Tissues
Classification of Tissues
In the body, cells depend on each other to maintain homeostasis
If a small group of cells fail, will be hazardous to homeostasis
Failure of cells can cause the whole body to shut down
Cell specialization is positive aspect because it allows the body to divide labor
and work more efficiently
Tissues: groups of cells that are similar in structure and function
4 types: epithelium, connective, nervous, muscle
Each tissue type has a distinct structure and function
Each tissue can be further subdivided into subcatagories
Organs: organized tissues that perform specific body functions
Usually contains several types of tissues
The arrangement of tissues determines the organ’s structure and function
Histology: the study of tissues
Provides the basis for the study of physiology
Epithelial Tissue (epithelium): covers surfaces
Includes endocrine and exocrine glands because they develop from epithelial
tissues
Functions: protection, absorption, filtration, excretion, secretion, sensory
reception
Distinguishing Characteristics
1. cellularity and specialized contacts: cells form membranes or sheets of
cells and are bound together by specialized junctions
2. polarity: membranes have one free surface called the apical surface
3. connective tissue support: cells are attached to a basement membrane
that is secreted by the basal lamina
4. no vascular supply: there is no blood supply to the cells themselves
Cells depend on diffusion from underlying connective tissue
5. regeneration: can easily regenerate, if receiving proper nutrients
Is one of the most important characteristics because cells are
exposed to high amounts of friction
Classifications based on arrangement:
Simple: one layer of cells attached to a basement membrane
Stratified: 2 or more layers of cells attached to a basement membrane
Classifications based on shape:
Squamous: scalelike
Cuboidal: cubelike
Columnar: column shaped
Types that do not fit classification
Pseudostratified epithelium: is actually simple columnar, but the cells vary
in height and the nuclei lie at different levels above the
basement membrane
Gives a false appearance of being stratified
Is often ciliated
Transitional epithelium: type of stratified squamous
Made up of rounded cells with the ability to stretch and slide over
each other, giving the organ the ability to stretch
Only found in the bladder
2 types of glands:
Endocrine: are ductless glands because they have no opening to the
external surface
Secretions are all hormones
All secretions go straight into the blood or lymph vessels
Exocrine: have ducts/openings to the external surfaces
Include sweat and oil glands, liver and pancreas
Connective Tissue: found in all parts of the body
Is the most abundant and widely distributed of all the tissue types
Connective Tissues:
Functions: protection, support, binding together of other tissues
Areolar Connective Tissues: a general type of connective tissue that cushions and
protects organs
Adipose: type of areolar tissue that provides insulation for the body and is
a source of stored food
Hematopoietic: type of areolar tissue that is the site of red blood cell
production and repair of other tissues
Characteristics of connective tissues:
1. have a good blood supply
Exceptions: cartilage, tendons, and ligaments
2. are made up of many types of cells
3. has a lot of noncellular, nonliving material within and between the cells
Components of connective tissue cells:
Ground substance: made mainly of interstitial fluid, cell adhesion proteins,
and proteoglycans
Depending on the tissue in which you find it, can range from liquid
to very hard
When hard, the cells are found in cavities called lacunae
Functions: filter through which substances can diffuse between
capillaries and cells
Collagen Fibers: provide support
Sometimes called white fibers because light color
Are the most abundant
Elastic Fibers: provide support and allow for movement
Reticular Fibers: provide support
4 Main types of adult connective tissue:
1. Connective tissue proper: includes areolar, adipose, reticular, and dense
connective tissue
2. Cartilage
3. Bone
4. Blood
All arise from the embryonic tissue called mesenchyme.
Muscle Tissue: highly specialized tissue that contracts and produces body movements
Cells are long which gives a long axis for contraction
3 Basic Types:
1. Skeletal muscle: is attached at the skeleton
Is under voluntary control
Moves the limbs and other external body parts
The cells are long, round, multinucleate and have striations
2. Cardiac muscle: is found only in the heart
Has striations, but only one nucleus
The cells meet at intercalated discs that allow the cells to work
together
Is involuntary
3. Smooth muscle: found in the walls of the hollow organs
Has two layers that run at right angles to each other
No striations
Have one nucleus
Nervous Tissue: 2 major cell populations
Neuroglia: supporting cells
Protect, support, insulate, etc.
Neurons: specialized cells that receive stimulus
Send messages all over the body
Have one nucleus