Human Anatomy: Systems, Chemistry, and Cell Biology

Posted on Jan 7, 2026 in Biology

Organ Systems and Their Functions

Homeostasis and Its Importance to Survival

• Homeostasis is the body’s ability to maintain a stable internal environment.

• Importance: It keeps body functions in balance despite external changes, such as regulating body temperature or pH levels.

Negative and Positive Feedback Mechanisms

• Negative Feedback: Counteracts a change to return the system to a set point. Example: Regulation of blood sugar by insulin.

• Positive Feedback: Amplifies a change. Example: Contractions during childbirth via oxytocin release.

Both aim to promote homeostasis, but negative feedback restores balance, while positive feedback reinforces the change.

Chapter 2: Basic Chemistry

Elements, Atoms, Molecules, and Compounds

• Element: A pure substance consisting of one type of atom (e.g., oxygen, carbon).

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

• Molecule: Two or more atoms bonded together (e.g., O₂, H₂O).

• Compound: A molecule containing two or more different elements (e.g., NaCl, CO₂).

Note: All compounds are molecules, but not all molecules are compounds.

Chemical Bonds: Ionic vs. Covalent

Chemical Bonds form when atoms gain, lose, or share electrons to achieve stability.

Ionic Bonds

• Formed when electrons are transferred from one atom to another.
• Creates charged particles called Cations (positive) and Anions (negative).
• Example: Na⁺ + Cl⁻ → NaCl

Covalent Bonds

• Formed when atoms share electrons.
• Nonpolar Covalent: Electrons are shared equally (e.g., O₂, CH₄).
• Polar Covalent: Electrons are shared unequally, creating partial charges (e.g., H₂O).

Chemical Reactions: Anabolism and Catabolism

• Anabolism (Dehydration Synthesis): Builds larger molecules from smaller ones. Water is removed. Example: Building proteins from amino acids.

• Catabolism (Hydrolysis): Breaks down larger molecules into smaller ones. Water is added. Example: Breaking down carbohydrates into glucose.

Organic vs. Inorganic Compounds

• Organic Compounds: Always contain carbon and hydrogen; they are larger and more complex (e.g., proteins, lipids).

• Inorganic Compounds: Generally do not contain carbon (exceptions include CO₂ and HCO₃⁻); they are simpler molecules (e.g., water, salts, acids, bases).

Characteristics of Salts, Acids, and Bases

• Salts: Ionic compounds that dissociate in water to release ions (e.g., NaCl).

• Acids: Release H⁺ (protons) in solution (e.g., HCl).

• Bases: Accept H⁺ or release OH⁻ in solution (e.g., NaOH).

The pH Scale and Solution Acidity

• pH: Measures the concentration of hydrogen ions (H⁺) in a solution.

• The pH Scale (0–14):

  • 0–6.9: Acidic (higher H⁺ concentration)
  • 7: Neutral (pure water)
  • 7.1–14: Basic/Alkaline (higher OH⁻ concentration)

Organic Compounds and Their Building Blocks

Structure and Functions

• Carbohydrates: CHO in a 1:2:1 ratio. Used as a quick energy source (e.g., glucose, starch).

• Proteins: Chains of amino acids. Used for enzymes, hormones, and muscle structure (e.g., hemoglobin).

• Lipids: Glycerol plus 1–3 fatty acids. Used for long-term energy, insulation, and cell membranes (e.g., triglycerides, steroids).

• Nucleic Acids: Sugar, phosphate, and nitrogen base. Used to store and transmit genetic information (DNA, RNA).

Chapter 3: Cells and Tissues

Cellular Compartments and Organelles

• Plasma Membrane: The outer boundary that regulates entry and exit.

• Cytoplasm: Jelly-like fluid containing organelles.

• Nucleus: The control center containing DNA, surrounded by a nuclear envelope.

• Ribosomes: Synthesize proteins; can be free or attached to the ER.

• Endoplasmic Reticulum (ER): Rough ER processes proteins; Smooth ER synthesizes lipids and detoxifies.

• Golgi Apparatus: Modifies, packages, and ships proteins and lipids.

• Mitochondria: The powerhouse of the cell; produces ATP.

• Centrioles: Involved in cell division and spindle fiber organization.

Membrane Transport: Passive and Active

Passive Transport (No energy required)

• Diffusion: Movement from high to low concentration.
• Facilitated Diffusion: Uses proteins to move substances down a gradient.
• Osmosis: Diffusion of water through a selectively permeable membrane.

Active Transport (Requires ATP)

• Solute Pumping: Moves substances against the gradient (e.g., Na⁺/K⁺ pump).
• Endocytosis: Cell engulfs materials (Phagocytosis for eating, Pinocytosis for drinking).
• Exocytosis: Vesicles expel substances from the cell.

The Cell Cycle and Mitosis Phases

• Interphase: The cell grows and DNA replicates (G₁, S, G₂ phases).

• Mitosis (Nuclear Division):

  • Prophase: Chromatin condenses; nuclear envelope disappears.
  • Metaphase: Chromosomes line up at the equator.
  • Anaphase: Sister chromatids are pulled to opposite poles.
  • Telophase: Nuclear envelope reforms; chromosomes uncoil.

• Cytokinesis: The cytoplasm divides, forming two daughter cells.

Histology and Tissue Organization

• Histology: The study of tissues.

• Tissues: Groups of similar cells performing a common function; the level of organization between cells and organs.

The Four General Tissue Types

1. Epithelial
2. Connective
3. Muscle
4. Nervous

Epithelial Tissue Characteristics and Types

• Characteristics: Closely packed cells, avascular (no blood vessels), and regenerates easily.

• Functions: Protection, absorption, filtration, and secretion.

• Specific Types:

  • Simple Squamous: Thin/flat; found in lungs and capillaries.
  • Simple Cuboidal: Cube-shaped; found in kidney tubules.
  • Simple Columnar: Tall cells; found in the digestive tract.
  • Stratified Squamous: Multiple layers; found in the skin and mouth.

Connective Tissue Types and Functions

Connective tissue has fewer cells and more extracellular matrix. It is generally vascular (except cartilage).

Muscle Tissue Features and Locations

Nervous Tissue Structure and Function

• Neuron: The main nerve cell that conducts impulses.

• Structure: Includes the Cell Body (nucleus), Axon (sends signals), and Dendrites (receive signals).

• Functional Characteristics: Irritability (response to stimuli) and Conductivity (transmission of electrical impulses).