Introduction to Physiology and Cell Membranes

Introduction and History of Physiology

• Physiology studies the functions and mechanisms in living organisms.
• It examines how organs, tissues, cells, and molecules work together to maintain life.
• Ancient civilizations studied physiology, with Greek physicians like Hippocrates and Aristotle contributing.
• Galen (129-200 AD) performed animal dissections to understand systems, though some findings were inaccurate.
• The 17th century saw William Harvey's discovery of blood circulation.
• The 19th century marked a more experimental approach to physiology, with figures like Claude Bernard introducing the concept of the internal environment and homeostasis.
• The 20th and 21st centuries integrated physiology with other fields like biochemistry, genetics, and biophysics, leading to detailed cellular and molecular-level understanding.

Structure and Functions of Cell Membranes

• Cell membranes, also known as plasma membranes, are primarily composed of a phospholipid bilayer.
• Phospholipids have hydrophilic heads (attracted to water) and hydrophobic tails (repelled by water), forming a semi-permeable barrier.
• Integral and peripheral proteins assist in transport, signaling, and interactions.
• Cholesterol contributes to membrane stability and fluidity, crucial for animal cells.
• Carbohydrates attached to proteins or lipids aid in cell recognition and signaling.
• Functions include cell communication, selective permeability, maintaining structure and support, and signal transduction.

Transport Processes

• Transport processes move molecules across membranes.
• Passive transport occurs without energy input, moving molecules down their concentration gradient.
  • Diffusion involves movement of small, non-polar molecules (e.g., oxygen).
  • Facilitated diffusion uses carrier or channel proteins to move larger or polar molecules across.
  • Osmosis is the diffusion of water across a semi-permeable membrane.
• Active transport requires energy (ATP) to move molecules against their concentration gradient.
  • Primary active transport directly uses ATP to move substances.
  • Secondary active transport uses energy from an ion gradient created by primary active transport.

Special Transport Mechanisms in Specific Organs and Tissues

• These mechanisms facilitate specific functions in various organs.
• Amphibian bladders regulate water and ion balance.
• Kidneys filter, reabsorb, and secrete substances to maintain electrolyte and water balance.
• Gall bladders concentrate bile for fat digestion via water and ion transport.
• Intestines absorb nutrients like glucose, amino acids, and lipids through specific transporters.
• Astrocytes regulate ion balance in the brain.
• Exocrine glands use active transport and vesicles for secretion.

Biophysical Principles

• Diffusion spreads molecules from high to low concentration due to thermal energy.
• Osmosis is water movement through a semi-permeable membrane toward higher solute concentration.
• Electrochemical gradients influence ion movement based on concentration and charge differences across membranes.
• Membrane potentials are voltage differences across membranes due to ion distributions influencing nerve impulse transmission.
• Thermodynamics governs energy transfer and generation within cells.

Homeostasis and Control Systems

• Homeostasis maintains a stable internal environment despite external changes.
• Control systems maintain homeostasis through feedback mechanisms.
  • Negative feedback counteracts stimuli, like blood glucose regulation.
  • Positive feedback enhances the initial stimulus, like childbirth.

Temperature Regulation

• Thermoregulation maintains body temperature within a narrow range, a crucial aspect of homeostasis.
• Heat production arises from metabolic activities, especially muscle contraction.
• Heat loss mechanisms include radiation, conduction, convection, and evaporation.
• The hypothalamus acts as a thermostat, detecting temperature changes and initiating responses like shivering or sweating.

Adaptations

• Adaptations include behavioral responses (seeking shade, drinking water).
• Physiological responses (vasoconstriction or vasodilation) regulate heat loss and gain.

Explore the fascinating history of physiology, from ancient Greek contributions to modern discoveries. This quiz will cover key figures, essential concepts like homeostasis, and the structure and function of cell membranes in living organisms.