The study of tissue is known as histology or, in connection with disease, histopathology. The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.
Animal tissues
The epithelium in all animals is derived from the ectoderm and endoderm with a small contribution from the mesoderm, forming the endothelium, a specialized type of epithelium that comprises the vasculature. By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions, to create a selectively permeable barrier. This tissue covers all organismal surfaces that come in contact with the external environment such as the skin, the airways, and the digestive tract. It serves functions of protection, secretion, and absorption, and is separated from other tissues below by a basal lamina.
Connective tissue
Main article: Connective tissue
Connective tissues are fibrous tissues. They are made up of cells separated by non-living material, which is called extracellular matrix.
Connective tissue gives shape to organs and holds them in place. Both
blood and bone are examples of connective tissue. As the name. It
supports and binds other tissues. Unlike epithelial tissue, connective
tissue typically has cells scattered throughout an extracellular
matrix2.Muscle tissue
Main article: Muscle tissue
Muscle cells form the active contractile tissue of the body known as muscle tissue
or muscular tissue. Muscle tissue functions to produce force and cause
motion, either locomotion or movement within internal organs. Muscle
tissue is separated into three distinct categories: visceral or smooth muscle, which is found in the inner linings of organs; skeletal muscle, in which is found attached to bone providing for gross movement; and cardiac muscle which is found in the heart, allowing it to contract and pump blood throughout an organism.Nervous tissue
Main article: Nervous tissue
Cells comprising the central nervous system and peripheral nervous system are classified as neural tissue. In the central nervous system, neural tissue forms the brain and spinal cord and, in the peripheral nervous system forms the cranial nerves and spinal nerves, inclusive of the motor neurons. Nervous tissue functions to transmit messages in form of impulse.Epithelial tissue
Main article: Epithelium
The epithelial tissues are formed by cells that cover the organ surfaces such as the surface of the skin, the airways, the reproductive tract, and the inner lining of the digestive tract. The cells comprising an epithelial layer are linked via semi-permeable, tight junctions;
hence, this tissue provides a barrier between the external environment
and the organ it covers. In addition to this protective function,
epithelial tissue may also be specialized to function in secretion and absorption. Epithelial tissue helps to protect organisms from microorganisms, injury, and fluid loss. Functions:- the cell of the body surface form the outer layer of skin.
- inside the body,epithelial cells forms lining of mouth & alimentary canal & protect these organ.
- epithelial tissues help in absorption of water & nutrient.
- epithelial tissues help in elimination of waste product.
- Squamous epithelium,
- Cuboidal epithelium,
- Columnar epithelium,
- Glandular epithelium,
- Ciliated epithelium.
Plant tissues
1. Pith,
2. Protoxylem,
3. Xylem I,
4. Phloem I,
5. Sclerenchyma (bast fibre),
6. Cortex,
7. Epidermis
- Epidermis - Cells forming the outer surface of the leaves and of the young plant body.
- Vascular tissue - The primary components of vascular tissue are the xylem and phloem. These transport fluid and nutrients internally.
- Ground tissue - Ground tissue is less differentiated than other tissues. Ground tissue manufactures nutrients by photosynthesis and stores reserve nutrients.
- Meristematic tissues
- Permanent tissues.
Meristematic tissues
Meristematic tissue consists of actively dividing cells, and leads to increase in length and thickness of the plant. The primary growth of a plant occurs only in certain, specific regions, such as in the tips of stems or roots. It is in these regions that meristematic tissue is present. Cells in these tissues are roughly spherical or polyhedral, to rectangular in shape, and have thin cell walls. New cells produced by meristem are initially those of meristem itself, but as the new cells grow and mature, their characteristics slowly change and they become differentiated as components of the region of occurrence of meristimatic tissues, they are classified as:-
- a) Apical Meristem - It is present at the growing tips of stems and roots and increases the length of the stem and root. They form growing parts at the apices of roots and stems and are responsible for increase in length,also called primary growth.This meristem is responsible for the linear growth of an organ.
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- b) Lateral Meristem - This meristem consist of cells which mainly divide in one plane and cause the organ to increase in diameter and growth. Lateral Meristem usually occurs beneath the bark of the tree in the form of Cork Cambium and in vascular bundles of dicots in the form of vascular cambium. The activity of this cambium results in the formation of secondary growth.
Meristemetic tissue cells have a large nucleus with small or no vacuoles, they have no inter cellular spaces.
Permanent tissues
The meristematic tissues that take up a specific role lose the ability to divide. This process of taking up a permanent shape, size and a function is called cellular differentiation. Cells of meristematic tissue differentiate to form different types of permanent tissue. There are 3 types of permanent tissues:- 1. simple permanent tissues
- 2. complex permanent tissues
- 3. special or secretory tissues (glandular).
Simple permanent tissues
These tissues are called simple because they are composed of similar types of cells which have common origin and function. They are further classified into:Parenchyma
Parenchyma (para - beside ;chyma - in filling) is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants. It consists of relatively unspecialised cells with thin cell walls. They are living cells. They are usually loosely packed, so that large spaces between cells(intercellular spaces)are found in this tissue. This tissue provides support to plants and also stores food.In some situations, it contains chlorophyll and performs photosynthesis, and then it is called chlorenchyma. In aquatic plants,large air cavities are present in parenchyma to give support to them to float on water. Such a parenchyma type is called aerenchyma.Collenchyma
Collenchymatous tissue acts as a supporting tissue in stems of young plants. It provides mechanical support, elasticity, and tensile strength to the plant body. It helps in manufacturing sugar and storing it as starch. It is present in the margin of leaves and resist tearing effect of the wind.
Sclerenchyma
Sclerenchyma is Greek word where "Sclrenes" means hard and "enchyma" means infusion. This tissue consists of thick-walled, dead cells. These cells have hard and extremely thick secondary walls due to uniform distribution of lignin. Lignin deposition is so thick that the cell walls become strong, rigid and impermeable to water. Sclerenchymatous cells are closely packed without inter-cellular spaces between them. Thus, they appear as hexagonal net in transverse section. The cells are cemented with the help of lamella. The middle lamella is a wall that lies between adjacent cells. Sclerenchymatous cells mainly occur in hypodermis, pericycle, secondary xylem and phloem. They also occur in endocorp of almond and coconut. It is made of pectin, lignin, protein. The cells of sclerenchymatous cells can be classified as :- Fibres- Fibres are long, elongated sclerenchymatous cells with pointed ends.
- Sclerides- Sclerenchymatous cells which are short and possess extremely thick, lamellated, lignified walls with long singular piths. They are called sclerides.
Epidermis
The entire surface of the plant consists of a single layer of cells called epidermis or surface tissue. The entire surface of the plant has this outer layer of epidermis. Hence it is also called surface tissue. Most of the epidermal cells are relatively flat. the outer and lateral walls of the cell are often thicker than the inner walls. The cells forms a continuous sheet without inter cellular spaces. It protects all parts of the plant.Complex permanent tissue
The complex tissue consists of more than one type of cells which work together as a unit. Complex tissues help in the transportation of organic material,water and mineral up and down the plants. That is why it is also known as conducting and vascular tissue. The common types of complex permanent tissue are:- Xylem or wood
- Phloem or bast.
Xylem
Xylem consists of:- Tracheid
- Trachea
- Xylem fibers
- Xylem parenchyma.
Xylem is a very important plant tissue as it is part of the ‘plumbing’ of a plant. Think of bundles of pipes running along the main axis of stems and roots. It carries water and dissolved substances throughout and consists of a combination of parenchyma cells, fibers, vessels, tracheids and ray cells. Long tubes made up of individual cells are the vessels, while vessel members are open at each end. Internally, there may be bars of wall material extending across the open space. These cells are joined end to end to form long tubes. Vessel members and tracheids are dead at maturity. Tracheids have thick secondary cell walls and are tapered at the ends. They do not have end openings such as the vessels. The tracheids ends overlap with each other, with pairs of pits present. The pit pairs allow water to pass from cell to cell. While most conduction in the xylem is up and down, there is some side-to-side or lateral conduction via rays. Rays are horizontal rows of long-living parenchyma cells that arise out of the vascular cambium. In trees, and other woody plants, ray will radiate out from the center of stems and roots and in cross-section will look like the spokes of a wheel.
Phloem
Phloem consists of:- Sieve tube
- Sieve cell
- Companion cell
- Phloem fiber
- Phloem parenchyma.
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