Body Cavities and Directional Terms

Major Body Cavities

The human body contains several major cavities that house and protect internal organs. Understanding these cavities is essential for describing anatomical locations and relationships.

• Thoracic cavity: Contains the mediastinum, pleural cavities, pericardial cavity, and is separated from the abdominal cavity by the thoracic diaphragm.

• Abdominopelvic cavity: Includes the abdominal and pelvic cavities.

• Posterior aspect: Includes the cranial cavity (brain) and vertebral canal (spinal cord).

Abdominopelvic Cavity Regions and Quadrants

• Regions: Right hypochondriac, epigastric, left hypochondriac, right lumbar, umbilical, left lumbar, right iliac, hypogastric, left iliac.

• Quadrants: Right upper, left upper, right lower, left lower.

Directional Terms

Directional terms are used to describe the locations of structures relative to other structures or locations in the body.

• Anterior (ventral): Towards the front

• Posterior (dorsal): Towards the back

• Superior (cranial): Towards the head

• Inferior (caudal): Towards the feet

• Medial: Toward the midline

• Lateral: Away from the midline

• Proximal: Closer to the point of attachment to trunk

• Distal: Farther from the point of attachment to trunk

• Superficial: Closer to the surface

• Deep: Farther from the surface

Example: The heart is medial to the lungs and superior to the diaphragm.

Levels of Organization in the Human Body

Hierarchy of Biological Organization

The human body is organized into a hierarchy of structural levels, each building upon the previous one.

• Atom

• Cell

• Tissue

• Organ

• Organ system

• Organism

Examples: Muscle cell, connective tissue, heart, digestive system, human.

Basic Chemistry for Anatomy & Physiology

Atoms, Elements, and Molecules

• Atom: The smallest unit of matter that retains the properties of an element.

• Element: A pure substance made of only one type of atom.

• Molecule: Two or more atoms bonded together.

• Compound: A substance made of two or more different types of atoms chemically combined.

Electrons are negatively charged and move around the nucleus in energy levels. Protons are positively charged, and neutrons are neutral; both are found in the atomic nucleus.

Atomic Structure and Chemical Bonds

• The number of electrons in an atom's electron shells relates to chemical stability and bonding.

• Atoms with full valence shells are stable; those with incomplete shells tend to react to achieve stability.

• Ions: Atoms that have gained or lost electrons.

• Electrolyte: A substance that dissolves in water to produce ions that conduct electricity.

• Isotope: Atoms of the same element with different numbers of neutrons.

• Radioisotope: An unstable isotope that emits radiation as it decays.

Covalent bonds: Atoms share electrons. Ionic bonds: Electrons are transferred between atoms. Hydrogen bonds: Weak attractions between polar molecules.

Water and Its Importance

• Universal solvent: Dissolves many substances.

• Moves nutrients, gases, and waste products in and out of cells.

• Helps regulate body temperature and participates in many biochemical reactions.

• Provides lubrication and shock absorption.

Solutions and pH

• Solution: Homogeneous mixture of two or more substances.

• Solvent: Substance that dissolves the solute.

• Solute: Substance dissolved in the solvent.

• pH: A measure of solution acidity or alkalinity.

• Acidic: pH below 7

• Neutral: pH 7

• Basic (alkaline): pH above 7

Buffer: A solution that resists changes in pH.

Macromolecules and Biochemistry

Major Biological Macromolecules

• Carbohydrates: Quick energy source, polysaccharides are long chains of glucose.

• Proteins: Polymers of amino acids, functions depend on sequence and folding.

• Lipids: Long hydrocarbon chains, hydrophobic, energy-dense, insulation, cell membranes.

• Nucleic acids: Polymers of nucleotides, store and transfer genetic information.

Protein Structure

• Primary: Sequence of amino acids in a polypeptide chain.

• Secondary: Local folding (alpha helix, beta sheet) due to hydrogen bonding.

• Tertiary: Overall 3D shape of a single polypeptide, interactions among R-groups.

• Quaternary: Arrangement of multiple polypeptide chains.

Enzymes are proteins that speed up reactions by lowering activation energy.

Cell Structure and Function

Cell Membrane and Transport

• Phospholipid bilayer: Main component of cell membranes, hydrophilic heads and hydrophobic tails.

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

• Carbohydrates: Attached to proteins and lipids, involved in cell recognition.

Transport Mechanisms

• Simple diffusion: Passive movement of molecules from high to low concentration.

• Facilitated diffusion: Passive, but requires transport proteins for polar molecules.

• Active transport: Requires ATP to move substances against their concentration gradient.

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

Osmolarity and Tonicity

• Osmolarity: Reflects the concentration of solute particles in a solution.

• Tonicity: The ability of a solution to change the volume and pressure of a cell.

• Hypertonic: Solution has higher solute concentration than the cell; cell shrinks.

• Hypotonic: Solution has lower solute concentration than the cell; cell swells.

• Isotonic: Equal solute concentration; no net water movement.

Cell Cycle and Division

• Interphase: Cell prepares for division (G1, S, G2 phases).

• G1: Cell grows and produces new organelles.

• S phase: DNA replication occurs.

• G2: Final preparations for mitosis.

• Mitosis: Division of the nucleus (prophase, metaphase, anaphase, telophase).

• Cytokinesis: Division of the cytoplasm.

Cellular Organelles

Membrane-Bound Organelles

• Rough ER: Produces, transports, and stores proteins.

• Smooth ER: Synthesizes, transports, and stores lipids.

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

• Lysosomes: Digestive enzymes, breakdown of waste.

• Peroxisomes: More enzymes, breakdown of fatty acids.

• Mitochondria: Powerhouse of the cell, synthesizes ATP.

Non-Membrane Bound Organelles

• Ribosomes: Synthesize proteins.

• Centrosome: Organizes microtubules, cell division.

• Cytoskeleton: Framework, cell support, movement.

Genetic Information and Protein Synthesis

RNA Synthesis (Transcription and Translation)

• Initiation: RNA polymerase binds to DNA and starts reading the gene.

• Elongation: RNA strand is synthesized.

• Termination: RNA synthesis ends.

mRNA: Carries genetic code from DNA to ribosome. tRNA: Brings amino acids to the ribosome. rRNA: Forms part of the ribosome structure.

Cellular Respiration and Metabolism

• Cellular respiration: The process by which cells break down glucose in the presence of oxygen to produce ATP.

• Glycolysis: One glucose molecule is split into 2 pyruvate molecules.

• Citric acid cycle (Krebs cycle): Further breakdown of pyruvate, producing ATP, NADH, and FADH2.

• Electron transport chain (ETC): Uses electrons from NADH and FADH2 to produce ATP.

Homeostasis and Feedback Mechanisms

Homeostasis

• Homeostasis: The maintenance of a stable internal environment.

• Setpoint: The normal target value for a physiological variable.

• Variable: The condition being regulated.

Feedback Loops

• Negative feedback: The most common mechanism; the response counteracts the stimulus (e.g., body temperature regulation).

• Positive feedback: The response amplifies the stimulus (e.g., oxytocin release during childbirth).

Regulated variable: Body condition kept within a normal range by homeostasis. Controlled variable: Mechanism or factor the body changes to influence the regulated variable. Response pathway: Stimulus → sensor → control center → effector → response.

Example: When blood glucose rises, the pancreas releases insulin to lower it (negative feedback).

Table: Types of Chemical Bonds (Comparison)

Table: Cell Transport Mechanisms

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curricula.