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Human Tissue Notes - Human Anatomy and Physiology, Tissue types.
Typology: Lecture notes
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A tissue is a group of cells that usually have a common embryonic origin and function together to carry out specialized activities. Histology (histo= tissue; - logy= study of) is the science that deals with the study of tissues. A pathologist is a physician who specializes in laboratory studies of cells and tissues to help other physicians make accurate diagnoses. Types of Tissues in Body: Body tissues can be classified into four basic types according to structure and function:
Structure of Epithelial Tissue: ➢ The apical (free) surface of an epithelial cell faces the body surface, a body cavity, the lumen (interior space) of an internal organ, or a tubular duct that receives cell secretions. Apical surfaces may contain cilia or microvilli. ➢ The lateral surfaces of an epithelial cell face the adjacent cells on either side. ➢ The basal surface of an epithelial cell is opposite the apical surface, and the basal surfaces of the deepest layer of cells adhere to extracellular materials. ➢ The basement membrane is a thin extracellular layer that commonly consists of two layers, the basal lamina and reticular lamina. ➢ The basal lamina (thin layer) is closer to and secreted by the epithelial cells. It contains proteins such as laminin and collagen, as well as glycoproteins and proteoglycans. ➢ The reticular lamina is closer to the underlying connective tissue and contains proteins such as collagen produced by connective tissue cells called fibroblasts. ➢ The basement membrane functions as a point of attachment and support for the overlying epithelial tissue. ➢ Epithelial tissue has its own nerve supply, but is avascular; it lacks its own blood supply. Epithelial tissue may be divided into two types. (1) Covering and lining epithelium forms the outer covering of the skin and some internal organs. It also forms the inner lining of blood vessels, ducts, and body cavities, and the interior of the respiratory, digestive, urinary, and reproductive systems. (2) Glandular epithelium makes up the secreting portion of glands such as the thyroid gland, adrenal glands, and sweat glands.
Combining the two characteristics (arrangements of layers and cell shapes), the types of covering and lining epithelia are as follows:
A. Simple squamous epithelium: Description: Single layer of flat cells; centrally located nucleus. Location: Lines heart, blood vessels, lymphatic vessels, air sacs of lungs, glomerular (Bowman’s) capsule of kidneys, and inner surface of the tympanic membrane (eardrum); forms epithelial layer of serous membranes, such as the peritoneum, pericardium, and pleura. Function: Filtration, diffusion, osmosis, and secretion in serous membranes. B. Simple cuboidal epithelium: Description: Single layer of cube-shaped cells; centrally located nucleus. Location: Covers surface of ovary, lines anterior surface of capsule of the lens of the eye, forms the pigmented epithelium at the posterior surface of the eye, lines kidney tubules and smaller ducts of many glands, and makes up the secreting portion of some glands such as the thyroid gland and the ducts of some glands such as the pancreas. Function: Secretion and absorption.
E. Pseudostratified columnar epithelium: Description: Not a true stratified tissue; nuclei of cells are at different levels; all cells are attached to basement membrane, but not all reach the apical surface. Location: Pseudostratified ciliated columnar epithelium lines the airways of most of upper respiratory tract; pseudostratified nonciliated columnar epithelium lines larger ducts of many glands, epididymis, and part of male urethra. Function: Secretion and movement of mucus by ciliary action . F. Stratified squamous epithelium: Description: Several layers of cells; cuboidal to columnar shape in deep layers; squamous cells form the apical layer and several layers deep to it; cells from the basal layer replace surface cells as they are lost. Location: Keratinized variety forms superficial layer of skin; nonkeratinized variety lines wet surfaces, such as lining of the mouth, esophagus, part of larynx, part of pharynx, and vagina, and covers the tongue. Function: Protection.
G. Stratified cuboidal epithelium: Description: Two or more layers of cells in which the cells in the apical layer are cube-shaped. Location: Ducts of adult sweat glands and esophageal glands and part of male urethra. Function: Protection and limited secretion and absorption. H. Stratified columnar epithelium: Description: Several layers of irregularly shaped cells; only the apical layer has columnar cells. Location: Lines part of urethra, large excretory ducts of some glands, such as esophageal glands, small areas in anal mucous membrane, and part of the conjunctiva of the eye. Function: Protection and secretion. I. Transitional epithelium: Description: Appearance is variable (transitional); shape of cells in apical layer ranges from squamous (when stretched) to cuboidal (when relaxed). Location: Lines urinary bladder and portions of ureters and urethra.
B. Exocrine glands: Description: Secretory products released into ducts. Location: Sweat, oil, and earwax glands of the skin; digestive glands such as salivary glands, which secrete into mouth cavity, and pancreas, which secretes into the small intestine. Function: Produce substances such as sweat, oil, earwax, saliva, or digestive enzymes. SUMMARY OF EPITHELIAL TISSUE:
I. Mesenchyme: Description: Consists of irregularly shaped mesenchymal cells embedded in a semifluid ground substance that contains reticular fibers. Location: Under skin and along developing bones of embryo; some mesenchymal cells are found in adult connective tissue, especially along blood vessels. Function: Forms all other types of connective tissue.
II. Mucous connective tissue: Description: Consists of widely scattered fibroblasts embedded in a viscous, jellylike ground substance that contains fine collagen fibers. Location: Umbilical cord of fetus. Function: Support. MATURE CONNECTIVE TISSUES LOOSE CONNECTIVE TISSUE: A. Areolar connective tissue: Description: Consists of fibers (collagen, elastic, and reticular) and several kinds of cells (fibroblasts, macrophages, plasma cells, adipocytes, and mast cells) embedded in a semifluid ground substance. Location: Subcutaneous layer deep to skin; papillary (superficial) region of dermis of skin; lamina propria of mucous membranes; and around blood vessels, nerves, and body organs.
Description: A network of interlacing reticular fibers and reticular cells. Location: Stroma (supporting framework) of liver, spleen, lymph nodes; red bone marrow, which gives rise to blood cells; reticular lamina of the basement membrane; and around blood vessels and muscles. Function: Forms stroma of organs; binds together smooth muscle tissue cells; filters and removes worn- out blood cells in the spleen and microbes in lymph nodes. DENSE CONNECTIVE TISSUE: D. Dense regular connective tissue: Description: Extracellular matrix looks shiny white; consists mainly of collagen fibers regularly arranged in bundles; fibroblasts present in rows between bundles. Location: Forms tendons (attach muscle to bone), most ligaments (attach bone to bone), and aponeuroses (sheetlike tendons that attach muscle to muscle or muscle to bone). Function: Provides strong attachment between various structures. E. Dense irregular connective tissue:
Description: Consists predominantly of collagen fibers randomly arranged and a few fibroblasts. Location: Fasciae (tissue beneath skin and around muscles and other organs), reticular (deeper) region of dermis of skin, periosteum of bone, perichondrium of cartilage, joint capsules, membrane capsules around various organs (kidneys, liver, testes, lymph nodes), pericardium of the heart, and heart valves. Function: Provides strength. F.Elastic connective tissue: Description: Consists predominantly of freely branching elastic fibers; fibroblasts are present in spaces between fibers. Location: Lung tissue, walls of elastic arteries, trachea, bronchial tubes, true vocal cords, suspensory ligament of penis, and some ligaments between vertebrae. Function: Allows stretching of various organs.