Specialized tissues, organs, and organ systems comprise the body of most multicellular organisms. Tissue is composed of many similar cells specialized to carry out specific functions. An organ is made up of various tissues organized to form a functional unit. An organ system is composed of a group of organs forming a functional complex.
Objectives: Upon completion of this lab, students should be able to:
1. Recognize different human tissue and cell types.
2. Know the functions of the tissue and cell types studied in lab.
There are 4 major categories of animal tissues:
1. Epithelial
2. Connective
3. Muscle
4. Nerve
Each category in turn is subdivided into different types. This classification of animal tissues applies primarily to vertebrate tissues and is not entirely applicable to invertebrate tissues.
This tissue type forms the external covering or internal linings of body surfaces. The epithelium of skin (external covering), the epithelium of the small intestine (internal lining), and the epithelium of blood vessels (internal lining) are examples of epithelial tissues. Epithelial cells are tightly arranged, forming a continuous layer of cells. The function of epithelial tissues is protection, secretion, and control of permeability.
The 2 major types of epithelium are simple and stratified. If an epithelial tissue is only one cell layer thick, it is called simple epithelium. If an epithelium is 2 or more cell layers thick, it is called stratified epithelium. Different types of simple epithelium are squamous (flattened), cuboidal (square), and columnar (elongate). Different types of stratified epithelium include squamous, cuboidal, and columnar. Therefore, the different types of epithelial tissues are simple and stratified squamous epithelium, simple and stratified cuboidal epithelium, and simple and stratified columnar epithelium. An extracellular layer of collagen fibers called the basement membrane is found at the base of epithelial tissues. The basement membrane anchors epithelial cells to the underlying connective tissue.
1. Stained human cheek epithelium: squamous epithelial cells - wet mount:
The epithelial lining of the oral cavity is a stratified squamous epithelium, but a wet mount of individual cells will be used to visualize squamous epithelial cells.
PROCEDURE:
a. Use the broad end of a clean toothpick to gently scrape the inside of your cheek. Smear the material on a slide and add a small drop of methylene blue.
b. Stir the stained material gently with the toothpick and place a plastic cover slip over the preparation.
c. Invert the slide on a piece of paper toweling and apply a slight amount of pressure to the slide with your finger. The paper toweling will remove excess stain from the slide.
d. Examine the preparation under scanning power and find the stained epithelial cells on your slide - a number of cells should be on the slide.
e. Examine the cells more closely under low and high power. Note the flattened nature of the cells, which is why they are referred to as squamous epithelial cells. Also, note the nucleus present in each cell.
f. Make a drawing of a cell and label it squamous epithelium.
2. Slide of intestinal cross section: columnar epithelium
The tissue lining the intestinal lumen of mammals is a simple columnar epithelium.
PROCEDURE:
a. Examine the cross-section of intestine under scanning power and identify the innermost layer of cells, which line the lumen.
b. Switch to low and high power to observe the columnar epithelial cells more clearly. The sections on your slide are relatively thin paraffin sections (about 7 um thick), so it is possible to see quite clearly the elongate nature of the individual columnar cells.
c. Try to identify the nucleus within each cell.
3. Slide of section of Caucasian skin: stratified squamous epithelium
The outer epithelial layer of human skin is a stratified squamous epithelium.
PROCEDURE:
a. Examine the section of skin under scanning power and identify the relatively thin, dark purplish epithelial layer on the outer surface of the skin tissue.
b. Switch over to low and high power to examine the epidermis more closely. The outermost layers of squamous epithelium, called the stratum corneum, are non-living and serve to prevent excessive loss of water. The cells of the basal layer, called the stratum basale (next to the dermis), divide mitotically to replace the lost cells. Note the large nuclei present in the basal layer, which indicates that these cells are less flattened than those cells closer to the surface of the skin. The cells become more flattened as they move toward the surface of the skin.
c. Make a drawing of the epidermis and label the stratum corneum, and stratum basale.
4. Demonstration slide of simple cuboidal epithelium:
Examine the demonstration of simple cuboidal epithelium. Note that cells lining the ducts in this section are essentially square in shape. Contrast the shape of these cells with the columnar epithelial cells lining the intestine of mammals.
This is the most diverse type of tissue, but in general it is characterized by having relatively few cells. The space between the cells is occupied by a filling or packing material called the matrix. The matrix, which is produced by the connective tissue cells, may be liquid, semisolid, or solid. Cells of the connective tissue produce the matrix. There are 4 types of connective tissue based on the nature of the matrix:
- Connective tissue proper (major category of connective tissue)
- Cartilage
- Bone
- Vascular tissue (blood and lymph).
This type of connective tissue serves to support and hold other tissues of the body together. The matrix of the tissue plays an important role in carrying out this function. The nature of different types of connective tissue proper is quite variable. The matrix contains numerous fibers (extracellular fibers) produced by the connective tissue cells. These fibers can be collagen fibers which are relatively large protein fibers, elastic fibers which are composed of a type of protein which allows stretching, or reticular fibers which are small fibers that branch and cross to form complex networks. Connective tissue proper is made up of several different types of cells. One type is the fibroblast, which is responsible for secreting the proteins making up the various types of fibers.
1. Loose (areolar) connective tissue:
This type of connective tissue proper is characterized by having a loose arrangement of fibers in an extensive matrix. This common type of connective tissue found throughout the body forms the framework of certain organs, such as the liver and lymph glands. It also surrounds and supports structures such as muscles and blood vessels.
a. Slide section of Caucasian skin: loose connective tissue
The subcutaneous layer beneath the dermis of the skin is an example of loose connective tissue.
PROCEDURE:
1. Examine this slide under scanning power and identify the subcutaneous layer. Note the large groups of fat cells and the connective tissue between and below the clusters of adipose (fat) cells.
2. Switch over to low and high and examine the connective tissue below the adipose cells. Note the cells with purple nuclei and the reddish stained fibers.
3. Examine the groups of adipose cells and look for an intact cell showing the large central vacuole of fat and the peripheral ring of cytoplasm where the nucleus is located. Adipose cells are specialized for fat storage. When many adipose cells are present in connective tissue, it is called adipose tissue.
4. Make a drawing of a group of adipose cells and label the cell membrane, central vacuole, and peripherally located nucleus.
b. Slide of adipose tissue: loose connective tissue
PROCEDURE:
1. Examine the cells and note the characteristic appearance of adipose cells - large fat vacuole, peripheral cytoplasm, and peripheral nucleus.
2. Dense connective tissue:
This type of connective tissue proper is characterized by compact arrangement of its numerous fibers. Dense connective tissue makes up tendons, ligaments, and the dermis of skin.
a. Slide of section of Caucasian skin: Dense connective tissue
PROCEDURE:
1. Examine the slide under scanning power and identify the dermis (stained pink) and note the red staining fibers (mostly collagen fibers) which are irregular in arrangement. Also, note the cells present in the matrix of the dermis, especially those just beneath the epidermis. There are also sweat glands, hair follicles and associated sebaceous glands in the dermis
Cartilage is a specialized type of dense connective tissue. The matrix has a rubbery consistency and the cells (chondrocytes) are located in spaces (lacunae) in the matrix. Cartilage is found in the nose, ears, larynx, and intervertebral discs.
1. Demonstration slide of cartilage: Specialized type of dense connective tissue
Examine the demonstration slide under low power and note the cells (chondrocytes) in the lacunae and the dense matrix.
Bone is a specialized type of dense connective tissue. The matrix of bone is rigid since it contains inorganic salts (Calcium carbonate and Calcium phosphate). Bone cells, called osteocytes, are located in cavities (lacunae) in a calcified matrix. Small canals called canaliculi connect the lacunae and the canaliculi in turn connect to large canals within the bone called Haversian canals. Small blood vessels and nerves are found in the Haversian canals.
1. Slide of bone: Specialized type of dense connective tissue
Examine the slide under high power and identify the following structures: osteocytes in the lacunae, canaliculi connecting the lacunae, and the central Haversian canal.
Blood is a specialized type of connective tissue in which the matrix (plasma) is fluid.
1. Slide of Human Blood: Specialized type of connective tissue (fluid matrix)
The formed elements present in the plasma of the blood are the erythrocytes (red blood cells), leukocytes (white blood cells) and platelets. The erythrocytes (RBCs) are the most numerous type of cell in the plasma of the blood (~5 million/cubic millimeter). They are small disc-shaped cells lacking nuclei. The RBCs contain the respiratory pigment hemoglobin, which serves as a carrier of oxygen for respiratory exchange.
Leukocytes or white blood cells (WBC) are much less numerous (~5,000-10,000/cubic millimeter) in plasma than RBCs. In contrast to RBCs, all WBCs possess a nucleus (nuclei stain a purplish color). There are different types of Leukocytes that are divided into 2 groups based on the presence of cytoplasmic granules (neutrophils, eosinophils, and basophils), or absence of cytoplasmic granules (monocytes, lymphocytes). The number of WBCs found in the bloodstream increases following infection by certain pathogens.
PROCEDURE:
1. Examine the slide under high power and, with the help of the descriptions below and the images, see if you can identify some of the Leukocytes; neutrophil, eosinophil, lymphocyte, and monocyte. The basophils are rarely seen on blood film slides.
a. Neutrophils make up 65-75% of the WBCs. The characteristic nucleus is composed of 3-4 lobes. The cytoplasmic granules are usually not readily evident.
b. Eosinophils make up 2-3% of the WBCs. The nucleus is bilobate and the cytoplasm granules are large, red granules.
c. Lymphocytes make up 20-30% of the WBCs. There are small, medium, and large-sized lymphocytes. The nucleus is spherical and the cytoplasm appears as a narrow blue rim around the cytoplasm.
d. Monocytes make up 4-7% of the WBCs. The large nucleus is pale in color and sometimes shows an indentation. The cytoplasm is blue.
e. Basophils make up 2-3% of the WBCs. The cytoplasm contains bluish granules of different sizes.
Muscle cells are specialized for contraction and are responsible for body movements. The 3 types of muscular tissue are striated muscle (voluntary), smooth muscle (involuntary), and cardiac muscle (heart).
1. Skeletal Muscle:
Skeletal muscle is called striated muscle because of the alternating light and dark bands (striations) exhibited by myofibrils present in the cells. The elongate muscle cells are referred to as fibers or muscle fibers. Each fiber contains many nuclei, which are located at the periphery of the cell. The cell membrane of muscle fibers is called the sarcolemma and the cytoplasm the sarcoplasm. Muscle cells are bound together into bundles by connective tissue, and in turn, a number of bundles are bound together by connective tissue to form a muscle.
PROCEDURE:
a. Examine the slide of mammalian muscle and identify the section of striated muscle under scanning power.
b. Examine the muscle under low and high power and note the large individual fibers in longitudinal section and the location of the nuclei in the periphery of the fiber. Observe the striations exhibited by the fibers - it may be necessary to reduce the light intensity to see the striations.
Smooth muscle is found lining blood vessels, the intestine, and the urogenital tract. The relatively small spindle-shaped cells lack the striations characteristic of skeletal muscle fibers. Each cell has a single centrally located nucleus.
PROCEDURE:
a. Examine the slide of mammalian muscle and identify the section of smooth muscle under scanning power.
b. Switch over to low and high power and identify the muscle cells, each with a single nucleus.
Cardiac muscle is found only in the heart and in the aortic arch. Striations are present, but the cells have a single, centrally located nucleus. A specialized junction zone, called the intercalated disc, is present where cardiac muscle fibers are joined end to end. At intercalated discs, fibers often divide into 2 or more branches, which fuse to adjacent cells.
PROCEDURE:
a. Examine the slide under scanning power and identify the section of cardiac muscle.
b. Examine the muscle under low and high power and note the individual fibers in longitudinal section and the location of the nucleus within each fiber.
c. Observe the striations exhibited by the fibers - it may be necessary to reduce the light intensity to see the striations.
Nerve cells (neurons) are specialized for conducting electrochemical nerve impulses. Nerve cells are easily stimulated and transmit nerve impulses rapidly. Neurons consist of 3 major regions: the cell body, axons, and dendrites. Dendrites conduct nerve impulses toward the cell body and axons conduct nerve impulses away from the cell body. The junction of 2 neurons is called a synapse. Groups of nerve cells are held together by connective tissue and collectively make up a nerve.
Examine the slide of a neuron and note the large cell body, the relatively long axon and the shorter dendrites. Make a drawing of a neuron. Label the axon, dendrites, and cell body.