Homeostasis in Cells - Biology Chapter

Homeostasis in Cells

• Homeostasis is the maintenance of stable internal conditions in living organisms, allowing optimal function despite external changes.
• All cells require homeostasis for survival.
• Homeostasis is achieved through negative feedback loops.

Negative Feedback Loops

• A negative feedback loop is a regulatory mechanism where the product of a process inhibits its own production.
• In humans, body temperature is maintained around 98.6°F.
• When body temperature rises, mechanisms like sweating and vasodilation (widening of blood vessels) cool the body.
• When body temperature falls, mechanisms like shivering and vasoconstriction (narrowing of blood vessels) warm the body.
• Similar negative feedback loops maintain water balance, glucose levels, blood pressure, and other crucial factors.

Glucose Homeostasis

• Blood glucose levels increase after eating.
• The pancreas releases insulin, allowing cells to absorb glucose from the blood, lowering blood sugar.
• If blood sugar falls too low, the pancreas releases glucagon, stimulating the liver to release glucose into the bloodstream.
• This cycle ensures stable blood glucose levels.
• Imbalances in glucose regulation can lead to diseases like diabetes.

Cell Membrane and Homeostasis

• The cell membrane regulates the passage of materials into and out of the cell, crucial for homeostasis.
• The membrane is a phospholipid bilayer, with hydrophilic heads facing outward and hydrophobic tails inside.
• Cholesterol and short tails maintain membrane fluidity, enabling material transport.
• Membrane proteins facilitate the movement of large or charged molecules.

Osmosis Across the Cell Membrane

• Osmosis is the movement of water from areas of high water concentration to low water concentration (or low solute to high solute).
• Water, although small, is polar.
• Aquaporins, protein channels in the membrane, allow regulated water movement.
• This regulation ensures appropriate water balance within the cell.

Ion Regulation

• The cell membrane controls ion levels to maintain optimal cellular function.
• High potassium concentrations are maintained inside the cell; high sodium outside the cell.
• Active transport pumps maintain these gradients, using energy.
• Ion channels can be regulated by ligands or other stimuli for precise control of ion flow.
  • For example, neurotransmitters in nerve cells regulate ion channel opening.