Anatomy & Physiology: Foundational Concepts, Chemistry, and Cell Structure

Homeostasis and Anatomical Foundations

Homeostasis: Negative vs. Positive Feedback

Homeostasis refers to the body's ability to maintain a stable internal environment despite changes in external conditions. Feedback mechanisms are essential for this regulation.

• Negative Feedback: A process that reverses a change to keep a variable within a set range. Most homeostatic mechanisms use negative feedback (e.g., body temperature regulation).

• Positive Feedback: A process that amplifies a change, moving the system further from its starting state (e.g., blood clotting, childbirth).

• Three Components of Feedback Loop:

  1. Receptor: Detects changes in the environment.

  2. Control Center: Processes information and determines response.

  3. Effector: Carries out the response to restore balance.

Anatomical Position and Planes

Understanding anatomical position and planes is crucial for describing locations and directions in the body.

• Anatomical Position: Standing upright, facing forward, arms at sides, palms facing forward.

• Body Planes:

  • Sagittal Plane: Divides body into left and right parts.

  • Frontal (Coronal) Plane: Divides body into anterior and posterior parts.

  • Transverse Plane: Divides body into superior and inferior parts.

• Directional Terms: Used to describe locations (e.g., superior, inferior, anterior, posterior, medial, lateral).

Body Regions, Cavities, and Membranes

The body is organized into regions and cavities, each with specific membranes and contents.

• Body Cavities:

  • Dorsal Cavity: Contains brain and spinal cord.

  • Ventral Cavity: Contains thoracic and abdominopelvic cavities.

• Membranes:

  • Visceral Membrane: Covers organs.

  • Parietal Membrane: Lines cavity walls.

• Abdominal Quadrants & Regions: Used to locate organs and describe pain or injury.

Chapter 2: Chemistry in Anatomy & Physiology

pH, Acids, and Bases

pH measures the concentration of hydrogen ions in a solution, indicating its acidity or alkalinity.

• Acid: Substance that donates hydrogen ions ($H^+$).

• Base: Substance that accepts hydrogen ions.

• pH Scale: Ranges from 0 (most acidic) to 14 (most basic); 7 is neutral.

• Buffer: Solution that resists changes in pH when acids or bases are added.

$\text{pH} = -\log_{10}[H^+]$

Solutions, Colloids, and Mixtures

Understanding the differences between types of mixtures is important for physiology.

• Solution: Homogeneous mixture of solute and solvent.

• Colloid: Mixture with larger particles that do not settle out (e.g., cytoplasm).

• Mixture: Combination of substances not chemically bonded.

Chemical Bonds and Electrons

Chemical bonds form when atoms share or transfer electrons. The type of bond affects molecular properties.

• Covalent Bond: Atoms share electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

• Ionic Bond: Atoms transfer electrons, creating charged ions.

• Hydrogen Bond: Weak attraction between a hydrogen atom and an electronegative atom (e.g., oxygen, nitrogen).

• Valence Electrons: Electrons in the outermost shell, involved in bonding.

Redox Reactions and Ionization

Redox (reduction-oxidation) reactions involve the transfer of electrons between molecules.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Ionization: Formation of ions (charged particles) from neutral atoms.

Electrolytes and Elements

Electrolytes are substances that dissociate into ions in solution, conducting electricity.

• Mineral: Inorganic element essential for body function.

• Electrolyte: Ionized mineral in body fluids (e.g., sodium, potassium).

• Element: Pure substance made of one type of atom.

Organic Compounds

Organic compounds are molecules containing carbon and are essential for life.

• Carbohydrates: Provide energy; include monosaccharides, disaccharides, polysaccharides.

• Lipids: Store energy, form cell membranes.

• Proteins: Perform structural, enzymatic, and regulatory functions.

• Nucleic Acids: Store genetic information (DNA, RNA).

Nucleotides

Nucleotides are the building blocks of nucleic acids.

• Components: Phosphate group, pentose sugar, nitrogenous base.

Cell Structure and Function

Types of Gradients

Gradients drive movement of substances across membranes.

• Concentration Gradient: Difference in concentration across a space.

• Electrical Gradient: Difference in charge across a membrane.

• Electrochemical Gradient: Combined effect of concentration and electrical gradients.

Cell Theory and Junctions

Cell theory states that all living things are composed of cells. Cell junctions connect cells and facilitate communication.

• Tight Junctions: Prevent leakage between cells.

• Desmosomes: Anchor cells together.

• Gap Junctions: Allow passage of ions and small molecules.

Plasma Membrane Structure

The plasma membrane is a phospholipid bilayer with embedded proteins, controlling entry and exit of substances.

• Phospholipid Bilayer: Hydrophilic heads face outward, hydrophobic tails face inward.

• Transmembrane Proteins: Span the membrane, serving as channels, carriers, or receptors.

• Ligand-Gated Channels: Open in response to specific molecules.

• Voltage-Gated Channels: Open in response to changes in membrane potential.

Membrane Transport

Substances move across membranes by passive or active transport.

• Passive Transport: No energy required; includes diffusion, osmosis, filtration.

• Active Transport: Requires energy (ATP); includes pumps and vesicular transport.

• Endocytosis: Cell takes in substances by engulfing them.

• Exocytosis: Cell expels substances.

• Phagocytosis: Cell engulfs large particles.

Osmolarity and Fluid Movement

Osmolarity measures the concentration of solutes in a solution and affects fluid movement.

• Osmosis: Movement of water across a semipermeable membrane.

• Filtration: Movement of fluid due to pressure.

• Effect of Osmolarity: Changes in osmolarity can cause cells to shrink or swell.

Cell Organelles and Functions

Organelles perform specialized functions within the cell.

Organelle	Function
Smooth ER	Lipid synthesis, detoxification
Rough ER	Protein synthesis (ribosomes attached)
Nucleus	Contains genetic material (DNA)
Golgi Apparatus	Modifies, sorts, and packages proteins
Vesicles	Transport materials within the cell
Mitochondria	ATP production (cellular respiration)
Peroxisome	Breakdown of fatty acids, detoxification
Lysosome	Digestion of cellular waste
Cytoskeleton	Structural support, cell movement

Transcription and Translation

Genetic information is expressed through transcription and translation.

• Transcription: DNA is copied into messenger RNA (mRNA) in the nucleus.

• Translation: mRNA is used to assemble proteins at ribosomes.

• Codon: Sequence of three nucleotides on mRNA that codes for an amino acid.

• Anti-codon: Sequence of three nucleotides on tRNA that pairs with the mRNA codon.

Additional info: Some content was inferred and expanded for clarity and completeness, such as definitions, examples, and the table of organelles.