التنسيق الداخلي للكائنات الحية

Introduction to Physiology

• Physiology is a branch of life sciences, encompassing anatomy, histology, cytology, and other related fields.
• It focuses on the vital processes enabling living organisms' functions and activities.
• It studies the entire organism's functions or the functions of organs, tissues, and cells.
• Physiology has been a longstanding field, evolving alongside human civilization, particularly in medicine and anatomy.
• Key figures like Ibn al-Nafis (discoverer of the small blood circulation) and al-Razi (investigating environmental influences on health) contributed significantly.
• Ancient Greek and Roman contributions, enhanced by Arab scholars, collectively formed the basis of the scientific method.

Principles of Physiology

• Material exchange with the environment: Living beings differ from the surrounding environment in chemical and organizational aspects. Essential for survival is exchange with the environment through organs like lungs, kidneys, digestive tract, and skin. These organs feature large surface areas connected to capillaries, facilitating efficient exchange. For instance, the small intestine has ~10 square meters of surface area, the lungs ~55 square meters, and the kidneys ~6 square meters.

• Metabolism: Organisms derive energy from food via complex chemical reactions to build tissues, release energy, and perform life processes. Energy is released through the breakdown of complex molecules into simpler ones and their oxidation through respiration. Water and carbon dioxide are byproducts, as shown in the equation: C6H12O6 + O2 > Energy + CO2 + H2O.

  • Catabolism: The breakdown of complex molecules into simpler ones, with associated energy release.
  • Anabolism: The building of complex molecules from simpler ones.
  • Metabolism: The overall result of catabolic and anabolic processes.

Internal Coordination

• Coordination: Essential for maintaining life is the coordination between an organism's internal and external environments. It depends on the size of the organism. Simple organisms exchange materials directly with the environment through the cell membrane, while complex organisms, like humans, have intricate systems for coordination.
  • Circulatory system: Carries food and oxygen to cells and removes waste products (CO2) for elimination.
  • Endocrine system: Composed of glands producing hormones transported through the blood to target tissues/organs. Hormonal action is slower than the nervous system's.

External Coordination

• External environment changes affect the organism's activity and behavior.
• Sensory organs and the nervous system help organisms detect and respond to the environment.
  • Receptors: Receive stimuli from the environment.
  • Central nervous system: Receives and processes stimuli from receptors.
  • Motor nerves: Transmit responses to effector organs (glands and muscles).
  • Reflexes: Quick, involuntary responses to a stimulus, avoiding harm, without conscious thought.
  • Complex responses: More involved responses involving brain activity, such as instincts (gathering food, migration, hibernation, shelter-building, etc.).

Homeostasis

• Internal constancy: Maintaining stable internal conditions is a crucial function of internal coordination. Parameters like temperature, pH, body fluids, and glucose levels remain within narrow ranges.
  • Feedback mechanisms: Essential for maintaining homeostasis when deviations from the normal ranges occur. Two main types:
    • Positive feedback: A response reinforces the stimulus, as seen in hormonal fluctuations during the menstrual cycle.
    • Negative feedback: A response counteracts the stimulus, as observed in regulating blood sugar levels (insulin response to high blood sugar).

Cell Membrane and Transport

• Membrane structure: Cell membranes are double-layered phospholipid structures with interspersed cholesterol molecules and embedded proteins. Polar heads face outward, and nonpolar tails face inward.
• Membrane proteins: Functions range from transporters and enzymes to structural components.
• Transport processes: Materials move into and out of cells through different processes; some are energy-dependent (active transport) while others are not (passive transport).
  • Passive transport:
    • Diffusion: Movement of substances from higher to lower concentrations. Dependent on factors such as molecule size, lipid solubility, and charge. Key factors influencing are molecule size, lipid solubility, and molecular charge.
    • Facilitated diffusion: Large or non-lipid-soluble molecules utilize membrane proteins for passage.
    • Osmosis: Movement of water across a semipermeable membrane from a lower to higher solute concentration.
  • Active transport: Energy-demanding movement of substances against their concentration gradient (e.g., pumping ions). This energy is sourced from ATP.
  • Endocytosis: Uptake of substances into the cell through vesicle formation (e.g., phagocytosis, pinocytosis).
  • Exocytosis: Release of substances out of the cell via vesicle fusion with the membrane.

Additional Transport Mechanisms

• Filtration: Movement of substances through a membrane due to pressure differences.
• Osmotic pressure: Pressure exerted by water across a semipermeable membrane.
• Hypertonic, isotonic, and hypotonic solutions: Comparisons of solute concentrations across the cell membrane.