Medical brain notes 27

  EPITHELIAL TISSUE Epithelial tissues  are found on surfaces as either cov-erings (outer surfaces) or linings (inner surfaces). Because they have no capillaries of their own, epithe-lial tissues receive oxygen and nutrients from the blood supply of the connective tissue beneath them. Many epithelial tissues are capable of secretion and may be called glandular epithelium, or more simply,  glands . Classification of the epithelial tissues is based on the type of cell of which the tissue is made, its charac-teristic shape, and the number of layers of cells. There are three distinctive shapes:  squamous  cells are flat,  cuboidal  cells are cube shaped, and  columnar  cells   are tall and narrow. “ Simple ” is the term for a single layer of cells, and “ stratified ” means that many layers of cells are present (Fig. 4–1). Figure 4–1.  Classification of epithelial tissues   based on the shape of the cells and the number of layers of...

  CONNECTIVE TISSUE There are several kinds of  connective tissue , some of which may at first seem more different than alike. The types of connective tissue include areolar, adipose, fibrous, and elastic tissue as well as blood, bone, and cartilage; these are summarized in Table 4–2. A char-acteristic that all connective tissues have in common is the presence of a matrix in addition to cells. The  matrix  is a structural network or solution of non-living intercellular material.  Each connective tissue has its own specific kind of matrix. The matrix of blood, for example, is blood plasma, which is mostly water. The matrix of bone is made primarily of cal-cium salts, which are hard and strong. As each type of connective tissue is described in the following sec-tions, mention will be made of the types of cells pres-ent as well as the kind of matrix. BLOOD Blood consists of cells and plasma; cells are the living portion. The matrix of blood is  plasma , which ...

  MUSCLE TISSUE Muscle tissue is specialized for contraction. When muscle cells contract, they shorten and bring about some type of movement. There are three types of muscle tissue: skeletal, smooth, and cardiac (Table 4–3). The movements each can produce have very different purposes.   SKELETAL MUSCLE       Skeletal muscle may also be called striated muscle or voluntary muscle. Each name describes a particular aspect of this tissue, as you will see. The skeletal muscle cells are cylindrical, have several nuclei each, and appear striated, or striped (Fig. 4–6). The striations are the result of the precise arrangement of the contracting proteins within the cells Figure 4–6.   Muscle tissues. ( A ) Skeletal. ( B ) Smooth. ( C ) Cardiac.  QUESTION:  Which kinds of muscle cells have striations? What forms these striations? Skeletal muscle tissue makes up the muscles that are attached to bones. These muscles are supplied with motor nerve...

  NERVE TISSUE   Nerve tissue  consists of nerve cells called  neurons  and some specialized cells found only in the nervous system. The nervous system has two divisions: the central nervous system (CNS) and the peripheral nervous system (PNS). The brain and spinal cord are the organs of the CNS. They are made of neurons and specialized cells called neuroglia. The PNS consists of all of the nerves that emerge from the CNS and supply the rest of the body. These nerves are made of neurons and specialized cells called Schwann cells. The Schwann cells form the myelin sheath to electrically insulate neurons. Figure 4–7.  Nerve tissue of the central nervous system   (CNS). QUESTION:  How many processes does the central neu-ron have, and what are they called?   Neurons are capable of generating and transmit-ting electrochemical impulses. There are many differ-ent kinds of neurons, but they all have the same basic structure (Fig. 4–7). The  cell...

  MEMBRANES   Membranes  are sheets of tissue that cover or line sur-faces or that separate organs or parts (lobes) of organs from one another. Many membranes produce secre tions that have specific functions. The two major cat-egories of membranes are epithelial membranes and connective tissue membranes.   EPITHELIAL MEMBRANES   There are two types of epithelial membranes, serous and mucous. Each type is found in specific locations within the body and secretes a fluid. These fluids are called serous fluid and mucus.   Serous Membranes   Serous membranes  are sheets of simple squamous   epithelium that line some closed body cavities and cover the organs in these cavities (Fig. 4–8). The  pleural membranes  are the serous membranes of the   thoracic cavity. The parietal pleura lines the chest wall and the visceral pleura covers the lungs. (Notice that  line  means “on the inside” and  cover  means “on the ...