Recall:
SYSTEMS are composed of one or more organs, all serving a common function
ORGANS are composed of one or more types of tissues, all serving a common function
TISSUES are composed of one or more types of cells and their products, all serving a common function
The study of structure at the level of tissues is called histology.
Epithelium lines internal and external surfaces, including hollow organs. Forms glands.
Connective Tissue provides support and fills spaces
Muscle Tissue produces force and movement
Nervous Tissue carries and integrates electrical information
Each of these can have one or more subtypes
With only a few, rare exceptions, all organs of the human body are composed of four types of tissue:
Epithelium
- Covers body surfaces (e.g. skin, cornea)
- Lines body cavities (e.g. peritoneal & pericardial cavities
- Lines insides of hollow organs (e.g. stomach, heart, lung, aorta, oviduct)
- Forms glands (e.g. sweat glands, pancreas, salivary glands)
Characteristics of Epithelium
- Highly cellular, with very little extracellular matrix
- Cells form close contacts with each other
- Avascular
- High capacity for regeneration
Functional characteristics of epithelia depend on the cells, rather than the extracellular matrix which is unspecialized
Epithelium always supported by connective tissueand separated from it by a basement membrane.Depends on connective tissue for vessels, nerves, etc. Epithelium Basement membrane Connective tissue
Mucous Membrane orSerous Membrane
Epithelium
Different types for different functions.
Classified according to:a) Number of layers of cells
b) Shape of cells in the top layer
Single layer = "simple" Two or more layers = "stratified"
Actually one layer but looks like more = "pseudostratified"
Flat = "squamous" Cube-shaped = "cuboidal" Taller than wide = "columnar"
Change shape from squamous to cuboidal = "transitional"
Epithelium
Number of layers Shape of surface cells
Squamous Simple CuboidalStratified ColumnarPseudostratified Transitional
Simple Squamous Epithelium
Simple Cuboidal Epithelium
Simple Columnar EpitheliumPseudostratified Columnar Epithelium
Stratified Squamous Epithelium Stratified Cuboidal Epithelium
(Stratified) Transitional EpitheliumStratified Columnar Epithelium
Epithelium also forms all glands in the body
Glands classified by
a) Whether or not they have ducts
b) Their method of secretion
Yes = Exocrine; Duct carries product to surfaceNo = Endocrine; Product secreted into surrounding extracellular matrix, picked up by blood vessels
Merocrine: Product released from undamaged cellsApocrine: Top part of cell lost during secretionHolocrine: Entire cell lost during secretion
Exocrine glands also classified by
c) Shape, and whether or not either the duct and/or the secretory part branches
Connective Tissue
- Lots of extracellular matrix; Relatively few cells
- Cells usually do not communicate with each other
- Highly vascular
- Different types of CT all arise from embryonic mesenchyme
Functional characteristics of connective tissues depend primarily on the extracellular matrix, which is often highly specialized, and not on the cells.
Connective Tissues
Common cells Fibers
Fibroblasts / Fibrocytes Collagen Adipocytes ElasticMast cells ReticularPlasma cellsMacrophagesLymphocytes (many others)
How those cells and fibers are arranged determines the specific type of connective tissue
Connective Tissues
Ordinary connective tissues
Specialized connective tissues
Loose (areolar) connective tissueAdipose connective tissueReticular connective tissueElastic connective tissueDense regular connective tissueDense irregular connective tissue
BloodBoneCartilage
Specialized Connective Tissues: Cartilage
Hyaline Cartilage Elastic Cartilage
Fibrous Cartilage
More detail on cartilages and their cells when we discuss the skeletal system
Specialized Connective Tissues:
Bone
Blood
More detail on these tissues and their cells when we discuss the skeletal and circulatory systems
Muscle Tissue:
Skeletal Muscle
Cardiac Muscle
Smooth Muscle
Striated
NonstriatedInvoluntary
Voluntary
Very longUnbranched
ShorterBranched
ShortUnbranchedSpindle-shaped
Hundreds per cellPeripheral
One or two per cellCentral
One per cell
Central
Yes Yes No
Skeletal Cardiac Smooth Muscle Muscle Muscle
Myocytes
Nuclei
Striations
Skeletal
Cardiac
Smooth
More detail on muscle tissues and their cells when we discuss the muscular system