Summary of General Physiology
General physiology is the study of the mechanical, physical, and biochemical functions of living organisms. It explores how cells, tissues, organs, and systems within the body work both individually and together to maintain life. Understanding general physiology is crucial for comprehending how the human body adapts to various internal and external conditions, and how disruptions in these processes can lead to disease.
Body Composition and Water Distribution
- The human body is composed of various molecules, including water (approximately 60% of total body weight), proteins (18%), lipids (15%), minerals (5%), nucleic acids, and carbohydrates (less than 1%).
- Total body water (TBW) varies with age, gender, and body composition. Infants have a higher percentage of body water (75-80%), while adults have around 60% (males) and 50-55% (females).
- Body water is distributed into intracellular fluid (ICF), which is located inside cells and constitutes about 40% of body weight, and extracellular fluid (ECF), which is located outside cells and comprises about 20% of body weight (interstitial fluid 15% and plasma 5%).
Transport Across Cell Membranes
- Transport across the cell membrane is essential for maintaining cellular homeostasis and enabling the exchange of substances between the cell and extracellular space.
- Passive Transport: This type of transport does not require energy and follows the concentration gradient.
- Simple Diffusion: Movement of small molecules directly through the lipid bilayer (e.g., oxygen and carbon dioxide).
- Facilitated Diffusion: Movement of larger molecules across the membrane via specific transport proteins (e.g., glucose, ions).
- Osmosis: Movement of water across a semipermeable membrane according to the concentration gradient.
- Active Transport: This type of transport requires energy (ATP) to move substances against their concentration gradient.
- Primary Active Transport: Direct use of ATP to transport molecules (e.g., Na+/K+-ATPase pump). The Na+/K+-ATPase pump maintains resting membrane potential, regulates cell volume, and is essential for nerve impulse transmission and muscle contraction.
- Secondary Active Transport: Uses the energy from primary active transport to move another molecule. Symport involves molecules moving in the same direction, while antiport involves molecules moving in opposite directions.
- Bulk Transport: This involves the movement of large molecules or particles via vesicles and requires energy.
- Endocytosis: The cell membrane engulfs material to form a vesicle that brings substances into the cell (e.g., phagocytosis, pinocytosis, receptor-mediated endocytosis).
- Exocytosis: Vesicles fuse with the cell membrane to release their contents outside the cell (e.g., secretion of neurotransmitters from neurons).
Homeostasis
- Homeostasis is the maintenance of a stable internal environment despite changes in external conditions. Most control systems maintain homeostasis through negative feedback.
- Components of a Negative Feedback Loop:
- Receptor (Sensor): Detects changes in the environment and sends information to the control center.
- Control Center: Interprets the information from receptors and determines the appropriate response.
- Effector: Executes the necessary adjustments to restore homeostasis.
- Importance of Homeostasis:
- Maintains optimal conditions for cell function, including enzyme activity and cellular processes.
- Supports survival by keeping the body's environment constant within a range that supports life.
- Prevents diseases and disorders caused by imbalances in the body's internal environment.
- Examples of Negative Feedback:
- Temperature Regulation: Thermoreceptors detect an increase in body temperature, the hypothalamus initiates sweating and vasodilation to release heat, decreasing body temperature.
- Blood Glucose Regulation: Beta cells in the pancreas detect an increase in blood glucose levels, the pancreas releases insulin, cells take up glucose, and the liver stores glucose as glycogen, decreasing blood glucose levels.
- Examples of Positive Feedback:
- Blood Clotting: Platelets detect injury to a blood vessel, release chemicals, and attract more platelets to the site, forming a blood clot to seal the injury.
- Childbirth: Pressure of the baby's head against the cervix stimulates stretch receptors, the hypothalamus releases oxytocin, uterine muscles contract, and increased contractions continue until delivery.
- Homeostasis in Different Organs:
- Blood Glucose Regulation: Insulin and glucagon secretion by the pancreas.
- Osmoregulation: Regulation of water and electrolyte balance by the kidneys, hypothalamus, and pituitary gland.
- pH Balance: Buffer systems, respiratory rate adjustment, and renal function by the lungs, kidneys, and blood.
- Calcium Homeostasis: Regulation of calcium levels via parathyroid hormone (PTH) and calcitonin by the bones, kidneys, intestines, and parathyroid glands.
Conclusion:
Understanding general physiology involves grasping the composition of the human body, the mechanisms of transport across cell membranes, and the principles of homeostasis. These concepts are essential for understanding how the body functions in health and how disruptions can lead to disease, providing a foundation for further studies in specialized areas of physiology and medicine.
