Anatomy and Physiology: Foundational Concepts and Systems

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Chemical Level of Organization

Atoms and Atomic Structure

The atom is the smallest unit of matter, composed of subatomic particles: protons (positive charge), neutrons (neutral), and electrons (negative charge). The arrangement and number of these particles determine the atom's properties and interactions.

Atomic Number: Number of protons in the nucleus; defines the element.
Isotopes: Atoms of the same element with different numbers of neutrons.
Electron Shells: Electrons occupy energy levels (shells) around the nucleus; the outermost shell (valence shell) determines chemical reactivity.

Three forms of hydrogen atoms: hydrogen-1, deuterium, tritium Arrangement of electrons into energy levels for lithium and neon

Chemical Bonds and Molecules

Atoms combine to form molecules and compounds through chemical bonds, which involve the sharing, gaining, or losing of electrons.

Ionic Bonds: Formed when one atom donates electrons to another, resulting in oppositely charged ions that attract each other (e.g., NaCl).
Covalent Bonds: Atoms share electrons to achieve stability; can be single, double, or triple bonds.
Hydrogen Bonds: Weak attractions between polar molecules, important in water and biological molecules.

Formation of ionic bonds between sodium and chlorine Covalent bonds in common molecules Hydrogen bonds between water molecules

Types of Chemical Reactions

Chemical reactions involve the making or breaking of bonds. Major types include:

Decomposition (Catabolism): AB → A + B
Hydrolysis: AB + H2O → AH + BOH
Synthesis (Anabolism): A + B → AB

Enzymes and Metabolism

Enzymes are biological catalysts that lower activation energy, speeding up metabolic reactions essential for life.

Inorganic vs. Organic Compounds

Inorganic Compounds: Usually lack carbon-hydrogen bonds (e.g., water, salts, acids, bases).
Organic Compounds: Contain carbon and hydrogen; include carbohydrates, proteins, lipids, and nucleic acids.

Properties of Water

Water is vital for life due to its role as a universal solvent, its high heat capacity, reactivity, and lubricating properties. It supports hydrophilic (water-loving) and hydrophobic (water-fearing) interactions.

pH and Its Importance

pH measures hydrogen ion concentration. Human blood pH is tightly regulated (7.35–7.45). Acids have pH < 7, bases > 7.

Cellular Level of Organization

Cell Structure and Function

Cells are the basic units of life, with specialized structures (organelles) performing distinct functions.

Plasma Membrane: Phospholipid bilayer with embedded proteins; regulates exchange, provides protection, and supports communication.
Cytoplasm: Contains cytosol and organelles.
Organelles: Include nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and more.

Labeled diagram of a typical animal cell

Nucleus and Genetic Code

The nucleus houses DNA, which encodes the genetic instructions for protein synthesis.

Structure of the nucleus with labeled components

Membrane Transport

Cells regulate movement of substances via passive (diffusion, osmosis) and active (carrier-mediated, vesicular) transport mechanisms.

Diffusion: Movement from high to low concentration.
Osmosis: Diffusion of water across a selectively permeable membrane.

Stages of diffusion in a beaker

Tissue Level of Organization

Major Tissue Types

The body contains four primary tissue types: epithelial, connective, muscle, and nervous tissue.

Epithelial Tissue

Epithelial tissue covers surfaces and forms glands. Functions include protection, absorption, secretion, and sensation.

Polarity: Apical (top) and basal (bottom) surfaces.
Attachment: To basement membrane.
Cell Junctions: Tight junctions, gap junctions, desmosomes, hemidesmosomes.

Polarity of epithelial cells Gap junction structure Tight junction structure Types of cell junctions in epithelial tissue

Nervous Tissue

Nervous tissue is specialized for communication via electrical impulses. It consists of neurons and supporting neuroglia.

Structure of a neuron and neuroglia

Integumentary System

Structure and Function

The integumentary system includes the skin (epidermis and dermis) and accessory structures (hair, glands, nails). It protects, regulates temperature, synthesizes vitamin D, and provides sensory information.

Overview of the integumentary system: cutaneous membrane and accessory structures

Epidermis and Dermis

The epidermis is a stratified squamous epithelium, while the dermis contains connective tissue, blood vessels, and nerves.

Thin skin structure with labeled layers Dermal layers and blood supply

Skeletal System

Axial and Appendicular Skeleton

The skeleton is divided into axial (skull, vertebral column, thoracic cage) and appendicular (limbs and girdles) components.

Axial skeleton overview Anterior and posterior views of the axial skeleton Vertebral column regions and curves Thoracic cage: ribs and sternum Appendicular skeleton with labeled bones

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