Lab - Blood, Connective tissue and Epithelia

Blood

Slide - Normal blood smear

The cells of the blood fall into two types, the red and the white cells. Here we will be concerned only with the white cells or leukocytes. Using the blood smear you should find and identify the various cells present. The leukocytes are classified into two groups; the granulocytes contain cytoplasmic granules which stain according to the type present, the agranulocytes contain few stainable cytoplasmic organelles. The granulocytes can be differentiated according to the presence of specific granules, and the presence of multilobed nuclei. Neutrophils contain fine granules that do not stain intensely. The multilobed nucleus can usually be clearly seen. In the blood smear these cells should be quite common. Eosinophils have irregularly shaped nuclei and red-staining granules, while basophils contain blue-staining granules which may obscure the nucleus. The agranulocyte series is made up of lymphocytes and monocytes. Small and large lymphocytes may be present in the smear and can be distinguished from other leukocytes by the presence of a small amount of pale-staining cytoplasm around a rounded nucleus. Monocytes are much larger with more cytoplasm and a large indented nucleus.

Slide - Abnormal blood smear

Now that you have become an expert, examine this slide and try to determine what is different.

Connective Tissue

You have been provided with examples of loose and dense connective tissue. In each of these you should consider the types of cells present and the organization of the matrix in which the cells are embedded.

Slide - Mesenteric spread: Loose connective tissue

This slide has been prepared from the mesentery which suspends parts of the gut tube from the body wall. The two major components, the cells and fibres, can be clearly seen. You should find the numerous, small fibroblasts in which only the nuclei stain. More obvious, but fewer in number are the mast cells which contain basophilic granules which may be ruptured due to the method of preparation. Other cells such as macrophages, plasma cells and fat cells are present but are very difficult to distinguish in this preparation. The cells are embedded in a matrix of ground substance and fibres. Only the fibres can be seen. The large pink-staining fibres are collagen, while the fine straight, branching fibres are elastin. Small blood vessels, capillaries, are present. Note the loose nature of this tissue in which there are large numbers of cells embedded in a matrix containing fibres travelling in all directions. Compare this with the slide of tendon.

Slide - Tendon: Dense connective tissue

In this section the predominant visible component is collagen, arranged in parallel bundles in the long axis of the tendon. There are fibroblasts lying between the fibre bundles. Note that there are very few blood vessels. What are the major differences between these two types of connective tissue? Consider how they are adapted to their function, and how they may react to disease or injury!

Bone and cartilage are also types of specialized connective tissue. At this stage it is sufficient for you to be aware of the basic composition of these tissues i.e. that they have a structure which is common to all connective tissue - cells embedded in a matrix. In bone the primary cell type is the osteocyte, however other cell types such as osteoclasts are also present. In cartilage the primary cell type is the chondrocyte. In both hard tissues the matrix is highly specialized containing fibres such as collagen embedded in a unique matrix. The detailed structure of bone and cartilage will be examined later in this lab.

Epithelia

The following slides are examples of some types of epithelia. You should examine each in the same way, attempting to answer the questions: how many layers of cells are present? If there is only one layer, how does the cell shape change from the deep to the superficial layers? Is there any specialization of the epithelium such as the presence of secretory cells, or a brush border, or cilia? What lies below the epithelium?

Simple squamous epithelium lines all of the cardiovascular system and exists as a mesothelium lining the body cavities. An example of a simple squamous mesothelium is the visceral pleura covering the lung, visible in the lung section.

Slide - Gallbladder: Simple columnar epithelium

In this slide the lining of the gallbladder can be clearly seen, lying on connective tissue. From an examination of the epithelium, what can you say about the function of this organ?

Slide - Colon: Simple columnar epithelium

How does this example of epithelium differ from that of the previous slide? How might this reflect a functional difference? How close are the blood vessels to the epithelium?

Slide - Trachea

There are many tissues present in the trachea. You should concentrate on the epithelial lining. You should be able to establish the type of epithelium present. Note the distribution of goblet cells and the cilia.

Slide - Lung

In this section many types of epithelium can be seen. Simple squamous epithelium lines the blood vessels, pseudostratified columnar epithelium lines the conducting airways and cuboidal and simple squamous epithelium continues on from the conducting to the respiratory airways. Examine and compare these epithelial types.

Slide - Esophagus

Note the number of cell layers, the change in cell shape through the layers, and the density of cells in the basal or germinal layer.

Slide - Thin skin: keratinized stratified squamous epithelium

Identify the layers in the epidermis. Note the features of the dermis which include hair follicles, sebaceous and sweat glands. Compare the structure of the epidermis of thin skin with that of thick skin in the next section. The skin is being examined here as an example of stratified squamous epithelium. The other features of skin will be considered later (nervous system, vascular system).

Slide - Thick skin: keratinized stratified squamous epithelium

Examine the stratum corneum. What features of the epithelium of skin suit it to its function?

Compare thick and thin skin.

Slide - Bladder: Transitional epithelium

Compare this form of stratified epithelium with the previous examples. What features of this epithelium suit it to its function? Where does cell division and replacement occur?

This type of epithelium is only found in the urinary tract. What problems exist in this system which the epithelium must overcome?

Bone and Cartilage

Bone and cartilage are specialized forms of connective tissue. They do however conform to the basic plan. They are formed of cells embedded in a matrix composed of fibres and ground substance. Cartilage is classified according to the type and density of fibres present in the matrix. Bone is specialized in that the matrix is calcified. You should become familiar with the structure of bone and cartilage and understand the development and growth of bone by intramembranous and endochondral processes.

Slide - Hyaline cartilage

In this slide note the perichondrium, uniform matrix and chondrocytes. Around the cartilage there are bundles of collagen fibres and muscle.

Slide - Elastic cartilage

Compare this slide which has been specifically stained to show elastin fibres with the previous slide. Note the concentration of elastin fibres around cell nests.

Slide - Human ground bone

In this unstained preparation you will see the typical organization of compact bone. The osteocytes are organized into concentric circles forming Haversian systems. At the centre of each Haversian system is a Haversian canal which contains vessels and nerves. Where one Haversian system meets another a dark cement line can be seen. The fine canaliculi connecting adjacent lacunae can be seen as black lines. The organic material has been removed from this preparation.

Slide - Rabbit femur

In this preparation, the organic material is present and the bone appears as a solid pink mass with blue-staining osteocyte nuclei. Some impressions of Haversian systems can be seen. This is part of a section of a long bone and the bone marrow can be seen as a fine network containing densely packed blood precursor cells.

Slide - Fetal rat joint

In this longitudinal section of a rat leg, the formation of bone by endochondral ossification is demonstrated. Cartilage cells are dividing, hypertrophying and dying in the epiphyseal plate. At the site of cartilage cell death, the matrix is becoming calcified and osteoblasts are taking over the formation of the matrix. Examine this area carefully. Further down in the long bone can be seen spongy bone, compact bone and bone marrow.

Slide - Adult rat joint

This section illustrates a further stage in the development of a long bone in which the primary and secondary ossification centres have almost met and lie on either side of the epiphyseal plate.

Slide - Embryonic rat skull

The flat bones of the skull are formed by this method. You will see a band of cells condensed into a 'membrane'. This membrane gives rise to osteoblasts which form bone.

Slide - Newborn rat skull

Notice in this specimen how the skull bones are now continuous and how much the layer of bone has thickened. In this specimen you will see endochondral ossification at the base of the skull.

The membrane cells have transformed into osteoblasts and osteocytes. The osteocytes start to lay down bone matrix. Bone is remodelled by the activity of osteoclasts.

Objectives - connective tissue and epithelia histology

By the end of this lab you should be able to:

- identify all types of leucocytes on a blood smear and describe their functions.

- recognise connective tissue and identify the cellular and matrix components.

- classify epithelia and identify specific types.

- recognize the layers of the skin, and define the layers of the epidermis.

- describe endochondral and intramembranous ossification.