Structural Levels of Organization
Chemical Level
Different kinds of atoms join together to form molecules which make up all living matter
Ex. Molecules, organelles
Cellular Level
Cells is structural & functional unit of all living things
Ex. Red blood cell
Tissue Level
Cells with common origin, appearance & function
Each tissue has one or more specialized funtion
Ex. Connective tissue
Cell differentiation- groups of cells having common origin become specialized for certain
physiological functions at an early embryonic stage
Organ Level
Different tissues joined together & adapted for a special (vital) function
Ex. Stomach
System Level
Groups of organs acting together to perform a complex but specialized function
Ex. Digestive system
Organism Level
Group of systems that can live on its own
Ex. Human
Intro to Anatomical Language
Bilateral symmetry
Found in humans & other vertebrates
Body can be dissected vertically into equal left & right segments
One cut down midline will result in identical (exterior) mirror image halves
Sagittal plane
Runs vertically & divides the body into two portions
Midsagittal plane divides the body into two identical halves
Frontal (Coronal) plane
At right angle to midsagitatal plane
Divides body into ventral (anterior, front) and dorsal (posterior, back) portions
Transverse plane
At right angle to sagittal plane
Divides body into superior (upper) and inferior (lower) portions
Body Cavities
Dorsal (posterior) cavity- found within skull & vertebral column
Cranial cavity- contains brain
Spinal cavity- contains spinal cord
Ventral (anterior) cavity- larger of two & divided by diaphragm
Thoracic cavity- above diaphragm; contains lungs & air passages, esophagus,
heart & major blood vessels
Abdominal cavity- below diaphragm; organs here are known as viscera &
include the digestive system, kidneys & spleen
Pelvic cavity- lowest part of abdominal cavity; contains urinary bladder,
rectum & reproductive system
Body systems
Responsible for maintaining & adjusting its activities to provide the proper internal environment
(homeostasis) for each cell
Major body systems & their main job
Integumentary- external support & protection of body
Skeletal- internal support & flexible framework for body movements
Muscular- body movement
Nervous- control & regulation f other systems in body
Endocrine- secretion of hormones for chemical regulation
Circulatory- transport of nutrients & removal of wastes from cells
Lymphatic—body immunity
Respiratory- gaseous exchange between external environment & blood
Digestive- breakdown & absorption of food materials
Urinary- filtration of blood & removal of metabolic wastes
Reproductive- production of sex cells, union of sex cells & development of fetus
Histology- Study of tissues
Four primary tissue types based on cellular composition, function & appearance
Epithelial, Connective, Muscular, Nervous
Tissues made of cells surrounded & bound together by nonliving intercellular matrix
Matrix is secreted by the cells & can be liquid, semisolid, or solid
Some tissues also contain intercellular fibers
Epithelial tissue
Main job: protect, absorb, secrete, regulate movement of materials in/out by passive & active
Cover surfaces & lines all internal structures/cavities of body
Structure: cells are close together & usually arranged in one or more layers; cells held together
by basement membrane & intercellular fibers; little matrix present
No blood vessels in layers so nutrients must be transported by diffusion
Can replace at a high rate; cells divide more often than other tissue types
Two main categories: membranous & glandular
Membranous epithelial
Found throughout body; forms linings, coverings, etc.
Always has one free surface exposed; may be one or several cell layers thick but always
supported by basement membrane
Cells tightly packed with little matrix
Regenerate (reproduce) quickly since often exposed to friction & harmful substances
Classified by the number of layers & cell shape
Simple- single cell layer thick; absorb, filter, diffuse & secrete; surface often covered by
mucus to keep tissue from drying out
Simple squamous- flat scale-like cells forming very thin tissue; found lining blood
vessels (endothelium), heart & lungs; secrete fluid to help reduce
friction; allows for rapid movement of molecules by filtration/diffusion
Simple cuboidal- square shaped cells; found lining ducts & tube portions of
glands, kidney tubules & tissue around ovary; line glands & digestive
tract; absorb/secrete
Simple columnar- column shaped; tightly packed to form protective covering
for inner surface of organ; can produce secretions such as goblet cells in
stomach; used for absorption in intestine (microvilli on free surface);
can replace itself every 2-3 days
Simple ciliated columnar- has cilia on free surface used to transport materials
through tubes such as in uterine tubes, sperm tubes or trachea
Stratified- 2 or more layers of cells; primarily protective function found in areas subject
to abrasion or stress
Stratified squamous- basement membrane is cuboidal or columnar & cells
flatten as they reach free surface; outermost cells may contain keratin
to protect delicate layers below; main job is to cover/protect
Cheek cells are nonkeratinized stratified squamous epithelial
Skin is keratinized stratified squamous epithelial
Stratified cuboidal- 2-3 layers of cuboidal cells; found lining large ducts; mainly
for protection/strength
Glandular epithelial
Specialized tissues that form the secretory portion of glands
Unicellular glands- made of single cell; modified columnar cells within most epithelial tissues;
ex. Goblet cells
Multicellular glands- made of both secretory cells & cells that form the walls of ducts
Classified based on how they secrete or release their product
Merocrine- secrete watery substance through cell membrane by packaging the
secretions into vesicles that release by exocytosis
Ex. Salivary glands, pancreatic glands, tear glands, sweat glands
Apocrine- secretions accumulate on the surface of cell & then part of the cell
pinches off & is discharged with the secretion
Ex. Mammary glands & some sweat glands
Holocrine- entire secretory cell is discharged along with the product; secretion
is a mixture of cell fragments & product cell made
Ex. Oil secreting sebaceous gland
Connective Tissue
Main job: support the body by connecting tissues; connect, support, bind together, protect,
storage, transport
Most widespread & abundant tissue in body
Structure: tightly packed cells, fibers & intercellular matrix; fewer cells than matrix & cells
normally do not touch each other; matrix made of proteins, carbohydrates & water;
three types of protein fibers (collagen, elastin & reticular)
Highly vascular tissue; well nourished; can replicate (reproduce)
Different types classified based on matrix that binds the cells together
Connective Tissue Proper
Contain many types of cells- both resident & wandering
Loose flexible matrix
Contains all types of fibers
Collagen fibers are white fibers; flexible & have great strength
Elastin fibers are yellow fibers; thinner in size but are elastic
Reticular fibers form a reinforcing lattice structure; tough but flexible fibers
Loose Connective Tissue
Areolar tissue- few cells in semifluid matrix; fibers are loosely arranged; found in dermis
of skin where it provides nutrients; also found between/around organs to
support/cushion; provides flexibility & strength in any direction (permits skin to
move when part of body is rubbed); major part of subcutaneous layer
Reticular tissue- jellylike matrix with network of interwoven reticular fibers; some cells
are phagocytic & can eat foreign materials; found in liver, spleen, lymph nodes
& bone marrow
Adipose tissue- fat storage tissue; large cells with single vacuole containing fat droplet;
serves as reserve energy supply, padding to absorb jolts & insulation to keep in
heat; found on surface of viscera, in membranes, bone marrow
Dense Connective Tissue- more protein fibers & less matrix
Dense regular tissue- white fibrous tissue with large amounts of densely packed
collagenous fibers running parallel to the direction of force placed on tissues;
contain few blood vessels so takes long time to heal; ex. Tendons & ligaments
Dense irregular tissue- large amounts of densely packed collagenous fibers that are
interwoven in all directions; form fibrous capsules around organs & joints
Elastic- composed primarily of irregularly arranged yellowish elastic fibers; found in
artery walls, larynx, trachea, vocal cords
Supporting Connective Tissue
Cartilage- consists of cartilage cells & semisolid matrix; supportive/protective functions;
mature tissue has no blood vessels so must get nutrients from surrounding tissue; heals
slowly; some types ossify to become bone
Hyaline- “gristle”; fine collagenous fibers with clear glassy appearance; most abundant
type of cartilage; covers bone surface, supports trachea, reinforces nose, larynx,
rib connections
Fibrocartilage- matrix reinforced with collagenous fibers; part of knee (meniscus) &
intervertebral discs; allows for shock absorption & resists compression
Elastic- contains more elastin fibers; very flexible but otherwise similar to hyaline tissue;
found in outer ear, larynx, epiglottis & auditory canal
Bone- osseous tissue; most rigid connective tissue; hardness due to calcium phosphate
deposited in matrix; some collage fibers for flexibility; cells are called osteocytes
Blood- vascular tissue; fluid connective tissue made of cells (erythryocytes, leukocytes, thrombocytes)
suspended in liquid matrix (plasma); protein fibers are dissolved in plasma & then become
modified to be insoluble & helpful in clotting
Nervous Tissue
Main job: responds to certain changes in external/internal environments
Vary in structure & function but all adapted to collect/transmit nerve impulses; specialized to
respond to physical/chemical stimuli, convert stimuli into nerve impulses & conduct
Basic unit of structure is neuron
Neurons are excitable, have a high metabolic rate, exhibit extreme longevity, but are
nonmitotic (non-dividing)
3 parts: cell body that contains nucleus & other organelles; dendrites that receive
nerve impulses & send them to cell body; axons carry nerve impulses away from
cell body
Types of neurons: sensory neurons receive impulses from environment; motor neurons
carry impulses to muscles/glands; associative (interneurons) neurons relay
impulses between sensory & motor neurons
Besides neurons there are also glial cells
Glial cells are 5 times more abundant but are nonexcitable (can’t carry impulses) but are
Muscle Tissue
Main job: produce movement of body parts with respect to each other or for movement of
materials through the body
Composed of cells that contract & change shape; very little matrix
Very vascular due to heavy demand for oxygen
Can shorten by about 1/3 of resting length
Make up 40-50% of body mass
Rate & control of movement depends on kind of cells in muscle tissue
Types of muscle tissue
Skeletal- voluntary muscle that requires conscious effort to move; relatively large/very
active cells so contain more than one nuclei/cell; also known as striated muscle;
long cylindrical cells called fibers; require nerve-bone impulse
Smooth- involuntary muscles which are not consciously controlled; lack striations; only
one nuclei/cell; found in walls of digestive organs, arteries/veins; long spindle
shaped cells; help to propel materials along cavities
Cardiac- only found in heart (forms the myocardial layer); branched cells forming a
network; nuclei in middle of cells; can contract without being stimulated by
nerve-bone impulse so considered involuntary; don’t regenerate (reproduce)

Structural Levels of Organization Chemical Level Different kinds of