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Animal tissue

Tissue

  • A tissue is defined as a group of cells having a common origin with more or less similar structure and function.
  • Study of tissue is called histology.
  • Mayer coined the term histology.
  • Bichat coined the term tissue.

Animal Tissue

  • Composed of one or more layers of cells. 
  • Cells are compactly arranged with no intercellular spaces and matrix.
  • Cells of lower most layer rest on non-living basement membrane.
  • Blood vessels absent.

Types of Tissue
Based on structure, Location and function, animal tissues are of four types

Chart  of Animal Tissue
Types of Animal Tissue

Epithelium Tissue  

  • Epithelium described by Ruysh.
  • Ectodermal, mesodermal, endodermal in origin.
  • Covers the body surface.
  • Cilia, flagella, and demososomes are usually associated with such tissue.

Simple Epithelium Tissues
Epithelium is one-celled thick they are of four types

  1. Squamous Epithelium
    • Consists of being layer of flat polygonal cells, which are closely filted together like the tiles of a mosaic, thus also called as pavement epithelium.
    • The length and breath of the cells are more than the thickness of the cell.
    • Examples are alveolar epithelium, pleura the inner lining of bowman’s capsule , capillary epithelium, endothelium Coelomic cavity Peritonium, heart couering pericardium.
  2. Columnar Epithelium
    • Consists of single layer of tall and narrow column like cells.
    • It has mucus secreting goblet cells.
    • such epithelium lining is found in organs of alimentary canal.
    • Examples are – Acini of pancreas, lining of gall bladder, minativum of skin and lining of stomach, gastric gland, Intestinal gland.
  3. Cuboidal Epithelium
    • Consists of single layer of cuboidal cells.
    • The cells are cuboidal having similar length height and breadth.
    • Examples are germinal epithelium, follicular cells, lining of DCT, ascending limb of Henle, thyroid gland, iris of eye.
  4. Specialized Epithelium
    They are divided into 4 types
    1. Pepithelium 
      • It is simple but appears multilayered.
      • Epithelium is single cell thick but appears to double layers due to the presence of a different level of height of cells and position of nuclei.
      • The tall cells are ciliated where as shorter cells are nonciliated.
      • Examples are epithelium of trachea and bronchioles, larynx, eustachian tube.  
    2.  Sensory Epithelium
      • Consists of single layer of modified columnar cells.
      • These are innervated with nerves and receive various types of stimuli .
      • Examples are retina, schenedarian membreans and labyrinth.
    3.  Brush Bordered
      • Cuboidal cells with microrilli are called brush bordered cuboidal epithelium.
      • Cells containing microvilli are called brush bordered columnar epithelium.
      • These microvilli may be small or regular and increase the surface area for absorption.
      • Examples; Brush bordered cuboidal epithelium form PCT, brush bordered columnar epithelium forms small intestine.
    4. Ciliated Epithelium
      •  Surface of cuboidal and columnar cells bear cilia and are called ciliated.
      •  These cells help in movement of sperm in vas deferens ,ova in oviduct or movement of muscus from trachea into pharynx.

Stratifed Epithelium or Compound Epithelium

  • The epithelium is two more than two layered thick epithelium.
  • Basement membrane is present at the base or lowermost layer of cells.
  • Main function is protection.

Types of compound Epitheliums

  1. Stratified Squamous epithelium
    • Cells of lower most layer are cuboidal or columnar shaped.
    • These cells divided by mitosis to form other layers, thus called stratum germinatirum.
    • Cells of intermediate layers are polygonal shaped.
    • Cells of outer most layer are flat cells.
      On the basis of presence of keratin protein, this epithelium is of two types;
      1. Keratinized Stratified Squamous Epithelium
        • Presence of dead and water proof fibrous keratin in outer most layer,this called stratum carnium.Example: Epidermis of skin, nail, hair.
      2. Non - Keratinized Stratified  Squamous Epithelium
        • Absence of keratin in outer most layer, cells are living. Examples; Oral cavity, Pharynx, Oesophagus and Canal, Vagina,Carnea
  2. Stratified Cuboidal Epithelium 
    • Cells of innermost layer cuboidaler collumnar shaped.
    • Cells of middle layer polygonal shaped.
    • Celles of outer most layer cube like, nucleated and living.
    • Example; Secretory duet of sweat glands, mammary glands salirary glands and pancreas
  3. Stratified Colunar Epithelium
    • Cells of inner most layer cuboidal or columnar shaped.
    • Cells of middle layer polygonal shaped
    • Cells of outermost layer tall pillar shaped nucleated cells.
    • These cells may bear cilia or may not.Examples; Ciliated stratified columnar epithelium forms male urethra, mucus layer near anus, Non-ciliated stratified calumnar epithelium from epiglottis.
  4. Transitional Epithelium
    • It is 2-6 cell thick,Basement membrane absent.
    • It occurs in the area where stretchings is required or flexon and exlension.
    • Example are in urinary bladder,ureter and pelvis.This called Urothelium

Muscular Tissue 

  • They help in movements of the body.
  • Muscular tissue is mesodermal in origin.
  • Muscular tissue consists of elongated muscle called myocytes fibres.
  • Myofibrils are present in the cytoplasm of muscular fibres.
  • Myofibrils contains ATP, Actin, myosin.

Muscular of further 3 types

  1. Striated Muscles or Striped Muscles
    • Muscles fibres are cylindrical and have one or more than one nuclei.i.e Syncytium
    • They have sarcolemma.
    • Myofibrils posses alternate dark and light bands.
    • Dark bands are called" A "bands and light bands are called I bands.
    • A band has myosin filament and I-band  has action filament.
    • H-Zone is found at the centre of A band.
    • Dark Z - line is found at the centre of I-band. The portion of myofibrils between two Z- lines called as the sarcomere.
    • Sarcomere is the functional unit.
    • They get fatigued.
    • They are attached to bones so-called skeletal muscles.
    • They are called voluntary muscles as they are under control of our will. Examples, muscles of limbs, trunk, eyelids, tongue.
  2. Smooth muscles or Unstriped muscles.
    • These are the smaller than striped muscles.
    • They have spindles shaped and uni nucleate structures.
    • Sarcolemma absent.
    • Sarcoplasm contains granules.
    • They are known as visceral muscles.
    • They are called involuntary muscles as they are not under the control of our will.
    • They do not get fatigued. Examples; blood vessel, stomach, intestine, urinary bladder, iris etc.
  3. Cardiac muscles
    • They are intermediate between striped and un-striped muscles.
    • They have long cylinderical branched and uni nucleated cells.
    • The presence of intercalated disc.
    • They work throughout life without getting fatigued.
    • Contractions and relaxations are rhythmical, under the control of ANS.
    • These are present in the wall of heart.

Extra knowledges 

  • In I band- only actin filaments are present.
  • In A - band – both actin and myosin filaments are present.
  • In H - band – only myosin filaments are present.
  • In Z - line – members on both sides of which ,actin filaments are attached.
    fig1
    Muscular Tissue

Connective tissue

  • It is mesodermal in origin and helps to bind the different structures together.
  • Most abundant tissue in the body.
  • It is made up of matrix living cells and fibres.
  • Matrix is intercellular substance or ground substance made up of proteoglyeans and glyco-proteins.
  • Connective tissue are of two types i.e embryonic and adult connective tissue is also called mucous connective tissue.
  • It has jelly like matrix called Whaston's jelly. Examples; Umbilicalcord, vitrous humor,cock's comb.
    Adult connective Tissue.
    Adult Connective Tissue

Proper Connective tissue

  1. Loose or Areolar Connective Tissue
    fig 2
    • Matrix is Jelly like with loosely arranged fibers and cells.
    • Its consists of following types of cells.
      1. Mast cells are modified basophils secret heparin, histamine and serotonin.
        • Histamine is vasodilators and lower Blood pressure.
        • Serotonin is vasoconstrictor and increases Blood pressure.
        • Heparin stops blood clotting inside blood vessels.
      2. Macrophages also known as clasmatocytes are phagocytic cells. These are modified monocytes. 
      3. Fibroblast cells produces white and yellow fibers such cells are largest and main cells of an areolar tissue. They secrete matrix also.
      4. Plasma cells
        • These cells are modified B-lymphocytes.
        • They secrete antibodies.
      5. Fat cells (adipocytes)
        • These are fat staring cells.
        • They have a large fat droplet called blob in the cytoplasm or may have many fat droplets.
      6. Chromatophores
        • These are pigmented cells with melanin pigment.
      7. Mesenchyme cells
        • These are undifferentiated cells.

Fibres

Yellow Fibres White Fibres  Reticular Fibres
  • Made up of elastin protein
  • Made up of protein 
  • Made up of Reticulin protein 
  • Straight branched and singly arranged
  • Way, Unbranched and arranged in bundles.
  • Highly branched.Forming network.
  • Elastic
  • Tough
  • inelastic
    •  
  1. Adipose Tissue
    fig 4
    1. It is modified areolar tissue.
    2. It has closely packed cell called adipocytes containing fat globules.
    3. The intercellular matrix is negligible.
    4. These adipocytes are of further of 2 types ,named monolocular (white fat cell) and multilocular (Brown fat cells).
    5. White fat cell has a single large fat globule (bolb) and less cytoplassm. Brown fat cell has many fat globules and more cytoplasm. 
    6. Brown fat cell produces 20 times more energy than white fat cell.
  2. Dense Connective Tissue
    Matrix has compactly I densely arranged fibres and connective tissue cell. These are of following types;
    1. White Fibrous Connective Tissue
      • Only collagen fibres are present in the matrix and cells are mainly fibroblasts and mast cells.
      • Cells and fibres are riss-crossed arranged. Example; Periostium, Perichondrium, Epimysium, Dura mater
    2. Tendon
      • Bundles of collagen fibres are distributed in regular patter in matrix.
      • Fibroblasts (tendocytes) are arranged in series.
      • Mast cells are scattered. Examples; Tendon that connects muscles to bones.
    3. Yellow Fibrous Connective Tissues
      • Mostly yellow elastin fibres are present in the matrix and cells are mainl fibroblasts.
      • Irregular distribution of yellow elastin fibres in matrix. Examples; wall of alveoli, wall of small pronchioles, vocal cords.
    4. Ligaments
      • Yellow elastin fibres form dense network in matrix.
      • Example; ligaments that connects bones to bones.
  3. Reticular Connective Tissue
    • Matrix is lymph like.
    • Matrix has dense network of reticulin fibres around star like reticular cells.
    • A few mascrophages, lymphocytes and adipocytes are also present.
    • Present in Lymphnodes, Thymus, Tonsil, Spleen, Bone marrow
    • These are associated with phogocytosis and provide strength and support to soft organs.

Skeletal Connective Tissue
This tissue includes bone and cartilages. 

  1. Bone
    Bone-outer covering contains white fibrous connective tissues called Periosteum. Bone- forming cells are called Osteoblasts. Proteins of bone is Ossein.
    • Matrix is hard and is composed of ossein protein 
    • It forms thin plates called lamellae 
    • Matrix has phosphates and driumcarbonates of calcium and magnesium. Ca3(Po4)is abundant (80%).
    • Matrix has longitudinal canals called Haversian canals and transverse canals called Volkmann's Canals.
    • Haversian canal has blood vessels, Lumph vessels and nerve fibres.
    • Haversian canals are interconnected by volkmann's canals.
    • Lamellae have small cavities called lacunae which gives fine branching tubules called canaliculi.
    • Lacuna has bone forming cells called osteocytes with filopodia.
    • Endosteum is present outer to the bone marrow cavity.
    • Marrow cavity is filled with bone marrow (soft connective tissue).
    • It is of two types; Red bone marrow and Yellow bone marrow.
    • Red bone marrow helps in blood cell formation.
    • Yellow bone marrow stores fats.
    • Bones form endoskeleton.
  2. Cartilages
    Outer covering in which white fibrous connective tissue of cartilage is perichondrium. Cartilage forming cells are chondroblasts. Its protein is Chondrin. Chondrocytes are scattered in matrix.
    • Matrix is rubber like and translucent.
    • Each lacuna has 2-4 chondrocytes (Cell nest).
    • Depending upon types of fibres present, cartilage is classified as:
      1. Hyaline Cartilage
        • Matrix has no fibres or a few collagen fibres.
        • Matrix is glassy and bluish.
        • It is found is nasal septum, rings of trachea, larynx, ends of long bones(articular cartilage)
        • Most of the embryonic skeleton is made up of Hyaline cartilage.
      2. Fibro-elastic cartilage
        • Matrix has networks of elastic fibers.
        • Matrix is yellowish.
        • Highly elestic cartilage.
        • It is found in tip of nose, ear pinnae, epiglottis, wall of eustachian tubes.
      3. White fibrous cartilage
        • Strongest cartilage
        • matrix has bundles of collagen fibers
        • Perichondrium absent.
        • It forms public symphysis, intervertebral dises, adhesive capsules.
      4. Calcified Cartilage
        • It is formed by calcification of Hyaline cartilage.
        • Less elastic and more rigid.
        • It is found in head of femur and humerous, suprascapula, xiphisternum.

Fluid Connective Tissue or Vascular tissue
It include blood and lymph.

  1. Blood
    • It is made up of plasma and blood cells (formed elements).
    • Plasma is transparent, yellowish fluid form 55 % of blood.
    • It has 90 % water, 8 % plasma proteins and 2 % other dissolved substances.
    • Important plasma proteins are albumin, globulins, fibrinogen, antibodies, prothrombin
    • Blood cells forms 45% of blood.
    • Blood cells are RBCs, WBCs and Platelets.
    • RBCs (erythrocytes) are circular, biconcave and denucleated. 
    • Total RBC Count is 4.5-5 million/mm3.
    • It is made up of haemoglobin respiratory pigment also provide red colour to blood.
    • Formation of RBC is called erythropoiesis.
    • It occurs in red bone marrow.
    • It life span is 120 days.
    • Destruction of RBC is called erythrolysis that occurs in spleen, bone marrow and liver.
    • WBCs (leucocytes) are colourless, nucleated and complete cells.
    • Total leucocyte count is 4000-11000/mm3 of blood.
    • They are formed in bone marrow, spleen, thymus and lymph nodes and the process is called Leukopoiesis. 
      • Life span is 10-13 days.
      • WBCs are of two types: granulocytes and agranulocytes
        • Granulocytes
          Lobed nucleus and granules in cytoplasm;
          Eosinophils Basophils Neutrophils
          • bilobed nucleus
          • 's'- shaped nucleus
          • multilobed nucleus
          • absorb acdic stains
          • absorb basic stains.
          • absorb both acidic as well as basic stains
          • secrete histamine and protect the body against allergy and parastic infection
          • Secrete heparin and histamine
          • Phagocytic
        • Agranulocytes
          Simple nucleus and clear cytoplesm
          Monocytes Lymphocytes
          • Largest cells with eccentrically placed kidney-shaped nucleus.
          • Rounded cells with large Spherical nucleus.
          • Motile and Phagocytic
          • Secrete antibodies.

          • Blood platelets(thrombocytes) are pragments of gaint megakaryocytes of bone marrow.
          • Total blood platelet count is 3 lacs /mm3
          • Life span is about 7 days.
          • Blood platelets contain thromboplastin that helps in clotting of blood.
  2. Lymph
    • Colourless fluid formed by filtration of blood.
    • Contains plasma, lymphocytes, dissolved O2 and CO2, insoluble protains, nutrients etc.
    • Provide immunity to body and helps in exchange of materials between blood and tissues.

Nervous Tissue
Ectodermal in origin.
Nervous tissue is composed of neurons (nerve cells) and supporting and protective cells called neuroglial cells, nerves, ependymal cells and neurosecretory cells.

Neurons
These are 3 types-

  1. Unipolar or Pseudounipolar neurons
    in such neurons ,single process arises from the body of cell and bifuracetes ,to form the Axon and dendrites.
    Examples are dorsal root ganglion of spinal cords.
  2. Bipolar neurons
    they have two poles, one dendrite and one axon arising from the cell body.Example neurons arising from the retina and internal ear.
  3. Multipolar neurons
    • Such neurons have one or more than one dendrites.
    • 99% of the dendrites are multipolar types.

The structure of Neurons

  • It consists of three parts Dendrites, cyton and axon.
  • System is irregularly spherical or oval shaped and certain abundant neuroplasm.
  • Cyton contains large nucleus ribosomes, Nissl granules, Golgibodies, Mitochondria and Neuro fibrils.
  • The centrosome is absent in cyton and can’t be the divide.
  • Dendrites are shorter and branched processes arising from system.
  • They carry impulse towards towards system.
  • Axon is long process with highly branched terminal arborization with terminal battery.
  • Axon has plasma membrane called axolemma and cytoplasm called axoplasm.
  • Axon may be myelinated are non myelinated. It is externally covered by neurilemma made up of flat schwann’s cells.
  • Myelinated axon has gaps called node of Ranviers.

Structure of Nerve

  • Bundles of nerve fibres is called Nerve.
  • The outer covering or the connective tissue covering the nerve is called epineurium.
  • These are several bundles of neurons embedded in epineurium and such bundles are known to  be fascicula.
  • Each nerve fasciculus has a connective tissue called perineurium.
  • Single neurons are also surrounded by connecting tissue covering called Endoneurium.

Types of nerves
On the basis of their function, the nerve is 3 types

  1. Sensory
    These impulses is carried from receptors (skin, retina etc) to the CNS. EG optic nerve.
  2. Motor
    These are carried by an impulse from CNS to effector organs. Eg trochlear nerve.
  3. Mixed
    In such nerves, some fibres carry impulses towards CNS and other away from the Brain of CNS.
    fig 1

Neuroglia cells
These are mesodermal in origin. These are supporting cells essential for normal functioning of nervous tissue.
These are of following types

  • Microglia
    Phagocytes of brain
  • Astrocytes
    Control microenvironment of neuron.
  • Oligodendrocytes
    Form myelin in Neurons.

Ependymal cells
Lines the cavities of brain and spinal cord.

Neurosecretory cells
Neurons of Hypothalamus that secret neurotransmitters which stimulates anterior lobe of pituitary to secret trophic hormones.


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