Tissues, Organs, Organ System, Organism | Part 2
Cell are organized into four types of tissues in higher animals including man
(i) Epithelial tissue : –
It is a protective covering tissue and forms a continuous layer on the entire body surface and cavities inside the body and its parts.
The skin, surface layers of mouth, alimentary canal and lungs are made of epithelial tissues.
It helps in the exchange of materials between the body and the external environment and between different part of body.
Depending upon the shape and function of the cells, the epithelial tissues are classified as.
(a) Squamous epithelium
(b) Cuboidal epithelium
(c) Columnar epithelium
(d) Glandular epithelium
(a) Squamous epithelium : –
These are thin, flat, form a delicate lining the oesophagus and the lining of the mouth are also covered with squamous epithelium.
The skin, is also made of squamous epithelium, these skin cells are arranged in many layers to prevent wear and tear of the body.
Those epithelium which are arranged in a pattern of layers are called stratified squamous epithelium.
(b) Cuboidal epithelium (with cube shaped cells) : –
These forms the lining of the kidney tubules and ducts of salivary glands.
Epithelial cells often acquires additional specialization as gland cell, which can secrete substances at the epithelial surface.
(C) Columnar (Ciliated) epithelium : –
In the inner lining of the intestine, secretion and absorption is occurs through it.
In the respiratory tract, the columnar epithelial tissue also has cilia, which are hair like projection on the outer surfaces of epithelial cells, they can move and their movement pushes the mucus forward to clear it. This type of epithelium is thus called ciliated columnar epithelium.
(d) Glandular epithelium : –
Some times a portion of the epithelial tissue folds inward, and a multicellular gland is formed. Thus they are called is glandular epithelium.
It performs the functions of binding, supporting and packing other different organs of the body.
Functions of connective tissues
Connective tissue binds different structures with one another e.g. muscles with skin muscles with bones.
Adipose connective tissue helps in storage of fats. It also forms shock proof cushions around kidneys ovaries and eye balls.
These forms a supporting frame work of cartilage and bones in the body.
Vascular connective tissue helps in transpiration of materials such as gases, food, wastes, hormones etc inside the body.
These form a protective sheaths around delicate organs such as kidneys testes etc.
Haemopoietic tissues of bone marrow helps in the formation of blood cells.
White blood corpuscles of blood and lymph act as phagocytes and they provide protection against bacterial infections.
Collagen fibers of connective tissue help in the repair of injured tissue.
The major connective tissues of the human body are
(a) Areloar connective tissue
(b) Tendons and ligaments
(c) Cartilage and bone
(d) Blood and Lymph.
Areolar connective tissue
Three types of cells are present in the matrix of the areolar tissue.
(i) Fibroblasts: These cells secrete yellow and white fibres.
(ii) Histocytes: These are phagocytic in nature and they engulf bacteria and other microbes
(iii) Mast cells: These cells secrete matrix.
Functions of Areolar tissue
Areolar connective tissue binds the skin with muscles, attaches blood vessels and nerves to the surrounding tissues.
It forms dermis of the skin.
It serves as packing material for almost all organs
The tendons in the matrix bundles of white fibres run parallel to one another. Tendons are tough and inelastic and they connect muscles with bones.
It contain matrix with numerous and closely packed yellow or elastic fibres, made up of elastin proteins. They are elastic and connect one bone with the other.
Cartilage consists of matrix impregnated with chondrin cartilage is bounded externally by white fibrous connective tissue called certichondrium.
In human beings, cartilage is present in the larynx, trachea, at the end of the bones nasal septum, and in between ribs and sternum.
The bone cells are called osteocytes. These are star shaped and each cell is enclosed in a small cavity called the lacuna. Lacunae are given out into conaliculi in which processes of osteocytes are present.
In mammalian bone the osteolytes are present in concentric rings around the central canal called the Haversian canal.
The Concentric rings of bone cells along with the Haversian canal is called Haversian system
The bones are bounded externally by a connective tissue called periosteum .
Blood consists of plasma and blood Corpuscles. Plasma is a straw-coloured fluid which contains 85-90% water and 5-10% of the organic and inorganic substances of sulphates.
Blood cell are of three types-
(i) Red blood cells (RBC) or Erythrocytes.
(ii) White blood cells (WBC) or Leucocyles.
(iii) Blood platelets.
It is a transparent yellow flied. It is chemically similar to blood plasma except that it contains very little proteins and it does not contain. R.B.C.
Due the absence of R.B.C. its colour is not red but it contain the another type of cells called W.B.C.
Lymph is present in the inter cellular spaces hence it is also called tissue fluid.
Muscles of the body are made of muscles cells or muscles fibres.
The movement of the body or limbs is brought about by contraction and relaxation of contractile proteins present in muscle cell.
The movement of the heart and alimentary canal are all caused by muscle tissue
There are three types of muscle fibres:-
(i) Striated muscle (skeletal muscle or voluntary muscle).
The skeletal muscles are attached to the bones and help in movement.
Cells of this tissue are long cylindrical, non tapering and Unbranched.
There are many nuclei (multinucleated) which are situated towards the periphery of the muscle fibre.
(ii) Unstriated muscle (Smooth muscle or involuntary muscle)
The smooth muscle tissues are found within the walls of all the tubular organs such as stomach, intertine, ureter, bronchi etc
The cells are long with pointed ends (spindle shaped)
The cell has only one nucleus (uninucleate) situated in the centre.
It does not show any stripes or striations across the muscle.
(iii) Cardiac muscle: –
This type of muscle tissue is exclusively present in the heart.
Composed of non-tapering cells with faint cross striations
Each cell contains one or two nuclei situated at the centre.
The function is rhythmic contraction and relaxation throughout life with out fatigue under normal condition.
The cells one cylindrical and branched.
Nerve cell or neurons are the structural and functional unit of nervous tissue.
In cytoplasm, Nissle’s granules are made up of neurofibrils and RNA. Cell organelles like mitochondria golgi-bodies etc are also present in the cytoplasm of nerve cell.
The axon is covered from outside by three layers- the innermost layer is called axulemna, the middle layer is called myselin sheath, or modularly sheath and outer most layer is called neurilemma.
The axolemma and neurilemma are continuous sheath, they are constricted at intervals. These constrictions are known as Nodes of Ranvier
The Loose connection between the axon endings of one nerve cells and the cyton of the next nerve cell is called Synapses
The small branches given out by cyton are called dendrons, which farther divide to form dendrites.
In dendrons and dendrites, Eytoplasm and Nissl’s granules are present.