Essential Concepts in Anatomy & Physiology: Chemistry, Biomolecules, and Cell Structure

Survival Needs and Requirements for Life

Five Survival Needs

Organisms require certain conditions to survive and maintain homeostasis. These survival needs are fundamental for cellular and systemic function.

• Nutrients: Chemical substances used for energy and cell building.

• Oxygen: Required for cellular respiration and energy production.

• Water: The most abundant chemical in the body, vital for chemical reactions and transport.

• Stable Body Temperature: Necessary for proper metabolic reactions.

• Appropriate Atmospheric Pressure: Essential for breathing and gas exchange.

Five Things Necessary for Life

In addition to survival needs, life requires certain processes and conditions:

• Metabolism: All chemical reactions in the body.

• Responsiveness: Ability to sense and respond to stimuli.

• Movement: Includes locomotion and movement of substances.

• Growth: Increase in size and number of cells.

• Reproduction: Production of offspring.

Homeostasis and Feedback Loops

Homeostasis

Homeostasis is the maintenance of a stable internal environment despite external changes. It is achieved through feedback mechanisms.

• Negative Feedback: Reduces the effect of the stimulus (e.g., regulation of body temperature).

• Positive Feedback: Enhances the effect of the stimulus (e.g., blood clotting, childbirth).

Example: When body temperature rises, negative feedback mechanisms (such as sweating) help lower it back to normal.

Basic Chemistry for Anatomy & Physiology

Elements and Subatomic Particles

An element is a pure substance consisting of only one type of atom. Atoms are composed of:

• Proton: Charge: +1, Weight: 1 amu, Location: Nucleus

• Neutron: Charge: 0, Weight: 1 amu, Location: Nucleus

• Electron: Charge: -1, Weight: ~0 amu, Location: Electron cloud/orbitals

Types of Mixtures

Mixtures are combinations of two or more substances physically blended together.

• Solutions: Homogeneous mixtures (e.g., salt water).

• Colloids: Heterogeneous mixtures with larger particles (e.g., cytoplasm).

• Suspensions: Particles settle out over time (e.g., blood).

Chemical Bonds

Chemical bonds hold atoms together in molecules and compounds.

• Ionic Bonds: Transfer of electrons between atoms, forming charged ions.

• Covalent Bonds: Sharing of electrons between atoms.

• Hydrogen Bonds: Weak attractions between polar molecules.

Chemical Reactions

Chemical reactions involve the making or breaking of bonds between atoms.

• Synthesis Reaction: $A + B \rightarrow AB$ (e.g., formation of proteins from amino acids)

• Decomposition Reaction: $AB \rightarrow A + B$ (e.g., breakdown of glycogen)

• Exchange Reaction: $AB + CD \rightarrow AC + BD$

Endergonic vs. Exergonic Reactions

Reactions can be classified by their energy changes:

• Endergonic: Absorb energy; products have more energy than reactants.

• Exergonic: Release energy; products have less energy than reactants.

Example: ATP synthesis is endergonic; ATP hydrolysis is exergonic.

Factors Influencing Chemical Reaction Rates

• Temperature: Higher temperature increases reaction rate.

• Concentration: Higher concentration increases reaction rate.

• Catalysts: Enzymes speed up reactions.

• Particle Size: Smaller particles react faster.

Properties of Water Vital to Life

• High Heat Capacity: Absorbs and releases heat slowly.

• Polarity/Solvency: Universal solvent for many substances.

• Chemical Reactivity: Participates in hydrolysis and dehydration reactions.

• Cushioning: Protects organs (e.g., cerebrospinal fluid).

Acids, Bases, and pH

Acids and bases are substances that alter the concentration of hydrogen ions in a solution.

• Acids: Release $H^+$ ions; pH < 7.

• Bases: Release $OH^-$ ions; pH > 7.

• pH Scale: Measures hydrogen ion concentration; $pH = -\log[H^+]$

Example: Stomach acid (pH ~2) vs. blood (pH ~7.4).

Buffers

Buffers resist changes in pH by absorbing or releasing $H^+$ ions.

• Example: Bicarbonate buffer system in blood: $HCO_3^- + H^+ \leftrightarrow H_2CO_3$

Biomolecules: Structure and Function

Carbohydrates

• Monomers: Monosaccharides (e.g., glucose).

• Polymerization: Joined by dehydration synthesis to form disaccharides and polysaccharides.

Example: Glucose + Glucose $\rightarrow$ Maltose + Water

Lipids

• Fatty Acids: Long hydrocarbon chains with a carboxyl group.

• Triglycerides: Glycerol + 3 fatty acids.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group; major component of cell membranes.

Proteins

• Monomers: Amino acids.

• Polymerization: Joined by peptide bonds (dehydration synthesis).

• Protein Folding: Process by which a polypeptide assumes its functional shape (primary, secondary, tertiary, quaternary structure).

Nucleic Acids

• Monomers: Nucleotides (composed of a sugar, phosphate, and nitrogenous base).

• Polymerization: Joined by phosphodiester bonds to form DNA and RNA.

Cell Structure and Function

Cellular Components Outside the Cell

• Extracellular Matrix: Network of proteins and carbohydrates outside cells.

• Interstitial Fluid: Fluid between cells.

• Cell Junctions: Structures connecting cells.

Plasma Membrane

The plasma membrane is a selectively permeable barrier that surrounds the cell.

• Phospholipid Bilayer: Provides fluidity and barrier function.

• Proteins: Serve as channels, receptors, and enzymes.

• Carbohydrates: Involved in cell recognition.

• Cholesterol: Stabilizes membrane fluidity.

Specialized Cell Junctions

• Tight Junctions: Prevent leakage between cells.

• Desmosomes: Anchor cells together.

• Gap Junctions: Allow communication between cells.

Diffusion and Osmosis

• Diffusion: Movement of molecules from high to low concentration.

• Simple Diffusion: Direct movement through membrane.

• Facilitated Diffusion: Movement via protein channels.

• Osmosis: Diffusion of water across a selectively permeable membrane.

Example: RBC in hypertonic solution shrinks; in hypotonic solution swells; in isotonic solution remains unchanged.

Sodium-Potassium Pump

The sodium-potassium pump is an active transport mechanism that moves $Na^+$ out and $K^+$ into the cell against their concentration gradients, using ATP.

• Function: Maintains electrochemical gradients essential for nerve impulse transmission.

• Mechanism: 3 $Na^+$ out, 2 $K^+$ in per ATP hydrolyzed.

Equation: $ATP + 3Na^+_{in} + 2K^+_{out} \rightarrow ADP + P_i + 3Na^+_{out} + 2K^+_{in}$

Type of Cell Junction	Structure	Function
Tight Junction	Interlocking proteins	Seals spaces between cells
Desmosome	Protein plaques and filaments	Anchors cells together
Gap Junction	Connexon channels	Allows passage of ions and small molecules

*Additional info: Some explanations and examples were expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.*