Transcript Chapter 4- Tissues/Histology

Chapter 4: Tissues
Anatomy 32
A tissue is composed of a group of cells with similar structure that perform
related functions and are surrounded by extracellular material (non-living). The
four different tissue types can be associated with a general function: epithelial
for covering, connective for support, muscle for movement, and nervous for
control.
I. Epithelia and Glands- Epithelial tissue serves as a lining for organs that
have an opening to the environment. It has several functions: boundary
layer, interface layer, protection, transport such as secretion and
absorption.
A.
Special Characteristics of Epithelia- because every tissue type has
a specific function and structure, each as distinguishing
characteristics
1. Cellularity- dense cell areas, multiple points of connection between
cells, few extracellular matrix material.
2. Specialized contacts- multiple cell junctions tightly connect
neighboring cells.
3. Polarity- each cell has a distinguishable apical (top) and basal
(bottom) side The nuclei tend to be towards the basal side. The cells
are anchored at the basal side by basal lamina which is part of the
basement membrane.
4. Support by connective tissue- an underlying layer of connective
tissue supports epithelial tissue.
5. Avascular but innervated- blood vessels to not cross into epithelial
tissue but nerve ending do.
6. Regenetration- because they line organs epithelial cells are
exposed to many conditions that destroy the cells, thus they have a
great ability to regenerate quickly.
Lateral Cell Junctions
b. Classification of Epithelia- this tissue
is identified by two names one describes
cell layers and the other the shape.
1. Simple epithelia- a single layer of epithelia is called simple epithelia,
it is design to allow molecules to cross the membrane quickly, such as in
the capillaries and lungs.
i. Simple squamous epithelia- a flat layer of cells. Endothelium
produces a slick slippery surface. Mesothelium serves as a
middle covering as part of serosa found in body cavities.
• Simple cuboidal epithelia- a layer of cube
like cells, their height and width are just
about equal. It form gland ducts and tubules.
•iii. Simple columnar epithelium- a layer of tall cells that line the
digestive tract. It functions in absorption, secretion, and ion
movement, some as cilia in their apical side.
iiii. Pseudostratified Columnar Epithelium- a single layer with cells of
different heights which makes it appearing as if there are different
layers. Short cells are undifferentiated and give rise to tall cells. Tall
cells function in secretion and absorption.
2. Stratified epithelia- two or more layers of cells, cells rise from basal
side, main function is protection.
i. Stratified squamous epithelium- many layers of cuboidal or
columnar cells with squamous cells at the surface. It is the best for
protection and lines areas that are often-abraded. They make up the
skin and MAY OR MAY NOT have keratin.
ii. Stratified cuboidal and columnar epithelium- rare and forms
only large ducts of glands.
iii Transitional epithelium- lines hollow urinary organs and has the
ability to stretch from six to three cells thick.
What type of tissue is found in
endothelium?
c.
Epithelial Surface Features- each side of the cells has a
special feature.
1. Apical Surface Features: Microvilli and Cilia- are
extensions on the apical side that increase surface areas.
They can move to push substances in a certain direction.
2. Lateral Surface Features: Cell Junctions-cells are held
together by proteins that attach lateral cell surfaces. Gap
junctions are special openings that allow substances to flow
from cell to cell. Desmosomes are proteins that support and
link two different cell walls. Tight junctions also attach cell
surfaces but use a different structure than desmosomes.
3. Basal Surface Features: The Basal Lamina- thin
noncellular support sheet made up of proteins, controls what
enters epithelium, assist in regeneration. Below basal lamina is
the basal membrane which is thicker.
Lateral Cell Junctions
d.
Glands- groups of epithelial cells that make and secrete a
substance. Glands may be unicellular or multicellulaer.
1. Exocrine Glands- substances like mucus, sweat, and saliva are
secreted onto body surfaces or cavities. Multicellular exocrine glands
have ducts and can be classified by the number and arrangement of
the ducts (see page 79).
2. Endocrine Glands- have no ducts, secrete hormones into the
blood stream.
II. Connective Tissue- this tissue type is the most abundant and diverse. It
has cells separated by a large amount of nonliving extracellular matrix.
All cells originate from embryonic tissue called mesenchyme and do
not have an apical or basal side. There are four main types of tissue:
connective tissue proper, cartilage, bone, and blood. Table 4.2
summarizes and compares the different types of connective tissue.
Mesenchyme gives rise to all types of connective tissue.
The four basic functions of
connective tissue are:
1. Support and bind other
tissues- ligaments and
tendon support joints and
attach bone to bone and
muscle to bone
2. Hold body fluids- blood
contains plasma which holds
a high percentage of water
3. Defends the body against
infection- immune system
cells arise from mesenchyme
and are found in many
different types of connective
tissue.
4. Store nutrients- adipose cells
store fat, bone cells store
calcium.
a. Connective Tissue Proper- forms the supportive framework of
different organs and is made up of the following main components
fibers, ground substance, immune cells, and adipose cells. A great
example or connective tissue proper is areolar connective tissue.
Areolar Tissue: A Model Connective Tissue- most abundant type,
supports and binds other tissues, holds fluids, stores nutrients and
defends against infection (see page 85). The fibers are created by cells
called fibroblast.
1. Fibers: Collagen fibers are the strongest and withstand pulling.
Reticular fibers are bundles of collagen fibrils forming a
network for support.
Elastic fibers are long and thin and form wide networks within
extracellular matrix, allow tissues to reshape when stretched
2. Ground substance: this is a jelly-like substance that holds
interstitia fluid (tissue fluid). It allows materials to cross to and
from capillaries because areolar connective tissues lies between
capillaries and other tissues.
3. Defense cells: these are immune system cells that help in
preventing disease causing organisms to enter the blood stream.
Know the cells in general: Macrophages are “big eaters” that
engulf (phagocytic) foreign materials, Plasma cells secrete
antibodies (proteins that destroy cells), mast cells cause
inflammation, neurtophils, lymphocytes, and eosinophils go to
infected areas and phagocytoze bacteria
4. Fat cells: also called adipose cells hold fat
(nutrient), they are large cells and doesn’t divide.
• Connective Tissue Proper
b. Other Loose Connective Tissues- these are connective tissues that
resemble areolar connective tissue.
1. Adipose
Tissue- 90% fat cells (white adipose), highly
vascularized, found below skin and mesenteries, cushions kidneys and eyes.
In babies brown adipose keeps them warm.
2. Reticular connective- only has reticular fibers in the matrix that
forms a supportive mesh. Found in bone marrow, spleen, and lymph
nodes
c.
Dense Connective Tissue- contains a high percentage of collagen.
1. Irregular dense connective tissue has thick collagen fibers
running in different planes, it is found in the dermis and capsules around
organs.
2. Regular dense connective tissue have fibers that run parallel to the pull
direction, poorly vascularized, makes up tendons and ligaments, high amount
of elastic fibers.
d. Other Connective Tissues: Cartilage, Bone, and Blood- connective tissue
types that resist compression.
1. Cartilage- firm but flexible, high tissue fluid, no blood or nerves,
has chondrocytes and chondroblasts . There are three types of cartilage:
Hyaline, Elastic, and Fribrocartilage.
2. Bone Tissue- highly supportive and protective, matrix has inorganic salts,
high collagen fiber content, has osteocytes
3. Blood- most unusual connective tissue, develops from mesenchyme cells
and has plasma (nonliving matrix). It transport nutrients and cell
III. Muscle Tissue- involved in body movement because cells are capable
of contraction, contains myofilaments (muscle filaments), there are three
types.
a. Skeletal muscle- attatches to bones, striated, multiple nucleic cells
III. Muscle Tissue- involved in
body movement because
cells are capable of
contraction, contains
myofilaments (muscle
filaments), there are three
types.
a. Skeletal muscleattatches to bones, striated,
multiple nucleic cells
b. Cardiac muscle-makes the heart, striated, single nucleated cells, involuntary,
pumps blood.
b. Cardiac musclemakes the heart,
striated, single
nucleated cells,
involuntary,
pumps blood.
•c. Smooth muscle- lines organs, no striations, spindle shaped cells,
involuntary, moves substances inside the body.
• c. Smooth
muscle- lines
organs, no
striations,
spindle
shaped cells,
involuntary,
moves
substances
inside the
body.
IV.
Nervous Tissue- makes
up the brain, spinal cord,
and nerves that innervate
the body. Some nervous
system cells have the
ability to create electrical
impulses and stimulate
other tissue.
a. Neurons- nerve cells
that extend long
distances and can
send an impulse to
activate a cell. These
control body function.
b. Glial- nerve cells that
form supportive
structures, insulate,
and nourish neurons.
These cells come in
direct contact with
neurons but do not
control body function
V.
Tissue Response- Mechanisms such as a skin
layer, secretion of mucus, and tears assist in
protection against invading organism. However, when
an injury occurs that breaks the skin, the physical
barrier is removed. The tissue reacts by using
inflammation and a immune response to protect the
body.
a.
b.
Inflammation- when tissue is injured the damaged cells
release inflammatory chemicals that signal the blood vessels
to bring more blood. The excess blood flow causes the area
to become red and hot. The heat can serve as a general
mechanism to destroy bacteria. As fluid from blood
accumulates the area swells and the swelling causes pain
because it puts pressure on pain receptors.
An immune response takes place at this site. The chemicals
released during the injury call immune sytem cells to fight the
infection. Some cells specialize in detecting and killing
bacteria, others specialize in phagocytosis to clear off dead
cells.
b. Repair-after a scab forms
healing tissues may replace
themselves (regeneration) or
develop fibrous tissues also known
as a scar (fibrosis).
1. Tissues have different abilities
to heal: epithelia, areolar
connective tissue, fat tissue, dense
irregular connective tissue (fascia),
and blood forming tissue regerenate
readily, smooth muscle and dense
regular tissue (tendons) regenerates
moderately, skeletal muscle and
cartilage regenerate poorly, and
cardiac muscle and nervous tissue
do not regenerate.
VI The Tissue Throughout Life
Connective, endothelium and muscle = mesenchyme
mesoderm
Epithelial tissues, brain and spinal cord = embryonic
epithelium ectoderm and endoderm
Primary tissues all formed by the 2nd month and rapid
growth continues in prenatal period.
Nerve cells stop by fetal period and cell division slows
down in adult hood.
Stem cells are maintained throughout life for
regeneration. Good nutrition and circulation helps in
tissue regeneration. Tissue repair becomes less efficient
with age and bone, muscle, and nervous tissues
deregenerate.