Keshav Bhatia, Academic Content writer at Edumarz
A group of cells that are similar in structure and perform a specialized function is called tissues.
Tissues in animals are built a certain way to accommodate the unique needs and functions of animals.
Animals have to move around(locomotion) in search of food, mates, and shelter, they consume more energy than plants.
Cell growth in animals is uniform, there is no demarcation of dividing and non-dividing regions in animals.
Structural organization in animals is complex and they have complex feeding methods.
Usually, animals do not grow after reaching maturity.
Most of the animal tissue is living.
There are several types of tissues in the animal body,
Epithelial Tissue
Connective Tissue
Muscular Tissue
Nervous Tissue
Epithelial Tissue
Features of Epithelial tissue:
Cells in Epithelial tissue are tightly packed and arranged in a form of a continuous sheet.
They have almost no intercellular space and a small amount of cementing material between them.
All epithelial tissue is separated from the underlying tissue by an extracellular fibrous basement membrane.
Epithelial tissue covers most organs and cavities within the body.
Epithelial tissue also forms a barrier to keep organs and organ systems separate.
Anything that goes into the body has to cross at least one layer of epithelium.
Permeability plays an important role in regulating the exchange of material between the body and the external environment.
Epithelial tissue is divided into a few main categories and each of them have a function of their own:
Squamous Epithelium
Stratified Squamous Epithelium
Columnar Epithelium
Cuboidal Epithelium
Squamous Epithelium
Squamous epithelium is made of a single thin layer of flattened cells with irregular boundaries.
Squamous epithelium forms a diffusion boundary.
Simple squamous epithelium is flat and thin and forms a very delicate lining.
Simple Squamous epithelium makes the lining of blood vessels and lung alveoli, as transportation occurs through a thin selectively permeable surface in these parts of the body.
Oesophagus and the lining of the mouth are also made of simple squamous epithelial cells which form a delicate lining.
Stratified squamous epithelium
Epithelial cells are arranged in a pattern of layers to prevent wear and tear.
Skin epithelial cells are an example of Stratified Squamous epithelium.
Columnar Epithelium
Made of a single layer of slender and tall cells.
Found in the lining of the stomach, intestine, and respiratory tract.
It facilitates movement across the epithelial barrier.
The columnar epithelium in the respiratory tract(mainly bronchioles) has cilia that move and push the mucus to clear it.
Ciliated cells are also found in the endometrium and fallopian tube, where their main function is to push Ovum and other particles.
Cuboidal Epithelium
A single layer of cube-shaped cells makes cuboidal epithelium.
Mainly found in ducts of the salivary gland where it provides mechanical support and the lining of kidney tubules.
The epithelium of proximal convoluted tubule of nephrons in the Kidney has microvilli.
Glandular Epithelium
Additional specialization for secretion is acquired by epithelial cells and they act as gland cells.
Sometimes, A portion of epithelial tissue folds inwards to form a multicellular gland.
Usually, Columnar or cuboidal epithelium are the ones that get specialized for
secretion.
Connective Tissue
Connective tissues have a special function of linking and supporting other tissues organs of the body.
The cells are loosely spread and embedded in an intercellular matrix
The nature of the matrix differs according to the function of the connective tissue, it can be rigid, dense, loose, or fluid.
Types of Connective tissues
Blood
The blood plasma has salts, proteins, and hormones it also hosts Red blood Corpuscles, white blood Corpuscles, and platelets.
The blood flows and carries oxygen and nutrition to every nook and corner of the body.
It also carries hormones and waste materials to and from different parts of the body.
Bone
Bone is the main tissue that provides a structural frame to the body.
Bones anchor the muscles & support and protect soft tissues and organs.
Bone cells(Osteocytes) are embedded in a hard matrix that is made of calcium and phosphorus compounds.
Bones interact with skeletal muscles to bring about movements in the body
Bone marrow present in bones plays an important role in the production of healthy blood cells
Ligaments
The ligament connects two bones with each other
Ligaments have fibroblasts and fibers and are very elastic and strong.
Ligaments contain very little matrix
Tendons
Tendons join bones to muscles
Tendons have limited flexibility
Tendons are also very strong
Cartilage
Widely spaced cells
The matrix is made of protein and sugars
Plays important role in smoothening joints
The nose, trachea, ears, and larynx have cartilage in them
Areolar Connective Tissue
Serves as a support framework for epithelium
Fills space inside the organs and helps in tissue repair
Mainly found in the bone marrow, between the skin and muscles, around blood vessels and nerves.
Adipose tissue
Located mainly beneath the skin
Specialized to store fat
*Cells are filled with fat globules
*Body converts excess nutrients to fats and stores it in these cells
Acts as an insulator due to fat storage
Responsible for movement in our body
Muscles have special contractile proteins which contract and relax to cause movement
Elongated cells called muscle fibers to make up Muscular tissue
Muscle fibers contract in response to stimulation then relaxes to their uncontracted state in a coordinated fashion.
There are three types of muscle tissues:
Skeletal Muscle Tissue
Smooth muscle tissue
Cardiac muscle tissue
Skeletal Muscle Tissue
-Mostly attached to skeletal bones
-Help in the movement of the body
-Striated muscles: as they show a striated appearance under the microscope
-cells are long cylindrical, unbranched, and multinucleate
Smooth Muscle Tissue
-Controls the movement of food in the digestive tract
-Contraction and relaxation of blood vessels
-Also found in the iris, the uterus, and in bronchi of the lungs
-Uninucleate
-They do not show striations under a microscope(unstriated)
-Cell junctions hold them together and they are bundled in a connective tissue sheath
Cardiac Muscle Tissue
-Present only in the heart
-Cells are cylindrical branched and uninucleate
-Cell Junctions fuse the plasma together
-Communication junctions(intercalated discs) at some fusion points allow the cells to contract as a unit
-When one cell receives a signal to contract, its neighbors are also stimulated to contract
Neural/Nervous Tissue
-Neural tissues exert the greatest control over the body’s responsiveness to stimuli.
-Nervous tissue is highly specialized for being stimulated and then transmitting the stimulus very rapidly from one place to another.
-Neural tissue cells are called neurons.
-Neurons are found in the nerves, brain, and spinal cord.
Structure and function of a neuron
Three parts make up a Neuron: Cell body, dendrites, and Axon
Cell body with a nucleus and cytoplasm
A single long part, called the axon and short branched parts called dendrites
Can be up to a meter long in Size
Nerve fibers bind together by connective tissue to make up a nerve
Dendrites transport impulses toward the cell body
Nerve impulse
+ Signal that passes along the nerve fibers is called a nerve impulse
+ Allow us to move our muscles when we want to
+ Muscles and Nerves work together and enable animals to move in response to stimuli