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Subjects /Biology / Study of Tissues - Animal Tissues

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INTRODUCTION
19 Apr 2021

The tissues that are present in the living organisms other than the plants are animal tissues. The types of animal tissues include:

  • Epithelial tissues
  • Connective tissues
  • Muscular tissues
  • Nervous tissues

These tissues perform wide range of functions including movement of the body, transportation of food and minerals in the body and protection of the body system from the outer atmosphere.

Epithelial Tissue

Epithelial tissue is also called the protective tissue. The reasons are:
  • It covers the body system and protects it from the external environment.
  • It covers most organs and cavities in the body. It also forms a barrier to keep different body systems separate.
  • For example: the skin, the lining of the blood vessels, lung alveoli and kidney tubules.
  • Epithelial cells are closely packed without inter-cellular space and form a continuous sheet.

Epithelial tissues are classified into different types according to their structure. These are:

  • Squamous epithelium
    • The cells are extremely thin and flat and form a delicate lining.
    • For example: the oesophagus and lining of mouth.
  • Stratified Squamous epithelium
    • The skin cells are also made of squamous epithelium.
    • Skin cells are arranged into many layers to prevent wear and tear. That is why it is called stratified squamous epithelium.
  • Columnar epithelium
    • Columnar means pillar like.
    • Where absorption and secretion occur, for example, in small intestine, tall columnar cells are present.
    • It facilitates movement across epithelial tissue.
    • The cells have elongated nucleus.
  • Ciliated epithelium
    • The columnar epithelium cells that have cilia are called ciliated epithelium tissues.
    • In respiratory tract, the columnar tissues also have cilia (hair like structure) on the outer surface of epithelial cells.
    • These cilia can move and their movement pushes the mucus forward to clear it.
  • Cuboidal epithelium
    • The cells are cube-like and have centrally placed nucleus.
    • It forms the lining of kidney tubules and ducts of salivary glands.
    • It provides mechanical support.
  • Glandular epithelium
    • The epithelial tissue folds inside and forms a multicellular gland. It is called glandular epithelium.
    • The cells are modified to secrete some substances on epithelial surface.
  • Sensory epithelium
    • These are present in the sensory cells.
    • The free end of these cells contains sensitive hair eg. auditory epithelium in the taste buds.

Connective Tissue

  • Connective tissue joins and supports various parts of the body forms packing around organs, to protect and also form supporting framework.
  • The cells of the connective tissue are loosely packed and they have liquid, jelly or dense fluid between cells which is called matrix. The nature of matrix depends upon the type of connective tissue it is supporting.

Depending upon the structure and function, the tissue is classified into three types:

1. Fluid Tissue

These tissues help in the transport of oxygen, carbon dioxide and nutrients along with the removal of the waste materials. The types of fluid connective tissues are:

Blood

  • Blood has fluid matrix called plasma in which red blood cells, white blood cells and plasma are suspended.
  • The plasma contains protein, salts and hormones.
  • Blood transports gases, digested food, hormones and waste material to different parts of the body.
  • RBCs contains haemoglobin which transports oxygen. It is red in colour.
  • WBCs are colourless and contains nucleus. They help in fighting the infections in our body.
  • Platelets help in the clotting of the blood.

Lymph

  • It is the colourless fluid without RBCs.

Difference between Blood and Lymph

Blood

Lymph

Colour is red

Colourless

Haemoglobin is present

Haemoglobin is absent

RBC is present

RBC is absent

2. Connective tissue proper

Areolar tissue:

  • It is present between the skin and muscles, around blood vessels, nerves and bone marrow.
  • It fills the space inside the organs, support internal organs and helps in repair of tissues.

Yellow fibrous tissue:

  • It is located in the ligaments.
  • It is elastic and joins the movable bones.

White fibrous tissue:

  • It is located in tendons and connects muscles to bones.
  • It is formed of white collagen fibres.

Adipose tissue:

  • It is a fat storing tissue.
  • The cells are large and circular.
  • It is found below the skin and between the organs.
  • The cells of this tissue are filled with fat globules.
  • The storage of fat makes adipose tissue an insulator.

3. Skeletal Tissue

These tissues form the endoskeleton of the vertebrate animals.

It includes the following types of tissues:

Bone

  • It forms the framework that supports the body.
  • It also anchors the muscles and supports the main organs of the body.
  • It is strong and non-flexible tissue in the body.
  • Bone cells are embedded into hard matrix. This matrix is composed of calcium and phosphorus compounds.

Ligaments

  • These tissues connect the two bones together.
  • This tissue is very elastic.
  • It is very strong.
  • Ligaments contain very little matrix.

Tendons

  • These tissues connect bones to the muscles.
  • These tissues are fibrous with great strength but limited flexibility.

Cartilage

  • This type of cartilage tissue has widely spaced cells.
  • The cells are suspended into solid matrix composed of protein and sugars.
  • Cartilage smoothens bone surfaces at joint.
  • It is present in nose, ear and larynx.

Muscular Tissue

 

Important Facts!!

Largest muscle of human body: Gluteus Maximus (muscle of the hip).

Smallest muscle of the human body: Stapedius

There are 639 muscles in human body.  

  • These tissues are also called as contractile tissues. Because muscle cells contain special protein called contractile proteins which help in contraction and relaxation to cause movement.
  • The cytoplasma of the muscle fibre is called as sarcoplasm and is bound by a membrane called as sarcolemma.
  • All the muscles of the body are made up of this tissue.
  • Muscle tissues consists of elongated cells called as muscle fibres.

These muscle cells help in the movement of different body parts.

Types of Muscular Tissues

Muscular tissues are of three types:

1. Straited muscles/Skeletal muscles/voluntary muscles

  • Muscles present in the limbs move when we want them to, and stop when we decide so. That is why these are called voluntary muscles.
  • These muscles are also called skeletal muscles because these are attached to bones and help in movement.
  • When seen under the microscope, these muscles show alternate light and dark bands or striations. That is why these are called straited muscles.
  • The tissues are long and cylindrical. These occur in bundles.
  • These are multi-nucleate.
  • These connect to bones as tendons.

2. Unstraited muscles/Smooth muscles/involuntary muscles

  • The movement of these muscles are involuntary because we cannot start or stop these movements. For example: movement of food in alimentary canal or contraction or relaxation of blood vessels.
  • The cells are long with pointed ends.
  • These cells have one nucleus (uninucleate).

3. Cardiac Muscles

  • The muscles of the heart show rhythmic contraction and relaxation throughout life.
  • These involuntary muscles are called cardiac muscles.
  • These are found in the wall of heart.

Nervous Tissue


These cells are very specialised to respond to any kind of stimuli and then transmit the stimulus very rapidly from one part of the body to another.

For example, if your finger touches anything very hot, then that information is transferred to your brain at lighting speed so that you can remove your finger.

The brain, spinal cord and nerves are all composed of nervous tissue.

The cells of nervous tissues are nerve cells or neurons.

The composition of neuron includes:

Cell body: It consist of nucleus and cytoplasm from which long thin hair like part arises.

Dendrite: It is the hair like part arising from the cell body. These help in transferring the stimulus from one neuron cell to another.

Axon: The axon forms the nerve fibre. It is covered nu a sheath, medullary sheath and is covered by a membrane called neurilemma.

Nerve Ending or Axon Terminals: the nerve ending of one nerve cell is connected with dendrite of another to transfer the stimulus.