Introduction

Levels of Organization and Body Planes

The human body is organized into hierarchical levels, each contributing to overall function and structure. Understanding these levels and directional terms is essential for describing anatomical relationships.

• Levels of Organization: Chemical, cellular, tissue, organ, organ system, organism.

• Body Cavities: Major cavities include cranial, thoracic, abdominal, and pelvic.

• Body Planes: Sagittal (left/right), frontal (anterior/posterior), transverse (superior/inferior).

• Directional Terms: Used to describe locations (e.g., medial, lateral, proximal, distal).

• Homeostasis: The body's ability to maintain stable internal conditions through negative and positive feedback mechanisms.

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

Chemistry (Basic, Organic, Enzymes)

Elements, Atoms, and Molecules

Chemistry underpins all biological processes. Understanding atomic structure and chemical bonds is crucial for grasping physiology.

• Major Elements: Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur.

• Atomic Structure: Atoms consist of protons, neutrons, and electrons. Atomic number = number of protons.

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

• Molecules and Compounds: Formed by chemical bonds (ionic, covalent, hydrogen).

Example: Water (H2O) is a compound formed by covalent bonds between hydrogen and oxygen.

Biologically Important Molecules

• Inorganic Compounds: Water, salts, acids, bases.

• Organic Compounds: Carbohydrates, lipids, proteins, nucleic acids.

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides/Polysaccharides: Sucrose, starch, glycogen.

• Fatty Acids: Saturated (no double bonds) vs. unsaturated (one or more double bonds).

• Proteins: Made of amino acids; function as enzymes, structural components, etc.

• Nucleic Acids: DNA and RNA; store and transmit genetic information.

Example: Enzymes are proteins that catalyze biochemical reactions.

Chemical Reactions and Enzymes

• Catalysis: Enzymes lower activation energy, increasing reaction rates.

• Dehydration Synthesis: Forms larger molecules by removing water.

• Hydrolysis: Breaks down molecules by adding water.

• Catabolic vs. Anabolic: Catabolic reactions break down molecules; anabolic reactions build them.

Formula:

Cell (Structure, Plasma Membrane, Cell Division)

Cell Structure and Function

Cells are the basic units of life, each containing specialized organelles that perform distinct functions.

• Organelles: Nucleus (DNA storage), mitochondria (energy production), ribosomes (protein synthesis), endoplasmic reticulum (protein/lipid processing), Golgi apparatus (packaging).

• Plasma Membrane: Phospholipid bilayer with embedded proteins; regulates entry/exit of substances.

• Membrane Transport: Passive (diffusion, osmosis, facilitated diffusion) vs. active (requires energy, e.g., pumps).

• Factors Affecting Diffusion: Concentration gradient, temperature, membrane permeability.

Example: Oxygen diffuses into cells passively due to concentration gradients.

Cell Division

• Mitosis: Produces two identical daughter cells for growth and repair.

• Phases: Prophase, metaphase, anaphase, telophase, cytokinesis.

• DNA Replication: Occurs before cell division; ensures genetic continuity.

Formula:

Protein Synthesis

Transcription and Translation

Protein synthesis involves two main processes: transcription (DNA to RNA) and translation (RNA to protein).

• Transcription: DNA is used as a template to synthesize messenger RNA (mRNA).

• Translation: mRNA is read by ribosomes to assemble amino acids into a polypeptide chain.

• Codons: Three-base sequences on mRNA that specify amino acids.

• Anticodons: Complementary sequences on tRNA.

Formula:

Example: The codon AUG codes for the amino acid methionine.

Tissue

Types and Functions of Tissues

Tissues are groups of similar cells performing specific functions. There are four primary tissue types in the human body.

• Epithelial Tissue: Covers surfaces, lines cavities, forms glands. Shapes: squamous, cuboidal, columnar.

• Connective Tissue: Supports, binds, and protects organs. Types: loose, dense, cartilage, bone, blood.

• Muscle Tissue: Produces movement. Types: skeletal, cardiac, smooth.

• Nervous Tissue: Transmits electrical impulses; found in brain, spinal cord, nerves.

Example: Adipose tissue stores fat and insulates the body.

Table: Types of Muscle Tissue

Integumentary System

Structure and Function of Skin

The integumentary system protects the body and regulates temperature. It consists of skin, hair, nails, and associated glands.

• Epidermis: Outer layer; provides barrier and creates skin tone.

• Dermis: Middle layer; contains connective tissue, hair follicles, sweat glands.

• Subcutaneous Layer: Fat and connective tissue; insulates and cushions.

• Accessory Structures: Hair, nails, glands (sebaceous, sweat), receptors.

• Functions: Protection, sensation, thermoregulation, vitamin D synthesis.

Example: Sweat glands help cool the body through evaporation.

Skeletal System

Bone Structure and Function

The skeletal system provides support, protection, and enables movement. Bones are classified by shape and internal structure.

• Bone Shapes: Long, short, flat, irregular, sesamoid.

• Microscopic Structure: Compact bone (dense), spongy bone (porous).

• Bone Cells: Osteoblasts (build bone), osteoclasts (break down bone), osteocytes (maintain bone).

• Calcium Homeostasis: Regulated by parathyroid hormone (PTH) and calcitonin.

• Bone Growth and Repair: Involves ossification, lengthening, thickening, and resorption.

• Fracture Repair Steps: Hematoma formation, fibrocartilaginous callus, bony callus, bone remodeling.

Formula:

Example: Osteoporosis results from decreased bone mass and increased fracture risk.