Connective Tissues

Learning Objectives:

o   Describe the general microscopic structure and function of connective tissue

o   Correlate morphology of resident and wandering CT cells with their locations and functions

o   Compare the molecular makeup, structural organization, location, and functions of the three main fiber types of connective tissue

o   Correlate the histological compositions and organizations of CT proper, reticular CT, and adipose CT and their locations and functions

General Connective Tissues

No Slide:

How do we classify connective tissues? Map out a “decision tree” to help you determine what type of connective tissue you’re looking at.

Metacogntive Tip: A Decision tree is a good way to help you make distinctions between different, related structures. A concept map might also be a helpful way to study and think about connective tissues.

We classify connective tissues based on the density of cells vs. fibers, the type of fibers, and the orientation of fibers. Your decision tree may vary from mine.

What is the main (resident) cell of connective tissue? Draw one in your notebook, and describe it in words.

Fibroblasts – They are spindle shaped, with somewhat scant, pale cytoplasm 

What are three types of fibers that exist in connective tissue?

Collagen fibers, reticular fibers, elastic fibers.

What are the two categories of cell that exist in connective tissues, and what are examples of each?

Jejunum

Resident cells: E.g., Mesenchymal cells, adipocytes, and fibroblasts

“Wandering” cells: E.g., Macrophages, plasma cells, mast cells, etc. (These are all related to immune function) 

Loose (Areolar) Connective Tissue

SLU Slide 14: Ileum

Iowa Virtual Slidebox: Jejunum (396); Colon (393)

Examine these slides at lower power and note that one surface is lined by a columnar epithelium and the other by smooth muscle. Loose connective tissue lies in between these layers in a layer called the lamina propria. Why do we call it “loose” connective tissue?

Because its fibers are more loosely packed together than those found in “dense” connective tissue. 

Examine this section to observe collagen fibers and their fibroblasts. You will also see other structures passing through this layer. Make note of these structures and draw them in your notebook if you wish. 

Reticular Connective Tissue Fibers

SLU Slide 73: Lymph Node, Silver Stain

Iowa Virtual Slidebox: Lymph node, silver stain (175)

Examine this slide at low and medium (~24x) power to see the outer connective tissue capsule surrounding this lymph node, as well as trabeculae that invaginate into the node and provide it with structure. These fibers help to support the parenchyma of different organs. 

(No answer required, but you may want to make a drawing or take a screenshot and add it to your notes or notebook.)

Elastic Fibers

SLU Slide 47: Aorta

Iowa Virtual Slidebox: Aorta (295)

Examine this slide to observe long, coiled (i.e., wavy), darkly staining elastic fibers. Why might a vascular structure like the aorta require this type of fibers within its walls? (Draw/take a screenshot and add it to your notes).

To respond to differences in pressure that might occur at different times. A “loose” aorta will have a hard time transporting blood to where it needs to go, and a “tight” aorta won’t be able to handle a large capacity of blood. Elastic fibers allow the aorta to stretch and shrink as is appropriate for the amount of blood.

Adipose Tissue

Examine thes tissues at low magnification (4x) to observe adipocytes. Why do adipocytes appear empty in histological preparation? Now move to higher magnification. Where is an adipocyte’s nucleus? Draw or take a screenshot of one of these cells below.

Adipocytes appear clear because their lipid substance is dissolved during histological processing. Adipocyte nuclei are found at the periphery of the cell.

Embryonic Connective Tissue

SLU Slide 85: Developing membrane bone; SLU Slide 24: umbilical cord

Iowa Virtual Slidebox: Umbilical cord (160)

Sketch the two different types of embryonic connective tissue shown in these slides. Pay attention to the shape of the cells, the shape and distribution of collagen fibers, and the matrix.

Your sketch of mesenchymal connective tissue as seen in the developing membrane bone should include cells ranging from dendritic to fusiform (mesenchymal cells) with fine collagenous fibers. The matrix may appear “washed out,” or pale.

Your sketch of mucous connective tissue, as demonstrated in the umbilical cord, should include thin collagen fibers with sparse cells. The cells (fibroblasts or mesenchymal cells) should be stellate in shape.

SLU Slide 77: tendon

Iowa Virtual Slidebox: Tendon (235)

What type of connective tissue is this? What is the ratio of cells:fibers:matrix? (i.e., high/low) What types of fibers exist in this preparation?

Dense regular connective tissue. Few cells, many fibers, little matrix