Tissues

Epithelial tissues are surface tissues that consist of numerous cells, with each cell forming membrane to membrane contact with its neighbors. As a general rule, descriptions of epithelial tissues are based on the shape of

their cells and on the number of cell layers present. By combining the shape names — squamous (fl at cells), cuboidal, and columnar — with the term simple if there is a single layer of cells or the term stratifi ed if there is more than one layer of cells, almost all of the epithelial tissues can be described and named. The photomicrographs on this page and the facing page represent the simple (single cell layer) epithelial tissues.

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Simple cuboidal epithelium

Urinary tubes in kidney - transverse section, 630x (left); longitudinal section, 400x (right)

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Connective tissues have relatively few cells and the cells are surrounded by an extracellular matrix of fi bers, which the cells secrete. The classifi cation and names of connective tissues arise from the type

and arrangement of the fi bers produced by the cells and secreted into the surrounding matrix. There are three named

fibers in the matrix — collagen fi bers, reticular fi bers (actually a thin form of collagen), and elastic fi bers. The fi bers are deposited in varying degrees of density and are arranged in different patterns. The tissue names are based on the different

fiber types and patterns in the matrix.

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Loose (areolar) connective tissue

Section of subcutaneous layer of integument, 400x

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Adipose tissue

Section of epicardial fat, 200x

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The supporting tissue category consists of the skeletal tissues— cartilage and bone. Like the connective tissues, the supporting tissues have relatively few cells surrounded by a signifi cant amount of extracellular

matrix, which for the most part the cells produce. However, unlike the soft matrix of the connective tissues, the extracellular matrix of the supporting tissues is firm and rubber-like in cartilage and hard in bone tissue.

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10Canaliculi

11Lacuna

12Lamella

13Central canal

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Hyaline cartilage

Section of cartilage in developing fetal bone, 200x

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The tissues blood and lymph traditionally were classified as connective tissues because, like all connective tissues, the extracellular matrix

is a greater percentage of the tissue then are the cells. However, the extracellular matrix of blood and lymph is a liquid matrix called plasma, rather than the soft, fi rm matrix of connective tissues. The most recent Terminologia Histologica places blood and lymph in their own subcategory called the hematolymphoid complex.

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Blood smear

Wright’s stain, 200x; enlargement, 630x; individual cells, 1500x

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Muscle cells are long, slender cells that have special arrangements of the proteins actin and myosin within the cytoplasm. The architectural design of these proteins forms the muscle cell “machinery” that allows the cell to specialize at contracting

(shortening). The names of the different types of muscle tissues arise from the arrangement of the contractile proteins within their cells. In some tissues the protein arrangement gives the cell a striated, or striped, appearance (striated muscle), while in other tissues the striped appearance is not evident (non-striated or smooth muscle).

1 Nucleus

2 Sarcoplasm

3 Smooth muscle cell

4 Cardiac muscle cell

5 Skeletal muscle cell

6 Intercalated disc

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Smooth (nonstriated) muscle tissue

Longitudinal section of muscular wall of intestine, 500x

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