What connective tissue consists of large round densely packed cells with the nucleus pushed to one side?

1. Introduction to histology (Part 1)

Tissues are composed of similar types of cells that work in a coordinated fashion to perform a common task, and the study of the tissue level of biological organization is histology. Four basic types of tissues are found in animals.

Epithelium is a type of tissue whose main function is to cover and protect body surfaces but can also form ducts and glands or be specialized for secretion, excretion, absorption and lubrication.

Epithelial tissues are classified according to the number of cell layers that make up the tissue and the shape of the cells. Simple epithelium is composed of a single layer of cells while stratified epithelium contains several layers. 

Epithelial sells can be flat (squamous = "scale-like"), cube-shaped (cuboidal) or tall (columnar). So, to correctly identify the type of tissue requires three words (e.g., simple columnar epithelium, stratified, squamous epithelium, etc.

2. Introduction to histology (Part 2)

Connective tissue performs such diverse functions as binding, support, protection, insulation and transport. Despite their diversity, all connective tissues are comprised of living cells embedded in a non-living cellular matrix consisting of extracellular fibers or some type of ground substance. Thus, what distinguishes the different connective tissues is the type of matrix. Examples of connective tissue would include bone, cartilage, tendons, ligaments, loose connective tissue, adipose (fat) tissue, and even blood (although some authorities would classify blood as a vascular tissue).

Muscle tissue is specialized for contraction. There are three kinds of muscle tissue:

1. Smooth muscle (designed for slow, sustained, involuntary contractions) is made up of spindle-shaped cells with one nucleus per cell.
2. Skeletal, or striated muscle, which is associated with voluntary contractions, contains cylindrical cells with many nuclei per cell arranged in bundles.
3. Cardiac (heart) muscle is striated like skeletal muscle, but each cell contains only one nucleus.

3. Introduction to histology (Part 3)

Nervous tissue  is specialized for the reception of stimuli and conduction of nerve impulses. The tissue is composed of nerve cells (neurons), each of which is made up of a cell body and cell processes that carry impulses toward (dendrites) or away from (axons) the cell body.   In the following pages of this lab unit, you will have an opportunity to examine a few (of the many) types of animal tissue.

In terms of understanding the workings of the multicellular animal body, however, you should realize that tissues are but one of many connected levels of biological organization. Tissues rarely work alone but instead, they are grouped into organs.  Organs are combined to form organ systems (e.g., the circulatory system, nervous system, skeletal system, muscular system, excretory system, reproductive system, etc.) that function as an integrated unit called an organism. 

In subsequent units of the Zoo Lab website, you will be introduced to the diversity of animal life that results from the interaction of all of these key components.

4. Simple squamous epithelium (frog skin)

 Lab-2 01

This slide shows a thin section of frog skin. The outermost portion of this skin is composed of a single layer of irregularly-shaped, flat (squamous) cells, which gives the tissue its name.   Note:  You are viewing this tissue section from the top! This slide shows a thin section of frog skin. The outermost portion of this skin is composed of a single layer of irregularly-shaped, flat (squamous) cells, which gives the tissue its name.   Note:  You are viewing this tissue section from the top!

5. Simple cuboidal epithelium (cross section of the kidney)

 Lab-2 02

The red and blue arrows point to simple cuboidal epithelial tissue 

This is a slide of a thin section taken from the mammalian kidney showing the many tubular ducts that make up much of this organ. The walls of these ducts (pointed to by the red arrows) are comprised of simple cuboidal epithelial cells, which are usually six-sided in shape but may appear square from a side view. Note also the thin wall of simple cuboidal epithelium (pointed to by the blue arrow) that forms the top edge of this section.

6. Simple columnar epithelium (cross section of the small intestine)

 Lab-2 03

1. Smooth muscle (long. layer)
2. Smooth muscle (circ. layer)
3. Simple columnar epithelium
4. Goblet cell
5. Lumen of the intestine

This slide is a cross section from the small intestine. Projecting into the intestinal lumen (space) are numerous finger-like projections called villi, which function to slow the passage of food and increase the surface area for the absorption of nutrients. The lining of these villi is a tissue layer called the mucosa, which is made up of simple columnar epithelial cells. Interspersed among these columnar cells are goblet cells that secrete mucus into the lumen of the intestine. During routine histological preparation, the mucus is lost, leaving a clear or lightly stained cytoplasm. Beneath a thin, outer covering of the intestine called the serosa is a thick layer of smooth muscle cells called the muscularis externa. The muscularis externa is divided into an outer longitudinal muscle layer with cells that run along the axis of the intestine and an inner, circular muscle layer whose fibers encircle the organ. Peristaltic contraction of these two muscle layers keeps food moving through the digestive tract.

1- Smooth muscle (long. layer) & 2 - Smooth muscle (circ. layer)

1. Longitudinal muscle layer
2. Circular muscle layer
3. Columnar epithelial cells

3 - Simple columnar epithelium & 2 - Goblet cell

Lab-2 04

1. Goblet cell
2. Columnar epithelial cells
3. Epithelial cell nucleus
4. Lumen of the intestine

7. Stratified squamous epithelium (cross section of the esophagus)

Lab-2 06

1. Stratified squamous epithelium
2. Lumen of the esophagus
3. Connective tissue

This slide shows a cross section of the esophagus, the first portion of the digestive tract that leads to the stomach. Note that the organ is lined with a many layers of cells referred to collectively as stratified squamous epithelium. By convention, stratified epithelial tissues are named by the shape of their outermost cells. Thus, although the deeper and basal layers are composed of cuboidal and sometimes even columnar cells, those cells at the surface are squamous (flat) in shape, giving the tissue its name.

1 - Stratified squamous epithelium

 Lab-2 07

1. Stratified epithelial layer
2. Outer squamous cells
3. Lumen of the esophagus 

8. Loose connective tissue (spread film of fascia)

 Lab-2 08

1. Collagen fiber
2. Elastin fiber 

This slide shows a thin section of loose connective tissue (sometimes called areolar tissue). This type of tissue is used extensively throughout the body for fastening down the skin, membranes, blood vessels and nerves as well as binding muscles and other tissues together. It often fills in the spaces between epithelial, muscle and nervous tissue, forming what is known as the stroma of an organ, while the term parenchyma refers to the functional components of an organ. The tissue consists of an extensive network of fibers secreted by cells called fibroblasts. The most numerous of these fibers are the thicker, lightly staining (pink) collagen fibers (1). Thinner, dark-staining elastic fibers (2) composed of the protein elastin can also be seen in the section. s is a slide of a thin section taken from the mammalian kidney showing the many tubular ducts that make up much of this organ. The walls of these ducts (pointed to by the red arrows) are comprised of simple cuboidal epithelial cells, which are usually six-sided in shape but may appear square from a side view. Note also the thin wall of simple cuboidal epithelium (pointed to by the blue arrow) that forms the top edge of this section.

9. Hyaline cartilage (cross section of the trachea)

Lab-2 09

1. Lumen of the trachea
2. Pseudostratified (ciliated)columnar epithelium
3. Hyaline cartilage (100x)
4. Adipose tissue

This slide showing a cross section of the mammalian trachea (wind pipe) contains examples of several different kinds of tissues. Supporting the trachea is a ring of connective tissue called hyaline cartilage. The chondrocytes (cartilage cells) that secrete this supporting matrix are located in spaces called lacunae.

3 - Hyaline cartilage (100x)

 Lab-2 10

1. Hyaline cartilage (400x)
2. Adipose tissue 

Lab-2 11

1. Lacuna
2. Chondrocyte (cartilage cell)
3. Perichondrium

10. Pseudostratified columnar epithelium (cross section of the trachea)

 Lab-2 09

1. Lumen of the trachea
2. Pseudostratified columnar epithelium (close-up view)
3. Hyaline cartilage
4. Adipose tissue

This slide showing a cross section of the mammalian trachea (wind pipe) contains examples of several different kinds of tissues. The lining of the trachea consists of a type of tissue called pseudostratified (ciliated) columnar epithelium. This single layer of ciliated cells appears stratified because the cells vary in their thickness and because their nuclei are located at different levels.

Lab-2 12

1. Ciliated border
2. Epithelial layer

11. Adipose tissue (cross section of the trachea)

 Lab-2 09

1. Lumen of the trachea
2. Pseudostratified columnar epithelium (close-up view)
3. Hyaline cartilage
4. Adipose tissue (100x)

This slide showing a cross section of the mammalian trachea (wind pipe) contains examples of several different kinds of tissues. In addition to the pseudostratified columnar epithelium lining the trachea and hyaline cartilage, also seen on this slide is an extensive area of adipose tissue, which is specialized for fat storage. On prepared slides, the fat has been removed from the cells giving the tissue the appearance of fish net.

4 - Adipose tissue (100x)

 Lab-2 10

1. Hyaline cartilage
2. Adipose tissue (400x)

2 - Adipose tissue (400x)

1. Adipose (fat) cells
2. Cell nucleus

12. Compact bone (cross section of dried bone)

Lab-2 14

This slide contains a section of dried compact bone. Note that the bone matrix is deposited in concentric layers called lamellae. The basic unit of structure in compact bone is the osteon. In each osteon, the lamellae are arranged around a central Haversian canal that houses nerves and blood vessels in living bone. The osteocytes (bone cells) are located in spaces called lacunae, which are connected by slender branching tubules called canaliculi. These "little canals" radiate out from the lacunae to form an extensive network connecting bone cells to each other and to the blood supply. 

Close-Up View of an Haversian System

 Lab-2 15

13. Smooth muscle (separated fibers)

 Lab-2 16

This is a slide of a bundle of smooth muscle tissue that has been teased apart to reveal the individual cells. Each of these spindle shaped muscle cells has a single, elongated nucleus. In most animals, smooth muscle tissue is arranged in circular and longitudinal layers that act antagonistically to shorten or lengthen and constrict or expand the body or organ. For an example of such an arrangement, see the two smooth muscle layers on a cross section of mammalian gut. 

14. Skeletal muscle (cross section of the tongue)

 Lab-2 17

1. Stratified squamous epithelium
2. Duct composed of simple cuboidal epithelium
3. Skeletal muscle
4. Adipose tissue
5. Dense irregular connective tissue

Close-Up View of the Tongue

1. Adipose tissue
2. Skeletal muscle (longitudinal view)
3. Simple cuboidal epithelium

15. Cardiac muscle (sectioned to show intercalated disks)

 Lab-2 20

This slide contains a section of cardiac muscle, which is striated like skeletal muscle but adapted for involuntary, rhythmic contractions like smooth muscle. Although the myofibrils are transversely striated, each cell has only one centrally located nucleus. Note the faintly stained transverse bands, which are called intercalated disks, (indicated by the blue arrows) that mark the boundaries between the ends of the cells. These specialized junctional zones are unique to cardiac muscle. 

16. Nervous tissue (multipolar neuron)

 Lab-2 19

1. Nerve cell body
2. Nerve cell process

17. Dense regular connective tissue (tendon)

 Lab-2 21

This slide contains a longitudinal section of a tendon, which is composed of dense regular connective tissue. Note the regularly arranged bundles of closely packed collagen fibers running in the same direction, which results in flexible tissue with great resistance to pulling forces. 

18. Simple squamous epithelium model

 Lab-2 22

Because it is made up a single layer of scale-like cells, simple squamous epithelium is well suited for rapid diffusion and filtration. These cells look hexagonal in surface view but when viewed from the side (as shown in the image of the model above), they appear flat with bulges where nuclei are located. Simple squamous epithelium forms the inside walls of blood vessels (endothelium), the wall of Bowman's capsule of the kidney, the lining of the body cavity and viscera (parietal and visceral peritoneum) and the walls of the air sacs (alveoli) and respiratory ducts of the lung.

Surface view

 Lab-2 23

19. Simple cuboidal epithelium model

 Lab-2 24

Simple cuboidal epithelial cells are usually six-sided (cube shaped), but they appear square in side view (as shown on the above image of the model) and polygonal or hexagonal when viewed from the top. Their spherical nuclei stain darkly and often give the layer an appearance of a string of beads. This type of tissue is adapted for secretion and absorption. It can be found in such areas as the kidney tubules, the covering of the ovary and as a component of the ducts of many glands.

Viewed from the top

 Lab-2 25

20. Simple columnar epithelium model

 Lab-2 26

Simple columnar epithelium is composed of tall (columnar) cells that are closely packed together. Viewed from the surface they appear hexagonal but when viewed from the side (as shown on the image of the model above), they appear as a row of rectangles with the elongated nuclei frequently located at the same level, usually in the lower part of the cell. Simple columnar epithelial cells may be specialized for secretion (such as the goblet cells that secrete a protective layer of mucus in the small intestine), for absorption or for protection from abrasion. Columnar epithelial cells line a large part of the digestive tract, oviducts and many glands. 

Viewed from the surface

 Lab-2 27

21. Pseudostratified columnar epithelium model

 Lab-2 28

The image to the left shows a model of pseudostratified columnar epithelium. This type of tissue consists of a single layer of cells resting on a noncellular basement membrane that secures the epithelium. The tissue appears stratified (occurring in several layers) because the cells are not all the same height and because their nuclei (shown as black oval structures) are located at different levels. Pseudostratified ciliated columnar epithelium lines the trachea (windpipe) and larger respiratory passage ways.  

22. Skeletal (striated) muscle model

 Lab-2 29

Skeletal muscle is the most abundant type of muscle tissue found in the vertebrate body, making up at least 40% of its mass. Although it is often activated by reflexes that function in automatically in response to an outside stimulus, skeletal muscle is also called voluntary muscle because it is the only type subject to conscious control. Because skeletal muscle fibers have obvious bands called striations that can be observed under a microscope, it is also called striated muscle. Note that skeletal muscle cells are multinucleate, that is, each cell has more than one nucleus. 

23. Smooth muscle model

 Lab-2 30

Smooth muscle is the simplest of the three kinds of muscle. It is found where slow, sustained, involuntary contractions are needed such as in the digestive tract, reproductive system and other internal organs. Smooth muscle cells are long and spindle shaped with a single, centrally located nucleus. Smooth muscle is often arranged in two layers that run perpendicular to one another, a circular layer whose fibers appear in cross section as shown on the model above and a longitudinal layer whose fibers appear like the ends of a cut cable when viewed on-end.

24. Cardiac muscle model

 Lab-2 31

Cardiac muscle is striated like skeletal muscle but adapted for involuntary, rhythmic contractions like smooth muscle. The myofibrils are transversely striated, but each cell has only one centrally located nucleus. Note the dark blue transverse bands on the model called intercalated disks that mark the boundaries between the ends of the muscle cells. These specialized junctional zones are unique to cardiac muscle. 

25. Compact bone model

 Lab-2 32

This model shows a cross section of compact bone. Observe that the matrix of the bone is deposited in concentric layers that are called lamellae (5). The basic unit of structure in this type of bone is the Haversian system, or osteon. In each of these osteons, the lamellae are arranged around a central Haversian canal (1) housing nerves (4) and blood vessels (2, 3) in living bone. Osteocytes or bone cells, (6) are located in spaces called lacunae (7) that are connected by slender branching tubules called canaliculi (8). These “little canals” radiate out from the lacunae to form an extensive network, allowing bone cells to communicate with one another and to exchange metabolites. 

26. Multipolar neuron model

 Lab-2 33

The image above is that of a greatly enlarged multipolar neuron, the most common type of neuron found in humans. Notice that the cell body (1) contains the nucleus (2) with its conspicuous darkly staining nucleolus (3). Branching from the cell body are cytoplasmic extensions called nerve cell processes. In motor neurons (which conduct nerve impulses toward muscle cells), these processes consist of a single, long axon (4) and many of shorter dendrites (5).

4 - Axon

 Lab-2 34

Note in this magnified view of an axon that it is surrounded by specialized cells called Schwann cells (1) whose plasma membranes form a covering of the axon called the neurilemma (2), which is shown in brown on the model. These Schwann cells secrete a fatty myelin sheath (3), which is shown in yellow on the model, that protects and insulates nerve fibers from one another and increases the speed of transmission of nerve impulses. Adjacent Schwann cells along an axon do not touch one another, leaving gaps in the sheath called nodes of Ranvier at regular intervals (4).