CHAPTER NO.4: ANIMAL TISSUE
GENERAL ZOOLOGY (LECTURE)
BS PSYCHOLOGY | Doc. Annie Gallardo | 3rd year – Junior Year
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OUTLINE
Epithelial Tissue
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Glandular epithelium
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Germinal epithelium
Connective tissues
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Bone
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Cartilages
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Areolar
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Dense connective tissues
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Adipose tissues
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Reticular connective tissue
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Blood/vascular tissues
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Hemopoietic/Hematopoietic tissues
Muscle tissues
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Skeletal
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Cardiac
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Smooth
Nervous tissues
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Neurons
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Glial cells
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EPITHELIAL TISSUE
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ANIMAL TISSUES
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Tissues - a group of cells that are similar in
structure and function

Histology - the study of tissues
EPITHELIAL TISSUES

Sometimes simply called epithelium
Basic type of epithelial tissues based on their
shape:

Squamous epithelium
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Cuboidal epithelium
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Columnar epithelium
Cells are completely placed with one another and with
very little intercellular or cementing substance between
the cells
They cover the external surface of the body and the
internal surfaces of cavities in the body
Epithelial tissues form the covering of all body surfaces
Composed of 1 layer of cells
They are said to be simple, i.e., the simple squamous,
the simple cuboidal, and the simple columnar
Stratified epithelium can be found in several layers of
cells
Epithelial tissues give rise to most glandular structures
The major tissues found in the glands are basically
epithelial in nature and they also form parts of all the
sense organs
Special characteristics of epithelial tissues:
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They form continuous sheets
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They are provided by a basement membrane
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They are said to be vascular (not so much provided
with blood vessels)
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They are regenerating
The basic function of the epithelial tissues:
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Protection - covering the outer and inner surfaces
of the body
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Absorption - some of the epithelial tissues are
provided with cilia
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Filtration - found in glands
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Secretion - being in glands, they are glandular in nature
and are also germinal in nature (the same epithelial cells
covering, e.g., the internal surfaces of the ovary and the
testes)
Formation of reproductive cells
Types of epithelial tissues based on the number of
cell layers:
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Simple
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Stratified
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Pseudostratified
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Transitional
Types of epithelium based on the shape of cells:
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Simple squamous
o Cells are sent to be flat and irregular
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Cuboidal
o Cells are seen to be shorter but wider
o In the form of cube
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Columnar
o Cells are tall and thinner
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Simple type of epithelium
o cells are one layer only, i.e., simple
squamous, simple cuboidal, and simple
columnar
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Stratified type of epithelium
o cell layers are two or more than two layers,
i.e., stratified squamous, stratified cuboidal,
and stratified columnar
Types of epithelial tissues based on the number of
cell layers:

Squamous epithelium
o Made up of thin flat cells that resemble the
blocks
o Also known as mesothelium because they
line the silom or body cavities
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Simple squamous epithelium
o Made up of 1 layer of flattened cells
o Also known as endothelium and found in the
lining of the inner surface of blood vessels, in
the ducts of numerous glands, and lining of
the membranous labyrinth of the inner ear.
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Stratified squamous epithelium
o Made up of two or more layers of flattened
cells
o Found lining the nose and mouth cavities,
lining of the vagina, the stratum corneum of
the epidermis, in the vertebrate skin, and the
outer portion of the cornea of the eye
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Simple columnar epithelium
o Made up of cells that are much taller than
their width
o Seen to have columnar cells adhering to each
other along the longitudinal or lateral surface
(magkakatabi), and then the nucleus is
elongated but commonly basal in position
o Mostly found in the tunica mucosa of the
gastrointestinal tract; the innermost lining of
the alimentary canal, or the digestive tract,
from the stomach to the anal regio
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Stratified columnar epithelium
o Made up of several layers of columnar cells
o
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Found in the stratum germinativum of the
skin; in the innermost layer of the epiglottis,
and part of the urethra, as well as faults of the
conjunctiva of the eye
Simple cuboidal epithelium
o The height of the cells is about as tall as their
weight, so they look like cubes
o Made up of 1 layer of these cuboidal cells
o Seen in the lining of ducks, in the glands like
the thyroid gland, the kidney's tubules such
as the uriniferous tubules
Stratified cuboidal epithelium
o Made up of several layers of cuboidal cells
o Found in the epidermis of many tailed
amphibians, specifically the urodeles
Ciliated or flagellated epithelium
o May be columnar or cuboidal cells, which are
provided with cilia or flagellum
o The columnar ciliated epithelium are
columnar cells with cilia
o Found at the innermost lining of the trachea
of the terrestrial animals, e.g., in the dog and
they are also found in the intestine of
earthworms
Cuboidal ciliated epithelium
o Cuboidal and yet they are provided with cilia
o Found in the sperm ducts of earthworms and
oviducts of the frog
Flagellated epithelium
o Provided with flagella
o Found at the inner layer of the hydra and the
regional canals of sponges
Pseudostratified epithelium
o The tissues are formed by a single layer of
cells but hey are of different heights
o Gives the appearance of being stratified, but
in reality they are only made up of a single
layer of the cells and that the nuclei are of
different heights
o Generally, the cells are elongated and their
nuclei are more densely packed within the
tissue
o Found in the respiratory tract and inner ear of
the mammals, in the epididymis, in the
prostate gland, and also in the vas deferens
Pseudostratified ciliated columnar epithelium
o Found along the respiratory tract
o Help trap and transport particles brought
in through the nasal passages, and these
are through among the mammals
Transitional epithelium
o Also known as eutrothilium
o Made up of multiple layers of cells that
become flattened when stretched
o It lines most of the animals urinary tract, such
as the urethra, the ureter and the urinary
bladder, and it allows specially or specifically
the cells of the urinary bladder to expand
when it is filled with urine and the cells will go
back to its natural shape, which is typically
squamous when it is distended, meaning
when the urine is removed or excreted out.
So it can go back to its natural shape when
distended, and this is in its columnar shape
(referring to the diagram)
o Specialized to change in shape in response
to increased tension
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Called transitional cells because they
represent a transition between two desperate
epithelial cell types, so from squamous to a
columnar cell type (in relation to the previous
bullet)
Type of epithelium based on function
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Glandular epithelium
o Specialized for secretion of substances or
materials
o Also called the exocrine glands because
these glands are provided with tubules for the
passage of their secretion
o (REFER TO THE DIAGRAM)
 So if you're going to look at the diagram
of a gland, this is how the glandular
epithelium looks like forming the gland.
These are the glandular epithelium and
they have a space in between them,
forming the dock of the gland, and then
we have this glandular epithelium which
are actually the secretory cells and the
glandular
epithelium
are
again
specialized for secretion
Types of glands based on the number of cells
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Unicellular gland
o Made up of only one cell, just like in the GID
or the gastrointestinal tract where you find the
goblet cells
o Goblet cells are unicellular glands, they are
one celled glands, so these spaces here are
the goblet cells (referring to the diagram)
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Multicellular gland
o The rest of the glands are multicellular
o Made up of many cells just like what we have
in these two diagrams (referring)
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(REFER TO THE DIAGRAM)
o For the multicellular glands, we have tubular
glands and we have saccular glands, they
look like sacs or alveolar glands or saccular
glands. Simple types if they only have one
tubule and if they branch out, then we call
that as branch tubular; they can be called
tubular and still these tubular glands are
producing alveolus at the terminal end. We
have this branch alveolar which are a more
complex form of glands found in mammals,
which are the compound tubular acinar and
we have the compound acinar.
Multicellular glands
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Simple tubular glands
o Short blind tubes
o Found on the tampads of male salientants
(what?) in the mental glands of some
salamanders
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Simple coiled tubular glands
o Provided with a long narrow tube and the
distal end of which is coiled into a small ball
o Found in the sweat glands in the skin of
mammals
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Simple branched tubular glands
o A simple tube which divides its distal end into
two or more branches. There are terminal
portions which may or may not be coiled.
These are found in the large sweat glands of
the axilla or the armpits.
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Compound tubular glands
o The compound tubular glands are with
varying numbers of tubules.
o Ex: Mammary glands of the monotremes.
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Simple saccular glands
o The simple saccular glands are provided with
one expanded bulb at the end of the duct.
These are found in the mucus and poison
glands in the skin of amphibians.
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Simple branch saccular glands
o Provided with several acini arranged along a
single excretory duct, like in the meibomian
glands of the eyelid. These are found in
reptiles or a single acini appears to be divided
by partitions into several smaller acini, as in
that is found in the sebaceous or oil glands of
the skin.
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Compound saccular glands
o Consists of several portions called lobules,
corresponding to the simple saccular glands.
These several units are structures entering a
common duct.
o Ex: In mammary glands of the metatherians
and the Eutherians.
Germinal Epithelium
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From the word germ, referring to the germ cells,
these epithelial cells lining the walls of the testis
and the ovary will later on give rise to the sperm
cell and the egg cell.
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Found in the lining of the seminiferous tubules of
the testes.
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Germinal epithelium diagram:
o Known as the wall of the seminiferous
tubules. These cells are connected via the
tight junction.
o These are the same cells which are the
germinal epithelium and will later on become
the
spermatogonium,
the
primary
spermatocyte, the secondary Spermatocyte
will grow into the spermatim, and later on to
become the spermatozoa.
o This is also the cells lining the ovary. So, the
epithelium is found along the wall of the
ovaries or the ovarian surface epithelium.
o This is also called the germinal epithelium of
the Waldeyer
o This is a layer of simple squamous
epithelium.
o From a simple squamous to cuboidal
epithelial cells covering the ovary, and this
same covering of the ovary will later on
become the oogonium, the primary oogonia,
oocyte, the secondary oocyte, the ootid, and
will later on become the egg cell.
CONNECTIVE TISSUE
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2nd type of animal tissue is the connective tissues.
Common characteristics of the connective tissues:
1. Cells are loosely arranged; seem to be far
apart from each other.
2. They are embedded on a matrix and the
matrix contains a large amount of intercellular
substance or cementing substance between
the cells. This matrix could either be a solid
matrix or a liquid or fluid matrix.
3. The cells are usually enclosed within an
empty space called lacuna, such as in the
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bone and in the cartilage type of connective
tissue. This matrix also is provided with fibers,
they are called based on the protein
component of these fibers – Collagenous
fibers: Contains collagen;
Elastin fibers:
contains elastin protein.
4. They are well vascularized – they are
provided with many blood vessels except for
tendons, for ligaments and cartilages.
5. There is an abundant intercellular matrix.
6. They
show
a
very
slow
regeneration
compared to our epithelial cells.
Type of connective tissue/substantive tissues
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Elastic Connective Tissues
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Dense Connective Tissues
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Loose Connective Tissues
o Adipose
o Cartilage
o Bone or osseous tissues
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Blood/Hemopoietic tissues
Main functions of connective tissues
1. Binds structures together.
2. Forms framework and support.
3. Stores fat.
4. Transport substances.
5. Protects against diseases.
Specialized Types of Tissues
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Bone/Osseous Tissues
o Made up of cells called bone cells or
osteocytes, located in a space called lacunae,
lacuna in plural form.
o Embedded on a hard matrix.
o Lacuna are arranged around a cavity called
Harvesian Canal and this communicates with
one another through canaliculi
o The unit structure of the bone is the
Haversian system, and it is composed of all
the Haversian canals and all the lacunae with
bone cells surrounding it.
o These bone cells are found in the bones of
animals.
o Main function of the bone is for support.
Hence, it is known as the framework of the
body.
o Periosteum
 The cross and transverse section of a
bone showing the outer covering.
o Two types of tissues found in the bone:
 Compact Tissue
 where muscles are attached via
the tendons, and which ultimately
provide
the
structural
and
locomotor support to the body.
 It also functions to protect the vital
organs of the body as it is the layer
of tissue above the important flat
bones, such as the ribs that
protects the thoracic cavity where
you find inside the lungs and the
heart, the respiratory and the
cardiovascular organs.
 The skull or the brain case that
protects the brain and the vertebral
column that encloses and protects
the spinal cord.
 The compact bone tissues are
found under the periosteum and in
the shaft or diaphysis of a long
bone
 Example of a long bone is the
femur and the surface of flat
bones, such as the cranium.
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Spongy Bone Tissue
 Shock absorber during periods
of movement, such as in
jumping,
in,
walking,
and
running.
 Handles
the
more
active
functions of the bone, which is
the
hemopoiesis,
or
the
production of blood cells as
well as in ion exchange.
 Found in joints as a shock
absorber in the ends of long
bones, which we call epiphysis,
and in the interior of flat, short
and ankle bones, and irregular
bones such as the maxilla.
Cartilage
o The cartilages have the intercellular
substance called the matrix, which is
sometimes calcified.
o It is impregnated with inorganic substances
like calcium and the membrane, covering a
cartilage is called perichondrium.
o There are three types of cartilages found in
the adult body of animals and in the human
body:
 Hyaline Cartilage
 Most abundant type of cartilage.
 Found at the of the ribs, at the
ends of long bones, in the nose,
parts of larynx, the trachea, the
bronchi, the bronchial tubes, in the
embryonic and fetal skeleton.
 Also found in the endoskeleton of
adult sharks and rays.
 Has no fiber in it.
 Weakest type of cartilage.
 Can be fractured while performing
its function of providing flexibility,
support and providing smooth
surfaces for movements at joints.
 Elastic Cartilage
 Found in the auditory tubes, in the
part of the external ears or Oracle
in animals, this is found in the
external ear called the pinna of the
ear, in the epiglottis or the lid on
top of the larynx
 Can also be found in the cartilage
of the eustachian tube.
 Contains elastic fibers that are
branch.
 Maintains
shape
of
certain
structures.
 Provides structural strength and
elasticity.
 Fibrocartilage
 The
intercellular
substance
contains the collagenous fibers
that are not branch.
 It is found in the intervertebral disc
that is in between vertebrae, in the
pubic symphysis or in joints which
are subject to severe strain.
 It is also found in the cartilage
pads of the knee called menisci
and portions of tendons that are
inserted into the cartilage.
 Rigid but is the strongest type of
cartilage and is reliable in
supporting and joining structures
together.
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Fibrous Connective Tissues
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The next type of connective tissues are the
fibrous connective tissues, and under this we
have the loose connective or the areolar
connective tissues
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Areolar connective tissues
o The fibroblast are oval cells or round
supported
by
a
matrix
with
the
collagenous and elastic fibers.
o These are found in the subcutaneous
tissues in the papillary dermis, in the
lamina propria of the mucous membrane
around the nerves, the blood vessels and
body organs they are also found in the
mesenteries and omenta.
o This is how a loose connective or areolar
connective tissue is seen.
o You find here the thick, collagenous fiber,
and thinner, but branched elastic fibers
and you find here the oval or round
fibroblast cells.
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Dense connective tissues
o now the dense term here is referring to
the collagen fibers that are found in the
matrix of the connective tissue.
o The cells are also called fibroblasts and
they are found at random embedded on
the fibers.
o There are fibers that are seen to be
compactly arranged, and we have two
types of these arrangements:
 Regularly
arranged
dense
connective tissues
 The regularly arranged connective
tissues forms the tendons which
attaches the muscle to the bone.
 Most ligaments, which attaches
bone to bone.
 And aponeurosis which are
sheet like tendons that attaches
the muscle to muscle or muscle
to the bone.
 Irregularly
arranged
dense
connective tissues.
 They often occur in sheets,
such as in fascia – tissue
beneath the skin and around
muscles, and other organs, in
the dermis of the skin, in the
fibrous
pericardium
of
the
heart, the periosteum of the
bones,
perichondrium
of
cartilage,
in
the
articular
cartilage
or
capsules,
the
capsules
around
various
organs, such as surrounding
the liver, kidney, testes, lymph
nodes, and heart valves.
Adipose Tissues
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Found under the Group of Areolar Tissues
because they have some scattered fibers,
which are loosely arranged.
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The adipose tissues are made up of cells
which are called fat cells or adipocytes.
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The cells are rounded with thin walls and very
little cytoplasm.
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The nucleus is situated on one side of the
cytoplasm.
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Because the cytoplasmic area is almost
occupied by fat cells.
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These are used to store fats so the main
function of adipose tissues is to reduce heat
loss
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They are also energy reserves they support
and protect organs, and they generate heat.
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Examples of these are found in the
subcutaneous tissues around the heart and
kidneys, yellow bone marrow, the padding
around the joints. they are also found behind
eyeballs in eye sockets and very good
example of these are also the fat bodies, or
the corpora adipose in the frog.
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The microscopic view of the adipose tissues
where you find the cytoplasmic areas almost
empty because these are reserved issues, but
you can find a very thin cell membrane and
you will find the darkly-stained structures
there which are the nucleus found at the
periphery of the cells.
Reticular connective tissues
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A diagram showing a cross section of a lymph
node, which is an example of a reticular connective
tissues.
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In this type of tissue, the cells are called fibroblast
and they are provided with processes and all of
these processes in the fibroblasts are forming a
network, hence the term reticular.
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The fibroblasts are supported by a matrix with
reticular fibers.
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This connective tissue supports the blood cells in
lymphoid organs.
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They form the stroma of organs.
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They bind smooth muscle tissue cells.
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Fillers, and remove worn out blood cells in the
spleen and microbes in lymph nodes.
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The reticular connective tissue is found in the
stroma of the liver in the spleen, in the lymph node,
in the red bone marrow, the reticular lamina of the
basement membrane around the blood vessels
and muscles.
Blood Tissues or Vascular Tissues
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The blood is made up of specialized connective
tissue, which transports substances.
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The cells are called blood cells or corpuscles, and
these are supported by a fluid matrix called the
plasma.
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The blood vascular tissues are the vehicle for the
cardiovascular system.
o It is composed of the plasma, which is the
fluid part which functions to transport
substances and constitutes 55% of the blood,
and it is also made up of the formed elements
or cells which constitute 45% of blood cells.
o RBC or red blood cells or the red blood
corpuscles
 this is also called erythrocytes and they
are specialized for transport of gases.
o WBC, the white blood cells, or white blood
corpuscles
 what we call the leucocytes, and they
are considered as the soldier cells of the
body.
o Platelets
 the platelets are the cells which are
involved in blood clotting or blood
coagulation.
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We have another diagram here, so showing
the RBC, the WBC in different forms, and
platelets, then together with the blood
vascular tissues, we find also the hemopoietic
or hematopoietic tissues
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These are tissues that are specially involved in the
formation and maturation of blood cells
The type of hemopoietic tissues are the lymphoid
tissues which form the lymphocytes and the
monocytes, and they are found in the lymph nodes
in the liver, in the spleen.
o Myeloid tissues.
 They form the erythrocytes and the
granulocytes and they are found in the
bone marrow
The following are the different types of WBC or
white blood cells.
o The agranulocytes or the mononuclear
leukocytes
 Between the two, we have monocytes
and lymphocytes.
 The darkly stained here is the monocyte
and this darkly stained structure here is
the lymphocyte.
 The monocytes are bigger spherical
cells and the nucleus inside is bean
shaped.
 It has no indentation, and we say that 2
to 6% of the total WBC are the
monocytes.
o Lymphocytes.
 The lymphocytes, compared to the
monocytes, are smaller spherical cells,
and their nucleus are almost occupying
the entire cell.
 The cytoplasm is very small, in amount:
20 to 25% of the WBC are the
lymphocytes.
o Granulocytes
 because they have granules in the
cytoplasm and their nucleus are seen to
be varying in shape. They are also
called
the
polymorphonuclear
leukocytes.
 Basophil.
 The basophil has one low nucleus
which is twisted like an “S”.
 There are granules in the
cytoplasm and are the granules
that are very large, but few.
 They can be stained by basic dyes.
 And 0.5% of the total number of
WBC's are the basophils.
 Eosinophil.
 The eosinophil is made up of
nucleus, consisting of two lobes,
and the granules in the cytoplasm
are fewer but coarser, and they
can be stained by the acidic dyes
during the preparation of WBC 3 to
4% of the total number of WBC are
the eosinophils.
 Neutrophils
 whose nucleus consist of three or
more lobes.
 The granules in the cytoplasm are
fine and numerous
 They are not stained by acidic nor
by basic dyes, and we say that 60
to 70% of the total number of
WBCs are the neutrophils.
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MUSCLE TISSUE
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The muscular tissues or muscle tissues, and these
tissues are specialized for contraction, the cells have the
ability to contract, and these cells are called muscle cells
or muscle fibers, and they are enclosed by a
sarcolemma.
Myofibrils
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This is the contractile fibrils contains of the
sarcoplasm of the cell and muscle cell contraction
involves the interaction between filaments of
myosin and actin.
Muscle tissues are highly masked cellular, and they are
well supplied with blood vessels. That's why when you
cut the muscle, it bleeds a lot. The muscle cells or
muscle fibers are long and slender, and they are
basically made-up of protein called actin and myosin.
Most of the muscle tissues are voluntary and under
conscious control and some are involuntary. You know
the voluntary are these skeletal muscles that are found
attached to the skeleton of animal cells. While the
involuntary muscles are those that are found in the heart
and found in the internal organs or the smooth muscle
cells.
In animals, 50 to 60% of the total body weight is made
by the muscles.
Skeletal muscle
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The striated voluntary muscle
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The cells are filamentous or elongated cells, and
they are found to have striations, so they are said
to be striated muscles. They are multinucleated
cells and as the nervous control, they are voluntary
in action. They are the muscles that are found
attached to the skeleton or to the bones. Hence,
the word skeletal muscles
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The movement being accomplished by the skeletal
muscle is for the movement of the general body
movement.
Cardiac muscle
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The striated involuntary muscle
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The cardiac muscles are also striated. The cells
are branching and each of these cells are found to
have striations of both the myosin and the actin
filaments. There are one to three central nuclei.
Cardiac muscles are also mononucleated and then
it is involuntary as to nervous control.

The cardiac muscles are involved in the contraction
of the heart
Smooth muscle

The smooth involuntary muscle or visceral muscle.

They are found not to be striated so they are said
to be nonstriated. They are mononucleated, they
have a single central nucleus. The cells are slender
and tapering at its end, and as to nervous control, it
is involuntary in action.
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The smooth muscles are for the movements of the
parts of organs.
NERVOUS TISSUE
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The last type of Animal tissues are the nervous tissues
and this tissue is specialized for the reception of stimuli
and transmission of impulses.
Majority of the neural tissue in the body of the animal is
concentrated in the brain and the spinal cord, which
comprises the central nervous tissues.
Neurons

The first type are the neurons or the nerve cells. So
the nervous tissues are made-up of cells called
neurons, and they are the one which transmits
signals they carry impulses.
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Soma
o The soma or the cell body containing the
nucleus.
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Dendrites
o There are protoplasmic processes in the form
of the dendrites.
o There are more than dendrites and these
dendrites transmits impulses towards the
soma

Axon
o which transmits impulses from the soma
towards the synapse. The synapse is a
specialized intercellular junction where the
axon ends.
The main function of our Nervous tissues is to
coordinate and control body activities and the protein
that made-up our nervous tissues is the myelin.
Basic types of neurons based on the number of cell
processes.

The unipolar neuron
o The unipolar neuron is a type of neuron with
one process.
o There is only one process this is the soma or
the cell body.
o It has one process which will branch into an
Axon.
o The dendrites are beyond the perikaryon and
then we find this type of unipolar neuron from
the dorsal root ganglion of the spinal cord.
o Most of the sensory neurons are unipolar and
in animals they are found in earthworms.
o

The bipolar neuron
o The bipolar neuron with one Axon, and one
dendrite.
o The bipolar are found in the cones and rods.
These are in the fovea of the eyes, and it is
also found in the nose
o

The multipolar neuron.
o The multipolar neuron with one Axon and
several dendrites.
o We can find the multipolar neuron from the
grey matter of the ventral horn of the spinal
cord.
o The multipolar, all the motor and interneurons
are multipolar type of neurons, and these are
again found in the roots of the spinal nerves.
o Most of the multipolar shapes are basically for
thinking, memory and decision making in the
human body.
Types of neurons, based on the action, the sensory
type, the motor, and the associative interneuron or
integrative type of neurons.

The unipolar are mostly the sensory neurons,
o The sensory neurons carry impulses from the
receptors to the spinal cord.

The bipolar are the interneurons
o Interneurons are located entirely within the
central nervous system, and these are 99.8%
of the central nervous system.

The multipolar are the motor neurons
o The motor neurons carry impulses from the
brain to the effectors while the relaying
neurons or Interneurons carry impulses to
and from the spinal cord and the brain.


The Schwann cells

wrapped around an Axon.

They are the glial cells that surround the neuron,
and they myelinate the axons or cover them with a
myelin sheath.

The Schwann cells are the major glial cells found in
the peripheral nervous system and they play
essential roles in the development, in the
maintenance, in the function and regeneration of
peripheral nerves. So as a whole these Schwann
cells support the nerves.
The other type of nerve cells is the neuroglia or the glial
cell. The neuroglia are also all three parts or three types,
the oligodendrocytes, the microglia, and astrocytes. So,
we say that there are three main types of neuroglial cells
that are recognized.

Oligodendrocytes or oligodendroglia
o They form the myelin sheath that surrounds
many neuronal axons, and these increase the
rate of conduction.

Microglia
o on the other hand, has a phagocytic role in
response to the nervous system's damage.

Astrocytes
o The ones that provide biochemical support for
endothelial cells that form the blood brain
barrier, so these are supporting cells of the
neurons or the nervous system.
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