Chapter 4 - Lecture notes 4 PDF

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Chapter 4: Tissue Level of Organization Atoms  Molecules  Cells  Tissues Tissue is a group of cells working together to perform a specific function Four types of Tissue make up the body  Epithelial  Connective  Muscle  Neural Study of tissues is called histology Divisions of Epithelial Tissue 1. Epithelia o Cover exposed surfaces o Lines internal cavities and passageways o Often contain secretory or gland cells scattered among other cell types 2. Glands – Two Types o Exocrine glands  Secrete onto external surfaces or into ducts  Three Types of Exocrine Gland Secretion: 1. Merocrine Secretion – product released from secretory vesicles by exocytosis a. Mucin – merocrine secretion that mixes with water to form mucus 2. Apocrine Secretion – Apical cytoplasm packed with secretory vesicles b. Cell releases cytoplasm as well as secretory product 3. Holocrine Secretion – destroys gland cell, entire cell bursts, releasing secretions and killing cell c. Cells are replaced by stem cell division  Multicellular Exocrine Glad Classification  Based on Duct Structure o Simple – single duct that doesn’t divide

o Compound – duct that divides one or more times  Based on the shape of the secretory area o Tubular – glandular cells form tubes o Alveolar or acinar – glandular cells form sacs o Tubuloalveolar – glandular cells form both tubes and sacs  Unicellular Exocrine Gland Classification  Mucous (goblet) cells o Only unicellular exocrine glands – independent, scattered secretory cells in epithelium o Secrete mucin o Endocrine glands  Secrete hormones into interstitial fluid  Hormones then distributed by bloodstream Function of Epithelial Tissue 1. Provide physical protection o Protects surfaces from abrasion, dehydration, or destruction by chemical or biological agents 2. Control permeability o Most epithelia are capable of selective absorption or secretion o Ex. Calluses 3. Provide Sensation o Specialized epithelial cells detect changes in environment o Neuroepithelium - sensory epithelium found in special sense organs 4. Produce specialized secretions o Glandular epithelial cells produce secretions Features of Epithelial Tissue 1. Surfaces o Apical surface (upper) - exposed to the environment, faces exterior of body  Lumen - when an apical surface is lining a tube and is exposed to space inside the tube  Microvilli and cilia found on this surface is certain tracts o Base – attached to underlying tissues  Basolateral surface – includes base and sides attached to neighboring cells

2. Polarity o Refers to structural differences between exposed and attached surfaces 3. Epithelial cells – Three Basic Shapes 1. Squamous – thin and flat – can be both simple and stratified o Simple Squamous – most delicate, functions include absorption, diffusion, reduction of friction  Mesothelium – lining ventral body cavities  Endothelium – lining heart and blood vessels o Stratified Squamous – located where severe mechanical or chemical stresses exist – forms surface of skin and lines mouth, throat, esophagus, rectum, anus, vagina  Keratinized – packed with keratin – tough and water resistant, found on surface of skin and in hair and nails  Nonkeratinized – resists abrasion but can dry out, found lining oral cavity, pharynx, esophagus, anus, vagina 2. Cuboidal – cube-shapes like little boxes – can be both simple and stratified o Simple Cuboidal – functions in secretion and absorption - Lines exocrine glands and ducts, part of kidney tubules and thyroid gland o Stratified Cuboidal- rare tissue – found in sweat glands and mammary glands 3. Columnar – taller than they are wide, slender rectangles o Transitional Epithelium – unusual stratified epithelium that can stretch and recoil without damage – found only in urinary system – changes between relaxed and stretched  Simple Columnar – found where absorption or secretion takes place – lines stomach, intestine, gallbladder, uterine tubes, kidney ducts – may have microvilli (for absorption) or cilia (for movement) on apical surface  Pseudostratified Columnar – cells of varying shapes and functions – cells usually have cilia – lines nasal cavities, trachea, larger airways in lungs

 Stratified Columnar – rare tissue, found lining large ducts such as those of salivary glands or pancreas o Simple Epithelium – single layer of cells o Stratified Epithelium – several layers of cells, found in areas that need protection from abrasion or chemical stress 4. Epithelial Attachments o Extensive attachments between adjacent cells and adjacent tissues  To function as a barrier, must have intact, complete lining  Must be able to replace damaged or lost cells  **Avascular -No Blood Vessels Types of Intercellular Connections in Epithelial Tissues 1. Hemidesmosomes o Attach deepest epithelial cells to basement membrane 2. Tight (Occluding) Junctions o Interlocking membrane proteins bind adjacent plasma membranes o Prevent passage of water and solutes between cells 3. Gap Junctions o Held together by interlocking transmembrane proteins – connexons o Assist chemical communication to help coordinate functions such as secretion or beating cilia 4. Desmosomes o Provide firm attachments by interlocking adjacent cells’ cytoskeletons o Opposing plasma membranes locked together by cell adhesion molecules (CAMs) o Very strong; resist stretching and twisting o Found in superficial layers of skin Overview of Membranes  Lines or cover body surfaces  Consist of epithelium supported by connected tissue  Four types in the body: o Mucous Membranes  Lines passageways open to the exterior of the body

 Must be kept moist to facilitate movement, absorption, or secretion  Lubricated by mucus or bodily fluids  Supported by areolar connective tissue o Serous Membranes  Thin and delicate, never connected to exterior  Watery serous fluid coats surface  Three line subdivisions of ventral body cavity  Pleura (pleural cavity and lungs)  Pericardium (pericardial cavity and heart)  Peritoneum (peritoneal cavity and visceral organs)  Supported by areolar connective tissue o Cutaneous Membrane  Covers surface of body (skin)  Composed of stratified squamous epithelium  Layer of areolar tissue  Underlying dense irregular connective tissue  Relatively thick, waterproof, and dry o Synovial Membranes  Lines freely moveable joint cavities, lubricating them with synovial fluid  Provides oxygen and nutrients to cartilage cells  Not true epithelium  Develops within connective tissue, but lacks basement membrane  Contains gaps between cells  Synovial fluid and capillaries continuously exchange fluid an solutes Muscle and Nervous Tissue Types of Muscle Tissue:  Skeletal Muscle Tissue o Moves the body – Voluntary Muscle o Found in skeletal muscles o Elongated cylindrical, banded (striated) cells with multiple nuclei (multinucleate) o Functions:

 Move and stabilized skeleton  Guard entrances and exits to digestive, respiratory, and urinary tracts  Generate heat  Protect internal organs  Cardiac Muscle Tissue o Found only in your heart – Involuntary Muscle o Cells (cardiocytes) are short, branched, and usually have a single nucleus  Interconnected with special junctions (intercalated discs) that help synchronize cardiocyte contractions o Functions:  Moves blood within the heart and through blood vessels  Smooth Muscle Tissue o Involuntary Muscle o Found throughout body (skin, blood vessel walls, many organs of various systems) o Cells are short, spindle-shaped, nonstriated, have a single nucleus o Functions:  Moves fluids and solids along digestive tract  Regulates diameter of small arteries, among other functions Nervous Tissue:  Specialized for conduction of electrical impulses – communication  98% found in brain and spinal cord  Two basic types of cells o Neurons (nerve)  Longest cells in the body  Transfer info around body and perform info processing o Neuron Structure:  Dendrites – receive information  Axon ( Nerve Fibers ) – conduct info to other cells  Cell Body – contains large nucleus and other organelles  Control center and site of info processing  Most lack centrioles and cannot divide o Neuroglia or glial cells (supporting cells)  Several different structural types with associated functions

The Response To Tissue Injury  Tissues respond in a coordinated way to restore homeostasis  Two restoration Processes o Inflammation o Regeneration  Occurs after damaged tissue has stabilized  Fibroblasts produce collagen fibers to stabilize injury site  Produces dense, collagenous framework called scar tissue  Scar tissue usually remodeled and normal tissue conditions restored...