produced from respiration powers cellular work.
- Maintaining concentration gradients requires energy, and gradients themselves are a form of stored energy.
2. Cellular Communication
- Cells communicate using chemical signals (often proteins) and electrical signals.
- Signal transduction describes how signals trigger changes inside cells despite the plasma membrane barrier.
- The body contains intracellular fluid (cytosol), interstitial fluid, and plasma, each with different compositions.
- Plasma proteins are found in plasma but not in interstitial fluid; cytosol has the most protein.
- Potassium is high inside cells, sodium and chloride are high outside; rates may match but concentrations differ.
3. Structure and Function
- The structure of proteins, cells, and tissues determines their functions.
- Compliance is the ability of cells/tissues to stretch; elastance is their recoil ability.
- Changes in structure can alter function, affecting communication and energy use.
4. Control Systems and Homeostasis
- Control systems process sensory input, generate output, and maintain internal stability (homeostasis).
- The central nervous system (CNS: brain/spinal cord) processes input and sends output to effectors (e.g., muscles, glands).
- Negative feedback loops reduce stimulus intensity to maintain a set point (e.g., sweating cools body, shivering warms body).
- Positive feedback loops amplify a stimulus and are not homeostatic (e.g., blood clotting, childbirth).
Key Terms & Definitions
- Dynamic Steady State — Condition with equal input/output rates but maintained concentration gradients using energy.
- Homeostasis — Maintenance of a stable internal environment.
- Signal Transduction — Process of converting external signals into cellular responses.
- Compliance — Ability of a tissue or cell to stretch.
- Elastance — Ability to return to the original shape after being stretched.
- Negative Feedback — Response reduces original stimulus, maintaining balance.
- Positive Feedback — Response increases original stimulus, used in special cases only.
Action Items / Next Steps
- Review notes on aerobic respiration for energy use.
- Prepare for upcoming modules: cell communication and signal transduction.
- Understand examples of negative and positive feedback in physiology.