Chapter 4 The Tissue Level of Organization

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Chapter 4 The Tissue Level of Organization

• Jeff Laborda
• BSC 2085C
• Fall 2005

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Introduction

• Definition of tissue a group of similar cells
  that usually have a similar embryological origin
  and are specialized for a particular function.
• What is a histologist?
• What is a pathologist?

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Types of Tissues and their Origins

• Epithelial tissue
• covers body surfaces, line hollow organs, body
  cavities and ducts and forms glands.
• Connective tissue
• protects and supports the body and its organs,
  binds organs together, stores energy reserves as
  fat, and provides immunity.
• Muscle tissue
• is responsible for movement and generation of
  force.
• Nervous tissue
• Initiates and transmits action potentials (nerve
  impulses) that help coordinate body activities.

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Origin of Tissues

• Primary germ layers within the embryo
• Endoderm from which is derived epithelium
• Mesoderm from which is derived epithelium,
  connective, and muscle
• Ectoderm from which is derived epithelium, and
  nervous tissue
• Table 29.1 list of structures derived from
  primary germ layers

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Cell Junctions

• Cell Junctions are points of contact between
  adjacent plasma membranes
• Depending on their structure, cell junctions may
  serve one of three functions.
• Some form fluid-tight seals between cells.
• Others anchor cells together or to extracellular
  material.
• Still others act as channels, which allow ions
  and molecules to pass from cell to cell within a
  tissue.

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Cell Junctions
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Tight Junctions

• Watertight seal between cells
• Plasma membranes fused with a strip of proteins
• Common between cells that line GI and bladder
• Retard passage of substances between cells and
  prevent contents of these organs from leaking
  into blood or surrounding tissues

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Adherens Junctions

• Holds epithelial cells together
• Structural components
• plaque dense layer of proteins inside the cell
  membrane
• microfilaments extend into cytoplasm
• integral membrane proteins connect to membrane of
  other cell
• They help epithelial surfaces resist separation
  during various contractile activities, as when
  food moves through the intestines

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Gap Junctions

• Tiny space between plasma membranes of 2 cells
• Crossed by protein channels called connexons
  forming fluid filled tunnels
• Cell communication with ions small molecules
• Muscle and nerve impulses spread from cell to
  cell
• heart and smooth muscle of gut

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Desmosomes

• Resists cellular separation and cell disruption
• Similar structure to adherens junction except
  intracellular intermediate filaments cross
  cytoplasm of cell
• Cellular support of cardiac muscle and epidermal
  cells

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Hemidesmosomes

• Half a desmosome
• Connect cells to extracellular material
• basement membrane

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EPITHELIAL Tissue General Features

• Composed of tightly connected cells arranged in
  sheets
• Epithelial cells have apical, lateral, and basal
  surfaces
• Attached to basement membrane
• Avascular
• nutrients and wastes must move by diffusion
• Good nerve supply
• Rapid cell division (high mitotic rate)
• Functions
• protection, filtration, lubrication, secretion,
  digestion, absorption, transportation, excretion,
  sensory reception, and reproduction.

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Epithelial - Basement Membrane

• Basal lamina
• from epithelial cells
• collagen fibers
• Reticular lamina
• secreted by connective tissue cells
• reticular fibers
• Functions
• guide for cell migration during development
• may become thickened due to increased collagen
  and laminin production
• Example In diabetes mellitus, the basement
  membrane of small blood vessels, especially those
  in the retina and kidney, thickens.

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Types of Epithelium

• Covering and lining epithelium
• epidermis of skin
• lining of blood vessels and ducts
• lining respiratory, reproductive, urinary GI
  tract
• Arrangement of cells in layers
• Simple epithelium
• Stratified epithelium
• Pseudostratified epithelium cells contact BM
  but all cells do not reach apical surfacenuclei
  are located at various levels so it looks layered
• Cell shapes
• Squamous
• Cuboidal
• Columnar
• Transitional shape varies with tissue stretching

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Types of Epithelium

• Glandular epithelium
• secreting portion of glands
• thyroid, adrenal, and sweat glands
• Two categories
• Endocrine Glands
• Release secretions directly into surrounding
  environment
• Also called ductless glands covered in
  chapter 18
• Exocrine Glands
• Release secretions into ducts
• Ducts lead to surface of skin or into the lumen
  of a hollow organ
• Examples Sudoriferous (sweat) glands, mucus
  glands, mammary glands, salivary glands

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Epithelial Tissue

• Structural and Functional Classification of
  Glands will NOT be covered.with the exception of
  following slide info

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Methods of Glandular SecretionEpithelial

• Merocrine -- most glands
• saliva, digestive enzymes watery (sudoriferous)
  sweat
• Apocrine
• smelly sweat
• Holocrine -- oil gland
• cells die rupture to release products

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CONNECTIVE TISSUE

• abundant and widely distributed
• derived from mesoderm
• Immature cells have names that end in -blast(
  e.g., fibroblast, chondroblast)
• Mature cells have names that end in -cyte (e.g.,
  osteocyte).

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Connective Tissues

• Cells rarely touch due to extracellular matrix.
• Matrix (fibers ground substance) is secreted by
  cells
• Fibers
• Collagen impart strength (bone, cartilage,
  tendons, and ligaments)
• Elastic impart stretchability and elasticity
  (skin, blood vessels, and lungs)
• Reticular network of fibers for strength (found
  around fat cells, nerve fibers, and skeletal and
  smooth muscle fibers)
• Ground substance supportive medium in which
  connective tissue cells are suspended
• Consistency varies
• liquid, gel or solid
• Good nerve blood supply except in cartilage
  tendons

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Connective Tissue Cells

• Fibroblasts (secrete fibers matrix)
• Adipocytes (fat cells store energy in form of
  fat)
• White Blood Cells (leukocytes)
• Macrophages engulf debris bacteria by
  phagocytosis
• Plasma cells produce antibodies to fight
  foreign invaders
• Mast cells produce histamine that dilate small
  blood vessels

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Clinical Application Marfan Syndrome

• Inherited disorder of fibrillin gene
• Fibrillin is a glycoprotein that surrounds
  elastin in elastic fibers
• Abnormal development of elastic fibers
• Tendency to be tall with very long legs, arms,
  fingers and toes
• Life-threatening weakening of aorta (elastic
  fibers line blood vessels) may lead to rupture

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Classification of Connective Tissue

• Embryonic Connective Tissue
• Connective tissue that is present primarily in
  the embryo or fetus is called embryonic
  connective tissue.
• Mesenchyme, found almost exclusively in the
  embryo, is the tissue form from which all other
  connective tissue eventually arises. (Table 4.3A)
• Mucous connective tissue (Whartons jelly) is
  found in the umbilical cord of the fetus.(Table
  4.3B)

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Classification of Connective Tissue

• Types of Mature Connective Tissue
• Loose connective tissue
• Areolar CT
• Adipose CT
• Reticular CT
• Dense connective tissue
• Dense Regular CT
• Dense Irregular CT
• Elastic CT
• Cartilage
• Hyaline, elastic, fibrocartilage
• bone tissue
• compact and trabecular
• Blood and Lymph

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Membranes

• Flat sheets of tissue that cover or line parts of
  the body
• Two categories of membranes
• Epithelial Membranes
• Mucous Membrane
• Lines body cavities that open to the exterior
  (Fig. 4.7a) e.g., mouth, stomach, vagina,
  urethra, etc
• Epithelial cells secrete mucous mucous protects
  from pathogens, prevents dehydration, lubricates
  food, traps inhaled particles
• Have an underlying CT layer which anchors
  membrane to surrounding environment (Lamina
  propria)
• Tight junctions prevent simple diffusion of most
  substances

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Mucous Membranes
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Membranes

• Flat sheets of tissue that cover or line parts of
  the body
• Two categories of membranes
• Epithelial Membranes
• Mucous Membranes
• Serous Membranes
• Lines body cavities that do not open to the
  exterior
• Pleura, peritoneum, pericardium
• Consists of simple squamous spithelium and
  areolar CT
• Surrounds organs within cavities, reduces
  friction
• Visceral layer
• Parietal layer

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Membranes

• Flat sheets of tissue that cover or line parts of
  the body
• Two categories of membranes
• Synovial Membranes
• Located in cavities of freely moving joints
• Contain areolar CT, elastic fibers, and
  adipocytes
• Synovial fluid nourishes and lubricates the
  cartilage on the joint surfaces

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• Muscle Tissue covered in chapter 10
• Nervous tissue covered in chapter 12
• Tissue Repair Restoring Homeostasis NOT
  covered
• Aging and Tissues NOT covered
• END CHAPTER 4