Histology

TRAN DUNG

September 2007

LAB REPORT 1. TISSUES I.

Abstract

During this lab, we examined different types of tissues. The purpose of lab #1 is basic morphological differences between different tissues and how to identify them.

II.

Introduction

Tissue is an organized group of cells that have the same function. There are four basic types of tissue: - Epithelium: main function is protection. It is characterized by contagious cells which form single or multiple layers, usually line at the surface. - Connective tissue: support other tissues and various other functions (store heat, cushion, transportation…). The tissue contains cells and rich extracellular matrix. The cells are separated from one another. In some types of connective tissue where strength is required, the fibers are numerous. - Muscle tissue: responsible for movement. It is characterized by rich and highly ordered elongated cells. - Nerve tissue: receive, process and deliver information Notice the staining methods that are used in the samples.

III.

Materials and Methods

Five slides were examined: mammal artery, stratified squamous epithelium, human muscle, mammal mucous and human spinal cord. We observed, identified tissue types, drew pictures and compared them.

IV.

Results

Fig. 1: Mammal artery and vein – cross section The inner diameter of artery is smaller than that of vein, since artery has thicker muscle layer. Components of artery from the centre: thin endothelium, elastic lamellae (dense area of thin, elongated nuclei), circularly-arranged smooth muscle. We can see numerous arterioles and venules, which are much smaller and less stained than artery and vein. This is an example of muscle tissue. However, in this slide we can also observe dense irregular connective tissue, which has typical irregular shape

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TRAN DUNG

September 2007

Fig. 2: Stratified squamous epithelium The cells near basal layer are denser and may have cuboidal shape. At the upper layer, cells become regular shape – almost round. The cells are small, dense, the background is also stained.

Fig. 3: Mammal cardiac muscle – longitudinal section Very dense, elongated fibers Nuclei are centrally located and can be easily observed This is an example of muscle tissue

Fig. 4: Mammal mucous Surrounding the ducts are slightly stained cells. There’s a large amount of ground substance. Cells and fibers are sparse. Mucous is a form of connective tissue.

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TRAN DUNG

September 2007

Fig. 5: Human spinal cord (cross section) This is an example of nervous tissue. There’s a symmetrical, butterfly-shaped cellular matrix of gray matter, which is very dense at the centre. Peripheral region contains white matter. Cells are equally stained, nuclei are at the centre of cells.

V. -

Discussion

Cells of epithelium, muscle and connective tissues has very typical morphological characteristics, while nerve tissue cells are harder to recognize by observation. Nerve tissue is defined by function. Cells’ shape and arrangement are adapted to their function: Muscle and dense connective tissue have dense fibers which provide strength. Epithelium has dense cells and is located at inner or outer surface. When there’s a cluster of small dots, it could be either small blood vessels or nerve cells. The difference is that nerve cells have nuclei, while blood vessels have nothing inside. Sometimes it may be difficult to tell whether a cluster is blood vessels or nerve cells. We may need to know the origin and function of tissue to tell exactly..

VI.

References

Ross, M. et al. 2003. Histology, A text and Atlas. 4th ed. Lippincott Williams and Wilkins.

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TRAN DUNG

September 2007

LAB REPORT 2. EPITHELIAL TISSUE I.

Abstract

During this lab, we examined different types of epithelial tissue. The cell types and their arrangement are key points to identify epithelial tissue types.

II.

Introduction

Epithelium is usually found at the surface, in single or multiple layer. Epithelial cells are often contiguous, the background is often blank. There are 3 different cell shapes: squamous (flattened), cuboidal and columnar. Cells may be arranged in simple (one layer) or stratified (multiple layers) structure. Here are the main types of epithelium, followed by their location and fuction (respectively): - Simple squamous: line vascular system, body cavities, Bowman’s capsule and respiratory spaces in lung. Function: exchange and barrier. - Simple cuboidal: line small ducts of exocrine glands, surface of ovary and kidney tubules. Function: absorption and barrier. - Simple columnar: line small intestine and colon, stomach, gastric glands and gallbladder. Function: absorption and secretion. - Stratified squamous: epidermis, oral cavity, vagina. Function: barrier and protection. - Stratified cuboidal: sweat gland ducts, exocrine glands. Function: barrier and conduit. - Stratified columnar: largest ducts of exocrine glands, anorectal junction. Function: barrier and conduit. - Pseudostratified: trachea, ductus deferens. Function: secretion, absorption, conduit. Note that in this type, the cells’ arrangement looks like multiple layers but actually all cells contact with basal membrane. Simple types include only one cell layer, usually used for absorption, while stratified types usually serve as barrier.

III.

Materials and Methods

6 slides were provided: endothelium, simple cuboidal epithelium, simple columnar epithelium, pseudostratified ciliated columnar epithelium, stratified columnar epithelium, stratified squamous epithelium (skin and scalp).

IV.

Results

Fig. 1: Simple cuboidal There’s a thin line of cuboidal or square shaped cells at the surface. We can see nuclei at cells’ centre but the cytoplasm looks almost blank. The background is slightly stained but there’s nothing can be observed. Beneath the epithelium is connective tissue.

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TRAN DUNG

September 2007

Simple columnar epithelium This tissue is easy to recognize because of conspicuous and typical cell shape (the height is much greater than the width). Nuclei are highly stained. The cells line the ducts, therefore, their function would be absorption or secretion.

Stratified squamous epithelium There are many layers of squamous cells without any space between them. Cells are most dense at the inner layer (basal cells), where they contact with connective tissue

Pseudostratified ciliated columnar epithelium Cells are columnar shaped and dense; their nuclei are located at the inner side. By careful observation we can find that all cells contact with basal membrane. There are cilia on outer surface. There’s a thin line of shorter cells underneath columnar cells – this is basal membrane

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TRAN DUNG

September 2007

Fig. 5: Scalp (Stratified squamous epithelium) At the root of hair is stratified squamous epithelium tissue. The cells appear as described in Fig. 3

Fig. 6: Stratified ciliated columnar epithelium The top layer is columnar cells, while the inner layer is cuboidal cells. The nuclei are highly stained. Different from pseudostratified columnar epithelium, the cells here are more organized. There are only 2-3 layers of cells.

Fig. 7: Endothelium silver (squamous epithelium) The specimen has the typical brown – orange color. We can see dark small dots in cytoplasm. Cell borders are conspicuous, while nuclei are less stained

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September 2007

VII. Discussion -

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Difference between squamous and cuboidal epithelium: Squamous epithelium cells are very dense, every cell is contiguous with others; there’s no space between cells. On the contrary, in cuboidal epithelium we can observe extracellular space, as cells are not too close to each other. Cuboidal cells’ nuclei are more highly stained and round shaped. Squamous cells are usually found at the surfaces, with protective function. Cuboidal and columnar cells usually line along the ducts, their function is secretion. Columnar cells are easy to recognize because of their rectangular shape. Nuclei tend to locate near the inner side. When they form stratified tissue, there are only 1 or 2 layers of columnar cells, and a layer of cuboidal cells beneath. However, stratified epithelium is named after the upper layer, so such tissue is called stratified columnar epithelium. Among stratified epithelium: stratified squamous epithelium is most dense, with many layers of cells and there’s no space between them. Beside the familiar H&E stain, we can see the application of silver stain (with stratified squamous epithelium) and Picro Mallory (with scalp). The shortcoming of H&E stain is that it may not reveal basement membranes, cytoplasmic materials (mostly small particles). Silver stain can fix this problem.

VIII. References Ross, M. et al. 2003. Histology, A text and Atlas. 4th ed. Lippincott Williams and Wilkins.

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TRAN DUNG

September 2007

LAB REPORT 3. CONNECTIVE TISSUE I.

Abstract

During this lab, we examined 8 slides of connective tissue. We learned how the fiber types and matrix components vary in different types of connective tissue, depends on its function.

II.

Introduction

Connective tissue consists of cells and extracellular matrix which includes fibers, ground substance and fluid. Connective tissue is a broad category which is found almost everywhere in the body, with different functions: from structural support (eg. Tendons, ligaments), metabolism (eg. Adipose), blood’s component to defense. In lab #3 we looked at the following types of connective tissue: - Connective tissue proper: loose connective tissue and dense connective tissue (including irregular and regular) Loose connective tissue (areolar) has thin and sparse collagen but rich ground substance. We can see numerous nuclei. Loose connective tissue is located underneath the epithelium; therefore, it is the second barrier to prevent pathogens. It can also fills the place between muscle fibers, surrounds blood and lymph vessels. On the contrary, dense regular connective tissue has dense and well-organized fibers. The tissue may contain a small number of cells. The most common type of dense regular connective tissue is tendon. Tendon connects muscle to bone and is built to resist tension. Its fibers are arranged in bundles and may be surrounded by loose connective tissue Dense irregular connective tissue has random fibers and comprises a large portion of the epidermis. -

Specialized connective tissue: there are many types of specialized connective tissue. In this lab we’ll only look at adipose and cartilage. + Adipose is mostly composed of adipocytes, which contain fat droplets. This tissue stores energy and cushions the body. + Cartilage is avascular, with a large amount of hyaluronic acid. Cells (chondrocytes), fibers and matrix, which is composed of proteoglycans. * Hyaline cartilage: matrix contains type II collagen. Hyaline cartilage is characterized by the homogenous, amorphous matrix. It is both resilent and pliable, therefore, usually appear in synovial joints to distribute forces to joint’s components. * Elastic cartilage: characterized by elastic fibers and interconnecting sheets of elastic materials. It is found in external ear and epiglottis of the larynx. * Fibrocartilage: mostly consist of collagen fibers. There is no perichondrium and very small amount of amorphous matrix. Fibrocartilage is the combination of dense regular connective tissue and hyaline cartilage. Function : It resists compression and shock. -

III.

Mucous connective tissue: found in umbilical cord. Its gelatin-like matrix (Wharton’s jelly) fills the space between collagen fibers. The spindle-shaped cells are sparse and appear like fibroblasts.

Materials and Methods 8

TRAN DUNG

September 2007

In this lab we looked at 8 slides: fibrocartilage, hyaline cartilage, elastic cartilage, elastic tissue, adipose, areola (loose connective tissue), tendons (dense regular connective tissue), mucous connective tissue

IV. Results Fig. 1: Dense regular connective tissue: Tendons The collagen bulk has a homogenous appearance, therefore, it is impossible to distinguish one collagen fiber from another. Tendon cells are very dense and well organized. There are numerous flattened nuclei of tendon cells. Sometimes endotendineum (darker line) can be observed.

Fig. 2: Loose connective tissue – Aerolar There are numerous fibers. Some areas are very dense while some are not. Nuclei are round or a little bit flattened, usually located at cell’s centre. This tissue is characterized by large number of nuclei and un-organized fibers

Fig. 3: Elastic tissue In this cross section, we see the very dense fibers with little blank space between them

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TRAN DUNG

September 2007

Fig. 4: Fibrocartilage This tissue has dense, irregular fibers. There are more fibers than cells. The matrix appear blank. Fibers are stained blue, while nuclei are stained red. There are 2 types of nuclei: round-shaped nuclei (cartilage cells’) and few flat, elongated nuclei (fibroblasts’)

Fig. 5: Hyaline Cells are almost round shaped, always located in lacunae. Each lacuna may be occupied by 1 or few cells. The area around lacunae (capsule/territorial matrix) is highly stained. Cell cytoplasm and extracellular spaces appear blank.

Fig. 6: Elastic cartilage – H&E and orcein stain There are numerous cells (chondrocytes) on dark background. The elastic fibers appear as dark, elongated threads, usually at the edge of the tissue We can also observe adipose tissue in this sample.

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TRAN DUNG

September 2007

Fig. 7:Adipose The cells are almost round and blank. Nuclei are at the edge of cells. On background we can find some cluster of blood vessels

Fig. 8: Mammal mucous tissue The collagen fibers scatter on the blank background, around the ducts. This blank space would normally be fluid-filled. At higher magnification, we can see the network of collagen fibers and nuclei of fibroblasts.

V.

Discussion

Cells of epithelium, muscle and connective tissues has very typical morphological

VI.

References

Ross, M. et al. 2003. Histology, A text and Atlas. 4th ed. Lippincott Williams and Wilkins.

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