That portion of the liver which is exposed in the abdominal cavity is covered by a reflection of the peritoneum, closely attached to the organ, because its deeper side is continuous with the fibrous structures or interstitial tissue of the liver itself. This serous covering is so thin that the substance of the liver can be readily seen through it. At the portal fissure, the serous coat having been reflected from it, the liver is covered with a loose areolar tissue in which the main trunks of all but one of the vessels connected with it are situated: namely, the portal vein, hepatic artery, gall-duct, and lymphatics.
The typical cell of cartilage is round or oval in shape, rich in cytoplasm, and possesses one (rarely two) nucleus of oval form and vesicular and reticulated structure. Within the cytoplasm there are frequently one or more clear spots, which are drops of homogeneous fluid, " vacuoles."
Epithelial tissue, also referred to as epithelium, refers to the sheets of cells that cover exterior surfaces of the body, lines internal cavities and passageways, and forms certain glands. Connective tissue, as its name implies, binds the cells and organs of the body together and functions in the protection, support, and integration of all parts of the body. Muscle tissue is excitable, responding to stimulation and contracting to provide movement, and occurs as three major types: skeletal (voluntary) muscle, smooth muscle, and cardiac muscle in the heart. Nervous tissue is also excitable, allowing the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body. The next level of organization is the organ, where several types of tissues come together to form a working unit. Just as knowing the structure and function of cells helps you in your study of tissues, knowledge of tissues will help you understand how organs function. The epithelial and connective tissues are discussed in detail in this chapter. Muscle and nervous tissues will be discussed only briefly in this chapter.
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