Skip to main content

Renin Angiotensin Mechanism.

Epithelium Tissue.

 Tissue level of organization: Epithelium Tissue.

Introduction:

  • Also called “Epithelium”.

  • It forms the covering of organs.

  • They are derived from all three embryonic layers.

Epithelium Tissue.

Location of Epithelial Tissue:

  • Covering of the organs exposed to the outer environment e.g. skin, GI tract, respiratory tract, urinary and reproductive tract etc.

  • Epithelium tissue forms much of the glandular tissue. 

  • It forms the internal lining of the cavities and hollow organs.

Basic Functions of Epithelium Tissue:

  1. Protects the body from physical, biological and chemical wear and tear.

  2. Selective transport: Act as gatekeeper as forms covering the tissues.

  3. Secretion: Secretes mucus and other chemicals.

  4. Absorption: Intestinal columnar epithelium.

  5. Excretion: Sweat Glands.

Structural Features of Epithelium Tissue:

  • Epithelium tissue is tightly packed.

  • Non vascular: No blood supply (Receives nutrients and oxygen by diffusion)

  • Cells shows intracellular junctions for communication.

  • Cell has three surfaces;

    • Apical: Upper Surface

    • Lateral: Side.

    • Basal: Lower.

  • The basal layer secretes certain substances like collagen and glycoproteins which form basal lamina, basal lamina separates epithelium from underlying connective tissue.

  • The underlying connective tissue secretes and forms reticular lamina.

  • The reticular lamina and basal lamina together form the basement membrane which acts as a site of attachment for the epithelium tissue.

Classification of Epithelial Tissues:

  1. Simple Epithelium:

    1. Simple Squamous Epithelium.

    2. Simple Cuboidal Epithelium

    3. Simple Columnar Epithelium.

  2. Stratified Epithelium:

    1. Stratified Squamous Epithelium.

    2. Stratified Cuboidal Epithelium

    3. Stratified Columnar Epithelium.

    4. Transitional Epithelium

  3. Pseudostratified Epithelium.

Simple Squamous Epithelium:

  • The cells are flat polygonal in shape and are tightly packed.

  • There is no direct blood supply and the transfer of materials takes place by diffusion from blood vessels of the underlying connective tissue.

  • The cells show the presence of intracellular junctions for communication.

  • The simple squamous epithelium that lines blood vessels and lymph vessels is specialized for faster chemical transfer and called “Endothelium”.

  • The simple squamous epithelium that lines the serous membranes is called “Mesothelium”, it secretes a secretion called “Serous Fluid” which serves as lubricating fluid and acts as a shock absorber.

  • The alveoli of the lungs where gases diffuse, segments of kidney tubules, and the lining of capillaries are also made of simple squamous epithelial tissue.

Simple Cuboidal Epithelium:

  • The cells are “Cube” like in structure hence called  Cuboidal epithelium.

  • Width is more as compared to height.

  • This tissue forms internal linings of Thyroid gland, salivary glands, nephrons etc.

Simple Columnar Epithelium:

  • The cells have a “Column” like structure hence called  Columnar epithelium.

  • Height is more as compared to width.

  • This tissue forms internal linings of intestines  etc.

  • They are specialized in functions of absorption and excretion.

  • Columnar epithelium of the intestine has “microvilli” which increases the surface area of the cells for absorption.

  • Goblet cells of the intestinal lining and the lining of parts of the respiratory tract such as the trachea have secretory function and secretes mucus.

Ciliated Columnar Epithelium:

  • Ciliated epithelium consists of columnar cells that have cilia on their apical surface.

  • Ciliated epithelium lines the nasal cavities, larynx, trachea, and large bronchial tubes.

  • The cilia sweep mucus, with trapped dust and bacteria from the inhaled air, toward the pharynx to be swallowed. 

  • Another location of ciliated epithelium in women is the lining of the fallopian tubes, the cilia here sweep the ovum, toward the uterus.

Stratified epithelium:

  • Stratified epithelia consist of several layers of cells of various shapes. 

  • Continual cell division in the lower (basal) layers pushes cells above nearer and nearer to the surface, where they are worn off.

  • Basement membranes are usually absent. 

  • The main function of stratified epithelium is “Protection”

  • There are two main types:

    • Keratinized stratified epithelium

    • Nonkeratinized stratified epithelium

Keratinised stratified epithelium:

  • This is found on dry surfaces subjected to wear and tear, i.e. skin, hair and nails. 

  • The surface layer consists of dead epithelial cells that have lost their nuclei and contain the protein keratin. 

  • This forms a tough, relatively waterproof protective layer that prevents drying of the live cells underneath. 

Non-keratinised stratified epithelium:

  • This protects moist surfaces subjected to wear and tear, and prevents them from drying out. 

  • e.g. the conjunctiva of the eyes, the lining of the mouth, the pharynx, the oesophagus and the vagina.

Commonly Asked Questions.

  1. Write a note on Epithelial tissue and explain its different types.

  2. Explain in detail the structure and functions of epithelium tissue.
Labels:

Popular posts from this blog

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called ...
Read more

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and ...
Read more

Flash Distillation.

  Principle: When a hot mixture is allowed to enter from a high-pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization .  During this process, the chamber is cooled.  The less volatile fraction is condensed and the more volatile component remains in the vapor phase .  This process requires time, hence liquid and vapor are kept in intimate contact until equilibrium is achieved. Flash distillation is also called equilibrium distillation because separation of two liquids takes place when liquid and vapor phases are at equilibrium. Equipment used for Flash Distillation: Construction: It consists of a pump, which is connected to a feed reservoir.  Pumps help in pumping the feed into the heating chamber.  The heating chamber is heat supplied by steam.  The other end of the pipe is directly introduced into the vapor-liquid separator through a reducing valve.  The vapor outlet...
Read more