Download Loose Connective Tissues

Chapter 4
The Tissue Level
of Organization
Copyright © John Wiley & Sons, Inc. All rights reserved.
Tissues

Tissues are a group of cells with a common embryonic
origin that function together to carry out specialized
activities.
 They include various types,
ranging from hard (bone)
to semisolid (fat) to
liquid (blood).
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Tissues

Histology is the study of the microscopic anatomy of
cells and tissues.

Of the 10 trillion cells in our body, no single cell type
can said to be “typical”. A trained histologist can
recognize over 200 distinct human cell types under the
microscope and is able to distinguish a cell from
pancreatic tissue as opposed to a cell from the skin.
• Each cell type has features particular to its function.
Copyright © John Wiley & Sons, Inc. All rights reserved.
Intercellular Junctions

Tissues are formed by
grouping cells together using
a variety of Intercellular
Junctions .
 Intercellular Junctions
connect adjacent cells
mechanically at the cell
membranes or through
cytoskeletal elements
within and between cells.
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Intercellular Junctions

Tight Junctions are found where a leakproof seal is
needed between cells.
 They keep materials from leaking out of organs like
the stomach and bladder.
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Intercellular Junctions

Adherens Junctions make an adhesion belt (like the belt
on your pants) that keeps tissues from separating as they
stretch and contract like in the intestines.

Cadherin is a glycoprotein
that forms the belt-like
“plaque”.
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Intercellular Junctions

Desmosomes act as “spot welds” to prevent separation
under tension. They also use cadherin glycoprotein
(plus intermediate filaments) to hook into the cytoplasm.

Common in epidermis
and cardiac muscle.
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Intercellular Junctions

Hemidesmosomes are half-welds that join cells to the
basement membrane.
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

Intercellular
Junctions
Gap Junctions have pores
(connexons) that allow
small substances like ions
to pass between cells. If
one of the cells gets sick
or dies, these seal like a
hatch to prevent damage
to other cells.
Allow nerve and muscle
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The 4 Basic Tissues

Connective tissues (C.T.) protect, support, and
bind organs.
 Fat is a type of C.T. that stores energy.
 Red blood cells, white blood cells, and
platelets are all C.T.
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The 4 Basic Tissues

Muscular tissues generate the physical force needed to
make body structures move. They also generate heat
used by the body.

Nervous tissues detect changes in the body and respond
by generating nerve impulses.
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The 4 Basic Tissues

Of all the cells in the body, they combine to make only 4
basic tissue types:
 Epithelial tissues
 Connective tissues
 Muscular tissues
 Nervous tissues
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The 4 Basic Tissues

Epithelial tissues cover body surfaces and form glands
and line hollow organs, body cavities, and ducts.
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Epithelium

Epithelium is used to line surfaces and form protective
barriers. Epithelium is also good at secreting things like
mucous, hormones, and
other substances .

All epithelia have a
free apical surface
and an attached
basal surface.
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Epithelium

The basal layer of the epithelium secretes a basal lamina;
the underlying C.T. secretes a reticular lamina.
 Together the basal
lamina and the reticular
lamina form a non-
cellular basement
membrane on which
the epithelium sits.
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Epithelium

Epithelia are named according to the shape of their
cells, and the thickness or arrangement of their layers
(of cells).
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Epithelium
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Epithelium

Naming epithelia according to shape
Flat, wide “paving stone”
cells
Cells as tall as they are wide
Cells taller than they are
wide
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Epithelium

Naming epithelia according to arrangement
One layer. All cells in
contact with basement
membrane
Appears to have layers, but in
reality all cells go from the
apex to the base
Two or more layers. Only
basal layer in contact with
basement membrane
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Epithelium

Simple Squamous Epithelium is composed of a single
layer of flat cells found:
 In the air sacs of lungs
 In the lining of blood
vessels, the heart, and lymphatic vessels
 In all capillaries
 As the major part of a
serous membrane
simple squamous
pseudostratified squamous
stratified squamous
simple cuboidal
pseudostratified cuboidal
stratified cuboidal
simple columnar
pseudostratified columnar
stratified columnar
transitional
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Epithelium

Simple Cuboidal Epithelium is composed of a single layer
of cube shaped cells.
 It is often found lining
the tubules of the
kidneys and many
other glands.
simple squamous
pseudostratified squamous
stratified squamous
simple cuboidal
pseudostratified cuboidal
stratified cuboidal
simple columnar
pseudostratified columnar
stratified columnar
transitional
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Epithelium

Simple Columnar Epithelium forms a single layer of
column-like cells, ± cilia, ± microvilli, ± mucous (goblet
cells). Found in entire gastrointestinal tract
 Goblet cells are simple
columnar cells that
have differentiated to
acquire the ability to
secrete mucous.
simple squamous
pseudostratified squamous
stratified squamous
simple cuboidal
pseudostratified cuboidal
stratified cuboidal
simple columnar
pseudostratified columnar
stratified columnar
transitional
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
Epithelium
Pseudostratified Columnar Epithelium appears to have
layers, due to nuclei which are at various depths. In
reality, all cells are attached to the basement
membrane in a single
layer, but some do not
extend to the apical surface..
Found in respiratory tract

Ciliated tissue has
goblet cells that
simple squamous
pseudostratified squamous
stratified squamous
simple cuboidal
pseudostratified cuboidal
stratified cuboidal
simple columnar
pseudostratified
columnar
stratified columnar
transitional
secrete mucous.
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Epithelium

Stratified Squamous Epithelium has an apical surface that
is made up of squamous (flat) cells.
 The other layers have different
shapes, but the name is based
on the apical layer.
 The many layers are ideal for
protection against
strong friction
forces.
simple squamous
pseudostratified squamous
stratified squamous
simple cuboidal
pseudostratified cuboidal
stratified cuboidal
simple columnar
pseudostratified columnar
stratified columnar
transitional
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Epithelium

Stratified Cuboidal Epithelium has an apical surface made
up of two or more layers of cube-shaped cells.
 Locations include the sweat
glands and part of the
male urethra

Stratified Columnar Epithelium is very rare
 Lines esophageal glands
and part of anal mucous
membrane
simple squamous
pseudostratified squamous
stratified squamous
simple cuboidal
pseudostratified cuboidal
stratified cuboidal
simple columnar
pseudostratified columnar
stratified columnar
Copyright © Johntransitional
Wiley & Sons, Inc. All rights reserved.
Epithelium

The cells of Transitional Epithelium change shape
depending on the state of stretch in the tissue.
 The apical “dome cells” of
the top layer (seen here in
relaxation) are an
identifiable feature and
signify an empty bladder.
 In a full bladder, the
cells are flattened.
simple squamous
pseudostratified squamous
stratified squamous
simple cuboidal
pseudostratified cuboidal
stratified cuboidal
simple columnar
pseudostratified columnar
stratified columnar
transitional
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Epithelium

Although epithelia are found throughout the body,
certain ones are
associated with specific
body locations.
 Stratified squamous
epithelium is a
prominent feature
of the outer layers
of the skin.
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Epithelium
 Simple squamous makes up epithelial membranes and lines
the blood vessels.
 Columnar is common in the digestive tract.
 Pseudostratified ciliated
columnar is characteristic
of the upper respiratory tract.
 Transitional is found in
the bladder.
 Cuboidal lines ducts and
sweat glands.
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
Tissues of the body develop from three primary germ
layers: Endoderm, Mesoderm, and Ectoderm
 Epithelial tissues from
all three germ layers
 C.T. and muscle are
derived from mesoderm.
 Nervous tissue
develops from
ectoderm.
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Covering and Lining Epithelium

Endothelium is a specialized simple squamous
epithelium that lines the entire circulatory system from
the heart to the smallest capillary – it is extremely
important in reducing turbulence of flow of blood.

Mesothelium is found in serous membranes such as the
pericardium, pleura, and peritoneum.
 Unlike other epithelial tissue, both are derived from
embryonic mesoderm (the middle layer of the 3
primary germ layers of the embryo).
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Connective Tissue

Connective Tissues are the most abundant and widely
distributed tissues in the body – they are also the most
heterogeneous of the tissue groups.
 They perform numerous functions:
• Bind tissues together
• Support and strengthen tissue
• Protect and insulate internal organs
• Compartmentalize and transport
• Energy reserves and immune responses
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Connective Tissues

Collagen is the main protein of C.T. and the most
abundant protein in the body, making up about 25% of
total protein content.

Connective tissue is usually
highly vascular and supplied
with many nerves.
 The exception is cartilage and
tendon - both have little or no
blood supply and no nerves.
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Connective Tissues

Although they are a varied group, all C.T. share a
common “theme”:
 Sparse cells
 Surrounded by an extracellular matrix

The extracellular matrix is a non-cellular material
located between and around the cells.
 It consists of protein fibers and ground substance (the
ground substance may be fluid, semifluid, gelatinous,
or calcified.)
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Cells Of Connective Tissues

Common C.T. cells
 Fibroblasts are the most numerous cell of connective
tissues. These cells secrete protein fibers (collagen,
elastin, & reticular
fibers) and a
“ground substance”
which varies from
one C.T. to another.
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Cells of Connective Tissues

Of the other common C.T. cells:
 Chondrocytes make the various cartilaginous C.T.
 Adipocytes store triglycerides.
 Osteocytes make up bone.
 White blood cells provide immune response.
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Connective Tissues

There are 5 types of white blood cells (WBCs):
 Macrophages are the “big eaters” that swallow and
destroy invaders or debris. They can be fixed or
wandering.
 Neutrophils are also macrophages (“small eaters”) that
are numerous in the blood.
 Mast cells and Eosinophils play an important role in
inflammation.
 Lymphocytes secrete antibody proteins and attack
invaders.
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Connective Tissues

C.T. cells secrete 3 common fibers:
 Collagen fibers
• Strong and tension resistant
• Usually found in parallel bundles
• Found in most connective tissues but very abundant
in dense regular, bone, and cartilage
 Elastic fibers
• Can be stretched and then returned to original shape
• Found in skin, blood vessel walls, lung tissue, and
bone coverings
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Connective Tissues

Reticular fibers
 Provide support and strength
 Create a “net-like” framework that is abundant in
reticular tissue
 Thinner than collagen fibers
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Connective Tissue Classification
Outline

Embryonic connective tissue
 Mesenchyme
 Mucous connective tissue

Mature connective tissue
 Loose connective tissue
 Dense connective tissue
 Cartilage
 Bone
 Liquid
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Embryonic Connective Tissues

There are 2 Embryonic Connective Tissues:
 Mesenchyme gives rise to all other connective tissues.
 Mucous C.T. is a gelatinous substance within the umbilical
cord and is a rich source of stem cells.
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Mature Connective Tissues

Loose Connective Tissues
 Areolar Connective Tissue is the most widely distributed in
the body. It contains several types of cells and all three
fiber types.
• It is used to attach skin and underlying tissues, and as a
packing between glands, muscles, and nerves.
 Adipose
 Reticular
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Mature Connective Tissues

Loose Connective Tissues
 Loose areolar
 Adipose tissue is located in the subcutaneous layer
deep to the skin and around organs and joints.
• It reduces heat loss and serves as padding and as an
energy source.
 Reticular
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Mature Connective Tissues

Loose Connective Tissues
 Loose areolar
 Adipose
 Reticular connective tissue is a network of interlacing
reticular fibers and cells.
• It forms a scaffolding used by cells of lymphoid
tissues such as the
spleen and
lymph nodes.
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Mature Connective Tissues

Dense Connective Tissues
 Dense Irregular Connective Tissue consists
predominantly of fibroblasts and collagen fibers
randomly arranged.
• It provides strength when forces are pulling from
many different directions. Occur in sheets around
organs and in the dermis
 Dense regular
 Elastic
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Mature Connective Tissues

Dense Connective Tissues
 Dense Irregular
 Dense regular Connective Tissue comprise tendons,
ligaments, and other strong attachments where the
need for strength along one axis is mandatory (a
muscle pulling on a bone).
 Elastic
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Mature Connective Tissues

Dense Connective Tissues
 Dense Irregular
 Dense regular
 Elastic Connective Tissue consists predominantly of
fibroblasts and freely branching elastic fibers.
• It allows stretching of certain tissues like the elastic
arteries (the
aorta).
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Mature Connective Tissues

Cartilage is a tissue with poor blood supply that grows
slowly. When injured or inflamed, repair is slow.
 Hyaline cartilage is the most abundant type of
cartilage; it covers the ends of long bones and parts of
the ribs, nose, trachea, bronchi, and larynx.
• It provides a smooth surface for joint movement.
 Fibrocartilage
 Elastic cartilage
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Mature Connective Tissues

Cartilage
 Hyaline cartilage
 Fibrocartilage, with its thick bundles of collagen fibers,
is a very strong, tough cartilage.
• Fibrocartilage discs in the intervertebral spaces and
the knee joints support the huge loads up and down
the long axis
of the body.
 Elastic cartilage
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Mature Connective Tissues

Cartilage
 Hyaline cartilage
 Fibrocartilage
 Elastic cartilage consists of chondrocytes located in a
threadlike network of elastic fibers.
• It makes up the malleable part of the external ear and
the
epiglottis.
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Mature Connective Tissues

Cartilage
 Two types of growth
• Interstitial – from within
• Appositional – growth from outer surface
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Mature Connective Tissues

Bone is a connective tissue with a calcified intracellular
matrix. In the right circumstances, the chondrocytes of
cartilage are capable of turning into the osteocytes that
make up bone tissue.
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Mature Connective Tissues

Blood and lymph are atypical liquid connective tissues.
As we have seen, blood has many cells. It also has fibers
(such as fibrin that makes blood clot).
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Summary of Mature Connective Tissues
Muscle and Nerve Tissues

Muscles and nerve tissues are the last of the 4 basic
tissue types.

Neurons and muscle fibers are considered excitable cells
because they exhibit electrical excitability, the ability to
respond to certain stimuli by producing electrical signals
such as action potentials.
 Action potentials can propagate (travel) along the
plasma membrane of a neuron or muscle fiber due to
the presence of specific voltage-gated ion channels.
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Muscle Tissue

Skeletal Muscle
 Under voluntary control
 Attached to bones via tendons
 Functions: Provide motion, heat production,
protection, posture
 Multi-nucleated
 Contains long, cylindrical fibers that are striated
• Striations – alternating light and dark bands (stripes)
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Skeletal
muscle
Skeletal muscle
fiber (cell)
Nucleus
Striations
LM 400x
Longitudinal section of skeletal muscle tissue
Skeletal muscle fiber
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Muscle Tissue

Cardiac Muscle
 Under involuntary control
 Found in the heart wall
 Function: Pump blood to the body
 Usually one nucleus per cell
 Has branched, striated fibers with intercalated discs
• Intercalated discs – help hold the tissue together
under a lot of stress and allow for quick electrical
signals
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Nucleus
Cardiac
muscle fiber
(cell)
Intercalated
disc
Heart
Striations
LM 500x
Longitudinal section of cardiac muscle tissue
Cardiac muscle fibers
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Muscle Tissue

Smooth Muscle
 Under involuntary control
 Found in the walls of hollow structures like blood
vessels and intestines
 Function: Motion
 One nucleus per cell
 No visible striations
 Cells are tapered at each end
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Smooth
muscle
Smooth muscle
fiber (cell)
Nucleus of
smooth
muscle fiber
Artery
LM 500x
Longitudinal section of smooth muscle tissue
Smooth muscle fiber
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Nervous Tissue

Consists of Neurons (nerve cells) and neuroglia (support
cells)

Neurons transmit nerve impulses throughout the body.
We will talk about this in much more detail later in the
year.
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Dendrite
Nucleus of
neuroglial
cell
Nucleus in
cell body
Spinal
cord
Axon
LM 400x
Neuron of spinal cord
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Muscle and Nerve Tissues
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Epithelial Membranes

Combining two tissues creates an organ. However, most
of the organs and all of the organs systems studied this
year contain all 4 basic types of tissues.
 Epithelial membranes are the simplest organs in the
body, constructed of only epithelium and a little bit of
connective tissue.
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Epithelial Membranes

Epithelial membranes = epithelium + connective tissue
 Mucous membranes
 Serous membranes
 Cutaneous membrane = skin
• Skin is not a simple organ
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Epithelial Membranes

Mucous membranes line “interior” body surfaces open
to the outside:
 Digestive tract
 Respiratory tract
 Reproductive tract

Serous membranes line some internal surfaces:
 Parietal layer next to body wall
 Serous fluid between layers
 Visceral layer next to organ
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Synovial Membranes

Synovial membranes enclose certain joints and are
made of connective tissue only.
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Glands

Epithelial glands are another example of simple organs
 Glands that secrete their contents directly into the
blood are called endocrine glands.
 Glands that secrete their contents into a lumen or duct
are called exocrine glands.
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Exocrine Glands

Exocrine glands secrete substances through ducts to the
surface of the skin or into the lumen of a hollow organ.
 Secretions of the exocrine gland include mucus, sweat,
oil, earwax, saliva, and digestive enzymes.
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Exocrine Glands

The two criteria for categorizing multicellular glands
according to structure:
 Whether the ducts are branched or unbranched…
• In a simple gland the duct does not branch.
• In a compound gland the duct branches.
 … and the shape of the secretory portion of the gland
• Tubular glands have tubular secretory parts.
• Acinar glands have rounded secretory parts.
• Tubuloacinar glands have features of both.
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Exocrine Glands
unbranched
duct
(simple)
branched duct
(compound)
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Exocrine Glands
tubular shape in
secretory portion
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Exocrine Glands
acinar or alveolar
(grape-like) shape
in secretory
portion
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Exocrine Glands

The criteria for categorizing multicellular glands
according to function is based on the manner in which
the gland secretes its product from inside the cell to the
outside environment.
 Merocrine
 Apocrine
 Holocrine
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Exocrine Glands

Merocrine secretion is the most common manner of
secretion.
 The gland releases its product by exocytosis and no
part of the gland is lost or damaged .
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Exocrine Glands

Apocrine glands “bud” their secretions off through the
plasma membrane, producing membrane-bound vesicles
in the lumen of the gland.
 The end of the cell breaks off by “decapitation”, leaving
a milky, viscous odorless fluid.
 This type of sweat only develops a strong odor
when it comes into contact with bacteria on the skin
surface.
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Exocrine Glands

Holocrine secretions are produced by rupture of the
plasma membrane, releasing the entire cellular contents
into the lumen and killing the cell (cells are replaced by
rapid division of stem cells.)
 The sebaceous gland is an example of a holocrine
gland, because its secretion (sebum) is released with
remnants of
dead cells.
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Tissue Repair

A convenient way to refer to certain cells when
discussing a tissue is Parenchyma or Stroma.
 The parenchymal cells of an organ consist of that
tissue which conducts the specific function of the
organ. Cells of the stroma are everything else—
connective tissue, blood vessels, nerves.

For example: The parenchyma of the heart is cardiac
muscle cells. The nerves, intrinsic blood vessels, and
connective tissue of the heart comprise the stroma.
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Tissue Repair

Parenchyma is interesting. Because organ-specific
function usually centers on parenchymal cells (“how’s
your heart working?”), histological and physiological
descriptions of the tissues of an organ often emphasize
parenchyma.

Unfortunately, stroma is commonly ignored as just
boring background tissue. No organ, however, can
function without the mechanical and nutritional support
provided by the stroma.
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Tissue Repair

When tissue damage is extensive, return to homeostasis
depends on active repair of both parenchymal cells and
stroma.
 Fibroblasts divide rapidly.
 New collagen fibers are manufactured.
 New blood capillaries supply materials for healing.

All of these processes create an actively growing
connective tissue called granulation tissue.
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Aging and Tissues

Tissue heals faster in young adults.

Surgery of a fetus normally leaves no scars.

Young tissues have a better nutritional state, blood
supply, and higher metabolic rate.

Extracellular components also change with age.

Changes in the body’s use of glucose, collagen, and
elastic fibers contribute to the aging process.
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