Supplementary LessonKinds of Tissues

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http://www.anselm.edu/homepage/jpitocch/genbio/organizationnot.html

Systems composed of Organs

Organs composed of Tissues

Tissues composed of Cells

Tissues - major components of systems and organs

What are tissues?

Muscular tissue: Muscular tissues make up the major part of the soft tissues of the body & by means of its contraction power helps in locomotion. e.g. – Skeletal muscle, cardiac muscle.

Nervous tissue: Nervous tissue is highly specialized tissue which controls & co-ordinates the body functions by forming nervous system. e.g – Neuralgia, White matter, Grey matter.

Types of Tissue:

Connective tissue: Connects different structures of the body & also helps to provide framework of the body. e.g. – Blood, Bones.

Epithelial tissue: are formed of cells that line the cavities in the body and also cover flat surfaces. Of the four major tissue types found in the human body epithelial cells are by far the most prolific.

The muscular, connective and nervous tissues mentioned on the previous slides will be discussed further in the Organ System discussion for that particular organ.

The succeeding slides will focus on Epithelial tissues.

1) Epithelial - linings and coverings a) simple - single layer (found in the

intestineb) stratified - multiple layers c) cuboidal - cube shaped (secretory)d) columnar - column shaped (found in

the intestine)e) squamous - flat for diffusion (found in

the lungs)

Special types of tissues Epithelial tissue: Covering the external & internal body surfaces. e.g. – Skin, internal covering of (Gastro-intestinal Tract) GIT.

Where can be found?

Tissues of the stomach

An epithelium may be one or more cells thick and the cells may be of very different shapes and sizes. Some are thin and flat. They form pavement or squamous epithelium which is found, for example, in the lining of parts of the kidney tubes.

Epithelial cells line the major cavities of the body.Epithelia form the structure of the lung, including the alveoli or air sacs where gas exhange occurs.• Cells line most organs, such as the

stomach and small intestine, kidney, and pancreas. They also line the esophagus.

• Cells are also found in ducts and glands, like the bile duct and sailvary glands.

Where Are Epithelial Cells Found? 

•The skin is made of epithelial cells. Its striated layers demonstrate the extensive morphology of epithelia.•Capillary beds are made of epithelium.•Epithelia is the first type of cell to differentiate in the embryo. This occurs during the eight-cell stage.

•Epithelia can specialize to act as sensory receptors. They form taste buds, line the nose, and are in the ear. They are also found in the eye.•Female reproductive organs are lined with ciliated epithelial cells.

How Do Epithelial Cells Differ From Other Cells?Avascular•Capillaries do not reside within epithelial cell tissues.Sensory•Endings of neurons are present within epithelial cell tissues•Perceive external stimulus (i.e. Tactile)

Gliding surface layer•Epithelial cells slough off and glide in order to replace dead cells.•This function allows epithelial cells to maintain a closed barrier to the external environment.

Transitional•Multi-layered epithelia are able to stretch•Allows the urinary bladder to distended or contracted without compromising itTight barrier•tight junctions•Epithelium is held together more tightly than other cells•Aids cells in withstanding mechanical stress

Different from endothelial cells•Endothelial cells line the insides of structures that aren’t exposed to the “outside”•Ex. Blood vessels

Structure of Epithelial Tissue

Epithelial cells are bound together in sheets of tissue called epithelia. These sheets are held together through several types of interactions, including tight junctions, adherence, and gap junctions.

One type of junction found only in epithelium is the tight junction, which is considered by most scientists as the closest junction in the world. http://www.bio.davidson.edu/people/kabernd/BerndCV/Lab/EpithelialInfoWeb

/index.html

Tight junctions act as the delineation between the apical (upper) and basal (lower) regions of an epithelial cell in conjunction with polarization between the two regions. Epithelium is supported on the basal side by a basement membrane called the basal lamina.

Below the basal lamina lies the capillary bed, which provides epithelia with required nutrients and disposal of waste products. In addition, the nucleus in the epithelial cell is usually found closer to the basal surface than the apical surface.

When the cells of squamous epithelium have wavy outlines (e.g., cells lining the blood vessels) they are said to be tessellated. Other cells are approximately as wide as they are tall. These form cuboidal or cubical epithelium which is found in many glands (e.g., the liver). In columnar epithelium the cells are tall and column-shaped. Such epithelium lines most of the gut. 

If columnar cells bear cilia the epithelium is known as ciliated columnar epithelium. Ciliated cells occur in the lining of the trachea (windpipe). The cilia beat to help remove dirt particles. 

The outer cells of the skin and the lining of the cheek form stratified squamous epithelium. It is also found in the front, transparent layer of the eye (cornea). 

A layer or sheet of cells that lines a body cavity; they show an unusually high cell-turnover rate. Epithelial cells are held together by a small amount of cementing substance. The outer covering of the body (the skin), the lining of the gastrointestinal tract and other organs, such as the lungs and blood vessels, and the inner lining of the ducts in glands are examples. 

Below most epithelia is a thin sheet of connective tissue, the basement membrane. The free surface of most types of epithelium (the surface that is not attached to other tissue) may have on it short hair-like structures called cilia. 

The ones forming the outer covering of the skin are mainly protective and water-resistant, while the cells of the lung lining produce the wet mucusin which oxygen dissolves before passing to the blood. 

http://www.daviddarling.info/encyclopedia/E/epithelium.html

When the epithelium is several layers of cells thick it is said to stratified. 

The cells of epithelia may serve very different purposes. Those lining the salivary glands, and the glands in the intestine for example, produce the enzymes that digest food.

Functions 

Boundary & Protection

Epithelial cells cover the inner and outer linings of body cavities, such as the stomach and the urinary tract. As the barrier between the outside world’s contaminants and the body, these cells replicate often to replace damaged or dead cells.

Many layers provide better protection, meaning if one layer is lost, the underlying tissue is still protected. Tight junctions, are very difficult to alter or break and create a semi-permeable seal that few macromolecules or microbes can penetrate.

Sensory

Although epithelial cells are avascular, they are innervated. These nerve endings provide signals for sensory sensations such as taste, sight, and smell. These cells exhibit specialized structure to fulfill their function.

AbsorptionThe ability of certain epithelial cells to use active-transport systems, as discussed above, enables them to absorb filtered material, such as glucose from the lumen of the intestine, which can then be circulated to the rest of the body. Cells are also able to endocytose other materials that are necessary for cell growth and signaling. For more information, see transcytosis.

TranportationSome epithelial cells, such as the ones found on the intestinal lining, aid in the transportation of filtered material through the use active-transport systems located on the apical side of their plasma membranes.  For example, the glucose-Na+ pump located within certain domains of the plasma membrane of epithelial cells lining the intestine enable the cells to generate Na+ concentration gradients across their plasma membranes, which provides the energy needed to uptake glucose, from the lumen of the intestine.

The glucose is then released into the underlying connective tissues and is transported into the blood supply through facilitated diffusion down its concentration gradient.

Secretion & LubricationSome epithelial cells, such as the goblet cells, secrete fluids that are necessary for other processes such as digestion, protection, excretion of waste products, lubrication, reproduction, and the regulation of metabolic processes of the body. As part of its excretory role, certain epithelial cells secrete mucus, which lubricate the body cavities (i.e. peritoneum, pericardium, pleura, and tunica vaginalis) and passageways that they line.

In the trachea, goblet epithelial cells secrete mucous which provides the lubrication to aid ciliated epithelial cells in sweeping bacteria and dust away from the lungs. In addition, type II alveolar cells excrete pulmonary surfactant, which decreases surface tension, allowing for normal lung function.

Movement

Some epithelial cells have cilia, which aid in moving substances in the lumen by creating a current via coordinated "sweeping" of the cilia.

In the trachea, goblet epithelial cells secrete mucous which provides the lubrication to aid ciliated epithelial cells in sweeping bacteria and dust away from the lungs. In addition, type II alveolar cells excrete pulmonary surfactant, which decreases surface tension, allowing for normal lung function.

For instance, ciliated columnar epithelial cells are instrumental in the movement of the ovum through the Fallopian tubes to the uterus.

Answer the following:Send your answer through:

arlene_salustiano@teacher.gov.ph

1. What are the four major classification of tissues?

2. For each kind of tissues give at least three organs where it can be found.

I would like to thank the following:http://www.anselm.edu/home

page/jpitocch/genbio/organizationnot.html

http://www.bio.davidson.edu/people/kabernd/BerndCV/Lab/EpithelialInfoWeb/index.html

Prepared by: Arlene G. Salustiano