Histology PDF

Histology  LEVELS OF Cells Tissues ORGANIZATION Cells Organism Organs Tissues Organs Organ Organ Systems Systems...

Histology  LEVELS OF Cells Tissues ORGANIZATION Cells Organism Organs Tissues Organs Organ Organ Systems Systems Organism  Histology The study of tissues of the body. From the 3 embryonic layers: ectoderm, mesoderm and endoderm, 5 basics tissue types will develop: Epithelial tissue. Connective tissue. Vascular tissue. Muscular tissue. Nervous tissue.  I. Epithelial Tissue Cellularity - Consists almost entirely of cells Covers body surfaces, lines hollow organs, and forms glands, for example Outside surface of the body Lining of digestive, respiratory and urogenital systems Polarity - Has apical, basal, and lateral surfaces Rests on a basement membrane Specialized cell contacts bind adjacent cells together Avascular - no blood vessels Mitotic ability -Replaces lost cells by cell division Epithelial Structure Apical Basement Membrane  Protecting underlying structures; e.g., epithelium lining the mouth Functions Acting as barriers; e.g., skin of Epithelia Permitting the passage of substances; e.g., cells lining air sacs in lungs and nephrons in kidney Secreting substances; e.g., pancreatic cells Absorbing substances; e.g., lining of stomach and small intestine Classifications of Epithelia  Number of layers of cells Simple- one layer of cells. Each extends from Classification basement membrane to the free surface of Stratified- more than one layer. Pseudostratified- tissue appears to be stratified, Epithelium but all cells contact basement membrane so it is in fact simple. Shape of cells Squamous- flat, scale-like Cuboidal- about equal in height and width Columnar- taller than wide Surface Modification Simple Columnar Epithelium  Contain two or more layers of cells. Stratified Epithelia Regenerate from below. Major role is protection. Are named according to the shape of cells at apical layer.  Function – Protects Stratified underlying tissues in areas Squamous subject to abrasion Epithelium Location Non-keratinized – forms Keratinized – forms lining of esophagus and epidermis mouth. Stratified Squamous Epithelium  Epithelium: Glandular A gland is one or more cells that makes and secretes an aqueous fluid. Two types of glands formed by enfolding of epithelium: Endocrine: no contact with exterior of body; ductless; produce hormones (pituitary, thyroid, adrenals, pancreas). Exocrine: open to exterior of body via ducts (sweat, oil). Exocrine glands classified either by structure or by the method of secretion. Classified by structure Unicellular: goblet cells. Multicellular: sweat, oil, pituitary, adrenal. Unicellualr Multicellualr e.g. Goblet cells  Method of Secretion ◼Merocrine- products are secreted by exocytosis. This is seen with most glands ◼Holocrine- the cell ruptures and releases the product. New cells replace the spent cells. The only example in humans are the sebaceous (sweat) glands ◼Apocrine-the top of the cell pinches off. Possibly seen in the lactating mammary gland although this is generally considered merocrine in nature.  Connective Tissue Enclose organs as a capsule and separate organs into layers. Areolar Connect tissues to one another. Tendons and ligaments. Support and movement. Bones. Storage. Fat. Insulation. Fat. Transport. Protection. Bone.  Ground substance – Structural unstructured material that fills the space between cells Elements of Fibers – collagen, elastic, or Connective reticular Tissue Cells – fibroblasts, chondroblasts, osteoblasts, and others Areolar Connective Tissue Adipose Tissue Hyaline Cartilage Bone Tissue  Characteristics Cells are referred to as fibers Contracts or shortens with force when stimulated Moves entire body and pumps blood Muscle Tissue Types Skeletal: attached to bones Cardiac: muscle of the heart. Smooth: muscle associated with tubular structures and with the skin. Nonstriated and involuntary. Cardiac Muscle Tissue