Biology Chapter on Osmosis and Osmotic Pressure

Osmosis

• Movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration.
• Water moves from high concentration of water to lower concentration of water (and from lower concentration of solutes to higher concentration of solutes).
• Important at cellular level, causing cells to shrink or swell.
• Important at tissue level, osmosis occurs through epithelial cells in the GIT and renal system. It also occurs through capillary walls.

Osmotic Pressure

• The osmotic pressure inside human cells is equal to the concentration of a 0.9% solution of sodium chloride (99.1 g water + 0.9 g NaCl).
• 0.9% NaCl solution is called “normal or physiologic saline”.
• Hypotonic: OP in extracellular fluid is less than OP intracellular fluid, causing water to enter the cell.
• Hypertonic: OP in extracellular fluid is greater than OP intracellular fluid, causing the cell to lose water.
• Isotonic: OP in extracellular fluid is equal to OP intracellular fluid, resulting in hydrostatic equilibrium.

Active Transport

• Carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration.
• Examples: glucose, amino acids, sodium ions, potassium, calcium, and Hydrogen ions.
• It is carrier-mediated and requires energy to move “uphill” against an electrical or pressure gradient.

Primary Active Transport

• Energy comes directly from the breakdown of ATP or some other high-energy phosphate compound.
• Examples:
  • Na+/K+ pump found in all cells.
  • Ca++ active transport in cell membrane and inside the cell.
  • Active transport of H+ found in gastric glands of the stomach and distal and collecting tubules of the kidney.
  • H+/K+ pump (proton pump at the stomach).

Secondary Active Transport

• Energy is derived secondarily from energy stored in the form of ionic concentration differences between the two sides of the membrane, created by primary active transport.
• Examples:
  • Na+/glucose co-transport.
  • Na+/amino acid co-transport.

Body Fluids

• Extracellular fluid (ECF): fluid environment in which the cells live (fluid outside the cells), containing ions, O2, nutrients, and waste products.
  • Includes:
    • Plasma (inside blood cells)
    • Interstitial fluid (around the cells)
• Intracellular fluid (ICF): fluid contained within all body cells, high in K+ and low in Na+. It contains protein with a negative charge.
• ICF:ECF ratio: 2:1, meaning that ICF accounts for 2/3 and ECF for 1/3 of total body water.

Homeostasis

• Maintenance of a relatively constant/stable internal environment (extracellular fluids).
• Maintaining a dynamic steady state in the internal environment.
• The internal environment remains relatively constant despite changes in the external environment.
• Stable does not mean rigid, values can vary within a narrow limit (normal physiological range).
• Essential for survival and function of all cells.

Factors Homeostatically Regulated

• Concentration of nutrients (e.g., glucose, O2, CO2, and waste products).
• Concentration of water, salt, and other electrolytes.
• pH.
• Blood volume and pressure.
• Body temperature.

Homeostatic Control Mechanisms

• Three components:
  • Receptor: provides information about the stimuli.
  • Control Center: tells what a particular value should be (called the set point).
  • Effector: elicits responses that change conditions in the internal environment.

Negative Feedback Loops

• Sensor: monitors internal conditions, detects changes.
• Integrating Center (Controller): receives and integrates information.
• Effector: responds to changes, activity of effectors results in return of the condition to normal levels.

Movements Into and Out of the Cell

Explore the fundamental concepts of osmosis and osmotic pressure in this quiz. Understand how water movement influences cellular behavior and the impact of different saline solutions on human cells. Test your knowledge of hypotonic, hypertonic, and isotonic environments.