Difficulty: Introductory | Prerequisites: None (this is foundational material for the entire course)
These three chapters lay the groundwork for everything else in Anatomy and Physiology. Chapter 1 gives you the shared language: the directional terms, body planes, and levels of organisation that every later topic assumes you know cold. Chapter 2 zooms into the cell, the smallest living unit, and its internal machinery. Chapter 4 steps back out to tissues, the first level of cooperative structure above individual cells. If you are behind on any of these, every subsequent system (skeletal, muscular, nervous, cardiovascular) will be harder than it needs to be.
The body is organised from atoms up to organisms in a strict hierarchy. Cells are the smallest living units, built from a plasma membrane, cytoplasm, and a nucleus. Cells group into four tissue types (epithelial, connective, muscle, nervous), each with a one-word function you should be able to recall on sight.
Anatomical position
The standard reference posture: standing erect, facing forward, feet together, arms at the sides, palms facing forward. Every directional term in anatomy assumes this stance.
Superior
Toward the top (head end) of the body. In simple terms, "above."
Inferior
Toward the bottom (foot end) of the body. In simple terms, "below."
Anterior (ventral)
Toward the front of the body. Think of the belly side.
Posterior (dorsal)
Toward the back of the body. Think of the spine side.
Proximal
Closer to the point of attachment to the trunk. In simple terms, nearer to where a limb connects to the body.
Distal
Farther from the point of attachment to the trunk. Your fingers are distal to your elbow.
Superficial
On or near the body surface.
Deep
Away from the body surface, further inward.
Ipsilateral
On the same side of the body. Your right hand and right foot are ipsilateral.
Contralateral
On opposite sides of the body. Your right hand and left foot are contralateral.
Frontal (coronal) plane
An imaginary vertical slice that divides the body into anterior and posterior portions.
Transverse (horizontal) plane
A horizontal slice that divides the body into superior and inferior portions. Think of slicing a loaf of bread.
Sagittal (median) plane
A vertical slice that divides the body into equal left and right halves. A parasagittal plane divides left and right but not into equal halves.
Plasma membrane
The phospholipid bilayer that forms the outer boundary of a cell. Described by the fluid mosaic model: a sea of phospholipids studded with proteins, cholesterol, and carbohydrates, all able to drift laterally.
Fluid mosaic model
The accepted description of membrane structure: the bilayer is fluid (components move), and the mix of lipids, proteins, and carbohydrates forms a mosaic pattern.
Organelle
A specialised structure within a cell that performs a specific function. Think of organelles as the cell's internal organs.
Tissue
A group of similar cells working together to perform a common function. The step between individual cells and organs.
Extracellular matrix (ECM)
The non-living material secreted by cells that sits between them. Especially prominent in connective tissue, where it often makes up more of the tissue's volume than the cells themselves.
Epithelial tissue
Tissue that covers body surfaces, lines cavities, and forms glands. One-word function: covering (or protection).
Connective tissue (CT)
The most abundant and diverse tissue type. One-word function: support. Distinguished from other tissue types by having cells scattered within an extensive extracellular matrix.
Muscle tissue
Tissue specialised for contraction and movement. One-word function: movement.
Nervous tissue
Tissue specialised for transmitting electrical signals. One-word function: control.
Hierarchy of structural organisation (AMOCTOOO)
Atoms, molecules, organelles, cells, tissues, organs, organ systems, organisms
Each level builds on the one below it
The mnemonic AMOCTOOO follows the first letters in order
Anatomical position and directional terms
All descriptions assume anatomical position (see Key Terms above)
Paired terms work as opposites: superior/inferior, anterior/posterior, medial/lateral, proximal/distal, superficial/deep
Ipsilateral and contralateral describe same-side versus opposite-side relationships
Body planes
Frontal (coronal): divides front from back
Transverse (horizontal): divides top from bottom
Sagittal (median): divides into equal left and right halves
Parasagittal: divides left and right but not equally
Oblique planes also exist (angled cuts), though less commonly tested
Smallest living unit
The cell is the smallest living unit in the body. Atoms, molecules, and organelles are not independently alive.
Three main structural components of any cell
Plasma membrane (outer boundary)
Cytoplasm (everything between the membrane and the nucleus, including cytosol and organelles)
Nucleus (control centre, houses DNA)
Plasma membrane, fluid mosaic model
Phospholipid bilayer: hydrophilic heads face outward, hydrophobic tails face inward
Integral proteins span the membrane; peripheral proteins sit on one surface
Cholesterol stiffens the bilayer and reduces permeability
Glycoproteins and glycolipids on the outer surface serve as cell identity markers
Membrane junctions
Tight junctions: seal neighbouring cells together so nothing leaks between them. Found where you need a watertight barrier (e.g. bladder epithelium).
Desmosomes: riveted anchoring junctions that resist mechanical stress. Common in skin and cardiac muscle.
Gap junctions: channels that allow ions and small molecules to pass directly between cells. Enable electrical coupling (e.g. in cardiac muscle so the heart beats in unison).
Cilia, flagella, and microvilli
Cilia: short, hair-like projections that move in coordinated waves. Found lining the respiratory tract to sweep mucus.
Flagella: long, whip-like projections used for locomotion. In humans, only sperm cells have a flagellum.
Microvilli: tiny finger-like extensions of the plasma membrane that increase surface area for absorption. Abundant in the small intestine.
Major organelles and their functions
Nucleus: stores DNA, directs protein synthesis
Ribosomes: sites of protein synthesis (free ribosomes make cytoplasmic proteins; bound ribosomes on rough ER make membrane and exported proteins)
Rough endoplasmic reticulum (rough ER): studded with ribosomes, processes and packages proteins
Smooth endoplasmic reticulum (smooth ER): lipid synthesis, detoxification, calcium storage
Golgi apparatus: modifies, sorts, and packages proteins for secretion or delivery within the cell
Lysosomes: contain digestive enzymes to break down waste, debris, and worn-out organelles
Mitochondria: produce ATP through aerobic respiration; the cell's power generators
Peroxisomes: detoxify harmful substances (e.g. hydrogen peroxide, fatty acids)
Cytoskeleton: network of microfilaments, intermediate filaments, and microtubules providing structural support and enabling movement
Centrioles: organise the mitotic spindle during cell division
Four basic tissue types and their one-word functions
Epithelial: covering
Connective: support
Muscle: movement
Nervous: control
Epithelial tissue, special features
Cellularity: cells fit tightly together with minimal extracellular material
Polarity: has an apical surface (free, exposed) and a basal surface (attached to basement membrane)
Avascular: no blood vessels; nutrients diffuse from underlying connective tissue
Highly regenerative: replaces itself rapidly
Supported by a basement membrane (thin extracellular sheet between epithelium and underlying CT)
Naming epithelial types
First word = number of layers: simple (one layer), stratified (multiple layers), pseudostratified (appears layered but all cells touch the basement membrane)
Second word = cell shape: squamous (flat), cuboidal (cube-shaped), columnar (tall, column-shaped)
Examples: simple squamous (one layer of flat cells, found in alveoli), stratified squamous (many layers of flat cells, found in skin and oral cavity), simple columnar (one layer of tall cells, found in stomach and intestinal lining), pseudostratified columnar (appears stratified but is a single layer, found in the trachea)
Transitional epithelium: a special stratified type that stretches; found in the urinary bladder
Connective tissue
Most abundant and diverse tissue type
General arrangement: cells scattered within an extracellular matrix of ground substance and protein fibres
This is how CT differs from epithelium (tightly packed cells, little matrix) and muscle (cells are the dominant component)
CT fibre types
Collagen fibres: thick, strong, resist tension. The most abundant protein in the body.
Elastic fibres: thinner, stretchy, allow tissue to recoil. Found in skin, lungs, blood vessel walls.
Reticular fibres: fine, branching collagen fibres that form supportive meshworks. Found in lymphoid organs, bone marrow.
Muscle tissues
Skeletal muscle: striated (visible banding), voluntary, multinucleated, long cylindrical fibres. Attached to bones.
Cardiac muscle: striated, involuntary, usually one nucleus per cell, branching fibres connected by intercalated discs. Found only in the heart.
Smooth muscle: no visible striations, involuntary, one nucleus, spindle-shaped cells. Found in walls of hollow organs (stomach, blood vessels, bladder).
Nervous tissue
Neurons: the excitable cells that transmit electrical impulses. Made of a cell body, dendrites (receive signals), and an axon (sends signals).
Neuroglia (glial cells): supporting cells that insulate, protect, and nourish neurons. They do not transmit impulses themselves.
Students often confuse the sagittal plane with the frontal plane. Remember: sagittal splits left and right; frontal splits front and back.
"Pseudostratified" epithelium looks layered, but every cell contacts the basement membrane. It is a single layer, not truly stratified.
Connective tissue is not always "connective" in the everyday sense. Blood and bone are both classified as connective tissue, which surprises many students.
The hypodermis is sometimes discussed alongside skin tissue, but it is not one of the four basic tissue types on its own; it is a layer composed primarily of adipose (a type of CT).
⚠️ You will be expected to identify tissue types from images. Practise recognising striations (skeletal and cardiac muscle), the tightly packed arrangement of epithelium versus the spacious matrix of CT, and the branching pattern of neurons.
⚠️ Naming epithelial types from descriptions is a classic exam question. If the description says "one layer of flat cells," the answer is simple squamous. Practise translating descriptions into proper names.
⚠️ Directional terms are used throughout the entire course. If you mix up proximal/distal or anterior/posterior now, it compounds in every later chapter.
⚠️ Know all three membrane junctions and what makes each functionally distinct: sealing (tight), anchoring (desmosome), communicating (gap).
True or false: The transverse plane divides the body into left and right halves.
Fill in the blank: The three main structural components of any cell are the plasma membrane, __________, and the nucleus.
True or false: Connective tissue is characterised by tightly packed cells with minimal extracellular matrix.
Fill in the blank: The type of membrane junction that allows direct passage of ions between cells is the __________ junction.
True or false: Cardiac muscle is voluntary and non-striated.
Answers: 1. False (transverse divides superior/inferior). 2. Cytoplasm. 3. False (that describes epithelium; CT has abundant ECM). 4. Gap. 5. False (cardiac muscle is involuntary and striated).
Q: List the levels of structural organisation from simplest to most complex.
A: Atoms, molecules, organelles, cells, tissues, organs, organ systems, organisms (AMOCTOOO).
Q: A patient has a wound on the front of the body, near the surface. Using anatomical terminology, describe the wound's position.
A: The wound is on the anterior (ventral) and superficial aspect of the body.
Q: What is the fluid mosaic model?
A: It describes the plasma membrane as a fluid phospholipid bilayer embedded with a mosaic of proteins, cholesterol, and carbohydrates that can move laterally within the membrane.
Q: Name the four basic tissue types and give the one-word function of each.
A: Epithelial (covering), connective (support), muscle (movement), nervous (control).
Q: How does connective tissue differ structurally from epithelial tissue?
A: Connective tissue has cells dispersed within an extensive extracellular matrix of ground substance and fibres. Epithelial tissue has cells tightly packed together with minimal extracellular material.
Q: You are shown a tissue image with branching, striated fibres joined by intercalated discs. What tissue is this?
A: Cardiac muscle tissue.
Q: A single layer of flat cells lines the alveoli of the lungs. What is this epithelial type called?
A: Simple squamous epithelium.
Directional terminology (Ch. 1) is the language you will use to describe every bone landmark (Chs. 7-8), joint movement (Ch. 9), and muscle location (Chs. 10-11).
The four tissue types (Ch. 4) reappear constantly: the integumentary system (Ch. 5) layers epithelium over connective tissue, the heart wall (Ch. 19) stacks all three muscle-related layers, and nervous tissue (Ch. 12) forms entire organs.
Membrane junctions from Ch. 2 are directly relevant to cardiac muscle (gap junctions at intercalated discs, Ch. 19) and epithelial barriers throughout the body.
anatomical position, directional terms, body planes, sagittal, coronal, transverse, frontal plane, structural hierarchy, levels of organisation, AMOCTOOO, cell structure, plasma membrane, fluid mosaic model, organelles, mitochondria, rough ER, smooth ER, Golgi apparatus, lysosomes, tight junctions, desmosomes, gap junctions, cilia, flagella, microvilli, tissue types, epithelial tissue, connective tissue, muscle tissue, nervous tissue, simple squamous, stratified squamous, pseudostratified columnar, collagen fibres, elastic fibres, reticular fibres, skeletal muscle, cardiac muscle, smooth muscle, neurons, neuroglia, extracellular matrix, APK2100C, anatomy and physiology, UF