Connective Tissues - Histology Histology > Tissue Types > Tissue Types

Home , Loose connective tissue, Stroma (tissue), White adipose tissue

Be aware that there are many ways to categorize connective tissues, and, in some cases, intertextual nomenclature variation exists.

CONNECTIVE TISSUE&NBSP;

• Comprises cells suspended in an extracellular matrix of protein fibers and ground substance. The specific types and relative proportions of cells, fibers, and ground substance determine the overall structure and function of connective tissues.

Areolar connective tissue

• Very loosely organized, with diverse cellular and fibrous components.

• This organization creates spaces; in fact, "areolar" means "small space."

• Supports organs and vasculature, and participates in the inflammatory response.

• Present throughout the body.

Be aware that many texts use the terms "areolar" and "loose connective tissue" interchangeably.

Gel-like ground substance

• Non-living protein and carbohydrate molecules suspended in water

Fiber types

• Collagen Fibers

Broad, pink-staining fibers provide tensile strength Elastic fibers

• Thin, dark-staining elastic fibers, which form a network

Reticular fibers

• Fine, branching reticular fibers, which form a lose meshwork (reticular fibers comprise type III collagen).

1 / 3 Cell Types

• Fibroblasts are spindle-shaped cells that synthesize the ground substance and protein fibers (these are the most common cell type)

• Mast cells are granular cells that release histamine and heparin as part of the inflammatory response

• Large macrophages engage in phagocytosis; other white blood cells may also be present.

White Adipose Tissue

• Aka, fat, tissue

• Often categorized as a specialized loose connective tissue.

Adipocytes

• Look like soap bubbles in histological preparation

• Clusters of circular cells press against each other, with their nuclei pushed toward their edges; notice that there is relatively little extracellular matrix, and no fibers are present.

• In life, each cell holds a single fat droplet, formed by the fusion of lipid droplets; the fat is not present in the slide preparation, but we can still see the space it occupied.

• Cushions the organs, insulates the body, and stores energy as triglycerides.

Reticular Connective Tissue

• Comprises an abundance of reticular fibers that form complicated branching and interweaving patterns

• Fine reticular fibers stain faintly; may anchor to collagenous septa, which divide organs into lobes.

• Reticular cells are specialized fibroblasts that synthesize and hold the fibers.

• Lymphocytes and other white blood cells may also be present.

• Reticular tissue forms a mesh-like network of support, aka, stroma, for blood cells within the lymph nodes, spleen, liver, and bone marrow.

Dense regular connective tissue:

• Comprises bundles of tightly packed collagen fibers running in parallel waves

• Fibroblasts lie between the collagen fibers.

• The wavy organization of collagen fibers allow for a limited amount of stretch in a single direction

• Present in tendons, which hold muscle to bone; ligaments, which hold bone to bone; and, fascia, which wraps and binds structures throughout the body.

2 / 3 Dense Irregular Connective Tissue

• Comprises collagen fibers and fibroblasts;

• Fibers are irregularly organized, which enables dense irregular connective tissue to withstand tension from many directions.

• Found in the fibrous capsules of joints, in the dermis of the skin,

and in the submucosa of the digestive tract. Elastic connective tissue proper

• Comprises closely packed elastic fibers that run in parallel; in preparatory slides, its ground substance often appears dark pink.

• Pure elastic connective tissue is rare, but elastic fibers are present where recoil and stretching are necessary – for example, in the walls of muscular arteries, elastic fibers interweave with smooth muscle cells.

• Elastic fibers and/or connective tissue is also found in some ligaments of the vertebral column, and in the walls of large arteries and bronchial tubes.

Clinical correlation: Marfan Syndrome is an inherited disease of the connective tissues; it's multi-organ system deficits underlies the widespread importance of connective tissues. Patients with Marfan's syndrome have numerous ailments from ocular lens dislocation to structural abnormalities of the heart valves and blood vessels, and joint abnormalities, and even disproportionately long bones. References: McKinley, MP, O'Loughlin VD. 2012. Human Anatomy 3rd Ed. McGraw Hill Eroschenko VP. 2008. DiFiore's Atlas of Histology with Functional Correlations. Lippincott Williams & Wilkins Ovalle WK, Nahirney PC. 2013. Netter's Essential Histology 2nd Ed. Elsevier Young B, O'Dowd G, Woodford P. 2014. Wheater's Functional Histology: A Text and Color Atlas. 6th Ed. Elsevier. Images: Histology (Mark Braun, MD, & Indiana University: http://medsci.indiana.edu/c602web/602/c602web/toc.htm; http://www.indiana.edu/~anat215/virtualscope2/start.htm)