Exercise 3: Tissues

Figure 3.1 Histological image above is the skin, which is made up of the four types of tissues: epithelial, connective, nervous, muscle.

Exercise 3 Learning Goals

After completing this lab, you should be able to: 

• Describe and identify the four types of tissues found in the human body
• Describe the relationship between form and function regarding the different types of tissues
• Understand the shape, structure, and type of cells found in all tissue types
• Know the layers of the skin and what tissue type is found in each layer
• Describe the different layers and structures found within the epidermis and dermis
• Describe and label the structures of special connective tissues like bone and blood

Pre-Lab for Exercise 3

Pre-Lab Activity 3.1

In the chart below (Table 3.1), describe the characteristics, examples, and subdivisions for each tissue type. Use information from your textbook to guide you.

Table 3.1: Tissue Types

Pre-Lab Activity 3.2: Epithelium

Draw the different shapes and layers of epithelial cells. Use your textbook or lecture notes as a guide to complete the chart below (Table 3.2).

Table 3.2: Types of epithelium in the human body

Pre-Lab Activity 3.3: Cell Junctions

Figure 3.2 Cell to cell junctions of the human body

Describe each cell junction and indicate where each can be found in the body in the space below (Table 3.3):

Table 3.3: Types of cell junctions in the human body.

Exercise 3: In Class Activities

Observe and Describe Epithelial Tissues

Epithelial tissues line surfaces and form glands. There are two primary characteristics of epithelial tissues that should help you with identification: you will find cells close together (no interstitial fluid) and you will see a “free surface.” The free surface may be present at a lumen or on the surface of the body. The presence of a free surface gives epithelial cells direction: a top and a bottom. The top of the epithelial cell is called the apical region (free surface) and the bottom is called the base (basal surface). Because cells in epithelial tissue are in such close contact, they are usually stitched together by intercellular junctions. Cell junctions come in a few varieties, including desmosomes, tight junctions, and gap junctions. Hemidesmosomes anchor epithelial cells to the basement membrane.

Activity 3.1 Fill in the Table

Using either a slide and microscope, or pictures provided by your instructor, view histological sections of epithelial tissue. Locate the free edge. Notice how cells are adjacent to one another. Draw your observations, labeling the lumen, apical region/free edge, basal surface, lateral surfaces, and basement membrane (Table 3.4).

Table 3.4: Microscopic view of epithelial tissue.

Epithelial Tissue Types

Epithelial tissues can be divided into distinct types based on the shape of the cells (squamous, cuboidal, or columnar) and the number of layers present (simple or stratified).

Classification based on shape:

Epithelial cells can be flat, cube shaped, or cylindrical/rectangular. When epithelial cells appear flattened, they are called “squamous,” when they appear square, they are called “cuboidal” and when they appear cylindrical or rectangular, they are called “columnar.”

Figure 3.3 Demonstrating shapes of epithelial cells.

Classification based on layer:

Epithelial tissues can be made of a single layer of cells (simple) or multiple layers of cells (stratified). Pseudostratified appears to be multilayered but is not. Some of the cells in pseudostratified do not reach the apical surface and the cell nuclei are not uniformly distributed giving it a “pseudo” (fake; false) layered appearance.

Figure 3.4 Demonstrating layers or arrangements of epithelial cells.

Identifying Epithelial Tissue Types

Use the following chart to identify the “unknown” tissue types in the exercise below.

Figure 3.5 Simple epithelia. Micrographs by Tony Matthews.

Exercise 3.2: Identify the Tissues

Your instructor will provide you with images of simple epithelial tissue to complete the activity below.

Identification of Epithelial Tissue:

Microscope/Image A: __________________

Microscope/Image B: __________________

Microscope/Image C: __________________

Microscope/Image D: _____________________

Microscope/Image E: __________________

Figure 3.6: Stratified and Pseudostratified epithelia. Images by Tony Matthews

Exercise 3.3: Identify the Tissues

Your instructor will provide you with images of epithelial tissues to complete the activity below.

Identification of Stratified/Pseudostratified Epithelial Tissue:

Microscope/Image F: __________________

Microscope/Image G: __________________

Microscope/Image H: __________________

Microscope/Image I: ___________________

Microscope/Image J: __________________

Microscope/Image K: __________________

Microscope/Image L: __________________

Identification of Connective Tissue Types

Connective tissues differ from epithelial tissues in two primary ways: cells are spaced far apart, and cells are separated by an extracellular matrix. The extracellular matrix (region of material outside of the cells) is also called the interstitial space. The cells in connective tissue build this matrix, which is made up of non-living material (water, minerals, etc.) and distinct types of proteins. The specific composition of this extracellular matrix and the type of cells in the tissue define the type of connective tissue. The extracellular matrix and cells differ based on the function of the tissue. For example, some connective tissues have more elastic fibers in their extracellular matrix which makes them stretchy.

• Can you think of an area of the body where you would find more elastic connective tissue? (Hint: dilates and constricts to accommodate increase/decrease in blood flow) ____________________________________________.

Connective Tissue can be divided into various categories. The following divisions can be used to categorize connective tissue (Table 3.5):

Table 3.5: Connective tissue classifications.

Exercise 3.4: Identify the Tissues

Your instructor will provide you with images of connective tissues to complete the activity.

Identification of Connective Tissues:

Microscope/Image M: __________________

Microscope/Image N: __________________

Microscope/Image O: __________________

Microscope/Image P: ___________________

Microscope/Image Q: __________________

Microscope/Image R: ___________________

Select a connective tissue slide provided, then sketch & label the tissue below. List the unique identifying features and where it is typically found in the human body.

Additional Types of Connective Tissue

Bone is a hard connective tissue, because the extracellular matrix is composed of a mineral, called hydroxyapatite. The hydroxyapatite is embedded in bands of collagen and elastin. All three components help bone remain hard and rigid for muscle attachment, but also strong and flexible so that it does not break under force.

Figure 3.7 Bone Model

TERMS TO KNOW

• Central canal (Haversian canal)
• Osteon
• Concentric lamellae
• Circumferential lamellae
• Volkmann’s canal (Perforating canal)
• Lacunae
• Periosteum
• Osteocyte
• Canaliculi

Label the parts of compact bone in the image above (figure 3.7). Note: the terms listed will not all be indicated on the model.

What structure would contain an osteocyte from the options provided above in the “terms to know”?

Blood is a nontraditional connective tissue because the extracellular matrix is liquid. There are three ‘formed elements’ in blood: red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). These formed elements are suspended in plasma, which is the liquid portion of blood.

Figure 3.8 Blood cell smear. Photograph and labels by Amber Howard.

Critical Thinking

Compare the structures of the extracellular matrix of bone and blood to how each tissue functions in the human body.

Skin Includes All 4 Tissue Types

The skin is composed of two layers, an epidermis, which is made up of several layers of stratified squamous and simple cuboidal epithelial tissue and the dermis, which is made up of two layers of connective tissue: a papillary layer and a reticular layer. In this image, note the 5 layers of epithelial tissue from superficial to deep: stratum corneum, stratum lucidum (found only in the thick skin of palms and soles), the stratum granulosum, the stratum spinosum, and the stratum basale. Thin skin is the largest organ of the body, it covers most of the body and is associated with hair. Thin skin lacks stratum lucidum and has a thinner stratum corneum. In the table below, describe the appearance, features, and general function(s) of each layer.

Figure 3.9 Epidermal strata and associated cell types. This represents the outermost/upper layer of skin.

Activity 3.5: Complete the Table Below

Use your textbook or lecture notes to complete the information about each epidermal layer (Table 3.6).

Table 3.6: Strata of the epidermis

Activity 3.6 Observe and Label the Histological Images of Skin.

Identify each stratum by labeling the space provided, then determine which image is thick and thin skin.

Figure 3.10: Two epidermis samples.

Post-Lab 3 Review Questions 

1. List the 4 types of tissue.
2. Describe the important characteristics of epithelial tissues (cell spacing, etc.) and connective tissues.
3. Which of the following protein fibers is found in a high quantity in dense regular and dense irregular connective tissue?
   1. Reticular b. Collagen c. Elastin d. Troponin
4. You peer into a microscope to observe rectangular cells with purple nuclei situated closely together, with little to no space between them. You also observe an open space or lumen on their apical surface. What type of tissue are you looking at?
   1. Simple squamous b. Simple columnar c. Simple cuboidal d. Dense regular
5. What type of tissue is the epidermis of the skin?
   1. Simple squamous b. Simple cuboidal c. Stratified squamous d. Connective tissue
6. Where would you expect to find simple cuboidal cells?
   1. Colon lining b. Lining kidney tubules c. Lining esophagus d. Making up serous membranes
7. Where would you expect to find elastic cartilage?
   1. In the nose and part of the ear
   2. Between the bones of the pubic symphysis, where little to no movement occurs
   3. Between vertebral discs
   4. At the ends of the long bones, such as the femur or the humerus
8. Which layer of the epidermis is composed of simple cuboidal cells that act as a germ layer, producing layers of squamous epithelium above?
   1. Stratum spinosum b. Stratum lucidum c. Stratum corneum d. Stratum basale
9. Bone tissues differ from other types of connective tissue because _______.
   1. It has a high amount of cartilage in its extracellular matrix
   2. It has a high amount of collagen in its extracellular matrix
   3. It has a high amount of mineral (hydroxy apatite) in its extracellular matrix
   4. It has more fibroblasts embedded in its extracellular matrix
   5. All of the above
10. Matching