Histology

Chapter 4 Lab Histology

Directions: Follow the lab procedures. Fill out the document, type your answers in red or a different color. Make sure your answers are clear and in full sentences.

Objectives: After completing this lab, students will be able to:
• Identify the following tissues:

 Simple squamous epithelium
 Stratified squamous epithelium (skin, esophagus, vagina)
 Simple columnar epithelium
 Cuboidal epithelium
 Dense regular connective tissue
 Areolar connective tissue
 Dense Irregular Connective Tissue
 Hyaline cartilage
 Elastic cartilage
 Bone
 Skeletal muscle
 Cardiac muscle
 Smooth muscle

• Describe the functions of the different types of epithelium
• Describe what is common among all types of connective tissue

Histology is the study of microscopic anatomy, or tissues. Tissues are composed of cells, which act as the functional unit of the tissue. These cells are living units that are generally capable or replicating or reproducing themselves. In addition to the living cells, tissues may also be surrounded by a non-living ground substance or rest on a basement membrane, which may have both living cells and non-living substances. There are four basic tissue types in the human body: epithelium, connective tissue, muscle, and nervous tissue. These four tissue types have many sub-types with a great variety of structural and functional differences.

Procedure:

The following pages describe the tissues in more detail. Read the descriptions and, in the spaces following each description, insert a picture from the internet. Suggestion is to use this website but other images will be accepted. At the end of this lab there are discussion questions make sure to fill them out as well.

http://www.histologyguide.com/index.html

Part I: Epithelium

Epithelium is a tissue that covers and lines organs of the body. It covers the body, the insides of blood vessels, and other hollow organs. It is also found in many glands and ducts in the body. Epithelium can be specialized for protection, secretion or absorption. Epithelium is named on the basis of three things:
1) Its shape: A cell that is flat or scaly looking is said to be squamous, while cells that are taller than they are wide are called columnar. If the cell is basically the same height, width and depth, it is said to be cuboidal.
2) The number of layers of cells present: If there is just one layer of cells, it is said to be simple. If there are multiple layers it is said to be stratified. If the bottom layer of stratified epithelium looks different from the top, the tissue will be named for the type of epithelium on the top.
3) surface modifications: Often times columnar epithelium has cilia on the surface. It will then be called ciliated epithelium.

The specific types of epithelium we will be looking at are listed below.

Simple Squamous Epithelium
Slide: Lung, cheek
Simple squamous epithelium is a flat tissue that, viewed from above looks similar to a fried egg and viewed from the side will appear very flat. It is a single layer of squamous epithelium. It is present in areas where diffusion of gasses or fluids is the main function, such as the lungs and capillaries.

Stratified Squamous Epithelium
Slide: Skin, esophagus
Individual stratified squamous epithelial cells are identical to the simple squamous cells, except there are multiple layers. Where simple squamous epithelium is a tissue that allows for easy diffusion, stratified squamous epithelium acts as a protective tissue and generally keeps things on one side or the other. It is the tissue that makes the skin as effective as it is at keeping fluids and organisms out of the body. It is also found in the lining of the esophagus, the urethra and the vagina, all areas that can be exposed to significant stresses and potential traumas, as well as areas that are exposed to the outside environment.

Cuboidal Epithelium
Slide: Kidney, skin (sweat glands)
Cuboidal epithelium is the tissue found in tubes and ducts inside the body. It is equally tall as it is wide and appears cube-like in the microscope. The kidney is a great location to see cuboidal epithelium. When you view the slides of the kidney in lower magnification, you see structures that look like balls inside of a circle. What you are actually looking at is a cluster of capillaries (simple squamous epithelium) in a space surrounded by the glomerulus – a capsule made of cuboidal epithelium.

Columnar Epithelium
Slide: Intestines, stomach, trachea
Columnar epithelium is a tall, narrow epithelial cell. It is used to absorb or secrete and may have one or more of several different modifications. The most common modifications are cilia and goblet cells. Cilia are small hairs on the end farthest from the basement membranes. In the trachea the cilia acts to trap particles in the air and force them away from the lungs. In the intestines, the cilia helps pull digested food particles close to the cell and help it absorb through the cells. Goblet cells appear as a light, goblet shaped cell in between the columnar cells. They secrete mucus fluids that protect and lubricate the lining.

Connective Tissue
Connective tissue covers a wide variety of tissues; in fact, it is probably the most diverse group of tissues in the body. It can be as solid as bones or as fluid as blood. There are a few things that can be said of all connective tissues. First it will connect different organs or tissues to one another. In addition, all connective tissue will have living cells in a non-living matrix. Connective tissues are classified by their cells, fibers and matrix. Below are the connective tissues we will be studying:

Areolar (Loose) Connective Tissue
Slide: Areolar connective tissue
In areolar connective tissue, fibers are randomly scattered. There are two common fibers that are seen: collagen fibers and elastic fibers. Collagen fibers appear as thick, pink-staining, ribbon-like fibers. Elastic fibers are very thin, black staining fibers. In addition, there are several cells including fibroblasts (cells that make the fibers), mast cells, macrophages, and plasma cells (all immune cells.

Dense Regular Connective Tissue
Slide: Dense Regular CT, tendon
In dense regular connective tissue, collagen fibers are arranged in dense, thick, parallel, unbranching bundles. These bundles are packed together very tightly causing the fibroblasts to be flattened. These cells can be found in between the parallel rows of fibers.

Dense Irregular Connective Tissue
Slide: Dense Irregular CT, ligament
Dense irregular connective tissue is a tightly packed tissue whose living cells are primarily fibroblasts (the cells that produce the fibers found in the tissue). The arrangement of this tissue makes it tougher and more durable than loose connective tissue. The fact that fibers go in every direction makes it better able to protect against stresses from multiple directions. Because of this, it can be found in ligaments, which connect bones to bones, whereas dense regular connective tissue (with fibers all going in the same direction) is found in tendons which connect muscle to bone.

Hyaline Cartilage
Slide: Hyaline cartilage, cartilaginous bone formation
Cartilage provides support while giving flexibility. Hyaline cartilage is found at the ends of long bones and acts as a cushion. It is also the tissue that makes the framework for new bone growth. It has a translucent matrix (ground substance). The cells, called chondrocytes, are found in openings in the matrix called lacunae. The staining process may remove much of the cellular makeup of the chondrocytes; in fact all that may be left in some of them is the nucleus inside the lacunae.

Elastic Cartilage
Slide: Elastic cartilage
Elastic cartilage is very similar to hyaline cartilage, except that it has more elastic fibers that give it more elasticity. It can be found in ears, the nose, and the last epiglottis. When you look at this slide, notice the lacunae (the openings in which the chondrocytes lived) that is similar to those of hyaline cartilage. Also, note the fibers that can be found in the extracellular matrix.

Bone
Slide: Ground Bone
Bones are the main building block of the skeleton. They help protect our vital organs, store minerals and help produce blood cells. A typical bone has both compact and trabeculated or spongy bone. Bone is a connective tissue because it helps connect different organs to one another and it has living cells (osteocytes) in a non-living matrix (composed of calcium, magnesium and phosphorus). The structural unit of bone is called an osteon. It consists of a central canal and several osteocytes. Osteocytes arrange themselves around a central canal that carries blood vessels and supplies the cells with nutrients. The central canal travels parallel to the shaft of the long bone. The osteocytes will continuously reproduce and lay calcium down around them. As calcium continues to be laid down, some of the cells will migrate toward the outside and live further from the central canal. They will create rings around the central canal and live in spaces called lacunae. These rings are called concentric lamellae. As the cells move from one ring to the next, they create connections between the lamellae for nutrients to flow from the central canal to the more distal lamellae. These connections are called caniliculi. From time to time the vessels of the central canal give off a perpendicular branch to give collateral blood supply to other regions of the bone.

Adipose
Slide: Adipose tissue, skin
Adipose cells are fat cells. They provide protection, store energy, and insulate the body. They contain lipid droplets and are light in color a relatively lucent. The nucleus is pushed out to the edge and is dark staining. It can be found in the hypodermis (layer just beneath the skin

Blood
Slide: Blood smear
Blood is a connective tissue that has many different functions. When you look at a slide of blood, the majority of cells will be erythrocytes (red blood cells). These are biconcave discs when viewed from the side and like doughnuts from above. When viewed from above, the edges appear darker than the middle, due to the higher amounts of hemoglobin present in the outer edge.

Muscle
Muscle is tissue that is specialized for contractility. There are three different types of muscle cell: skeletal muscle, cardiac muscle, and smooth muscle.

Skeletal Muscle
Slide: skeletal muscle, tongue
Skeletal muscle is the tissue that most people think of as muscle. It makes up the voluntary muscles that attach to the skeleton and help move the body. The skeletal muscle cell (or fiber) is a thin cylindrical fiber with striations (perpendicular stripes). It may have multiple nuclei which are pushed to the outside of the fiber, just beneath its membrane (called the sarcolemma). It may appear that nucleus is on the inside in some areas, but that is because it is a thin, relatively transparent cell and three dimensional, so that the nucleus may be seen when it is on the other side of the cell.

Cardiac Muscle
Slide: Cardiac muscle, heart aorta
Cardiac muscle is involuntary muscle found in the heart and in the proximal great vessels. It is striated muscle, just like skeletal muscle. However, there are some important differences. Cardiac muscle is not cylindrical, it has many branches. It appears to separate and unite repeatedly. This branching is known as syncytium. Secondly, the nuclei are always found on the inside of the cell. In addition to the striations that are present, there are also much thicker bands, running parallel to the striations, called intercalated discs. These discs are actually the boundaries of the individual cardiac muscle cells. Depending on the staining used, they may appear as dark bands or clear bands, but they will generally be thicker than the striations with a jagged border.

Smooth Muscle
Slide: smooth muscle, intestine
Smooth muscle is muscle is involuntary muscle found in the walls of hollow organs, such as blood vessels and the digestive tract. The individual cells are cigar-shaped with one nucleus and no striations. It is arranged in sheets of muscle. In most organs, there are two layers of smooth muscle, an inner circular layer that wraps around the organ, and an outer longitudinal layer that runs the length of the organ.

Discussion Questions:

1. What special cellular junction does cardiac muscle demonstrate that skeletal muscle does not? What purpose does this have?
2. How can you tell the difference between the three muscle types when you view them?
3. Which of the muscle types is/are voluntary?
4. Which of the muscle types is/are involuntary?
5. Which of the muscle types is/are striated?
6. Which of the muscle types is/are multinucleate?
7. What makes adipose a connective tissue?
8. What makes blood a connective tissue?
9. Which blood cells do you see?
10. Arrange the types of red and white blood cells from most common to least common.
11. What makes up the non-living matrix in blood?