Animals > Tissues
Reading: Campbell, 40.2.
The study of tissues is called histology. The purpose of this lab is to give you a brief introduction to some of the major tissue types found in mammalian bodies.
The slides you look at in lab are usually labeled with a specific tissue type — e.g., "cuboidal epithelium." However, each slide shows more than one tissue type. There may be some cuboidal epithelium on that slide, but you may also be able to find good examples of other tissues on the same slide. Pay attention to this; on the next lab exam, you may find a slide that's labeled for one tissue type being used as an example for another tissue type.
Esophagus and trachea
This slide shows a cross section of two big tubes in the neck of a mammal:
The esophagus is the passage that carries food from the mouth down to the stomach. The esophagus is soft and muscular; it can collapse when there is no food in it. The lumen is the space where a food bolus can pass through on its way to the stomach. The layer of smooth muscle on the outside moves food boli downward by peristalsis. The lumen, like all the surfaces of the body, is lined with a layer of epithelium.
The trachea carries air into and out of the lungs. The lumen is the space that air passes through. The trachea is reinforced with rings of cartilage so it won't collapse. The inner surface is lined with a layer of ciliated epithelium; the cilia help move small particles out of the air passages.
Here is the trachea at higher magnification (seen in a different slide):
Olfactory epithelium occurs in the nose; as part of the airway, it contains similar tissues to those found in the trachea.
In the above image, you can see several types of tissues:
Ciliated epithelial cells line the narrow air passage. As usual, this epithelium forms a distinct layer that serves as a boundary between the outside world and the body's tissues. Nothing gets into your body's tissues without passing through an epithelial layer.
Adjacent to the ciliated epithelium is a layer of loose connective tissue. On the right, you can see a mucous gland, lined by a layer of cuboidal epithelium. Compared to the ciliated epithelium, the cuboidal epithelial cells are shorter (cube-shaped), and they lack cilia.
On the upper left there is a blood vessel, lined by a very thin epithelial layer and filled with erythrocytes (red blood cells).
On the far left is a layer of cartilage.
The digestive tract is similar to the airway; has a lumen that materials must pass through in order to allow the body's cells to absorb needed substances. Both are lined with epithelium, which is supported by other tissue types.
The surface of the small intestine is deeply folded, forming villi that increase surface area for both secretion of digestive juices and absorption of nutrients from food. The villi are covered with columnar epithelium.
Smooth muscle surrounds the outside of the intestine and generates peristaltic contractions to keep the chyme (partially digested food) flowing though the digestive tract.
Intestinal epithelium at higher magnification:
Columnar epithelium lines the surface of the intestine. These cells are similar to the ciliated columnar epithelium of the respiratory passages -- except that there aren't any cilia. The intestinal epithelium also has goblet cells, which secrete mucus to protect the tissues and aid in digestion. The image above shows a fold between two villi. Beneath the epithelium is a layer of loose connective tissue with blood vessels and lymph vessels running through it.
Smooth muscle of intestinal wall:
Smooth muscle is characterized by a large amount of protein fibers, all oriented in more or less the same direction. The nuclei of the smooth muscle cells are long and thin. Each smooth muscle cell typically has a single nucleus. In this image, it's difficult or impossible to see the membranes dividing one cell from another.
The image above also shows a thin-walled blood vessel snaking through the smooth muscle.
Adipose tissue is fat tissue. These cells are specialized for storing energy in the form of fat. Each cell is essentially a large, fat-filled container, with the nucleus pushed to the side of the cell by the big blob of fat. The fat itself is not visible in this image; you just see empty-looking cells.
Note that these are very large cells -- as much as 200 microns across.