Anatomy & Physiology: Foundations, Chemistry, and Cellular Structure

Homeostasis and Anatomical Organization

Homeostasis: Negative vs. Positive Feedback

Homeostasis is the process by which the body maintains a stable internal environment. Feedback loops are mechanisms that help regulate physiological processes.

• Negative Feedback: A process that reverses a change to keep a variable within a normal 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 contractions).

• Three Components of Feedback Loops:

  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 Body Organization

• Anatomical Position: The standard reference position for the body: standing upright, facing forward, arms at sides, palms facing forward.

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

• Body Sections/Planes:

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

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

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

• Body Regions and Quadrants:

  • Abdominal Quadrants: Right Upper, Left Upper, Right Lower, Left Lower.

  • Abdominal Regions: Epigastric, umbilical, hypogastric, right/left hypochondriac, right/left lumbar, right/left iliac.

• Body Cavities: Spaces within the body that contain organs (e.g., cranial, thoracic, abdominal, pelvic).

• Membranes:

  • Visceral: Covers organs.

  • Parietal: Lines cavity walls.

Chemistry for Anatomy & Physiology

pH, Acids, and Bases

Chemistry is fundamental to understanding physiological processes. pH measures the acidity or alkalinity of a solution.

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

• Acid: Substance that releases hydrogen ions (H+) in solution.

• Base: Substance that accepts hydrogen ions or releases hydroxide ions (OH-).

• Buffer: A solution that resists changes in pH when acids or bases are added. Buffers are important for maintaining homeostasis in body fluids.

Solutions, Colloids, and Mixtures

• Solution: Homogeneous mixture of two or more substances (e.g., salt water).

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

• Mixture: Combination of substances not chemically bonded (e.g., sand and water).

• Difference: Solutions are clear and particles are molecular in size; colloids are cloudy and particles are larger; mixtures can be separated physically.

Cell Structure and Function

Gradients

Gradients are differences in concentration, pressure, or electrical charge between two regions. They drive many physiological processes.

• Types of Gradients: Chemical, electrical, pressure, and temperature gradients.

• Example: Sodium-potassium gradient across the cell membrane is essential for nerve impulse transmission.

Cell Theory and Principles

• Cell Theory: All living things are composed of cells; the cell is the basic unit of life; all cells arise from pre-existing cells.

• Major Principles: Structure and function are closely related; cells maintain homeostasis.

Cell Junctions

• Tight Junctions: Seal adjacent cells to prevent leakage.

• Desmosomes: Anchor cells together.

• Gap Junctions: Allow communication between cells.

Plasma Membrane Structure and Function

• Phospholipid Bilayer: Double layer of phospholipids with hydrophilic heads and hydrophobic tails.

• Membrane Proteins: Integral and peripheral proteins serve as channels, receptors, enzymes, and anchors.

• Functions: Selective permeability, communication, structural support.

Transport Across Membranes

• Passive Transport: Movement of substances without energy input (e.g., diffusion, osmosis, facilitated diffusion).

• Active Transport: Movement of substances against a gradient, requiring energy (e.g., sodium-potassium pump).

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

• Filtration: Movement of water and solutes due to hydrostatic pressure.

Membrane Potential and Signaling

• Ligand-Gated Channels: Open in response to binding of a chemical messenger.

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

Cellular Processes

• Endocytosis: Uptake of materials into the cell by vesicle formation.

• Exocytosis: Release of materials from the cell.

• Phagocytosis: "Cell eating"; engulfing large particles.

• Pinocytosis: "Cell drinking"; uptake of fluid.

Motility and Organelles

• Motility: Movement via cilia, flagella, or cytoskeleton.

• Organelles: Specialized structures within cells (e.g., mitochondria, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes).

• Functions:

  • Smooth ER: Lipid synthesis, detoxification.

  • Rough ER: Protein synthesis (with ribosomes).

  • Golgi Apparatus: Modifies, sorts, and packages proteins.

  • Mitochondria: ATP production via cellular respiration.

  • Ribosomes: Protein synthesis.

  • Cytoskeleton: Structural support, cell movement.

Protein Synthesis and Genetic Code

• Transcription: Process by which mRNA is synthesized from DNA in the nucleus.

• Translation: Process by which ribosomes synthesize proteins using mRNA as a template.

• Codon: Three-nucleotide sequence on mRNA that codes for an amino acid.

• Anticodon: Three-nucleotide sequence on tRNA complementary to mRNA codon.

• mRNA: Messenger RNA; carries genetic information from DNA to ribosome.

• tRNA: Transfer RNA; brings amino acids to ribosome during translation.

• rRNA: Ribosomal RNA; structural and functional component of ribosomes.

Reading a Codon Table

A codon table is used to determine which amino acid corresponds to each mRNA codon during translation.

Codon (mRNA)	Amino Acid
AUG	Methionine (Start)
UUU	Phenylalanine
UAA, UAG, UGA	Stop codons

Example: The mRNA sequence AUG-GCU-UGA codes for Methionine, Alanine, and a stop signal.

Additional info: Some details, such as the full list of organelle functions and codon table entries, have been expanded for academic completeness.