Animal Tissue
Group of cells with similar origin, structure and function is called tissue. Study of tissue is called Histology. Xavier Bichat is regarded as father of histology while Marcello Malpighi is founder of histology. The term tissue is coined by Mayer. Coelenterates are first group of organisms with tissue.
Types of animal tissue:
1. Epithelial tissue- origin ectodermal or mesodermal or endodermal.
2. Connective tissue- origin mesodermal
3. Muscular tissue- origin Mesodermal and
4. Nervous tissue- origin ectodermal.
# Epithelial tissue: (Epi- up and thelial- to grow) tissue which grow up on the surface of other tissue is called epithelial tissue. No cells are present above them. Cells of epithelium are tightly packed with no or negligible intercellular space. The neighboring cells are held together by cell junctions or desmosomes.
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| Cell junctions |
Epithelial cells may have cilia, stereocilia, microvilli etc on their free ends. They rest on a membrane called basement membrane.
They are avascular i.e. without blood supply. Thus, get nutrients by diffusion from adjacent cells as well as passes metabolic waste by diffusion. They have own nerve supply.
They form covering of outer body surface, covering/lining of cavities of body like (pleural cavity, coelom, peritoneal cavity etc.), inner lining of blood vessel/heart, lining of all ducts which open outside( gastrointestinal tract, urino-genital tract, respiratory tract etc.).
The functions of epithelium are Protection, absorption, secretion, sensory & filtration. (@PASSF)
The epithelium may be membranous, present in the form of long sheet or folded as in glands. The cells in epithelium may be of different shapes like flat, cuboidal or columnar. On the basis of shape of cells epithelium may be,
# Squamous epithelium:- The cells are flat( width>height) and centrally placed nucleus. They are found in alveoli, Bowmans capsule etc.
# Cuboidal epithelium:- The cells are cube like(height=width) and are found in kidney tubules, ducts of glands etc.
# Columnar epithelium:- The cells are column like (height>width) and nucleus is present towards the base. They are found in stomach , intestine etc.
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| Types of simple epithelium |
Types of epithelium on the basis on
number of layers of cells
Two types of epithelium are found on the basis of number of layers of cells which are Simple epithelium and compound epithelium.
# Simple epithelium:- Epithelium with single layer of cells. All cells rest on basement membrane. They perform all functions except protection. As they have single layer, are not suitable for protection.
On the basis of structure/shape of cells simple epithelium may be of following types;
· Simple squamous epithelium:- Epithelium with single layer of flat cells. They are also called pavement epithelium. They do everything except protection. All cells rest on basement membrane. They are found in alveoli, Bowman’s capsule. Capillaries etc.
· Simple cuboidal epithelium:- Epithelium with single layer of cuboidal cells. They do everything except protection. All cells rest on basement membrane. They are found in ducts of glands, tubule of kidney etc.
· Simple columnar epithelium:- Epithelium with single layer of columnar cells. They do everything except protection. All cells rest on basement membrane. They are found in stomach, intestine etc.
In case of
cuboidal and columnar epithelium apical (free) end may contain cilia or
microvilli. Epithelium with cilia is
called ciliated epithelium while epithelium with microvilli is called brush
bordered epithelium.
· Pseudo-stratified epithelium:- The epithelium that appears multilayered though consists of a single layer of irregularly shaped and differently sized columnar cells. It is mainly due to variation in height of cell. In pseudostratified epithelium, nuclei of neighboring cells appear at different levels rather than clustered in the basal end. The arrangement gives the appearance of stratification but in fact all the cells are in contact with the basal membrane although some do not reach the apical surface. Pseudostratified columnar epithelium is found in the respiratory tract, where some of these cells have cilia.
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| Pseudostratified epithelium |
# Compound epithelium:- The epithelium with many layers of cells is called as Stratified Epithelium or compound epithelium. It has four to eight layers of cell. Only the cells of lower layer rest on basement membrane. The cells in different layers may be of different types. In general, columnar cells are present towards the basal level on the basis of shape of cells on the top layer Compound epithelium may be Stratified squamous epithelium, Stratified cuboidal epithelium or stratified columnar epithelium.
*Stratified squamous epithelium:- Stratified epithelium with top layer of flat cells is called as stratified squamous epithelium. It is found in those areas where cells are regularly damaged and need to be replaced. The cells of middle layer have high power of multiplication by mitotic division and this layer is also called as stratum germinativum. The flat cells in upper layer may produce fibrous protein called keratin. On the basis of presence or absence of Protein Keratin, Stratified squamous epithelium may be keratinized stratified squamous epithelium and non-keratinised Stratified squamous epithelium.
· Keratinized stratified squamous epithelium:- The cells of top layer produces sclero-protein( Fibrous protein) keratin which forms the outer layer. The cells of top layer regularly degenerate and shed off. It is found in hairs, nails and skin.
· Non-keratinized stratified squamous epithelium:- It is without keratin layer on top. Example buccal chamber, vagina, Pharynx etc.
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| Types of stratified epithelium |
*Stratified columnar epithelium cells are columnar on the top layer. Eg. Urethra, epiglottis,
ducts of mammary glands etc.
* stratified cuboidal epithelium cells are cuboidal on the top layer. Eg. Ducts of sweat/salivary glands.
· *Transitional Epithelium:- Stratified Epithelium with cells having capability to stretch is called transitional epithelium. It has four to six layers of cells in relaxed condition while When get stretched number of layer of cells decreases to two to three layers. It is found in urinary bladder, renal pelvis, uterus etc.
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| Transitional epithelium |
Glandular epithelium :- Modified columnar or cuboidal epithelium Which can secrete chemical substances is called glandular epithelium. It is folded epithelium.
Types
of glandular epithelium
# On the basis of number of cells; the gland may be of two types:
Unicellular gland :- A single epithelial cell behave as gland and can secrete chemical substance example goblet cell.
Multicellular gland:- Many cells behave as gland and are responsible to secrete chemical substance like salivary gland, pancreas, Liver etc.
# On the basis of Presence or absence of
duct;
Exocrine gland:- Glands with duct. Eg. Salivary gland, liver, lachrymal gland etc.
Endocrine gland:- Glands without duct. Eg. Pituitary gland, thyroid gland, adrenal gland etc.
# On the basis of shape/nature of the Secretary
Unit;
Tubular gland: Secretary Part is tube like.
Alveolar gland: Secretary Part is sac like.
Tubulo-alveolar: The secretary part is tubular as well as sac like with a number of branches. It is
also called as mixed type.
# On the basis of nature/structure of secretary part;
· Simple glands: They may be
Simple tubular gland: Secretary Part is simple tubular.
Simple coiled Tubular: The secretary part is coiled tubular.
Simple alveolar: The secretary part is sac like.
Simple branched alveolar: The secretary part is Sac like with a number of smaller sac like branches in the main sac.
· Compound glands: They may be
Branched tubular gland: Secretary Part is tubular with a number of branches.
Branched alveolar: Secretary part is sac like with a number of branches.
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| Types of gland |
# On the basis of mode/nature of secretion;
Merocrine gland: Gland in which substances are secreted by diffusion and don't harm the cell.
Apocrine gland: Gland in which the substances of secretion remain at apical part of the cell and are passed out along with cytoplasm of apical part.
Holocrine gland: Gland in which the substances of secretion are present in cytoplasm of all parts and are passed out by burst of cell.
# On the basis of nature of secretion;
Serous gland: The secretion is watery and cells are called a serocytes.
Mucous gland: The secretion is viscous and cells are called mucocytes.
Mixed gland: Gland with both serocytes and mucocytes.
Muscular tissue
Its origin is mesodermal exception is iridial and ciliary muscles which are ectodermal in origin.
Study of muscles is called as myology or sarcology. The main function of Muscular tissue is they are responsible for the movement of body parts. It consists of muscle cells also called as myofibril. Myoblast cells are muscle forming cells of embryo. In embryonic stage, many myoblast cells get fused with each other to form single muscle cell called as muscle fiber or myocyte. The most special property is their contractibility which is due to protein filaments myosin and actin in their cytoplasm. Main feature of muscle is contraction or contractability.
They make 40% of body weight in mammal. They are supplied with blood vessels and have own nerve supply.
Basic structure of muscle: All muscles are made-up of thin elongated cell called muscle fibers. The muscle fibers contain special cytoplasm called sarcoplasm which contains sarcoplasmic reticulum. The muscle fibers remain bounded by sarcolemma. Each muscle fiber contains numerous thin fibrils called myofibrils.
On the basis of location, structure and function Muscles are of three types;
Striated/Voluntary/skeletal muscle, smooth/involuntary muscle and cardiac muscle.
Striated/Voluntary/skeletal muscle
Striated/voluntary/skeletal
muscles are found on the surface of bone and have alternate dark and light
strips (bands) when viewed under microscope. Their movement is under the
control of will. They remain attached on the surface of bone with the help of
tendon. They are also found on tongue, upper part of Oesophagus, anal sphincter
and external urethral sphincter.
The alternate dark or A bands and light or I bands. I stands for isotropic which allows light to pass while A stands for anisotropic which does not allow light to pass. A muscle is composed of numerous muscle fibers. Each fiber consists of numerous myofibrils. The muscle fibers are bundled together in Parallel fashion. A sheath of tough connective tissue encloses several bundles of muscle fibres.
They get fatigued or tired quickly.
Structure of muscle fiber:
It is
elongated un-branched, blunt at ends and cylindrical in shape. A number of
muscle fibers are arranged parallel to each other and are bound together by
vascular connective tissue. Muscle fibers are multinucleated. The nuclei are
present towards periphery. The myofibrils are arranged along the axis of fiber.
Structure of myofibril:
Each myofibril shows alternate I-band and A-band. Within the centre of I- band there is dark line called Z-band ( Krause’s membrane). Within the center of A-band there is light band called H-line/ zone ( Hensen’s disc). The I and A bands are due to specific arrangement of two proteins actin and myosin present in the form of filament. A-band is formed of Myosin while I- band is formed of actin.
Muscle fiber remains covered by endomysium, a layer of connective tissue and number of muscle fibers remain in bundle to form muscle fasciculus.
A number of muscle fasciculi remain in bundle and remains covered by Perimycium. Externally bundles of fascicule further remain covered by Epimycium.
The space between two Z line is called sarcomere which is functional unit of muscle.
A- band = Myosin and actin.
H- line= Myosin
I-band = Actin.
Z- line= Actin
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| Structure of striated muscle |
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Titin is the largest protein found in body is present
in muscle.
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Myoblasts fuse to form muscle
fibre which remains covered by endomycium.
Group of muscle fibres is called muscle fasciculus
which remains covered by perimycium. Group of
many muscle fasciculi form muscle which remains
covered by epimycium.
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Myoglobin oxygen carrying iron pigment in muscle also
called haemoglobin of muscle.
Smooth/involuntary muscle:
They are muscles with no alternate dark and light bands and their movement is not under the control of will. They never remain attached on the surface of bone. They are found in alimentary canal, respiratory tract, urino-genital tract etc.
They are also called visceral muscles.
They are Spindle shaped with only one centrally placed nucleus. They don't get fatigued and need less energy. They are supplied by autonomic nerves.
Cardiac muscle:
They are present only in the wall of heart. They function throughout lifetime. They need maximum amount of energy and never get tired.
These muscles have long, cylindrical, branched and uninucleated cells divided at places by intercalated discs and interconnected by oblique bridges. These muscles are intermediate between voluntary and involuntary muscle as they have alternate dark and light bands but are involuntary.
They are supplied with both central and autonomic nervous system.
