Anatomy & Physiology: Homeostasis, Biochemistry, and Cell Membrane Transport Study Notes

Homeostasis and Feedback Mechanisms

Overview of Homeostasis

Homeostasis refers to the maintenance of a stable internal environment within the body, essential for the proper functioning of cells and organs. The body uses feedback mechanisms to regulate physiological variables such as temperature, pH, and blood glucose levels.

• Stimulus: A change in the environment that disrupts homeostasis.

• Receptor: Detects the change and sends information to the control center.

• Control Center: Processes the information and determines the response.

• Effector: Carries out the response to restore balance.

Negative vs. Positive Feedback Mechanisms

• Negative Feedback: The most common feedback mechanism in the body. It reduces or shuts off the original stimulus, helping to maintain homeostasis. Examples: Regulation of body temperature, blood sugar levels, and blood pressure.

• Positive Feedback: Enhances or exaggerates the original stimulus, often leading to a cascade or amplification of the effect. Examples: Blood clotting, labor contractions.

If homeostasis fails: The body may experience disease or dysfunction, such as shock due to blood loss or overshooting immune responses.

Biochemistry: Water, Solutions, and Chemical Reactions

Types of Mixtures

• Solution: Homogeneous mixture with evenly distributed solute particles (e.g., salt water).

• Colloid: Heterogeneous mixture with larger particles that do not settle (e.g., milk).

• Suspension: Heterogeneous mixture with large solute particles that settle out (e.g., blood).

Factors Affecting Chemical Reactions

• Temperature: Higher temperature increases reaction rate.

• Concentration: Higher concentration of reactants increases reaction rate.

• Particle Size: Smaller particles react faster.

• Catalysts: Substances that increase the rate of reaction without being consumed (e.g., enzymes).

ATP and Cellular Energy

Adenosine triphosphate (ATP) is the primary energy carrier in cells. It stores energy in its high-energy phosphate bonds, which can be released for cellular processes such as muscle contraction, nerve impulse transmission, and biosynthesis.

• ATP is produced mainly by cellular respiration in the mitochondria.

• ATP is used in all cells for energy-requiring processes.

Electrolytes and pH

• Electrolytes: Substances that conduct electricity in solution (e.g., Na+, K+, Ca2+, Cl-).

• pH: Measures the acidity or alkalinity of a solution, based on hydrogen ion concentration ($pH = -\log[H^+]$). Lower pH = more acidic; higher pH = more alkaline.

Enzymes

Definition and Function

Enzymes are biological catalysts, usually proteins, that speed up biochemical reactions by lowering the activation energy. They are specific to substrates and are not consumed in the reaction.

• Enzymes position substrates to facilitate reactions.

• They do not change during the reaction.

Enzyme Action Diagram

• E: Enzyme

• S: Substrate

• P: Product

• Circle: Protein (enzyme)

• Underline: Carbohydrates

Carbohydrates: Monosaccharides and Disaccharides

• Monosaccharides: Simple sugars (e.g., glucose, galactose)

• Disaccharides: Two monosaccharides joined together (e.g., lactose)

• Enzyme Example: Lactase breaks down lactose (a disaccharide)

Other Biological Molecules

• Lipids: Phospholipids (cell membranes), steroids (hormones), triglycerides (energy storage)

• Nucleic Acids: DNA and RNA (genetic information)

Cell Membrane and Transport Mechanisms

Types of Membrane Transport

• Passive Transport: No energy required; moves substances down their concentration gradient.

  • Simple diffusion

  • Facilitated diffusion (via carrier or channel proteins)

• Active Transport: Requires energy (ATP); moves substances against their concentration gradient.

  • Primary and secondary active transport

  • Vesicular transport (endocytosis, exocytosis)

Osmosis and Tonicity

Osmosis is the movement of water across a semipermeable membrane. Tonicity describes the effect of a solution on cell volume:

Solution Type	Effect on Cell
Hypotonic	Cell swells (water enters cell)
Hypertonic	Cell shrinks (water leaves cell; crenation)
Isotonic	No net change in cell volume

Egg Osmosis Experiment

Egg 1 (Syrup)	Egg 2 (Water)	Egg 3 (Salt Water)
Egg shrivels (hypertonic)	Egg appears normal (isotonic)	Egg swells (hypotonic)

Membrane Potential and Na+/K+ Pump

The Na+/K+ pump is a protein that actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell, using ATP. This maintains the resting membrane potential (about -70 mV), which is essential for nerve and muscle function.

• Na+ leaks into the cell; K+ leaks out.

• The pump maintains higher Na+ outside and higher K+ inside the cell.

• This gradient is vital for electrical signaling in nerves and muscles.

Additional info: The notes also reference the importance of water and electrolytes in maintaining homeostasis, and the role of buffers in regulating pH.