BIO 240 HISTOLOGY REVIEW Connective Tissues Dr. Tim Ballard Department of Biology and Marine Biology

Mesentery spread – Verhoeff – 4x objective This is a loose connective tissue. See how widely spread the fibers and cells are separated from one another. Areolar connective tissue Verhoeff’s stain is used to visualize both collagen and elastin fibers in the same sample. Collagen fibers are pink while elastin fibers are purple-black.

Elastin fiber (black arrowhead); collagen fiber (blue arrowhead); the nuclei are of various cell types, some of which are permanent and others that wander through Mesentery spread – Verhoeff – 10x objective Areolar connective tissue The spaces between fibers and cells are filled with water-based ground substance.

Elastin fiber (black arrowhead); collagen fiber (blue arrowhead); the nuclei are of various cell types, some of which are permanent and others that wander through Mesentery spread – Verhoeff – 40x objective Areolar connective tissue The loose arrangement of the fibers gives plenty of room for the wandering cells to pass through the tissue.

Adipose tissue – section – H&E – 4x objective This honey-combed appearance is characteristic of adipose tissue. Adipose tissue The H-E stain requires a series of alcohol dehydration steps. As a result, the fat droplets within the cells are “washed out” of the sample. You are looking at the remainder of the cell.

Adipose tissue – section – H&E – 10x objective The arrowheads point out individual cells. Adipose tissue

Adipose tissue – section – H&E – 40x objective Black arrowhead – nucleus of an adipocyte; blue arrowhead – capillary within the adipose tissue. Adipose tissue Adipocytes are said to have a “signet ring” appearance. Like a class ring, for example, the stone and engraving are on one side connected by a thin band wrapping around.

Spleen – section – silver – 10x objective Reticular tissue consists of very small collagenous fibers. They are visualized as brownish-black fibers with the silver stain. Reticular connective tissue Reticular fibers are used to form the stroma or framework (think infrastructure) of some organs. For example, the spleen and lymph nodes are made by a meshwork of reticular fibers. Lymphocytes and macrophages then invade the organ and take up residence in the spaces.

Arrowheads point out reticular fibers. The rounded nuclei are of lymphocytes residing in the organ. lymphocyte Spleen – section – silver – 40x objective Reticular connective tissue

Lymph node – section – H&E – 40x objective Notice that with the H&E stain individual reticular fibers are difficult to visualize. The nuclei are those of lymphocytes. This slide isn’t in our set. Reticular connective tissue

Trachea – cross section – H&E – 10x objective The bar with arrows indicates the thickness of the plate of hyaline cartilage located in the wall of the trachea. Hyaline cartilage Ciliated pseudostratified columnar epithelium The matrix of hyaline cartilage stains a light to dark bluish-purple with H&E. Newer matrix (immediately adjacent to the cells) stains darker than older matrix.

Arrowheads indicate chondrocytes, the cell type of cartilage. The cells sit in spaces called lacuna and are surrounded by the matrix they have secreted. lumen Trachea – cross section – H&E – 40x objective Hyaline cartilage The matrix is rich in collagen (giving it a pink color) and cartilage-specific molecules called chondroitin sulfates (giving it a purplish color).

Mouse ear – section – Verhoeff – 10x objective Elastic cartilage lumen Remember that the Verhoeff stain is specific of elastin fibers, staining them purple-black. There is a counterstain for collagen that is pink. This is a weakly-stained specimen. In a better preparation, the matrix would be stained intensely purple-black. The bar with arrows indicates the thickness of a plate of elastic cartilage located in the ear, giving it structure and flexibiility.

Mouse ear – section – Verhoeff – 40x objective Elastic cartilage Chondrocytes in elastic cartilage retain a fairly high mitotic rate throughout life. As result, there are many more cells than you would see in hyaline cartilage. Chondrocyte within its lacuna (arrowhead). Although a weak stain, notice all of the dark-stained elastin fibers in the matrix.

Pubic symphysis –section – Mallory’s – 4x objective All of the bluish fibers are collagen. Notice all of the rounded cells (chondrocytes) sitting inside lacunae. Fibrocartilage

Pubic symphysis –section – Mallory’s – 10x objective Fibrocartilage All of the bluish fibers are collagen. Notice all of the rounded cells (chondrocytes) sitting inside lacunae (arrowheads).

lacuna Pubic symphysis –section – Mallory’s – 40x objective Fibrocartilage Chondrocytes (arrowhead) within its lacuna; collagen fibers (arrow)