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Physiology 2015
Tissues
Tissues:
The Cell Theory states that the cell is the basic unit of structure and function.
When a group of cells with similar structure are found together performing a
common function and possess similar extra-cellular substances located between
the cells the result is a tissue. The microscopic study of tissue structure is called
histology, which you have been and will continue to cover in lab.
Our objective for this unit - is to discuss how the structure of specific tissues,
(and the cells that comprise the tissue) relate to the tissue’s function as well as
the growth, aging and trauma of tissues and the changes that occur.
The four basic tissue types are:
A. Epithelium or epithelial is found throughout the body where it covers
internal and external surfaces. It also forms most of our glands.
a. Common features – most epithelial tissue posses the following
characteristics
i. Very little extra-cellular matrix between cells.
ii. Free surface – side of cells not in contact with other cells
iii. Basement membrane –
1. attaches epithelial cells to underlying tissues
2. produced by the epithelial cells and the underlying cells
3. composed of carbohydrates and proteins
b. General Functions of Epithelial Tissue
i. Protecting underlying structures – epithelium of the oral
cavity protects the underlying structures from abrasion
ii. Acting as barriers – prevents the movement of many
substances through, i.e. the skin acts as a barrier to water and
prevents the water loss from the body.
iii. Permitting the passage of substances – allows the
movement of certain substances through. i.e. oxygen and
carbon dioxide are exchanged between the air and blood by
diffusion through the epithelium in the lungs
iv. Secreting substances – examples are sweat and mucus
glands
v. Absorbing substances – epithelial in the intestinal tract
absorb digested nutrients, vitamins and ions
c. Classification/Types of Epithelia (refer to your coloring packet)
Number of Layers
Simple – one layer
Cell Shape
Squamous
Cuboidal
Columnar
Pseudostratified (modified form of simple)
Columnar
Stratified – more than one layer
Squamous –
Keratinized – outer skin layer with a
layer of dead cells – dry
Non – keratinized – found in the
mouth – moist and protects
against abrasion
Transitional (modified form of stratified)
Cuboidal to columnar when NOT stretched
i.e.empty bladder
Squamous-like when stretched – i.e. full
bladder
d. Structural and Functional Relationships
i. Cell Layers and Shapes – the number of cell layers and the
shapes of the cells reflect the function that they perform
1. Two important functions based on number of layers
a. controlling passage of materials through
i. Simple epithelium (single layer) found in
tissues in which the main function is
movement of materials as in diffusion of
gases or nutrients
b. protecting the underlying tissues
i. Stratified epithelium (more than one
layer) adapted for protective function.
As outer cell layers are damaged they
are replaced by the cells at the deeper
layers.
2. Functions differ based on cell shape
a. Cells that are flat and thin deal with diffusion,
for example the cells that make up the alveoli in the
lungs
c. Cuboidal or columnar cells deal with
secretion and absorption. These cells are
larger and contain more organelles that also
reflect the function.
i. For example – the stomach is lined with
simple columnar epithelium, which
contains many secretory vesicles filled
with mucus. When released the mucus
protects the stomach lining from the
digestive enzymes and acid.
3. Shape and Number of layers can change
a. if cells are subjected to long term irritation or
other abnormal conditions.
ii. Cigarette smokers – pseudostratified
ciliated epithelium which produces
mucus and helps to clean out
respiratory tract is replaced by stratified
squamous epithelium that is more
resistant to irritation, but does not
perform cleaning functions.
1. Lung cancer can result from the
changes in the epithelial tissue
ii. Free Cell Surfaces – epithelia have a free surface, which is
not in contact with other cells and lies away from underlying
tissues. The special features found on the free surface reflect
their function.
1. Smooth surfaces – reduce friction as in blood vessels
2. Microvilli – increase cell surface area as seen in the
intestine for absorption and secretion
3. Cilia – move material along the surface of the cells as
in the nasal cavity and trachea, usually with the aid of
mucus produced by specialized cells called goblet cells
B. Connective Tissue is a diverse group of tissues ranging from a liquid (blood)
to semi solid (cartilage) to a solid (bone). All of these tissue posses a
common characteristic, a large amount of extra-cellular material (matrix) that
separates the cells.
a. Common Structural Features –
i. Extra-cellular material has 3 major components
1. protein fibers – 3 types
a. collagen – resemble microscopic ropes, are
flexible but resist stretching
b. reticular – short collagen fibers that branch to
form a support network
c. elastic – fibers with the ability to recoil to
original shape after having been stretched
2. ground substance – shapeless, colorless background
in which the protein fibers and cells sit
a. made of a protein called prosteoglycan (protein
with a polysaccharide attached)
3. water
a. large amounts of water are trapped between
the polysaccharides of the prosteoglycan
molecule
ii. connective tissue cells are named by their function
a. -blast cells produce matrix
b. -cyte cells maintain the matrix
c. -clast cells break down the matrix
b. Functions of Connective Tissue – due to the diversity of cell structure
within this tissue category, there is also functional diversity. Here are
the major categories of function.
i. Enclosing and separating – sheets form capsules that cover
organs and layers that separate tissues and organs – i.e.
separation of muscles, blood vessels and nerves from on
another
ii. Connecting tissues to one another – example tendons connect
muscle to bone and act as strong cables.
iii. Supporting and moving – bones are rigid support for the body
and cartilage, which is semi rigid, supports the nose, ear and
joint surfaces. Joints allow one part of the body to move
relative to another
iv. Storing – many of the connective tissues are reservoirs for
minerals and ions needed for metabolic reactions. Bones
store calcium and phosphate, while adipose tissue stores high
energy molecules.
v. Cushioning and Insulating – adipose tissue cushions and
protects many of the organs, for example the kidneys and the
heart and provides and insulation layer under the skin that
helps to conserve heat.
vi. Transporting – blood transports a number of materials
throughout the body including oxygen and enzymes,
hormones and cells of the immune system.
vii. Protecting – Bones protect underlying structures, for example
the rib cage and immune system cells protect the body from
toxins and bacterial infection.
c. Classification/Types of Connective Tissues and where they are found
C. Muscle Tissue - is responsible for the movement of the internal organs and
the framework of the body due to its special property the ability of contraction.
1. 3 types of muscle
___________________
____________________
_______________________
a. Skeletal muscle
i.
ii.
iii.
iv.
v.
Meat of animals and what you eat
Makes up 40 % of a person’s body weight
Attaches to the skeleton
Enables body movement
Muscle cells are long, cylindrical and have several
nuclei per cell
vi. Striated or striped due to the banding patterns of the
muscle protein (actin and myosin) fibers
vii. Voluntary
b. Cardiac muscle
i. Muscle of the heart (myocardium) and responsible for
pumping blood
ii. Involuntary (unconscious) control
iii. Striated, with one nucleus per cell
iv. Specialized gap junctions present called intercalated
discs – allows for fast spread of bio-electrical signal
c. Smooth Muscle
i. Forms the walls of hollow organs (except the heart)
ii. Found also in skin and eyes
iii. Involuntary
iv. Tapered at each end, one nucleus and not striated
D. Nervous System – Nerve tissue is responsible for controlling and
coordinating many bodily activities. Many of these functions depend on the
ability of the nervous tissue cells to communicate with one another and with
other cells by electrical signals called action potentials.
1. composed of neurons and support cells
a. neurons or nerve cell
i. responsible for the conduction of the action potential
ii. made of 3 parts
1. cell body (soma)
2. dendrites
3. axons
b. support cells called neuroglia
i. do not conduct electrical impulses
ii. function to nourish, protect and insulate the neurons
iii. form myelin sheath around axon of cell
1. gaps in myelin sheaths called Nodes of Ranvier
serve as sites for accelerating an impulse
2. 3 categories of nerve cells
a. Sensory neurons
i. Found in eyes, ears, surface of skin
ii. Receive information about the body’s condition and the
external environment
b. Motor neurons
i. Found in brain and spinal cord
ii. Conducts impulses out of central nervous system
towards muscles and glands and stimulates them
c. Interneurons
i. Found in brain and spinal cord
ii. Integrate information – conducts information between
neurons within the central nervous system
II:
Tissue Inflammation, Repair, Aging and Death
A. Tissue Inflammation – a consequence of injury; is a body’s response to
maintain homeostasis when tissues are damaged. Inflammation mobilizes
the body’s defenses, isolates and destroys microorganisms, foreign materials
and damaged cells so that tissue repair can proceed.
a. five major responses/symptoms
a. heat
b. redness
c. pain
d. swelling
e. disturbance of function
b. responses initiated by release of chemicals called mediators of
inflammation which act on injured tissue and associated blood vessels
a. histamine – causes vessels to dilate and become more
permeable
i. produce responses of redness and heat
ii. also allow materials and blood cells to move out of the
blood vessels and into the damaged tissue with its
antibodies, oxygen and clotting factors
b. pain is caused by either
i. nerve cell endings are directly damaged
ii. as a consequence of fluid accumulation (edema) from
the vessels with increased permeability
c. pain, limitation of movement due to the edema, and tissue
destruction all contribute to disturbance of function
E. Tissue Repair - the substitution of viable cells for dead ones; can be
achieved by regeneration or replacement and is determined by the type of
tissues and severity of the wound.
a. Regeneration – new cells are the same type as those that were
destroyed and normal function resumes
b. Replacement – new type of tissue develops that causes scar
(accumulation of connective tissue) production and the loss of some
tissue function - usually occurs when the wound is severe
F. Tissue Aging – some changes are obvious while others subtle.
a. Affect cells and the extra-cellular matrix produced by those cells
b. Cells divide more slowly as one ages
c. Collagen fibers become more irregular in structure, even though they
increase in number.
i. As a result, tissues with collaged (i.e. tendons) become less
flexible and more fragile
d. Elastic fibers fragment and bond to calcium ions and become less
elastic
e. Reduced flexibility and elasticity are causes of wrinkles as well as
increased tendency for bones to break