1. LOOSE (AREOLAR) CONNECTIVE TISSUE

Vascular adventitia
Aorta. The tunica externa or adventitia consists of loose connective tissue. Amorphous ground substance is more abundant than cells. And cells (mainly fibroblasts) are relatively more abundant than fibers in loose connective tissue.

2. DENSE REGULAR CONNECTIVE TISSUE

Tendon
The fibers in dense connective tissue are more abundant than cells and amorphous ground substance. In the dense regular connective tissue the collagen fibers are oriented in a regular pattern. The great tensile strength of collagen tendons is reflected in their structure, being the fibers arranged in the same plane and direction.

3. DENSE IRREGULAR CONNECTIVE TISSUE

Dermis
Collagen fibers predominate in dense irregular connective tissue. They are generally arranged in bundles that cross each other at varying angles.

4. ADIPOSE TISSUE

White adipose tissue
Panniculus adiposus. Adipose tissue of the subcutis is called panniculus adiposus. The polygonal adipose cells contain a single large lipid droplet, and therefore are also called unilocular adipocytes. The lipid droplet is surrounded by a thin layer of cytoplasm that contains a flattened nucleus. The lipid inclusion is not membrane-bounded. Because fat is dissolved by the reagents used for the preparation of histological sections, adipose cells appear as large clear spaces surround by a thin layer of cytoplasm.

Brown adipose tissue
Brown fat cells are smaller than white ones, and contain multiple individual lipid droplets scattered throughout the cytoplasm, being called multilocular adipocytes. The high concentration of cytochromes in the large number of mitochondria is responsible for the brown color of the tissue.



5. CARTILAGE

Trachea
The matrix of the cartilage is intensely basophilic and PAS-positive. The chondrocytes vary in size; those immediately beneath the perichondrium are small, and their lacunae are elliptical with their long axes parallel to the surface. Deep within the cartilage, the cells are larger and more polyhedral in shape. The multicellular lacunae are called isogenous cell groups.

6. BONE

Compact or cortical bone
Diaphysis. Cat femur. The compact bone makes up the wall of a hollow cylinder enclosing the medullary or marrow cavity. Compact bone is composed of bony matrix deposited in layers or lamellae with lacunae between each layer. The osteocytes reside in the lacunae surrounded by the calcified interstitial substance. Concentric lamellae are layers of bone surrounding longitudinally oriented channels forming cylindric structures called osteons or Haversian systems. The external and internal surfaces of compact bone have the inner and outer circumferential lamellae.

Spongy or trabecular bone
Epiphysis. Cat femur. The ends of long bones, the epiphyses, are composed primarily of trabecular bone, and the communicating spaces, which are filled with marrow, are continuous with the marrow cavity of the diaphysis. There are not osteons.

7. SKELETAL MUSCLE

Longitudinal section: extremely long myofibers. Each myofiber has many nuclei, mainly located at the periphery of the myofiber. We can observe transverse striations appearing as a regular, cross-banding pattern.

Cross section: Polygonal, rounded myofibers with abundant cytoplasm and variable number of nuclei located in the periphery of the myofibers.

8. CARDIAC MUSCLE

Longitudinal section: cylindric striated cells containing a single nucleus always positioned in the center of the myofiber. Because a profuse capillary network is interposed between the muscle elements, nuclei of the endotehelial cells are seen at the periphery. The myofibers are anastomosed by the intercalated disks.

Cross section: rounded myofibers with a single nucleus in the center of the myofiber.

9. SMOOTH MUSCLE

Intestine. Tunica muscularis
The tunica muscularis consists of inner circular and outer longitudinal smooth muscle layers.
Longitudinal section: Each smooth myofiber is a small mononucleated spindle cell. The nucleus is located at the center of the myofiber. No cross-banding is visible.
Cross section: small rounded myofibers showing central nucleus (myofibers cut at midpoint), or absence of nuclear profiles (in cells cut nearer their ends).

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10. NERVOUS TISSUE

Spinal cord

Spinal cord consists of gray matter and white matter, as the other organs of the central nervous system. The gray matter is H-shaped and has bilateral small dorsal columns (horns) and large ventral columns. Gray matter is rich in neuronal cell bodies, and glial cells. The central canal is lined by a simple cuboidal epithelium (ependyma). White matter is formed by dense accumulations of axons. Glial cells are also observed.