Minggu, 28 Maret 2010

Epithelial Tissue

Chapter I

Introduction

A. Background

The body of Human, animal, and plant consist of cells because the characteristic of living things is that they are made of cells. The cell is the basic unit of life. Cell also known as the structural unit, functional unit, growth unit, and heredity unit of organism. As the consequence of development and specialization, cells show variety in shape and structure. The great variety of cell sructure reflects the evolutionary adaptations of cells to different environments, and to different specialised functions within a multicellular organism.

The group of cells which has similar structure to perform a similar function is known as tissue. Four primary tissue in our body are epithelial tissue, muscle tissue, connective tissue, and nerve tissue. The sheets of cells at epithelium may develop into covering of the outer and inner surfaces of the body and the glands. The cells f muscular tissue are of several varieties which are associated with movement of the skelton and contractility in many organs. Connective tissues serve to bind the organs one another and to maintain the shape of body. Meanwhile, the cells of nerve tissue are concerned primarily with rapid conduction of impulses in the integration of numerous functions, such as to receive stimuli from the environment, to transform stimuli into the nervous encitations, and to transmit them to the nervous centers where they are reorganized to call frth the appropriate responses.

As cells are agregated to form tissues, so they are combined and integrated in different manners to form functional structure of the organs of body.

To help us understand about our body, of course we shuld firstly understand about its structure. Thus, the first step that we ought to do is enrich our understanding about epithelial tissue. Why must we understand about epithelial tissue firstly? It is a simple question, but it will be able to help us to realize that epithelial tissue has an important rule in our body. Early histologist described epithelium as a layer of closely connected cells lining the cavities of the body. Epithelial tissue is the tissue which consists of the cells that have the same shape, and they are connected one another with a less amount of intercellular substances. Epithelium forms the outer protecting surface of the body and all the glands, and also furnishes important parts of the sense organs. Hence, it is imprtant for us to do this experiment, because we will have a chance to analyze the structure of epithelial tissue under the microscope.

B. Purpose

The purpose of this experiment is t observe the various type of epithelial tissue and glands.

C. Benefit

After doing this experiment, the students will be able to understand about the particular characteristics and particular functions of various epithelial tissue and glands.

CHAPTER II

PREVIEW OF LITERATURE

Early histologist described epithelium as a layer of colsely connected cells lining the cavities of the body. The term was later extended to the similar layers covering the body, and was further broadened when it was shown that vertebrate embryos pass through a stage during which they consist of three simple layer of cells (the embryonic germ layers called ectoderm, mesoderm, and endoderm). Part of the outer germ layer, or ectoderm, curves inward to form the neural tube, frm which develop the elements of the brain and spinal cord. The rest of the ectoderm keeps its epithelial form and gives rise to the epidermis, the lining of the oral cavity, and parts of the sense organs. The inner layer, the entoderm, furnishes the epithelial lining and the glands of the intestinal and respiratory system. The middle layer, or mesoderm, keeps its epithelial character in the epithelium os urinary and genital systems. The part of the mesoderm which line the celom (the peritoneal, pleural, and pericardial cavities) is an apithelium of special type and is called mesothelium (Bloom. 1964).

According to (Bevelander. 1988), Epithelial tissue has two kinds of structure and function, they are as follows:

1. Epithelial tissue may appears in sheets, the thickness is one or two layers. This kind of epithelium functions to cover the body surface or lining the cavity of body or shapes covering skin or lining membrane.

2. Epithelial tissue may appears in a group of cord, tubule, or folicula, which has develped as the branch of epithelial sheets and has a particular function for secretion, absrpsion r secretion. Such cells organisation is called glandular epithelium.

Simply, we can say that epithelial tissues are distinguished into covering epithelium and glandular epithelium. Epithelial tissue is the tissue which consists of cells with the same shape, and they are bound tightly one another by less extracellular matrix. Meanwhile, glandular epithelium is epithelial tissue which undergo invagination, pass through the low-lying tissue, and develops to be the cells of secretion or the cells of glandular (Halifah. 2004).

According to (Bevelander. 1988), the general function of epithelial tissue are as follows:

1. Its cells is regularly and it does nt have a large prtplasm prcesses; epithelial sheets generally bound tightly one another and is kept at such condition by a particular part of its cellsurface which is known as junctional complexes.

2. Less extracellular matrix among its cells. Its matrix consist of ground substance which contain mucopolysaccharide acid (glycosaminoglycan), such as hyaluronat acid and chondroitin sulfate. Calcium which is bound at its matrix has an imprtant rule in cell adhesion.

3. Epithelial tissue is avascular. Thus, it must be given fod strorage by the capilar through diffusion process.

4. Epithelial tissue is bound at connective tissue which located under the epithelium by a thin membrane called “Lamina Membrane”.

5. At epithelial tissue, we can observe a huge number of mitosis, and it is the sign of cells regeneration.

According to (Currey, 2005), there are a few functions of epithelial tissues. Such as:

1. Barrier

Epithelial tissue commonly functions as a covering or lining for organs and other tissues such at the skin, mucous membranes, intestinal tract, pleural cavity, etcetera. In this way, epithelial cells serve as selective barriers between the environment and the internal structures of the body. They protect underlying tissues from drying, and from mechanical and chemical injury. Tight junctions between individual cells play an important role in the barrier function of epithelium. Some barrier epithelial cells have motile cilia that propel fluid or particulate matter over tissue surfaces (e.g., cells lining the bronchi).

2. Absorption

Epithelial cells are found in those organs (e.g., small intestine) which are involved in absorption of substances important for life. These cells often have microscopic projections on the apical surface of their plasma membranes called microvilli which increase cell surface area in order to facilitate absorption. Groups of epithelial cells lining the small intestine are organized into larger finger-like structures called villi which project into the lumen of the gut to further increase its surface area and aid the process of nutrient absorption.

3. Secretion

The secretory cells of endocrine and exocrine glands are epithelia. Secretory epithelial cells are often collected together to form a gland that specializes in the secretion of a particular substance. As illustrated, exocrine glands secrete their products (such as tears, mucus, and gastric juice) into ducts. Meanwhile, endocrine glands secrete hormones into the blood.

4. Sensory

Many of the more complex sensory receptors of the nervous system are derived from specialized epithelia called neuroepithelia (e.g., the rods and cones of the retina, olfactory receptors of the nose, taste receptors on the tongue, etc.). Sensory receptors function by converting mechanical, chemical, or electromagnetic signals from the environment into nerve impulses which can be processed by the nervous system.

5. Contractility

Some very specialized epithelial cells (myoepithelia) contain the contractile proteins myosin and actin similar to muscle. Myoepithelia are associated with the ducts of sweat, salivary, lacrimal, amd mammary glands and assist in the secretory process.

Besides the function above, another functions of epithelial tissue according to (Anonyma. 2010) are as follows:

1. Protection

Epithelial cells from the skin protect underlying tissue from mechanical injury, harmful chemicals, invading bacteria and from excessive loss of water.

2. Diffusion

Simple epithelium promotes the diffusion of gases, liquids and nutrients. Because they form such a thin lining, they are ideal for the diffusion of gases (eg. walls of capillaries and lungs).

3. Cleaning

Ciliated epithelium assists in removing dust particles and foreign bodies which have entered the air passages.

4. Reduces Friction

The smooth, tightly-interlocking, epithelial cells that line the entire circulatory system reduce friction between the blood and the walls of the blood vessels.

According to (Currey. 2005), the nomenclature of epithelial tissues classifies them according to the shape of their component cells, whether they are organized in sheets of single-cells or layers of many cells, and by their general functions. The types of those epithelial tissues are as follows:

  1. Covering epithelia

1.1. Simple epithelium - Cells arranged in a single layer.

1.2. Simple squamous epithelium (squamous = scale-like) - Tissues composed of irregular, thin, flat cells with elongated and elliptical nuclei. Squamous cells are wider than they are tall.

1.2.1. Endothelium - the special term applied to the simple squamous epithelium lining blood vessels.

1.2.2. Mesothelium - the special term applied to the simple squamous epithelium lining the thoracic, abdominal, and pericardial cavities.

1.3. Simple cuboidal epithelium - Regularly shaped block-like cells with spherical nuclei. Found on the surface of ovaries and thyroid. The width and height of cuboidal cells are approximately equal.

1.4Simple columnar epithelium - Tall, elongated, column-like cells. Found in the lining of the stomach, intestine, gallbladder, and uterine tubes. Columnar cells are taller than they are wide.

1.5 Stratified epithelium - Cells arranged in two or more layers. Found primarily on the "wear and tear" surfaces of the body. In stratified epithelium, the height and width of cells vary from one layer to the next. Only the shape of the cells of the surface layer are used to classify stratified epithelium as squamous, cuboidal, or columnar.

1.6 Squamous keratinized stratified epithelium - Cells that are located near the basement membrane are block-like in shape, but gradually become flat and irregular as they migrate to the surface. Found primarily as covering on the dry surfaces of the body - e.g., the epidermis of the skin. The most superficial layers of the epidermis contain dead squamous cells composed mostly of the protein keratin. These cells are continually being lost from the surface of the body and replaced by new cells produced in the deeper (basal) layers.

1.7 Squamous nonkeratinized stratified epithelium - Stratified squamous cells that cover many of the moist surfaces of the body such as the mouth, vagina, and anal canal. Surface cells are not heavily keratinized.

1.8 Cuboidal stratified epithelium - Several layers of cuboidal cells. Found in the ducts of sweat and sebaceous glands, and ovarian follicles.

1.9 Transitional epithelium - Also called uroepithelium. Stratified epithelial tissue with unique dome-shaped surface cells giving it a cobblestoned appearance. Found exclusively in the urinary system (lining of bladder and ureter). They serve as a barrier preventing the exposure of underlying tissues to urine. They are also able to stretch in response to bladder filling.

1.10 Columnar stratified epithelium - Not very common. Found in the bulbar conjunctiva (membrane covering whites of eyes).

1.11 Pseudostratified epithelium - Intermediary between simple and stratified epithelium. Consists of one layer of irregularly shaped and sized cells attached to a basement membrane. Because these cells vary in height, their nuclei are at different levels, giving the appearance (under the microscope) of more than one layer of cells. Found in lining of the trachea, bronchi, pharynx, nasal cavity, and urethra.

2. Glandular Epithelia - Multicellular epithelial structures that specialize in synthesizing and secreting complex molecules. Glands are commonly classified by the mechanism they use to secrete their products:

2.1. Exocrine glands - Glandular tissue that have ducts that open onto a body surface or into a body cavity. Examples include sebaceous, sweat, and mammary glands. Salivary glands and certain glandular structures of the pancreas that secrete digestive enzymes are examples of exocrine glands secreting into a body cavity. The secretions of exocrine glands can be mucous (viscous), or serous (thin, watery). The ducts of exocrine glands may be simple straight tubes, or can be arranged as more complex branching tubes. Some of the more complex branching duct systems may terminate in multiple sac-like structures called acini giving them a "bunches of grapes" appearance. Exocrine glands can also be classified by their secretion mechanism.

2.1.1. Merocrine glands - Glands that secrete substances by the process of exocytosis (fusion of cytoplasmic vesicles with the plasma membrane resulting in the release of their contents into the extracellular space without compromising the integrity of the cell membrane). Sweat glands (eccrine sweat glands) and salivary glands are merocrine in nature. The lining of the respiratory and digestive tracts contain "goblet cells" - glandular epithelia that synthesize and secrete a complex glycoprotein called mucus. Mucus provides a protective function as well as serving as a lubricant.

2.1.2. Apocrine glands - Glands that secrete by shedding the apical portion

of their cytoplasm into a duct (e.g., mammary glands). Sweat glands in the axillae, perianal region, and external genitalia are also apocrine in nature.

2.1.3. Holocrine glands - Glands that secrete by shedding entire cells from the lining of a duct (e.g., sebaceous glands).

2.2. Endocrine glands - Glandular tissues that have no ducts opening onto a surface or into a cavity. Most endocrine glands secrete their products (hormones) across basement membranes into connective tissues where they are absorbed by nearby blood vessels and transported to target organs (e.g., pituitary, and adrenal glands).

3. Unicellular Glands - These are the simplest forms of glands which consist of single cells called goblet cells commonly found in the lining of the digestive and respiratory tracts. The secretory product of unicellular glands is mucous.

CHAPTER III

OBSERVATION METHOD

A. Time and Place

This experiment had been done at :

Day and date : Saturday, March 20th 2010

Time : 14.00 – 16.00

Place : Laboratory of Biology, Mathematic and Science Faculty of Makassar State University

B. Tool and Material

1. Tools : a. Microscope

b. Pipette

c. Drawing book

d. Pencil

2. Materials : The permanent speciment of:

a. Simple cuboidal epithelium at Mammal kidney

b.Simple columnar epithelium at Intestine/ Duodenum

c. Simple squamous epithelium at Mammal kidney

d. Pseudostratified ciliated epithelium at Trachea

e.Keratinized stratified sqoamous epithelium at Human skin

f. Mucous and serosa glands at Pancreas

C. Work Procedure

1. Prepared all the tools and materials which was needed

2. Set the misroscope to get the best lighting

3. Took and put the permanent speciment on the stage of microscope

4. Rotated the coarse adjustment knob and smooth adjustment knob of the microscope until

Get the best appearance of the speciment which would be observed.

5. When the best appearance of speciment could be found, stop rotating the smooth Adjustment knob

6. Drew the image which appeared at the microscope

7. After drawing, rotate the coarse adjusment knob to turn up the tube of microscope. Then, changed the speciment at the stage with the next speciment.

8. Repeated the steps above to get the best appearance of the speciment, and than draw each image of each speciments.

CHAPTER IV

OBSERVATION RESULT

A. Observation result

1. Simple cuboidal epithelium at Mammal kidney

Note: 1. Cytoplasm

2. Cell wall

3. Nucleus

4. Basement membrane

2. Simple squamous epithelium at Mammal kidney

Note: 1. Stratum korneum

2. Stratum lusidium

3. Stratum granulosum

4. Stratum spinosum

5. Stratum germinatifum

6. Basal membrane

3. Simple collumnar epithelium at Intestine/ Duodenum

Note: 1. Cytoplasm

2. Cell wall

3. Nucleus

4. Basement membrane

4. Pseudostratified ciliated apithelium at Trachea

Note: 1. Cillia

2. Goblet cell

3. ciliated cell

4. basement membrane

5. Connective tissue

5. Keratinized stratified squamous epithelium at Human skin

Note: 1. Epidermis

2. Dermis

3.Hypodermis

4. Subcutaneous fat tissue

5. Blood vessel

6. The mucous and serosa gland at Pancreas (Islets of Langerhans)

Note: 1. Islets of Langerhans

2. Interlobular connective tissue with

duct.

  1. Discussion

1. Simple cuboidal epithelium at Mammal Kidney

It has pink colour. The parts of its cells which are able to be observed are cytoplasm, cell wall, nucleus, and beasement membrane. As their name implies, cuboidal cells are roughly square or cuboidal in shape. The height of the cell body is about equal to the width. When seen from the free surface, the cells appear as small polygons. Meanwhile, when seen in a section perpendicular to he surface they appear square. Thus, they are also known as short prisms. Each cell has a spherical nucleus in the centre. Cuboidal epithelium is found in glands and in the lining of the kidney tubules as well as in the ducts of the glands. They also constitute the germinal epithelium which produces the egg cells in the female ovary and the sperm cells in the male testes.

2. Simple columnar epithelium at intestine

It appears in pink colour. Its parts of cells which are able to be observed are cytoplasm, cell wall, nuclues, and also basement membrane. The height of its cell greatly exceeds the width. In a section parallel to the surface the cells appear as a small polygons, but in a perpendicular section they appear as rectangels. They are irregular tall prisms. Columnar epithelial cells occur in one or more layers. The cells are elongated and column-shaped. The nuclei are elongated and are usually located near the base of the cells. Columnar epithelium forms the lining of the stomach and intestines. Some columnar cells are specialised for sensory reception such as in the nose, ears and the taste buds of the tongue. Goblet cells (unicellular glands) are also found between the columnar epithelial cells of the duodenum. They secrete mucus or slime, a lubricating substance which keeps the surface smooth.

3. Simple squamus epithelium at Mammal kidney

Its nuclei is stained purple, and its area of cytoplasm is stained pink. The height of the cell body is negligible in comparison with the other dimension. The cell is a thin layer. In profile it looks like a slender rod which is usually slightly thickened in the vicinity of the nuclues. The structure highlighted with normal color is in three-dimensions, a sphere composed of a thin outer wall of cells, a space that contains fluid, and an inner region of cells. The outer wall is composed of a single layer of flat cells (a simple squamous epithelium). The simple squamous epithelium shown here is the outer wall of the glomerular capsule.

4. Pseudostratified ciliated epithelium at trachea

Intermediary between simple and stratified epithelium. Consists of one layer of irregularly shaped and sized cells attached to a basement membrane. Because these cells vary in height, their nuclei are at different levels, giving the appearance (under the microscope) of more than one layer of cells. Found in lining of the trachea, bronchi, pharynx, nasal cavity, and urethra.

5. Keratinized stratified squamous epithelium at human skin

The skin covers the surface of the body and consists of two main layers, the surface epithelium, or epidermis, and the subjacent connective tissue layer which is called dermis or corium. Beneath the latter is a looser connective tissue layer, the superficial fascia, or hypodermis, which in many places is transformed into subcutaneous fatty tissue. The epidermis is stratified squamous epithelium, te external layer of which keratinizer or cornifies. It serves to continous rubbing, pressure, and other physical agents such as ultraviolet light, may cause a great thickening of he horny layer on exposed areas of the body surface.

Cells that are located near the basement membrane are block-like in shape, but gradually become flat and irregular as they migrate to the surface. The most superficial layers of the epidermis contain dead squamous cells composed mostly of the protein keratin. These cells are continually being lost from the surface of the body and replaced by new cells produced in the deeper (basal) layers.

6. Observe the mucous and serosa at pancreas (islets of langerhans)

The pancreas is the largest gland connected with the alimentary tract. It consists of an exocrine portion, which elaborates certain digestive juices, and an endocrine portion, whose secretion plays an important part in the control of the carbohydrate metabolism of the body. The exocrine and endocrine functions of the pancreas are carried on by distinctly different group of cells. In addition to the external-secreting portion of the gland, the pancreas also contains islets of langerhans. These are irregular masses of cells. The islets of langerhans seem to be composed of cords of irregularly prismatic cells distinctly paler than the surrounding acinas cells. The are three type of granular cell which can be found at Langerhans. The A cells have granules which are large and stain brilliant red. The B cells have smaller, brown-orange granular. While the third type of cell, called D, is filled with smal, blue stained granular.

CHAPTER V

CONCLUTION AND SUGGESTION

A. Conclusion

Based on the result of this experiment, we can conclude that epithelial tissue is classified according to its shape and layer. There are three kinds of epithelial tissue based on its layer, they are simple epithelial, stratified epithelial, and pseudostratified epithelial. Meanwhile, there are also three kinds of epithelial tissue based on its shape, they are squamous epithelial, cuboida epithelial, and columnar epithelial. In addition, The epithelial tissues can also be classified according to their functions, they are covering epithelial tissue and glandular epithelial tissue.

B. Suggestion

1. It will be better to learn about the topic of Epithelial Tissue before doing this experiment.

2. Be careful to analyze and draw each kind of tissue to get an accurate data.

3. While experimenting, use the microscope in the right and good manners.

Bibliography

Anonyma. 2010. “Epithelial Tissues.” http://

Accessed at March 20th 2010.

Bevelander, Gerrit. Dkk. 1988. “Dasar-Dasar Histologi”. Jakarta: Erlangga

Bloom, William. 1964. “A Text Book of Histology.” USA: W.B. Saunders Company.

Currey, Charles J. 2005. “Part II: Epithelial Tissue.” http://universityofflorida.com. Accessed at March 20th 2010.

Pagarra, Halifah, Ir. Drs, Adnan, M.S. 2004. “Struktur Hewan.” Makassar: FMIPA UNM

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