Anatomy Lec 2 PDF

Dr.Ali Alkhafajy Anatomy Lec 2 TISSUES&MEMBRANE 1  Dr.Ali Alkhafajy Anatomy Lec 2 A tissue is a group of cells with similar structure and function. There are four groups of tissues: These four groups are epit...

Dr.Ali Alkhafajy Anatomy Lec 2 TISSUES&MEMBRANE 1  Dr.Ali Alkhafajy Anatomy Lec 2 A tissue is a group of cells with similar structure and function. There are four groups of tissues: These four groups are epithelial, connective, muscle, and nerve tissue. Epithelial tissues—epithelial tissues are found on surfaces as either coverings (outer surfaces) or linings (inner surfaces). Because they have no capillaries of their own, epithelial 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 characteristic 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. 2  Dr.Ali Alkhafajy Anatomy Lec 2 Simple squamous epithelium is a single layer of flat cells. These cells are very thin and very smooth—these are important physical characteristics. The alveoli (air sacs) of the lungs are simple squamous epithelium. The thinness of the cells permits the diffusion of gases between the air and blood. Stratified squamous epithelium consists of many layers of mostly flat cells, although lower cells are rounded. This type of epithelium makes up the epidermis of the skin, where it is called “keratinizing” because the protein keratin is produced, and the surface cells are dead. Stratified squamous epithelium of the non-keratinizing type lines the oral cavity, the esophagus, and, in women, the vagina. Transitional epithelium is a type of stratified epithelium in which the surface cells change shape from round to squamous. The urinary bladder is lined with transitional epithelium. When the bladder is empty, the surface cells are rounded the bladder fills, these cells become flattened. Transitional epithelium enables the bladder to fill and stretch without tearing the lining. 3  Dr.Ali Alkhafajy Anatomy Lec 2 Simple cuboidal epithelium is a single layer of cube shaped cells. This type of tissue makes up the functional units of the thyroid gland and salivary glands. These are examples of glandular epithelium their function is secretion. In these glands the cuboidal cells are arranged in small spheres and secret into the cavity formed by the sphere. In the thyroid gland, the cuboidal epithelium secretes the thyroid hormones; thyroxine is an example. In the salivary glands the cuboidal cells secrete saliva. Cuboidal epithelium also makes up portions of the kidney tubules. Here the cells have microvilli, and their function is the reabsorption of useful materials back to the blood. SIMPLE COLUMNAR EPITHELIUM Columnar cells are taller than they are wide and are specialized for secretion and absorption. The stomach lining is made of columnar epithelium that secretes gastric juice for digestion. The lining of the small intestine secretes digestive enzymes, but these cells also absorb the end products of digestion from the cavity of the intestine into the blood and lymph. To absorb efficiently, the columnar cells of the small intestine have microvilli, which you may recall are folds of the cell membrane on their free surfaces. These microscopic folds greatly increase the surface area for absorption. Yet another type of columnar cell is the goblet cell which is a unicellular gland. Goblet cells secrete 4  Dr.Ali Alkhafajy Anatomy Lec 2 mucus and are found in the lining of the intestine and the lining of parts of the respiratory tract such as the trachea. Ciliated epithelium consists of columnar cells that have cilia on their free surfaces the function of cilia is to sweep materials across the cell surface. Ciliated epithelium lines the nasal cavities, larynx, trachea, and large bronchial tubes. The cilia sweep mucus, with trapped dust and bacteria from the inhaled air, toward the pharynx to be swallowed. Bacteria are then destroyed by the hydrochloric acid in the stomach. The air that reaches the lungs is almost entirely free of pathogens and particulate pollution. GLANDS Glands are cells or organs that secrete something; that is, they produce a substance that has a function either at that site or at a more distant site. Unicellular Glands Unicellular means “one cell.” Goblet cells are an example of unicellular glands. Goblet cells are found in the lining of the respiratory and digestive tracts. Their secretion is mucus. Multicellular Glands Most glands are made of many similar cells, or of a variety of cells with their secretions mingled into a collective secretion. Multicellular glands may be divided into two major groups: exocrine glands and endocrine glands. Exocrine glands have ducts (tubes) to take the secretion away from the gland to the site of its function. Salivary glands, for example, secrete saliva that is carried by ducts to the oral cavity. Sweat glands secrete sweat that is transported by ducts to the skin surface, where it can be evaporated by excess body heat. The gastric glands of the stomach lining contain different 5  Dr.Ali Alkhafajy Anatomy Lec 2 kinds of cells, which produce hydrochloric acid and the enzyme pepsin. Both of these secretions are part of gastric juice. Endocrine glands are ductless glands. The secretions of endocrine glands are a group of chemicals called hormones, which enter capillaries and are circulate throughout the body. Hormones then bring about specific effects in their target organs. These effects include aspects of growth, use of minerals and other nutrients, and regulation of blood pressure. Examples of endocrine glands are the thyroid gland, adrenal glands, and pituitary gland. The pancreas is an organ that is both an exocrine and an endocrine gland. The exocrine portions secrete digestive enzymes that are carried by ducts to the duodenum of the small intestine, their site of action. The endocrine portions of the pancreas, called pancreatic islets or islets of Langerhans, secrete the hormones insulin and glucagon directly into the blood. 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. A characteristic 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 nonliving intercellular material. Each connective tissue has its own specific kind of matrix. 6  Dr.Ali Alkhafajy Anatomy Lec 2 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 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. 7  Dr.Ali Alkhafajy Anatomy Lec 2 MEMBRANES Membranes are sheets of tissue that cover or line surfaces or that separate organs or parts (lobes) of organs from one another. Many membranes produce secretions that have specific functions. The two major categories 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. 8